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저 시-비 리- 경 지 20 한민
는 아래 조건 르는 경 에 한하여 게
l 저 물 복제 포 전송 전시 공연 송할 수 습니다
다 과 같 조건 라야 합니다
l 하는 저 물 나 포 경 저 물에 적 된 허락조건 명확하게 나타내어야 합니다
l 저 터 허가를 면 러한 조건들 적 되지 않습니다
저 에 른 리는 내 에 하여 향 지 않습니다
것 허락규약(Legal Code) 해하 쉽게 약한 것 니다
Disclaimer
저 시 하는 원저 를 시하여야 합니다
비 리 하는 저 물 리 목적 할 수 없습니다
경 지 하는 저 물 개 형 또는 가공할 수 없습니다
工
學碩士學位論文
포물
반사경용
역
피드
설계
어덩토야
바상재랜
2012年8月
工學碩士學位論文
포물 반사경용 역 피드 설계
DesignofaBroadbandFeedforParabolic
ReflectorApplication
忠 北 大 學 校 大 學 院
電波工學科 電波通信工學 攻
어덩토야 바상재랜 (OdontuyaBaasantseren)
2012年 8月
工學碩士學位論文
포물 반사경용 역 피드 설계
DesignofaBroadbandFeedforParabolic
ReflectorApplication
指 敎授 安 炳 哲
電波工學科 電波通信工學 攻
어덩토야 바상재랜 (OdontuyaBaasantseren)
이 論文을 工學碩士學位 論文으로 提出함
2012年 8月
本 論文을 金岐祿의 工學碩士學位 論文으로 認定함
審 査 委 員 長 안 재 형
審 査 委 員 안 병 철
審 査 委 員 방 재 훈
忠 北 大 學 校 大 學 院
2012年 8月
-i-
Contents
Abstract middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot ii
List of figures middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot iv
List of tables middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot ix
Ⅰ Indtroduction middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 1
Ⅱ Analysis of Circular and Square Waveguide Feeds middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 4
21 Circular Waveguide Radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 4
22 Square Waveguide Radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 10
23 Probe-Fed Circular Waveguide Radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 15
24 Probe-Fed Circular Waveguide Radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 20
Ⅲ Design of Compact Circular Waveguide Feeds middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 25
31 Narrow-Band Circular Waveguide Feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 25
32 Fabrication and Measurement middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 38
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod middotmiddotmiddotmiddotmiddotmiddot 40
41 Design of dielectric rod feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 40
V Design of Broadband Circular Waveguide Feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 50
51 Design of Broadband Circular Waveguide Feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 50
52 Fabrication and Measurement middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 82
Ⅳ Conclusion middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 85
REFERENCES middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 88
ACKNOWLEDGEMENT middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 89
-ii-
DesignofaBroadbandFeedforParabolic
ReflectorApplications
Odontuya Baasantseren
Department of Radio and Communications Engineering
Graduate School Chungbuk National University
Cheongju City South Korea
Supervised by Professor Bierng-Chearl Ahn Ph D
Abstract
In this thesis the design of a broadband feed for application in prime-focus
parabolic reflector antenna is described A feed for parabolic reflector antenna
requires radiation pattern with a good circular symmetry low back radiation
and low cross polarization This thesis proposes two feed designs one is a
dielectric ring-loaded circular waveguide operating over 171-197GHz and
fed by a coaxial probe The other is a choked and corrugated circular
waveguide fed by a probe-fed rectangular waveguide Before designing two
A thesis for the degree of Master in August 2012
-iii-
feeds performances of simple circular and square waveguide open ends are
investigated The improvement in the performance of the circular waveguide
open end by dielectric loading is also investigated The study shows that only
a narrow-band performance is possible with simple feeds
Based on this study the first feed is designed with the monocast(MC)
nylon as the dielectric-ring material for beamwidth equalization and a
quarter-wave choke around the aperture wall for back-radiation reduction A
coaxial probe is used to excite the feed The designed feed shows a good
performance over 171-197GHz
The second feed uses more complicated structures For broadband operation
the circular waveguide is fed by a probe-excited rectangular waveguide Four
quarter-wave chokes are used around the aperture wall for beamwidth
equalization and four corrugations are employed on the feeds outer surface
for further reduction in the back radiation
Prototypes of both feeds are fabricated and tested Test results are in good
agreement with the design objectives verifying the excellent performances of
the designed feeds
-iv-
List of Figures
Fig 21 Geometry of a circular waveguide open end radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 6
Fig 22 Reflection coefficient of a circular waveguide open end radiator middotmiddot 6
Fig 23 2D radiation pattern of a circular waveguide open end radiator middotmiddotmiddot 7
Fig 24 E-plane and H-plane patterns of a circular waveguide open end
radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 9
Fig 25 Geometry of a square waveguide open end radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 11
Fig 26 Reflection coefficient of a square waveguide open end radiator middot 12
Fig 27 2D radiation patterns of a square waveguide open end radiator middot 12
Fig 28 E-plane and H-plane patterns of square waveguide open end
radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 14
Fig 29 Probe-fed circular waveguide radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 16
Fig 210 Reflection coefficient of the probe-fed circular waveguide radiator
middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 17
Fig 211 2D radiation patterns of the probe-fed circular waveguide radiator
middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 17
Fig 212 E- and H-plane patterns of the probe-fed circular waveguide
radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 19
Fig 213 Probe-fed square waveguide radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 20
Fig 214 2D radiation pattern of the probe-fed square waveguide radiator 21
Fig 215 E- and H-plane pattern of the probe-fed square waveguide radiator
middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 23
Fig 216 Reflection coefficient of the probe-fed square waveguide radiator 24
Fig 31 Narrow-band circular waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 26
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Fig 32 Effect of the (a) the probe length lp (b) the probe distance sp on
the reflection coefficient middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 27
Fig 33 Feed performance versus the choke depth (a) E-plane pattern (b)
H- plane pattern (c) reflection coefficient middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 29
Fig 34 Feed performance versus the choke slot width (a) E-plane pattern
(b) H-plane pattern (c) reflection coefficient middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 30
Fig 35 Feed performance versus the dielectric ring length (a) E-plane
pattern (b) H-plane pattern and (c) reflection coefficient middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 31
Fig 36 Feed performance versus the dielectric ring thickness (a) E-plane
pattern (b) H-plane pattern (c) reflection coefficient middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 32
Fig 37 2D gain patterns of the narrow-band circular waveguide feed middotmiddotmiddot 34
Fig 38 E- and H-plane patterns of the narrow-band circular waveguide
feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 30
Fig 39 Photograph of the fabricated feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 37
Fig 310 Reflection coefficient of the fabricated feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 38
Fig 311 Gain patterns of the fabricated feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 39
Fig 41 Geometry of a circular waveguide loaded with a uniform dielectric
rod middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 40
Fig 42 Radiation pattern at 9GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 05λ0 middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 41
Fig 43 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 21 and L = 05λ0 at 10GHz middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 42
Fig 44 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 30 and L = 05λ0 at 8GHz middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 43
Fig 45 Radiation pattern of the circular waveguide loaded with a uniform
-vi-
dielectric rod with εr = 50 and L = 05λ0 at 18GHz middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 44
Fig 46 Radiation pattern at 10GHz of the circular waveguide loaded with
a uniform dielectric rod with εr = 25 and L = 10λ0 middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 45
Fig 47 Geometry of a circular waveguide loaded with a tapered dielectric
rod middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 46
Fig 48 Radiation pattern of a circular waveguide loaded with a tapered
dielectric rod with L = 1λ0 d = 1λ0 and εr =25 at 10GHz middotmiddotmiddotmiddotmiddotmiddotmiddot 47
Fig 49 Geometry of a circular waveguide loaded with a spherical ended
dielectric rod middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 48
Fig 410 Radiation pattern of a circular waveguide loaded wht a spherical
ended dielectric rod with d = 06λ0 L = 03λ0 and εr =25 at
10GHz middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 49
Fig 51 Structure of the proposed broadband circular waveguide feed middotmiddotmiddotmiddotmiddot 51
Fig 52 Reflection coefficient of the coaxial-to-rectangular adapter versus
(a) probe length lp and (b) the probe position sp middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 52
Fig 53 Structure of the rectangular-to-circular waveguide transition middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 53
Fig 54 Field distribution inside the mode converter middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 54
Fig 55 Reflection coefficient of the broadband circular waveguide feed
without chokes and corrugations middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 55
Fig 56 E-plane and H-plane patternsof the broadband circular waveguide
feed without chokes and corrugationsz middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 56
Fig 57 2D radiation patterns of the broadband cicular waveguide feed
without chokes and corrugations middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 58
Fig 58 Effect of chokes on the E-plane pattern of the broadband circular
waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 61
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Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 63
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection
coefficient middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 66
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and
(c) reflection coefficient middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 67
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 69
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 70
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection
coefficient middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 71
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 72
Fig 516 Reflection coefficient of the designed broadband circular
waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 75
Fig 517 2D radiation patterns of the designed broadband circular
waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 76
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 79
Fig 519 Phase center variation of the designed broadband circular
waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 81
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Fig 520 Photograph of the fabricated broadband circular waveguide feed 82
Fig 521 Reflection coefficient of the fabricated broadband circular
waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 82
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 84
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 84
-ix-
List of Tables
Table 21 Properties of a circular waveguide open end radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 10
Table 22 Properties of a square waveguide open end radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 15
Table 23 Properties of the probe-fed circular waveguide radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 20
Table 24 Properties of the probe-fed square waveguide radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 24
Table 31 Dimensions of the designed narrow-band circular feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 33
Table 32 Performance of the narrow-band circular waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 37
Table 51 Performance of the broadband circular waveguide feed without
chokes and corrugations middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 60
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 73
Table 53 Optimum dimensions of the broadband circular waveguide feed 74
Table 54 Performance of the designed broadband circular waveguide feed 81
-1-
I Introduction
The horns and waveguides are known for their high efficiency and
structural simplicity They are popular choices for feeding for reflectors in
high-gain antenna applications such as satellite and point-to-point microwave
communication links The theory of reflector antenna was developed in the
1940s and has been used to calculate the radiation patterns of various
reflector structures[1]
The basic structure of a prime-focus reflector antenna consists of a
parabolic reflecting surface a feed and its support The placement of the feed
is such that its phase center is at the focal point of the parabolic reflecting
surface The feed is often a circular waveguide because of its symmetric
radiation pattern with low back radiation and low cross polarization The
circular waveguide feed must have a small diameter to reduce the aperture
blockage of the reflector antenna[3]
A radiation pattern with a good circular symmetry in the main beam can
be found from circular waveguide feeds with dominant TE11 mode excitation
The radiation patterns depends on the diameter and wall thickness of the
waveguide[4] A coaxial probe can be inserted into a short-circuited circular
waveguide in the form of a coaxial-to-waveguide transition The diameter of
the circular waveguide is chosen such that only the dominant mode
propagates
When the waveguide dimension does not provide a circular symmteric
-2-
pattern a choke or multiple chokes around the aperture wall can be
employed to equalize radiation patterns and keep the back radiation in low
level If chokes are not enough for the suppression of the back radiation
corrugations on the outer surface of the feed is one way to reduce the back
radiation
In this thesis a broadband circular waveguide feed is developed for
prime-focus reflector antenna application After investigating the radiation
properties of simple circular and square waveguides methods are investigated
for bandwidth enhancement back radiation suppression and beamwidth
equalization in the circular waveguide feed
The first type of the circular waveguide feed consists of a probe-fed
circular waveguide a single quarter-wave choke on the aperture wall and a
dielectric-ring beamwidth equalizer Due to the simple feeding method the
first feed operates over 171-197GHz(141) which is not broadband in the
strict sense of the word
The second feed consists of a coaxial-to-rectangular waveguide transition a
rectangular-to-circular waveguide transition a circular waveguide section four
quarter-wave chokes on the aperture wall and four quarter-wave corrugations
on the feeds outer surface Due to the complicated feeding method the
second feed operates over 10-18GHz(571)
This thesis is arranged as follows Chapter I gives an introduction to the
thesis related works and objectives are stated Chapter II describes the
structure and excitation of the circular and square waveguide and the
operation of the coaxial-to-waveguide transitions Chapter III describes a
compact feed horn design and its fabrication and measurement Chapter IV
-3-
presents dielectric rod feed and its simulated performances Chapter V gives
design and optimization of feed for parabolic reflector antenna In this
chapter includes the detailed information of design procedures and operating
principle also the simulated and measured performances are provided Finally
conclusion is given in the Chapter VI
-4-
II Analysis of Circular and Square Waveguide Feeds
21 Circular Waveguide Radiator
Before design a complicated circular waveguide feed it is helpful to
investigate the impedance and radiation properties of a circular waveguide
open end
The circular waveguide is a cylindrical hollow metallic pipe with a uniform
circular section of radius a Circular waveguides are normally designed to
operate only with the dominant mode The dominant mode in a waveguide is
the mode having the lowest cutoff frequency given by equation (21)
(21)
where
(22)
and a is the waveguide radius The following chart[2] and table show the
cutoff frequencies of various modes in a circular waveguide
-5-
Modes c al11TEc cf f
TE11 341259 100000
TM01 261274 130613
TE21 205720 165885TE01 163979 208111
TM11 163979 208111TE31 149557 228180
TM21 122345 278932TE41 118159 288813
TE12 117852 289566
TM02 113824 299813TE02 0897986 380027
The recommended frequency range of the commercial circular waveguide is
given by the following equation This assumes that the TM01 mode is not
generated or suppressed if generated
11 21 11TE TE TE115 095 158 32 bandwidthc c cf f f fpound pound = reg (23)
Fig 21 shows the geometry of a circular waveguide with a diameter of 2a
When 2a is 2053mm the cutoff frequency of the TE11 mode is 857GHz
According to (23) the useful operating frequency range is from
986-1354GHz
Fig 22 shows the reflection of this waveguide excited with the dominant
TE11 mode The waveguide length l is 60mm The reflection occurs at the
open end of the circular waveguide The reflection coefficient is less than
-15dB over 10-18GHz
-6-
Fig 21 Geometry of a circular waveguide open end radiator
Fig 23 shows a 2D gain pattern of this waveguide antenna The
waveguide antenna has a gain of 80dB 99dB and 115dB at 10GHz
14GHz and 18GHz respectively Fig 24 shows the E- and H-plane patterns
of the circular waveguide antenna Table 21 summarizes the properties of a
circular waveguide antenna
Fig 22 Reflection coefficient of a circular waveguide open end radiator
-7-
(a)
(b)
Fig 23 2D radiation pattern of the circular waveguide open end radiator
at (a)10GHz (b) 14GHz and (c) 18GHz
-8-
(c)
Fig 23 continued
-9-
(a)
(b)
(c)
Fig 24 E-plane and H-plane patterns of the circular waveguide open end
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-10-
Table 21 Properties of a circular waveguide open end radiator of diameter
2053mm
Frequency(GHz)-10dB Beamwith(deg) Front-to-Back
Ratio(dB)E plane H plane
10 67 73 12
14 58 60 18
18 41 50 21
In a circular waveguide radiatoλr a good pattern symmetry and low back
radiation is obtained at 14GHz where 2aλ = 096
22 Square Waveguide Radiator
A square waveguide is often used as a dual-polarized feed To operate the
cutoff frequency of the dominant mode a square-waveguide wall width a
must be greater than one half of a wavelength The modes with cutoff
frequencies equal to or smaller than the operational frequency can exist inside
the waveguide wall The lower cutoff frequency and cutoff wavelength for
square waveguide is determined by the following equations
TE
(24)
TE
(25)
The next higher-order mode is TE11 mode with the cutoff wavelength
given by
-11-
TE
(26)
Similar to the circular waveguide the recommended operating frequency range
of a square waveguide is given by
TEleleTE
TErarr bandwidth (27)
Fig 25 shows the geometry of a square waveguide with a dimension of a
When a is 157mm the cutoff frequency is 95GHz The recommended
operating frequency of this waveguide is from 109GHz to 155GHz
Fig 26 shows the reflection of this waveguide excited with the dominant
TE10 mode The reflection coefficient is less than -15dB over 10-20GHz
Fig 25 Geometry of a square waveguide open end radiator
Fig 27 and shows the 2D radiation pattern of a square waveguide antenna
excited with the dominant TE10 mode The antenna has a gain of 73dB
85dB and 102dB at 10GHz 14GHz and 18GHz respectively Fig 28
shows the E- and H-plane radiation patterns of a square waveguide radiator
Table 22 summarizes the properties of a square waveguide open end radiator
-12-
Fig 26 Reflection coefficient of a square waveguide open end radiator
(a)
Fig 27 2D radiation patterns of a square waveguide radiator
at (a) 10GHz (b) 14GHz and (c) 18GHz
-13-
(b)
(c)
Fig 27 continued
-14-
(a)
(b)
(c)
Fig 28 E-plane and H-plane patterns of square waveguide open radiator
at (a) 10GHz(b) 14GHz and (c) 18GHz
-15-
Table 22 Properties of a square waveguide open end radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 69 71 11
14 47 60 25
18 58 62 16
The radiation pattern symmetry and back radiation performance of the
square waveguide are inferior to those of a circular waveguide
23 Probe-Fed Circular Waveguide Radiator
In Section 21 the radiation properties of a TE11-mode excited waveguide
is investigated In this section a circular waveguide fed by a coaxial probe
shown in Fig 29 is studied
The coaxial probes diameter is 127mm With the Teflon dielectric the
50-ohm coaxial lines outer conductor has a diameter of 41mm For a
circular waveguide the wave impedance of the TE11 mode is given by
∙ (28)
where λg is the guided wavelength given by
(29)
-16-
(a) (b)
Fig 29 Probe-fed circular waveguide radiator (a) Front view and (b) side
view
The combination of the probe length and the probe position from the
shorted wall enables a good impedance matching The probe distance sp from
the back short is close to a quarter wavelength at the design frequency
The designed feed has the following dimension d = 2053mm lp = 42
mm sp = 534mm wall thickness = 05mm and feed length = 400mm
Fig 210 shows the reflection coefficient of the designed probe-fed
circular waveguide radiator The reflection coefficient is less than -10dB over
138-187GHz Fig 211 and 212 shows the E-plane and H-plane radiation
patterns and 2D radiation patterns of the coaxial-to-circular waveguide
transition The radiation patterns symmetry distorted because of the high order
modes The coaxial-to-circular waveguide transition has 73dB 84dB and
79dB gain at 10GHz 14GHz and 18GHz frequencies respectively Table 23
shows the properties of the coaxial-to-circular waveguide transition
-17-
Fig 210 Reflection coefficient of the probe-fed circular waveguide radiator
(a)
Fig 211 2D radiation pattern of the probe-fed circular waveguide radiator
at (a) 10GHz (b) 14GHz and (c) 18GHz
-18-
(b)
(c)
Fig 211 continued
-19-
(a)
(b)
(c)
Fig 212 E- and H-plane patterns of the probe-fed circular waveguide
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-20-
Table 23 Properties of the probe-fed circular waveguide radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 73 70 1414 83 57 17
18 60 52 30
When a circular waveguide radiator is fed by a coaxial probe its radiation
properties are not good due to the excitation of higher-order modes
Therefore a probe-fed circular waveguide radiator can be used as a feed only
over a narrow frequency range
24 Probe-Fed Square Waveguide Radiator
In this section a probe-fed square waveguide radiator is investigated Fig
213 shows a coaxial probe-fed square waveguide radiator The designed
radiator has the following dimension a = b = 157mm lp = 35 mm sp =
50 mm wall thickness = 05mm and feed length = 40mm
(a) (b)
Fig 213 Probe-fed square waveguide radiator (a) Front view and (b) side
view
-21-
Fig 214 shows the 2D radiation patterns of the radiator at 10GHz
14GHz and 18GHz Fig 215 shows E- and H-plane patterns of the radiator
Fig 216 shows the reflection coefficient of the probe-fed square waveguide
radiator The reflection coefficient is less than -10dB over 13-20GHz Table
24 summarizes the properties of the probe-fed square waveguide radiator
(a)
Fig 214 2D radiation patterns of the probe-fed square waveguide radiator at
(a) 10GHz (b) 14GHz and (c) 18GHz
-22-
(b)
(c)
Fig 214 continued
-23-
(a)
(b)
(c)
Fig 216 E-plane and H-plane patterns of the probe-fed square waveguide
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-24-
Fig 216 Reflection coefficient of the probe-fed square waveguide radiator
Table 24 Properties of the probe-fed square waveguide radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 73 71 12
14 85 63 1418 27 65 28
When a square waveguide radiator is fed by a coaxial probe its radiation
properties are not good due to the excitation of higher-order modes as in the
case of the probe-fed circular waveguide radiator A probe-fed square
waveguide radiator can be used as a feed only over a narrow frequency
range
-25-
III Design of Compact Circular Waveguide Feeds
In this chapter the feed design is presented for a prime-focus reflector
antenna The prime-focus paraboloid reflector is one of the most commonly
used high-gain antenna It has been used in earth-station antennas and radio
telescopes It consists of a paraboloid reflector with a feed system at its focal
point
The feed should radiate a low level of cross-polar power over the
operating frequency These conditions not easy to achieve and most prime
focus feeds are compromises The shape and characteristic of the radiation
pattern of the feed are the most important parameter because these will
directly influence the fields which are directed at a reflector[6] Other
electrical factors which relevant to the choice of a feed are the cross-polar
level the gain efficiency the bandwidth and impedance matching
31 Narrow-Band Circular Waveguide Feed
Fig 31 shows the proposed narrow-band circular waveguide feed and its
design variables The feed consists of a circular waveguide open end excited
by a TE11 dominant mode A quarter wave choke is applied along the
circular aperture of the waveguide to equalize E- and H-plane radiation
patterns and to suppress the back radiation A dielectric ring is used to
control the radiation pattern and change the power distribution over the
aperture The control of the amplitude over the aperture are essential to the
design of symmetric radiation pattern The material used for dielectric loading
-26-
is the monocast(MC) nylon with a dielectric constant of 30 The feed is
designed to operate over 171-197GHz
(a)
(b)
Fig 31 Narrow-band circular waveguide feed (a) CAD model and (b) a
cross sectional view
The impedance matching is achieved by a proper combination of the probe
height lp and its distance sp from the waveguide shorted end Here the
-27-
circular waveguide is terminated with an open end with a wall thickness of
2mm radiating into the free space
Fig 32 shows the effect of the probe length lp and the probe distance sp
on the reflection coefficient The best performance is obtained when lp =
363mm and sp = 616mm The feeds reflection coefficient is less than -10dB
over 170-195GHz
(a)
(b)
Fig 32 Effect of the (a) the probe length lp and (b) the probe
distance sp on the reflection coefficient
-28-
Fig 33 shows the effect of the choke depth The E-plane pattern is more
sensitive to the choke depth than the H-plane pattern The choke depth has a
strong influence on the reflection coefficient when it is 360mm By properly
choosing the choke depth we can equalize the E- and H-plane patterns The
optimum value of the choke depth is 410mm which is 0249λ0 at 1825GHz
The choke slot width tch in the range of 06-12mm has almost no effect
on the H-plane pattern and the reflection coefficient For the E-plane pattern
tch of 12mm has some effect on the E-plane radiation pattern as shown in
Fig 34
Fig 35 shows the feed performance versus the dielectric ring length We
observe in Fig 35 that the dielectric length ld has an optimum value of
1168mm which does no effect on the H-plane pattern and tha the value of
1048mm has some effect on the E-plane pattern and the reflection
coefficient
Fig 36 shows E-plane and H-plane patterns and the reflection coefficient
versus the dielectric thickness With the optimum value of the dielectric
thickness t obtained from the Fig 36 is 155mm The larger values of td has
much stronger effects on the E-plane pattern and the reflection coefficient
The H-plane pattern is not sensitive to the dielectric ring thickness
-29-
(a)
(b)
(c)
Fig 33 Feed performance versus the choke depth (a) E-plane pattern
(b) H-plane pattern and (c) reflection coefficient
-30-
(a)
(b)
(c)
Fig 34 Feed performance versus the choke slot width (a) E-plane pattern
(b) H-plane pattern and (c) reflection coefficient
-31-
(a)
(b)
(c)
Fig 35 Feed performance versus the dielectric ring length (a) E-plane
pattern (b) H-plane pattern and (c) reflection coefficient
-32-
(a)
(b)
(c)
Fig 36 Feed performance versus the dielectric ring thickness (a) E-plane
pattern(b) H-plane pattern and (c) reflection coefficient
-33-
From the above parametric analysis an optimum feed design is obtained
The result is shown in Table 31 Fig 37 shows the 2D gain patterns of
designed feed The antenna has a gain of 903dB 933dB and 956dB at
171GHz 1825GHz and 19GHz respectively
Fig 38 shows E- and H-plane radiation patterns of the designed feed The
feed has E- and H-plane 10-dB beamwidths of 60 and 59 degrees at 17GHz
The feed has a front-to-back ration of 1900dB 2490dB and 2200dB at
171GHz 1825GHz and 19GHz respectively Table 32 summarizes the
performance of the designed narrow-band circular waveguide feed
The designed feed has a greatly improved performance over that of a
simple coax-fed feed described in Section 23
Table 31 Dimensions of the designed narrow-band circular feed
Parameter Designation Value(mm)
a Waveguide inside radius 640
l Feed length 2890
lp Probe length 363
sp Probe position from the back short 616
din Probe diameter 127
dout Diameter of coaxial cables outer conductor 400
t Thickness of choked wall 050
tch Choke slot width 100
lch Choke depth 410
ld Dielectric ring length 1168
td Dielectric ring thickness 155
d1 Waveguide outside diameter 1680
-34-
(a)
(b)
Fig 37 2D gain patterns of the narrow-band circular waveguide feed at
(a) 17GHz (b) 1825GHz and (c) 19GHz
-35-
(c)
Fig 37 continued
-36-
(a)
(b)
(c)
Fig 38 E- and H-plane patterns of the narrow-band circular waveguide feed
at (a) 10GHz (b) 1825GHz and (c) 195GHz
-37-
Frequency(GHz)
Gain(dB)
E-H-plane10-dB beamwidths
(deg)
Front-to-back ratio(dB)
Phase centerlocation
(From feeds aperture plane
toward reflector)
(mm)
1700 903 6059 20 062
1825 933 6060 25 004
1900 956 5759 22 007
Table 32 Performance of the narrow-band circular waveguide feed
The designed narrow-band feed is fabricated and its performance is
measured and compared with the simulation results The designed feed is
fabricated in a numerically-controlled machining center The fabricated antenna
is shown in Fig 39
Fig 39 Photograph of the fabricated feed
-38-
Fig 310 shows a comparison of the measured and simulated reflection
coefficients The measured reflection coefficient is less than -10dB over
171-197GHz The agreement between simulated and measured results are
good
Fig 311 shows the E- and H-plane patterns of the fabricated feed at
187GHz The feed has 90dB gain simulation and measurement results are in
good agreement
The fabricated antennarsquos 10dB beamwidth is 60 degrees in both E and H
planes at 187GHz The front-to-back ratio is 21dB
Fig 310 Reflection coefficient of the fabricated feed
-39-
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Fee
d H
orn
Gain
- d
B
Angle - degree
(a)
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Feed H
orn
Gain
- d
B
Angle - degree
(b)
Fig 311 Gain patterns of the fabricated feed at 187 GHz (a) E-plane and
(b) H-plane
-40-
IV Design of Circular Waveguide Feeds Loaded with a
Dielectric Rod
In this section circular waveguide feeds loaded with a dielectric rod feed
are investigated A comprehensive discussion of the circular waveguide loaded
with a dielectric rod is given by Kumar[7] Inserting a dielectric material
inside the circular waveguide improves the E- and H-plane pattern symmetry
In general dielectric-loaded circular waveguide feeds show good performance
only over a narrow bandwidth
Fig 41 shows the geometry of a circular waveguide loaded with a
dielectric rod The waveguide length is 400mm and the wall thickness is
05mm The dielectric rods diameter is 207mm The dielectric rod is
extended 05 wavelength beyond the waveguide open end The dielectric
constant εr is changed and the feeds performance is observed
Fig 41 Geometry of a circular waveguide loaded with a uniform dielectric
rod
-41-
Fig 42 is the radiation pattern of the feed with εr = 25 and L = 05λ0 at
9GHz E- and H-plane 10-dB beamwidths are 810 and 807 degrees
respectively The front-to-back ratio is 18dB The antenna gain is 71dB
(a)
(b)
Fig 42 Radiation pattern at 9GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 05λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-42-
Fig 43 shows the radiation pattern of the feed with εr = 21 at 10GHz
E- and H-plane 10-dB beamwidths are 70 and 71 degrees respectively The
front-to-back ratio is 19dB The antenna gain is 83dB
(a)
(b)
Fig 43 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 21 and L = 05λ0 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-43-
Fig 44 shows the radiation pattern of the feed with εr = 30 at 8GHz
E- and H-plane 10-dB beamwidths are 83 and 824 degrees respectively The
front-to-back ratio is 17dB The antenna gain is 73dB
(a)
(b)
Fig 44 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 30 and L = 05λ0 at 8GHz (a) 2D radiation pattern
and (b) E- and H-plane patterns
-44-
Fig 45 shows the radiation pattern of the feed with εr = 50 at 18GHz
E- and H-plane 10-dB beamwidths are 56 and 54 degrees respectively The
front-to-back ratio is 27dB The antenna gain is 105dB The feed has a good
pattern symmetry and low back radiation
(a)
(b)
Fig 45 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 50 and L = 05λ0 at 18GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-45-
Fig 46 is the radiation pattern of the feed with εr = 25 and L = 10λ0 at
10GHz E- and H-plane 10-dB beamwidths are 50 and 48 degrees
respectively The front-to-back ratio is 16dB The antenna gain is 105dB
(a)
(b)
Fig 46 Radiation pattern at 10GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 10λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-46-
Fig 47 shows the geometry of a circular waveguide with a tapered
dielectric rod The designed feed has the following dimension L = 1λ0 d =
1λ0 and εr =25 at 10GHz The waveguide length is 40mm and the wall
thickness is 05mm
L
Dielectricd3
Fig 47 Geometry of a circular waveguide loaded with a tapered dielectric
rod
Fig 48 shows the radiatio pattern of the designed feed E- and H-plane
10-dB beamwidths are 575 and 564 degrees respectively The front-to-back
ratio is 377dB The antenna gain is 94dB The designed feed has an
excellent beamwidth symmetry and a very low back radiation
-47-
(a)
(b)
Fig 48 Radiation pattern of a circular waveguide loaded with a tapered
dielectric rod with L = 1λ0 d = 1λ0 and εr =25 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-48-
Fig 49 shows the geometry of a spherical ended dielectric rod feed
diameter of 06λ0 at 10GHz with a dielectric constant of 25 and L= 03λ0
Fig 410 shows the radiation patterns of the designed feed E- and H-plane
10-dB beamwidths are both 63 degrees The front-to-back ratio is 24dB The
antenna gain is 864dB
Fig 49 Geometry of a circular waveguide loaded with a spherical ended
dielectric rod
-49-
(a)
(b)
Fig 410 Radiation pattern of a circular waveguide loaded wht a spherical
ended dielectric rod with d = 06λ0 L = 03λ0 and εr =25 at 10GHz (a) 3D
radiation pattern and (b) E- and H-plane patterns
-50-
V Design of a Broadband Circular Waveguide Feed
In this chapter the design of a broadband circular waveguide feed is
presented At microwave frequencies the feed is often a circular waveguide
with chokes and corrugations around the aperture Chokes and corrugations
equalize E- and H-plane patterns and reduce the back radiation
The proposed feed is designed to operate over 10-18GHz The design starts
with the optimization of the coaxial-to-rectangular waveguide adapter
employed for good mode purity over a broad frequency range Next a
rectangular-to-circular waveguide transition is optimized Finally chokes and
corrugations are designed for improved pattern symmetry and low back
radiation
The proposed feed structure is shown in Fig 51 The feed consist of the
following parts a coaxial-to-rectangular waveguide adapter a rectangular-to-
circular waveguide transition a circular waveguide section four quarter-wave
chokes around the feeds aperture and four corrugations on the feeds outer
surface
The computer simulation shows the above arrangement offers good radiation
patterns over a broad frequency range The broadband operation is obtained
by exciting the TE11 mode in the circular waveguide using the TE10 mode of
the rectangular waveguide which is in turn excited by a coaxial probe
-51-
Chokes
Coaxial-to-waveguide transition
Circular wavguide
Corrugations
Mode transition
(a)
(b)
Fig 51 Structure of the proposed broadband circular waveguide feed
(a) CAD model and (b) cross-sectional view
For the coaxial-to-rectangular waveguide adapter an SMA connector with
the probe diameter of 127 mm is employed The coaxial probe inserted into
the waveguide energizes the feed and excites the dominant TE10 mode in
-52-
the rectangular waveguide The impedance matching is achieved by adjusting
the probe distance sp from the back short and the probe length lp
(a)
(b)
Fig 52 Reflection coefficient of the coaxial-to-rectangular adapter versus
(a) probe length lp and (b) the probe position sp
Fig 52 shows the reflection coefficient versus the various values of probe
lengths lp and probe positions sp The probe length lp is adjusted to obtain
antenna impedance matching and the probe distance sp is adjusted to obtain a
-53-
desired resonant frequency
Next a transition between rectangular and circular waveguide is designed
The transition section converts the TE10 mode in the rectangular waveguide to
TE11 mode in the circular waveguide and vice versa The transition is built
in a form of a taper for easy fabrication[22]
(a)
(b)
Fig 53 Structure of the rectangular-to-circular waveguide transition
(a) 3D view and (b) cross sectional view
The dimensions of the final optimized transition are as follows The length
of the rectangular waveguide section is 143mm The rectangular waveguides
width a and height b are 207mm and 857mm respectively The length of
the circular waveguide section is 143mm The inside diameter of the circular
-54-
waveguide is 207mm(097 wavelength at 14GHz) The length of transition
region ltr is 4465mm(approximately equal to 2λ0 at 14GHz) Fig 54 shows
the field distribution inside the mode converter
(a)
(b)
Fig 54 Field distribution inside the mode converter at
(a) 10GHz (b) 14GHz and (c) 18GHz
-55-
(c)
Fig 54 continued
Finally multiple chokes are investigated Figs 55 56 and 57 show the
feed performance without chokes The reflection coefficient is less than -10dB
over 10-19GHz The antenna has a gain of 921dB to 1189dB over
10-19GHz
Fig 55 Reflection coefficient of the broadband circular waveguide feed
without chokes and corrugations
-56-
(a)
(b)
(c)
Fig 56 E- and H-plane patterns of the broadband circular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-57-
(d)
(e)
Fig 56 continued
-58-
(a)
(b)
Fig 57 2D radiation patterns of the broadband cicular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-59-
(c)
(d)
Fig 57 continued
-60-
(e)
Fig 57 continued
To achieve equal beamwidths in E and H planes over a wide frequency
range chokes and corrugations are employed Table51 summarizes the
performance of a feed without chokes and corrugations
Table 51 Performance of the broadband circular waveguide feed without
chokes and corrugations
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
1000 940 6061 15
1200 972 6159 17
1400 920 5957 21
1600 1070 4751 29
1800 1188 5352 21
-61-
Four quarter-wavelength chokes are introduced in the feed design which
has a slot depth of 75mm and slot width of 09mm The choke slot spacing
is 18mm The choke design is investigated by applying the choke one by
one and the effect on the E- and H-plane patterns are observed as illustrated
in Figs 58 and 59 The use of chokes makes the E-plane pattern narrower
The H-plane pattern is not affected Chokes increase the gain slightly and
reduce back radiation
(a)
(b)
Fig 58 Effect of chokes on the E-plane pattern of the broadband circular
waveguide feed at (a) 10GHz(b) 12GHz (c) 14GHz (d) 16GHz and (e)
18GHz
-62-
(c)
(d)
(e)
Fig 58 continued
-63-
(a)
(b)
(c)
Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-64-
(d)
(e)
Fig 59 continued
-65-
Fig 510 shows the feed performance versus the choke depth When the
choke depth is varied from 535mm to 95mm the E- and H-plane patterns
are strongly affected The optimum value of choke depth is 75mm(035λ0 at
14GHz) which gives equal E- and H-plane radiation patterns and leads to
low back radiation
Fig 511 shows the feed performance versus the choke slot width tch The
choke slot width is varied from 09mm to 21mm Radiation patterns and
reflection coefficients are not sensitive to the choke slot width The final
choke slot width is selected to be 09mm considering the feed diameter
minimization and the manufacturability The overall diameter of the proposed
feed is 369mm which is increased from the 207mm of the waveguide
inside diameter due to the use of four chokes
-66-
(a)
(b)
(c)
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection coefficient
-67-
(a)
(b)
(c)
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and (c)
reflection coefficient
-68-
Next we investigated corrugations placed on the outer wall of the feed
Four corrugations applied to the outer surface of the circular waveguide The
corrugation depth is 465mm(0215λ0 at 14GHz) The primary purpose of
using corrugations is to further reduce the back radiation Increasing the
number of corrugations beyond four has little effect in reducing the back
radiation
Figs 512 and 513 show the effect of corrugations on the E- and H-plane
patterns Fig 514 shows the parametric study of the corrugation depth lcor
The corrugation depth is varied from 40mm and 645mm The optimum
value of the corrugation depth is found to be 465mm
-69-
(a)
(b)
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern at (a) 12GHz and (b) 14GHz
-70-
(a)
(b)
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern at (a) 12GHz and (b) 14GHz
-71-
(a)
(b)
(c)
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection coefficient
-72-
The phase center location is important in placing the feed in a reflector
antenna[8] The phase center variation with frequency should be small Fig
515 shows the effect of chokes and corrugations on the phase center The
curve with circle corresponds to the case without chokes and corrugations
The phase center varies from -326mm and -190mm away from the feeds
aperture plane It means the phase center is located inside the waveguide
The curve with triangles corresponds to the case with chokes The curve with
squares to the case with chokes and corrugations The phase center varies
from 0mm to -302mm
From Fig 515 we can observed that phase center variation reduced by the
corrugation and three cases phase center calculated in φ=450 plane
parameter sweep values are given in Table 52
10 12 14 16 181
0
-1
-2
-3
-4
-5
-6
Pha
se c
ente
r (m
m)
Frequency (GHz)
choke+corrugatuion without choke corrugation with choke
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
-73-
Frequency
(GHz)
Phase center from the aperture plane
(mm)
Without
chokes and
corrugations
With
chokes
With chokes
and
corrugations
1000 -326 062 000
1100 -187 030 -002
1200 -563 -208 -065
1300 -296 -154 -202
1400 -319 -314 -302
1500 -201 -203 -241
1600 -242 -233 -207
1700 -208 -208 -186
1800 -190 -157 -132
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
Based on the foregoing parametric studies optimum dimensions of the
broadband circular waveguide feed are obtained as shown in Table 53
-74-
Table 53 Optimum dimensions of the broadband circular waveguide feed
Parameter Designation Value (mm)
2a Waveguide inside diameter 2070
d Waveguide outside diameter 3690
lcrLength of the circular waveguide section 1430
m Distance between the aperture plane and the first corrugation 950
xDistance from the last corrugation to the end of the cylindrical outer surface
550
ltrLength of the rectangular-to-circularwaveguide transition 4465
lrcLength of the rectangular waveguide section 1430
tch Choke slot width 090
lch Choke depth 750
t Choke metal width 090
lcor Corrugation depth 465
tcor Corrugation metal width 100
s Corrugation slot width 10
lp Probe length 530
sp Probe position from the back short 530
din Probe diameter 127
b Inside height of the rectangular waveguide 857
tw Waveguide wall thickness 500
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
工
學碩士學位論文
포물
반사경용
역
피드
설계
어덩토야
바상재랜
2012年8月
工學碩士學位論文
포물 반사경용 역 피드 설계
DesignofaBroadbandFeedforParabolic
ReflectorApplication
忠 北 大 學 校 大 學 院
電波工學科 電波通信工學 攻
어덩토야 바상재랜 (OdontuyaBaasantseren)
2012年 8月
工學碩士學位論文
포물 반사경용 역 피드 설계
DesignofaBroadbandFeedforParabolic
ReflectorApplication
指 敎授 安 炳 哲
電波工學科 電波通信工學 攻
어덩토야 바상재랜 (OdontuyaBaasantseren)
이 論文을 工學碩士學位 論文으로 提出함
2012年 8月
本 論文을 金岐祿의 工學碩士學位 論文으로 認定함
審 査 委 員 長 안 재 형
審 査 委 員 안 병 철
審 査 委 員 방 재 훈
忠 北 大 學 校 大 學 院
2012年 8月
-i-
Contents
Abstract middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot ii
List of figures middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot iv
List of tables middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot ix
Ⅰ Indtroduction middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 1
Ⅱ Analysis of Circular and Square Waveguide Feeds middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 4
21 Circular Waveguide Radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 4
22 Square Waveguide Radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 10
23 Probe-Fed Circular Waveguide Radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 15
24 Probe-Fed Circular Waveguide Radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 20
Ⅲ Design of Compact Circular Waveguide Feeds middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 25
31 Narrow-Band Circular Waveguide Feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 25
32 Fabrication and Measurement middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 38
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod middotmiddotmiddotmiddotmiddotmiddot 40
41 Design of dielectric rod feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 40
V Design of Broadband Circular Waveguide Feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 50
51 Design of Broadband Circular Waveguide Feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 50
52 Fabrication and Measurement middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 82
Ⅳ Conclusion middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 85
REFERENCES middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 88
ACKNOWLEDGEMENT middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 89
-ii-
DesignofaBroadbandFeedforParabolic
ReflectorApplications
Odontuya Baasantseren
Department of Radio and Communications Engineering
Graduate School Chungbuk National University
Cheongju City South Korea
Supervised by Professor Bierng-Chearl Ahn Ph D
Abstract
In this thesis the design of a broadband feed for application in prime-focus
parabolic reflector antenna is described A feed for parabolic reflector antenna
requires radiation pattern with a good circular symmetry low back radiation
and low cross polarization This thesis proposes two feed designs one is a
dielectric ring-loaded circular waveguide operating over 171-197GHz and
fed by a coaxial probe The other is a choked and corrugated circular
waveguide fed by a probe-fed rectangular waveguide Before designing two
A thesis for the degree of Master in August 2012
-iii-
feeds performances of simple circular and square waveguide open ends are
investigated The improvement in the performance of the circular waveguide
open end by dielectric loading is also investigated The study shows that only
a narrow-band performance is possible with simple feeds
Based on this study the first feed is designed with the monocast(MC)
nylon as the dielectric-ring material for beamwidth equalization and a
quarter-wave choke around the aperture wall for back-radiation reduction A
coaxial probe is used to excite the feed The designed feed shows a good
performance over 171-197GHz
The second feed uses more complicated structures For broadband operation
the circular waveguide is fed by a probe-excited rectangular waveguide Four
quarter-wave chokes are used around the aperture wall for beamwidth
equalization and four corrugations are employed on the feeds outer surface
for further reduction in the back radiation
Prototypes of both feeds are fabricated and tested Test results are in good
agreement with the design objectives verifying the excellent performances of
the designed feeds
-iv-
List of Figures
Fig 21 Geometry of a circular waveguide open end radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 6
Fig 22 Reflection coefficient of a circular waveguide open end radiator middotmiddot 6
Fig 23 2D radiation pattern of a circular waveguide open end radiator middotmiddotmiddot 7
Fig 24 E-plane and H-plane patterns of a circular waveguide open end
radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 9
Fig 25 Geometry of a square waveguide open end radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 11
Fig 26 Reflection coefficient of a square waveguide open end radiator middot 12
Fig 27 2D radiation patterns of a square waveguide open end radiator middot 12
Fig 28 E-plane and H-plane patterns of square waveguide open end
radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 14
Fig 29 Probe-fed circular waveguide radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 16
Fig 210 Reflection coefficient of the probe-fed circular waveguide radiator
middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 17
Fig 211 2D radiation patterns of the probe-fed circular waveguide radiator
middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 17
Fig 212 E- and H-plane patterns of the probe-fed circular waveguide
radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 19
Fig 213 Probe-fed square waveguide radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 20
Fig 214 2D radiation pattern of the probe-fed square waveguide radiator 21
Fig 215 E- and H-plane pattern of the probe-fed square waveguide radiator
middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 23
Fig 216 Reflection coefficient of the probe-fed square waveguide radiator 24
Fig 31 Narrow-band circular waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 26
-v-
Fig 32 Effect of the (a) the probe length lp (b) the probe distance sp on
the reflection coefficient middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 27
Fig 33 Feed performance versus the choke depth (a) E-plane pattern (b)
H- plane pattern (c) reflection coefficient middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 29
Fig 34 Feed performance versus the choke slot width (a) E-plane pattern
(b) H-plane pattern (c) reflection coefficient middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 30
Fig 35 Feed performance versus the dielectric ring length (a) E-plane
pattern (b) H-plane pattern and (c) reflection coefficient middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 31
Fig 36 Feed performance versus the dielectric ring thickness (a) E-plane
pattern (b) H-plane pattern (c) reflection coefficient middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 32
Fig 37 2D gain patterns of the narrow-band circular waveguide feed middotmiddotmiddot 34
Fig 38 E- and H-plane patterns of the narrow-band circular waveguide
feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 30
Fig 39 Photograph of the fabricated feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 37
Fig 310 Reflection coefficient of the fabricated feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 38
Fig 311 Gain patterns of the fabricated feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 39
Fig 41 Geometry of a circular waveguide loaded with a uniform dielectric
rod middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 40
Fig 42 Radiation pattern at 9GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 05λ0 middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 41
Fig 43 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 21 and L = 05λ0 at 10GHz middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 42
Fig 44 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 30 and L = 05λ0 at 8GHz middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 43
Fig 45 Radiation pattern of the circular waveguide loaded with a uniform
-vi-
dielectric rod with εr = 50 and L = 05λ0 at 18GHz middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 44
Fig 46 Radiation pattern at 10GHz of the circular waveguide loaded with
a uniform dielectric rod with εr = 25 and L = 10λ0 middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 45
Fig 47 Geometry of a circular waveguide loaded with a tapered dielectric
rod middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 46
Fig 48 Radiation pattern of a circular waveguide loaded with a tapered
dielectric rod with L = 1λ0 d = 1λ0 and εr =25 at 10GHz middotmiddotmiddotmiddotmiddotmiddotmiddot 47
Fig 49 Geometry of a circular waveguide loaded with a spherical ended
dielectric rod middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 48
Fig 410 Radiation pattern of a circular waveguide loaded wht a spherical
ended dielectric rod with d = 06λ0 L = 03λ0 and εr =25 at
10GHz middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 49
Fig 51 Structure of the proposed broadband circular waveguide feed middotmiddotmiddotmiddotmiddot 51
Fig 52 Reflection coefficient of the coaxial-to-rectangular adapter versus
(a) probe length lp and (b) the probe position sp middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 52
Fig 53 Structure of the rectangular-to-circular waveguide transition middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 53
Fig 54 Field distribution inside the mode converter middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 54
Fig 55 Reflection coefficient of the broadband circular waveguide feed
without chokes and corrugations middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 55
Fig 56 E-plane and H-plane patternsof the broadband circular waveguide
feed without chokes and corrugationsz middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 56
Fig 57 2D radiation patterns of the broadband cicular waveguide feed
without chokes and corrugations middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 58
Fig 58 Effect of chokes on the E-plane pattern of the broadband circular
waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 61
-vii-
Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 63
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection
coefficient middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 66
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and
(c) reflection coefficient middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 67
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 69
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 70
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection
coefficient middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 71
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 72
Fig 516 Reflection coefficient of the designed broadband circular
waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 75
Fig 517 2D radiation patterns of the designed broadband circular
waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 76
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 79
Fig 519 Phase center variation of the designed broadband circular
waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 81
-viii-
Fig 520 Photograph of the fabricated broadband circular waveguide feed 82
Fig 521 Reflection coefficient of the fabricated broadband circular
waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 82
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 84
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 84
-ix-
List of Tables
Table 21 Properties of a circular waveguide open end radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 10
Table 22 Properties of a square waveguide open end radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 15
Table 23 Properties of the probe-fed circular waveguide radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 20
Table 24 Properties of the probe-fed square waveguide radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 24
Table 31 Dimensions of the designed narrow-band circular feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 33
Table 32 Performance of the narrow-band circular waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 37
Table 51 Performance of the broadband circular waveguide feed without
chokes and corrugations middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 60
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 73
Table 53 Optimum dimensions of the broadband circular waveguide feed 74
Table 54 Performance of the designed broadband circular waveguide feed 81
-1-
I Introduction
The horns and waveguides are known for their high efficiency and
structural simplicity They are popular choices for feeding for reflectors in
high-gain antenna applications such as satellite and point-to-point microwave
communication links The theory of reflector antenna was developed in the
1940s and has been used to calculate the radiation patterns of various
reflector structures[1]
The basic structure of a prime-focus reflector antenna consists of a
parabolic reflecting surface a feed and its support The placement of the feed
is such that its phase center is at the focal point of the parabolic reflecting
surface The feed is often a circular waveguide because of its symmetric
radiation pattern with low back radiation and low cross polarization The
circular waveguide feed must have a small diameter to reduce the aperture
blockage of the reflector antenna[3]
A radiation pattern with a good circular symmetry in the main beam can
be found from circular waveguide feeds with dominant TE11 mode excitation
The radiation patterns depends on the diameter and wall thickness of the
waveguide[4] A coaxial probe can be inserted into a short-circuited circular
waveguide in the form of a coaxial-to-waveguide transition The diameter of
the circular waveguide is chosen such that only the dominant mode
propagates
When the waveguide dimension does not provide a circular symmteric
-2-
pattern a choke or multiple chokes around the aperture wall can be
employed to equalize radiation patterns and keep the back radiation in low
level If chokes are not enough for the suppression of the back radiation
corrugations on the outer surface of the feed is one way to reduce the back
radiation
In this thesis a broadband circular waveguide feed is developed for
prime-focus reflector antenna application After investigating the radiation
properties of simple circular and square waveguides methods are investigated
for bandwidth enhancement back radiation suppression and beamwidth
equalization in the circular waveguide feed
The first type of the circular waveguide feed consists of a probe-fed
circular waveguide a single quarter-wave choke on the aperture wall and a
dielectric-ring beamwidth equalizer Due to the simple feeding method the
first feed operates over 171-197GHz(141) which is not broadband in the
strict sense of the word
The second feed consists of a coaxial-to-rectangular waveguide transition a
rectangular-to-circular waveguide transition a circular waveguide section four
quarter-wave chokes on the aperture wall and four quarter-wave corrugations
on the feeds outer surface Due to the complicated feeding method the
second feed operates over 10-18GHz(571)
This thesis is arranged as follows Chapter I gives an introduction to the
thesis related works and objectives are stated Chapter II describes the
structure and excitation of the circular and square waveguide and the
operation of the coaxial-to-waveguide transitions Chapter III describes a
compact feed horn design and its fabrication and measurement Chapter IV
-3-
presents dielectric rod feed and its simulated performances Chapter V gives
design and optimization of feed for parabolic reflector antenna In this
chapter includes the detailed information of design procedures and operating
principle also the simulated and measured performances are provided Finally
conclusion is given in the Chapter VI
-4-
II Analysis of Circular and Square Waveguide Feeds
21 Circular Waveguide Radiator
Before design a complicated circular waveguide feed it is helpful to
investigate the impedance and radiation properties of a circular waveguide
open end
The circular waveguide is a cylindrical hollow metallic pipe with a uniform
circular section of radius a Circular waveguides are normally designed to
operate only with the dominant mode The dominant mode in a waveguide is
the mode having the lowest cutoff frequency given by equation (21)
(21)
where
(22)
and a is the waveguide radius The following chart[2] and table show the
cutoff frequencies of various modes in a circular waveguide
-5-
Modes c al11TEc cf f
TE11 341259 100000
TM01 261274 130613
TE21 205720 165885TE01 163979 208111
TM11 163979 208111TE31 149557 228180
TM21 122345 278932TE41 118159 288813
TE12 117852 289566
TM02 113824 299813TE02 0897986 380027
The recommended frequency range of the commercial circular waveguide is
given by the following equation This assumes that the TM01 mode is not
generated or suppressed if generated
11 21 11TE TE TE115 095 158 32 bandwidthc c cf f f fpound pound = reg (23)
Fig 21 shows the geometry of a circular waveguide with a diameter of 2a
When 2a is 2053mm the cutoff frequency of the TE11 mode is 857GHz
According to (23) the useful operating frequency range is from
986-1354GHz
Fig 22 shows the reflection of this waveguide excited with the dominant
TE11 mode The waveguide length l is 60mm The reflection occurs at the
open end of the circular waveguide The reflection coefficient is less than
-15dB over 10-18GHz
-6-
Fig 21 Geometry of a circular waveguide open end radiator
Fig 23 shows a 2D gain pattern of this waveguide antenna The
waveguide antenna has a gain of 80dB 99dB and 115dB at 10GHz
14GHz and 18GHz respectively Fig 24 shows the E- and H-plane patterns
of the circular waveguide antenna Table 21 summarizes the properties of a
circular waveguide antenna
Fig 22 Reflection coefficient of a circular waveguide open end radiator
-7-
(a)
(b)
Fig 23 2D radiation pattern of the circular waveguide open end radiator
at (a)10GHz (b) 14GHz and (c) 18GHz
-8-
(c)
Fig 23 continued
-9-
(a)
(b)
(c)
Fig 24 E-plane and H-plane patterns of the circular waveguide open end
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-10-
Table 21 Properties of a circular waveguide open end radiator of diameter
2053mm
Frequency(GHz)-10dB Beamwith(deg) Front-to-Back
Ratio(dB)E plane H plane
10 67 73 12
14 58 60 18
18 41 50 21
In a circular waveguide radiatoλr a good pattern symmetry and low back
radiation is obtained at 14GHz where 2aλ = 096
22 Square Waveguide Radiator
A square waveguide is often used as a dual-polarized feed To operate the
cutoff frequency of the dominant mode a square-waveguide wall width a
must be greater than one half of a wavelength The modes with cutoff
frequencies equal to or smaller than the operational frequency can exist inside
the waveguide wall The lower cutoff frequency and cutoff wavelength for
square waveguide is determined by the following equations
TE
(24)
TE
(25)
The next higher-order mode is TE11 mode with the cutoff wavelength
given by
-11-
TE
(26)
Similar to the circular waveguide the recommended operating frequency range
of a square waveguide is given by
TEleleTE
TErarr bandwidth (27)
Fig 25 shows the geometry of a square waveguide with a dimension of a
When a is 157mm the cutoff frequency is 95GHz The recommended
operating frequency of this waveguide is from 109GHz to 155GHz
Fig 26 shows the reflection of this waveguide excited with the dominant
TE10 mode The reflection coefficient is less than -15dB over 10-20GHz
Fig 25 Geometry of a square waveguide open end radiator
Fig 27 and shows the 2D radiation pattern of a square waveguide antenna
excited with the dominant TE10 mode The antenna has a gain of 73dB
85dB and 102dB at 10GHz 14GHz and 18GHz respectively Fig 28
shows the E- and H-plane radiation patterns of a square waveguide radiator
Table 22 summarizes the properties of a square waveguide open end radiator
-12-
Fig 26 Reflection coefficient of a square waveguide open end radiator
(a)
Fig 27 2D radiation patterns of a square waveguide radiator
at (a) 10GHz (b) 14GHz and (c) 18GHz
-13-
(b)
(c)
Fig 27 continued
-14-
(a)
(b)
(c)
Fig 28 E-plane and H-plane patterns of square waveguide open radiator
at (a) 10GHz(b) 14GHz and (c) 18GHz
-15-
Table 22 Properties of a square waveguide open end radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 69 71 11
14 47 60 25
18 58 62 16
The radiation pattern symmetry and back radiation performance of the
square waveguide are inferior to those of a circular waveguide
23 Probe-Fed Circular Waveguide Radiator
In Section 21 the radiation properties of a TE11-mode excited waveguide
is investigated In this section a circular waveguide fed by a coaxial probe
shown in Fig 29 is studied
The coaxial probes diameter is 127mm With the Teflon dielectric the
50-ohm coaxial lines outer conductor has a diameter of 41mm For a
circular waveguide the wave impedance of the TE11 mode is given by
∙ (28)
where λg is the guided wavelength given by
(29)
-16-
(a) (b)
Fig 29 Probe-fed circular waveguide radiator (a) Front view and (b) side
view
The combination of the probe length and the probe position from the
shorted wall enables a good impedance matching The probe distance sp from
the back short is close to a quarter wavelength at the design frequency
The designed feed has the following dimension d = 2053mm lp = 42
mm sp = 534mm wall thickness = 05mm and feed length = 400mm
Fig 210 shows the reflection coefficient of the designed probe-fed
circular waveguide radiator The reflection coefficient is less than -10dB over
138-187GHz Fig 211 and 212 shows the E-plane and H-plane radiation
patterns and 2D radiation patterns of the coaxial-to-circular waveguide
transition The radiation patterns symmetry distorted because of the high order
modes The coaxial-to-circular waveguide transition has 73dB 84dB and
79dB gain at 10GHz 14GHz and 18GHz frequencies respectively Table 23
shows the properties of the coaxial-to-circular waveguide transition
-17-
Fig 210 Reflection coefficient of the probe-fed circular waveguide radiator
(a)
Fig 211 2D radiation pattern of the probe-fed circular waveguide radiator
at (a) 10GHz (b) 14GHz and (c) 18GHz
-18-
(b)
(c)
Fig 211 continued
-19-
(a)
(b)
(c)
Fig 212 E- and H-plane patterns of the probe-fed circular waveguide
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-20-
Table 23 Properties of the probe-fed circular waveguide radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 73 70 1414 83 57 17
18 60 52 30
When a circular waveguide radiator is fed by a coaxial probe its radiation
properties are not good due to the excitation of higher-order modes
Therefore a probe-fed circular waveguide radiator can be used as a feed only
over a narrow frequency range
24 Probe-Fed Square Waveguide Radiator
In this section a probe-fed square waveguide radiator is investigated Fig
213 shows a coaxial probe-fed square waveguide radiator The designed
radiator has the following dimension a = b = 157mm lp = 35 mm sp =
50 mm wall thickness = 05mm and feed length = 40mm
(a) (b)
Fig 213 Probe-fed square waveguide radiator (a) Front view and (b) side
view
-21-
Fig 214 shows the 2D radiation patterns of the radiator at 10GHz
14GHz and 18GHz Fig 215 shows E- and H-plane patterns of the radiator
Fig 216 shows the reflection coefficient of the probe-fed square waveguide
radiator The reflection coefficient is less than -10dB over 13-20GHz Table
24 summarizes the properties of the probe-fed square waveguide radiator
(a)
Fig 214 2D radiation patterns of the probe-fed square waveguide radiator at
(a) 10GHz (b) 14GHz and (c) 18GHz
-22-
(b)
(c)
Fig 214 continued
-23-
(a)
(b)
(c)
Fig 216 E-plane and H-plane patterns of the probe-fed square waveguide
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-24-
Fig 216 Reflection coefficient of the probe-fed square waveguide radiator
Table 24 Properties of the probe-fed square waveguide radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 73 71 12
14 85 63 1418 27 65 28
When a square waveguide radiator is fed by a coaxial probe its radiation
properties are not good due to the excitation of higher-order modes as in the
case of the probe-fed circular waveguide radiator A probe-fed square
waveguide radiator can be used as a feed only over a narrow frequency
range
-25-
III Design of Compact Circular Waveguide Feeds
In this chapter the feed design is presented for a prime-focus reflector
antenna The prime-focus paraboloid reflector is one of the most commonly
used high-gain antenna It has been used in earth-station antennas and radio
telescopes It consists of a paraboloid reflector with a feed system at its focal
point
The feed should radiate a low level of cross-polar power over the
operating frequency These conditions not easy to achieve and most prime
focus feeds are compromises The shape and characteristic of the radiation
pattern of the feed are the most important parameter because these will
directly influence the fields which are directed at a reflector[6] Other
electrical factors which relevant to the choice of a feed are the cross-polar
level the gain efficiency the bandwidth and impedance matching
31 Narrow-Band Circular Waveguide Feed
Fig 31 shows the proposed narrow-band circular waveguide feed and its
design variables The feed consists of a circular waveguide open end excited
by a TE11 dominant mode A quarter wave choke is applied along the
circular aperture of the waveguide to equalize E- and H-plane radiation
patterns and to suppress the back radiation A dielectric ring is used to
control the radiation pattern and change the power distribution over the
aperture The control of the amplitude over the aperture are essential to the
design of symmetric radiation pattern The material used for dielectric loading
-26-
is the monocast(MC) nylon with a dielectric constant of 30 The feed is
designed to operate over 171-197GHz
(a)
(b)
Fig 31 Narrow-band circular waveguide feed (a) CAD model and (b) a
cross sectional view
The impedance matching is achieved by a proper combination of the probe
height lp and its distance sp from the waveguide shorted end Here the
-27-
circular waveguide is terminated with an open end with a wall thickness of
2mm radiating into the free space
Fig 32 shows the effect of the probe length lp and the probe distance sp
on the reflection coefficient The best performance is obtained when lp =
363mm and sp = 616mm The feeds reflection coefficient is less than -10dB
over 170-195GHz
(a)
(b)
Fig 32 Effect of the (a) the probe length lp and (b) the probe
distance sp on the reflection coefficient
-28-
Fig 33 shows the effect of the choke depth The E-plane pattern is more
sensitive to the choke depth than the H-plane pattern The choke depth has a
strong influence on the reflection coefficient when it is 360mm By properly
choosing the choke depth we can equalize the E- and H-plane patterns The
optimum value of the choke depth is 410mm which is 0249λ0 at 1825GHz
The choke slot width tch in the range of 06-12mm has almost no effect
on the H-plane pattern and the reflection coefficient For the E-plane pattern
tch of 12mm has some effect on the E-plane radiation pattern as shown in
Fig 34
Fig 35 shows the feed performance versus the dielectric ring length We
observe in Fig 35 that the dielectric length ld has an optimum value of
1168mm which does no effect on the H-plane pattern and tha the value of
1048mm has some effect on the E-plane pattern and the reflection
coefficient
Fig 36 shows E-plane and H-plane patterns and the reflection coefficient
versus the dielectric thickness With the optimum value of the dielectric
thickness t obtained from the Fig 36 is 155mm The larger values of td has
much stronger effects on the E-plane pattern and the reflection coefficient
The H-plane pattern is not sensitive to the dielectric ring thickness
-29-
(a)
(b)
(c)
Fig 33 Feed performance versus the choke depth (a) E-plane pattern
(b) H-plane pattern and (c) reflection coefficient
-30-
(a)
(b)
(c)
Fig 34 Feed performance versus the choke slot width (a) E-plane pattern
(b) H-plane pattern and (c) reflection coefficient
-31-
(a)
(b)
(c)
Fig 35 Feed performance versus the dielectric ring length (a) E-plane
pattern (b) H-plane pattern and (c) reflection coefficient
-32-
(a)
(b)
(c)
Fig 36 Feed performance versus the dielectric ring thickness (a) E-plane
pattern(b) H-plane pattern and (c) reflection coefficient
-33-
From the above parametric analysis an optimum feed design is obtained
The result is shown in Table 31 Fig 37 shows the 2D gain patterns of
designed feed The antenna has a gain of 903dB 933dB and 956dB at
171GHz 1825GHz and 19GHz respectively
Fig 38 shows E- and H-plane radiation patterns of the designed feed The
feed has E- and H-plane 10-dB beamwidths of 60 and 59 degrees at 17GHz
The feed has a front-to-back ration of 1900dB 2490dB and 2200dB at
171GHz 1825GHz and 19GHz respectively Table 32 summarizes the
performance of the designed narrow-band circular waveguide feed
The designed feed has a greatly improved performance over that of a
simple coax-fed feed described in Section 23
Table 31 Dimensions of the designed narrow-band circular feed
Parameter Designation Value(mm)
a Waveguide inside radius 640
l Feed length 2890
lp Probe length 363
sp Probe position from the back short 616
din Probe diameter 127
dout Diameter of coaxial cables outer conductor 400
t Thickness of choked wall 050
tch Choke slot width 100
lch Choke depth 410
ld Dielectric ring length 1168
td Dielectric ring thickness 155
d1 Waveguide outside diameter 1680
-34-
(a)
(b)
Fig 37 2D gain patterns of the narrow-band circular waveguide feed at
(a) 17GHz (b) 1825GHz and (c) 19GHz
-35-
(c)
Fig 37 continued
-36-
(a)
(b)
(c)
Fig 38 E- and H-plane patterns of the narrow-band circular waveguide feed
at (a) 10GHz (b) 1825GHz and (c) 195GHz
-37-
Frequency(GHz)
Gain(dB)
E-H-plane10-dB beamwidths
(deg)
Front-to-back ratio(dB)
Phase centerlocation
(From feeds aperture plane
toward reflector)
(mm)
1700 903 6059 20 062
1825 933 6060 25 004
1900 956 5759 22 007
Table 32 Performance of the narrow-band circular waveguide feed
The designed narrow-band feed is fabricated and its performance is
measured and compared with the simulation results The designed feed is
fabricated in a numerically-controlled machining center The fabricated antenna
is shown in Fig 39
Fig 39 Photograph of the fabricated feed
-38-
Fig 310 shows a comparison of the measured and simulated reflection
coefficients The measured reflection coefficient is less than -10dB over
171-197GHz The agreement between simulated and measured results are
good
Fig 311 shows the E- and H-plane patterns of the fabricated feed at
187GHz The feed has 90dB gain simulation and measurement results are in
good agreement
The fabricated antennarsquos 10dB beamwidth is 60 degrees in both E and H
planes at 187GHz The front-to-back ratio is 21dB
Fig 310 Reflection coefficient of the fabricated feed
-39-
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Fee
d H
orn
Gain
- d
B
Angle - degree
(a)
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Feed H
orn
Gain
- d
B
Angle - degree
(b)
Fig 311 Gain patterns of the fabricated feed at 187 GHz (a) E-plane and
(b) H-plane
-40-
IV Design of Circular Waveguide Feeds Loaded with a
Dielectric Rod
In this section circular waveguide feeds loaded with a dielectric rod feed
are investigated A comprehensive discussion of the circular waveguide loaded
with a dielectric rod is given by Kumar[7] Inserting a dielectric material
inside the circular waveguide improves the E- and H-plane pattern symmetry
In general dielectric-loaded circular waveguide feeds show good performance
only over a narrow bandwidth
Fig 41 shows the geometry of a circular waveguide loaded with a
dielectric rod The waveguide length is 400mm and the wall thickness is
05mm The dielectric rods diameter is 207mm The dielectric rod is
extended 05 wavelength beyond the waveguide open end The dielectric
constant εr is changed and the feeds performance is observed
Fig 41 Geometry of a circular waveguide loaded with a uniform dielectric
rod
-41-
Fig 42 is the radiation pattern of the feed with εr = 25 and L = 05λ0 at
9GHz E- and H-plane 10-dB beamwidths are 810 and 807 degrees
respectively The front-to-back ratio is 18dB The antenna gain is 71dB
(a)
(b)
Fig 42 Radiation pattern at 9GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 05λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-42-
Fig 43 shows the radiation pattern of the feed with εr = 21 at 10GHz
E- and H-plane 10-dB beamwidths are 70 and 71 degrees respectively The
front-to-back ratio is 19dB The antenna gain is 83dB
(a)
(b)
Fig 43 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 21 and L = 05λ0 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-43-
Fig 44 shows the radiation pattern of the feed with εr = 30 at 8GHz
E- and H-plane 10-dB beamwidths are 83 and 824 degrees respectively The
front-to-back ratio is 17dB The antenna gain is 73dB
(a)
(b)
Fig 44 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 30 and L = 05λ0 at 8GHz (a) 2D radiation pattern
and (b) E- and H-plane patterns
-44-
Fig 45 shows the radiation pattern of the feed with εr = 50 at 18GHz
E- and H-plane 10-dB beamwidths are 56 and 54 degrees respectively The
front-to-back ratio is 27dB The antenna gain is 105dB The feed has a good
pattern symmetry and low back radiation
(a)
(b)
Fig 45 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 50 and L = 05λ0 at 18GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-45-
Fig 46 is the radiation pattern of the feed with εr = 25 and L = 10λ0 at
10GHz E- and H-plane 10-dB beamwidths are 50 and 48 degrees
respectively The front-to-back ratio is 16dB The antenna gain is 105dB
(a)
(b)
Fig 46 Radiation pattern at 10GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 10λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-46-
Fig 47 shows the geometry of a circular waveguide with a tapered
dielectric rod The designed feed has the following dimension L = 1λ0 d =
1λ0 and εr =25 at 10GHz The waveguide length is 40mm and the wall
thickness is 05mm
L
Dielectricd3
Fig 47 Geometry of a circular waveguide loaded with a tapered dielectric
rod
Fig 48 shows the radiatio pattern of the designed feed E- and H-plane
10-dB beamwidths are 575 and 564 degrees respectively The front-to-back
ratio is 377dB The antenna gain is 94dB The designed feed has an
excellent beamwidth symmetry and a very low back radiation
-47-
(a)
(b)
Fig 48 Radiation pattern of a circular waveguide loaded with a tapered
dielectric rod with L = 1λ0 d = 1λ0 and εr =25 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-48-
Fig 49 shows the geometry of a spherical ended dielectric rod feed
diameter of 06λ0 at 10GHz with a dielectric constant of 25 and L= 03λ0
Fig 410 shows the radiation patterns of the designed feed E- and H-plane
10-dB beamwidths are both 63 degrees The front-to-back ratio is 24dB The
antenna gain is 864dB
Fig 49 Geometry of a circular waveguide loaded with a spherical ended
dielectric rod
-49-
(a)
(b)
Fig 410 Radiation pattern of a circular waveguide loaded wht a spherical
ended dielectric rod with d = 06λ0 L = 03λ0 and εr =25 at 10GHz (a) 3D
radiation pattern and (b) E- and H-plane patterns
-50-
V Design of a Broadband Circular Waveguide Feed
In this chapter the design of a broadband circular waveguide feed is
presented At microwave frequencies the feed is often a circular waveguide
with chokes and corrugations around the aperture Chokes and corrugations
equalize E- and H-plane patterns and reduce the back radiation
The proposed feed is designed to operate over 10-18GHz The design starts
with the optimization of the coaxial-to-rectangular waveguide adapter
employed for good mode purity over a broad frequency range Next a
rectangular-to-circular waveguide transition is optimized Finally chokes and
corrugations are designed for improved pattern symmetry and low back
radiation
The proposed feed structure is shown in Fig 51 The feed consist of the
following parts a coaxial-to-rectangular waveguide adapter a rectangular-to-
circular waveguide transition a circular waveguide section four quarter-wave
chokes around the feeds aperture and four corrugations on the feeds outer
surface
The computer simulation shows the above arrangement offers good radiation
patterns over a broad frequency range The broadband operation is obtained
by exciting the TE11 mode in the circular waveguide using the TE10 mode of
the rectangular waveguide which is in turn excited by a coaxial probe
-51-
Chokes
Coaxial-to-waveguide transition
Circular wavguide
Corrugations
Mode transition
(a)
(b)
Fig 51 Structure of the proposed broadband circular waveguide feed
(a) CAD model and (b) cross-sectional view
For the coaxial-to-rectangular waveguide adapter an SMA connector with
the probe diameter of 127 mm is employed The coaxial probe inserted into
the waveguide energizes the feed and excites the dominant TE10 mode in
-52-
the rectangular waveguide The impedance matching is achieved by adjusting
the probe distance sp from the back short and the probe length lp
(a)
(b)
Fig 52 Reflection coefficient of the coaxial-to-rectangular adapter versus
(a) probe length lp and (b) the probe position sp
Fig 52 shows the reflection coefficient versus the various values of probe
lengths lp and probe positions sp The probe length lp is adjusted to obtain
antenna impedance matching and the probe distance sp is adjusted to obtain a
-53-
desired resonant frequency
Next a transition between rectangular and circular waveguide is designed
The transition section converts the TE10 mode in the rectangular waveguide to
TE11 mode in the circular waveguide and vice versa The transition is built
in a form of a taper for easy fabrication[22]
(a)
(b)
Fig 53 Structure of the rectangular-to-circular waveguide transition
(a) 3D view and (b) cross sectional view
The dimensions of the final optimized transition are as follows The length
of the rectangular waveguide section is 143mm The rectangular waveguides
width a and height b are 207mm and 857mm respectively The length of
the circular waveguide section is 143mm The inside diameter of the circular
-54-
waveguide is 207mm(097 wavelength at 14GHz) The length of transition
region ltr is 4465mm(approximately equal to 2λ0 at 14GHz) Fig 54 shows
the field distribution inside the mode converter
(a)
(b)
Fig 54 Field distribution inside the mode converter at
(a) 10GHz (b) 14GHz and (c) 18GHz
-55-
(c)
Fig 54 continued
Finally multiple chokes are investigated Figs 55 56 and 57 show the
feed performance without chokes The reflection coefficient is less than -10dB
over 10-19GHz The antenna has a gain of 921dB to 1189dB over
10-19GHz
Fig 55 Reflection coefficient of the broadband circular waveguide feed
without chokes and corrugations
-56-
(a)
(b)
(c)
Fig 56 E- and H-plane patterns of the broadband circular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-57-
(d)
(e)
Fig 56 continued
-58-
(a)
(b)
Fig 57 2D radiation patterns of the broadband cicular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-59-
(c)
(d)
Fig 57 continued
-60-
(e)
Fig 57 continued
To achieve equal beamwidths in E and H planes over a wide frequency
range chokes and corrugations are employed Table51 summarizes the
performance of a feed without chokes and corrugations
Table 51 Performance of the broadband circular waveguide feed without
chokes and corrugations
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
1000 940 6061 15
1200 972 6159 17
1400 920 5957 21
1600 1070 4751 29
1800 1188 5352 21
-61-
Four quarter-wavelength chokes are introduced in the feed design which
has a slot depth of 75mm and slot width of 09mm The choke slot spacing
is 18mm The choke design is investigated by applying the choke one by
one and the effect on the E- and H-plane patterns are observed as illustrated
in Figs 58 and 59 The use of chokes makes the E-plane pattern narrower
The H-plane pattern is not affected Chokes increase the gain slightly and
reduce back radiation
(a)
(b)
Fig 58 Effect of chokes on the E-plane pattern of the broadband circular
waveguide feed at (a) 10GHz(b) 12GHz (c) 14GHz (d) 16GHz and (e)
18GHz
-62-
(c)
(d)
(e)
Fig 58 continued
-63-
(a)
(b)
(c)
Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-64-
(d)
(e)
Fig 59 continued
-65-
Fig 510 shows the feed performance versus the choke depth When the
choke depth is varied from 535mm to 95mm the E- and H-plane patterns
are strongly affected The optimum value of choke depth is 75mm(035λ0 at
14GHz) which gives equal E- and H-plane radiation patterns and leads to
low back radiation
Fig 511 shows the feed performance versus the choke slot width tch The
choke slot width is varied from 09mm to 21mm Radiation patterns and
reflection coefficients are not sensitive to the choke slot width The final
choke slot width is selected to be 09mm considering the feed diameter
minimization and the manufacturability The overall diameter of the proposed
feed is 369mm which is increased from the 207mm of the waveguide
inside diameter due to the use of four chokes
-66-
(a)
(b)
(c)
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection coefficient
-67-
(a)
(b)
(c)
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and (c)
reflection coefficient
-68-
Next we investigated corrugations placed on the outer wall of the feed
Four corrugations applied to the outer surface of the circular waveguide The
corrugation depth is 465mm(0215λ0 at 14GHz) The primary purpose of
using corrugations is to further reduce the back radiation Increasing the
number of corrugations beyond four has little effect in reducing the back
radiation
Figs 512 and 513 show the effect of corrugations on the E- and H-plane
patterns Fig 514 shows the parametric study of the corrugation depth lcor
The corrugation depth is varied from 40mm and 645mm The optimum
value of the corrugation depth is found to be 465mm
-69-
(a)
(b)
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern at (a) 12GHz and (b) 14GHz
-70-
(a)
(b)
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern at (a) 12GHz and (b) 14GHz
-71-
(a)
(b)
(c)
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection coefficient
-72-
The phase center location is important in placing the feed in a reflector
antenna[8] The phase center variation with frequency should be small Fig
515 shows the effect of chokes and corrugations on the phase center The
curve with circle corresponds to the case without chokes and corrugations
The phase center varies from -326mm and -190mm away from the feeds
aperture plane It means the phase center is located inside the waveguide
The curve with triangles corresponds to the case with chokes The curve with
squares to the case with chokes and corrugations The phase center varies
from 0mm to -302mm
From Fig 515 we can observed that phase center variation reduced by the
corrugation and three cases phase center calculated in φ=450 plane
parameter sweep values are given in Table 52
10 12 14 16 181
0
-1
-2
-3
-4
-5
-6
Pha
se c
ente
r (m
m)
Frequency (GHz)
choke+corrugatuion without choke corrugation with choke
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
-73-
Frequency
(GHz)
Phase center from the aperture plane
(mm)
Without
chokes and
corrugations
With
chokes
With chokes
and
corrugations
1000 -326 062 000
1100 -187 030 -002
1200 -563 -208 -065
1300 -296 -154 -202
1400 -319 -314 -302
1500 -201 -203 -241
1600 -242 -233 -207
1700 -208 -208 -186
1800 -190 -157 -132
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
Based on the foregoing parametric studies optimum dimensions of the
broadband circular waveguide feed are obtained as shown in Table 53
-74-
Table 53 Optimum dimensions of the broadband circular waveguide feed
Parameter Designation Value (mm)
2a Waveguide inside diameter 2070
d Waveguide outside diameter 3690
lcrLength of the circular waveguide section 1430
m Distance between the aperture plane and the first corrugation 950
xDistance from the last corrugation to the end of the cylindrical outer surface
550
ltrLength of the rectangular-to-circularwaveguide transition 4465
lrcLength of the rectangular waveguide section 1430
tch Choke slot width 090
lch Choke depth 750
t Choke metal width 090
lcor Corrugation depth 465
tcor Corrugation metal width 100
s Corrugation slot width 10
lp Probe length 530
sp Probe position from the back short 530
din Probe diameter 127
b Inside height of the rectangular waveguide 857
tw Waveguide wall thickness 500
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
工學碩士學位論文
포물 반사경용 역 피드 설계
DesignofaBroadbandFeedforParabolic
ReflectorApplication
忠 北 大 學 校 大 學 院
電波工學科 電波通信工學 攻
어덩토야 바상재랜 (OdontuyaBaasantseren)
2012年 8月
工學碩士學位論文
포물 반사경용 역 피드 설계
DesignofaBroadbandFeedforParabolic
ReflectorApplication
指 敎授 安 炳 哲
電波工學科 電波通信工學 攻
어덩토야 바상재랜 (OdontuyaBaasantseren)
이 論文을 工學碩士學位 論文으로 提出함
2012年 8月
本 論文을 金岐祿의 工學碩士學位 論文으로 認定함
審 査 委 員 長 안 재 형
審 査 委 員 안 병 철
審 査 委 員 방 재 훈
忠 北 大 學 校 大 學 院
2012年 8月
-i-
Contents
Abstract middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot ii
List of figures middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot iv
List of tables middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot ix
Ⅰ Indtroduction middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 1
Ⅱ Analysis of Circular and Square Waveguide Feeds middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 4
21 Circular Waveguide Radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 4
22 Square Waveguide Radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 10
23 Probe-Fed Circular Waveguide Radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 15
24 Probe-Fed Circular Waveguide Radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 20
Ⅲ Design of Compact Circular Waveguide Feeds middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 25
31 Narrow-Band Circular Waveguide Feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 25
32 Fabrication and Measurement middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 38
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod middotmiddotmiddotmiddotmiddotmiddot 40
41 Design of dielectric rod feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 40
V Design of Broadband Circular Waveguide Feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 50
51 Design of Broadband Circular Waveguide Feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 50
52 Fabrication and Measurement middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 82
Ⅳ Conclusion middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 85
REFERENCES middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 88
ACKNOWLEDGEMENT middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 89
-ii-
DesignofaBroadbandFeedforParabolic
ReflectorApplications
Odontuya Baasantseren
Department of Radio and Communications Engineering
Graduate School Chungbuk National University
Cheongju City South Korea
Supervised by Professor Bierng-Chearl Ahn Ph D
Abstract
In this thesis the design of a broadband feed for application in prime-focus
parabolic reflector antenna is described A feed for parabolic reflector antenna
requires radiation pattern with a good circular symmetry low back radiation
and low cross polarization This thesis proposes two feed designs one is a
dielectric ring-loaded circular waveguide operating over 171-197GHz and
fed by a coaxial probe The other is a choked and corrugated circular
waveguide fed by a probe-fed rectangular waveguide Before designing two
A thesis for the degree of Master in August 2012
-iii-
feeds performances of simple circular and square waveguide open ends are
investigated The improvement in the performance of the circular waveguide
open end by dielectric loading is also investigated The study shows that only
a narrow-band performance is possible with simple feeds
Based on this study the first feed is designed with the monocast(MC)
nylon as the dielectric-ring material for beamwidth equalization and a
quarter-wave choke around the aperture wall for back-radiation reduction A
coaxial probe is used to excite the feed The designed feed shows a good
performance over 171-197GHz
The second feed uses more complicated structures For broadband operation
the circular waveguide is fed by a probe-excited rectangular waveguide Four
quarter-wave chokes are used around the aperture wall for beamwidth
equalization and four corrugations are employed on the feeds outer surface
for further reduction in the back radiation
Prototypes of both feeds are fabricated and tested Test results are in good
agreement with the design objectives verifying the excellent performances of
the designed feeds
-iv-
List of Figures
Fig 21 Geometry of a circular waveguide open end radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 6
Fig 22 Reflection coefficient of a circular waveguide open end radiator middotmiddot 6
Fig 23 2D radiation pattern of a circular waveguide open end radiator middotmiddotmiddot 7
Fig 24 E-plane and H-plane patterns of a circular waveguide open end
radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 9
Fig 25 Geometry of a square waveguide open end radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 11
Fig 26 Reflection coefficient of a square waveguide open end radiator middot 12
Fig 27 2D radiation patterns of a square waveguide open end radiator middot 12
Fig 28 E-plane and H-plane patterns of square waveguide open end
radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 14
Fig 29 Probe-fed circular waveguide radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 16
Fig 210 Reflection coefficient of the probe-fed circular waveguide radiator
middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 17
Fig 211 2D radiation patterns of the probe-fed circular waveguide radiator
middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 17
Fig 212 E- and H-plane patterns of the probe-fed circular waveguide
radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 19
Fig 213 Probe-fed square waveguide radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 20
Fig 214 2D radiation pattern of the probe-fed square waveguide radiator 21
Fig 215 E- and H-plane pattern of the probe-fed square waveguide radiator
middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 23
Fig 216 Reflection coefficient of the probe-fed square waveguide radiator 24
Fig 31 Narrow-band circular waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 26
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Fig 32 Effect of the (a) the probe length lp (b) the probe distance sp on
the reflection coefficient middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 27
Fig 33 Feed performance versus the choke depth (a) E-plane pattern (b)
H- plane pattern (c) reflection coefficient middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 29
Fig 34 Feed performance versus the choke slot width (a) E-plane pattern
(b) H-plane pattern (c) reflection coefficient middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 30
Fig 35 Feed performance versus the dielectric ring length (a) E-plane
pattern (b) H-plane pattern and (c) reflection coefficient middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 31
Fig 36 Feed performance versus the dielectric ring thickness (a) E-plane
pattern (b) H-plane pattern (c) reflection coefficient middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 32
Fig 37 2D gain patterns of the narrow-band circular waveguide feed middotmiddotmiddot 34
Fig 38 E- and H-plane patterns of the narrow-band circular waveguide
feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 30
Fig 39 Photograph of the fabricated feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 37
Fig 310 Reflection coefficient of the fabricated feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 38
Fig 311 Gain patterns of the fabricated feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 39
Fig 41 Geometry of a circular waveguide loaded with a uniform dielectric
rod middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 40
Fig 42 Radiation pattern at 9GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 05λ0 middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 41
Fig 43 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 21 and L = 05λ0 at 10GHz middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 42
Fig 44 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 30 and L = 05λ0 at 8GHz middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 43
Fig 45 Radiation pattern of the circular waveguide loaded with a uniform
-vi-
dielectric rod with εr = 50 and L = 05λ0 at 18GHz middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 44
Fig 46 Radiation pattern at 10GHz of the circular waveguide loaded with
a uniform dielectric rod with εr = 25 and L = 10λ0 middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 45
Fig 47 Geometry of a circular waveguide loaded with a tapered dielectric
rod middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 46
Fig 48 Radiation pattern of a circular waveguide loaded with a tapered
dielectric rod with L = 1λ0 d = 1λ0 and εr =25 at 10GHz middotmiddotmiddotmiddotmiddotmiddotmiddot 47
Fig 49 Geometry of a circular waveguide loaded with a spherical ended
dielectric rod middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 48
Fig 410 Radiation pattern of a circular waveguide loaded wht a spherical
ended dielectric rod with d = 06λ0 L = 03λ0 and εr =25 at
10GHz middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 49
Fig 51 Structure of the proposed broadband circular waveguide feed middotmiddotmiddotmiddotmiddot 51
Fig 52 Reflection coefficient of the coaxial-to-rectangular adapter versus
(a) probe length lp and (b) the probe position sp middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 52
Fig 53 Structure of the rectangular-to-circular waveguide transition middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 53
Fig 54 Field distribution inside the mode converter middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 54
Fig 55 Reflection coefficient of the broadband circular waveguide feed
without chokes and corrugations middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 55
Fig 56 E-plane and H-plane patternsof the broadband circular waveguide
feed without chokes and corrugationsz middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 56
Fig 57 2D radiation patterns of the broadband cicular waveguide feed
without chokes and corrugations middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 58
Fig 58 Effect of chokes on the E-plane pattern of the broadband circular
waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 61
-vii-
Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 63
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection
coefficient middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 66
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and
(c) reflection coefficient middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 67
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 69
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 70
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection
coefficient middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 71
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 72
Fig 516 Reflection coefficient of the designed broadband circular
waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 75
Fig 517 2D radiation patterns of the designed broadband circular
waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 76
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 79
Fig 519 Phase center variation of the designed broadband circular
waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 81
-viii-
Fig 520 Photograph of the fabricated broadband circular waveguide feed 82
Fig 521 Reflection coefficient of the fabricated broadband circular
waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 82
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 84
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 84
-ix-
List of Tables
Table 21 Properties of a circular waveguide open end radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 10
Table 22 Properties of a square waveguide open end radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 15
Table 23 Properties of the probe-fed circular waveguide radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 20
Table 24 Properties of the probe-fed square waveguide radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 24
Table 31 Dimensions of the designed narrow-band circular feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 33
Table 32 Performance of the narrow-band circular waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 37
Table 51 Performance of the broadband circular waveguide feed without
chokes and corrugations middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 60
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 73
Table 53 Optimum dimensions of the broadband circular waveguide feed 74
Table 54 Performance of the designed broadband circular waveguide feed 81
-1-
I Introduction
The horns and waveguides are known for their high efficiency and
structural simplicity They are popular choices for feeding for reflectors in
high-gain antenna applications such as satellite and point-to-point microwave
communication links The theory of reflector antenna was developed in the
1940s and has been used to calculate the radiation patterns of various
reflector structures[1]
The basic structure of a prime-focus reflector antenna consists of a
parabolic reflecting surface a feed and its support The placement of the feed
is such that its phase center is at the focal point of the parabolic reflecting
surface The feed is often a circular waveguide because of its symmetric
radiation pattern with low back radiation and low cross polarization The
circular waveguide feed must have a small diameter to reduce the aperture
blockage of the reflector antenna[3]
A radiation pattern with a good circular symmetry in the main beam can
be found from circular waveguide feeds with dominant TE11 mode excitation
The radiation patterns depends on the diameter and wall thickness of the
waveguide[4] A coaxial probe can be inserted into a short-circuited circular
waveguide in the form of a coaxial-to-waveguide transition The diameter of
the circular waveguide is chosen such that only the dominant mode
propagates
When the waveguide dimension does not provide a circular symmteric
-2-
pattern a choke or multiple chokes around the aperture wall can be
employed to equalize radiation patterns and keep the back radiation in low
level If chokes are not enough for the suppression of the back radiation
corrugations on the outer surface of the feed is one way to reduce the back
radiation
In this thesis a broadband circular waveguide feed is developed for
prime-focus reflector antenna application After investigating the radiation
properties of simple circular and square waveguides methods are investigated
for bandwidth enhancement back radiation suppression and beamwidth
equalization in the circular waveguide feed
The first type of the circular waveguide feed consists of a probe-fed
circular waveguide a single quarter-wave choke on the aperture wall and a
dielectric-ring beamwidth equalizer Due to the simple feeding method the
first feed operates over 171-197GHz(141) which is not broadband in the
strict sense of the word
The second feed consists of a coaxial-to-rectangular waveguide transition a
rectangular-to-circular waveguide transition a circular waveguide section four
quarter-wave chokes on the aperture wall and four quarter-wave corrugations
on the feeds outer surface Due to the complicated feeding method the
second feed operates over 10-18GHz(571)
This thesis is arranged as follows Chapter I gives an introduction to the
thesis related works and objectives are stated Chapter II describes the
structure and excitation of the circular and square waveguide and the
operation of the coaxial-to-waveguide transitions Chapter III describes a
compact feed horn design and its fabrication and measurement Chapter IV
-3-
presents dielectric rod feed and its simulated performances Chapter V gives
design and optimization of feed for parabolic reflector antenna In this
chapter includes the detailed information of design procedures and operating
principle also the simulated and measured performances are provided Finally
conclusion is given in the Chapter VI
-4-
II Analysis of Circular and Square Waveguide Feeds
21 Circular Waveguide Radiator
Before design a complicated circular waveguide feed it is helpful to
investigate the impedance and radiation properties of a circular waveguide
open end
The circular waveguide is a cylindrical hollow metallic pipe with a uniform
circular section of radius a Circular waveguides are normally designed to
operate only with the dominant mode The dominant mode in a waveguide is
the mode having the lowest cutoff frequency given by equation (21)
(21)
where
(22)
and a is the waveguide radius The following chart[2] and table show the
cutoff frequencies of various modes in a circular waveguide
-5-
Modes c al11TEc cf f
TE11 341259 100000
TM01 261274 130613
TE21 205720 165885TE01 163979 208111
TM11 163979 208111TE31 149557 228180
TM21 122345 278932TE41 118159 288813
TE12 117852 289566
TM02 113824 299813TE02 0897986 380027
The recommended frequency range of the commercial circular waveguide is
given by the following equation This assumes that the TM01 mode is not
generated or suppressed if generated
11 21 11TE TE TE115 095 158 32 bandwidthc c cf f f fpound pound = reg (23)
Fig 21 shows the geometry of a circular waveguide with a diameter of 2a
When 2a is 2053mm the cutoff frequency of the TE11 mode is 857GHz
According to (23) the useful operating frequency range is from
986-1354GHz
Fig 22 shows the reflection of this waveguide excited with the dominant
TE11 mode The waveguide length l is 60mm The reflection occurs at the
open end of the circular waveguide The reflection coefficient is less than
-15dB over 10-18GHz
-6-
Fig 21 Geometry of a circular waveguide open end radiator
Fig 23 shows a 2D gain pattern of this waveguide antenna The
waveguide antenna has a gain of 80dB 99dB and 115dB at 10GHz
14GHz and 18GHz respectively Fig 24 shows the E- and H-plane patterns
of the circular waveguide antenna Table 21 summarizes the properties of a
circular waveguide antenna
Fig 22 Reflection coefficient of a circular waveguide open end radiator
-7-
(a)
(b)
Fig 23 2D radiation pattern of the circular waveguide open end radiator
at (a)10GHz (b) 14GHz and (c) 18GHz
-8-
(c)
Fig 23 continued
-9-
(a)
(b)
(c)
Fig 24 E-plane and H-plane patterns of the circular waveguide open end
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-10-
Table 21 Properties of a circular waveguide open end radiator of diameter
2053mm
Frequency(GHz)-10dB Beamwith(deg) Front-to-Back
Ratio(dB)E plane H plane
10 67 73 12
14 58 60 18
18 41 50 21
In a circular waveguide radiatoλr a good pattern symmetry and low back
radiation is obtained at 14GHz where 2aλ = 096
22 Square Waveguide Radiator
A square waveguide is often used as a dual-polarized feed To operate the
cutoff frequency of the dominant mode a square-waveguide wall width a
must be greater than one half of a wavelength The modes with cutoff
frequencies equal to or smaller than the operational frequency can exist inside
the waveguide wall The lower cutoff frequency and cutoff wavelength for
square waveguide is determined by the following equations
TE
(24)
TE
(25)
The next higher-order mode is TE11 mode with the cutoff wavelength
given by
-11-
TE
(26)
Similar to the circular waveguide the recommended operating frequency range
of a square waveguide is given by
TEleleTE
TErarr bandwidth (27)
Fig 25 shows the geometry of a square waveguide with a dimension of a
When a is 157mm the cutoff frequency is 95GHz The recommended
operating frequency of this waveguide is from 109GHz to 155GHz
Fig 26 shows the reflection of this waveguide excited with the dominant
TE10 mode The reflection coefficient is less than -15dB over 10-20GHz
Fig 25 Geometry of a square waveguide open end radiator
Fig 27 and shows the 2D radiation pattern of a square waveguide antenna
excited with the dominant TE10 mode The antenna has a gain of 73dB
85dB and 102dB at 10GHz 14GHz and 18GHz respectively Fig 28
shows the E- and H-plane radiation patterns of a square waveguide radiator
Table 22 summarizes the properties of a square waveguide open end radiator
-12-
Fig 26 Reflection coefficient of a square waveguide open end radiator
(a)
Fig 27 2D radiation patterns of a square waveguide radiator
at (a) 10GHz (b) 14GHz and (c) 18GHz
-13-
(b)
(c)
Fig 27 continued
-14-
(a)
(b)
(c)
Fig 28 E-plane and H-plane patterns of square waveguide open radiator
at (a) 10GHz(b) 14GHz and (c) 18GHz
-15-
Table 22 Properties of a square waveguide open end radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 69 71 11
14 47 60 25
18 58 62 16
The radiation pattern symmetry and back radiation performance of the
square waveguide are inferior to those of a circular waveguide
23 Probe-Fed Circular Waveguide Radiator
In Section 21 the radiation properties of a TE11-mode excited waveguide
is investigated In this section a circular waveguide fed by a coaxial probe
shown in Fig 29 is studied
The coaxial probes diameter is 127mm With the Teflon dielectric the
50-ohm coaxial lines outer conductor has a diameter of 41mm For a
circular waveguide the wave impedance of the TE11 mode is given by
∙ (28)
where λg is the guided wavelength given by
(29)
-16-
(a) (b)
Fig 29 Probe-fed circular waveguide radiator (a) Front view and (b) side
view
The combination of the probe length and the probe position from the
shorted wall enables a good impedance matching The probe distance sp from
the back short is close to a quarter wavelength at the design frequency
The designed feed has the following dimension d = 2053mm lp = 42
mm sp = 534mm wall thickness = 05mm and feed length = 400mm
Fig 210 shows the reflection coefficient of the designed probe-fed
circular waveguide radiator The reflection coefficient is less than -10dB over
138-187GHz Fig 211 and 212 shows the E-plane and H-plane radiation
patterns and 2D radiation patterns of the coaxial-to-circular waveguide
transition The radiation patterns symmetry distorted because of the high order
modes The coaxial-to-circular waveguide transition has 73dB 84dB and
79dB gain at 10GHz 14GHz and 18GHz frequencies respectively Table 23
shows the properties of the coaxial-to-circular waveguide transition
-17-
Fig 210 Reflection coefficient of the probe-fed circular waveguide radiator
(a)
Fig 211 2D radiation pattern of the probe-fed circular waveguide radiator
at (a) 10GHz (b) 14GHz and (c) 18GHz
-18-
(b)
(c)
Fig 211 continued
-19-
(a)
(b)
(c)
Fig 212 E- and H-plane patterns of the probe-fed circular waveguide
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-20-
Table 23 Properties of the probe-fed circular waveguide radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 73 70 1414 83 57 17
18 60 52 30
When a circular waveguide radiator is fed by a coaxial probe its radiation
properties are not good due to the excitation of higher-order modes
Therefore a probe-fed circular waveguide radiator can be used as a feed only
over a narrow frequency range
24 Probe-Fed Square Waveguide Radiator
In this section a probe-fed square waveguide radiator is investigated Fig
213 shows a coaxial probe-fed square waveguide radiator The designed
radiator has the following dimension a = b = 157mm lp = 35 mm sp =
50 mm wall thickness = 05mm and feed length = 40mm
(a) (b)
Fig 213 Probe-fed square waveguide radiator (a) Front view and (b) side
view
-21-
Fig 214 shows the 2D radiation patterns of the radiator at 10GHz
14GHz and 18GHz Fig 215 shows E- and H-plane patterns of the radiator
Fig 216 shows the reflection coefficient of the probe-fed square waveguide
radiator The reflection coefficient is less than -10dB over 13-20GHz Table
24 summarizes the properties of the probe-fed square waveguide radiator
(a)
Fig 214 2D radiation patterns of the probe-fed square waveguide radiator at
(a) 10GHz (b) 14GHz and (c) 18GHz
-22-
(b)
(c)
Fig 214 continued
-23-
(a)
(b)
(c)
Fig 216 E-plane and H-plane patterns of the probe-fed square waveguide
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-24-
Fig 216 Reflection coefficient of the probe-fed square waveguide radiator
Table 24 Properties of the probe-fed square waveguide radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 73 71 12
14 85 63 1418 27 65 28
When a square waveguide radiator is fed by a coaxial probe its radiation
properties are not good due to the excitation of higher-order modes as in the
case of the probe-fed circular waveguide radiator A probe-fed square
waveguide radiator can be used as a feed only over a narrow frequency
range
-25-
III Design of Compact Circular Waveguide Feeds
In this chapter the feed design is presented for a prime-focus reflector
antenna The prime-focus paraboloid reflector is one of the most commonly
used high-gain antenna It has been used in earth-station antennas and radio
telescopes It consists of a paraboloid reflector with a feed system at its focal
point
The feed should radiate a low level of cross-polar power over the
operating frequency These conditions not easy to achieve and most prime
focus feeds are compromises The shape and characteristic of the radiation
pattern of the feed are the most important parameter because these will
directly influence the fields which are directed at a reflector[6] Other
electrical factors which relevant to the choice of a feed are the cross-polar
level the gain efficiency the bandwidth and impedance matching
31 Narrow-Band Circular Waveguide Feed
Fig 31 shows the proposed narrow-band circular waveguide feed and its
design variables The feed consists of a circular waveguide open end excited
by a TE11 dominant mode A quarter wave choke is applied along the
circular aperture of the waveguide to equalize E- and H-plane radiation
patterns and to suppress the back radiation A dielectric ring is used to
control the radiation pattern and change the power distribution over the
aperture The control of the amplitude over the aperture are essential to the
design of symmetric radiation pattern The material used for dielectric loading
-26-
is the monocast(MC) nylon with a dielectric constant of 30 The feed is
designed to operate over 171-197GHz
(a)
(b)
Fig 31 Narrow-band circular waveguide feed (a) CAD model and (b) a
cross sectional view
The impedance matching is achieved by a proper combination of the probe
height lp and its distance sp from the waveguide shorted end Here the
-27-
circular waveguide is terminated with an open end with a wall thickness of
2mm radiating into the free space
Fig 32 shows the effect of the probe length lp and the probe distance sp
on the reflection coefficient The best performance is obtained when lp =
363mm and sp = 616mm The feeds reflection coefficient is less than -10dB
over 170-195GHz
(a)
(b)
Fig 32 Effect of the (a) the probe length lp and (b) the probe
distance sp on the reflection coefficient
-28-
Fig 33 shows the effect of the choke depth The E-plane pattern is more
sensitive to the choke depth than the H-plane pattern The choke depth has a
strong influence on the reflection coefficient when it is 360mm By properly
choosing the choke depth we can equalize the E- and H-plane patterns The
optimum value of the choke depth is 410mm which is 0249λ0 at 1825GHz
The choke slot width tch in the range of 06-12mm has almost no effect
on the H-plane pattern and the reflection coefficient For the E-plane pattern
tch of 12mm has some effect on the E-plane radiation pattern as shown in
Fig 34
Fig 35 shows the feed performance versus the dielectric ring length We
observe in Fig 35 that the dielectric length ld has an optimum value of
1168mm which does no effect on the H-plane pattern and tha the value of
1048mm has some effect on the E-plane pattern and the reflection
coefficient
Fig 36 shows E-plane and H-plane patterns and the reflection coefficient
versus the dielectric thickness With the optimum value of the dielectric
thickness t obtained from the Fig 36 is 155mm The larger values of td has
much stronger effects on the E-plane pattern and the reflection coefficient
The H-plane pattern is not sensitive to the dielectric ring thickness
-29-
(a)
(b)
(c)
Fig 33 Feed performance versus the choke depth (a) E-plane pattern
(b) H-plane pattern and (c) reflection coefficient
-30-
(a)
(b)
(c)
Fig 34 Feed performance versus the choke slot width (a) E-plane pattern
(b) H-plane pattern and (c) reflection coefficient
-31-
(a)
(b)
(c)
Fig 35 Feed performance versus the dielectric ring length (a) E-plane
pattern (b) H-plane pattern and (c) reflection coefficient
-32-
(a)
(b)
(c)
Fig 36 Feed performance versus the dielectric ring thickness (a) E-plane
pattern(b) H-plane pattern and (c) reflection coefficient
-33-
From the above parametric analysis an optimum feed design is obtained
The result is shown in Table 31 Fig 37 shows the 2D gain patterns of
designed feed The antenna has a gain of 903dB 933dB and 956dB at
171GHz 1825GHz and 19GHz respectively
Fig 38 shows E- and H-plane radiation patterns of the designed feed The
feed has E- and H-plane 10-dB beamwidths of 60 and 59 degrees at 17GHz
The feed has a front-to-back ration of 1900dB 2490dB and 2200dB at
171GHz 1825GHz and 19GHz respectively Table 32 summarizes the
performance of the designed narrow-band circular waveguide feed
The designed feed has a greatly improved performance over that of a
simple coax-fed feed described in Section 23
Table 31 Dimensions of the designed narrow-band circular feed
Parameter Designation Value(mm)
a Waveguide inside radius 640
l Feed length 2890
lp Probe length 363
sp Probe position from the back short 616
din Probe diameter 127
dout Diameter of coaxial cables outer conductor 400
t Thickness of choked wall 050
tch Choke slot width 100
lch Choke depth 410
ld Dielectric ring length 1168
td Dielectric ring thickness 155
d1 Waveguide outside diameter 1680
-34-
(a)
(b)
Fig 37 2D gain patterns of the narrow-band circular waveguide feed at
(a) 17GHz (b) 1825GHz and (c) 19GHz
-35-
(c)
Fig 37 continued
-36-
(a)
(b)
(c)
Fig 38 E- and H-plane patterns of the narrow-band circular waveguide feed
at (a) 10GHz (b) 1825GHz and (c) 195GHz
-37-
Frequency(GHz)
Gain(dB)
E-H-plane10-dB beamwidths
(deg)
Front-to-back ratio(dB)
Phase centerlocation
(From feeds aperture plane
toward reflector)
(mm)
1700 903 6059 20 062
1825 933 6060 25 004
1900 956 5759 22 007
Table 32 Performance of the narrow-band circular waveguide feed
The designed narrow-band feed is fabricated and its performance is
measured and compared with the simulation results The designed feed is
fabricated in a numerically-controlled machining center The fabricated antenna
is shown in Fig 39
Fig 39 Photograph of the fabricated feed
-38-
Fig 310 shows a comparison of the measured and simulated reflection
coefficients The measured reflection coefficient is less than -10dB over
171-197GHz The agreement between simulated and measured results are
good
Fig 311 shows the E- and H-plane patterns of the fabricated feed at
187GHz The feed has 90dB gain simulation and measurement results are in
good agreement
The fabricated antennarsquos 10dB beamwidth is 60 degrees in both E and H
planes at 187GHz The front-to-back ratio is 21dB
Fig 310 Reflection coefficient of the fabricated feed
-39-
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Fee
d H
orn
Gain
- d
B
Angle - degree
(a)
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Feed H
orn
Gain
- d
B
Angle - degree
(b)
Fig 311 Gain patterns of the fabricated feed at 187 GHz (a) E-plane and
(b) H-plane
-40-
IV Design of Circular Waveguide Feeds Loaded with a
Dielectric Rod
In this section circular waveguide feeds loaded with a dielectric rod feed
are investigated A comprehensive discussion of the circular waveguide loaded
with a dielectric rod is given by Kumar[7] Inserting a dielectric material
inside the circular waveguide improves the E- and H-plane pattern symmetry
In general dielectric-loaded circular waveguide feeds show good performance
only over a narrow bandwidth
Fig 41 shows the geometry of a circular waveguide loaded with a
dielectric rod The waveguide length is 400mm and the wall thickness is
05mm The dielectric rods diameter is 207mm The dielectric rod is
extended 05 wavelength beyond the waveguide open end The dielectric
constant εr is changed and the feeds performance is observed
Fig 41 Geometry of a circular waveguide loaded with a uniform dielectric
rod
-41-
Fig 42 is the radiation pattern of the feed with εr = 25 and L = 05λ0 at
9GHz E- and H-plane 10-dB beamwidths are 810 and 807 degrees
respectively The front-to-back ratio is 18dB The antenna gain is 71dB
(a)
(b)
Fig 42 Radiation pattern at 9GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 05λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-42-
Fig 43 shows the radiation pattern of the feed with εr = 21 at 10GHz
E- and H-plane 10-dB beamwidths are 70 and 71 degrees respectively The
front-to-back ratio is 19dB The antenna gain is 83dB
(a)
(b)
Fig 43 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 21 and L = 05λ0 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-43-
Fig 44 shows the radiation pattern of the feed with εr = 30 at 8GHz
E- and H-plane 10-dB beamwidths are 83 and 824 degrees respectively The
front-to-back ratio is 17dB The antenna gain is 73dB
(a)
(b)
Fig 44 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 30 and L = 05λ0 at 8GHz (a) 2D radiation pattern
and (b) E- and H-plane patterns
-44-
Fig 45 shows the radiation pattern of the feed with εr = 50 at 18GHz
E- and H-plane 10-dB beamwidths are 56 and 54 degrees respectively The
front-to-back ratio is 27dB The antenna gain is 105dB The feed has a good
pattern symmetry and low back radiation
(a)
(b)
Fig 45 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 50 and L = 05λ0 at 18GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-45-
Fig 46 is the radiation pattern of the feed with εr = 25 and L = 10λ0 at
10GHz E- and H-plane 10-dB beamwidths are 50 and 48 degrees
respectively The front-to-back ratio is 16dB The antenna gain is 105dB
(a)
(b)
Fig 46 Radiation pattern at 10GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 10λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-46-
Fig 47 shows the geometry of a circular waveguide with a tapered
dielectric rod The designed feed has the following dimension L = 1λ0 d =
1λ0 and εr =25 at 10GHz The waveguide length is 40mm and the wall
thickness is 05mm
L
Dielectricd3
Fig 47 Geometry of a circular waveguide loaded with a tapered dielectric
rod
Fig 48 shows the radiatio pattern of the designed feed E- and H-plane
10-dB beamwidths are 575 and 564 degrees respectively The front-to-back
ratio is 377dB The antenna gain is 94dB The designed feed has an
excellent beamwidth symmetry and a very low back radiation
-47-
(a)
(b)
Fig 48 Radiation pattern of a circular waveguide loaded with a tapered
dielectric rod with L = 1λ0 d = 1λ0 and εr =25 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-48-
Fig 49 shows the geometry of a spherical ended dielectric rod feed
diameter of 06λ0 at 10GHz with a dielectric constant of 25 and L= 03λ0
Fig 410 shows the radiation patterns of the designed feed E- and H-plane
10-dB beamwidths are both 63 degrees The front-to-back ratio is 24dB The
antenna gain is 864dB
Fig 49 Geometry of a circular waveguide loaded with a spherical ended
dielectric rod
-49-
(a)
(b)
Fig 410 Radiation pattern of a circular waveguide loaded wht a spherical
ended dielectric rod with d = 06λ0 L = 03λ0 and εr =25 at 10GHz (a) 3D
radiation pattern and (b) E- and H-plane patterns
-50-
V Design of a Broadband Circular Waveguide Feed
In this chapter the design of a broadband circular waveguide feed is
presented At microwave frequencies the feed is often a circular waveguide
with chokes and corrugations around the aperture Chokes and corrugations
equalize E- and H-plane patterns and reduce the back radiation
The proposed feed is designed to operate over 10-18GHz The design starts
with the optimization of the coaxial-to-rectangular waveguide adapter
employed for good mode purity over a broad frequency range Next a
rectangular-to-circular waveguide transition is optimized Finally chokes and
corrugations are designed for improved pattern symmetry and low back
radiation
The proposed feed structure is shown in Fig 51 The feed consist of the
following parts a coaxial-to-rectangular waveguide adapter a rectangular-to-
circular waveguide transition a circular waveguide section four quarter-wave
chokes around the feeds aperture and four corrugations on the feeds outer
surface
The computer simulation shows the above arrangement offers good radiation
patterns over a broad frequency range The broadband operation is obtained
by exciting the TE11 mode in the circular waveguide using the TE10 mode of
the rectangular waveguide which is in turn excited by a coaxial probe
-51-
Chokes
Coaxial-to-waveguide transition
Circular wavguide
Corrugations
Mode transition
(a)
(b)
Fig 51 Structure of the proposed broadband circular waveguide feed
(a) CAD model and (b) cross-sectional view
For the coaxial-to-rectangular waveguide adapter an SMA connector with
the probe diameter of 127 mm is employed The coaxial probe inserted into
the waveguide energizes the feed and excites the dominant TE10 mode in
-52-
the rectangular waveguide The impedance matching is achieved by adjusting
the probe distance sp from the back short and the probe length lp
(a)
(b)
Fig 52 Reflection coefficient of the coaxial-to-rectangular adapter versus
(a) probe length lp and (b) the probe position sp
Fig 52 shows the reflection coefficient versus the various values of probe
lengths lp and probe positions sp The probe length lp is adjusted to obtain
antenna impedance matching and the probe distance sp is adjusted to obtain a
-53-
desired resonant frequency
Next a transition between rectangular and circular waveguide is designed
The transition section converts the TE10 mode in the rectangular waveguide to
TE11 mode in the circular waveguide and vice versa The transition is built
in a form of a taper for easy fabrication[22]
(a)
(b)
Fig 53 Structure of the rectangular-to-circular waveguide transition
(a) 3D view and (b) cross sectional view
The dimensions of the final optimized transition are as follows The length
of the rectangular waveguide section is 143mm The rectangular waveguides
width a and height b are 207mm and 857mm respectively The length of
the circular waveguide section is 143mm The inside diameter of the circular
-54-
waveguide is 207mm(097 wavelength at 14GHz) The length of transition
region ltr is 4465mm(approximately equal to 2λ0 at 14GHz) Fig 54 shows
the field distribution inside the mode converter
(a)
(b)
Fig 54 Field distribution inside the mode converter at
(a) 10GHz (b) 14GHz and (c) 18GHz
-55-
(c)
Fig 54 continued
Finally multiple chokes are investigated Figs 55 56 and 57 show the
feed performance without chokes The reflection coefficient is less than -10dB
over 10-19GHz The antenna has a gain of 921dB to 1189dB over
10-19GHz
Fig 55 Reflection coefficient of the broadband circular waveguide feed
without chokes and corrugations
-56-
(a)
(b)
(c)
Fig 56 E- and H-plane patterns of the broadband circular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-57-
(d)
(e)
Fig 56 continued
-58-
(a)
(b)
Fig 57 2D radiation patterns of the broadband cicular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-59-
(c)
(d)
Fig 57 continued
-60-
(e)
Fig 57 continued
To achieve equal beamwidths in E and H planes over a wide frequency
range chokes and corrugations are employed Table51 summarizes the
performance of a feed without chokes and corrugations
Table 51 Performance of the broadband circular waveguide feed without
chokes and corrugations
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
1000 940 6061 15
1200 972 6159 17
1400 920 5957 21
1600 1070 4751 29
1800 1188 5352 21
-61-
Four quarter-wavelength chokes are introduced in the feed design which
has a slot depth of 75mm and slot width of 09mm The choke slot spacing
is 18mm The choke design is investigated by applying the choke one by
one and the effect on the E- and H-plane patterns are observed as illustrated
in Figs 58 and 59 The use of chokes makes the E-plane pattern narrower
The H-plane pattern is not affected Chokes increase the gain slightly and
reduce back radiation
(a)
(b)
Fig 58 Effect of chokes on the E-plane pattern of the broadband circular
waveguide feed at (a) 10GHz(b) 12GHz (c) 14GHz (d) 16GHz and (e)
18GHz
-62-
(c)
(d)
(e)
Fig 58 continued
-63-
(a)
(b)
(c)
Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-64-
(d)
(e)
Fig 59 continued
-65-
Fig 510 shows the feed performance versus the choke depth When the
choke depth is varied from 535mm to 95mm the E- and H-plane patterns
are strongly affected The optimum value of choke depth is 75mm(035λ0 at
14GHz) which gives equal E- and H-plane radiation patterns and leads to
low back radiation
Fig 511 shows the feed performance versus the choke slot width tch The
choke slot width is varied from 09mm to 21mm Radiation patterns and
reflection coefficients are not sensitive to the choke slot width The final
choke slot width is selected to be 09mm considering the feed diameter
minimization and the manufacturability The overall diameter of the proposed
feed is 369mm which is increased from the 207mm of the waveguide
inside diameter due to the use of four chokes
-66-
(a)
(b)
(c)
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection coefficient
-67-
(a)
(b)
(c)
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and (c)
reflection coefficient
-68-
Next we investigated corrugations placed on the outer wall of the feed
Four corrugations applied to the outer surface of the circular waveguide The
corrugation depth is 465mm(0215λ0 at 14GHz) The primary purpose of
using corrugations is to further reduce the back radiation Increasing the
number of corrugations beyond four has little effect in reducing the back
radiation
Figs 512 and 513 show the effect of corrugations on the E- and H-plane
patterns Fig 514 shows the parametric study of the corrugation depth lcor
The corrugation depth is varied from 40mm and 645mm The optimum
value of the corrugation depth is found to be 465mm
-69-
(a)
(b)
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern at (a) 12GHz and (b) 14GHz
-70-
(a)
(b)
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern at (a) 12GHz and (b) 14GHz
-71-
(a)
(b)
(c)
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection coefficient
-72-
The phase center location is important in placing the feed in a reflector
antenna[8] The phase center variation with frequency should be small Fig
515 shows the effect of chokes and corrugations on the phase center The
curve with circle corresponds to the case without chokes and corrugations
The phase center varies from -326mm and -190mm away from the feeds
aperture plane It means the phase center is located inside the waveguide
The curve with triangles corresponds to the case with chokes The curve with
squares to the case with chokes and corrugations The phase center varies
from 0mm to -302mm
From Fig 515 we can observed that phase center variation reduced by the
corrugation and three cases phase center calculated in φ=450 plane
parameter sweep values are given in Table 52
10 12 14 16 181
0
-1
-2
-3
-4
-5
-6
Pha
se c
ente
r (m
m)
Frequency (GHz)
choke+corrugatuion without choke corrugation with choke
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
-73-
Frequency
(GHz)
Phase center from the aperture plane
(mm)
Without
chokes and
corrugations
With
chokes
With chokes
and
corrugations
1000 -326 062 000
1100 -187 030 -002
1200 -563 -208 -065
1300 -296 -154 -202
1400 -319 -314 -302
1500 -201 -203 -241
1600 -242 -233 -207
1700 -208 -208 -186
1800 -190 -157 -132
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
Based on the foregoing parametric studies optimum dimensions of the
broadband circular waveguide feed are obtained as shown in Table 53
-74-
Table 53 Optimum dimensions of the broadband circular waveguide feed
Parameter Designation Value (mm)
2a Waveguide inside diameter 2070
d Waveguide outside diameter 3690
lcrLength of the circular waveguide section 1430
m Distance between the aperture plane and the first corrugation 950
xDistance from the last corrugation to the end of the cylindrical outer surface
550
ltrLength of the rectangular-to-circularwaveguide transition 4465
lrcLength of the rectangular waveguide section 1430
tch Choke slot width 090
lch Choke depth 750
t Choke metal width 090
lcor Corrugation depth 465
tcor Corrugation metal width 100
s Corrugation slot width 10
lp Probe length 530
sp Probe position from the back short 530
din Probe diameter 127
b Inside height of the rectangular waveguide 857
tw Waveguide wall thickness 500
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
工學碩士學位論文
포물 반사경용 역 피드 설계
DesignofaBroadbandFeedforParabolic
ReflectorApplication
指 敎授 安 炳 哲
電波工學科 電波通信工學 攻
어덩토야 바상재랜 (OdontuyaBaasantseren)
이 論文을 工學碩士學位 論文으로 提出함
2012年 8月
本 論文을 金岐祿의 工學碩士學位 論文으로 認定함
審 査 委 員 長 안 재 형
審 査 委 員 안 병 철
審 査 委 員 방 재 훈
忠 北 大 學 校 大 學 院
2012年 8月
-i-
Contents
Abstract middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot ii
List of figures middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot iv
List of tables middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot ix
Ⅰ Indtroduction middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 1
Ⅱ Analysis of Circular and Square Waveguide Feeds middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 4
21 Circular Waveguide Radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 4
22 Square Waveguide Radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 10
23 Probe-Fed Circular Waveguide Radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 15
24 Probe-Fed Circular Waveguide Radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 20
Ⅲ Design of Compact Circular Waveguide Feeds middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 25
31 Narrow-Band Circular Waveguide Feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 25
32 Fabrication and Measurement middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 38
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod middotmiddotmiddotmiddotmiddotmiddot 40
41 Design of dielectric rod feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 40
V Design of Broadband Circular Waveguide Feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 50
51 Design of Broadband Circular Waveguide Feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 50
52 Fabrication and Measurement middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 82
Ⅳ Conclusion middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 85
REFERENCES middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 88
ACKNOWLEDGEMENT middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 89
-ii-
DesignofaBroadbandFeedforParabolic
ReflectorApplications
Odontuya Baasantseren
Department of Radio and Communications Engineering
Graduate School Chungbuk National University
Cheongju City South Korea
Supervised by Professor Bierng-Chearl Ahn Ph D
Abstract
In this thesis the design of a broadband feed for application in prime-focus
parabolic reflector antenna is described A feed for parabolic reflector antenna
requires radiation pattern with a good circular symmetry low back radiation
and low cross polarization This thesis proposes two feed designs one is a
dielectric ring-loaded circular waveguide operating over 171-197GHz and
fed by a coaxial probe The other is a choked and corrugated circular
waveguide fed by a probe-fed rectangular waveguide Before designing two
A thesis for the degree of Master in August 2012
-iii-
feeds performances of simple circular and square waveguide open ends are
investigated The improvement in the performance of the circular waveguide
open end by dielectric loading is also investigated The study shows that only
a narrow-band performance is possible with simple feeds
Based on this study the first feed is designed with the monocast(MC)
nylon as the dielectric-ring material for beamwidth equalization and a
quarter-wave choke around the aperture wall for back-radiation reduction A
coaxial probe is used to excite the feed The designed feed shows a good
performance over 171-197GHz
The second feed uses more complicated structures For broadband operation
the circular waveguide is fed by a probe-excited rectangular waveguide Four
quarter-wave chokes are used around the aperture wall for beamwidth
equalization and four corrugations are employed on the feeds outer surface
for further reduction in the back radiation
Prototypes of both feeds are fabricated and tested Test results are in good
agreement with the design objectives verifying the excellent performances of
the designed feeds
-iv-
List of Figures
Fig 21 Geometry of a circular waveguide open end radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 6
Fig 22 Reflection coefficient of a circular waveguide open end radiator middotmiddot 6
Fig 23 2D radiation pattern of a circular waveguide open end radiator middotmiddotmiddot 7
Fig 24 E-plane and H-plane patterns of a circular waveguide open end
radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 9
Fig 25 Geometry of a square waveguide open end radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 11
Fig 26 Reflection coefficient of a square waveguide open end radiator middot 12
Fig 27 2D radiation patterns of a square waveguide open end radiator middot 12
Fig 28 E-plane and H-plane patterns of square waveguide open end
radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 14
Fig 29 Probe-fed circular waveguide radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 16
Fig 210 Reflection coefficient of the probe-fed circular waveguide radiator
middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 17
Fig 211 2D radiation patterns of the probe-fed circular waveguide radiator
middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 17
Fig 212 E- and H-plane patterns of the probe-fed circular waveguide
radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 19
Fig 213 Probe-fed square waveguide radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 20
Fig 214 2D radiation pattern of the probe-fed square waveguide radiator 21
Fig 215 E- and H-plane pattern of the probe-fed square waveguide radiator
middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 23
Fig 216 Reflection coefficient of the probe-fed square waveguide radiator 24
Fig 31 Narrow-band circular waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 26
-v-
Fig 32 Effect of the (a) the probe length lp (b) the probe distance sp on
the reflection coefficient middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 27
Fig 33 Feed performance versus the choke depth (a) E-plane pattern (b)
H- plane pattern (c) reflection coefficient middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 29
Fig 34 Feed performance versus the choke slot width (a) E-plane pattern
(b) H-plane pattern (c) reflection coefficient middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 30
Fig 35 Feed performance versus the dielectric ring length (a) E-plane
pattern (b) H-plane pattern and (c) reflection coefficient middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 31
Fig 36 Feed performance versus the dielectric ring thickness (a) E-plane
pattern (b) H-plane pattern (c) reflection coefficient middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 32
Fig 37 2D gain patterns of the narrow-band circular waveguide feed middotmiddotmiddot 34
Fig 38 E- and H-plane patterns of the narrow-band circular waveguide
feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 30
Fig 39 Photograph of the fabricated feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 37
Fig 310 Reflection coefficient of the fabricated feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 38
Fig 311 Gain patterns of the fabricated feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 39
Fig 41 Geometry of a circular waveguide loaded with a uniform dielectric
rod middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 40
Fig 42 Radiation pattern at 9GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 05λ0 middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 41
Fig 43 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 21 and L = 05λ0 at 10GHz middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 42
Fig 44 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 30 and L = 05λ0 at 8GHz middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 43
Fig 45 Radiation pattern of the circular waveguide loaded with a uniform
-vi-
dielectric rod with εr = 50 and L = 05λ0 at 18GHz middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 44
Fig 46 Radiation pattern at 10GHz of the circular waveguide loaded with
a uniform dielectric rod with εr = 25 and L = 10λ0 middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 45
Fig 47 Geometry of a circular waveguide loaded with a tapered dielectric
rod middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 46
Fig 48 Radiation pattern of a circular waveguide loaded with a tapered
dielectric rod with L = 1λ0 d = 1λ0 and εr =25 at 10GHz middotmiddotmiddotmiddotmiddotmiddotmiddot 47
Fig 49 Geometry of a circular waveguide loaded with a spherical ended
dielectric rod middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 48
Fig 410 Radiation pattern of a circular waveguide loaded wht a spherical
ended dielectric rod with d = 06λ0 L = 03λ0 and εr =25 at
10GHz middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 49
Fig 51 Structure of the proposed broadband circular waveguide feed middotmiddotmiddotmiddotmiddot 51
Fig 52 Reflection coefficient of the coaxial-to-rectangular adapter versus
(a) probe length lp and (b) the probe position sp middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 52
Fig 53 Structure of the rectangular-to-circular waveguide transition middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 53
Fig 54 Field distribution inside the mode converter middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 54
Fig 55 Reflection coefficient of the broadband circular waveguide feed
without chokes and corrugations middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 55
Fig 56 E-plane and H-plane patternsof the broadband circular waveguide
feed without chokes and corrugationsz middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 56
Fig 57 2D radiation patterns of the broadband cicular waveguide feed
without chokes and corrugations middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 58
Fig 58 Effect of chokes on the E-plane pattern of the broadband circular
waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 61
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Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 63
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection
coefficient middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 66
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and
(c) reflection coefficient middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 67
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 69
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 70
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection
coefficient middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 71
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 72
Fig 516 Reflection coefficient of the designed broadband circular
waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 75
Fig 517 2D radiation patterns of the designed broadband circular
waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 76
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 79
Fig 519 Phase center variation of the designed broadband circular
waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 81
-viii-
Fig 520 Photograph of the fabricated broadband circular waveguide feed 82
Fig 521 Reflection coefficient of the fabricated broadband circular
waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 82
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 84
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 84
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List of Tables
Table 21 Properties of a circular waveguide open end radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 10
Table 22 Properties of a square waveguide open end radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 15
Table 23 Properties of the probe-fed circular waveguide radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 20
Table 24 Properties of the probe-fed square waveguide radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 24
Table 31 Dimensions of the designed narrow-band circular feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 33
Table 32 Performance of the narrow-band circular waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 37
Table 51 Performance of the broadband circular waveguide feed without
chokes and corrugations middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 60
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 73
Table 53 Optimum dimensions of the broadband circular waveguide feed 74
Table 54 Performance of the designed broadband circular waveguide feed 81
-1-
I Introduction
The horns and waveguides are known for their high efficiency and
structural simplicity They are popular choices for feeding for reflectors in
high-gain antenna applications such as satellite and point-to-point microwave
communication links The theory of reflector antenna was developed in the
1940s and has been used to calculate the radiation patterns of various
reflector structures[1]
The basic structure of a prime-focus reflector antenna consists of a
parabolic reflecting surface a feed and its support The placement of the feed
is such that its phase center is at the focal point of the parabolic reflecting
surface The feed is often a circular waveguide because of its symmetric
radiation pattern with low back radiation and low cross polarization The
circular waveguide feed must have a small diameter to reduce the aperture
blockage of the reflector antenna[3]
A radiation pattern with a good circular symmetry in the main beam can
be found from circular waveguide feeds with dominant TE11 mode excitation
The radiation patterns depends on the diameter and wall thickness of the
waveguide[4] A coaxial probe can be inserted into a short-circuited circular
waveguide in the form of a coaxial-to-waveguide transition The diameter of
the circular waveguide is chosen such that only the dominant mode
propagates
When the waveguide dimension does not provide a circular symmteric
-2-
pattern a choke or multiple chokes around the aperture wall can be
employed to equalize radiation patterns and keep the back radiation in low
level If chokes are not enough for the suppression of the back radiation
corrugations on the outer surface of the feed is one way to reduce the back
radiation
In this thesis a broadband circular waveguide feed is developed for
prime-focus reflector antenna application After investigating the radiation
properties of simple circular and square waveguides methods are investigated
for bandwidth enhancement back radiation suppression and beamwidth
equalization in the circular waveguide feed
The first type of the circular waveguide feed consists of a probe-fed
circular waveguide a single quarter-wave choke on the aperture wall and a
dielectric-ring beamwidth equalizer Due to the simple feeding method the
first feed operates over 171-197GHz(141) which is not broadband in the
strict sense of the word
The second feed consists of a coaxial-to-rectangular waveguide transition a
rectangular-to-circular waveguide transition a circular waveguide section four
quarter-wave chokes on the aperture wall and four quarter-wave corrugations
on the feeds outer surface Due to the complicated feeding method the
second feed operates over 10-18GHz(571)
This thesis is arranged as follows Chapter I gives an introduction to the
thesis related works and objectives are stated Chapter II describes the
structure and excitation of the circular and square waveguide and the
operation of the coaxial-to-waveguide transitions Chapter III describes a
compact feed horn design and its fabrication and measurement Chapter IV
-3-
presents dielectric rod feed and its simulated performances Chapter V gives
design and optimization of feed for parabolic reflector antenna In this
chapter includes the detailed information of design procedures and operating
principle also the simulated and measured performances are provided Finally
conclusion is given in the Chapter VI
-4-
II Analysis of Circular and Square Waveguide Feeds
21 Circular Waveguide Radiator
Before design a complicated circular waveguide feed it is helpful to
investigate the impedance and radiation properties of a circular waveguide
open end
The circular waveguide is a cylindrical hollow metallic pipe with a uniform
circular section of radius a Circular waveguides are normally designed to
operate only with the dominant mode The dominant mode in a waveguide is
the mode having the lowest cutoff frequency given by equation (21)
(21)
where
(22)
and a is the waveguide radius The following chart[2] and table show the
cutoff frequencies of various modes in a circular waveguide
-5-
Modes c al11TEc cf f
TE11 341259 100000
TM01 261274 130613
TE21 205720 165885TE01 163979 208111
TM11 163979 208111TE31 149557 228180
TM21 122345 278932TE41 118159 288813
TE12 117852 289566
TM02 113824 299813TE02 0897986 380027
The recommended frequency range of the commercial circular waveguide is
given by the following equation This assumes that the TM01 mode is not
generated or suppressed if generated
11 21 11TE TE TE115 095 158 32 bandwidthc c cf f f fpound pound = reg (23)
Fig 21 shows the geometry of a circular waveguide with a diameter of 2a
When 2a is 2053mm the cutoff frequency of the TE11 mode is 857GHz
According to (23) the useful operating frequency range is from
986-1354GHz
Fig 22 shows the reflection of this waveguide excited with the dominant
TE11 mode The waveguide length l is 60mm The reflection occurs at the
open end of the circular waveguide The reflection coefficient is less than
-15dB over 10-18GHz
-6-
Fig 21 Geometry of a circular waveguide open end radiator
Fig 23 shows a 2D gain pattern of this waveguide antenna The
waveguide antenna has a gain of 80dB 99dB and 115dB at 10GHz
14GHz and 18GHz respectively Fig 24 shows the E- and H-plane patterns
of the circular waveguide antenna Table 21 summarizes the properties of a
circular waveguide antenna
Fig 22 Reflection coefficient of a circular waveguide open end radiator
-7-
(a)
(b)
Fig 23 2D radiation pattern of the circular waveguide open end radiator
at (a)10GHz (b) 14GHz and (c) 18GHz
-8-
(c)
Fig 23 continued
-9-
(a)
(b)
(c)
Fig 24 E-plane and H-plane patterns of the circular waveguide open end
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-10-
Table 21 Properties of a circular waveguide open end radiator of diameter
2053mm
Frequency(GHz)-10dB Beamwith(deg) Front-to-Back
Ratio(dB)E plane H plane
10 67 73 12
14 58 60 18
18 41 50 21
In a circular waveguide radiatoλr a good pattern symmetry and low back
radiation is obtained at 14GHz where 2aλ = 096
22 Square Waveguide Radiator
A square waveguide is often used as a dual-polarized feed To operate the
cutoff frequency of the dominant mode a square-waveguide wall width a
must be greater than one half of a wavelength The modes with cutoff
frequencies equal to or smaller than the operational frequency can exist inside
the waveguide wall The lower cutoff frequency and cutoff wavelength for
square waveguide is determined by the following equations
TE
(24)
TE
(25)
The next higher-order mode is TE11 mode with the cutoff wavelength
given by
-11-
TE
(26)
Similar to the circular waveguide the recommended operating frequency range
of a square waveguide is given by
TEleleTE
TErarr bandwidth (27)
Fig 25 shows the geometry of a square waveguide with a dimension of a
When a is 157mm the cutoff frequency is 95GHz The recommended
operating frequency of this waveguide is from 109GHz to 155GHz
Fig 26 shows the reflection of this waveguide excited with the dominant
TE10 mode The reflection coefficient is less than -15dB over 10-20GHz
Fig 25 Geometry of a square waveguide open end radiator
Fig 27 and shows the 2D radiation pattern of a square waveguide antenna
excited with the dominant TE10 mode The antenna has a gain of 73dB
85dB and 102dB at 10GHz 14GHz and 18GHz respectively Fig 28
shows the E- and H-plane radiation patterns of a square waveguide radiator
Table 22 summarizes the properties of a square waveguide open end radiator
-12-
Fig 26 Reflection coefficient of a square waveguide open end radiator
(a)
Fig 27 2D radiation patterns of a square waveguide radiator
at (a) 10GHz (b) 14GHz and (c) 18GHz
-13-
(b)
(c)
Fig 27 continued
-14-
(a)
(b)
(c)
Fig 28 E-plane and H-plane patterns of square waveguide open radiator
at (a) 10GHz(b) 14GHz and (c) 18GHz
-15-
Table 22 Properties of a square waveguide open end radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 69 71 11
14 47 60 25
18 58 62 16
The radiation pattern symmetry and back radiation performance of the
square waveguide are inferior to those of a circular waveguide
23 Probe-Fed Circular Waveguide Radiator
In Section 21 the radiation properties of a TE11-mode excited waveguide
is investigated In this section a circular waveguide fed by a coaxial probe
shown in Fig 29 is studied
The coaxial probes diameter is 127mm With the Teflon dielectric the
50-ohm coaxial lines outer conductor has a diameter of 41mm For a
circular waveguide the wave impedance of the TE11 mode is given by
∙ (28)
where λg is the guided wavelength given by
(29)
-16-
(a) (b)
Fig 29 Probe-fed circular waveguide radiator (a) Front view and (b) side
view
The combination of the probe length and the probe position from the
shorted wall enables a good impedance matching The probe distance sp from
the back short is close to a quarter wavelength at the design frequency
The designed feed has the following dimension d = 2053mm lp = 42
mm sp = 534mm wall thickness = 05mm and feed length = 400mm
Fig 210 shows the reflection coefficient of the designed probe-fed
circular waveguide radiator The reflection coefficient is less than -10dB over
138-187GHz Fig 211 and 212 shows the E-plane and H-plane radiation
patterns and 2D radiation patterns of the coaxial-to-circular waveguide
transition The radiation patterns symmetry distorted because of the high order
modes The coaxial-to-circular waveguide transition has 73dB 84dB and
79dB gain at 10GHz 14GHz and 18GHz frequencies respectively Table 23
shows the properties of the coaxial-to-circular waveguide transition
-17-
Fig 210 Reflection coefficient of the probe-fed circular waveguide radiator
(a)
Fig 211 2D radiation pattern of the probe-fed circular waveguide radiator
at (a) 10GHz (b) 14GHz and (c) 18GHz
-18-
(b)
(c)
Fig 211 continued
-19-
(a)
(b)
(c)
Fig 212 E- and H-plane patterns of the probe-fed circular waveguide
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-20-
Table 23 Properties of the probe-fed circular waveguide radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 73 70 1414 83 57 17
18 60 52 30
When a circular waveguide radiator is fed by a coaxial probe its radiation
properties are not good due to the excitation of higher-order modes
Therefore a probe-fed circular waveguide radiator can be used as a feed only
over a narrow frequency range
24 Probe-Fed Square Waveguide Radiator
In this section a probe-fed square waveguide radiator is investigated Fig
213 shows a coaxial probe-fed square waveguide radiator The designed
radiator has the following dimension a = b = 157mm lp = 35 mm sp =
50 mm wall thickness = 05mm and feed length = 40mm
(a) (b)
Fig 213 Probe-fed square waveguide radiator (a) Front view and (b) side
view
-21-
Fig 214 shows the 2D radiation patterns of the radiator at 10GHz
14GHz and 18GHz Fig 215 shows E- and H-plane patterns of the radiator
Fig 216 shows the reflection coefficient of the probe-fed square waveguide
radiator The reflection coefficient is less than -10dB over 13-20GHz Table
24 summarizes the properties of the probe-fed square waveguide radiator
(a)
Fig 214 2D radiation patterns of the probe-fed square waveguide radiator at
(a) 10GHz (b) 14GHz and (c) 18GHz
-22-
(b)
(c)
Fig 214 continued
-23-
(a)
(b)
(c)
Fig 216 E-plane and H-plane patterns of the probe-fed square waveguide
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-24-
Fig 216 Reflection coefficient of the probe-fed square waveguide radiator
Table 24 Properties of the probe-fed square waveguide radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 73 71 12
14 85 63 1418 27 65 28
When a square waveguide radiator is fed by a coaxial probe its radiation
properties are not good due to the excitation of higher-order modes as in the
case of the probe-fed circular waveguide radiator A probe-fed square
waveguide radiator can be used as a feed only over a narrow frequency
range
-25-
III Design of Compact Circular Waveguide Feeds
In this chapter the feed design is presented for a prime-focus reflector
antenna The prime-focus paraboloid reflector is one of the most commonly
used high-gain antenna It has been used in earth-station antennas and radio
telescopes It consists of a paraboloid reflector with a feed system at its focal
point
The feed should radiate a low level of cross-polar power over the
operating frequency These conditions not easy to achieve and most prime
focus feeds are compromises The shape and characteristic of the radiation
pattern of the feed are the most important parameter because these will
directly influence the fields which are directed at a reflector[6] Other
electrical factors which relevant to the choice of a feed are the cross-polar
level the gain efficiency the bandwidth and impedance matching
31 Narrow-Band Circular Waveguide Feed
Fig 31 shows the proposed narrow-band circular waveguide feed and its
design variables The feed consists of a circular waveguide open end excited
by a TE11 dominant mode A quarter wave choke is applied along the
circular aperture of the waveguide to equalize E- and H-plane radiation
patterns and to suppress the back radiation A dielectric ring is used to
control the radiation pattern and change the power distribution over the
aperture The control of the amplitude over the aperture are essential to the
design of symmetric radiation pattern The material used for dielectric loading
-26-
is the monocast(MC) nylon with a dielectric constant of 30 The feed is
designed to operate over 171-197GHz
(a)
(b)
Fig 31 Narrow-band circular waveguide feed (a) CAD model and (b) a
cross sectional view
The impedance matching is achieved by a proper combination of the probe
height lp and its distance sp from the waveguide shorted end Here the
-27-
circular waveguide is terminated with an open end with a wall thickness of
2mm radiating into the free space
Fig 32 shows the effect of the probe length lp and the probe distance sp
on the reflection coefficient The best performance is obtained when lp =
363mm and sp = 616mm The feeds reflection coefficient is less than -10dB
over 170-195GHz
(a)
(b)
Fig 32 Effect of the (a) the probe length lp and (b) the probe
distance sp on the reflection coefficient
-28-
Fig 33 shows the effect of the choke depth The E-plane pattern is more
sensitive to the choke depth than the H-plane pattern The choke depth has a
strong influence on the reflection coefficient when it is 360mm By properly
choosing the choke depth we can equalize the E- and H-plane patterns The
optimum value of the choke depth is 410mm which is 0249λ0 at 1825GHz
The choke slot width tch in the range of 06-12mm has almost no effect
on the H-plane pattern and the reflection coefficient For the E-plane pattern
tch of 12mm has some effect on the E-plane radiation pattern as shown in
Fig 34
Fig 35 shows the feed performance versus the dielectric ring length We
observe in Fig 35 that the dielectric length ld has an optimum value of
1168mm which does no effect on the H-plane pattern and tha the value of
1048mm has some effect on the E-plane pattern and the reflection
coefficient
Fig 36 shows E-plane and H-plane patterns and the reflection coefficient
versus the dielectric thickness With the optimum value of the dielectric
thickness t obtained from the Fig 36 is 155mm The larger values of td has
much stronger effects on the E-plane pattern and the reflection coefficient
The H-plane pattern is not sensitive to the dielectric ring thickness
-29-
(a)
(b)
(c)
Fig 33 Feed performance versus the choke depth (a) E-plane pattern
(b) H-plane pattern and (c) reflection coefficient
-30-
(a)
(b)
(c)
Fig 34 Feed performance versus the choke slot width (a) E-plane pattern
(b) H-plane pattern and (c) reflection coefficient
-31-
(a)
(b)
(c)
Fig 35 Feed performance versus the dielectric ring length (a) E-plane
pattern (b) H-plane pattern and (c) reflection coefficient
-32-
(a)
(b)
(c)
Fig 36 Feed performance versus the dielectric ring thickness (a) E-plane
pattern(b) H-plane pattern and (c) reflection coefficient
-33-
From the above parametric analysis an optimum feed design is obtained
The result is shown in Table 31 Fig 37 shows the 2D gain patterns of
designed feed The antenna has a gain of 903dB 933dB and 956dB at
171GHz 1825GHz and 19GHz respectively
Fig 38 shows E- and H-plane radiation patterns of the designed feed The
feed has E- and H-plane 10-dB beamwidths of 60 and 59 degrees at 17GHz
The feed has a front-to-back ration of 1900dB 2490dB and 2200dB at
171GHz 1825GHz and 19GHz respectively Table 32 summarizes the
performance of the designed narrow-band circular waveguide feed
The designed feed has a greatly improved performance over that of a
simple coax-fed feed described in Section 23
Table 31 Dimensions of the designed narrow-band circular feed
Parameter Designation Value(mm)
a Waveguide inside radius 640
l Feed length 2890
lp Probe length 363
sp Probe position from the back short 616
din Probe diameter 127
dout Diameter of coaxial cables outer conductor 400
t Thickness of choked wall 050
tch Choke slot width 100
lch Choke depth 410
ld Dielectric ring length 1168
td Dielectric ring thickness 155
d1 Waveguide outside diameter 1680
-34-
(a)
(b)
Fig 37 2D gain patterns of the narrow-band circular waveguide feed at
(a) 17GHz (b) 1825GHz and (c) 19GHz
-35-
(c)
Fig 37 continued
-36-
(a)
(b)
(c)
Fig 38 E- and H-plane patterns of the narrow-band circular waveguide feed
at (a) 10GHz (b) 1825GHz and (c) 195GHz
-37-
Frequency(GHz)
Gain(dB)
E-H-plane10-dB beamwidths
(deg)
Front-to-back ratio(dB)
Phase centerlocation
(From feeds aperture plane
toward reflector)
(mm)
1700 903 6059 20 062
1825 933 6060 25 004
1900 956 5759 22 007
Table 32 Performance of the narrow-band circular waveguide feed
The designed narrow-band feed is fabricated and its performance is
measured and compared with the simulation results The designed feed is
fabricated in a numerically-controlled machining center The fabricated antenna
is shown in Fig 39
Fig 39 Photograph of the fabricated feed
-38-
Fig 310 shows a comparison of the measured and simulated reflection
coefficients The measured reflection coefficient is less than -10dB over
171-197GHz The agreement between simulated and measured results are
good
Fig 311 shows the E- and H-plane patterns of the fabricated feed at
187GHz The feed has 90dB gain simulation and measurement results are in
good agreement
The fabricated antennarsquos 10dB beamwidth is 60 degrees in both E and H
planes at 187GHz The front-to-back ratio is 21dB
Fig 310 Reflection coefficient of the fabricated feed
-39-
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Fee
d H
orn
Gain
- d
B
Angle - degree
(a)
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Feed H
orn
Gain
- d
B
Angle - degree
(b)
Fig 311 Gain patterns of the fabricated feed at 187 GHz (a) E-plane and
(b) H-plane
-40-
IV Design of Circular Waveguide Feeds Loaded with a
Dielectric Rod
In this section circular waveguide feeds loaded with a dielectric rod feed
are investigated A comprehensive discussion of the circular waveguide loaded
with a dielectric rod is given by Kumar[7] Inserting a dielectric material
inside the circular waveguide improves the E- and H-plane pattern symmetry
In general dielectric-loaded circular waveguide feeds show good performance
only over a narrow bandwidth
Fig 41 shows the geometry of a circular waveguide loaded with a
dielectric rod The waveguide length is 400mm and the wall thickness is
05mm The dielectric rods diameter is 207mm The dielectric rod is
extended 05 wavelength beyond the waveguide open end The dielectric
constant εr is changed and the feeds performance is observed
Fig 41 Geometry of a circular waveguide loaded with a uniform dielectric
rod
-41-
Fig 42 is the radiation pattern of the feed with εr = 25 and L = 05λ0 at
9GHz E- and H-plane 10-dB beamwidths are 810 and 807 degrees
respectively The front-to-back ratio is 18dB The antenna gain is 71dB
(a)
(b)
Fig 42 Radiation pattern at 9GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 05λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-42-
Fig 43 shows the radiation pattern of the feed with εr = 21 at 10GHz
E- and H-plane 10-dB beamwidths are 70 and 71 degrees respectively The
front-to-back ratio is 19dB The antenna gain is 83dB
(a)
(b)
Fig 43 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 21 and L = 05λ0 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-43-
Fig 44 shows the radiation pattern of the feed with εr = 30 at 8GHz
E- and H-plane 10-dB beamwidths are 83 and 824 degrees respectively The
front-to-back ratio is 17dB The antenna gain is 73dB
(a)
(b)
Fig 44 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 30 and L = 05λ0 at 8GHz (a) 2D radiation pattern
and (b) E- and H-plane patterns
-44-
Fig 45 shows the radiation pattern of the feed with εr = 50 at 18GHz
E- and H-plane 10-dB beamwidths are 56 and 54 degrees respectively The
front-to-back ratio is 27dB The antenna gain is 105dB The feed has a good
pattern symmetry and low back radiation
(a)
(b)
Fig 45 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 50 and L = 05λ0 at 18GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-45-
Fig 46 is the radiation pattern of the feed with εr = 25 and L = 10λ0 at
10GHz E- and H-plane 10-dB beamwidths are 50 and 48 degrees
respectively The front-to-back ratio is 16dB The antenna gain is 105dB
(a)
(b)
Fig 46 Radiation pattern at 10GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 10λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-46-
Fig 47 shows the geometry of a circular waveguide with a tapered
dielectric rod The designed feed has the following dimension L = 1λ0 d =
1λ0 and εr =25 at 10GHz The waveguide length is 40mm and the wall
thickness is 05mm
L
Dielectricd3
Fig 47 Geometry of a circular waveguide loaded with a tapered dielectric
rod
Fig 48 shows the radiatio pattern of the designed feed E- and H-plane
10-dB beamwidths are 575 and 564 degrees respectively The front-to-back
ratio is 377dB The antenna gain is 94dB The designed feed has an
excellent beamwidth symmetry and a very low back radiation
-47-
(a)
(b)
Fig 48 Radiation pattern of a circular waveguide loaded with a tapered
dielectric rod with L = 1λ0 d = 1λ0 and εr =25 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-48-
Fig 49 shows the geometry of a spherical ended dielectric rod feed
diameter of 06λ0 at 10GHz with a dielectric constant of 25 and L= 03λ0
Fig 410 shows the radiation patterns of the designed feed E- and H-plane
10-dB beamwidths are both 63 degrees The front-to-back ratio is 24dB The
antenna gain is 864dB
Fig 49 Geometry of a circular waveguide loaded with a spherical ended
dielectric rod
-49-
(a)
(b)
Fig 410 Radiation pattern of a circular waveguide loaded wht a spherical
ended dielectric rod with d = 06λ0 L = 03λ0 and εr =25 at 10GHz (a) 3D
radiation pattern and (b) E- and H-plane patterns
-50-
V Design of a Broadband Circular Waveguide Feed
In this chapter the design of a broadband circular waveguide feed is
presented At microwave frequencies the feed is often a circular waveguide
with chokes and corrugations around the aperture Chokes and corrugations
equalize E- and H-plane patterns and reduce the back radiation
The proposed feed is designed to operate over 10-18GHz The design starts
with the optimization of the coaxial-to-rectangular waveguide adapter
employed for good mode purity over a broad frequency range Next a
rectangular-to-circular waveguide transition is optimized Finally chokes and
corrugations are designed for improved pattern symmetry and low back
radiation
The proposed feed structure is shown in Fig 51 The feed consist of the
following parts a coaxial-to-rectangular waveguide adapter a rectangular-to-
circular waveguide transition a circular waveguide section four quarter-wave
chokes around the feeds aperture and four corrugations on the feeds outer
surface
The computer simulation shows the above arrangement offers good radiation
patterns over a broad frequency range The broadband operation is obtained
by exciting the TE11 mode in the circular waveguide using the TE10 mode of
the rectangular waveguide which is in turn excited by a coaxial probe
-51-
Chokes
Coaxial-to-waveguide transition
Circular wavguide
Corrugations
Mode transition
(a)
(b)
Fig 51 Structure of the proposed broadband circular waveguide feed
(a) CAD model and (b) cross-sectional view
For the coaxial-to-rectangular waveguide adapter an SMA connector with
the probe diameter of 127 mm is employed The coaxial probe inserted into
the waveguide energizes the feed and excites the dominant TE10 mode in
-52-
the rectangular waveguide The impedance matching is achieved by adjusting
the probe distance sp from the back short and the probe length lp
(a)
(b)
Fig 52 Reflection coefficient of the coaxial-to-rectangular adapter versus
(a) probe length lp and (b) the probe position sp
Fig 52 shows the reflection coefficient versus the various values of probe
lengths lp and probe positions sp The probe length lp is adjusted to obtain
antenna impedance matching and the probe distance sp is adjusted to obtain a
-53-
desired resonant frequency
Next a transition between rectangular and circular waveguide is designed
The transition section converts the TE10 mode in the rectangular waveguide to
TE11 mode in the circular waveguide and vice versa The transition is built
in a form of a taper for easy fabrication[22]
(a)
(b)
Fig 53 Structure of the rectangular-to-circular waveguide transition
(a) 3D view and (b) cross sectional view
The dimensions of the final optimized transition are as follows The length
of the rectangular waveguide section is 143mm The rectangular waveguides
width a and height b are 207mm and 857mm respectively The length of
the circular waveguide section is 143mm The inside diameter of the circular
-54-
waveguide is 207mm(097 wavelength at 14GHz) The length of transition
region ltr is 4465mm(approximately equal to 2λ0 at 14GHz) Fig 54 shows
the field distribution inside the mode converter
(a)
(b)
Fig 54 Field distribution inside the mode converter at
(a) 10GHz (b) 14GHz and (c) 18GHz
-55-
(c)
Fig 54 continued
Finally multiple chokes are investigated Figs 55 56 and 57 show the
feed performance without chokes The reflection coefficient is less than -10dB
over 10-19GHz The antenna has a gain of 921dB to 1189dB over
10-19GHz
Fig 55 Reflection coefficient of the broadband circular waveguide feed
without chokes and corrugations
-56-
(a)
(b)
(c)
Fig 56 E- and H-plane patterns of the broadband circular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-57-
(d)
(e)
Fig 56 continued
-58-
(a)
(b)
Fig 57 2D radiation patterns of the broadband cicular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-59-
(c)
(d)
Fig 57 continued
-60-
(e)
Fig 57 continued
To achieve equal beamwidths in E and H planes over a wide frequency
range chokes and corrugations are employed Table51 summarizes the
performance of a feed without chokes and corrugations
Table 51 Performance of the broadband circular waveguide feed without
chokes and corrugations
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
1000 940 6061 15
1200 972 6159 17
1400 920 5957 21
1600 1070 4751 29
1800 1188 5352 21
-61-
Four quarter-wavelength chokes are introduced in the feed design which
has a slot depth of 75mm and slot width of 09mm The choke slot spacing
is 18mm The choke design is investigated by applying the choke one by
one and the effect on the E- and H-plane patterns are observed as illustrated
in Figs 58 and 59 The use of chokes makes the E-plane pattern narrower
The H-plane pattern is not affected Chokes increase the gain slightly and
reduce back radiation
(a)
(b)
Fig 58 Effect of chokes on the E-plane pattern of the broadband circular
waveguide feed at (a) 10GHz(b) 12GHz (c) 14GHz (d) 16GHz and (e)
18GHz
-62-
(c)
(d)
(e)
Fig 58 continued
-63-
(a)
(b)
(c)
Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-64-
(d)
(e)
Fig 59 continued
-65-
Fig 510 shows the feed performance versus the choke depth When the
choke depth is varied from 535mm to 95mm the E- and H-plane patterns
are strongly affected The optimum value of choke depth is 75mm(035λ0 at
14GHz) which gives equal E- and H-plane radiation patterns and leads to
low back radiation
Fig 511 shows the feed performance versus the choke slot width tch The
choke slot width is varied from 09mm to 21mm Radiation patterns and
reflection coefficients are not sensitive to the choke slot width The final
choke slot width is selected to be 09mm considering the feed diameter
minimization and the manufacturability The overall diameter of the proposed
feed is 369mm which is increased from the 207mm of the waveguide
inside diameter due to the use of four chokes
-66-
(a)
(b)
(c)
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection coefficient
-67-
(a)
(b)
(c)
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and (c)
reflection coefficient
-68-
Next we investigated corrugations placed on the outer wall of the feed
Four corrugations applied to the outer surface of the circular waveguide The
corrugation depth is 465mm(0215λ0 at 14GHz) The primary purpose of
using corrugations is to further reduce the back radiation Increasing the
number of corrugations beyond four has little effect in reducing the back
radiation
Figs 512 and 513 show the effect of corrugations on the E- and H-plane
patterns Fig 514 shows the parametric study of the corrugation depth lcor
The corrugation depth is varied from 40mm and 645mm The optimum
value of the corrugation depth is found to be 465mm
-69-
(a)
(b)
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern at (a) 12GHz and (b) 14GHz
-70-
(a)
(b)
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern at (a) 12GHz and (b) 14GHz
-71-
(a)
(b)
(c)
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection coefficient
-72-
The phase center location is important in placing the feed in a reflector
antenna[8] The phase center variation with frequency should be small Fig
515 shows the effect of chokes and corrugations on the phase center The
curve with circle corresponds to the case without chokes and corrugations
The phase center varies from -326mm and -190mm away from the feeds
aperture plane It means the phase center is located inside the waveguide
The curve with triangles corresponds to the case with chokes The curve with
squares to the case with chokes and corrugations The phase center varies
from 0mm to -302mm
From Fig 515 we can observed that phase center variation reduced by the
corrugation and three cases phase center calculated in φ=450 plane
parameter sweep values are given in Table 52
10 12 14 16 181
0
-1
-2
-3
-4
-5
-6
Pha
se c
ente
r (m
m)
Frequency (GHz)
choke+corrugatuion without choke corrugation with choke
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
-73-
Frequency
(GHz)
Phase center from the aperture plane
(mm)
Without
chokes and
corrugations
With
chokes
With chokes
and
corrugations
1000 -326 062 000
1100 -187 030 -002
1200 -563 -208 -065
1300 -296 -154 -202
1400 -319 -314 -302
1500 -201 -203 -241
1600 -242 -233 -207
1700 -208 -208 -186
1800 -190 -157 -132
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
Based on the foregoing parametric studies optimum dimensions of the
broadband circular waveguide feed are obtained as shown in Table 53
-74-
Table 53 Optimum dimensions of the broadband circular waveguide feed
Parameter Designation Value (mm)
2a Waveguide inside diameter 2070
d Waveguide outside diameter 3690
lcrLength of the circular waveguide section 1430
m Distance between the aperture plane and the first corrugation 950
xDistance from the last corrugation to the end of the cylindrical outer surface
550
ltrLength of the rectangular-to-circularwaveguide transition 4465
lrcLength of the rectangular waveguide section 1430
tch Choke slot width 090
lch Choke depth 750
t Choke metal width 090
lcor Corrugation depth 465
tcor Corrugation metal width 100
s Corrugation slot width 10
lp Probe length 530
sp Probe position from the back short 530
din Probe diameter 127
b Inside height of the rectangular waveguide 857
tw Waveguide wall thickness 500
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
本 論文을 金岐祿의 工學碩士學位 論文으로 認定함
審 査 委 員 長 안 재 형
審 査 委 員 안 병 철
審 査 委 員 방 재 훈
忠 北 大 學 校 大 學 院
2012年 8月
-i-
Contents
Abstract middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot ii
List of figures middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot iv
List of tables middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot ix
Ⅰ Indtroduction middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 1
Ⅱ Analysis of Circular and Square Waveguide Feeds middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 4
21 Circular Waveguide Radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 4
22 Square Waveguide Radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 10
23 Probe-Fed Circular Waveguide Radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 15
24 Probe-Fed Circular Waveguide Radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 20
Ⅲ Design of Compact Circular Waveguide Feeds middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 25
31 Narrow-Band Circular Waveguide Feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 25
32 Fabrication and Measurement middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 38
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod middotmiddotmiddotmiddotmiddotmiddot 40
41 Design of dielectric rod feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 40
V Design of Broadband Circular Waveguide Feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 50
51 Design of Broadband Circular Waveguide Feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 50
52 Fabrication and Measurement middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 82
Ⅳ Conclusion middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 85
REFERENCES middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 88
ACKNOWLEDGEMENT middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 89
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DesignofaBroadbandFeedforParabolic
ReflectorApplications
Odontuya Baasantseren
Department of Radio and Communications Engineering
Graduate School Chungbuk National University
Cheongju City South Korea
Supervised by Professor Bierng-Chearl Ahn Ph D
Abstract
In this thesis the design of a broadband feed for application in prime-focus
parabolic reflector antenna is described A feed for parabolic reflector antenna
requires radiation pattern with a good circular symmetry low back radiation
and low cross polarization This thesis proposes two feed designs one is a
dielectric ring-loaded circular waveguide operating over 171-197GHz and
fed by a coaxial probe The other is a choked and corrugated circular
waveguide fed by a probe-fed rectangular waveguide Before designing two
A thesis for the degree of Master in August 2012
-iii-
feeds performances of simple circular and square waveguide open ends are
investigated The improvement in the performance of the circular waveguide
open end by dielectric loading is also investigated The study shows that only
a narrow-band performance is possible with simple feeds
Based on this study the first feed is designed with the monocast(MC)
nylon as the dielectric-ring material for beamwidth equalization and a
quarter-wave choke around the aperture wall for back-radiation reduction A
coaxial probe is used to excite the feed The designed feed shows a good
performance over 171-197GHz
The second feed uses more complicated structures For broadband operation
the circular waveguide is fed by a probe-excited rectangular waveguide Four
quarter-wave chokes are used around the aperture wall for beamwidth
equalization and four corrugations are employed on the feeds outer surface
for further reduction in the back radiation
Prototypes of both feeds are fabricated and tested Test results are in good
agreement with the design objectives verifying the excellent performances of
the designed feeds
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List of Figures
Fig 21 Geometry of a circular waveguide open end radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 6
Fig 22 Reflection coefficient of a circular waveguide open end radiator middotmiddot 6
Fig 23 2D radiation pattern of a circular waveguide open end radiator middotmiddotmiddot 7
Fig 24 E-plane and H-plane patterns of a circular waveguide open end
radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 9
Fig 25 Geometry of a square waveguide open end radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 11
Fig 26 Reflection coefficient of a square waveguide open end radiator middot 12
Fig 27 2D radiation patterns of a square waveguide open end radiator middot 12
Fig 28 E-plane and H-plane patterns of square waveguide open end
radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 14
Fig 29 Probe-fed circular waveguide radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 16
Fig 210 Reflection coefficient of the probe-fed circular waveguide radiator
middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 17
Fig 211 2D radiation patterns of the probe-fed circular waveguide radiator
middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 17
Fig 212 E- and H-plane patterns of the probe-fed circular waveguide
radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 19
Fig 213 Probe-fed square waveguide radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 20
Fig 214 2D radiation pattern of the probe-fed square waveguide radiator 21
Fig 215 E- and H-plane pattern of the probe-fed square waveguide radiator
middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 23
Fig 216 Reflection coefficient of the probe-fed square waveguide radiator 24
Fig 31 Narrow-band circular waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 26
-v-
Fig 32 Effect of the (a) the probe length lp (b) the probe distance sp on
the reflection coefficient middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 27
Fig 33 Feed performance versus the choke depth (a) E-plane pattern (b)
H- plane pattern (c) reflection coefficient middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 29
Fig 34 Feed performance versus the choke slot width (a) E-plane pattern
(b) H-plane pattern (c) reflection coefficient middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 30
Fig 35 Feed performance versus the dielectric ring length (a) E-plane
pattern (b) H-plane pattern and (c) reflection coefficient middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 31
Fig 36 Feed performance versus the dielectric ring thickness (a) E-plane
pattern (b) H-plane pattern (c) reflection coefficient middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 32
Fig 37 2D gain patterns of the narrow-band circular waveguide feed middotmiddotmiddot 34
Fig 38 E- and H-plane patterns of the narrow-band circular waveguide
feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 30
Fig 39 Photograph of the fabricated feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 37
Fig 310 Reflection coefficient of the fabricated feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 38
Fig 311 Gain patterns of the fabricated feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 39
Fig 41 Geometry of a circular waveguide loaded with a uniform dielectric
rod middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 40
Fig 42 Radiation pattern at 9GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 05λ0 middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 41
Fig 43 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 21 and L = 05λ0 at 10GHz middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 42
Fig 44 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 30 and L = 05λ0 at 8GHz middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 43
Fig 45 Radiation pattern of the circular waveguide loaded with a uniform
-vi-
dielectric rod with εr = 50 and L = 05λ0 at 18GHz middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 44
Fig 46 Radiation pattern at 10GHz of the circular waveguide loaded with
a uniform dielectric rod with εr = 25 and L = 10λ0 middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 45
Fig 47 Geometry of a circular waveguide loaded with a tapered dielectric
rod middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 46
Fig 48 Radiation pattern of a circular waveguide loaded with a tapered
dielectric rod with L = 1λ0 d = 1λ0 and εr =25 at 10GHz middotmiddotmiddotmiddotmiddotmiddotmiddot 47
Fig 49 Geometry of a circular waveguide loaded with a spherical ended
dielectric rod middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 48
Fig 410 Radiation pattern of a circular waveguide loaded wht a spherical
ended dielectric rod with d = 06λ0 L = 03λ0 and εr =25 at
10GHz middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 49
Fig 51 Structure of the proposed broadband circular waveguide feed middotmiddotmiddotmiddotmiddot 51
Fig 52 Reflection coefficient of the coaxial-to-rectangular adapter versus
(a) probe length lp and (b) the probe position sp middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 52
Fig 53 Structure of the rectangular-to-circular waveguide transition middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 53
Fig 54 Field distribution inside the mode converter middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 54
Fig 55 Reflection coefficient of the broadband circular waveguide feed
without chokes and corrugations middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 55
Fig 56 E-plane and H-plane patternsof the broadband circular waveguide
feed without chokes and corrugationsz middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 56
Fig 57 2D radiation patterns of the broadband cicular waveguide feed
without chokes and corrugations middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 58
Fig 58 Effect of chokes on the E-plane pattern of the broadband circular
waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 61
-vii-
Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 63
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection
coefficient middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 66
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and
(c) reflection coefficient middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 67
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 69
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 70
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection
coefficient middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 71
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 72
Fig 516 Reflection coefficient of the designed broadband circular
waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 75
Fig 517 2D radiation patterns of the designed broadband circular
waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 76
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 79
Fig 519 Phase center variation of the designed broadband circular
waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 81
-viii-
Fig 520 Photograph of the fabricated broadband circular waveguide feed 82
Fig 521 Reflection coefficient of the fabricated broadband circular
waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 82
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 84
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 84
-ix-
List of Tables
Table 21 Properties of a circular waveguide open end radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 10
Table 22 Properties of a square waveguide open end radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 15
Table 23 Properties of the probe-fed circular waveguide radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 20
Table 24 Properties of the probe-fed square waveguide radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 24
Table 31 Dimensions of the designed narrow-band circular feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 33
Table 32 Performance of the narrow-band circular waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 37
Table 51 Performance of the broadband circular waveguide feed without
chokes and corrugations middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 60
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 73
Table 53 Optimum dimensions of the broadband circular waveguide feed 74
Table 54 Performance of the designed broadband circular waveguide feed 81
-1-
I Introduction
The horns and waveguides are known for their high efficiency and
structural simplicity They are popular choices for feeding for reflectors in
high-gain antenna applications such as satellite and point-to-point microwave
communication links The theory of reflector antenna was developed in the
1940s and has been used to calculate the radiation patterns of various
reflector structures[1]
The basic structure of a prime-focus reflector antenna consists of a
parabolic reflecting surface a feed and its support The placement of the feed
is such that its phase center is at the focal point of the parabolic reflecting
surface The feed is often a circular waveguide because of its symmetric
radiation pattern with low back radiation and low cross polarization The
circular waveguide feed must have a small diameter to reduce the aperture
blockage of the reflector antenna[3]
A radiation pattern with a good circular symmetry in the main beam can
be found from circular waveguide feeds with dominant TE11 mode excitation
The radiation patterns depends on the diameter and wall thickness of the
waveguide[4] A coaxial probe can be inserted into a short-circuited circular
waveguide in the form of a coaxial-to-waveguide transition The diameter of
the circular waveguide is chosen such that only the dominant mode
propagates
When the waveguide dimension does not provide a circular symmteric
-2-
pattern a choke or multiple chokes around the aperture wall can be
employed to equalize radiation patterns and keep the back radiation in low
level If chokes are not enough for the suppression of the back radiation
corrugations on the outer surface of the feed is one way to reduce the back
radiation
In this thesis a broadband circular waveguide feed is developed for
prime-focus reflector antenna application After investigating the radiation
properties of simple circular and square waveguides methods are investigated
for bandwidth enhancement back radiation suppression and beamwidth
equalization in the circular waveguide feed
The first type of the circular waveguide feed consists of a probe-fed
circular waveguide a single quarter-wave choke on the aperture wall and a
dielectric-ring beamwidth equalizer Due to the simple feeding method the
first feed operates over 171-197GHz(141) which is not broadband in the
strict sense of the word
The second feed consists of a coaxial-to-rectangular waveguide transition a
rectangular-to-circular waveguide transition a circular waveguide section four
quarter-wave chokes on the aperture wall and four quarter-wave corrugations
on the feeds outer surface Due to the complicated feeding method the
second feed operates over 10-18GHz(571)
This thesis is arranged as follows Chapter I gives an introduction to the
thesis related works and objectives are stated Chapter II describes the
structure and excitation of the circular and square waveguide and the
operation of the coaxial-to-waveguide transitions Chapter III describes a
compact feed horn design and its fabrication and measurement Chapter IV
-3-
presents dielectric rod feed and its simulated performances Chapter V gives
design and optimization of feed for parabolic reflector antenna In this
chapter includes the detailed information of design procedures and operating
principle also the simulated and measured performances are provided Finally
conclusion is given in the Chapter VI
-4-
II Analysis of Circular and Square Waveguide Feeds
21 Circular Waveguide Radiator
Before design a complicated circular waveguide feed it is helpful to
investigate the impedance and radiation properties of a circular waveguide
open end
The circular waveguide is a cylindrical hollow metallic pipe with a uniform
circular section of radius a Circular waveguides are normally designed to
operate only with the dominant mode The dominant mode in a waveguide is
the mode having the lowest cutoff frequency given by equation (21)
(21)
where
(22)
and a is the waveguide radius The following chart[2] and table show the
cutoff frequencies of various modes in a circular waveguide
-5-
Modes c al11TEc cf f
TE11 341259 100000
TM01 261274 130613
TE21 205720 165885TE01 163979 208111
TM11 163979 208111TE31 149557 228180
TM21 122345 278932TE41 118159 288813
TE12 117852 289566
TM02 113824 299813TE02 0897986 380027
The recommended frequency range of the commercial circular waveguide is
given by the following equation This assumes that the TM01 mode is not
generated or suppressed if generated
11 21 11TE TE TE115 095 158 32 bandwidthc c cf f f fpound pound = reg (23)
Fig 21 shows the geometry of a circular waveguide with a diameter of 2a
When 2a is 2053mm the cutoff frequency of the TE11 mode is 857GHz
According to (23) the useful operating frequency range is from
986-1354GHz
Fig 22 shows the reflection of this waveguide excited with the dominant
TE11 mode The waveguide length l is 60mm The reflection occurs at the
open end of the circular waveguide The reflection coefficient is less than
-15dB over 10-18GHz
-6-
Fig 21 Geometry of a circular waveguide open end radiator
Fig 23 shows a 2D gain pattern of this waveguide antenna The
waveguide antenna has a gain of 80dB 99dB and 115dB at 10GHz
14GHz and 18GHz respectively Fig 24 shows the E- and H-plane patterns
of the circular waveguide antenna Table 21 summarizes the properties of a
circular waveguide antenna
Fig 22 Reflection coefficient of a circular waveguide open end radiator
-7-
(a)
(b)
Fig 23 2D radiation pattern of the circular waveguide open end radiator
at (a)10GHz (b) 14GHz and (c) 18GHz
-8-
(c)
Fig 23 continued
-9-
(a)
(b)
(c)
Fig 24 E-plane and H-plane patterns of the circular waveguide open end
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-10-
Table 21 Properties of a circular waveguide open end radiator of diameter
2053mm
Frequency(GHz)-10dB Beamwith(deg) Front-to-Back
Ratio(dB)E plane H plane
10 67 73 12
14 58 60 18
18 41 50 21
In a circular waveguide radiatoλr a good pattern symmetry and low back
radiation is obtained at 14GHz where 2aλ = 096
22 Square Waveguide Radiator
A square waveguide is often used as a dual-polarized feed To operate the
cutoff frequency of the dominant mode a square-waveguide wall width a
must be greater than one half of a wavelength The modes with cutoff
frequencies equal to or smaller than the operational frequency can exist inside
the waveguide wall The lower cutoff frequency and cutoff wavelength for
square waveguide is determined by the following equations
TE
(24)
TE
(25)
The next higher-order mode is TE11 mode with the cutoff wavelength
given by
-11-
TE
(26)
Similar to the circular waveguide the recommended operating frequency range
of a square waveguide is given by
TEleleTE
TErarr bandwidth (27)
Fig 25 shows the geometry of a square waveguide with a dimension of a
When a is 157mm the cutoff frequency is 95GHz The recommended
operating frequency of this waveguide is from 109GHz to 155GHz
Fig 26 shows the reflection of this waveguide excited with the dominant
TE10 mode The reflection coefficient is less than -15dB over 10-20GHz
Fig 25 Geometry of a square waveguide open end radiator
Fig 27 and shows the 2D radiation pattern of a square waveguide antenna
excited with the dominant TE10 mode The antenna has a gain of 73dB
85dB and 102dB at 10GHz 14GHz and 18GHz respectively Fig 28
shows the E- and H-plane radiation patterns of a square waveguide radiator
Table 22 summarizes the properties of a square waveguide open end radiator
-12-
Fig 26 Reflection coefficient of a square waveguide open end radiator
(a)
Fig 27 2D radiation patterns of a square waveguide radiator
at (a) 10GHz (b) 14GHz and (c) 18GHz
-13-
(b)
(c)
Fig 27 continued
-14-
(a)
(b)
(c)
Fig 28 E-plane and H-plane patterns of square waveguide open radiator
at (a) 10GHz(b) 14GHz and (c) 18GHz
-15-
Table 22 Properties of a square waveguide open end radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 69 71 11
14 47 60 25
18 58 62 16
The radiation pattern symmetry and back radiation performance of the
square waveguide are inferior to those of a circular waveguide
23 Probe-Fed Circular Waveguide Radiator
In Section 21 the radiation properties of a TE11-mode excited waveguide
is investigated In this section a circular waveguide fed by a coaxial probe
shown in Fig 29 is studied
The coaxial probes diameter is 127mm With the Teflon dielectric the
50-ohm coaxial lines outer conductor has a diameter of 41mm For a
circular waveguide the wave impedance of the TE11 mode is given by
∙ (28)
where λg is the guided wavelength given by
(29)
-16-
(a) (b)
Fig 29 Probe-fed circular waveguide radiator (a) Front view and (b) side
view
The combination of the probe length and the probe position from the
shorted wall enables a good impedance matching The probe distance sp from
the back short is close to a quarter wavelength at the design frequency
The designed feed has the following dimension d = 2053mm lp = 42
mm sp = 534mm wall thickness = 05mm and feed length = 400mm
Fig 210 shows the reflection coefficient of the designed probe-fed
circular waveguide radiator The reflection coefficient is less than -10dB over
138-187GHz Fig 211 and 212 shows the E-plane and H-plane radiation
patterns and 2D radiation patterns of the coaxial-to-circular waveguide
transition The radiation patterns symmetry distorted because of the high order
modes The coaxial-to-circular waveguide transition has 73dB 84dB and
79dB gain at 10GHz 14GHz and 18GHz frequencies respectively Table 23
shows the properties of the coaxial-to-circular waveguide transition
-17-
Fig 210 Reflection coefficient of the probe-fed circular waveguide radiator
(a)
Fig 211 2D radiation pattern of the probe-fed circular waveguide radiator
at (a) 10GHz (b) 14GHz and (c) 18GHz
-18-
(b)
(c)
Fig 211 continued
-19-
(a)
(b)
(c)
Fig 212 E- and H-plane patterns of the probe-fed circular waveguide
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-20-
Table 23 Properties of the probe-fed circular waveguide radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 73 70 1414 83 57 17
18 60 52 30
When a circular waveguide radiator is fed by a coaxial probe its radiation
properties are not good due to the excitation of higher-order modes
Therefore a probe-fed circular waveguide radiator can be used as a feed only
over a narrow frequency range
24 Probe-Fed Square Waveguide Radiator
In this section a probe-fed square waveguide radiator is investigated Fig
213 shows a coaxial probe-fed square waveguide radiator The designed
radiator has the following dimension a = b = 157mm lp = 35 mm sp =
50 mm wall thickness = 05mm and feed length = 40mm
(a) (b)
Fig 213 Probe-fed square waveguide radiator (a) Front view and (b) side
view
-21-
Fig 214 shows the 2D radiation patterns of the radiator at 10GHz
14GHz and 18GHz Fig 215 shows E- and H-plane patterns of the radiator
Fig 216 shows the reflection coefficient of the probe-fed square waveguide
radiator The reflection coefficient is less than -10dB over 13-20GHz Table
24 summarizes the properties of the probe-fed square waveguide radiator
(a)
Fig 214 2D radiation patterns of the probe-fed square waveguide radiator at
(a) 10GHz (b) 14GHz and (c) 18GHz
-22-
(b)
(c)
Fig 214 continued
-23-
(a)
(b)
(c)
Fig 216 E-plane and H-plane patterns of the probe-fed square waveguide
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-24-
Fig 216 Reflection coefficient of the probe-fed square waveguide radiator
Table 24 Properties of the probe-fed square waveguide radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 73 71 12
14 85 63 1418 27 65 28
When a square waveguide radiator is fed by a coaxial probe its radiation
properties are not good due to the excitation of higher-order modes as in the
case of the probe-fed circular waveguide radiator A probe-fed square
waveguide radiator can be used as a feed only over a narrow frequency
range
-25-
III Design of Compact Circular Waveguide Feeds
In this chapter the feed design is presented for a prime-focus reflector
antenna The prime-focus paraboloid reflector is one of the most commonly
used high-gain antenna It has been used in earth-station antennas and radio
telescopes It consists of a paraboloid reflector with a feed system at its focal
point
The feed should radiate a low level of cross-polar power over the
operating frequency These conditions not easy to achieve and most prime
focus feeds are compromises The shape and characteristic of the radiation
pattern of the feed are the most important parameter because these will
directly influence the fields which are directed at a reflector[6] Other
electrical factors which relevant to the choice of a feed are the cross-polar
level the gain efficiency the bandwidth and impedance matching
31 Narrow-Band Circular Waveguide Feed
Fig 31 shows the proposed narrow-band circular waveguide feed and its
design variables The feed consists of a circular waveguide open end excited
by a TE11 dominant mode A quarter wave choke is applied along the
circular aperture of the waveguide to equalize E- and H-plane radiation
patterns and to suppress the back radiation A dielectric ring is used to
control the radiation pattern and change the power distribution over the
aperture The control of the amplitude over the aperture are essential to the
design of symmetric radiation pattern The material used for dielectric loading
-26-
is the monocast(MC) nylon with a dielectric constant of 30 The feed is
designed to operate over 171-197GHz
(a)
(b)
Fig 31 Narrow-band circular waveguide feed (a) CAD model and (b) a
cross sectional view
The impedance matching is achieved by a proper combination of the probe
height lp and its distance sp from the waveguide shorted end Here the
-27-
circular waveguide is terminated with an open end with a wall thickness of
2mm radiating into the free space
Fig 32 shows the effect of the probe length lp and the probe distance sp
on the reflection coefficient The best performance is obtained when lp =
363mm and sp = 616mm The feeds reflection coefficient is less than -10dB
over 170-195GHz
(a)
(b)
Fig 32 Effect of the (a) the probe length lp and (b) the probe
distance sp on the reflection coefficient
-28-
Fig 33 shows the effect of the choke depth The E-plane pattern is more
sensitive to the choke depth than the H-plane pattern The choke depth has a
strong influence on the reflection coefficient when it is 360mm By properly
choosing the choke depth we can equalize the E- and H-plane patterns The
optimum value of the choke depth is 410mm which is 0249λ0 at 1825GHz
The choke slot width tch in the range of 06-12mm has almost no effect
on the H-plane pattern and the reflection coefficient For the E-plane pattern
tch of 12mm has some effect on the E-plane radiation pattern as shown in
Fig 34
Fig 35 shows the feed performance versus the dielectric ring length We
observe in Fig 35 that the dielectric length ld has an optimum value of
1168mm which does no effect on the H-plane pattern and tha the value of
1048mm has some effect on the E-plane pattern and the reflection
coefficient
Fig 36 shows E-plane and H-plane patterns and the reflection coefficient
versus the dielectric thickness With the optimum value of the dielectric
thickness t obtained from the Fig 36 is 155mm The larger values of td has
much stronger effects on the E-plane pattern and the reflection coefficient
The H-plane pattern is not sensitive to the dielectric ring thickness
-29-
(a)
(b)
(c)
Fig 33 Feed performance versus the choke depth (a) E-plane pattern
(b) H-plane pattern and (c) reflection coefficient
-30-
(a)
(b)
(c)
Fig 34 Feed performance versus the choke slot width (a) E-plane pattern
(b) H-plane pattern and (c) reflection coefficient
-31-
(a)
(b)
(c)
Fig 35 Feed performance versus the dielectric ring length (a) E-plane
pattern (b) H-plane pattern and (c) reflection coefficient
-32-
(a)
(b)
(c)
Fig 36 Feed performance versus the dielectric ring thickness (a) E-plane
pattern(b) H-plane pattern and (c) reflection coefficient
-33-
From the above parametric analysis an optimum feed design is obtained
The result is shown in Table 31 Fig 37 shows the 2D gain patterns of
designed feed The antenna has a gain of 903dB 933dB and 956dB at
171GHz 1825GHz and 19GHz respectively
Fig 38 shows E- and H-plane radiation patterns of the designed feed The
feed has E- and H-plane 10-dB beamwidths of 60 and 59 degrees at 17GHz
The feed has a front-to-back ration of 1900dB 2490dB and 2200dB at
171GHz 1825GHz and 19GHz respectively Table 32 summarizes the
performance of the designed narrow-band circular waveguide feed
The designed feed has a greatly improved performance over that of a
simple coax-fed feed described in Section 23
Table 31 Dimensions of the designed narrow-band circular feed
Parameter Designation Value(mm)
a Waveguide inside radius 640
l Feed length 2890
lp Probe length 363
sp Probe position from the back short 616
din Probe diameter 127
dout Diameter of coaxial cables outer conductor 400
t Thickness of choked wall 050
tch Choke slot width 100
lch Choke depth 410
ld Dielectric ring length 1168
td Dielectric ring thickness 155
d1 Waveguide outside diameter 1680
-34-
(a)
(b)
Fig 37 2D gain patterns of the narrow-band circular waveguide feed at
(a) 17GHz (b) 1825GHz and (c) 19GHz
-35-
(c)
Fig 37 continued
-36-
(a)
(b)
(c)
Fig 38 E- and H-plane patterns of the narrow-band circular waveguide feed
at (a) 10GHz (b) 1825GHz and (c) 195GHz
-37-
Frequency(GHz)
Gain(dB)
E-H-plane10-dB beamwidths
(deg)
Front-to-back ratio(dB)
Phase centerlocation
(From feeds aperture plane
toward reflector)
(mm)
1700 903 6059 20 062
1825 933 6060 25 004
1900 956 5759 22 007
Table 32 Performance of the narrow-band circular waveguide feed
The designed narrow-band feed is fabricated and its performance is
measured and compared with the simulation results The designed feed is
fabricated in a numerically-controlled machining center The fabricated antenna
is shown in Fig 39
Fig 39 Photograph of the fabricated feed
-38-
Fig 310 shows a comparison of the measured and simulated reflection
coefficients The measured reflection coefficient is less than -10dB over
171-197GHz The agreement between simulated and measured results are
good
Fig 311 shows the E- and H-plane patterns of the fabricated feed at
187GHz The feed has 90dB gain simulation and measurement results are in
good agreement
The fabricated antennarsquos 10dB beamwidth is 60 degrees in both E and H
planes at 187GHz The front-to-back ratio is 21dB
Fig 310 Reflection coefficient of the fabricated feed
-39-
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Fee
d H
orn
Gain
- d
B
Angle - degree
(a)
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Feed H
orn
Gain
- d
B
Angle - degree
(b)
Fig 311 Gain patterns of the fabricated feed at 187 GHz (a) E-plane and
(b) H-plane
-40-
IV Design of Circular Waveguide Feeds Loaded with a
Dielectric Rod
In this section circular waveguide feeds loaded with a dielectric rod feed
are investigated A comprehensive discussion of the circular waveguide loaded
with a dielectric rod is given by Kumar[7] Inserting a dielectric material
inside the circular waveguide improves the E- and H-plane pattern symmetry
In general dielectric-loaded circular waveguide feeds show good performance
only over a narrow bandwidth
Fig 41 shows the geometry of a circular waveguide loaded with a
dielectric rod The waveguide length is 400mm and the wall thickness is
05mm The dielectric rods diameter is 207mm The dielectric rod is
extended 05 wavelength beyond the waveguide open end The dielectric
constant εr is changed and the feeds performance is observed
Fig 41 Geometry of a circular waveguide loaded with a uniform dielectric
rod
-41-
Fig 42 is the radiation pattern of the feed with εr = 25 and L = 05λ0 at
9GHz E- and H-plane 10-dB beamwidths are 810 and 807 degrees
respectively The front-to-back ratio is 18dB The antenna gain is 71dB
(a)
(b)
Fig 42 Radiation pattern at 9GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 05λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-42-
Fig 43 shows the radiation pattern of the feed with εr = 21 at 10GHz
E- and H-plane 10-dB beamwidths are 70 and 71 degrees respectively The
front-to-back ratio is 19dB The antenna gain is 83dB
(a)
(b)
Fig 43 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 21 and L = 05λ0 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-43-
Fig 44 shows the radiation pattern of the feed with εr = 30 at 8GHz
E- and H-plane 10-dB beamwidths are 83 and 824 degrees respectively The
front-to-back ratio is 17dB The antenna gain is 73dB
(a)
(b)
Fig 44 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 30 and L = 05λ0 at 8GHz (a) 2D radiation pattern
and (b) E- and H-plane patterns
-44-
Fig 45 shows the radiation pattern of the feed with εr = 50 at 18GHz
E- and H-plane 10-dB beamwidths are 56 and 54 degrees respectively The
front-to-back ratio is 27dB The antenna gain is 105dB The feed has a good
pattern symmetry and low back radiation
(a)
(b)
Fig 45 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 50 and L = 05λ0 at 18GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-45-
Fig 46 is the radiation pattern of the feed with εr = 25 and L = 10λ0 at
10GHz E- and H-plane 10-dB beamwidths are 50 and 48 degrees
respectively The front-to-back ratio is 16dB The antenna gain is 105dB
(a)
(b)
Fig 46 Radiation pattern at 10GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 10λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-46-
Fig 47 shows the geometry of a circular waveguide with a tapered
dielectric rod The designed feed has the following dimension L = 1λ0 d =
1λ0 and εr =25 at 10GHz The waveguide length is 40mm and the wall
thickness is 05mm
L
Dielectricd3
Fig 47 Geometry of a circular waveguide loaded with a tapered dielectric
rod
Fig 48 shows the radiatio pattern of the designed feed E- and H-plane
10-dB beamwidths are 575 and 564 degrees respectively The front-to-back
ratio is 377dB The antenna gain is 94dB The designed feed has an
excellent beamwidth symmetry and a very low back radiation
-47-
(a)
(b)
Fig 48 Radiation pattern of a circular waveguide loaded with a tapered
dielectric rod with L = 1λ0 d = 1λ0 and εr =25 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-48-
Fig 49 shows the geometry of a spherical ended dielectric rod feed
diameter of 06λ0 at 10GHz with a dielectric constant of 25 and L= 03λ0
Fig 410 shows the radiation patterns of the designed feed E- and H-plane
10-dB beamwidths are both 63 degrees The front-to-back ratio is 24dB The
antenna gain is 864dB
Fig 49 Geometry of a circular waveguide loaded with a spherical ended
dielectric rod
-49-
(a)
(b)
Fig 410 Radiation pattern of a circular waveguide loaded wht a spherical
ended dielectric rod with d = 06λ0 L = 03λ0 and εr =25 at 10GHz (a) 3D
radiation pattern and (b) E- and H-plane patterns
-50-
V Design of a Broadband Circular Waveguide Feed
In this chapter the design of a broadband circular waveguide feed is
presented At microwave frequencies the feed is often a circular waveguide
with chokes and corrugations around the aperture Chokes and corrugations
equalize E- and H-plane patterns and reduce the back radiation
The proposed feed is designed to operate over 10-18GHz The design starts
with the optimization of the coaxial-to-rectangular waveguide adapter
employed for good mode purity over a broad frequency range Next a
rectangular-to-circular waveguide transition is optimized Finally chokes and
corrugations are designed for improved pattern symmetry and low back
radiation
The proposed feed structure is shown in Fig 51 The feed consist of the
following parts a coaxial-to-rectangular waveguide adapter a rectangular-to-
circular waveguide transition a circular waveguide section four quarter-wave
chokes around the feeds aperture and four corrugations on the feeds outer
surface
The computer simulation shows the above arrangement offers good radiation
patterns over a broad frequency range The broadband operation is obtained
by exciting the TE11 mode in the circular waveguide using the TE10 mode of
the rectangular waveguide which is in turn excited by a coaxial probe
-51-
Chokes
Coaxial-to-waveguide transition
Circular wavguide
Corrugations
Mode transition
(a)
(b)
Fig 51 Structure of the proposed broadband circular waveguide feed
(a) CAD model and (b) cross-sectional view
For the coaxial-to-rectangular waveguide adapter an SMA connector with
the probe diameter of 127 mm is employed The coaxial probe inserted into
the waveguide energizes the feed and excites the dominant TE10 mode in
-52-
the rectangular waveguide The impedance matching is achieved by adjusting
the probe distance sp from the back short and the probe length lp
(a)
(b)
Fig 52 Reflection coefficient of the coaxial-to-rectangular adapter versus
(a) probe length lp and (b) the probe position sp
Fig 52 shows the reflection coefficient versus the various values of probe
lengths lp and probe positions sp The probe length lp is adjusted to obtain
antenna impedance matching and the probe distance sp is adjusted to obtain a
-53-
desired resonant frequency
Next a transition between rectangular and circular waveguide is designed
The transition section converts the TE10 mode in the rectangular waveguide to
TE11 mode in the circular waveguide and vice versa The transition is built
in a form of a taper for easy fabrication[22]
(a)
(b)
Fig 53 Structure of the rectangular-to-circular waveguide transition
(a) 3D view and (b) cross sectional view
The dimensions of the final optimized transition are as follows The length
of the rectangular waveguide section is 143mm The rectangular waveguides
width a and height b are 207mm and 857mm respectively The length of
the circular waveguide section is 143mm The inside diameter of the circular
-54-
waveguide is 207mm(097 wavelength at 14GHz) The length of transition
region ltr is 4465mm(approximately equal to 2λ0 at 14GHz) Fig 54 shows
the field distribution inside the mode converter
(a)
(b)
Fig 54 Field distribution inside the mode converter at
(a) 10GHz (b) 14GHz and (c) 18GHz
-55-
(c)
Fig 54 continued
Finally multiple chokes are investigated Figs 55 56 and 57 show the
feed performance without chokes The reflection coefficient is less than -10dB
over 10-19GHz The antenna has a gain of 921dB to 1189dB over
10-19GHz
Fig 55 Reflection coefficient of the broadband circular waveguide feed
without chokes and corrugations
-56-
(a)
(b)
(c)
Fig 56 E- and H-plane patterns of the broadband circular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-57-
(d)
(e)
Fig 56 continued
-58-
(a)
(b)
Fig 57 2D radiation patterns of the broadband cicular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-59-
(c)
(d)
Fig 57 continued
-60-
(e)
Fig 57 continued
To achieve equal beamwidths in E and H planes over a wide frequency
range chokes and corrugations are employed Table51 summarizes the
performance of a feed without chokes and corrugations
Table 51 Performance of the broadband circular waveguide feed without
chokes and corrugations
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
1000 940 6061 15
1200 972 6159 17
1400 920 5957 21
1600 1070 4751 29
1800 1188 5352 21
-61-
Four quarter-wavelength chokes are introduced in the feed design which
has a slot depth of 75mm and slot width of 09mm The choke slot spacing
is 18mm The choke design is investigated by applying the choke one by
one and the effect on the E- and H-plane patterns are observed as illustrated
in Figs 58 and 59 The use of chokes makes the E-plane pattern narrower
The H-plane pattern is not affected Chokes increase the gain slightly and
reduce back radiation
(a)
(b)
Fig 58 Effect of chokes on the E-plane pattern of the broadband circular
waveguide feed at (a) 10GHz(b) 12GHz (c) 14GHz (d) 16GHz and (e)
18GHz
-62-
(c)
(d)
(e)
Fig 58 continued
-63-
(a)
(b)
(c)
Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-64-
(d)
(e)
Fig 59 continued
-65-
Fig 510 shows the feed performance versus the choke depth When the
choke depth is varied from 535mm to 95mm the E- and H-plane patterns
are strongly affected The optimum value of choke depth is 75mm(035λ0 at
14GHz) which gives equal E- and H-plane radiation patterns and leads to
low back radiation
Fig 511 shows the feed performance versus the choke slot width tch The
choke slot width is varied from 09mm to 21mm Radiation patterns and
reflection coefficients are not sensitive to the choke slot width The final
choke slot width is selected to be 09mm considering the feed diameter
minimization and the manufacturability The overall diameter of the proposed
feed is 369mm which is increased from the 207mm of the waveguide
inside diameter due to the use of four chokes
-66-
(a)
(b)
(c)
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection coefficient
-67-
(a)
(b)
(c)
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and (c)
reflection coefficient
-68-
Next we investigated corrugations placed on the outer wall of the feed
Four corrugations applied to the outer surface of the circular waveguide The
corrugation depth is 465mm(0215λ0 at 14GHz) The primary purpose of
using corrugations is to further reduce the back radiation Increasing the
number of corrugations beyond four has little effect in reducing the back
radiation
Figs 512 and 513 show the effect of corrugations on the E- and H-plane
patterns Fig 514 shows the parametric study of the corrugation depth lcor
The corrugation depth is varied from 40mm and 645mm The optimum
value of the corrugation depth is found to be 465mm
-69-
(a)
(b)
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern at (a) 12GHz and (b) 14GHz
-70-
(a)
(b)
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern at (a) 12GHz and (b) 14GHz
-71-
(a)
(b)
(c)
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection coefficient
-72-
The phase center location is important in placing the feed in a reflector
antenna[8] The phase center variation with frequency should be small Fig
515 shows the effect of chokes and corrugations on the phase center The
curve with circle corresponds to the case without chokes and corrugations
The phase center varies from -326mm and -190mm away from the feeds
aperture plane It means the phase center is located inside the waveguide
The curve with triangles corresponds to the case with chokes The curve with
squares to the case with chokes and corrugations The phase center varies
from 0mm to -302mm
From Fig 515 we can observed that phase center variation reduced by the
corrugation and three cases phase center calculated in φ=450 plane
parameter sweep values are given in Table 52
10 12 14 16 181
0
-1
-2
-3
-4
-5
-6
Pha
se c
ente
r (m
m)
Frequency (GHz)
choke+corrugatuion without choke corrugation with choke
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
-73-
Frequency
(GHz)
Phase center from the aperture plane
(mm)
Without
chokes and
corrugations
With
chokes
With chokes
and
corrugations
1000 -326 062 000
1100 -187 030 -002
1200 -563 -208 -065
1300 -296 -154 -202
1400 -319 -314 -302
1500 -201 -203 -241
1600 -242 -233 -207
1700 -208 -208 -186
1800 -190 -157 -132
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
Based on the foregoing parametric studies optimum dimensions of the
broadband circular waveguide feed are obtained as shown in Table 53
-74-
Table 53 Optimum dimensions of the broadband circular waveguide feed
Parameter Designation Value (mm)
2a Waveguide inside diameter 2070
d Waveguide outside diameter 3690
lcrLength of the circular waveguide section 1430
m Distance between the aperture plane and the first corrugation 950
xDistance from the last corrugation to the end of the cylindrical outer surface
550
ltrLength of the rectangular-to-circularwaveguide transition 4465
lrcLength of the rectangular waveguide section 1430
tch Choke slot width 090
lch Choke depth 750
t Choke metal width 090
lcor Corrugation depth 465
tcor Corrugation metal width 100
s Corrugation slot width 10
lp Probe length 530
sp Probe position from the back short 530
din Probe diameter 127
b Inside height of the rectangular waveguide 857
tw Waveguide wall thickness 500
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-i-
Contents
Abstract middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot ii
List of figures middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot iv
List of tables middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot ix
Ⅰ Indtroduction middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 1
Ⅱ Analysis of Circular and Square Waveguide Feeds middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 4
21 Circular Waveguide Radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 4
22 Square Waveguide Radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 10
23 Probe-Fed Circular Waveguide Radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 15
24 Probe-Fed Circular Waveguide Radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 20
Ⅲ Design of Compact Circular Waveguide Feeds middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 25
31 Narrow-Band Circular Waveguide Feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 25
32 Fabrication and Measurement middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 38
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod middotmiddotmiddotmiddotmiddotmiddot 40
41 Design of dielectric rod feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 40
V Design of Broadband Circular Waveguide Feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 50
51 Design of Broadband Circular Waveguide Feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 50
52 Fabrication and Measurement middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 82
Ⅳ Conclusion middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 85
REFERENCES middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 88
ACKNOWLEDGEMENT middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 89
-ii-
DesignofaBroadbandFeedforParabolic
ReflectorApplications
Odontuya Baasantseren
Department of Radio and Communications Engineering
Graduate School Chungbuk National University
Cheongju City South Korea
Supervised by Professor Bierng-Chearl Ahn Ph D
Abstract
In this thesis the design of a broadband feed for application in prime-focus
parabolic reflector antenna is described A feed for parabolic reflector antenna
requires radiation pattern with a good circular symmetry low back radiation
and low cross polarization This thesis proposes two feed designs one is a
dielectric ring-loaded circular waveguide operating over 171-197GHz and
fed by a coaxial probe The other is a choked and corrugated circular
waveguide fed by a probe-fed rectangular waveguide Before designing two
A thesis for the degree of Master in August 2012
-iii-
feeds performances of simple circular and square waveguide open ends are
investigated The improvement in the performance of the circular waveguide
open end by dielectric loading is also investigated The study shows that only
a narrow-band performance is possible with simple feeds
Based on this study the first feed is designed with the monocast(MC)
nylon as the dielectric-ring material for beamwidth equalization and a
quarter-wave choke around the aperture wall for back-radiation reduction A
coaxial probe is used to excite the feed The designed feed shows a good
performance over 171-197GHz
The second feed uses more complicated structures For broadband operation
the circular waveguide is fed by a probe-excited rectangular waveguide Four
quarter-wave chokes are used around the aperture wall for beamwidth
equalization and four corrugations are employed on the feeds outer surface
for further reduction in the back radiation
Prototypes of both feeds are fabricated and tested Test results are in good
agreement with the design objectives verifying the excellent performances of
the designed feeds
-iv-
List of Figures
Fig 21 Geometry of a circular waveguide open end radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 6
Fig 22 Reflection coefficient of a circular waveguide open end radiator middotmiddot 6
Fig 23 2D radiation pattern of a circular waveguide open end radiator middotmiddotmiddot 7
Fig 24 E-plane and H-plane patterns of a circular waveguide open end
radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 9
Fig 25 Geometry of a square waveguide open end radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 11
Fig 26 Reflection coefficient of a square waveguide open end radiator middot 12
Fig 27 2D radiation patterns of a square waveguide open end radiator middot 12
Fig 28 E-plane and H-plane patterns of square waveguide open end
radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 14
Fig 29 Probe-fed circular waveguide radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 16
Fig 210 Reflection coefficient of the probe-fed circular waveguide radiator
middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 17
Fig 211 2D radiation patterns of the probe-fed circular waveguide radiator
middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 17
Fig 212 E- and H-plane patterns of the probe-fed circular waveguide
radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 19
Fig 213 Probe-fed square waveguide radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 20
Fig 214 2D radiation pattern of the probe-fed square waveguide radiator 21
Fig 215 E- and H-plane pattern of the probe-fed square waveguide radiator
middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 23
Fig 216 Reflection coefficient of the probe-fed square waveguide radiator 24
Fig 31 Narrow-band circular waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 26
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Fig 32 Effect of the (a) the probe length lp (b) the probe distance sp on
the reflection coefficient middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 27
Fig 33 Feed performance versus the choke depth (a) E-plane pattern (b)
H- plane pattern (c) reflection coefficient middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 29
Fig 34 Feed performance versus the choke slot width (a) E-plane pattern
(b) H-plane pattern (c) reflection coefficient middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 30
Fig 35 Feed performance versus the dielectric ring length (a) E-plane
pattern (b) H-plane pattern and (c) reflection coefficient middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 31
Fig 36 Feed performance versus the dielectric ring thickness (a) E-plane
pattern (b) H-plane pattern (c) reflection coefficient middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 32
Fig 37 2D gain patterns of the narrow-band circular waveguide feed middotmiddotmiddot 34
Fig 38 E- and H-plane patterns of the narrow-band circular waveguide
feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 30
Fig 39 Photograph of the fabricated feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 37
Fig 310 Reflection coefficient of the fabricated feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 38
Fig 311 Gain patterns of the fabricated feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 39
Fig 41 Geometry of a circular waveguide loaded with a uniform dielectric
rod middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 40
Fig 42 Radiation pattern at 9GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 05λ0 middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 41
Fig 43 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 21 and L = 05λ0 at 10GHz middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 42
Fig 44 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 30 and L = 05λ0 at 8GHz middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 43
Fig 45 Radiation pattern of the circular waveguide loaded with a uniform
-vi-
dielectric rod with εr = 50 and L = 05λ0 at 18GHz middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 44
Fig 46 Radiation pattern at 10GHz of the circular waveguide loaded with
a uniform dielectric rod with εr = 25 and L = 10λ0 middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 45
Fig 47 Geometry of a circular waveguide loaded with a tapered dielectric
rod middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 46
Fig 48 Radiation pattern of a circular waveguide loaded with a tapered
dielectric rod with L = 1λ0 d = 1λ0 and εr =25 at 10GHz middotmiddotmiddotmiddotmiddotmiddotmiddot 47
Fig 49 Geometry of a circular waveguide loaded with a spherical ended
dielectric rod middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 48
Fig 410 Radiation pattern of a circular waveguide loaded wht a spherical
ended dielectric rod with d = 06λ0 L = 03λ0 and εr =25 at
10GHz middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 49
Fig 51 Structure of the proposed broadband circular waveguide feed middotmiddotmiddotmiddotmiddot 51
Fig 52 Reflection coefficient of the coaxial-to-rectangular adapter versus
(a) probe length lp and (b) the probe position sp middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 52
Fig 53 Structure of the rectangular-to-circular waveguide transition middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 53
Fig 54 Field distribution inside the mode converter middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 54
Fig 55 Reflection coefficient of the broadband circular waveguide feed
without chokes and corrugations middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 55
Fig 56 E-plane and H-plane patternsof the broadband circular waveguide
feed without chokes and corrugationsz middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 56
Fig 57 2D radiation patterns of the broadband cicular waveguide feed
without chokes and corrugations middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 58
Fig 58 Effect of chokes on the E-plane pattern of the broadband circular
waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 61
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Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 63
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection
coefficient middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 66
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and
(c) reflection coefficient middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 67
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 69
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 70
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection
coefficient middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 71
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 72
Fig 516 Reflection coefficient of the designed broadband circular
waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 75
Fig 517 2D radiation patterns of the designed broadband circular
waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 76
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 79
Fig 519 Phase center variation of the designed broadband circular
waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 81
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Fig 520 Photograph of the fabricated broadband circular waveguide feed 82
Fig 521 Reflection coefficient of the fabricated broadband circular
waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 82
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 84
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 84
-ix-
List of Tables
Table 21 Properties of a circular waveguide open end radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 10
Table 22 Properties of a square waveguide open end radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 15
Table 23 Properties of the probe-fed circular waveguide radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 20
Table 24 Properties of the probe-fed square waveguide radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 24
Table 31 Dimensions of the designed narrow-band circular feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 33
Table 32 Performance of the narrow-band circular waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 37
Table 51 Performance of the broadband circular waveguide feed without
chokes and corrugations middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 60
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 73
Table 53 Optimum dimensions of the broadband circular waveguide feed 74
Table 54 Performance of the designed broadband circular waveguide feed 81
-1-
I Introduction
The horns and waveguides are known for their high efficiency and
structural simplicity They are popular choices for feeding for reflectors in
high-gain antenna applications such as satellite and point-to-point microwave
communication links The theory of reflector antenna was developed in the
1940s and has been used to calculate the radiation patterns of various
reflector structures[1]
The basic structure of a prime-focus reflector antenna consists of a
parabolic reflecting surface a feed and its support The placement of the feed
is such that its phase center is at the focal point of the parabolic reflecting
surface The feed is often a circular waveguide because of its symmetric
radiation pattern with low back radiation and low cross polarization The
circular waveguide feed must have a small diameter to reduce the aperture
blockage of the reflector antenna[3]
A radiation pattern with a good circular symmetry in the main beam can
be found from circular waveguide feeds with dominant TE11 mode excitation
The radiation patterns depends on the diameter and wall thickness of the
waveguide[4] A coaxial probe can be inserted into a short-circuited circular
waveguide in the form of a coaxial-to-waveguide transition The diameter of
the circular waveguide is chosen such that only the dominant mode
propagates
When the waveguide dimension does not provide a circular symmteric
-2-
pattern a choke or multiple chokes around the aperture wall can be
employed to equalize radiation patterns and keep the back radiation in low
level If chokes are not enough for the suppression of the back radiation
corrugations on the outer surface of the feed is one way to reduce the back
radiation
In this thesis a broadband circular waveguide feed is developed for
prime-focus reflector antenna application After investigating the radiation
properties of simple circular and square waveguides methods are investigated
for bandwidth enhancement back radiation suppression and beamwidth
equalization in the circular waveguide feed
The first type of the circular waveguide feed consists of a probe-fed
circular waveguide a single quarter-wave choke on the aperture wall and a
dielectric-ring beamwidth equalizer Due to the simple feeding method the
first feed operates over 171-197GHz(141) which is not broadband in the
strict sense of the word
The second feed consists of a coaxial-to-rectangular waveguide transition a
rectangular-to-circular waveguide transition a circular waveguide section four
quarter-wave chokes on the aperture wall and four quarter-wave corrugations
on the feeds outer surface Due to the complicated feeding method the
second feed operates over 10-18GHz(571)
This thesis is arranged as follows Chapter I gives an introduction to the
thesis related works and objectives are stated Chapter II describes the
structure and excitation of the circular and square waveguide and the
operation of the coaxial-to-waveguide transitions Chapter III describes a
compact feed horn design and its fabrication and measurement Chapter IV
-3-
presents dielectric rod feed and its simulated performances Chapter V gives
design and optimization of feed for parabolic reflector antenna In this
chapter includes the detailed information of design procedures and operating
principle also the simulated and measured performances are provided Finally
conclusion is given in the Chapter VI
-4-
II Analysis of Circular and Square Waveguide Feeds
21 Circular Waveguide Radiator
Before design a complicated circular waveguide feed it is helpful to
investigate the impedance and radiation properties of a circular waveguide
open end
The circular waveguide is a cylindrical hollow metallic pipe with a uniform
circular section of radius a Circular waveguides are normally designed to
operate only with the dominant mode The dominant mode in a waveguide is
the mode having the lowest cutoff frequency given by equation (21)
(21)
where
(22)
and a is the waveguide radius The following chart[2] and table show the
cutoff frequencies of various modes in a circular waveguide
-5-
Modes c al11TEc cf f
TE11 341259 100000
TM01 261274 130613
TE21 205720 165885TE01 163979 208111
TM11 163979 208111TE31 149557 228180
TM21 122345 278932TE41 118159 288813
TE12 117852 289566
TM02 113824 299813TE02 0897986 380027
The recommended frequency range of the commercial circular waveguide is
given by the following equation This assumes that the TM01 mode is not
generated or suppressed if generated
11 21 11TE TE TE115 095 158 32 bandwidthc c cf f f fpound pound = reg (23)
Fig 21 shows the geometry of a circular waveguide with a diameter of 2a
When 2a is 2053mm the cutoff frequency of the TE11 mode is 857GHz
According to (23) the useful operating frequency range is from
986-1354GHz
Fig 22 shows the reflection of this waveguide excited with the dominant
TE11 mode The waveguide length l is 60mm The reflection occurs at the
open end of the circular waveguide The reflection coefficient is less than
-15dB over 10-18GHz
-6-
Fig 21 Geometry of a circular waveguide open end radiator
Fig 23 shows a 2D gain pattern of this waveguide antenna The
waveguide antenna has a gain of 80dB 99dB and 115dB at 10GHz
14GHz and 18GHz respectively Fig 24 shows the E- and H-plane patterns
of the circular waveguide antenna Table 21 summarizes the properties of a
circular waveguide antenna
Fig 22 Reflection coefficient of a circular waveguide open end radiator
-7-
(a)
(b)
Fig 23 2D radiation pattern of the circular waveguide open end radiator
at (a)10GHz (b) 14GHz and (c) 18GHz
-8-
(c)
Fig 23 continued
-9-
(a)
(b)
(c)
Fig 24 E-plane and H-plane patterns of the circular waveguide open end
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-10-
Table 21 Properties of a circular waveguide open end radiator of diameter
2053mm
Frequency(GHz)-10dB Beamwith(deg) Front-to-Back
Ratio(dB)E plane H plane
10 67 73 12
14 58 60 18
18 41 50 21
In a circular waveguide radiatoλr a good pattern symmetry and low back
radiation is obtained at 14GHz where 2aλ = 096
22 Square Waveguide Radiator
A square waveguide is often used as a dual-polarized feed To operate the
cutoff frequency of the dominant mode a square-waveguide wall width a
must be greater than one half of a wavelength The modes with cutoff
frequencies equal to or smaller than the operational frequency can exist inside
the waveguide wall The lower cutoff frequency and cutoff wavelength for
square waveguide is determined by the following equations
TE
(24)
TE
(25)
The next higher-order mode is TE11 mode with the cutoff wavelength
given by
-11-
TE
(26)
Similar to the circular waveguide the recommended operating frequency range
of a square waveguide is given by
TEleleTE
TErarr bandwidth (27)
Fig 25 shows the geometry of a square waveguide with a dimension of a
When a is 157mm the cutoff frequency is 95GHz The recommended
operating frequency of this waveguide is from 109GHz to 155GHz
Fig 26 shows the reflection of this waveguide excited with the dominant
TE10 mode The reflection coefficient is less than -15dB over 10-20GHz
Fig 25 Geometry of a square waveguide open end radiator
Fig 27 and shows the 2D radiation pattern of a square waveguide antenna
excited with the dominant TE10 mode The antenna has a gain of 73dB
85dB and 102dB at 10GHz 14GHz and 18GHz respectively Fig 28
shows the E- and H-plane radiation patterns of a square waveguide radiator
Table 22 summarizes the properties of a square waveguide open end radiator
-12-
Fig 26 Reflection coefficient of a square waveguide open end radiator
(a)
Fig 27 2D radiation patterns of a square waveguide radiator
at (a) 10GHz (b) 14GHz and (c) 18GHz
-13-
(b)
(c)
Fig 27 continued
-14-
(a)
(b)
(c)
Fig 28 E-plane and H-plane patterns of square waveguide open radiator
at (a) 10GHz(b) 14GHz and (c) 18GHz
-15-
Table 22 Properties of a square waveguide open end radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 69 71 11
14 47 60 25
18 58 62 16
The radiation pattern symmetry and back radiation performance of the
square waveguide are inferior to those of a circular waveguide
23 Probe-Fed Circular Waveguide Radiator
In Section 21 the radiation properties of a TE11-mode excited waveguide
is investigated In this section a circular waveguide fed by a coaxial probe
shown in Fig 29 is studied
The coaxial probes diameter is 127mm With the Teflon dielectric the
50-ohm coaxial lines outer conductor has a diameter of 41mm For a
circular waveguide the wave impedance of the TE11 mode is given by
∙ (28)
where λg is the guided wavelength given by
(29)
-16-
(a) (b)
Fig 29 Probe-fed circular waveguide radiator (a) Front view and (b) side
view
The combination of the probe length and the probe position from the
shorted wall enables a good impedance matching The probe distance sp from
the back short is close to a quarter wavelength at the design frequency
The designed feed has the following dimension d = 2053mm lp = 42
mm sp = 534mm wall thickness = 05mm and feed length = 400mm
Fig 210 shows the reflection coefficient of the designed probe-fed
circular waveguide radiator The reflection coefficient is less than -10dB over
138-187GHz Fig 211 and 212 shows the E-plane and H-plane radiation
patterns and 2D radiation patterns of the coaxial-to-circular waveguide
transition The radiation patterns symmetry distorted because of the high order
modes The coaxial-to-circular waveguide transition has 73dB 84dB and
79dB gain at 10GHz 14GHz and 18GHz frequencies respectively Table 23
shows the properties of the coaxial-to-circular waveguide transition
-17-
Fig 210 Reflection coefficient of the probe-fed circular waveguide radiator
(a)
Fig 211 2D radiation pattern of the probe-fed circular waveguide radiator
at (a) 10GHz (b) 14GHz and (c) 18GHz
-18-
(b)
(c)
Fig 211 continued
-19-
(a)
(b)
(c)
Fig 212 E- and H-plane patterns of the probe-fed circular waveguide
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-20-
Table 23 Properties of the probe-fed circular waveguide radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 73 70 1414 83 57 17
18 60 52 30
When a circular waveguide radiator is fed by a coaxial probe its radiation
properties are not good due to the excitation of higher-order modes
Therefore a probe-fed circular waveguide radiator can be used as a feed only
over a narrow frequency range
24 Probe-Fed Square Waveguide Radiator
In this section a probe-fed square waveguide radiator is investigated Fig
213 shows a coaxial probe-fed square waveguide radiator The designed
radiator has the following dimension a = b = 157mm lp = 35 mm sp =
50 mm wall thickness = 05mm and feed length = 40mm
(a) (b)
Fig 213 Probe-fed square waveguide radiator (a) Front view and (b) side
view
-21-
Fig 214 shows the 2D radiation patterns of the radiator at 10GHz
14GHz and 18GHz Fig 215 shows E- and H-plane patterns of the radiator
Fig 216 shows the reflection coefficient of the probe-fed square waveguide
radiator The reflection coefficient is less than -10dB over 13-20GHz Table
24 summarizes the properties of the probe-fed square waveguide radiator
(a)
Fig 214 2D radiation patterns of the probe-fed square waveguide radiator at
(a) 10GHz (b) 14GHz and (c) 18GHz
-22-
(b)
(c)
Fig 214 continued
-23-
(a)
(b)
(c)
Fig 216 E-plane and H-plane patterns of the probe-fed square waveguide
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-24-
Fig 216 Reflection coefficient of the probe-fed square waveguide radiator
Table 24 Properties of the probe-fed square waveguide radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 73 71 12
14 85 63 1418 27 65 28
When a square waveguide radiator is fed by a coaxial probe its radiation
properties are not good due to the excitation of higher-order modes as in the
case of the probe-fed circular waveguide radiator A probe-fed square
waveguide radiator can be used as a feed only over a narrow frequency
range
-25-
III Design of Compact Circular Waveguide Feeds
In this chapter the feed design is presented for a prime-focus reflector
antenna The prime-focus paraboloid reflector is one of the most commonly
used high-gain antenna It has been used in earth-station antennas and radio
telescopes It consists of a paraboloid reflector with a feed system at its focal
point
The feed should radiate a low level of cross-polar power over the
operating frequency These conditions not easy to achieve and most prime
focus feeds are compromises The shape and characteristic of the radiation
pattern of the feed are the most important parameter because these will
directly influence the fields which are directed at a reflector[6] Other
electrical factors which relevant to the choice of a feed are the cross-polar
level the gain efficiency the bandwidth and impedance matching
31 Narrow-Band Circular Waveguide Feed
Fig 31 shows the proposed narrow-band circular waveguide feed and its
design variables The feed consists of a circular waveguide open end excited
by a TE11 dominant mode A quarter wave choke is applied along the
circular aperture of the waveguide to equalize E- and H-plane radiation
patterns and to suppress the back radiation A dielectric ring is used to
control the radiation pattern and change the power distribution over the
aperture The control of the amplitude over the aperture are essential to the
design of symmetric radiation pattern The material used for dielectric loading
-26-
is the monocast(MC) nylon with a dielectric constant of 30 The feed is
designed to operate over 171-197GHz
(a)
(b)
Fig 31 Narrow-band circular waveguide feed (a) CAD model and (b) a
cross sectional view
The impedance matching is achieved by a proper combination of the probe
height lp and its distance sp from the waveguide shorted end Here the
-27-
circular waveguide is terminated with an open end with a wall thickness of
2mm radiating into the free space
Fig 32 shows the effect of the probe length lp and the probe distance sp
on the reflection coefficient The best performance is obtained when lp =
363mm and sp = 616mm The feeds reflection coefficient is less than -10dB
over 170-195GHz
(a)
(b)
Fig 32 Effect of the (a) the probe length lp and (b) the probe
distance sp on the reflection coefficient
-28-
Fig 33 shows the effect of the choke depth The E-plane pattern is more
sensitive to the choke depth than the H-plane pattern The choke depth has a
strong influence on the reflection coefficient when it is 360mm By properly
choosing the choke depth we can equalize the E- and H-plane patterns The
optimum value of the choke depth is 410mm which is 0249λ0 at 1825GHz
The choke slot width tch in the range of 06-12mm has almost no effect
on the H-plane pattern and the reflection coefficient For the E-plane pattern
tch of 12mm has some effect on the E-plane radiation pattern as shown in
Fig 34
Fig 35 shows the feed performance versus the dielectric ring length We
observe in Fig 35 that the dielectric length ld has an optimum value of
1168mm which does no effect on the H-plane pattern and tha the value of
1048mm has some effect on the E-plane pattern and the reflection
coefficient
Fig 36 shows E-plane and H-plane patterns and the reflection coefficient
versus the dielectric thickness With the optimum value of the dielectric
thickness t obtained from the Fig 36 is 155mm The larger values of td has
much stronger effects on the E-plane pattern and the reflection coefficient
The H-plane pattern is not sensitive to the dielectric ring thickness
-29-
(a)
(b)
(c)
Fig 33 Feed performance versus the choke depth (a) E-plane pattern
(b) H-plane pattern and (c) reflection coefficient
-30-
(a)
(b)
(c)
Fig 34 Feed performance versus the choke slot width (a) E-plane pattern
(b) H-plane pattern and (c) reflection coefficient
-31-
(a)
(b)
(c)
Fig 35 Feed performance versus the dielectric ring length (a) E-plane
pattern (b) H-plane pattern and (c) reflection coefficient
-32-
(a)
(b)
(c)
Fig 36 Feed performance versus the dielectric ring thickness (a) E-plane
pattern(b) H-plane pattern and (c) reflection coefficient
-33-
From the above parametric analysis an optimum feed design is obtained
The result is shown in Table 31 Fig 37 shows the 2D gain patterns of
designed feed The antenna has a gain of 903dB 933dB and 956dB at
171GHz 1825GHz and 19GHz respectively
Fig 38 shows E- and H-plane radiation patterns of the designed feed The
feed has E- and H-plane 10-dB beamwidths of 60 and 59 degrees at 17GHz
The feed has a front-to-back ration of 1900dB 2490dB and 2200dB at
171GHz 1825GHz and 19GHz respectively Table 32 summarizes the
performance of the designed narrow-band circular waveguide feed
The designed feed has a greatly improved performance over that of a
simple coax-fed feed described in Section 23
Table 31 Dimensions of the designed narrow-band circular feed
Parameter Designation Value(mm)
a Waveguide inside radius 640
l Feed length 2890
lp Probe length 363
sp Probe position from the back short 616
din Probe diameter 127
dout Diameter of coaxial cables outer conductor 400
t Thickness of choked wall 050
tch Choke slot width 100
lch Choke depth 410
ld Dielectric ring length 1168
td Dielectric ring thickness 155
d1 Waveguide outside diameter 1680
-34-
(a)
(b)
Fig 37 2D gain patterns of the narrow-band circular waveguide feed at
(a) 17GHz (b) 1825GHz and (c) 19GHz
-35-
(c)
Fig 37 continued
-36-
(a)
(b)
(c)
Fig 38 E- and H-plane patterns of the narrow-band circular waveguide feed
at (a) 10GHz (b) 1825GHz and (c) 195GHz
-37-
Frequency(GHz)
Gain(dB)
E-H-plane10-dB beamwidths
(deg)
Front-to-back ratio(dB)
Phase centerlocation
(From feeds aperture plane
toward reflector)
(mm)
1700 903 6059 20 062
1825 933 6060 25 004
1900 956 5759 22 007
Table 32 Performance of the narrow-band circular waveguide feed
The designed narrow-band feed is fabricated and its performance is
measured and compared with the simulation results The designed feed is
fabricated in a numerically-controlled machining center The fabricated antenna
is shown in Fig 39
Fig 39 Photograph of the fabricated feed
-38-
Fig 310 shows a comparison of the measured and simulated reflection
coefficients The measured reflection coefficient is less than -10dB over
171-197GHz The agreement between simulated and measured results are
good
Fig 311 shows the E- and H-plane patterns of the fabricated feed at
187GHz The feed has 90dB gain simulation and measurement results are in
good agreement
The fabricated antennarsquos 10dB beamwidth is 60 degrees in both E and H
planes at 187GHz The front-to-back ratio is 21dB
Fig 310 Reflection coefficient of the fabricated feed
-39-
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Fee
d H
orn
Gain
- d
B
Angle - degree
(a)
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Feed H
orn
Gain
- d
B
Angle - degree
(b)
Fig 311 Gain patterns of the fabricated feed at 187 GHz (a) E-plane and
(b) H-plane
-40-
IV Design of Circular Waveguide Feeds Loaded with a
Dielectric Rod
In this section circular waveguide feeds loaded with a dielectric rod feed
are investigated A comprehensive discussion of the circular waveguide loaded
with a dielectric rod is given by Kumar[7] Inserting a dielectric material
inside the circular waveguide improves the E- and H-plane pattern symmetry
In general dielectric-loaded circular waveguide feeds show good performance
only over a narrow bandwidth
Fig 41 shows the geometry of a circular waveguide loaded with a
dielectric rod The waveguide length is 400mm and the wall thickness is
05mm The dielectric rods diameter is 207mm The dielectric rod is
extended 05 wavelength beyond the waveguide open end The dielectric
constant εr is changed and the feeds performance is observed
Fig 41 Geometry of a circular waveguide loaded with a uniform dielectric
rod
-41-
Fig 42 is the radiation pattern of the feed with εr = 25 and L = 05λ0 at
9GHz E- and H-plane 10-dB beamwidths are 810 and 807 degrees
respectively The front-to-back ratio is 18dB The antenna gain is 71dB
(a)
(b)
Fig 42 Radiation pattern at 9GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 05λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-42-
Fig 43 shows the radiation pattern of the feed with εr = 21 at 10GHz
E- and H-plane 10-dB beamwidths are 70 and 71 degrees respectively The
front-to-back ratio is 19dB The antenna gain is 83dB
(a)
(b)
Fig 43 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 21 and L = 05λ0 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-43-
Fig 44 shows the radiation pattern of the feed with εr = 30 at 8GHz
E- and H-plane 10-dB beamwidths are 83 and 824 degrees respectively The
front-to-back ratio is 17dB The antenna gain is 73dB
(a)
(b)
Fig 44 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 30 and L = 05λ0 at 8GHz (a) 2D radiation pattern
and (b) E- and H-plane patterns
-44-
Fig 45 shows the radiation pattern of the feed with εr = 50 at 18GHz
E- and H-plane 10-dB beamwidths are 56 and 54 degrees respectively The
front-to-back ratio is 27dB The antenna gain is 105dB The feed has a good
pattern symmetry and low back radiation
(a)
(b)
Fig 45 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 50 and L = 05λ0 at 18GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-45-
Fig 46 is the radiation pattern of the feed with εr = 25 and L = 10λ0 at
10GHz E- and H-plane 10-dB beamwidths are 50 and 48 degrees
respectively The front-to-back ratio is 16dB The antenna gain is 105dB
(a)
(b)
Fig 46 Radiation pattern at 10GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 10λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-46-
Fig 47 shows the geometry of a circular waveguide with a tapered
dielectric rod The designed feed has the following dimension L = 1λ0 d =
1λ0 and εr =25 at 10GHz The waveguide length is 40mm and the wall
thickness is 05mm
L
Dielectricd3
Fig 47 Geometry of a circular waveguide loaded with a tapered dielectric
rod
Fig 48 shows the radiatio pattern of the designed feed E- and H-plane
10-dB beamwidths are 575 and 564 degrees respectively The front-to-back
ratio is 377dB The antenna gain is 94dB The designed feed has an
excellent beamwidth symmetry and a very low back radiation
-47-
(a)
(b)
Fig 48 Radiation pattern of a circular waveguide loaded with a tapered
dielectric rod with L = 1λ0 d = 1λ0 and εr =25 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-48-
Fig 49 shows the geometry of a spherical ended dielectric rod feed
diameter of 06λ0 at 10GHz with a dielectric constant of 25 and L= 03λ0
Fig 410 shows the radiation patterns of the designed feed E- and H-plane
10-dB beamwidths are both 63 degrees The front-to-back ratio is 24dB The
antenna gain is 864dB
Fig 49 Geometry of a circular waveguide loaded with a spherical ended
dielectric rod
-49-
(a)
(b)
Fig 410 Radiation pattern of a circular waveguide loaded wht a spherical
ended dielectric rod with d = 06λ0 L = 03λ0 and εr =25 at 10GHz (a) 3D
radiation pattern and (b) E- and H-plane patterns
-50-
V Design of a Broadband Circular Waveguide Feed
In this chapter the design of a broadband circular waveguide feed is
presented At microwave frequencies the feed is often a circular waveguide
with chokes and corrugations around the aperture Chokes and corrugations
equalize E- and H-plane patterns and reduce the back radiation
The proposed feed is designed to operate over 10-18GHz The design starts
with the optimization of the coaxial-to-rectangular waveguide adapter
employed for good mode purity over a broad frequency range Next a
rectangular-to-circular waveguide transition is optimized Finally chokes and
corrugations are designed for improved pattern symmetry and low back
radiation
The proposed feed structure is shown in Fig 51 The feed consist of the
following parts a coaxial-to-rectangular waveguide adapter a rectangular-to-
circular waveguide transition a circular waveguide section four quarter-wave
chokes around the feeds aperture and four corrugations on the feeds outer
surface
The computer simulation shows the above arrangement offers good radiation
patterns over a broad frequency range The broadband operation is obtained
by exciting the TE11 mode in the circular waveguide using the TE10 mode of
the rectangular waveguide which is in turn excited by a coaxial probe
-51-
Chokes
Coaxial-to-waveguide transition
Circular wavguide
Corrugations
Mode transition
(a)
(b)
Fig 51 Structure of the proposed broadband circular waveguide feed
(a) CAD model and (b) cross-sectional view
For the coaxial-to-rectangular waveguide adapter an SMA connector with
the probe diameter of 127 mm is employed The coaxial probe inserted into
the waveguide energizes the feed and excites the dominant TE10 mode in
-52-
the rectangular waveguide The impedance matching is achieved by adjusting
the probe distance sp from the back short and the probe length lp
(a)
(b)
Fig 52 Reflection coefficient of the coaxial-to-rectangular adapter versus
(a) probe length lp and (b) the probe position sp
Fig 52 shows the reflection coefficient versus the various values of probe
lengths lp and probe positions sp The probe length lp is adjusted to obtain
antenna impedance matching and the probe distance sp is adjusted to obtain a
-53-
desired resonant frequency
Next a transition between rectangular and circular waveguide is designed
The transition section converts the TE10 mode in the rectangular waveguide to
TE11 mode in the circular waveguide and vice versa The transition is built
in a form of a taper for easy fabrication[22]
(a)
(b)
Fig 53 Structure of the rectangular-to-circular waveguide transition
(a) 3D view and (b) cross sectional view
The dimensions of the final optimized transition are as follows The length
of the rectangular waveguide section is 143mm The rectangular waveguides
width a and height b are 207mm and 857mm respectively The length of
the circular waveguide section is 143mm The inside diameter of the circular
-54-
waveguide is 207mm(097 wavelength at 14GHz) The length of transition
region ltr is 4465mm(approximately equal to 2λ0 at 14GHz) Fig 54 shows
the field distribution inside the mode converter
(a)
(b)
Fig 54 Field distribution inside the mode converter at
(a) 10GHz (b) 14GHz and (c) 18GHz
-55-
(c)
Fig 54 continued
Finally multiple chokes are investigated Figs 55 56 and 57 show the
feed performance without chokes The reflection coefficient is less than -10dB
over 10-19GHz The antenna has a gain of 921dB to 1189dB over
10-19GHz
Fig 55 Reflection coefficient of the broadband circular waveguide feed
without chokes and corrugations
-56-
(a)
(b)
(c)
Fig 56 E- and H-plane patterns of the broadband circular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-57-
(d)
(e)
Fig 56 continued
-58-
(a)
(b)
Fig 57 2D radiation patterns of the broadband cicular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-59-
(c)
(d)
Fig 57 continued
-60-
(e)
Fig 57 continued
To achieve equal beamwidths in E and H planes over a wide frequency
range chokes and corrugations are employed Table51 summarizes the
performance of a feed without chokes and corrugations
Table 51 Performance of the broadband circular waveguide feed without
chokes and corrugations
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
1000 940 6061 15
1200 972 6159 17
1400 920 5957 21
1600 1070 4751 29
1800 1188 5352 21
-61-
Four quarter-wavelength chokes are introduced in the feed design which
has a slot depth of 75mm and slot width of 09mm The choke slot spacing
is 18mm The choke design is investigated by applying the choke one by
one and the effect on the E- and H-plane patterns are observed as illustrated
in Figs 58 and 59 The use of chokes makes the E-plane pattern narrower
The H-plane pattern is not affected Chokes increase the gain slightly and
reduce back radiation
(a)
(b)
Fig 58 Effect of chokes on the E-plane pattern of the broadband circular
waveguide feed at (a) 10GHz(b) 12GHz (c) 14GHz (d) 16GHz and (e)
18GHz
-62-
(c)
(d)
(e)
Fig 58 continued
-63-
(a)
(b)
(c)
Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-64-
(d)
(e)
Fig 59 continued
-65-
Fig 510 shows the feed performance versus the choke depth When the
choke depth is varied from 535mm to 95mm the E- and H-plane patterns
are strongly affected The optimum value of choke depth is 75mm(035λ0 at
14GHz) which gives equal E- and H-plane radiation patterns and leads to
low back radiation
Fig 511 shows the feed performance versus the choke slot width tch The
choke slot width is varied from 09mm to 21mm Radiation patterns and
reflection coefficients are not sensitive to the choke slot width The final
choke slot width is selected to be 09mm considering the feed diameter
minimization and the manufacturability The overall diameter of the proposed
feed is 369mm which is increased from the 207mm of the waveguide
inside diameter due to the use of four chokes
-66-
(a)
(b)
(c)
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection coefficient
-67-
(a)
(b)
(c)
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and (c)
reflection coefficient
-68-
Next we investigated corrugations placed on the outer wall of the feed
Four corrugations applied to the outer surface of the circular waveguide The
corrugation depth is 465mm(0215λ0 at 14GHz) The primary purpose of
using corrugations is to further reduce the back radiation Increasing the
number of corrugations beyond four has little effect in reducing the back
radiation
Figs 512 and 513 show the effect of corrugations on the E- and H-plane
patterns Fig 514 shows the parametric study of the corrugation depth lcor
The corrugation depth is varied from 40mm and 645mm The optimum
value of the corrugation depth is found to be 465mm
-69-
(a)
(b)
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern at (a) 12GHz and (b) 14GHz
-70-
(a)
(b)
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern at (a) 12GHz and (b) 14GHz
-71-
(a)
(b)
(c)
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection coefficient
-72-
The phase center location is important in placing the feed in a reflector
antenna[8] The phase center variation with frequency should be small Fig
515 shows the effect of chokes and corrugations on the phase center The
curve with circle corresponds to the case without chokes and corrugations
The phase center varies from -326mm and -190mm away from the feeds
aperture plane It means the phase center is located inside the waveguide
The curve with triangles corresponds to the case with chokes The curve with
squares to the case with chokes and corrugations The phase center varies
from 0mm to -302mm
From Fig 515 we can observed that phase center variation reduced by the
corrugation and three cases phase center calculated in φ=450 plane
parameter sweep values are given in Table 52
10 12 14 16 181
0
-1
-2
-3
-4
-5
-6
Pha
se c
ente
r (m
m)
Frequency (GHz)
choke+corrugatuion without choke corrugation with choke
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
-73-
Frequency
(GHz)
Phase center from the aperture plane
(mm)
Without
chokes and
corrugations
With
chokes
With chokes
and
corrugations
1000 -326 062 000
1100 -187 030 -002
1200 -563 -208 -065
1300 -296 -154 -202
1400 -319 -314 -302
1500 -201 -203 -241
1600 -242 -233 -207
1700 -208 -208 -186
1800 -190 -157 -132
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
Based on the foregoing parametric studies optimum dimensions of the
broadband circular waveguide feed are obtained as shown in Table 53
-74-
Table 53 Optimum dimensions of the broadband circular waveguide feed
Parameter Designation Value (mm)
2a Waveguide inside diameter 2070
d Waveguide outside diameter 3690
lcrLength of the circular waveguide section 1430
m Distance between the aperture plane and the first corrugation 950
xDistance from the last corrugation to the end of the cylindrical outer surface
550
ltrLength of the rectangular-to-circularwaveguide transition 4465
lrcLength of the rectangular waveguide section 1430
tch Choke slot width 090
lch Choke depth 750
t Choke metal width 090
lcor Corrugation depth 465
tcor Corrugation metal width 100
s Corrugation slot width 10
lp Probe length 530
sp Probe position from the back short 530
din Probe diameter 127
b Inside height of the rectangular waveguide 857
tw Waveguide wall thickness 500
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-ii-
DesignofaBroadbandFeedforParabolic
ReflectorApplications
Odontuya Baasantseren
Department of Radio and Communications Engineering
Graduate School Chungbuk National University
Cheongju City South Korea
Supervised by Professor Bierng-Chearl Ahn Ph D
Abstract
In this thesis the design of a broadband feed for application in prime-focus
parabolic reflector antenna is described A feed for parabolic reflector antenna
requires radiation pattern with a good circular symmetry low back radiation
and low cross polarization This thesis proposes two feed designs one is a
dielectric ring-loaded circular waveguide operating over 171-197GHz and
fed by a coaxial probe The other is a choked and corrugated circular
waveguide fed by a probe-fed rectangular waveguide Before designing two
A thesis for the degree of Master in August 2012
-iii-
feeds performances of simple circular and square waveguide open ends are
investigated The improvement in the performance of the circular waveguide
open end by dielectric loading is also investigated The study shows that only
a narrow-band performance is possible with simple feeds
Based on this study the first feed is designed with the monocast(MC)
nylon as the dielectric-ring material for beamwidth equalization and a
quarter-wave choke around the aperture wall for back-radiation reduction A
coaxial probe is used to excite the feed The designed feed shows a good
performance over 171-197GHz
The second feed uses more complicated structures For broadband operation
the circular waveguide is fed by a probe-excited rectangular waveguide Four
quarter-wave chokes are used around the aperture wall for beamwidth
equalization and four corrugations are employed on the feeds outer surface
for further reduction in the back radiation
Prototypes of both feeds are fabricated and tested Test results are in good
agreement with the design objectives verifying the excellent performances of
the designed feeds
-iv-
List of Figures
Fig 21 Geometry of a circular waveguide open end radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 6
Fig 22 Reflection coefficient of a circular waveguide open end radiator middotmiddot 6
Fig 23 2D radiation pattern of a circular waveguide open end radiator middotmiddotmiddot 7
Fig 24 E-plane and H-plane patterns of a circular waveguide open end
radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 9
Fig 25 Geometry of a square waveguide open end radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 11
Fig 26 Reflection coefficient of a square waveguide open end radiator middot 12
Fig 27 2D radiation patterns of a square waveguide open end radiator middot 12
Fig 28 E-plane and H-plane patterns of square waveguide open end
radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 14
Fig 29 Probe-fed circular waveguide radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 16
Fig 210 Reflection coefficient of the probe-fed circular waveguide radiator
middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 17
Fig 211 2D radiation patterns of the probe-fed circular waveguide radiator
middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 17
Fig 212 E- and H-plane patterns of the probe-fed circular waveguide
radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 19
Fig 213 Probe-fed square waveguide radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 20
Fig 214 2D radiation pattern of the probe-fed square waveguide radiator 21
Fig 215 E- and H-plane pattern of the probe-fed square waveguide radiator
middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 23
Fig 216 Reflection coefficient of the probe-fed square waveguide radiator 24
Fig 31 Narrow-band circular waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 26
-v-
Fig 32 Effect of the (a) the probe length lp (b) the probe distance sp on
the reflection coefficient middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 27
Fig 33 Feed performance versus the choke depth (a) E-plane pattern (b)
H- plane pattern (c) reflection coefficient middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 29
Fig 34 Feed performance versus the choke slot width (a) E-plane pattern
(b) H-plane pattern (c) reflection coefficient middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 30
Fig 35 Feed performance versus the dielectric ring length (a) E-plane
pattern (b) H-plane pattern and (c) reflection coefficient middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 31
Fig 36 Feed performance versus the dielectric ring thickness (a) E-plane
pattern (b) H-plane pattern (c) reflection coefficient middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 32
Fig 37 2D gain patterns of the narrow-band circular waveguide feed middotmiddotmiddot 34
Fig 38 E- and H-plane patterns of the narrow-band circular waveguide
feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 30
Fig 39 Photograph of the fabricated feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 37
Fig 310 Reflection coefficient of the fabricated feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 38
Fig 311 Gain patterns of the fabricated feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 39
Fig 41 Geometry of a circular waveguide loaded with a uniform dielectric
rod middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 40
Fig 42 Radiation pattern at 9GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 05λ0 middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 41
Fig 43 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 21 and L = 05λ0 at 10GHz middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 42
Fig 44 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 30 and L = 05λ0 at 8GHz middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 43
Fig 45 Radiation pattern of the circular waveguide loaded with a uniform
-vi-
dielectric rod with εr = 50 and L = 05λ0 at 18GHz middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 44
Fig 46 Radiation pattern at 10GHz of the circular waveguide loaded with
a uniform dielectric rod with εr = 25 and L = 10λ0 middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 45
Fig 47 Geometry of a circular waveguide loaded with a tapered dielectric
rod middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 46
Fig 48 Radiation pattern of a circular waveguide loaded with a tapered
dielectric rod with L = 1λ0 d = 1λ0 and εr =25 at 10GHz middotmiddotmiddotmiddotmiddotmiddotmiddot 47
Fig 49 Geometry of a circular waveguide loaded with a spherical ended
dielectric rod middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 48
Fig 410 Radiation pattern of a circular waveguide loaded wht a spherical
ended dielectric rod with d = 06λ0 L = 03λ0 and εr =25 at
10GHz middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 49
Fig 51 Structure of the proposed broadband circular waveguide feed middotmiddotmiddotmiddotmiddot 51
Fig 52 Reflection coefficient of the coaxial-to-rectangular adapter versus
(a) probe length lp and (b) the probe position sp middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 52
Fig 53 Structure of the rectangular-to-circular waveguide transition middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 53
Fig 54 Field distribution inside the mode converter middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 54
Fig 55 Reflection coefficient of the broadband circular waveguide feed
without chokes and corrugations middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 55
Fig 56 E-plane and H-plane patternsof the broadband circular waveguide
feed without chokes and corrugationsz middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 56
Fig 57 2D radiation patterns of the broadband cicular waveguide feed
without chokes and corrugations middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 58
Fig 58 Effect of chokes on the E-plane pattern of the broadband circular
waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 61
-vii-
Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 63
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection
coefficient middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 66
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and
(c) reflection coefficient middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 67
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 69
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 70
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection
coefficient middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 71
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 72
Fig 516 Reflection coefficient of the designed broadband circular
waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 75
Fig 517 2D radiation patterns of the designed broadband circular
waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 76
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 79
Fig 519 Phase center variation of the designed broadband circular
waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 81
-viii-
Fig 520 Photograph of the fabricated broadband circular waveguide feed 82
Fig 521 Reflection coefficient of the fabricated broadband circular
waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 82
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 84
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 84
-ix-
List of Tables
Table 21 Properties of a circular waveguide open end radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 10
Table 22 Properties of a square waveguide open end radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 15
Table 23 Properties of the probe-fed circular waveguide radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 20
Table 24 Properties of the probe-fed square waveguide radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 24
Table 31 Dimensions of the designed narrow-band circular feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 33
Table 32 Performance of the narrow-band circular waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 37
Table 51 Performance of the broadband circular waveguide feed without
chokes and corrugations middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 60
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 73
Table 53 Optimum dimensions of the broadband circular waveguide feed 74
Table 54 Performance of the designed broadband circular waveguide feed 81
-1-
I Introduction
The horns and waveguides are known for their high efficiency and
structural simplicity They are popular choices for feeding for reflectors in
high-gain antenna applications such as satellite and point-to-point microwave
communication links The theory of reflector antenna was developed in the
1940s and has been used to calculate the radiation patterns of various
reflector structures[1]
The basic structure of a prime-focus reflector antenna consists of a
parabolic reflecting surface a feed and its support The placement of the feed
is such that its phase center is at the focal point of the parabolic reflecting
surface The feed is often a circular waveguide because of its symmetric
radiation pattern with low back radiation and low cross polarization The
circular waveguide feed must have a small diameter to reduce the aperture
blockage of the reflector antenna[3]
A radiation pattern with a good circular symmetry in the main beam can
be found from circular waveguide feeds with dominant TE11 mode excitation
The radiation patterns depends on the diameter and wall thickness of the
waveguide[4] A coaxial probe can be inserted into a short-circuited circular
waveguide in the form of a coaxial-to-waveguide transition The diameter of
the circular waveguide is chosen such that only the dominant mode
propagates
When the waveguide dimension does not provide a circular symmteric
-2-
pattern a choke or multiple chokes around the aperture wall can be
employed to equalize radiation patterns and keep the back radiation in low
level If chokes are not enough for the suppression of the back radiation
corrugations on the outer surface of the feed is one way to reduce the back
radiation
In this thesis a broadband circular waveguide feed is developed for
prime-focus reflector antenna application After investigating the radiation
properties of simple circular and square waveguides methods are investigated
for bandwidth enhancement back radiation suppression and beamwidth
equalization in the circular waveguide feed
The first type of the circular waveguide feed consists of a probe-fed
circular waveguide a single quarter-wave choke on the aperture wall and a
dielectric-ring beamwidth equalizer Due to the simple feeding method the
first feed operates over 171-197GHz(141) which is not broadband in the
strict sense of the word
The second feed consists of a coaxial-to-rectangular waveguide transition a
rectangular-to-circular waveguide transition a circular waveguide section four
quarter-wave chokes on the aperture wall and four quarter-wave corrugations
on the feeds outer surface Due to the complicated feeding method the
second feed operates over 10-18GHz(571)
This thesis is arranged as follows Chapter I gives an introduction to the
thesis related works and objectives are stated Chapter II describes the
structure and excitation of the circular and square waveguide and the
operation of the coaxial-to-waveguide transitions Chapter III describes a
compact feed horn design and its fabrication and measurement Chapter IV
-3-
presents dielectric rod feed and its simulated performances Chapter V gives
design and optimization of feed for parabolic reflector antenna In this
chapter includes the detailed information of design procedures and operating
principle also the simulated and measured performances are provided Finally
conclusion is given in the Chapter VI
-4-
II Analysis of Circular and Square Waveguide Feeds
21 Circular Waveguide Radiator
Before design a complicated circular waveguide feed it is helpful to
investigate the impedance and radiation properties of a circular waveguide
open end
The circular waveguide is a cylindrical hollow metallic pipe with a uniform
circular section of radius a Circular waveguides are normally designed to
operate only with the dominant mode The dominant mode in a waveguide is
the mode having the lowest cutoff frequency given by equation (21)
(21)
where
(22)
and a is the waveguide radius The following chart[2] and table show the
cutoff frequencies of various modes in a circular waveguide
-5-
Modes c al11TEc cf f
TE11 341259 100000
TM01 261274 130613
TE21 205720 165885TE01 163979 208111
TM11 163979 208111TE31 149557 228180
TM21 122345 278932TE41 118159 288813
TE12 117852 289566
TM02 113824 299813TE02 0897986 380027
The recommended frequency range of the commercial circular waveguide is
given by the following equation This assumes that the TM01 mode is not
generated or suppressed if generated
11 21 11TE TE TE115 095 158 32 bandwidthc c cf f f fpound pound = reg (23)
Fig 21 shows the geometry of a circular waveguide with a diameter of 2a
When 2a is 2053mm the cutoff frequency of the TE11 mode is 857GHz
According to (23) the useful operating frequency range is from
986-1354GHz
Fig 22 shows the reflection of this waveguide excited with the dominant
TE11 mode The waveguide length l is 60mm The reflection occurs at the
open end of the circular waveguide The reflection coefficient is less than
-15dB over 10-18GHz
-6-
Fig 21 Geometry of a circular waveguide open end radiator
Fig 23 shows a 2D gain pattern of this waveguide antenna The
waveguide antenna has a gain of 80dB 99dB and 115dB at 10GHz
14GHz and 18GHz respectively Fig 24 shows the E- and H-plane patterns
of the circular waveguide antenna Table 21 summarizes the properties of a
circular waveguide antenna
Fig 22 Reflection coefficient of a circular waveguide open end radiator
-7-
(a)
(b)
Fig 23 2D radiation pattern of the circular waveguide open end radiator
at (a)10GHz (b) 14GHz and (c) 18GHz
-8-
(c)
Fig 23 continued
-9-
(a)
(b)
(c)
Fig 24 E-plane and H-plane patterns of the circular waveguide open end
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-10-
Table 21 Properties of a circular waveguide open end radiator of diameter
2053mm
Frequency(GHz)-10dB Beamwith(deg) Front-to-Back
Ratio(dB)E plane H plane
10 67 73 12
14 58 60 18
18 41 50 21
In a circular waveguide radiatoλr a good pattern symmetry and low back
radiation is obtained at 14GHz where 2aλ = 096
22 Square Waveguide Radiator
A square waveguide is often used as a dual-polarized feed To operate the
cutoff frequency of the dominant mode a square-waveguide wall width a
must be greater than one half of a wavelength The modes with cutoff
frequencies equal to or smaller than the operational frequency can exist inside
the waveguide wall The lower cutoff frequency and cutoff wavelength for
square waveguide is determined by the following equations
TE
(24)
TE
(25)
The next higher-order mode is TE11 mode with the cutoff wavelength
given by
-11-
TE
(26)
Similar to the circular waveguide the recommended operating frequency range
of a square waveguide is given by
TEleleTE
TErarr bandwidth (27)
Fig 25 shows the geometry of a square waveguide with a dimension of a
When a is 157mm the cutoff frequency is 95GHz The recommended
operating frequency of this waveguide is from 109GHz to 155GHz
Fig 26 shows the reflection of this waveguide excited with the dominant
TE10 mode The reflection coefficient is less than -15dB over 10-20GHz
Fig 25 Geometry of a square waveguide open end radiator
Fig 27 and shows the 2D radiation pattern of a square waveguide antenna
excited with the dominant TE10 mode The antenna has a gain of 73dB
85dB and 102dB at 10GHz 14GHz and 18GHz respectively Fig 28
shows the E- and H-plane radiation patterns of a square waveguide radiator
Table 22 summarizes the properties of a square waveguide open end radiator
-12-
Fig 26 Reflection coefficient of a square waveguide open end radiator
(a)
Fig 27 2D radiation patterns of a square waveguide radiator
at (a) 10GHz (b) 14GHz and (c) 18GHz
-13-
(b)
(c)
Fig 27 continued
-14-
(a)
(b)
(c)
Fig 28 E-plane and H-plane patterns of square waveguide open radiator
at (a) 10GHz(b) 14GHz and (c) 18GHz
-15-
Table 22 Properties of a square waveguide open end radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 69 71 11
14 47 60 25
18 58 62 16
The radiation pattern symmetry and back radiation performance of the
square waveguide are inferior to those of a circular waveguide
23 Probe-Fed Circular Waveguide Radiator
In Section 21 the radiation properties of a TE11-mode excited waveguide
is investigated In this section a circular waveguide fed by a coaxial probe
shown in Fig 29 is studied
The coaxial probes diameter is 127mm With the Teflon dielectric the
50-ohm coaxial lines outer conductor has a diameter of 41mm For a
circular waveguide the wave impedance of the TE11 mode is given by
∙ (28)
where λg is the guided wavelength given by
(29)
-16-
(a) (b)
Fig 29 Probe-fed circular waveguide radiator (a) Front view and (b) side
view
The combination of the probe length and the probe position from the
shorted wall enables a good impedance matching The probe distance sp from
the back short is close to a quarter wavelength at the design frequency
The designed feed has the following dimension d = 2053mm lp = 42
mm sp = 534mm wall thickness = 05mm and feed length = 400mm
Fig 210 shows the reflection coefficient of the designed probe-fed
circular waveguide radiator The reflection coefficient is less than -10dB over
138-187GHz Fig 211 and 212 shows the E-plane and H-plane radiation
patterns and 2D radiation patterns of the coaxial-to-circular waveguide
transition The radiation patterns symmetry distorted because of the high order
modes The coaxial-to-circular waveguide transition has 73dB 84dB and
79dB gain at 10GHz 14GHz and 18GHz frequencies respectively Table 23
shows the properties of the coaxial-to-circular waveguide transition
-17-
Fig 210 Reflection coefficient of the probe-fed circular waveguide radiator
(a)
Fig 211 2D radiation pattern of the probe-fed circular waveguide radiator
at (a) 10GHz (b) 14GHz and (c) 18GHz
-18-
(b)
(c)
Fig 211 continued
-19-
(a)
(b)
(c)
Fig 212 E- and H-plane patterns of the probe-fed circular waveguide
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-20-
Table 23 Properties of the probe-fed circular waveguide radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 73 70 1414 83 57 17
18 60 52 30
When a circular waveguide radiator is fed by a coaxial probe its radiation
properties are not good due to the excitation of higher-order modes
Therefore a probe-fed circular waveguide radiator can be used as a feed only
over a narrow frequency range
24 Probe-Fed Square Waveguide Radiator
In this section a probe-fed square waveguide radiator is investigated Fig
213 shows a coaxial probe-fed square waveguide radiator The designed
radiator has the following dimension a = b = 157mm lp = 35 mm sp =
50 mm wall thickness = 05mm and feed length = 40mm
(a) (b)
Fig 213 Probe-fed square waveguide radiator (a) Front view and (b) side
view
-21-
Fig 214 shows the 2D radiation patterns of the radiator at 10GHz
14GHz and 18GHz Fig 215 shows E- and H-plane patterns of the radiator
Fig 216 shows the reflection coefficient of the probe-fed square waveguide
radiator The reflection coefficient is less than -10dB over 13-20GHz Table
24 summarizes the properties of the probe-fed square waveguide radiator
(a)
Fig 214 2D radiation patterns of the probe-fed square waveguide radiator at
(a) 10GHz (b) 14GHz and (c) 18GHz
-22-
(b)
(c)
Fig 214 continued
-23-
(a)
(b)
(c)
Fig 216 E-plane and H-plane patterns of the probe-fed square waveguide
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-24-
Fig 216 Reflection coefficient of the probe-fed square waveguide radiator
Table 24 Properties of the probe-fed square waveguide radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 73 71 12
14 85 63 1418 27 65 28
When a square waveguide radiator is fed by a coaxial probe its radiation
properties are not good due to the excitation of higher-order modes as in the
case of the probe-fed circular waveguide radiator A probe-fed square
waveguide radiator can be used as a feed only over a narrow frequency
range
-25-
III Design of Compact Circular Waveguide Feeds
In this chapter the feed design is presented for a prime-focus reflector
antenna The prime-focus paraboloid reflector is one of the most commonly
used high-gain antenna It has been used in earth-station antennas and radio
telescopes It consists of a paraboloid reflector with a feed system at its focal
point
The feed should radiate a low level of cross-polar power over the
operating frequency These conditions not easy to achieve and most prime
focus feeds are compromises The shape and characteristic of the radiation
pattern of the feed are the most important parameter because these will
directly influence the fields which are directed at a reflector[6] Other
electrical factors which relevant to the choice of a feed are the cross-polar
level the gain efficiency the bandwidth and impedance matching
31 Narrow-Band Circular Waveguide Feed
Fig 31 shows the proposed narrow-band circular waveguide feed and its
design variables The feed consists of a circular waveguide open end excited
by a TE11 dominant mode A quarter wave choke is applied along the
circular aperture of the waveguide to equalize E- and H-plane radiation
patterns and to suppress the back radiation A dielectric ring is used to
control the radiation pattern and change the power distribution over the
aperture The control of the amplitude over the aperture are essential to the
design of symmetric radiation pattern The material used for dielectric loading
-26-
is the monocast(MC) nylon with a dielectric constant of 30 The feed is
designed to operate over 171-197GHz
(a)
(b)
Fig 31 Narrow-band circular waveguide feed (a) CAD model and (b) a
cross sectional view
The impedance matching is achieved by a proper combination of the probe
height lp and its distance sp from the waveguide shorted end Here the
-27-
circular waveguide is terminated with an open end with a wall thickness of
2mm radiating into the free space
Fig 32 shows the effect of the probe length lp and the probe distance sp
on the reflection coefficient The best performance is obtained when lp =
363mm and sp = 616mm The feeds reflection coefficient is less than -10dB
over 170-195GHz
(a)
(b)
Fig 32 Effect of the (a) the probe length lp and (b) the probe
distance sp on the reflection coefficient
-28-
Fig 33 shows the effect of the choke depth The E-plane pattern is more
sensitive to the choke depth than the H-plane pattern The choke depth has a
strong influence on the reflection coefficient when it is 360mm By properly
choosing the choke depth we can equalize the E- and H-plane patterns The
optimum value of the choke depth is 410mm which is 0249λ0 at 1825GHz
The choke slot width tch in the range of 06-12mm has almost no effect
on the H-plane pattern and the reflection coefficient For the E-plane pattern
tch of 12mm has some effect on the E-plane radiation pattern as shown in
Fig 34
Fig 35 shows the feed performance versus the dielectric ring length We
observe in Fig 35 that the dielectric length ld has an optimum value of
1168mm which does no effect on the H-plane pattern and tha the value of
1048mm has some effect on the E-plane pattern and the reflection
coefficient
Fig 36 shows E-plane and H-plane patterns and the reflection coefficient
versus the dielectric thickness With the optimum value of the dielectric
thickness t obtained from the Fig 36 is 155mm The larger values of td has
much stronger effects on the E-plane pattern and the reflection coefficient
The H-plane pattern is not sensitive to the dielectric ring thickness
-29-
(a)
(b)
(c)
Fig 33 Feed performance versus the choke depth (a) E-plane pattern
(b) H-plane pattern and (c) reflection coefficient
-30-
(a)
(b)
(c)
Fig 34 Feed performance versus the choke slot width (a) E-plane pattern
(b) H-plane pattern and (c) reflection coefficient
-31-
(a)
(b)
(c)
Fig 35 Feed performance versus the dielectric ring length (a) E-plane
pattern (b) H-plane pattern and (c) reflection coefficient
-32-
(a)
(b)
(c)
Fig 36 Feed performance versus the dielectric ring thickness (a) E-plane
pattern(b) H-plane pattern and (c) reflection coefficient
-33-
From the above parametric analysis an optimum feed design is obtained
The result is shown in Table 31 Fig 37 shows the 2D gain patterns of
designed feed The antenna has a gain of 903dB 933dB and 956dB at
171GHz 1825GHz and 19GHz respectively
Fig 38 shows E- and H-plane radiation patterns of the designed feed The
feed has E- and H-plane 10-dB beamwidths of 60 and 59 degrees at 17GHz
The feed has a front-to-back ration of 1900dB 2490dB and 2200dB at
171GHz 1825GHz and 19GHz respectively Table 32 summarizes the
performance of the designed narrow-band circular waveguide feed
The designed feed has a greatly improved performance over that of a
simple coax-fed feed described in Section 23
Table 31 Dimensions of the designed narrow-band circular feed
Parameter Designation Value(mm)
a Waveguide inside radius 640
l Feed length 2890
lp Probe length 363
sp Probe position from the back short 616
din Probe diameter 127
dout Diameter of coaxial cables outer conductor 400
t Thickness of choked wall 050
tch Choke slot width 100
lch Choke depth 410
ld Dielectric ring length 1168
td Dielectric ring thickness 155
d1 Waveguide outside diameter 1680
-34-
(a)
(b)
Fig 37 2D gain patterns of the narrow-band circular waveguide feed at
(a) 17GHz (b) 1825GHz and (c) 19GHz
-35-
(c)
Fig 37 continued
-36-
(a)
(b)
(c)
Fig 38 E- and H-plane patterns of the narrow-band circular waveguide feed
at (a) 10GHz (b) 1825GHz and (c) 195GHz
-37-
Frequency(GHz)
Gain(dB)
E-H-plane10-dB beamwidths
(deg)
Front-to-back ratio(dB)
Phase centerlocation
(From feeds aperture plane
toward reflector)
(mm)
1700 903 6059 20 062
1825 933 6060 25 004
1900 956 5759 22 007
Table 32 Performance of the narrow-band circular waveguide feed
The designed narrow-band feed is fabricated and its performance is
measured and compared with the simulation results The designed feed is
fabricated in a numerically-controlled machining center The fabricated antenna
is shown in Fig 39
Fig 39 Photograph of the fabricated feed
-38-
Fig 310 shows a comparison of the measured and simulated reflection
coefficients The measured reflection coefficient is less than -10dB over
171-197GHz The agreement between simulated and measured results are
good
Fig 311 shows the E- and H-plane patterns of the fabricated feed at
187GHz The feed has 90dB gain simulation and measurement results are in
good agreement
The fabricated antennarsquos 10dB beamwidth is 60 degrees in both E and H
planes at 187GHz The front-to-back ratio is 21dB
Fig 310 Reflection coefficient of the fabricated feed
-39-
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Fee
d H
orn
Gain
- d
B
Angle - degree
(a)
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Feed H
orn
Gain
- d
B
Angle - degree
(b)
Fig 311 Gain patterns of the fabricated feed at 187 GHz (a) E-plane and
(b) H-plane
-40-
IV Design of Circular Waveguide Feeds Loaded with a
Dielectric Rod
In this section circular waveguide feeds loaded with a dielectric rod feed
are investigated A comprehensive discussion of the circular waveguide loaded
with a dielectric rod is given by Kumar[7] Inserting a dielectric material
inside the circular waveguide improves the E- and H-plane pattern symmetry
In general dielectric-loaded circular waveguide feeds show good performance
only over a narrow bandwidth
Fig 41 shows the geometry of a circular waveguide loaded with a
dielectric rod The waveguide length is 400mm and the wall thickness is
05mm The dielectric rods diameter is 207mm The dielectric rod is
extended 05 wavelength beyond the waveguide open end The dielectric
constant εr is changed and the feeds performance is observed
Fig 41 Geometry of a circular waveguide loaded with a uniform dielectric
rod
-41-
Fig 42 is the radiation pattern of the feed with εr = 25 and L = 05λ0 at
9GHz E- and H-plane 10-dB beamwidths are 810 and 807 degrees
respectively The front-to-back ratio is 18dB The antenna gain is 71dB
(a)
(b)
Fig 42 Radiation pattern at 9GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 05λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-42-
Fig 43 shows the radiation pattern of the feed with εr = 21 at 10GHz
E- and H-plane 10-dB beamwidths are 70 and 71 degrees respectively The
front-to-back ratio is 19dB The antenna gain is 83dB
(a)
(b)
Fig 43 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 21 and L = 05λ0 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-43-
Fig 44 shows the radiation pattern of the feed with εr = 30 at 8GHz
E- and H-plane 10-dB beamwidths are 83 and 824 degrees respectively The
front-to-back ratio is 17dB The antenna gain is 73dB
(a)
(b)
Fig 44 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 30 and L = 05λ0 at 8GHz (a) 2D radiation pattern
and (b) E- and H-plane patterns
-44-
Fig 45 shows the radiation pattern of the feed with εr = 50 at 18GHz
E- and H-plane 10-dB beamwidths are 56 and 54 degrees respectively The
front-to-back ratio is 27dB The antenna gain is 105dB The feed has a good
pattern symmetry and low back radiation
(a)
(b)
Fig 45 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 50 and L = 05λ0 at 18GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-45-
Fig 46 is the radiation pattern of the feed with εr = 25 and L = 10λ0 at
10GHz E- and H-plane 10-dB beamwidths are 50 and 48 degrees
respectively The front-to-back ratio is 16dB The antenna gain is 105dB
(a)
(b)
Fig 46 Radiation pattern at 10GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 10λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-46-
Fig 47 shows the geometry of a circular waveguide with a tapered
dielectric rod The designed feed has the following dimension L = 1λ0 d =
1λ0 and εr =25 at 10GHz The waveguide length is 40mm and the wall
thickness is 05mm
L
Dielectricd3
Fig 47 Geometry of a circular waveguide loaded with a tapered dielectric
rod
Fig 48 shows the radiatio pattern of the designed feed E- and H-plane
10-dB beamwidths are 575 and 564 degrees respectively The front-to-back
ratio is 377dB The antenna gain is 94dB The designed feed has an
excellent beamwidth symmetry and a very low back radiation
-47-
(a)
(b)
Fig 48 Radiation pattern of a circular waveguide loaded with a tapered
dielectric rod with L = 1λ0 d = 1λ0 and εr =25 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-48-
Fig 49 shows the geometry of a spherical ended dielectric rod feed
diameter of 06λ0 at 10GHz with a dielectric constant of 25 and L= 03λ0
Fig 410 shows the radiation patterns of the designed feed E- and H-plane
10-dB beamwidths are both 63 degrees The front-to-back ratio is 24dB The
antenna gain is 864dB
Fig 49 Geometry of a circular waveguide loaded with a spherical ended
dielectric rod
-49-
(a)
(b)
Fig 410 Radiation pattern of a circular waveguide loaded wht a spherical
ended dielectric rod with d = 06λ0 L = 03λ0 and εr =25 at 10GHz (a) 3D
radiation pattern and (b) E- and H-plane patterns
-50-
V Design of a Broadband Circular Waveguide Feed
In this chapter the design of a broadband circular waveguide feed is
presented At microwave frequencies the feed is often a circular waveguide
with chokes and corrugations around the aperture Chokes and corrugations
equalize E- and H-plane patterns and reduce the back radiation
The proposed feed is designed to operate over 10-18GHz The design starts
with the optimization of the coaxial-to-rectangular waveguide adapter
employed for good mode purity over a broad frequency range Next a
rectangular-to-circular waveguide transition is optimized Finally chokes and
corrugations are designed for improved pattern symmetry and low back
radiation
The proposed feed structure is shown in Fig 51 The feed consist of the
following parts a coaxial-to-rectangular waveguide adapter a rectangular-to-
circular waveguide transition a circular waveguide section four quarter-wave
chokes around the feeds aperture and four corrugations on the feeds outer
surface
The computer simulation shows the above arrangement offers good radiation
patterns over a broad frequency range The broadband operation is obtained
by exciting the TE11 mode in the circular waveguide using the TE10 mode of
the rectangular waveguide which is in turn excited by a coaxial probe
-51-
Chokes
Coaxial-to-waveguide transition
Circular wavguide
Corrugations
Mode transition
(a)
(b)
Fig 51 Structure of the proposed broadband circular waveguide feed
(a) CAD model and (b) cross-sectional view
For the coaxial-to-rectangular waveguide adapter an SMA connector with
the probe diameter of 127 mm is employed The coaxial probe inserted into
the waveguide energizes the feed and excites the dominant TE10 mode in
-52-
the rectangular waveguide The impedance matching is achieved by adjusting
the probe distance sp from the back short and the probe length lp
(a)
(b)
Fig 52 Reflection coefficient of the coaxial-to-rectangular adapter versus
(a) probe length lp and (b) the probe position sp
Fig 52 shows the reflection coefficient versus the various values of probe
lengths lp and probe positions sp The probe length lp is adjusted to obtain
antenna impedance matching and the probe distance sp is adjusted to obtain a
-53-
desired resonant frequency
Next a transition between rectangular and circular waveguide is designed
The transition section converts the TE10 mode in the rectangular waveguide to
TE11 mode in the circular waveguide and vice versa The transition is built
in a form of a taper for easy fabrication[22]
(a)
(b)
Fig 53 Structure of the rectangular-to-circular waveguide transition
(a) 3D view and (b) cross sectional view
The dimensions of the final optimized transition are as follows The length
of the rectangular waveguide section is 143mm The rectangular waveguides
width a and height b are 207mm and 857mm respectively The length of
the circular waveguide section is 143mm The inside diameter of the circular
-54-
waveguide is 207mm(097 wavelength at 14GHz) The length of transition
region ltr is 4465mm(approximately equal to 2λ0 at 14GHz) Fig 54 shows
the field distribution inside the mode converter
(a)
(b)
Fig 54 Field distribution inside the mode converter at
(a) 10GHz (b) 14GHz and (c) 18GHz
-55-
(c)
Fig 54 continued
Finally multiple chokes are investigated Figs 55 56 and 57 show the
feed performance without chokes The reflection coefficient is less than -10dB
over 10-19GHz The antenna has a gain of 921dB to 1189dB over
10-19GHz
Fig 55 Reflection coefficient of the broadband circular waveguide feed
without chokes and corrugations
-56-
(a)
(b)
(c)
Fig 56 E- and H-plane patterns of the broadband circular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-57-
(d)
(e)
Fig 56 continued
-58-
(a)
(b)
Fig 57 2D radiation patterns of the broadband cicular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-59-
(c)
(d)
Fig 57 continued
-60-
(e)
Fig 57 continued
To achieve equal beamwidths in E and H planes over a wide frequency
range chokes and corrugations are employed Table51 summarizes the
performance of a feed without chokes and corrugations
Table 51 Performance of the broadband circular waveguide feed without
chokes and corrugations
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
1000 940 6061 15
1200 972 6159 17
1400 920 5957 21
1600 1070 4751 29
1800 1188 5352 21
-61-
Four quarter-wavelength chokes are introduced in the feed design which
has a slot depth of 75mm and slot width of 09mm The choke slot spacing
is 18mm The choke design is investigated by applying the choke one by
one and the effect on the E- and H-plane patterns are observed as illustrated
in Figs 58 and 59 The use of chokes makes the E-plane pattern narrower
The H-plane pattern is not affected Chokes increase the gain slightly and
reduce back radiation
(a)
(b)
Fig 58 Effect of chokes on the E-plane pattern of the broadband circular
waveguide feed at (a) 10GHz(b) 12GHz (c) 14GHz (d) 16GHz and (e)
18GHz
-62-
(c)
(d)
(e)
Fig 58 continued
-63-
(a)
(b)
(c)
Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-64-
(d)
(e)
Fig 59 continued
-65-
Fig 510 shows the feed performance versus the choke depth When the
choke depth is varied from 535mm to 95mm the E- and H-plane patterns
are strongly affected The optimum value of choke depth is 75mm(035λ0 at
14GHz) which gives equal E- and H-plane radiation patterns and leads to
low back radiation
Fig 511 shows the feed performance versus the choke slot width tch The
choke slot width is varied from 09mm to 21mm Radiation patterns and
reflection coefficients are not sensitive to the choke slot width The final
choke slot width is selected to be 09mm considering the feed diameter
minimization and the manufacturability The overall diameter of the proposed
feed is 369mm which is increased from the 207mm of the waveguide
inside diameter due to the use of four chokes
-66-
(a)
(b)
(c)
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection coefficient
-67-
(a)
(b)
(c)
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and (c)
reflection coefficient
-68-
Next we investigated corrugations placed on the outer wall of the feed
Four corrugations applied to the outer surface of the circular waveguide The
corrugation depth is 465mm(0215λ0 at 14GHz) The primary purpose of
using corrugations is to further reduce the back radiation Increasing the
number of corrugations beyond four has little effect in reducing the back
radiation
Figs 512 and 513 show the effect of corrugations on the E- and H-plane
patterns Fig 514 shows the parametric study of the corrugation depth lcor
The corrugation depth is varied from 40mm and 645mm The optimum
value of the corrugation depth is found to be 465mm
-69-
(a)
(b)
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern at (a) 12GHz and (b) 14GHz
-70-
(a)
(b)
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern at (a) 12GHz and (b) 14GHz
-71-
(a)
(b)
(c)
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection coefficient
-72-
The phase center location is important in placing the feed in a reflector
antenna[8] The phase center variation with frequency should be small Fig
515 shows the effect of chokes and corrugations on the phase center The
curve with circle corresponds to the case without chokes and corrugations
The phase center varies from -326mm and -190mm away from the feeds
aperture plane It means the phase center is located inside the waveguide
The curve with triangles corresponds to the case with chokes The curve with
squares to the case with chokes and corrugations The phase center varies
from 0mm to -302mm
From Fig 515 we can observed that phase center variation reduced by the
corrugation and three cases phase center calculated in φ=450 plane
parameter sweep values are given in Table 52
10 12 14 16 181
0
-1
-2
-3
-4
-5
-6
Pha
se c
ente
r (m
m)
Frequency (GHz)
choke+corrugatuion without choke corrugation with choke
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
-73-
Frequency
(GHz)
Phase center from the aperture plane
(mm)
Without
chokes and
corrugations
With
chokes
With chokes
and
corrugations
1000 -326 062 000
1100 -187 030 -002
1200 -563 -208 -065
1300 -296 -154 -202
1400 -319 -314 -302
1500 -201 -203 -241
1600 -242 -233 -207
1700 -208 -208 -186
1800 -190 -157 -132
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
Based on the foregoing parametric studies optimum dimensions of the
broadband circular waveguide feed are obtained as shown in Table 53
-74-
Table 53 Optimum dimensions of the broadband circular waveguide feed
Parameter Designation Value (mm)
2a Waveguide inside diameter 2070
d Waveguide outside diameter 3690
lcrLength of the circular waveguide section 1430
m Distance between the aperture plane and the first corrugation 950
xDistance from the last corrugation to the end of the cylindrical outer surface
550
ltrLength of the rectangular-to-circularwaveguide transition 4465
lrcLength of the rectangular waveguide section 1430
tch Choke slot width 090
lch Choke depth 750
t Choke metal width 090
lcor Corrugation depth 465
tcor Corrugation metal width 100
s Corrugation slot width 10
lp Probe length 530
sp Probe position from the back short 530
din Probe diameter 127
b Inside height of the rectangular waveguide 857
tw Waveguide wall thickness 500
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-iii-
feeds performances of simple circular and square waveguide open ends are
investigated The improvement in the performance of the circular waveguide
open end by dielectric loading is also investigated The study shows that only
a narrow-band performance is possible with simple feeds
Based on this study the first feed is designed with the monocast(MC)
nylon as the dielectric-ring material for beamwidth equalization and a
quarter-wave choke around the aperture wall for back-radiation reduction A
coaxial probe is used to excite the feed The designed feed shows a good
performance over 171-197GHz
The second feed uses more complicated structures For broadband operation
the circular waveguide is fed by a probe-excited rectangular waveguide Four
quarter-wave chokes are used around the aperture wall for beamwidth
equalization and four corrugations are employed on the feeds outer surface
for further reduction in the back radiation
Prototypes of both feeds are fabricated and tested Test results are in good
agreement with the design objectives verifying the excellent performances of
the designed feeds
-iv-
List of Figures
Fig 21 Geometry of a circular waveguide open end radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 6
Fig 22 Reflection coefficient of a circular waveguide open end radiator middotmiddot 6
Fig 23 2D radiation pattern of a circular waveguide open end radiator middotmiddotmiddot 7
Fig 24 E-plane and H-plane patterns of a circular waveguide open end
radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 9
Fig 25 Geometry of a square waveguide open end radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 11
Fig 26 Reflection coefficient of a square waveguide open end radiator middot 12
Fig 27 2D radiation patterns of a square waveguide open end radiator middot 12
Fig 28 E-plane and H-plane patterns of square waveguide open end
radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 14
Fig 29 Probe-fed circular waveguide radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 16
Fig 210 Reflection coefficient of the probe-fed circular waveguide radiator
middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 17
Fig 211 2D radiation patterns of the probe-fed circular waveguide radiator
middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 17
Fig 212 E- and H-plane patterns of the probe-fed circular waveguide
radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 19
Fig 213 Probe-fed square waveguide radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 20
Fig 214 2D radiation pattern of the probe-fed square waveguide radiator 21
Fig 215 E- and H-plane pattern of the probe-fed square waveguide radiator
middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 23
Fig 216 Reflection coefficient of the probe-fed square waveguide radiator 24
Fig 31 Narrow-band circular waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 26
-v-
Fig 32 Effect of the (a) the probe length lp (b) the probe distance sp on
the reflection coefficient middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 27
Fig 33 Feed performance versus the choke depth (a) E-plane pattern (b)
H- plane pattern (c) reflection coefficient middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 29
Fig 34 Feed performance versus the choke slot width (a) E-plane pattern
(b) H-plane pattern (c) reflection coefficient middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 30
Fig 35 Feed performance versus the dielectric ring length (a) E-plane
pattern (b) H-plane pattern and (c) reflection coefficient middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 31
Fig 36 Feed performance versus the dielectric ring thickness (a) E-plane
pattern (b) H-plane pattern (c) reflection coefficient middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 32
Fig 37 2D gain patterns of the narrow-band circular waveguide feed middotmiddotmiddot 34
Fig 38 E- and H-plane patterns of the narrow-band circular waveguide
feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 30
Fig 39 Photograph of the fabricated feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 37
Fig 310 Reflection coefficient of the fabricated feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 38
Fig 311 Gain patterns of the fabricated feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 39
Fig 41 Geometry of a circular waveguide loaded with a uniform dielectric
rod middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 40
Fig 42 Radiation pattern at 9GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 05λ0 middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 41
Fig 43 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 21 and L = 05λ0 at 10GHz middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 42
Fig 44 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 30 and L = 05λ0 at 8GHz middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 43
Fig 45 Radiation pattern of the circular waveguide loaded with a uniform
-vi-
dielectric rod with εr = 50 and L = 05λ0 at 18GHz middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 44
Fig 46 Radiation pattern at 10GHz of the circular waveguide loaded with
a uniform dielectric rod with εr = 25 and L = 10λ0 middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 45
Fig 47 Geometry of a circular waveguide loaded with a tapered dielectric
rod middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 46
Fig 48 Radiation pattern of a circular waveguide loaded with a tapered
dielectric rod with L = 1λ0 d = 1λ0 and εr =25 at 10GHz middotmiddotmiddotmiddotmiddotmiddotmiddot 47
Fig 49 Geometry of a circular waveguide loaded with a spherical ended
dielectric rod middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 48
Fig 410 Radiation pattern of a circular waveguide loaded wht a spherical
ended dielectric rod with d = 06λ0 L = 03λ0 and εr =25 at
10GHz middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 49
Fig 51 Structure of the proposed broadband circular waveguide feed middotmiddotmiddotmiddotmiddot 51
Fig 52 Reflection coefficient of the coaxial-to-rectangular adapter versus
(a) probe length lp and (b) the probe position sp middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 52
Fig 53 Structure of the rectangular-to-circular waveguide transition middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 53
Fig 54 Field distribution inside the mode converter middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 54
Fig 55 Reflection coefficient of the broadband circular waveguide feed
without chokes and corrugations middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 55
Fig 56 E-plane and H-plane patternsof the broadband circular waveguide
feed without chokes and corrugationsz middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 56
Fig 57 2D radiation patterns of the broadband cicular waveguide feed
without chokes and corrugations middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 58
Fig 58 Effect of chokes on the E-plane pattern of the broadband circular
waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 61
-vii-
Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 63
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection
coefficient middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 66
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and
(c) reflection coefficient middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 67
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 69
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 70
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection
coefficient middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 71
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 72
Fig 516 Reflection coefficient of the designed broadband circular
waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 75
Fig 517 2D radiation patterns of the designed broadband circular
waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 76
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 79
Fig 519 Phase center variation of the designed broadband circular
waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 81
-viii-
Fig 520 Photograph of the fabricated broadband circular waveguide feed 82
Fig 521 Reflection coefficient of the fabricated broadband circular
waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 82
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 84
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 84
-ix-
List of Tables
Table 21 Properties of a circular waveguide open end radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 10
Table 22 Properties of a square waveguide open end radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 15
Table 23 Properties of the probe-fed circular waveguide radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 20
Table 24 Properties of the probe-fed square waveguide radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 24
Table 31 Dimensions of the designed narrow-band circular feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 33
Table 32 Performance of the narrow-band circular waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 37
Table 51 Performance of the broadband circular waveguide feed without
chokes and corrugations middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 60
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 73
Table 53 Optimum dimensions of the broadband circular waveguide feed 74
Table 54 Performance of the designed broadband circular waveguide feed 81
-1-
I Introduction
The horns and waveguides are known for their high efficiency and
structural simplicity They are popular choices for feeding for reflectors in
high-gain antenna applications such as satellite and point-to-point microwave
communication links The theory of reflector antenna was developed in the
1940s and has been used to calculate the radiation patterns of various
reflector structures[1]
The basic structure of a prime-focus reflector antenna consists of a
parabolic reflecting surface a feed and its support The placement of the feed
is such that its phase center is at the focal point of the parabolic reflecting
surface The feed is often a circular waveguide because of its symmetric
radiation pattern with low back radiation and low cross polarization The
circular waveguide feed must have a small diameter to reduce the aperture
blockage of the reflector antenna[3]
A radiation pattern with a good circular symmetry in the main beam can
be found from circular waveguide feeds with dominant TE11 mode excitation
The radiation patterns depends on the diameter and wall thickness of the
waveguide[4] A coaxial probe can be inserted into a short-circuited circular
waveguide in the form of a coaxial-to-waveguide transition The diameter of
the circular waveguide is chosen such that only the dominant mode
propagates
When the waveguide dimension does not provide a circular symmteric
-2-
pattern a choke or multiple chokes around the aperture wall can be
employed to equalize radiation patterns and keep the back radiation in low
level If chokes are not enough for the suppression of the back radiation
corrugations on the outer surface of the feed is one way to reduce the back
radiation
In this thesis a broadband circular waveguide feed is developed for
prime-focus reflector antenna application After investigating the radiation
properties of simple circular and square waveguides methods are investigated
for bandwidth enhancement back radiation suppression and beamwidth
equalization in the circular waveguide feed
The first type of the circular waveguide feed consists of a probe-fed
circular waveguide a single quarter-wave choke on the aperture wall and a
dielectric-ring beamwidth equalizer Due to the simple feeding method the
first feed operates over 171-197GHz(141) which is not broadband in the
strict sense of the word
The second feed consists of a coaxial-to-rectangular waveguide transition a
rectangular-to-circular waveguide transition a circular waveguide section four
quarter-wave chokes on the aperture wall and four quarter-wave corrugations
on the feeds outer surface Due to the complicated feeding method the
second feed operates over 10-18GHz(571)
This thesis is arranged as follows Chapter I gives an introduction to the
thesis related works and objectives are stated Chapter II describes the
structure and excitation of the circular and square waveguide and the
operation of the coaxial-to-waveguide transitions Chapter III describes a
compact feed horn design and its fabrication and measurement Chapter IV
-3-
presents dielectric rod feed and its simulated performances Chapter V gives
design and optimization of feed for parabolic reflector antenna In this
chapter includes the detailed information of design procedures and operating
principle also the simulated and measured performances are provided Finally
conclusion is given in the Chapter VI
-4-
II Analysis of Circular and Square Waveguide Feeds
21 Circular Waveguide Radiator
Before design a complicated circular waveguide feed it is helpful to
investigate the impedance and radiation properties of a circular waveguide
open end
The circular waveguide is a cylindrical hollow metallic pipe with a uniform
circular section of radius a Circular waveguides are normally designed to
operate only with the dominant mode The dominant mode in a waveguide is
the mode having the lowest cutoff frequency given by equation (21)
(21)
where
(22)
and a is the waveguide radius The following chart[2] and table show the
cutoff frequencies of various modes in a circular waveguide
-5-
Modes c al11TEc cf f
TE11 341259 100000
TM01 261274 130613
TE21 205720 165885TE01 163979 208111
TM11 163979 208111TE31 149557 228180
TM21 122345 278932TE41 118159 288813
TE12 117852 289566
TM02 113824 299813TE02 0897986 380027
The recommended frequency range of the commercial circular waveguide is
given by the following equation This assumes that the TM01 mode is not
generated or suppressed if generated
11 21 11TE TE TE115 095 158 32 bandwidthc c cf f f fpound pound = reg (23)
Fig 21 shows the geometry of a circular waveguide with a diameter of 2a
When 2a is 2053mm the cutoff frequency of the TE11 mode is 857GHz
According to (23) the useful operating frequency range is from
986-1354GHz
Fig 22 shows the reflection of this waveguide excited with the dominant
TE11 mode The waveguide length l is 60mm The reflection occurs at the
open end of the circular waveguide The reflection coefficient is less than
-15dB over 10-18GHz
-6-
Fig 21 Geometry of a circular waveguide open end radiator
Fig 23 shows a 2D gain pattern of this waveguide antenna The
waveguide antenna has a gain of 80dB 99dB and 115dB at 10GHz
14GHz and 18GHz respectively Fig 24 shows the E- and H-plane patterns
of the circular waveguide antenna Table 21 summarizes the properties of a
circular waveguide antenna
Fig 22 Reflection coefficient of a circular waveguide open end radiator
-7-
(a)
(b)
Fig 23 2D radiation pattern of the circular waveguide open end radiator
at (a)10GHz (b) 14GHz and (c) 18GHz
-8-
(c)
Fig 23 continued
-9-
(a)
(b)
(c)
Fig 24 E-plane and H-plane patterns of the circular waveguide open end
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-10-
Table 21 Properties of a circular waveguide open end radiator of diameter
2053mm
Frequency(GHz)-10dB Beamwith(deg) Front-to-Back
Ratio(dB)E plane H plane
10 67 73 12
14 58 60 18
18 41 50 21
In a circular waveguide radiatoλr a good pattern symmetry and low back
radiation is obtained at 14GHz where 2aλ = 096
22 Square Waveguide Radiator
A square waveguide is often used as a dual-polarized feed To operate the
cutoff frequency of the dominant mode a square-waveguide wall width a
must be greater than one half of a wavelength The modes with cutoff
frequencies equal to or smaller than the operational frequency can exist inside
the waveguide wall The lower cutoff frequency and cutoff wavelength for
square waveguide is determined by the following equations
TE
(24)
TE
(25)
The next higher-order mode is TE11 mode with the cutoff wavelength
given by
-11-
TE
(26)
Similar to the circular waveguide the recommended operating frequency range
of a square waveguide is given by
TEleleTE
TErarr bandwidth (27)
Fig 25 shows the geometry of a square waveguide with a dimension of a
When a is 157mm the cutoff frequency is 95GHz The recommended
operating frequency of this waveguide is from 109GHz to 155GHz
Fig 26 shows the reflection of this waveguide excited with the dominant
TE10 mode The reflection coefficient is less than -15dB over 10-20GHz
Fig 25 Geometry of a square waveguide open end radiator
Fig 27 and shows the 2D radiation pattern of a square waveguide antenna
excited with the dominant TE10 mode The antenna has a gain of 73dB
85dB and 102dB at 10GHz 14GHz and 18GHz respectively Fig 28
shows the E- and H-plane radiation patterns of a square waveguide radiator
Table 22 summarizes the properties of a square waveguide open end radiator
-12-
Fig 26 Reflection coefficient of a square waveguide open end radiator
(a)
Fig 27 2D radiation patterns of a square waveguide radiator
at (a) 10GHz (b) 14GHz and (c) 18GHz
-13-
(b)
(c)
Fig 27 continued
-14-
(a)
(b)
(c)
Fig 28 E-plane and H-plane patterns of square waveguide open radiator
at (a) 10GHz(b) 14GHz and (c) 18GHz
-15-
Table 22 Properties of a square waveguide open end radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 69 71 11
14 47 60 25
18 58 62 16
The radiation pattern symmetry and back radiation performance of the
square waveguide are inferior to those of a circular waveguide
23 Probe-Fed Circular Waveguide Radiator
In Section 21 the radiation properties of a TE11-mode excited waveguide
is investigated In this section a circular waveguide fed by a coaxial probe
shown in Fig 29 is studied
The coaxial probes diameter is 127mm With the Teflon dielectric the
50-ohm coaxial lines outer conductor has a diameter of 41mm For a
circular waveguide the wave impedance of the TE11 mode is given by
∙ (28)
where λg is the guided wavelength given by
(29)
-16-
(a) (b)
Fig 29 Probe-fed circular waveguide radiator (a) Front view and (b) side
view
The combination of the probe length and the probe position from the
shorted wall enables a good impedance matching The probe distance sp from
the back short is close to a quarter wavelength at the design frequency
The designed feed has the following dimension d = 2053mm lp = 42
mm sp = 534mm wall thickness = 05mm and feed length = 400mm
Fig 210 shows the reflection coefficient of the designed probe-fed
circular waveguide radiator The reflection coefficient is less than -10dB over
138-187GHz Fig 211 and 212 shows the E-plane and H-plane radiation
patterns and 2D radiation patterns of the coaxial-to-circular waveguide
transition The radiation patterns symmetry distorted because of the high order
modes The coaxial-to-circular waveguide transition has 73dB 84dB and
79dB gain at 10GHz 14GHz and 18GHz frequencies respectively Table 23
shows the properties of the coaxial-to-circular waveguide transition
-17-
Fig 210 Reflection coefficient of the probe-fed circular waveguide radiator
(a)
Fig 211 2D radiation pattern of the probe-fed circular waveguide radiator
at (a) 10GHz (b) 14GHz and (c) 18GHz
-18-
(b)
(c)
Fig 211 continued
-19-
(a)
(b)
(c)
Fig 212 E- and H-plane patterns of the probe-fed circular waveguide
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-20-
Table 23 Properties of the probe-fed circular waveguide radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 73 70 1414 83 57 17
18 60 52 30
When a circular waveguide radiator is fed by a coaxial probe its radiation
properties are not good due to the excitation of higher-order modes
Therefore a probe-fed circular waveguide radiator can be used as a feed only
over a narrow frequency range
24 Probe-Fed Square Waveguide Radiator
In this section a probe-fed square waveguide radiator is investigated Fig
213 shows a coaxial probe-fed square waveguide radiator The designed
radiator has the following dimension a = b = 157mm lp = 35 mm sp =
50 mm wall thickness = 05mm and feed length = 40mm
(a) (b)
Fig 213 Probe-fed square waveguide radiator (a) Front view and (b) side
view
-21-
Fig 214 shows the 2D radiation patterns of the radiator at 10GHz
14GHz and 18GHz Fig 215 shows E- and H-plane patterns of the radiator
Fig 216 shows the reflection coefficient of the probe-fed square waveguide
radiator The reflection coefficient is less than -10dB over 13-20GHz Table
24 summarizes the properties of the probe-fed square waveguide radiator
(a)
Fig 214 2D radiation patterns of the probe-fed square waveguide radiator at
(a) 10GHz (b) 14GHz and (c) 18GHz
-22-
(b)
(c)
Fig 214 continued
-23-
(a)
(b)
(c)
Fig 216 E-plane and H-plane patterns of the probe-fed square waveguide
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-24-
Fig 216 Reflection coefficient of the probe-fed square waveguide radiator
Table 24 Properties of the probe-fed square waveguide radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 73 71 12
14 85 63 1418 27 65 28
When a square waveguide radiator is fed by a coaxial probe its radiation
properties are not good due to the excitation of higher-order modes as in the
case of the probe-fed circular waveguide radiator A probe-fed square
waveguide radiator can be used as a feed only over a narrow frequency
range
-25-
III Design of Compact Circular Waveguide Feeds
In this chapter the feed design is presented for a prime-focus reflector
antenna The prime-focus paraboloid reflector is one of the most commonly
used high-gain antenna It has been used in earth-station antennas and radio
telescopes It consists of a paraboloid reflector with a feed system at its focal
point
The feed should radiate a low level of cross-polar power over the
operating frequency These conditions not easy to achieve and most prime
focus feeds are compromises The shape and characteristic of the radiation
pattern of the feed are the most important parameter because these will
directly influence the fields which are directed at a reflector[6] Other
electrical factors which relevant to the choice of a feed are the cross-polar
level the gain efficiency the bandwidth and impedance matching
31 Narrow-Band Circular Waveguide Feed
Fig 31 shows the proposed narrow-band circular waveguide feed and its
design variables The feed consists of a circular waveguide open end excited
by a TE11 dominant mode A quarter wave choke is applied along the
circular aperture of the waveguide to equalize E- and H-plane radiation
patterns and to suppress the back radiation A dielectric ring is used to
control the radiation pattern and change the power distribution over the
aperture The control of the amplitude over the aperture are essential to the
design of symmetric radiation pattern The material used for dielectric loading
-26-
is the monocast(MC) nylon with a dielectric constant of 30 The feed is
designed to operate over 171-197GHz
(a)
(b)
Fig 31 Narrow-band circular waveguide feed (a) CAD model and (b) a
cross sectional view
The impedance matching is achieved by a proper combination of the probe
height lp and its distance sp from the waveguide shorted end Here the
-27-
circular waveguide is terminated with an open end with a wall thickness of
2mm radiating into the free space
Fig 32 shows the effect of the probe length lp and the probe distance sp
on the reflection coefficient The best performance is obtained when lp =
363mm and sp = 616mm The feeds reflection coefficient is less than -10dB
over 170-195GHz
(a)
(b)
Fig 32 Effect of the (a) the probe length lp and (b) the probe
distance sp on the reflection coefficient
-28-
Fig 33 shows the effect of the choke depth The E-plane pattern is more
sensitive to the choke depth than the H-plane pattern The choke depth has a
strong influence on the reflection coefficient when it is 360mm By properly
choosing the choke depth we can equalize the E- and H-plane patterns The
optimum value of the choke depth is 410mm which is 0249λ0 at 1825GHz
The choke slot width tch in the range of 06-12mm has almost no effect
on the H-plane pattern and the reflection coefficient For the E-plane pattern
tch of 12mm has some effect on the E-plane radiation pattern as shown in
Fig 34
Fig 35 shows the feed performance versus the dielectric ring length We
observe in Fig 35 that the dielectric length ld has an optimum value of
1168mm which does no effect on the H-plane pattern and tha the value of
1048mm has some effect on the E-plane pattern and the reflection
coefficient
Fig 36 shows E-plane and H-plane patterns and the reflection coefficient
versus the dielectric thickness With the optimum value of the dielectric
thickness t obtained from the Fig 36 is 155mm The larger values of td has
much stronger effects on the E-plane pattern and the reflection coefficient
The H-plane pattern is not sensitive to the dielectric ring thickness
-29-
(a)
(b)
(c)
Fig 33 Feed performance versus the choke depth (a) E-plane pattern
(b) H-plane pattern and (c) reflection coefficient
-30-
(a)
(b)
(c)
Fig 34 Feed performance versus the choke slot width (a) E-plane pattern
(b) H-plane pattern and (c) reflection coefficient
-31-
(a)
(b)
(c)
Fig 35 Feed performance versus the dielectric ring length (a) E-plane
pattern (b) H-plane pattern and (c) reflection coefficient
-32-
(a)
(b)
(c)
Fig 36 Feed performance versus the dielectric ring thickness (a) E-plane
pattern(b) H-plane pattern and (c) reflection coefficient
-33-
From the above parametric analysis an optimum feed design is obtained
The result is shown in Table 31 Fig 37 shows the 2D gain patterns of
designed feed The antenna has a gain of 903dB 933dB and 956dB at
171GHz 1825GHz and 19GHz respectively
Fig 38 shows E- and H-plane radiation patterns of the designed feed The
feed has E- and H-plane 10-dB beamwidths of 60 and 59 degrees at 17GHz
The feed has a front-to-back ration of 1900dB 2490dB and 2200dB at
171GHz 1825GHz and 19GHz respectively Table 32 summarizes the
performance of the designed narrow-band circular waveguide feed
The designed feed has a greatly improved performance over that of a
simple coax-fed feed described in Section 23
Table 31 Dimensions of the designed narrow-band circular feed
Parameter Designation Value(mm)
a Waveguide inside radius 640
l Feed length 2890
lp Probe length 363
sp Probe position from the back short 616
din Probe diameter 127
dout Diameter of coaxial cables outer conductor 400
t Thickness of choked wall 050
tch Choke slot width 100
lch Choke depth 410
ld Dielectric ring length 1168
td Dielectric ring thickness 155
d1 Waveguide outside diameter 1680
-34-
(a)
(b)
Fig 37 2D gain patterns of the narrow-band circular waveguide feed at
(a) 17GHz (b) 1825GHz and (c) 19GHz
-35-
(c)
Fig 37 continued
-36-
(a)
(b)
(c)
Fig 38 E- and H-plane patterns of the narrow-band circular waveguide feed
at (a) 10GHz (b) 1825GHz and (c) 195GHz
-37-
Frequency(GHz)
Gain(dB)
E-H-plane10-dB beamwidths
(deg)
Front-to-back ratio(dB)
Phase centerlocation
(From feeds aperture plane
toward reflector)
(mm)
1700 903 6059 20 062
1825 933 6060 25 004
1900 956 5759 22 007
Table 32 Performance of the narrow-band circular waveguide feed
The designed narrow-band feed is fabricated and its performance is
measured and compared with the simulation results The designed feed is
fabricated in a numerically-controlled machining center The fabricated antenna
is shown in Fig 39
Fig 39 Photograph of the fabricated feed
-38-
Fig 310 shows a comparison of the measured and simulated reflection
coefficients The measured reflection coefficient is less than -10dB over
171-197GHz The agreement between simulated and measured results are
good
Fig 311 shows the E- and H-plane patterns of the fabricated feed at
187GHz The feed has 90dB gain simulation and measurement results are in
good agreement
The fabricated antennarsquos 10dB beamwidth is 60 degrees in both E and H
planes at 187GHz The front-to-back ratio is 21dB
Fig 310 Reflection coefficient of the fabricated feed
-39-
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Fee
d H
orn
Gain
- d
B
Angle - degree
(a)
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Feed H
orn
Gain
- d
B
Angle - degree
(b)
Fig 311 Gain patterns of the fabricated feed at 187 GHz (a) E-plane and
(b) H-plane
-40-
IV Design of Circular Waveguide Feeds Loaded with a
Dielectric Rod
In this section circular waveguide feeds loaded with a dielectric rod feed
are investigated A comprehensive discussion of the circular waveguide loaded
with a dielectric rod is given by Kumar[7] Inserting a dielectric material
inside the circular waveguide improves the E- and H-plane pattern symmetry
In general dielectric-loaded circular waveguide feeds show good performance
only over a narrow bandwidth
Fig 41 shows the geometry of a circular waveguide loaded with a
dielectric rod The waveguide length is 400mm and the wall thickness is
05mm The dielectric rods diameter is 207mm The dielectric rod is
extended 05 wavelength beyond the waveguide open end The dielectric
constant εr is changed and the feeds performance is observed
Fig 41 Geometry of a circular waveguide loaded with a uniform dielectric
rod
-41-
Fig 42 is the radiation pattern of the feed with εr = 25 and L = 05λ0 at
9GHz E- and H-plane 10-dB beamwidths are 810 and 807 degrees
respectively The front-to-back ratio is 18dB The antenna gain is 71dB
(a)
(b)
Fig 42 Radiation pattern at 9GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 05λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-42-
Fig 43 shows the radiation pattern of the feed with εr = 21 at 10GHz
E- and H-plane 10-dB beamwidths are 70 and 71 degrees respectively The
front-to-back ratio is 19dB The antenna gain is 83dB
(a)
(b)
Fig 43 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 21 and L = 05λ0 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-43-
Fig 44 shows the radiation pattern of the feed with εr = 30 at 8GHz
E- and H-plane 10-dB beamwidths are 83 and 824 degrees respectively The
front-to-back ratio is 17dB The antenna gain is 73dB
(a)
(b)
Fig 44 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 30 and L = 05λ0 at 8GHz (a) 2D radiation pattern
and (b) E- and H-plane patterns
-44-
Fig 45 shows the radiation pattern of the feed with εr = 50 at 18GHz
E- and H-plane 10-dB beamwidths are 56 and 54 degrees respectively The
front-to-back ratio is 27dB The antenna gain is 105dB The feed has a good
pattern symmetry and low back radiation
(a)
(b)
Fig 45 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 50 and L = 05λ0 at 18GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-45-
Fig 46 is the radiation pattern of the feed with εr = 25 and L = 10λ0 at
10GHz E- and H-plane 10-dB beamwidths are 50 and 48 degrees
respectively The front-to-back ratio is 16dB The antenna gain is 105dB
(a)
(b)
Fig 46 Radiation pattern at 10GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 10λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-46-
Fig 47 shows the geometry of a circular waveguide with a tapered
dielectric rod The designed feed has the following dimension L = 1λ0 d =
1λ0 and εr =25 at 10GHz The waveguide length is 40mm and the wall
thickness is 05mm
L
Dielectricd3
Fig 47 Geometry of a circular waveguide loaded with a tapered dielectric
rod
Fig 48 shows the radiatio pattern of the designed feed E- and H-plane
10-dB beamwidths are 575 and 564 degrees respectively The front-to-back
ratio is 377dB The antenna gain is 94dB The designed feed has an
excellent beamwidth symmetry and a very low back radiation
-47-
(a)
(b)
Fig 48 Radiation pattern of a circular waveguide loaded with a tapered
dielectric rod with L = 1λ0 d = 1λ0 and εr =25 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-48-
Fig 49 shows the geometry of a spherical ended dielectric rod feed
diameter of 06λ0 at 10GHz with a dielectric constant of 25 and L= 03λ0
Fig 410 shows the radiation patterns of the designed feed E- and H-plane
10-dB beamwidths are both 63 degrees The front-to-back ratio is 24dB The
antenna gain is 864dB
Fig 49 Geometry of a circular waveguide loaded with a spherical ended
dielectric rod
-49-
(a)
(b)
Fig 410 Radiation pattern of a circular waveguide loaded wht a spherical
ended dielectric rod with d = 06λ0 L = 03λ0 and εr =25 at 10GHz (a) 3D
radiation pattern and (b) E- and H-plane patterns
-50-
V Design of a Broadband Circular Waveguide Feed
In this chapter the design of a broadband circular waveguide feed is
presented At microwave frequencies the feed is often a circular waveguide
with chokes and corrugations around the aperture Chokes and corrugations
equalize E- and H-plane patterns and reduce the back radiation
The proposed feed is designed to operate over 10-18GHz The design starts
with the optimization of the coaxial-to-rectangular waveguide adapter
employed for good mode purity over a broad frequency range Next a
rectangular-to-circular waveguide transition is optimized Finally chokes and
corrugations are designed for improved pattern symmetry and low back
radiation
The proposed feed structure is shown in Fig 51 The feed consist of the
following parts a coaxial-to-rectangular waveguide adapter a rectangular-to-
circular waveguide transition a circular waveguide section four quarter-wave
chokes around the feeds aperture and four corrugations on the feeds outer
surface
The computer simulation shows the above arrangement offers good radiation
patterns over a broad frequency range The broadband operation is obtained
by exciting the TE11 mode in the circular waveguide using the TE10 mode of
the rectangular waveguide which is in turn excited by a coaxial probe
-51-
Chokes
Coaxial-to-waveguide transition
Circular wavguide
Corrugations
Mode transition
(a)
(b)
Fig 51 Structure of the proposed broadband circular waveguide feed
(a) CAD model and (b) cross-sectional view
For the coaxial-to-rectangular waveguide adapter an SMA connector with
the probe diameter of 127 mm is employed The coaxial probe inserted into
the waveguide energizes the feed and excites the dominant TE10 mode in
-52-
the rectangular waveguide The impedance matching is achieved by adjusting
the probe distance sp from the back short and the probe length lp
(a)
(b)
Fig 52 Reflection coefficient of the coaxial-to-rectangular adapter versus
(a) probe length lp and (b) the probe position sp
Fig 52 shows the reflection coefficient versus the various values of probe
lengths lp and probe positions sp The probe length lp is adjusted to obtain
antenna impedance matching and the probe distance sp is adjusted to obtain a
-53-
desired resonant frequency
Next a transition between rectangular and circular waveguide is designed
The transition section converts the TE10 mode in the rectangular waveguide to
TE11 mode in the circular waveguide and vice versa The transition is built
in a form of a taper for easy fabrication[22]
(a)
(b)
Fig 53 Structure of the rectangular-to-circular waveguide transition
(a) 3D view and (b) cross sectional view
The dimensions of the final optimized transition are as follows The length
of the rectangular waveguide section is 143mm The rectangular waveguides
width a and height b are 207mm and 857mm respectively The length of
the circular waveguide section is 143mm The inside diameter of the circular
-54-
waveguide is 207mm(097 wavelength at 14GHz) The length of transition
region ltr is 4465mm(approximately equal to 2λ0 at 14GHz) Fig 54 shows
the field distribution inside the mode converter
(a)
(b)
Fig 54 Field distribution inside the mode converter at
(a) 10GHz (b) 14GHz and (c) 18GHz
-55-
(c)
Fig 54 continued
Finally multiple chokes are investigated Figs 55 56 and 57 show the
feed performance without chokes The reflection coefficient is less than -10dB
over 10-19GHz The antenna has a gain of 921dB to 1189dB over
10-19GHz
Fig 55 Reflection coefficient of the broadband circular waveguide feed
without chokes and corrugations
-56-
(a)
(b)
(c)
Fig 56 E- and H-plane patterns of the broadband circular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-57-
(d)
(e)
Fig 56 continued
-58-
(a)
(b)
Fig 57 2D radiation patterns of the broadband cicular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-59-
(c)
(d)
Fig 57 continued
-60-
(e)
Fig 57 continued
To achieve equal beamwidths in E and H planes over a wide frequency
range chokes and corrugations are employed Table51 summarizes the
performance of a feed without chokes and corrugations
Table 51 Performance of the broadband circular waveguide feed without
chokes and corrugations
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
1000 940 6061 15
1200 972 6159 17
1400 920 5957 21
1600 1070 4751 29
1800 1188 5352 21
-61-
Four quarter-wavelength chokes are introduced in the feed design which
has a slot depth of 75mm and slot width of 09mm The choke slot spacing
is 18mm The choke design is investigated by applying the choke one by
one and the effect on the E- and H-plane patterns are observed as illustrated
in Figs 58 and 59 The use of chokes makes the E-plane pattern narrower
The H-plane pattern is not affected Chokes increase the gain slightly and
reduce back radiation
(a)
(b)
Fig 58 Effect of chokes on the E-plane pattern of the broadband circular
waveguide feed at (a) 10GHz(b) 12GHz (c) 14GHz (d) 16GHz and (e)
18GHz
-62-
(c)
(d)
(e)
Fig 58 continued
-63-
(a)
(b)
(c)
Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-64-
(d)
(e)
Fig 59 continued
-65-
Fig 510 shows the feed performance versus the choke depth When the
choke depth is varied from 535mm to 95mm the E- and H-plane patterns
are strongly affected The optimum value of choke depth is 75mm(035λ0 at
14GHz) which gives equal E- and H-plane radiation patterns and leads to
low back radiation
Fig 511 shows the feed performance versus the choke slot width tch The
choke slot width is varied from 09mm to 21mm Radiation patterns and
reflection coefficients are not sensitive to the choke slot width The final
choke slot width is selected to be 09mm considering the feed diameter
minimization and the manufacturability The overall diameter of the proposed
feed is 369mm which is increased from the 207mm of the waveguide
inside diameter due to the use of four chokes
-66-
(a)
(b)
(c)
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection coefficient
-67-
(a)
(b)
(c)
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and (c)
reflection coefficient
-68-
Next we investigated corrugations placed on the outer wall of the feed
Four corrugations applied to the outer surface of the circular waveguide The
corrugation depth is 465mm(0215λ0 at 14GHz) The primary purpose of
using corrugations is to further reduce the back radiation Increasing the
number of corrugations beyond four has little effect in reducing the back
radiation
Figs 512 and 513 show the effect of corrugations on the E- and H-plane
patterns Fig 514 shows the parametric study of the corrugation depth lcor
The corrugation depth is varied from 40mm and 645mm The optimum
value of the corrugation depth is found to be 465mm
-69-
(a)
(b)
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern at (a) 12GHz and (b) 14GHz
-70-
(a)
(b)
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern at (a) 12GHz and (b) 14GHz
-71-
(a)
(b)
(c)
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection coefficient
-72-
The phase center location is important in placing the feed in a reflector
antenna[8] The phase center variation with frequency should be small Fig
515 shows the effect of chokes and corrugations on the phase center The
curve with circle corresponds to the case without chokes and corrugations
The phase center varies from -326mm and -190mm away from the feeds
aperture plane It means the phase center is located inside the waveguide
The curve with triangles corresponds to the case with chokes The curve with
squares to the case with chokes and corrugations The phase center varies
from 0mm to -302mm
From Fig 515 we can observed that phase center variation reduced by the
corrugation and three cases phase center calculated in φ=450 plane
parameter sweep values are given in Table 52
10 12 14 16 181
0
-1
-2
-3
-4
-5
-6
Pha
se c
ente
r (m
m)
Frequency (GHz)
choke+corrugatuion without choke corrugation with choke
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
-73-
Frequency
(GHz)
Phase center from the aperture plane
(mm)
Without
chokes and
corrugations
With
chokes
With chokes
and
corrugations
1000 -326 062 000
1100 -187 030 -002
1200 -563 -208 -065
1300 -296 -154 -202
1400 -319 -314 -302
1500 -201 -203 -241
1600 -242 -233 -207
1700 -208 -208 -186
1800 -190 -157 -132
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
Based on the foregoing parametric studies optimum dimensions of the
broadband circular waveguide feed are obtained as shown in Table 53
-74-
Table 53 Optimum dimensions of the broadband circular waveguide feed
Parameter Designation Value (mm)
2a Waveguide inside diameter 2070
d Waveguide outside diameter 3690
lcrLength of the circular waveguide section 1430
m Distance between the aperture plane and the first corrugation 950
xDistance from the last corrugation to the end of the cylindrical outer surface
550
ltrLength of the rectangular-to-circularwaveguide transition 4465
lrcLength of the rectangular waveguide section 1430
tch Choke slot width 090
lch Choke depth 750
t Choke metal width 090
lcor Corrugation depth 465
tcor Corrugation metal width 100
s Corrugation slot width 10
lp Probe length 530
sp Probe position from the back short 530
din Probe diameter 127
b Inside height of the rectangular waveguide 857
tw Waveguide wall thickness 500
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-iv-
List of Figures
Fig 21 Geometry of a circular waveguide open end radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 6
Fig 22 Reflection coefficient of a circular waveguide open end radiator middotmiddot 6
Fig 23 2D radiation pattern of a circular waveguide open end radiator middotmiddotmiddot 7
Fig 24 E-plane and H-plane patterns of a circular waveguide open end
radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 9
Fig 25 Geometry of a square waveguide open end radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 11
Fig 26 Reflection coefficient of a square waveguide open end radiator middot 12
Fig 27 2D radiation patterns of a square waveguide open end radiator middot 12
Fig 28 E-plane and H-plane patterns of square waveguide open end
radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 14
Fig 29 Probe-fed circular waveguide radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 16
Fig 210 Reflection coefficient of the probe-fed circular waveguide radiator
middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 17
Fig 211 2D radiation patterns of the probe-fed circular waveguide radiator
middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 17
Fig 212 E- and H-plane patterns of the probe-fed circular waveguide
radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 19
Fig 213 Probe-fed square waveguide radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 20
Fig 214 2D radiation pattern of the probe-fed square waveguide radiator 21
Fig 215 E- and H-plane pattern of the probe-fed square waveguide radiator
middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 23
Fig 216 Reflection coefficient of the probe-fed square waveguide radiator 24
Fig 31 Narrow-band circular waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 26
-v-
Fig 32 Effect of the (a) the probe length lp (b) the probe distance sp on
the reflection coefficient middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 27
Fig 33 Feed performance versus the choke depth (a) E-plane pattern (b)
H- plane pattern (c) reflection coefficient middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 29
Fig 34 Feed performance versus the choke slot width (a) E-plane pattern
(b) H-plane pattern (c) reflection coefficient middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 30
Fig 35 Feed performance versus the dielectric ring length (a) E-plane
pattern (b) H-plane pattern and (c) reflection coefficient middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 31
Fig 36 Feed performance versus the dielectric ring thickness (a) E-plane
pattern (b) H-plane pattern (c) reflection coefficient middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 32
Fig 37 2D gain patterns of the narrow-band circular waveguide feed middotmiddotmiddot 34
Fig 38 E- and H-plane patterns of the narrow-band circular waveguide
feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 30
Fig 39 Photograph of the fabricated feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 37
Fig 310 Reflection coefficient of the fabricated feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 38
Fig 311 Gain patterns of the fabricated feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 39
Fig 41 Geometry of a circular waveguide loaded with a uniform dielectric
rod middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 40
Fig 42 Radiation pattern at 9GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 05λ0 middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 41
Fig 43 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 21 and L = 05λ0 at 10GHz middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 42
Fig 44 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 30 and L = 05λ0 at 8GHz middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 43
Fig 45 Radiation pattern of the circular waveguide loaded with a uniform
-vi-
dielectric rod with εr = 50 and L = 05λ0 at 18GHz middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 44
Fig 46 Radiation pattern at 10GHz of the circular waveguide loaded with
a uniform dielectric rod with εr = 25 and L = 10λ0 middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 45
Fig 47 Geometry of a circular waveguide loaded with a tapered dielectric
rod middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 46
Fig 48 Radiation pattern of a circular waveguide loaded with a tapered
dielectric rod with L = 1λ0 d = 1λ0 and εr =25 at 10GHz middotmiddotmiddotmiddotmiddotmiddotmiddot 47
Fig 49 Geometry of a circular waveguide loaded with a spherical ended
dielectric rod middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 48
Fig 410 Radiation pattern of a circular waveguide loaded wht a spherical
ended dielectric rod with d = 06λ0 L = 03λ0 and εr =25 at
10GHz middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 49
Fig 51 Structure of the proposed broadband circular waveguide feed middotmiddotmiddotmiddotmiddot 51
Fig 52 Reflection coefficient of the coaxial-to-rectangular adapter versus
(a) probe length lp and (b) the probe position sp middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 52
Fig 53 Structure of the rectangular-to-circular waveguide transition middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 53
Fig 54 Field distribution inside the mode converter middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 54
Fig 55 Reflection coefficient of the broadband circular waveguide feed
without chokes and corrugations middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 55
Fig 56 E-plane and H-plane patternsof the broadband circular waveguide
feed without chokes and corrugationsz middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 56
Fig 57 2D radiation patterns of the broadband cicular waveguide feed
without chokes and corrugations middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 58
Fig 58 Effect of chokes on the E-plane pattern of the broadband circular
waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 61
-vii-
Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 63
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection
coefficient middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 66
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and
(c) reflection coefficient middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 67
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 69
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 70
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection
coefficient middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 71
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 72
Fig 516 Reflection coefficient of the designed broadband circular
waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 75
Fig 517 2D radiation patterns of the designed broadband circular
waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 76
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 79
Fig 519 Phase center variation of the designed broadband circular
waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 81
-viii-
Fig 520 Photograph of the fabricated broadband circular waveguide feed 82
Fig 521 Reflection coefficient of the fabricated broadband circular
waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 82
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 84
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 84
-ix-
List of Tables
Table 21 Properties of a circular waveguide open end radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 10
Table 22 Properties of a square waveguide open end radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 15
Table 23 Properties of the probe-fed circular waveguide radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 20
Table 24 Properties of the probe-fed square waveguide radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 24
Table 31 Dimensions of the designed narrow-band circular feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 33
Table 32 Performance of the narrow-band circular waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 37
Table 51 Performance of the broadband circular waveguide feed without
chokes and corrugations middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 60
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 73
Table 53 Optimum dimensions of the broadband circular waveguide feed 74
Table 54 Performance of the designed broadband circular waveguide feed 81
-1-
I Introduction
The horns and waveguides are known for their high efficiency and
structural simplicity They are popular choices for feeding for reflectors in
high-gain antenna applications such as satellite and point-to-point microwave
communication links The theory of reflector antenna was developed in the
1940s and has been used to calculate the radiation patterns of various
reflector structures[1]
The basic structure of a prime-focus reflector antenna consists of a
parabolic reflecting surface a feed and its support The placement of the feed
is such that its phase center is at the focal point of the parabolic reflecting
surface The feed is often a circular waveguide because of its symmetric
radiation pattern with low back radiation and low cross polarization The
circular waveguide feed must have a small diameter to reduce the aperture
blockage of the reflector antenna[3]
A radiation pattern with a good circular symmetry in the main beam can
be found from circular waveguide feeds with dominant TE11 mode excitation
The radiation patterns depends on the diameter and wall thickness of the
waveguide[4] A coaxial probe can be inserted into a short-circuited circular
waveguide in the form of a coaxial-to-waveguide transition The diameter of
the circular waveguide is chosen such that only the dominant mode
propagates
When the waveguide dimension does not provide a circular symmteric
-2-
pattern a choke or multiple chokes around the aperture wall can be
employed to equalize radiation patterns and keep the back radiation in low
level If chokes are not enough for the suppression of the back radiation
corrugations on the outer surface of the feed is one way to reduce the back
radiation
In this thesis a broadband circular waveguide feed is developed for
prime-focus reflector antenna application After investigating the radiation
properties of simple circular and square waveguides methods are investigated
for bandwidth enhancement back radiation suppression and beamwidth
equalization in the circular waveguide feed
The first type of the circular waveguide feed consists of a probe-fed
circular waveguide a single quarter-wave choke on the aperture wall and a
dielectric-ring beamwidth equalizer Due to the simple feeding method the
first feed operates over 171-197GHz(141) which is not broadband in the
strict sense of the word
The second feed consists of a coaxial-to-rectangular waveguide transition a
rectangular-to-circular waveguide transition a circular waveguide section four
quarter-wave chokes on the aperture wall and four quarter-wave corrugations
on the feeds outer surface Due to the complicated feeding method the
second feed operates over 10-18GHz(571)
This thesis is arranged as follows Chapter I gives an introduction to the
thesis related works and objectives are stated Chapter II describes the
structure and excitation of the circular and square waveguide and the
operation of the coaxial-to-waveguide transitions Chapter III describes a
compact feed horn design and its fabrication and measurement Chapter IV
-3-
presents dielectric rod feed and its simulated performances Chapter V gives
design and optimization of feed for parabolic reflector antenna In this
chapter includes the detailed information of design procedures and operating
principle also the simulated and measured performances are provided Finally
conclusion is given in the Chapter VI
-4-
II Analysis of Circular and Square Waveguide Feeds
21 Circular Waveguide Radiator
Before design a complicated circular waveguide feed it is helpful to
investigate the impedance and radiation properties of a circular waveguide
open end
The circular waveguide is a cylindrical hollow metallic pipe with a uniform
circular section of radius a Circular waveguides are normally designed to
operate only with the dominant mode The dominant mode in a waveguide is
the mode having the lowest cutoff frequency given by equation (21)
(21)
where
(22)
and a is the waveguide radius The following chart[2] and table show the
cutoff frequencies of various modes in a circular waveguide
-5-
Modes c al11TEc cf f
TE11 341259 100000
TM01 261274 130613
TE21 205720 165885TE01 163979 208111
TM11 163979 208111TE31 149557 228180
TM21 122345 278932TE41 118159 288813
TE12 117852 289566
TM02 113824 299813TE02 0897986 380027
The recommended frequency range of the commercial circular waveguide is
given by the following equation This assumes that the TM01 mode is not
generated or suppressed if generated
11 21 11TE TE TE115 095 158 32 bandwidthc c cf f f fpound pound = reg (23)
Fig 21 shows the geometry of a circular waveguide with a diameter of 2a
When 2a is 2053mm the cutoff frequency of the TE11 mode is 857GHz
According to (23) the useful operating frequency range is from
986-1354GHz
Fig 22 shows the reflection of this waveguide excited with the dominant
TE11 mode The waveguide length l is 60mm The reflection occurs at the
open end of the circular waveguide The reflection coefficient is less than
-15dB over 10-18GHz
-6-
Fig 21 Geometry of a circular waveguide open end radiator
Fig 23 shows a 2D gain pattern of this waveguide antenna The
waveguide antenna has a gain of 80dB 99dB and 115dB at 10GHz
14GHz and 18GHz respectively Fig 24 shows the E- and H-plane patterns
of the circular waveguide antenna Table 21 summarizes the properties of a
circular waveguide antenna
Fig 22 Reflection coefficient of a circular waveguide open end radiator
-7-
(a)
(b)
Fig 23 2D radiation pattern of the circular waveguide open end radiator
at (a)10GHz (b) 14GHz and (c) 18GHz
-8-
(c)
Fig 23 continued
-9-
(a)
(b)
(c)
Fig 24 E-plane and H-plane patterns of the circular waveguide open end
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-10-
Table 21 Properties of a circular waveguide open end radiator of diameter
2053mm
Frequency(GHz)-10dB Beamwith(deg) Front-to-Back
Ratio(dB)E plane H plane
10 67 73 12
14 58 60 18
18 41 50 21
In a circular waveguide radiatoλr a good pattern symmetry and low back
radiation is obtained at 14GHz where 2aλ = 096
22 Square Waveguide Radiator
A square waveguide is often used as a dual-polarized feed To operate the
cutoff frequency of the dominant mode a square-waveguide wall width a
must be greater than one half of a wavelength The modes with cutoff
frequencies equal to or smaller than the operational frequency can exist inside
the waveguide wall The lower cutoff frequency and cutoff wavelength for
square waveguide is determined by the following equations
TE
(24)
TE
(25)
The next higher-order mode is TE11 mode with the cutoff wavelength
given by
-11-
TE
(26)
Similar to the circular waveguide the recommended operating frequency range
of a square waveguide is given by
TEleleTE
TErarr bandwidth (27)
Fig 25 shows the geometry of a square waveguide with a dimension of a
When a is 157mm the cutoff frequency is 95GHz The recommended
operating frequency of this waveguide is from 109GHz to 155GHz
Fig 26 shows the reflection of this waveguide excited with the dominant
TE10 mode The reflection coefficient is less than -15dB over 10-20GHz
Fig 25 Geometry of a square waveguide open end radiator
Fig 27 and shows the 2D radiation pattern of a square waveguide antenna
excited with the dominant TE10 mode The antenna has a gain of 73dB
85dB and 102dB at 10GHz 14GHz and 18GHz respectively Fig 28
shows the E- and H-plane radiation patterns of a square waveguide radiator
Table 22 summarizes the properties of a square waveguide open end radiator
-12-
Fig 26 Reflection coefficient of a square waveguide open end radiator
(a)
Fig 27 2D radiation patterns of a square waveguide radiator
at (a) 10GHz (b) 14GHz and (c) 18GHz
-13-
(b)
(c)
Fig 27 continued
-14-
(a)
(b)
(c)
Fig 28 E-plane and H-plane patterns of square waveguide open radiator
at (a) 10GHz(b) 14GHz and (c) 18GHz
-15-
Table 22 Properties of a square waveguide open end radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 69 71 11
14 47 60 25
18 58 62 16
The radiation pattern symmetry and back radiation performance of the
square waveguide are inferior to those of a circular waveguide
23 Probe-Fed Circular Waveguide Radiator
In Section 21 the radiation properties of a TE11-mode excited waveguide
is investigated In this section a circular waveguide fed by a coaxial probe
shown in Fig 29 is studied
The coaxial probes diameter is 127mm With the Teflon dielectric the
50-ohm coaxial lines outer conductor has a diameter of 41mm For a
circular waveguide the wave impedance of the TE11 mode is given by
∙ (28)
where λg is the guided wavelength given by
(29)
-16-
(a) (b)
Fig 29 Probe-fed circular waveguide radiator (a) Front view and (b) side
view
The combination of the probe length and the probe position from the
shorted wall enables a good impedance matching The probe distance sp from
the back short is close to a quarter wavelength at the design frequency
The designed feed has the following dimension d = 2053mm lp = 42
mm sp = 534mm wall thickness = 05mm and feed length = 400mm
Fig 210 shows the reflection coefficient of the designed probe-fed
circular waveguide radiator The reflection coefficient is less than -10dB over
138-187GHz Fig 211 and 212 shows the E-plane and H-plane radiation
patterns and 2D radiation patterns of the coaxial-to-circular waveguide
transition The radiation patterns symmetry distorted because of the high order
modes The coaxial-to-circular waveguide transition has 73dB 84dB and
79dB gain at 10GHz 14GHz and 18GHz frequencies respectively Table 23
shows the properties of the coaxial-to-circular waveguide transition
-17-
Fig 210 Reflection coefficient of the probe-fed circular waveguide radiator
(a)
Fig 211 2D radiation pattern of the probe-fed circular waveguide radiator
at (a) 10GHz (b) 14GHz and (c) 18GHz
-18-
(b)
(c)
Fig 211 continued
-19-
(a)
(b)
(c)
Fig 212 E- and H-plane patterns of the probe-fed circular waveguide
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-20-
Table 23 Properties of the probe-fed circular waveguide radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 73 70 1414 83 57 17
18 60 52 30
When a circular waveguide radiator is fed by a coaxial probe its radiation
properties are not good due to the excitation of higher-order modes
Therefore a probe-fed circular waveguide radiator can be used as a feed only
over a narrow frequency range
24 Probe-Fed Square Waveguide Radiator
In this section a probe-fed square waveguide radiator is investigated Fig
213 shows a coaxial probe-fed square waveguide radiator The designed
radiator has the following dimension a = b = 157mm lp = 35 mm sp =
50 mm wall thickness = 05mm and feed length = 40mm
(a) (b)
Fig 213 Probe-fed square waveguide radiator (a) Front view and (b) side
view
-21-
Fig 214 shows the 2D radiation patterns of the radiator at 10GHz
14GHz and 18GHz Fig 215 shows E- and H-plane patterns of the radiator
Fig 216 shows the reflection coefficient of the probe-fed square waveguide
radiator The reflection coefficient is less than -10dB over 13-20GHz Table
24 summarizes the properties of the probe-fed square waveguide radiator
(a)
Fig 214 2D radiation patterns of the probe-fed square waveguide radiator at
(a) 10GHz (b) 14GHz and (c) 18GHz
-22-
(b)
(c)
Fig 214 continued
-23-
(a)
(b)
(c)
Fig 216 E-plane and H-plane patterns of the probe-fed square waveguide
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-24-
Fig 216 Reflection coefficient of the probe-fed square waveguide radiator
Table 24 Properties of the probe-fed square waveguide radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 73 71 12
14 85 63 1418 27 65 28
When a square waveguide radiator is fed by a coaxial probe its radiation
properties are not good due to the excitation of higher-order modes as in the
case of the probe-fed circular waveguide radiator A probe-fed square
waveguide radiator can be used as a feed only over a narrow frequency
range
-25-
III Design of Compact Circular Waveguide Feeds
In this chapter the feed design is presented for a prime-focus reflector
antenna The prime-focus paraboloid reflector is one of the most commonly
used high-gain antenna It has been used in earth-station antennas and radio
telescopes It consists of a paraboloid reflector with a feed system at its focal
point
The feed should radiate a low level of cross-polar power over the
operating frequency These conditions not easy to achieve and most prime
focus feeds are compromises The shape and characteristic of the radiation
pattern of the feed are the most important parameter because these will
directly influence the fields which are directed at a reflector[6] Other
electrical factors which relevant to the choice of a feed are the cross-polar
level the gain efficiency the bandwidth and impedance matching
31 Narrow-Band Circular Waveguide Feed
Fig 31 shows the proposed narrow-band circular waveguide feed and its
design variables The feed consists of a circular waveguide open end excited
by a TE11 dominant mode A quarter wave choke is applied along the
circular aperture of the waveguide to equalize E- and H-plane radiation
patterns and to suppress the back radiation A dielectric ring is used to
control the radiation pattern and change the power distribution over the
aperture The control of the amplitude over the aperture are essential to the
design of symmetric radiation pattern The material used for dielectric loading
-26-
is the monocast(MC) nylon with a dielectric constant of 30 The feed is
designed to operate over 171-197GHz
(a)
(b)
Fig 31 Narrow-band circular waveguide feed (a) CAD model and (b) a
cross sectional view
The impedance matching is achieved by a proper combination of the probe
height lp and its distance sp from the waveguide shorted end Here the
-27-
circular waveguide is terminated with an open end with a wall thickness of
2mm radiating into the free space
Fig 32 shows the effect of the probe length lp and the probe distance sp
on the reflection coefficient The best performance is obtained when lp =
363mm and sp = 616mm The feeds reflection coefficient is less than -10dB
over 170-195GHz
(a)
(b)
Fig 32 Effect of the (a) the probe length lp and (b) the probe
distance sp on the reflection coefficient
-28-
Fig 33 shows the effect of the choke depth The E-plane pattern is more
sensitive to the choke depth than the H-plane pattern The choke depth has a
strong influence on the reflection coefficient when it is 360mm By properly
choosing the choke depth we can equalize the E- and H-plane patterns The
optimum value of the choke depth is 410mm which is 0249λ0 at 1825GHz
The choke slot width tch in the range of 06-12mm has almost no effect
on the H-plane pattern and the reflection coefficient For the E-plane pattern
tch of 12mm has some effect on the E-plane radiation pattern as shown in
Fig 34
Fig 35 shows the feed performance versus the dielectric ring length We
observe in Fig 35 that the dielectric length ld has an optimum value of
1168mm which does no effect on the H-plane pattern and tha the value of
1048mm has some effect on the E-plane pattern and the reflection
coefficient
Fig 36 shows E-plane and H-plane patterns and the reflection coefficient
versus the dielectric thickness With the optimum value of the dielectric
thickness t obtained from the Fig 36 is 155mm The larger values of td has
much stronger effects on the E-plane pattern and the reflection coefficient
The H-plane pattern is not sensitive to the dielectric ring thickness
-29-
(a)
(b)
(c)
Fig 33 Feed performance versus the choke depth (a) E-plane pattern
(b) H-plane pattern and (c) reflection coefficient
-30-
(a)
(b)
(c)
Fig 34 Feed performance versus the choke slot width (a) E-plane pattern
(b) H-plane pattern and (c) reflection coefficient
-31-
(a)
(b)
(c)
Fig 35 Feed performance versus the dielectric ring length (a) E-plane
pattern (b) H-plane pattern and (c) reflection coefficient
-32-
(a)
(b)
(c)
Fig 36 Feed performance versus the dielectric ring thickness (a) E-plane
pattern(b) H-plane pattern and (c) reflection coefficient
-33-
From the above parametric analysis an optimum feed design is obtained
The result is shown in Table 31 Fig 37 shows the 2D gain patterns of
designed feed The antenna has a gain of 903dB 933dB and 956dB at
171GHz 1825GHz and 19GHz respectively
Fig 38 shows E- and H-plane radiation patterns of the designed feed The
feed has E- and H-plane 10-dB beamwidths of 60 and 59 degrees at 17GHz
The feed has a front-to-back ration of 1900dB 2490dB and 2200dB at
171GHz 1825GHz and 19GHz respectively Table 32 summarizes the
performance of the designed narrow-band circular waveguide feed
The designed feed has a greatly improved performance over that of a
simple coax-fed feed described in Section 23
Table 31 Dimensions of the designed narrow-band circular feed
Parameter Designation Value(mm)
a Waveguide inside radius 640
l Feed length 2890
lp Probe length 363
sp Probe position from the back short 616
din Probe diameter 127
dout Diameter of coaxial cables outer conductor 400
t Thickness of choked wall 050
tch Choke slot width 100
lch Choke depth 410
ld Dielectric ring length 1168
td Dielectric ring thickness 155
d1 Waveguide outside diameter 1680
-34-
(a)
(b)
Fig 37 2D gain patterns of the narrow-band circular waveguide feed at
(a) 17GHz (b) 1825GHz and (c) 19GHz
-35-
(c)
Fig 37 continued
-36-
(a)
(b)
(c)
Fig 38 E- and H-plane patterns of the narrow-band circular waveguide feed
at (a) 10GHz (b) 1825GHz and (c) 195GHz
-37-
Frequency(GHz)
Gain(dB)
E-H-plane10-dB beamwidths
(deg)
Front-to-back ratio(dB)
Phase centerlocation
(From feeds aperture plane
toward reflector)
(mm)
1700 903 6059 20 062
1825 933 6060 25 004
1900 956 5759 22 007
Table 32 Performance of the narrow-band circular waveguide feed
The designed narrow-band feed is fabricated and its performance is
measured and compared with the simulation results The designed feed is
fabricated in a numerically-controlled machining center The fabricated antenna
is shown in Fig 39
Fig 39 Photograph of the fabricated feed
-38-
Fig 310 shows a comparison of the measured and simulated reflection
coefficients The measured reflection coefficient is less than -10dB over
171-197GHz The agreement between simulated and measured results are
good
Fig 311 shows the E- and H-plane patterns of the fabricated feed at
187GHz The feed has 90dB gain simulation and measurement results are in
good agreement
The fabricated antennarsquos 10dB beamwidth is 60 degrees in both E and H
planes at 187GHz The front-to-back ratio is 21dB
Fig 310 Reflection coefficient of the fabricated feed
-39-
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Fee
d H
orn
Gain
- d
B
Angle - degree
(a)
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Feed H
orn
Gain
- d
B
Angle - degree
(b)
Fig 311 Gain patterns of the fabricated feed at 187 GHz (a) E-plane and
(b) H-plane
-40-
IV Design of Circular Waveguide Feeds Loaded with a
Dielectric Rod
In this section circular waveguide feeds loaded with a dielectric rod feed
are investigated A comprehensive discussion of the circular waveguide loaded
with a dielectric rod is given by Kumar[7] Inserting a dielectric material
inside the circular waveguide improves the E- and H-plane pattern symmetry
In general dielectric-loaded circular waveguide feeds show good performance
only over a narrow bandwidth
Fig 41 shows the geometry of a circular waveguide loaded with a
dielectric rod The waveguide length is 400mm and the wall thickness is
05mm The dielectric rods diameter is 207mm The dielectric rod is
extended 05 wavelength beyond the waveguide open end The dielectric
constant εr is changed and the feeds performance is observed
Fig 41 Geometry of a circular waveguide loaded with a uniform dielectric
rod
-41-
Fig 42 is the radiation pattern of the feed with εr = 25 and L = 05λ0 at
9GHz E- and H-plane 10-dB beamwidths are 810 and 807 degrees
respectively The front-to-back ratio is 18dB The antenna gain is 71dB
(a)
(b)
Fig 42 Radiation pattern at 9GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 05λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-42-
Fig 43 shows the radiation pattern of the feed with εr = 21 at 10GHz
E- and H-plane 10-dB beamwidths are 70 and 71 degrees respectively The
front-to-back ratio is 19dB The antenna gain is 83dB
(a)
(b)
Fig 43 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 21 and L = 05λ0 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-43-
Fig 44 shows the radiation pattern of the feed with εr = 30 at 8GHz
E- and H-plane 10-dB beamwidths are 83 and 824 degrees respectively The
front-to-back ratio is 17dB The antenna gain is 73dB
(a)
(b)
Fig 44 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 30 and L = 05λ0 at 8GHz (a) 2D radiation pattern
and (b) E- and H-plane patterns
-44-
Fig 45 shows the radiation pattern of the feed with εr = 50 at 18GHz
E- and H-plane 10-dB beamwidths are 56 and 54 degrees respectively The
front-to-back ratio is 27dB The antenna gain is 105dB The feed has a good
pattern symmetry and low back radiation
(a)
(b)
Fig 45 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 50 and L = 05λ0 at 18GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-45-
Fig 46 is the radiation pattern of the feed with εr = 25 and L = 10λ0 at
10GHz E- and H-plane 10-dB beamwidths are 50 and 48 degrees
respectively The front-to-back ratio is 16dB The antenna gain is 105dB
(a)
(b)
Fig 46 Radiation pattern at 10GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 10λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-46-
Fig 47 shows the geometry of a circular waveguide with a tapered
dielectric rod The designed feed has the following dimension L = 1λ0 d =
1λ0 and εr =25 at 10GHz The waveguide length is 40mm and the wall
thickness is 05mm
L
Dielectricd3
Fig 47 Geometry of a circular waveguide loaded with a tapered dielectric
rod
Fig 48 shows the radiatio pattern of the designed feed E- and H-plane
10-dB beamwidths are 575 and 564 degrees respectively The front-to-back
ratio is 377dB The antenna gain is 94dB The designed feed has an
excellent beamwidth symmetry and a very low back radiation
-47-
(a)
(b)
Fig 48 Radiation pattern of a circular waveguide loaded with a tapered
dielectric rod with L = 1λ0 d = 1λ0 and εr =25 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-48-
Fig 49 shows the geometry of a spherical ended dielectric rod feed
diameter of 06λ0 at 10GHz with a dielectric constant of 25 and L= 03λ0
Fig 410 shows the radiation patterns of the designed feed E- and H-plane
10-dB beamwidths are both 63 degrees The front-to-back ratio is 24dB The
antenna gain is 864dB
Fig 49 Geometry of a circular waveguide loaded with a spherical ended
dielectric rod
-49-
(a)
(b)
Fig 410 Radiation pattern of a circular waveguide loaded wht a spherical
ended dielectric rod with d = 06λ0 L = 03λ0 and εr =25 at 10GHz (a) 3D
radiation pattern and (b) E- and H-plane patterns
-50-
V Design of a Broadband Circular Waveguide Feed
In this chapter the design of a broadband circular waveguide feed is
presented At microwave frequencies the feed is often a circular waveguide
with chokes and corrugations around the aperture Chokes and corrugations
equalize E- and H-plane patterns and reduce the back radiation
The proposed feed is designed to operate over 10-18GHz The design starts
with the optimization of the coaxial-to-rectangular waveguide adapter
employed for good mode purity over a broad frequency range Next a
rectangular-to-circular waveguide transition is optimized Finally chokes and
corrugations are designed for improved pattern symmetry and low back
radiation
The proposed feed structure is shown in Fig 51 The feed consist of the
following parts a coaxial-to-rectangular waveguide adapter a rectangular-to-
circular waveguide transition a circular waveguide section four quarter-wave
chokes around the feeds aperture and four corrugations on the feeds outer
surface
The computer simulation shows the above arrangement offers good radiation
patterns over a broad frequency range The broadband operation is obtained
by exciting the TE11 mode in the circular waveguide using the TE10 mode of
the rectangular waveguide which is in turn excited by a coaxial probe
-51-
Chokes
Coaxial-to-waveguide transition
Circular wavguide
Corrugations
Mode transition
(a)
(b)
Fig 51 Structure of the proposed broadband circular waveguide feed
(a) CAD model and (b) cross-sectional view
For the coaxial-to-rectangular waveguide adapter an SMA connector with
the probe diameter of 127 mm is employed The coaxial probe inserted into
the waveguide energizes the feed and excites the dominant TE10 mode in
-52-
the rectangular waveguide The impedance matching is achieved by adjusting
the probe distance sp from the back short and the probe length lp
(a)
(b)
Fig 52 Reflection coefficient of the coaxial-to-rectangular adapter versus
(a) probe length lp and (b) the probe position sp
Fig 52 shows the reflection coefficient versus the various values of probe
lengths lp and probe positions sp The probe length lp is adjusted to obtain
antenna impedance matching and the probe distance sp is adjusted to obtain a
-53-
desired resonant frequency
Next a transition between rectangular and circular waveguide is designed
The transition section converts the TE10 mode in the rectangular waveguide to
TE11 mode in the circular waveguide and vice versa The transition is built
in a form of a taper for easy fabrication[22]
(a)
(b)
Fig 53 Structure of the rectangular-to-circular waveguide transition
(a) 3D view and (b) cross sectional view
The dimensions of the final optimized transition are as follows The length
of the rectangular waveguide section is 143mm The rectangular waveguides
width a and height b are 207mm and 857mm respectively The length of
the circular waveguide section is 143mm The inside diameter of the circular
-54-
waveguide is 207mm(097 wavelength at 14GHz) The length of transition
region ltr is 4465mm(approximately equal to 2λ0 at 14GHz) Fig 54 shows
the field distribution inside the mode converter
(a)
(b)
Fig 54 Field distribution inside the mode converter at
(a) 10GHz (b) 14GHz and (c) 18GHz
-55-
(c)
Fig 54 continued
Finally multiple chokes are investigated Figs 55 56 and 57 show the
feed performance without chokes The reflection coefficient is less than -10dB
over 10-19GHz The antenna has a gain of 921dB to 1189dB over
10-19GHz
Fig 55 Reflection coefficient of the broadband circular waveguide feed
without chokes and corrugations
-56-
(a)
(b)
(c)
Fig 56 E- and H-plane patterns of the broadband circular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-57-
(d)
(e)
Fig 56 continued
-58-
(a)
(b)
Fig 57 2D radiation patterns of the broadband cicular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-59-
(c)
(d)
Fig 57 continued
-60-
(e)
Fig 57 continued
To achieve equal beamwidths in E and H planes over a wide frequency
range chokes and corrugations are employed Table51 summarizes the
performance of a feed without chokes and corrugations
Table 51 Performance of the broadband circular waveguide feed without
chokes and corrugations
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
1000 940 6061 15
1200 972 6159 17
1400 920 5957 21
1600 1070 4751 29
1800 1188 5352 21
-61-
Four quarter-wavelength chokes are introduced in the feed design which
has a slot depth of 75mm and slot width of 09mm The choke slot spacing
is 18mm The choke design is investigated by applying the choke one by
one and the effect on the E- and H-plane patterns are observed as illustrated
in Figs 58 and 59 The use of chokes makes the E-plane pattern narrower
The H-plane pattern is not affected Chokes increase the gain slightly and
reduce back radiation
(a)
(b)
Fig 58 Effect of chokes on the E-plane pattern of the broadband circular
waveguide feed at (a) 10GHz(b) 12GHz (c) 14GHz (d) 16GHz and (e)
18GHz
-62-
(c)
(d)
(e)
Fig 58 continued
-63-
(a)
(b)
(c)
Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-64-
(d)
(e)
Fig 59 continued
-65-
Fig 510 shows the feed performance versus the choke depth When the
choke depth is varied from 535mm to 95mm the E- and H-plane patterns
are strongly affected The optimum value of choke depth is 75mm(035λ0 at
14GHz) which gives equal E- and H-plane radiation patterns and leads to
low back radiation
Fig 511 shows the feed performance versus the choke slot width tch The
choke slot width is varied from 09mm to 21mm Radiation patterns and
reflection coefficients are not sensitive to the choke slot width The final
choke slot width is selected to be 09mm considering the feed diameter
minimization and the manufacturability The overall diameter of the proposed
feed is 369mm which is increased from the 207mm of the waveguide
inside diameter due to the use of four chokes
-66-
(a)
(b)
(c)
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection coefficient
-67-
(a)
(b)
(c)
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and (c)
reflection coefficient
-68-
Next we investigated corrugations placed on the outer wall of the feed
Four corrugations applied to the outer surface of the circular waveguide The
corrugation depth is 465mm(0215λ0 at 14GHz) The primary purpose of
using corrugations is to further reduce the back radiation Increasing the
number of corrugations beyond four has little effect in reducing the back
radiation
Figs 512 and 513 show the effect of corrugations on the E- and H-plane
patterns Fig 514 shows the parametric study of the corrugation depth lcor
The corrugation depth is varied from 40mm and 645mm The optimum
value of the corrugation depth is found to be 465mm
-69-
(a)
(b)
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern at (a) 12GHz and (b) 14GHz
-70-
(a)
(b)
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern at (a) 12GHz and (b) 14GHz
-71-
(a)
(b)
(c)
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection coefficient
-72-
The phase center location is important in placing the feed in a reflector
antenna[8] The phase center variation with frequency should be small Fig
515 shows the effect of chokes and corrugations on the phase center The
curve with circle corresponds to the case without chokes and corrugations
The phase center varies from -326mm and -190mm away from the feeds
aperture plane It means the phase center is located inside the waveguide
The curve with triangles corresponds to the case with chokes The curve with
squares to the case with chokes and corrugations The phase center varies
from 0mm to -302mm
From Fig 515 we can observed that phase center variation reduced by the
corrugation and three cases phase center calculated in φ=450 plane
parameter sweep values are given in Table 52
10 12 14 16 181
0
-1
-2
-3
-4
-5
-6
Pha
se c
ente
r (m
m)
Frequency (GHz)
choke+corrugatuion without choke corrugation with choke
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
-73-
Frequency
(GHz)
Phase center from the aperture plane
(mm)
Without
chokes and
corrugations
With
chokes
With chokes
and
corrugations
1000 -326 062 000
1100 -187 030 -002
1200 -563 -208 -065
1300 -296 -154 -202
1400 -319 -314 -302
1500 -201 -203 -241
1600 -242 -233 -207
1700 -208 -208 -186
1800 -190 -157 -132
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
Based on the foregoing parametric studies optimum dimensions of the
broadband circular waveguide feed are obtained as shown in Table 53
-74-
Table 53 Optimum dimensions of the broadband circular waveguide feed
Parameter Designation Value (mm)
2a Waveguide inside diameter 2070
d Waveguide outside diameter 3690
lcrLength of the circular waveguide section 1430
m Distance between the aperture plane and the first corrugation 950
xDistance from the last corrugation to the end of the cylindrical outer surface
550
ltrLength of the rectangular-to-circularwaveguide transition 4465
lrcLength of the rectangular waveguide section 1430
tch Choke slot width 090
lch Choke depth 750
t Choke metal width 090
lcor Corrugation depth 465
tcor Corrugation metal width 100
s Corrugation slot width 10
lp Probe length 530
sp Probe position from the back short 530
din Probe diameter 127
b Inside height of the rectangular waveguide 857
tw Waveguide wall thickness 500
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-v-
Fig 32 Effect of the (a) the probe length lp (b) the probe distance sp on
the reflection coefficient middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 27
Fig 33 Feed performance versus the choke depth (a) E-plane pattern (b)
H- plane pattern (c) reflection coefficient middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 29
Fig 34 Feed performance versus the choke slot width (a) E-plane pattern
(b) H-plane pattern (c) reflection coefficient middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 30
Fig 35 Feed performance versus the dielectric ring length (a) E-plane
pattern (b) H-plane pattern and (c) reflection coefficient middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 31
Fig 36 Feed performance versus the dielectric ring thickness (a) E-plane
pattern (b) H-plane pattern (c) reflection coefficient middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 32
Fig 37 2D gain patterns of the narrow-band circular waveguide feed middotmiddotmiddot 34
Fig 38 E- and H-plane patterns of the narrow-band circular waveguide
feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 30
Fig 39 Photograph of the fabricated feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 37
Fig 310 Reflection coefficient of the fabricated feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 38
Fig 311 Gain patterns of the fabricated feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 39
Fig 41 Geometry of a circular waveguide loaded with a uniform dielectric
rod middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 40
Fig 42 Radiation pattern at 9GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 05λ0 middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 41
Fig 43 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 21 and L = 05λ0 at 10GHz middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 42
Fig 44 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 30 and L = 05λ0 at 8GHz middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 43
Fig 45 Radiation pattern of the circular waveguide loaded with a uniform
-vi-
dielectric rod with εr = 50 and L = 05λ0 at 18GHz middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 44
Fig 46 Radiation pattern at 10GHz of the circular waveguide loaded with
a uniform dielectric rod with εr = 25 and L = 10λ0 middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 45
Fig 47 Geometry of a circular waveguide loaded with a tapered dielectric
rod middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 46
Fig 48 Radiation pattern of a circular waveguide loaded with a tapered
dielectric rod with L = 1λ0 d = 1λ0 and εr =25 at 10GHz middotmiddotmiddotmiddotmiddotmiddotmiddot 47
Fig 49 Geometry of a circular waveguide loaded with a spherical ended
dielectric rod middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 48
Fig 410 Radiation pattern of a circular waveguide loaded wht a spherical
ended dielectric rod with d = 06λ0 L = 03λ0 and εr =25 at
10GHz middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 49
Fig 51 Structure of the proposed broadband circular waveguide feed middotmiddotmiddotmiddotmiddot 51
Fig 52 Reflection coefficient of the coaxial-to-rectangular adapter versus
(a) probe length lp and (b) the probe position sp middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 52
Fig 53 Structure of the rectangular-to-circular waveguide transition middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 53
Fig 54 Field distribution inside the mode converter middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 54
Fig 55 Reflection coefficient of the broadband circular waveguide feed
without chokes and corrugations middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 55
Fig 56 E-plane and H-plane patternsof the broadband circular waveguide
feed without chokes and corrugationsz middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 56
Fig 57 2D radiation patterns of the broadband cicular waveguide feed
without chokes and corrugations middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 58
Fig 58 Effect of chokes on the E-plane pattern of the broadband circular
waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 61
-vii-
Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 63
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection
coefficient middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 66
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and
(c) reflection coefficient middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 67
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 69
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 70
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection
coefficient middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 71
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 72
Fig 516 Reflection coefficient of the designed broadband circular
waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 75
Fig 517 2D radiation patterns of the designed broadband circular
waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 76
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 79
Fig 519 Phase center variation of the designed broadband circular
waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 81
-viii-
Fig 520 Photograph of the fabricated broadband circular waveguide feed 82
Fig 521 Reflection coefficient of the fabricated broadband circular
waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 82
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 84
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 84
-ix-
List of Tables
Table 21 Properties of a circular waveguide open end radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 10
Table 22 Properties of a square waveguide open end radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 15
Table 23 Properties of the probe-fed circular waveguide radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 20
Table 24 Properties of the probe-fed square waveguide radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 24
Table 31 Dimensions of the designed narrow-band circular feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 33
Table 32 Performance of the narrow-band circular waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 37
Table 51 Performance of the broadband circular waveguide feed without
chokes and corrugations middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 60
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 73
Table 53 Optimum dimensions of the broadband circular waveguide feed 74
Table 54 Performance of the designed broadband circular waveguide feed 81
-1-
I Introduction
The horns and waveguides are known for their high efficiency and
structural simplicity They are popular choices for feeding for reflectors in
high-gain antenna applications such as satellite and point-to-point microwave
communication links The theory of reflector antenna was developed in the
1940s and has been used to calculate the radiation patterns of various
reflector structures[1]
The basic structure of a prime-focus reflector antenna consists of a
parabolic reflecting surface a feed and its support The placement of the feed
is such that its phase center is at the focal point of the parabolic reflecting
surface The feed is often a circular waveguide because of its symmetric
radiation pattern with low back radiation and low cross polarization The
circular waveguide feed must have a small diameter to reduce the aperture
blockage of the reflector antenna[3]
A radiation pattern with a good circular symmetry in the main beam can
be found from circular waveguide feeds with dominant TE11 mode excitation
The radiation patterns depends on the diameter and wall thickness of the
waveguide[4] A coaxial probe can be inserted into a short-circuited circular
waveguide in the form of a coaxial-to-waveguide transition The diameter of
the circular waveguide is chosen such that only the dominant mode
propagates
When the waveguide dimension does not provide a circular symmteric
-2-
pattern a choke or multiple chokes around the aperture wall can be
employed to equalize radiation patterns and keep the back radiation in low
level If chokes are not enough for the suppression of the back radiation
corrugations on the outer surface of the feed is one way to reduce the back
radiation
In this thesis a broadband circular waveguide feed is developed for
prime-focus reflector antenna application After investigating the radiation
properties of simple circular and square waveguides methods are investigated
for bandwidth enhancement back radiation suppression and beamwidth
equalization in the circular waveguide feed
The first type of the circular waveguide feed consists of a probe-fed
circular waveguide a single quarter-wave choke on the aperture wall and a
dielectric-ring beamwidth equalizer Due to the simple feeding method the
first feed operates over 171-197GHz(141) which is not broadband in the
strict sense of the word
The second feed consists of a coaxial-to-rectangular waveguide transition a
rectangular-to-circular waveguide transition a circular waveguide section four
quarter-wave chokes on the aperture wall and four quarter-wave corrugations
on the feeds outer surface Due to the complicated feeding method the
second feed operates over 10-18GHz(571)
This thesis is arranged as follows Chapter I gives an introduction to the
thesis related works and objectives are stated Chapter II describes the
structure and excitation of the circular and square waveguide and the
operation of the coaxial-to-waveguide transitions Chapter III describes a
compact feed horn design and its fabrication and measurement Chapter IV
-3-
presents dielectric rod feed and its simulated performances Chapter V gives
design and optimization of feed for parabolic reflector antenna In this
chapter includes the detailed information of design procedures and operating
principle also the simulated and measured performances are provided Finally
conclusion is given in the Chapter VI
-4-
II Analysis of Circular and Square Waveguide Feeds
21 Circular Waveguide Radiator
Before design a complicated circular waveguide feed it is helpful to
investigate the impedance and radiation properties of a circular waveguide
open end
The circular waveguide is a cylindrical hollow metallic pipe with a uniform
circular section of radius a Circular waveguides are normally designed to
operate only with the dominant mode The dominant mode in a waveguide is
the mode having the lowest cutoff frequency given by equation (21)
(21)
where
(22)
and a is the waveguide radius The following chart[2] and table show the
cutoff frequencies of various modes in a circular waveguide
-5-
Modes c al11TEc cf f
TE11 341259 100000
TM01 261274 130613
TE21 205720 165885TE01 163979 208111
TM11 163979 208111TE31 149557 228180
TM21 122345 278932TE41 118159 288813
TE12 117852 289566
TM02 113824 299813TE02 0897986 380027
The recommended frequency range of the commercial circular waveguide is
given by the following equation This assumes that the TM01 mode is not
generated or suppressed if generated
11 21 11TE TE TE115 095 158 32 bandwidthc c cf f f fpound pound = reg (23)
Fig 21 shows the geometry of a circular waveguide with a diameter of 2a
When 2a is 2053mm the cutoff frequency of the TE11 mode is 857GHz
According to (23) the useful operating frequency range is from
986-1354GHz
Fig 22 shows the reflection of this waveguide excited with the dominant
TE11 mode The waveguide length l is 60mm The reflection occurs at the
open end of the circular waveguide The reflection coefficient is less than
-15dB over 10-18GHz
-6-
Fig 21 Geometry of a circular waveguide open end radiator
Fig 23 shows a 2D gain pattern of this waveguide antenna The
waveguide antenna has a gain of 80dB 99dB and 115dB at 10GHz
14GHz and 18GHz respectively Fig 24 shows the E- and H-plane patterns
of the circular waveguide antenna Table 21 summarizes the properties of a
circular waveguide antenna
Fig 22 Reflection coefficient of a circular waveguide open end radiator
-7-
(a)
(b)
Fig 23 2D radiation pattern of the circular waveguide open end radiator
at (a)10GHz (b) 14GHz and (c) 18GHz
-8-
(c)
Fig 23 continued
-9-
(a)
(b)
(c)
Fig 24 E-plane and H-plane patterns of the circular waveguide open end
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-10-
Table 21 Properties of a circular waveguide open end radiator of diameter
2053mm
Frequency(GHz)-10dB Beamwith(deg) Front-to-Back
Ratio(dB)E plane H plane
10 67 73 12
14 58 60 18
18 41 50 21
In a circular waveguide radiatoλr a good pattern symmetry and low back
radiation is obtained at 14GHz where 2aλ = 096
22 Square Waveguide Radiator
A square waveguide is often used as a dual-polarized feed To operate the
cutoff frequency of the dominant mode a square-waveguide wall width a
must be greater than one half of a wavelength The modes with cutoff
frequencies equal to or smaller than the operational frequency can exist inside
the waveguide wall The lower cutoff frequency and cutoff wavelength for
square waveguide is determined by the following equations
TE
(24)
TE
(25)
The next higher-order mode is TE11 mode with the cutoff wavelength
given by
-11-
TE
(26)
Similar to the circular waveguide the recommended operating frequency range
of a square waveguide is given by
TEleleTE
TErarr bandwidth (27)
Fig 25 shows the geometry of a square waveguide with a dimension of a
When a is 157mm the cutoff frequency is 95GHz The recommended
operating frequency of this waveguide is from 109GHz to 155GHz
Fig 26 shows the reflection of this waveguide excited with the dominant
TE10 mode The reflection coefficient is less than -15dB over 10-20GHz
Fig 25 Geometry of a square waveguide open end radiator
Fig 27 and shows the 2D radiation pattern of a square waveguide antenna
excited with the dominant TE10 mode The antenna has a gain of 73dB
85dB and 102dB at 10GHz 14GHz and 18GHz respectively Fig 28
shows the E- and H-plane radiation patterns of a square waveguide radiator
Table 22 summarizes the properties of a square waveguide open end radiator
-12-
Fig 26 Reflection coefficient of a square waveguide open end radiator
(a)
Fig 27 2D radiation patterns of a square waveguide radiator
at (a) 10GHz (b) 14GHz and (c) 18GHz
-13-
(b)
(c)
Fig 27 continued
-14-
(a)
(b)
(c)
Fig 28 E-plane and H-plane patterns of square waveguide open radiator
at (a) 10GHz(b) 14GHz and (c) 18GHz
-15-
Table 22 Properties of a square waveguide open end radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 69 71 11
14 47 60 25
18 58 62 16
The radiation pattern symmetry and back radiation performance of the
square waveguide are inferior to those of a circular waveguide
23 Probe-Fed Circular Waveguide Radiator
In Section 21 the radiation properties of a TE11-mode excited waveguide
is investigated In this section a circular waveguide fed by a coaxial probe
shown in Fig 29 is studied
The coaxial probes diameter is 127mm With the Teflon dielectric the
50-ohm coaxial lines outer conductor has a diameter of 41mm For a
circular waveguide the wave impedance of the TE11 mode is given by
∙ (28)
where λg is the guided wavelength given by
(29)
-16-
(a) (b)
Fig 29 Probe-fed circular waveguide radiator (a) Front view and (b) side
view
The combination of the probe length and the probe position from the
shorted wall enables a good impedance matching The probe distance sp from
the back short is close to a quarter wavelength at the design frequency
The designed feed has the following dimension d = 2053mm lp = 42
mm sp = 534mm wall thickness = 05mm and feed length = 400mm
Fig 210 shows the reflection coefficient of the designed probe-fed
circular waveguide radiator The reflection coefficient is less than -10dB over
138-187GHz Fig 211 and 212 shows the E-plane and H-plane radiation
patterns and 2D radiation patterns of the coaxial-to-circular waveguide
transition The radiation patterns symmetry distorted because of the high order
modes The coaxial-to-circular waveguide transition has 73dB 84dB and
79dB gain at 10GHz 14GHz and 18GHz frequencies respectively Table 23
shows the properties of the coaxial-to-circular waveguide transition
-17-
Fig 210 Reflection coefficient of the probe-fed circular waveguide radiator
(a)
Fig 211 2D radiation pattern of the probe-fed circular waveguide radiator
at (a) 10GHz (b) 14GHz and (c) 18GHz
-18-
(b)
(c)
Fig 211 continued
-19-
(a)
(b)
(c)
Fig 212 E- and H-plane patterns of the probe-fed circular waveguide
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-20-
Table 23 Properties of the probe-fed circular waveguide radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 73 70 1414 83 57 17
18 60 52 30
When a circular waveguide radiator is fed by a coaxial probe its radiation
properties are not good due to the excitation of higher-order modes
Therefore a probe-fed circular waveguide radiator can be used as a feed only
over a narrow frequency range
24 Probe-Fed Square Waveguide Radiator
In this section a probe-fed square waveguide radiator is investigated Fig
213 shows a coaxial probe-fed square waveguide radiator The designed
radiator has the following dimension a = b = 157mm lp = 35 mm sp =
50 mm wall thickness = 05mm and feed length = 40mm
(a) (b)
Fig 213 Probe-fed square waveguide radiator (a) Front view and (b) side
view
-21-
Fig 214 shows the 2D radiation patterns of the radiator at 10GHz
14GHz and 18GHz Fig 215 shows E- and H-plane patterns of the radiator
Fig 216 shows the reflection coefficient of the probe-fed square waveguide
radiator The reflection coefficient is less than -10dB over 13-20GHz Table
24 summarizes the properties of the probe-fed square waveguide radiator
(a)
Fig 214 2D radiation patterns of the probe-fed square waveguide radiator at
(a) 10GHz (b) 14GHz and (c) 18GHz
-22-
(b)
(c)
Fig 214 continued
-23-
(a)
(b)
(c)
Fig 216 E-plane and H-plane patterns of the probe-fed square waveguide
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-24-
Fig 216 Reflection coefficient of the probe-fed square waveguide radiator
Table 24 Properties of the probe-fed square waveguide radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 73 71 12
14 85 63 1418 27 65 28
When a square waveguide radiator is fed by a coaxial probe its radiation
properties are not good due to the excitation of higher-order modes as in the
case of the probe-fed circular waveguide radiator A probe-fed square
waveguide radiator can be used as a feed only over a narrow frequency
range
-25-
III Design of Compact Circular Waveguide Feeds
In this chapter the feed design is presented for a prime-focus reflector
antenna The prime-focus paraboloid reflector is one of the most commonly
used high-gain antenna It has been used in earth-station antennas and radio
telescopes It consists of a paraboloid reflector with a feed system at its focal
point
The feed should radiate a low level of cross-polar power over the
operating frequency These conditions not easy to achieve and most prime
focus feeds are compromises The shape and characteristic of the radiation
pattern of the feed are the most important parameter because these will
directly influence the fields which are directed at a reflector[6] Other
electrical factors which relevant to the choice of a feed are the cross-polar
level the gain efficiency the bandwidth and impedance matching
31 Narrow-Band Circular Waveguide Feed
Fig 31 shows the proposed narrow-band circular waveguide feed and its
design variables The feed consists of a circular waveguide open end excited
by a TE11 dominant mode A quarter wave choke is applied along the
circular aperture of the waveguide to equalize E- and H-plane radiation
patterns and to suppress the back radiation A dielectric ring is used to
control the radiation pattern and change the power distribution over the
aperture The control of the amplitude over the aperture are essential to the
design of symmetric radiation pattern The material used for dielectric loading
-26-
is the monocast(MC) nylon with a dielectric constant of 30 The feed is
designed to operate over 171-197GHz
(a)
(b)
Fig 31 Narrow-band circular waveguide feed (a) CAD model and (b) a
cross sectional view
The impedance matching is achieved by a proper combination of the probe
height lp and its distance sp from the waveguide shorted end Here the
-27-
circular waveguide is terminated with an open end with a wall thickness of
2mm radiating into the free space
Fig 32 shows the effect of the probe length lp and the probe distance sp
on the reflection coefficient The best performance is obtained when lp =
363mm and sp = 616mm The feeds reflection coefficient is less than -10dB
over 170-195GHz
(a)
(b)
Fig 32 Effect of the (a) the probe length lp and (b) the probe
distance sp on the reflection coefficient
-28-
Fig 33 shows the effect of the choke depth The E-plane pattern is more
sensitive to the choke depth than the H-plane pattern The choke depth has a
strong influence on the reflection coefficient when it is 360mm By properly
choosing the choke depth we can equalize the E- and H-plane patterns The
optimum value of the choke depth is 410mm which is 0249λ0 at 1825GHz
The choke slot width tch in the range of 06-12mm has almost no effect
on the H-plane pattern and the reflection coefficient For the E-plane pattern
tch of 12mm has some effect on the E-plane radiation pattern as shown in
Fig 34
Fig 35 shows the feed performance versus the dielectric ring length We
observe in Fig 35 that the dielectric length ld has an optimum value of
1168mm which does no effect on the H-plane pattern and tha the value of
1048mm has some effect on the E-plane pattern and the reflection
coefficient
Fig 36 shows E-plane and H-plane patterns and the reflection coefficient
versus the dielectric thickness With the optimum value of the dielectric
thickness t obtained from the Fig 36 is 155mm The larger values of td has
much stronger effects on the E-plane pattern and the reflection coefficient
The H-plane pattern is not sensitive to the dielectric ring thickness
-29-
(a)
(b)
(c)
Fig 33 Feed performance versus the choke depth (a) E-plane pattern
(b) H-plane pattern and (c) reflection coefficient
-30-
(a)
(b)
(c)
Fig 34 Feed performance versus the choke slot width (a) E-plane pattern
(b) H-plane pattern and (c) reflection coefficient
-31-
(a)
(b)
(c)
Fig 35 Feed performance versus the dielectric ring length (a) E-plane
pattern (b) H-plane pattern and (c) reflection coefficient
-32-
(a)
(b)
(c)
Fig 36 Feed performance versus the dielectric ring thickness (a) E-plane
pattern(b) H-plane pattern and (c) reflection coefficient
-33-
From the above parametric analysis an optimum feed design is obtained
The result is shown in Table 31 Fig 37 shows the 2D gain patterns of
designed feed The antenna has a gain of 903dB 933dB and 956dB at
171GHz 1825GHz and 19GHz respectively
Fig 38 shows E- and H-plane radiation patterns of the designed feed The
feed has E- and H-plane 10-dB beamwidths of 60 and 59 degrees at 17GHz
The feed has a front-to-back ration of 1900dB 2490dB and 2200dB at
171GHz 1825GHz and 19GHz respectively Table 32 summarizes the
performance of the designed narrow-band circular waveguide feed
The designed feed has a greatly improved performance over that of a
simple coax-fed feed described in Section 23
Table 31 Dimensions of the designed narrow-band circular feed
Parameter Designation Value(mm)
a Waveguide inside radius 640
l Feed length 2890
lp Probe length 363
sp Probe position from the back short 616
din Probe diameter 127
dout Diameter of coaxial cables outer conductor 400
t Thickness of choked wall 050
tch Choke slot width 100
lch Choke depth 410
ld Dielectric ring length 1168
td Dielectric ring thickness 155
d1 Waveguide outside diameter 1680
-34-
(a)
(b)
Fig 37 2D gain patterns of the narrow-band circular waveguide feed at
(a) 17GHz (b) 1825GHz and (c) 19GHz
-35-
(c)
Fig 37 continued
-36-
(a)
(b)
(c)
Fig 38 E- and H-plane patterns of the narrow-band circular waveguide feed
at (a) 10GHz (b) 1825GHz and (c) 195GHz
-37-
Frequency(GHz)
Gain(dB)
E-H-plane10-dB beamwidths
(deg)
Front-to-back ratio(dB)
Phase centerlocation
(From feeds aperture plane
toward reflector)
(mm)
1700 903 6059 20 062
1825 933 6060 25 004
1900 956 5759 22 007
Table 32 Performance of the narrow-band circular waveguide feed
The designed narrow-band feed is fabricated and its performance is
measured and compared with the simulation results The designed feed is
fabricated in a numerically-controlled machining center The fabricated antenna
is shown in Fig 39
Fig 39 Photograph of the fabricated feed
-38-
Fig 310 shows a comparison of the measured and simulated reflection
coefficients The measured reflection coefficient is less than -10dB over
171-197GHz The agreement between simulated and measured results are
good
Fig 311 shows the E- and H-plane patterns of the fabricated feed at
187GHz The feed has 90dB gain simulation and measurement results are in
good agreement
The fabricated antennarsquos 10dB beamwidth is 60 degrees in both E and H
planes at 187GHz The front-to-back ratio is 21dB
Fig 310 Reflection coefficient of the fabricated feed
-39-
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Fee
d H
orn
Gain
- d
B
Angle - degree
(a)
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Feed H
orn
Gain
- d
B
Angle - degree
(b)
Fig 311 Gain patterns of the fabricated feed at 187 GHz (a) E-plane and
(b) H-plane
-40-
IV Design of Circular Waveguide Feeds Loaded with a
Dielectric Rod
In this section circular waveguide feeds loaded with a dielectric rod feed
are investigated A comprehensive discussion of the circular waveguide loaded
with a dielectric rod is given by Kumar[7] Inserting a dielectric material
inside the circular waveguide improves the E- and H-plane pattern symmetry
In general dielectric-loaded circular waveguide feeds show good performance
only over a narrow bandwidth
Fig 41 shows the geometry of a circular waveguide loaded with a
dielectric rod The waveguide length is 400mm and the wall thickness is
05mm The dielectric rods diameter is 207mm The dielectric rod is
extended 05 wavelength beyond the waveguide open end The dielectric
constant εr is changed and the feeds performance is observed
Fig 41 Geometry of a circular waveguide loaded with a uniform dielectric
rod
-41-
Fig 42 is the radiation pattern of the feed with εr = 25 and L = 05λ0 at
9GHz E- and H-plane 10-dB beamwidths are 810 and 807 degrees
respectively The front-to-back ratio is 18dB The antenna gain is 71dB
(a)
(b)
Fig 42 Radiation pattern at 9GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 05λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-42-
Fig 43 shows the radiation pattern of the feed with εr = 21 at 10GHz
E- and H-plane 10-dB beamwidths are 70 and 71 degrees respectively The
front-to-back ratio is 19dB The antenna gain is 83dB
(a)
(b)
Fig 43 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 21 and L = 05λ0 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-43-
Fig 44 shows the radiation pattern of the feed with εr = 30 at 8GHz
E- and H-plane 10-dB beamwidths are 83 and 824 degrees respectively The
front-to-back ratio is 17dB The antenna gain is 73dB
(a)
(b)
Fig 44 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 30 and L = 05λ0 at 8GHz (a) 2D radiation pattern
and (b) E- and H-plane patterns
-44-
Fig 45 shows the radiation pattern of the feed with εr = 50 at 18GHz
E- and H-plane 10-dB beamwidths are 56 and 54 degrees respectively The
front-to-back ratio is 27dB The antenna gain is 105dB The feed has a good
pattern symmetry and low back radiation
(a)
(b)
Fig 45 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 50 and L = 05λ0 at 18GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-45-
Fig 46 is the radiation pattern of the feed with εr = 25 and L = 10λ0 at
10GHz E- and H-plane 10-dB beamwidths are 50 and 48 degrees
respectively The front-to-back ratio is 16dB The antenna gain is 105dB
(a)
(b)
Fig 46 Radiation pattern at 10GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 10λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-46-
Fig 47 shows the geometry of a circular waveguide with a tapered
dielectric rod The designed feed has the following dimension L = 1λ0 d =
1λ0 and εr =25 at 10GHz The waveguide length is 40mm and the wall
thickness is 05mm
L
Dielectricd3
Fig 47 Geometry of a circular waveguide loaded with a tapered dielectric
rod
Fig 48 shows the radiatio pattern of the designed feed E- and H-plane
10-dB beamwidths are 575 and 564 degrees respectively The front-to-back
ratio is 377dB The antenna gain is 94dB The designed feed has an
excellent beamwidth symmetry and a very low back radiation
-47-
(a)
(b)
Fig 48 Radiation pattern of a circular waveguide loaded with a tapered
dielectric rod with L = 1λ0 d = 1λ0 and εr =25 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-48-
Fig 49 shows the geometry of a spherical ended dielectric rod feed
diameter of 06λ0 at 10GHz with a dielectric constant of 25 and L= 03λ0
Fig 410 shows the radiation patterns of the designed feed E- and H-plane
10-dB beamwidths are both 63 degrees The front-to-back ratio is 24dB The
antenna gain is 864dB
Fig 49 Geometry of a circular waveguide loaded with a spherical ended
dielectric rod
-49-
(a)
(b)
Fig 410 Radiation pattern of a circular waveguide loaded wht a spherical
ended dielectric rod with d = 06λ0 L = 03λ0 and εr =25 at 10GHz (a) 3D
radiation pattern and (b) E- and H-plane patterns
-50-
V Design of a Broadband Circular Waveguide Feed
In this chapter the design of a broadband circular waveguide feed is
presented At microwave frequencies the feed is often a circular waveguide
with chokes and corrugations around the aperture Chokes and corrugations
equalize E- and H-plane patterns and reduce the back radiation
The proposed feed is designed to operate over 10-18GHz The design starts
with the optimization of the coaxial-to-rectangular waveguide adapter
employed for good mode purity over a broad frequency range Next a
rectangular-to-circular waveguide transition is optimized Finally chokes and
corrugations are designed for improved pattern symmetry and low back
radiation
The proposed feed structure is shown in Fig 51 The feed consist of the
following parts a coaxial-to-rectangular waveguide adapter a rectangular-to-
circular waveguide transition a circular waveguide section four quarter-wave
chokes around the feeds aperture and four corrugations on the feeds outer
surface
The computer simulation shows the above arrangement offers good radiation
patterns over a broad frequency range The broadband operation is obtained
by exciting the TE11 mode in the circular waveguide using the TE10 mode of
the rectangular waveguide which is in turn excited by a coaxial probe
-51-
Chokes
Coaxial-to-waveguide transition
Circular wavguide
Corrugations
Mode transition
(a)
(b)
Fig 51 Structure of the proposed broadband circular waveguide feed
(a) CAD model and (b) cross-sectional view
For the coaxial-to-rectangular waveguide adapter an SMA connector with
the probe diameter of 127 mm is employed The coaxial probe inserted into
the waveguide energizes the feed and excites the dominant TE10 mode in
-52-
the rectangular waveguide The impedance matching is achieved by adjusting
the probe distance sp from the back short and the probe length lp
(a)
(b)
Fig 52 Reflection coefficient of the coaxial-to-rectangular adapter versus
(a) probe length lp and (b) the probe position sp
Fig 52 shows the reflection coefficient versus the various values of probe
lengths lp and probe positions sp The probe length lp is adjusted to obtain
antenna impedance matching and the probe distance sp is adjusted to obtain a
-53-
desired resonant frequency
Next a transition between rectangular and circular waveguide is designed
The transition section converts the TE10 mode in the rectangular waveguide to
TE11 mode in the circular waveguide and vice versa The transition is built
in a form of a taper for easy fabrication[22]
(a)
(b)
Fig 53 Structure of the rectangular-to-circular waveguide transition
(a) 3D view and (b) cross sectional view
The dimensions of the final optimized transition are as follows The length
of the rectangular waveguide section is 143mm The rectangular waveguides
width a and height b are 207mm and 857mm respectively The length of
the circular waveguide section is 143mm The inside diameter of the circular
-54-
waveguide is 207mm(097 wavelength at 14GHz) The length of transition
region ltr is 4465mm(approximately equal to 2λ0 at 14GHz) Fig 54 shows
the field distribution inside the mode converter
(a)
(b)
Fig 54 Field distribution inside the mode converter at
(a) 10GHz (b) 14GHz and (c) 18GHz
-55-
(c)
Fig 54 continued
Finally multiple chokes are investigated Figs 55 56 and 57 show the
feed performance without chokes The reflection coefficient is less than -10dB
over 10-19GHz The antenna has a gain of 921dB to 1189dB over
10-19GHz
Fig 55 Reflection coefficient of the broadband circular waveguide feed
without chokes and corrugations
-56-
(a)
(b)
(c)
Fig 56 E- and H-plane patterns of the broadband circular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-57-
(d)
(e)
Fig 56 continued
-58-
(a)
(b)
Fig 57 2D radiation patterns of the broadband cicular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-59-
(c)
(d)
Fig 57 continued
-60-
(e)
Fig 57 continued
To achieve equal beamwidths in E and H planes over a wide frequency
range chokes and corrugations are employed Table51 summarizes the
performance of a feed without chokes and corrugations
Table 51 Performance of the broadband circular waveguide feed without
chokes and corrugations
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
1000 940 6061 15
1200 972 6159 17
1400 920 5957 21
1600 1070 4751 29
1800 1188 5352 21
-61-
Four quarter-wavelength chokes are introduced in the feed design which
has a slot depth of 75mm and slot width of 09mm The choke slot spacing
is 18mm The choke design is investigated by applying the choke one by
one and the effect on the E- and H-plane patterns are observed as illustrated
in Figs 58 and 59 The use of chokes makes the E-plane pattern narrower
The H-plane pattern is not affected Chokes increase the gain slightly and
reduce back radiation
(a)
(b)
Fig 58 Effect of chokes on the E-plane pattern of the broadband circular
waveguide feed at (a) 10GHz(b) 12GHz (c) 14GHz (d) 16GHz and (e)
18GHz
-62-
(c)
(d)
(e)
Fig 58 continued
-63-
(a)
(b)
(c)
Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-64-
(d)
(e)
Fig 59 continued
-65-
Fig 510 shows the feed performance versus the choke depth When the
choke depth is varied from 535mm to 95mm the E- and H-plane patterns
are strongly affected The optimum value of choke depth is 75mm(035λ0 at
14GHz) which gives equal E- and H-plane radiation patterns and leads to
low back radiation
Fig 511 shows the feed performance versus the choke slot width tch The
choke slot width is varied from 09mm to 21mm Radiation patterns and
reflection coefficients are not sensitive to the choke slot width The final
choke slot width is selected to be 09mm considering the feed diameter
minimization and the manufacturability The overall diameter of the proposed
feed is 369mm which is increased from the 207mm of the waveguide
inside diameter due to the use of four chokes
-66-
(a)
(b)
(c)
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection coefficient
-67-
(a)
(b)
(c)
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and (c)
reflection coefficient
-68-
Next we investigated corrugations placed on the outer wall of the feed
Four corrugations applied to the outer surface of the circular waveguide The
corrugation depth is 465mm(0215λ0 at 14GHz) The primary purpose of
using corrugations is to further reduce the back radiation Increasing the
number of corrugations beyond four has little effect in reducing the back
radiation
Figs 512 and 513 show the effect of corrugations on the E- and H-plane
patterns Fig 514 shows the parametric study of the corrugation depth lcor
The corrugation depth is varied from 40mm and 645mm The optimum
value of the corrugation depth is found to be 465mm
-69-
(a)
(b)
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern at (a) 12GHz and (b) 14GHz
-70-
(a)
(b)
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern at (a) 12GHz and (b) 14GHz
-71-
(a)
(b)
(c)
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection coefficient
-72-
The phase center location is important in placing the feed in a reflector
antenna[8] The phase center variation with frequency should be small Fig
515 shows the effect of chokes and corrugations on the phase center The
curve with circle corresponds to the case without chokes and corrugations
The phase center varies from -326mm and -190mm away from the feeds
aperture plane It means the phase center is located inside the waveguide
The curve with triangles corresponds to the case with chokes The curve with
squares to the case with chokes and corrugations The phase center varies
from 0mm to -302mm
From Fig 515 we can observed that phase center variation reduced by the
corrugation and three cases phase center calculated in φ=450 plane
parameter sweep values are given in Table 52
10 12 14 16 181
0
-1
-2
-3
-4
-5
-6
Pha
se c
ente
r (m
m)
Frequency (GHz)
choke+corrugatuion without choke corrugation with choke
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
-73-
Frequency
(GHz)
Phase center from the aperture plane
(mm)
Without
chokes and
corrugations
With
chokes
With chokes
and
corrugations
1000 -326 062 000
1100 -187 030 -002
1200 -563 -208 -065
1300 -296 -154 -202
1400 -319 -314 -302
1500 -201 -203 -241
1600 -242 -233 -207
1700 -208 -208 -186
1800 -190 -157 -132
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
Based on the foregoing parametric studies optimum dimensions of the
broadband circular waveguide feed are obtained as shown in Table 53
-74-
Table 53 Optimum dimensions of the broadband circular waveguide feed
Parameter Designation Value (mm)
2a Waveguide inside diameter 2070
d Waveguide outside diameter 3690
lcrLength of the circular waveguide section 1430
m Distance between the aperture plane and the first corrugation 950
xDistance from the last corrugation to the end of the cylindrical outer surface
550
ltrLength of the rectangular-to-circularwaveguide transition 4465
lrcLength of the rectangular waveguide section 1430
tch Choke slot width 090
lch Choke depth 750
t Choke metal width 090
lcor Corrugation depth 465
tcor Corrugation metal width 100
s Corrugation slot width 10
lp Probe length 530
sp Probe position from the back short 530
din Probe diameter 127
b Inside height of the rectangular waveguide 857
tw Waveguide wall thickness 500
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-vi-
dielectric rod with εr = 50 and L = 05λ0 at 18GHz middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 44
Fig 46 Radiation pattern at 10GHz of the circular waveguide loaded with
a uniform dielectric rod with εr = 25 and L = 10λ0 middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 45
Fig 47 Geometry of a circular waveguide loaded with a tapered dielectric
rod middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 46
Fig 48 Radiation pattern of a circular waveguide loaded with a tapered
dielectric rod with L = 1λ0 d = 1λ0 and εr =25 at 10GHz middotmiddotmiddotmiddotmiddotmiddotmiddot 47
Fig 49 Geometry of a circular waveguide loaded with a spherical ended
dielectric rod middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 48
Fig 410 Radiation pattern of a circular waveguide loaded wht a spherical
ended dielectric rod with d = 06λ0 L = 03λ0 and εr =25 at
10GHz middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 49
Fig 51 Structure of the proposed broadband circular waveguide feed middotmiddotmiddotmiddotmiddot 51
Fig 52 Reflection coefficient of the coaxial-to-rectangular adapter versus
(a) probe length lp and (b) the probe position sp middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 52
Fig 53 Structure of the rectangular-to-circular waveguide transition middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 53
Fig 54 Field distribution inside the mode converter middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 54
Fig 55 Reflection coefficient of the broadband circular waveguide feed
without chokes and corrugations middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 55
Fig 56 E-plane and H-plane patternsof the broadband circular waveguide
feed without chokes and corrugationsz middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 56
Fig 57 2D radiation patterns of the broadband cicular waveguide feed
without chokes and corrugations middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 58
Fig 58 Effect of chokes on the E-plane pattern of the broadband circular
waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 61
-vii-
Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 63
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection
coefficient middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 66
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and
(c) reflection coefficient middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 67
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 69
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 70
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection
coefficient middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 71
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 72
Fig 516 Reflection coefficient of the designed broadband circular
waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 75
Fig 517 2D radiation patterns of the designed broadband circular
waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 76
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 79
Fig 519 Phase center variation of the designed broadband circular
waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 81
-viii-
Fig 520 Photograph of the fabricated broadband circular waveguide feed 82
Fig 521 Reflection coefficient of the fabricated broadband circular
waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 82
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 84
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 84
-ix-
List of Tables
Table 21 Properties of a circular waveguide open end radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 10
Table 22 Properties of a square waveguide open end radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 15
Table 23 Properties of the probe-fed circular waveguide radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 20
Table 24 Properties of the probe-fed square waveguide radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 24
Table 31 Dimensions of the designed narrow-band circular feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 33
Table 32 Performance of the narrow-band circular waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 37
Table 51 Performance of the broadband circular waveguide feed without
chokes and corrugations middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 60
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 73
Table 53 Optimum dimensions of the broadband circular waveguide feed 74
Table 54 Performance of the designed broadband circular waveguide feed 81
-1-
I Introduction
The horns and waveguides are known for their high efficiency and
structural simplicity They are popular choices for feeding for reflectors in
high-gain antenna applications such as satellite and point-to-point microwave
communication links The theory of reflector antenna was developed in the
1940s and has been used to calculate the radiation patterns of various
reflector structures[1]
The basic structure of a prime-focus reflector antenna consists of a
parabolic reflecting surface a feed and its support The placement of the feed
is such that its phase center is at the focal point of the parabolic reflecting
surface The feed is often a circular waveguide because of its symmetric
radiation pattern with low back radiation and low cross polarization The
circular waveguide feed must have a small diameter to reduce the aperture
blockage of the reflector antenna[3]
A radiation pattern with a good circular symmetry in the main beam can
be found from circular waveguide feeds with dominant TE11 mode excitation
The radiation patterns depends on the diameter and wall thickness of the
waveguide[4] A coaxial probe can be inserted into a short-circuited circular
waveguide in the form of a coaxial-to-waveguide transition The diameter of
the circular waveguide is chosen such that only the dominant mode
propagates
When the waveguide dimension does not provide a circular symmteric
-2-
pattern a choke or multiple chokes around the aperture wall can be
employed to equalize radiation patterns and keep the back radiation in low
level If chokes are not enough for the suppression of the back radiation
corrugations on the outer surface of the feed is one way to reduce the back
radiation
In this thesis a broadband circular waveguide feed is developed for
prime-focus reflector antenna application After investigating the radiation
properties of simple circular and square waveguides methods are investigated
for bandwidth enhancement back radiation suppression and beamwidth
equalization in the circular waveguide feed
The first type of the circular waveguide feed consists of a probe-fed
circular waveguide a single quarter-wave choke on the aperture wall and a
dielectric-ring beamwidth equalizer Due to the simple feeding method the
first feed operates over 171-197GHz(141) which is not broadband in the
strict sense of the word
The second feed consists of a coaxial-to-rectangular waveguide transition a
rectangular-to-circular waveguide transition a circular waveguide section four
quarter-wave chokes on the aperture wall and four quarter-wave corrugations
on the feeds outer surface Due to the complicated feeding method the
second feed operates over 10-18GHz(571)
This thesis is arranged as follows Chapter I gives an introduction to the
thesis related works and objectives are stated Chapter II describes the
structure and excitation of the circular and square waveguide and the
operation of the coaxial-to-waveguide transitions Chapter III describes a
compact feed horn design and its fabrication and measurement Chapter IV
-3-
presents dielectric rod feed and its simulated performances Chapter V gives
design and optimization of feed for parabolic reflector antenna In this
chapter includes the detailed information of design procedures and operating
principle also the simulated and measured performances are provided Finally
conclusion is given in the Chapter VI
-4-
II Analysis of Circular and Square Waveguide Feeds
21 Circular Waveguide Radiator
Before design a complicated circular waveguide feed it is helpful to
investigate the impedance and radiation properties of a circular waveguide
open end
The circular waveguide is a cylindrical hollow metallic pipe with a uniform
circular section of radius a Circular waveguides are normally designed to
operate only with the dominant mode The dominant mode in a waveguide is
the mode having the lowest cutoff frequency given by equation (21)
(21)
where
(22)
and a is the waveguide radius The following chart[2] and table show the
cutoff frequencies of various modes in a circular waveguide
-5-
Modes c al11TEc cf f
TE11 341259 100000
TM01 261274 130613
TE21 205720 165885TE01 163979 208111
TM11 163979 208111TE31 149557 228180
TM21 122345 278932TE41 118159 288813
TE12 117852 289566
TM02 113824 299813TE02 0897986 380027
The recommended frequency range of the commercial circular waveguide is
given by the following equation This assumes that the TM01 mode is not
generated or suppressed if generated
11 21 11TE TE TE115 095 158 32 bandwidthc c cf f f fpound pound = reg (23)
Fig 21 shows the geometry of a circular waveguide with a diameter of 2a
When 2a is 2053mm the cutoff frequency of the TE11 mode is 857GHz
According to (23) the useful operating frequency range is from
986-1354GHz
Fig 22 shows the reflection of this waveguide excited with the dominant
TE11 mode The waveguide length l is 60mm The reflection occurs at the
open end of the circular waveguide The reflection coefficient is less than
-15dB over 10-18GHz
-6-
Fig 21 Geometry of a circular waveguide open end radiator
Fig 23 shows a 2D gain pattern of this waveguide antenna The
waveguide antenna has a gain of 80dB 99dB and 115dB at 10GHz
14GHz and 18GHz respectively Fig 24 shows the E- and H-plane patterns
of the circular waveguide antenna Table 21 summarizes the properties of a
circular waveguide antenna
Fig 22 Reflection coefficient of a circular waveguide open end radiator
-7-
(a)
(b)
Fig 23 2D radiation pattern of the circular waveguide open end radiator
at (a)10GHz (b) 14GHz and (c) 18GHz
-8-
(c)
Fig 23 continued
-9-
(a)
(b)
(c)
Fig 24 E-plane and H-plane patterns of the circular waveguide open end
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-10-
Table 21 Properties of a circular waveguide open end radiator of diameter
2053mm
Frequency(GHz)-10dB Beamwith(deg) Front-to-Back
Ratio(dB)E plane H plane
10 67 73 12
14 58 60 18
18 41 50 21
In a circular waveguide radiatoλr a good pattern symmetry and low back
radiation is obtained at 14GHz where 2aλ = 096
22 Square Waveguide Radiator
A square waveguide is often used as a dual-polarized feed To operate the
cutoff frequency of the dominant mode a square-waveguide wall width a
must be greater than one half of a wavelength The modes with cutoff
frequencies equal to or smaller than the operational frequency can exist inside
the waveguide wall The lower cutoff frequency and cutoff wavelength for
square waveguide is determined by the following equations
TE
(24)
TE
(25)
The next higher-order mode is TE11 mode with the cutoff wavelength
given by
-11-
TE
(26)
Similar to the circular waveguide the recommended operating frequency range
of a square waveguide is given by
TEleleTE
TErarr bandwidth (27)
Fig 25 shows the geometry of a square waveguide with a dimension of a
When a is 157mm the cutoff frequency is 95GHz The recommended
operating frequency of this waveguide is from 109GHz to 155GHz
Fig 26 shows the reflection of this waveguide excited with the dominant
TE10 mode The reflection coefficient is less than -15dB over 10-20GHz
Fig 25 Geometry of a square waveguide open end radiator
Fig 27 and shows the 2D radiation pattern of a square waveguide antenna
excited with the dominant TE10 mode The antenna has a gain of 73dB
85dB and 102dB at 10GHz 14GHz and 18GHz respectively Fig 28
shows the E- and H-plane radiation patterns of a square waveguide radiator
Table 22 summarizes the properties of a square waveguide open end radiator
-12-
Fig 26 Reflection coefficient of a square waveguide open end radiator
(a)
Fig 27 2D radiation patterns of a square waveguide radiator
at (a) 10GHz (b) 14GHz and (c) 18GHz
-13-
(b)
(c)
Fig 27 continued
-14-
(a)
(b)
(c)
Fig 28 E-plane and H-plane patterns of square waveguide open radiator
at (a) 10GHz(b) 14GHz and (c) 18GHz
-15-
Table 22 Properties of a square waveguide open end radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 69 71 11
14 47 60 25
18 58 62 16
The radiation pattern symmetry and back radiation performance of the
square waveguide are inferior to those of a circular waveguide
23 Probe-Fed Circular Waveguide Radiator
In Section 21 the radiation properties of a TE11-mode excited waveguide
is investigated In this section a circular waveguide fed by a coaxial probe
shown in Fig 29 is studied
The coaxial probes diameter is 127mm With the Teflon dielectric the
50-ohm coaxial lines outer conductor has a diameter of 41mm For a
circular waveguide the wave impedance of the TE11 mode is given by
∙ (28)
where λg is the guided wavelength given by
(29)
-16-
(a) (b)
Fig 29 Probe-fed circular waveguide radiator (a) Front view and (b) side
view
The combination of the probe length and the probe position from the
shorted wall enables a good impedance matching The probe distance sp from
the back short is close to a quarter wavelength at the design frequency
The designed feed has the following dimension d = 2053mm lp = 42
mm sp = 534mm wall thickness = 05mm and feed length = 400mm
Fig 210 shows the reflection coefficient of the designed probe-fed
circular waveguide radiator The reflection coefficient is less than -10dB over
138-187GHz Fig 211 and 212 shows the E-plane and H-plane radiation
patterns and 2D radiation patterns of the coaxial-to-circular waveguide
transition The radiation patterns symmetry distorted because of the high order
modes The coaxial-to-circular waveguide transition has 73dB 84dB and
79dB gain at 10GHz 14GHz and 18GHz frequencies respectively Table 23
shows the properties of the coaxial-to-circular waveguide transition
-17-
Fig 210 Reflection coefficient of the probe-fed circular waveguide radiator
(a)
Fig 211 2D radiation pattern of the probe-fed circular waveguide radiator
at (a) 10GHz (b) 14GHz and (c) 18GHz
-18-
(b)
(c)
Fig 211 continued
-19-
(a)
(b)
(c)
Fig 212 E- and H-plane patterns of the probe-fed circular waveguide
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-20-
Table 23 Properties of the probe-fed circular waveguide radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 73 70 1414 83 57 17
18 60 52 30
When a circular waveguide radiator is fed by a coaxial probe its radiation
properties are not good due to the excitation of higher-order modes
Therefore a probe-fed circular waveguide radiator can be used as a feed only
over a narrow frequency range
24 Probe-Fed Square Waveguide Radiator
In this section a probe-fed square waveguide radiator is investigated Fig
213 shows a coaxial probe-fed square waveguide radiator The designed
radiator has the following dimension a = b = 157mm lp = 35 mm sp =
50 mm wall thickness = 05mm and feed length = 40mm
(a) (b)
Fig 213 Probe-fed square waveguide radiator (a) Front view and (b) side
view
-21-
Fig 214 shows the 2D radiation patterns of the radiator at 10GHz
14GHz and 18GHz Fig 215 shows E- and H-plane patterns of the radiator
Fig 216 shows the reflection coefficient of the probe-fed square waveguide
radiator The reflection coefficient is less than -10dB over 13-20GHz Table
24 summarizes the properties of the probe-fed square waveguide radiator
(a)
Fig 214 2D radiation patterns of the probe-fed square waveguide radiator at
(a) 10GHz (b) 14GHz and (c) 18GHz
-22-
(b)
(c)
Fig 214 continued
-23-
(a)
(b)
(c)
Fig 216 E-plane and H-plane patterns of the probe-fed square waveguide
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-24-
Fig 216 Reflection coefficient of the probe-fed square waveguide radiator
Table 24 Properties of the probe-fed square waveguide radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 73 71 12
14 85 63 1418 27 65 28
When a square waveguide radiator is fed by a coaxial probe its radiation
properties are not good due to the excitation of higher-order modes as in the
case of the probe-fed circular waveguide radiator A probe-fed square
waveguide radiator can be used as a feed only over a narrow frequency
range
-25-
III Design of Compact Circular Waveguide Feeds
In this chapter the feed design is presented for a prime-focus reflector
antenna The prime-focus paraboloid reflector is one of the most commonly
used high-gain antenna It has been used in earth-station antennas and radio
telescopes It consists of a paraboloid reflector with a feed system at its focal
point
The feed should radiate a low level of cross-polar power over the
operating frequency These conditions not easy to achieve and most prime
focus feeds are compromises The shape and characteristic of the radiation
pattern of the feed are the most important parameter because these will
directly influence the fields which are directed at a reflector[6] Other
electrical factors which relevant to the choice of a feed are the cross-polar
level the gain efficiency the bandwidth and impedance matching
31 Narrow-Band Circular Waveguide Feed
Fig 31 shows the proposed narrow-band circular waveguide feed and its
design variables The feed consists of a circular waveguide open end excited
by a TE11 dominant mode A quarter wave choke is applied along the
circular aperture of the waveguide to equalize E- and H-plane radiation
patterns and to suppress the back radiation A dielectric ring is used to
control the radiation pattern and change the power distribution over the
aperture The control of the amplitude over the aperture are essential to the
design of symmetric radiation pattern The material used for dielectric loading
-26-
is the monocast(MC) nylon with a dielectric constant of 30 The feed is
designed to operate over 171-197GHz
(a)
(b)
Fig 31 Narrow-band circular waveguide feed (a) CAD model and (b) a
cross sectional view
The impedance matching is achieved by a proper combination of the probe
height lp and its distance sp from the waveguide shorted end Here the
-27-
circular waveguide is terminated with an open end with a wall thickness of
2mm radiating into the free space
Fig 32 shows the effect of the probe length lp and the probe distance sp
on the reflection coefficient The best performance is obtained when lp =
363mm and sp = 616mm The feeds reflection coefficient is less than -10dB
over 170-195GHz
(a)
(b)
Fig 32 Effect of the (a) the probe length lp and (b) the probe
distance sp on the reflection coefficient
-28-
Fig 33 shows the effect of the choke depth The E-plane pattern is more
sensitive to the choke depth than the H-plane pattern The choke depth has a
strong influence on the reflection coefficient when it is 360mm By properly
choosing the choke depth we can equalize the E- and H-plane patterns The
optimum value of the choke depth is 410mm which is 0249λ0 at 1825GHz
The choke slot width tch in the range of 06-12mm has almost no effect
on the H-plane pattern and the reflection coefficient For the E-plane pattern
tch of 12mm has some effect on the E-plane radiation pattern as shown in
Fig 34
Fig 35 shows the feed performance versus the dielectric ring length We
observe in Fig 35 that the dielectric length ld has an optimum value of
1168mm which does no effect on the H-plane pattern and tha the value of
1048mm has some effect on the E-plane pattern and the reflection
coefficient
Fig 36 shows E-plane and H-plane patterns and the reflection coefficient
versus the dielectric thickness With the optimum value of the dielectric
thickness t obtained from the Fig 36 is 155mm The larger values of td has
much stronger effects on the E-plane pattern and the reflection coefficient
The H-plane pattern is not sensitive to the dielectric ring thickness
-29-
(a)
(b)
(c)
Fig 33 Feed performance versus the choke depth (a) E-plane pattern
(b) H-plane pattern and (c) reflection coefficient
-30-
(a)
(b)
(c)
Fig 34 Feed performance versus the choke slot width (a) E-plane pattern
(b) H-plane pattern and (c) reflection coefficient
-31-
(a)
(b)
(c)
Fig 35 Feed performance versus the dielectric ring length (a) E-plane
pattern (b) H-plane pattern and (c) reflection coefficient
-32-
(a)
(b)
(c)
Fig 36 Feed performance versus the dielectric ring thickness (a) E-plane
pattern(b) H-plane pattern and (c) reflection coefficient
-33-
From the above parametric analysis an optimum feed design is obtained
The result is shown in Table 31 Fig 37 shows the 2D gain patterns of
designed feed The antenna has a gain of 903dB 933dB and 956dB at
171GHz 1825GHz and 19GHz respectively
Fig 38 shows E- and H-plane radiation patterns of the designed feed The
feed has E- and H-plane 10-dB beamwidths of 60 and 59 degrees at 17GHz
The feed has a front-to-back ration of 1900dB 2490dB and 2200dB at
171GHz 1825GHz and 19GHz respectively Table 32 summarizes the
performance of the designed narrow-band circular waveguide feed
The designed feed has a greatly improved performance over that of a
simple coax-fed feed described in Section 23
Table 31 Dimensions of the designed narrow-band circular feed
Parameter Designation Value(mm)
a Waveguide inside radius 640
l Feed length 2890
lp Probe length 363
sp Probe position from the back short 616
din Probe diameter 127
dout Diameter of coaxial cables outer conductor 400
t Thickness of choked wall 050
tch Choke slot width 100
lch Choke depth 410
ld Dielectric ring length 1168
td Dielectric ring thickness 155
d1 Waveguide outside diameter 1680
-34-
(a)
(b)
Fig 37 2D gain patterns of the narrow-band circular waveguide feed at
(a) 17GHz (b) 1825GHz and (c) 19GHz
-35-
(c)
Fig 37 continued
-36-
(a)
(b)
(c)
Fig 38 E- and H-plane patterns of the narrow-band circular waveguide feed
at (a) 10GHz (b) 1825GHz and (c) 195GHz
-37-
Frequency(GHz)
Gain(dB)
E-H-plane10-dB beamwidths
(deg)
Front-to-back ratio(dB)
Phase centerlocation
(From feeds aperture plane
toward reflector)
(mm)
1700 903 6059 20 062
1825 933 6060 25 004
1900 956 5759 22 007
Table 32 Performance of the narrow-band circular waveguide feed
The designed narrow-band feed is fabricated and its performance is
measured and compared with the simulation results The designed feed is
fabricated in a numerically-controlled machining center The fabricated antenna
is shown in Fig 39
Fig 39 Photograph of the fabricated feed
-38-
Fig 310 shows a comparison of the measured and simulated reflection
coefficients The measured reflection coefficient is less than -10dB over
171-197GHz The agreement between simulated and measured results are
good
Fig 311 shows the E- and H-plane patterns of the fabricated feed at
187GHz The feed has 90dB gain simulation and measurement results are in
good agreement
The fabricated antennarsquos 10dB beamwidth is 60 degrees in both E and H
planes at 187GHz The front-to-back ratio is 21dB
Fig 310 Reflection coefficient of the fabricated feed
-39-
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Fee
d H
orn
Gain
- d
B
Angle - degree
(a)
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Feed H
orn
Gain
- d
B
Angle - degree
(b)
Fig 311 Gain patterns of the fabricated feed at 187 GHz (a) E-plane and
(b) H-plane
-40-
IV Design of Circular Waveguide Feeds Loaded with a
Dielectric Rod
In this section circular waveguide feeds loaded with a dielectric rod feed
are investigated A comprehensive discussion of the circular waveguide loaded
with a dielectric rod is given by Kumar[7] Inserting a dielectric material
inside the circular waveguide improves the E- and H-plane pattern symmetry
In general dielectric-loaded circular waveguide feeds show good performance
only over a narrow bandwidth
Fig 41 shows the geometry of a circular waveguide loaded with a
dielectric rod The waveguide length is 400mm and the wall thickness is
05mm The dielectric rods diameter is 207mm The dielectric rod is
extended 05 wavelength beyond the waveguide open end The dielectric
constant εr is changed and the feeds performance is observed
Fig 41 Geometry of a circular waveguide loaded with a uniform dielectric
rod
-41-
Fig 42 is the radiation pattern of the feed with εr = 25 and L = 05λ0 at
9GHz E- and H-plane 10-dB beamwidths are 810 and 807 degrees
respectively The front-to-back ratio is 18dB The antenna gain is 71dB
(a)
(b)
Fig 42 Radiation pattern at 9GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 05λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-42-
Fig 43 shows the radiation pattern of the feed with εr = 21 at 10GHz
E- and H-plane 10-dB beamwidths are 70 and 71 degrees respectively The
front-to-back ratio is 19dB The antenna gain is 83dB
(a)
(b)
Fig 43 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 21 and L = 05λ0 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-43-
Fig 44 shows the radiation pattern of the feed with εr = 30 at 8GHz
E- and H-plane 10-dB beamwidths are 83 and 824 degrees respectively The
front-to-back ratio is 17dB The antenna gain is 73dB
(a)
(b)
Fig 44 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 30 and L = 05λ0 at 8GHz (a) 2D radiation pattern
and (b) E- and H-plane patterns
-44-
Fig 45 shows the radiation pattern of the feed with εr = 50 at 18GHz
E- and H-plane 10-dB beamwidths are 56 and 54 degrees respectively The
front-to-back ratio is 27dB The antenna gain is 105dB The feed has a good
pattern symmetry and low back radiation
(a)
(b)
Fig 45 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 50 and L = 05λ0 at 18GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-45-
Fig 46 is the radiation pattern of the feed with εr = 25 and L = 10λ0 at
10GHz E- and H-plane 10-dB beamwidths are 50 and 48 degrees
respectively The front-to-back ratio is 16dB The antenna gain is 105dB
(a)
(b)
Fig 46 Radiation pattern at 10GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 10λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-46-
Fig 47 shows the geometry of a circular waveguide with a tapered
dielectric rod The designed feed has the following dimension L = 1λ0 d =
1λ0 and εr =25 at 10GHz The waveguide length is 40mm and the wall
thickness is 05mm
L
Dielectricd3
Fig 47 Geometry of a circular waveguide loaded with a tapered dielectric
rod
Fig 48 shows the radiatio pattern of the designed feed E- and H-plane
10-dB beamwidths are 575 and 564 degrees respectively The front-to-back
ratio is 377dB The antenna gain is 94dB The designed feed has an
excellent beamwidth symmetry and a very low back radiation
-47-
(a)
(b)
Fig 48 Radiation pattern of a circular waveguide loaded with a tapered
dielectric rod with L = 1λ0 d = 1λ0 and εr =25 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-48-
Fig 49 shows the geometry of a spherical ended dielectric rod feed
diameter of 06λ0 at 10GHz with a dielectric constant of 25 and L= 03λ0
Fig 410 shows the radiation patterns of the designed feed E- and H-plane
10-dB beamwidths are both 63 degrees The front-to-back ratio is 24dB The
antenna gain is 864dB
Fig 49 Geometry of a circular waveguide loaded with a spherical ended
dielectric rod
-49-
(a)
(b)
Fig 410 Radiation pattern of a circular waveguide loaded wht a spherical
ended dielectric rod with d = 06λ0 L = 03λ0 and εr =25 at 10GHz (a) 3D
radiation pattern and (b) E- and H-plane patterns
-50-
V Design of a Broadband Circular Waveguide Feed
In this chapter the design of a broadband circular waveguide feed is
presented At microwave frequencies the feed is often a circular waveguide
with chokes and corrugations around the aperture Chokes and corrugations
equalize E- and H-plane patterns and reduce the back radiation
The proposed feed is designed to operate over 10-18GHz The design starts
with the optimization of the coaxial-to-rectangular waveguide adapter
employed for good mode purity over a broad frequency range Next a
rectangular-to-circular waveguide transition is optimized Finally chokes and
corrugations are designed for improved pattern symmetry and low back
radiation
The proposed feed structure is shown in Fig 51 The feed consist of the
following parts a coaxial-to-rectangular waveguide adapter a rectangular-to-
circular waveguide transition a circular waveguide section four quarter-wave
chokes around the feeds aperture and four corrugations on the feeds outer
surface
The computer simulation shows the above arrangement offers good radiation
patterns over a broad frequency range The broadband operation is obtained
by exciting the TE11 mode in the circular waveguide using the TE10 mode of
the rectangular waveguide which is in turn excited by a coaxial probe
-51-
Chokes
Coaxial-to-waveguide transition
Circular wavguide
Corrugations
Mode transition
(a)
(b)
Fig 51 Structure of the proposed broadband circular waveguide feed
(a) CAD model and (b) cross-sectional view
For the coaxial-to-rectangular waveguide adapter an SMA connector with
the probe diameter of 127 mm is employed The coaxial probe inserted into
the waveguide energizes the feed and excites the dominant TE10 mode in
-52-
the rectangular waveguide The impedance matching is achieved by adjusting
the probe distance sp from the back short and the probe length lp
(a)
(b)
Fig 52 Reflection coefficient of the coaxial-to-rectangular adapter versus
(a) probe length lp and (b) the probe position sp
Fig 52 shows the reflection coefficient versus the various values of probe
lengths lp and probe positions sp The probe length lp is adjusted to obtain
antenna impedance matching and the probe distance sp is adjusted to obtain a
-53-
desired resonant frequency
Next a transition between rectangular and circular waveguide is designed
The transition section converts the TE10 mode in the rectangular waveguide to
TE11 mode in the circular waveguide and vice versa The transition is built
in a form of a taper for easy fabrication[22]
(a)
(b)
Fig 53 Structure of the rectangular-to-circular waveguide transition
(a) 3D view and (b) cross sectional view
The dimensions of the final optimized transition are as follows The length
of the rectangular waveguide section is 143mm The rectangular waveguides
width a and height b are 207mm and 857mm respectively The length of
the circular waveguide section is 143mm The inside diameter of the circular
-54-
waveguide is 207mm(097 wavelength at 14GHz) The length of transition
region ltr is 4465mm(approximately equal to 2λ0 at 14GHz) Fig 54 shows
the field distribution inside the mode converter
(a)
(b)
Fig 54 Field distribution inside the mode converter at
(a) 10GHz (b) 14GHz and (c) 18GHz
-55-
(c)
Fig 54 continued
Finally multiple chokes are investigated Figs 55 56 and 57 show the
feed performance without chokes The reflection coefficient is less than -10dB
over 10-19GHz The antenna has a gain of 921dB to 1189dB over
10-19GHz
Fig 55 Reflection coefficient of the broadband circular waveguide feed
without chokes and corrugations
-56-
(a)
(b)
(c)
Fig 56 E- and H-plane patterns of the broadband circular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-57-
(d)
(e)
Fig 56 continued
-58-
(a)
(b)
Fig 57 2D radiation patterns of the broadband cicular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-59-
(c)
(d)
Fig 57 continued
-60-
(e)
Fig 57 continued
To achieve equal beamwidths in E and H planes over a wide frequency
range chokes and corrugations are employed Table51 summarizes the
performance of a feed without chokes and corrugations
Table 51 Performance of the broadband circular waveguide feed without
chokes and corrugations
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
1000 940 6061 15
1200 972 6159 17
1400 920 5957 21
1600 1070 4751 29
1800 1188 5352 21
-61-
Four quarter-wavelength chokes are introduced in the feed design which
has a slot depth of 75mm and slot width of 09mm The choke slot spacing
is 18mm The choke design is investigated by applying the choke one by
one and the effect on the E- and H-plane patterns are observed as illustrated
in Figs 58 and 59 The use of chokes makes the E-plane pattern narrower
The H-plane pattern is not affected Chokes increase the gain slightly and
reduce back radiation
(a)
(b)
Fig 58 Effect of chokes on the E-plane pattern of the broadband circular
waveguide feed at (a) 10GHz(b) 12GHz (c) 14GHz (d) 16GHz and (e)
18GHz
-62-
(c)
(d)
(e)
Fig 58 continued
-63-
(a)
(b)
(c)
Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-64-
(d)
(e)
Fig 59 continued
-65-
Fig 510 shows the feed performance versus the choke depth When the
choke depth is varied from 535mm to 95mm the E- and H-plane patterns
are strongly affected The optimum value of choke depth is 75mm(035λ0 at
14GHz) which gives equal E- and H-plane radiation patterns and leads to
low back radiation
Fig 511 shows the feed performance versus the choke slot width tch The
choke slot width is varied from 09mm to 21mm Radiation patterns and
reflection coefficients are not sensitive to the choke slot width The final
choke slot width is selected to be 09mm considering the feed diameter
minimization and the manufacturability The overall diameter of the proposed
feed is 369mm which is increased from the 207mm of the waveguide
inside diameter due to the use of four chokes
-66-
(a)
(b)
(c)
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection coefficient
-67-
(a)
(b)
(c)
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and (c)
reflection coefficient
-68-
Next we investigated corrugations placed on the outer wall of the feed
Four corrugations applied to the outer surface of the circular waveguide The
corrugation depth is 465mm(0215λ0 at 14GHz) The primary purpose of
using corrugations is to further reduce the back radiation Increasing the
number of corrugations beyond four has little effect in reducing the back
radiation
Figs 512 and 513 show the effect of corrugations on the E- and H-plane
patterns Fig 514 shows the parametric study of the corrugation depth lcor
The corrugation depth is varied from 40mm and 645mm The optimum
value of the corrugation depth is found to be 465mm
-69-
(a)
(b)
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern at (a) 12GHz and (b) 14GHz
-70-
(a)
(b)
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern at (a) 12GHz and (b) 14GHz
-71-
(a)
(b)
(c)
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection coefficient
-72-
The phase center location is important in placing the feed in a reflector
antenna[8] The phase center variation with frequency should be small Fig
515 shows the effect of chokes and corrugations on the phase center The
curve with circle corresponds to the case without chokes and corrugations
The phase center varies from -326mm and -190mm away from the feeds
aperture plane It means the phase center is located inside the waveguide
The curve with triangles corresponds to the case with chokes The curve with
squares to the case with chokes and corrugations The phase center varies
from 0mm to -302mm
From Fig 515 we can observed that phase center variation reduced by the
corrugation and three cases phase center calculated in φ=450 plane
parameter sweep values are given in Table 52
10 12 14 16 181
0
-1
-2
-3
-4
-5
-6
Pha
se c
ente
r (m
m)
Frequency (GHz)
choke+corrugatuion without choke corrugation with choke
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
-73-
Frequency
(GHz)
Phase center from the aperture plane
(mm)
Without
chokes and
corrugations
With
chokes
With chokes
and
corrugations
1000 -326 062 000
1100 -187 030 -002
1200 -563 -208 -065
1300 -296 -154 -202
1400 -319 -314 -302
1500 -201 -203 -241
1600 -242 -233 -207
1700 -208 -208 -186
1800 -190 -157 -132
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
Based on the foregoing parametric studies optimum dimensions of the
broadband circular waveguide feed are obtained as shown in Table 53
-74-
Table 53 Optimum dimensions of the broadband circular waveguide feed
Parameter Designation Value (mm)
2a Waveguide inside diameter 2070
d Waveguide outside diameter 3690
lcrLength of the circular waveguide section 1430
m Distance between the aperture plane and the first corrugation 950
xDistance from the last corrugation to the end of the cylindrical outer surface
550
ltrLength of the rectangular-to-circularwaveguide transition 4465
lrcLength of the rectangular waveguide section 1430
tch Choke slot width 090
lch Choke depth 750
t Choke metal width 090
lcor Corrugation depth 465
tcor Corrugation metal width 100
s Corrugation slot width 10
lp Probe length 530
sp Probe position from the back short 530
din Probe diameter 127
b Inside height of the rectangular waveguide 857
tw Waveguide wall thickness 500
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-vii-
Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 63
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection
coefficient middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 66
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and
(c) reflection coefficient middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 67
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 69
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 70
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection
coefficient middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 71
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 72
Fig 516 Reflection coefficient of the designed broadband circular
waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 75
Fig 517 2D radiation patterns of the designed broadband circular
waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 76
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 79
Fig 519 Phase center variation of the designed broadband circular
waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 81
-viii-
Fig 520 Photograph of the fabricated broadband circular waveguide feed 82
Fig 521 Reflection coefficient of the fabricated broadband circular
waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 82
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 84
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 84
-ix-
List of Tables
Table 21 Properties of a circular waveguide open end radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 10
Table 22 Properties of a square waveguide open end radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 15
Table 23 Properties of the probe-fed circular waveguide radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 20
Table 24 Properties of the probe-fed square waveguide radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 24
Table 31 Dimensions of the designed narrow-band circular feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 33
Table 32 Performance of the narrow-band circular waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 37
Table 51 Performance of the broadband circular waveguide feed without
chokes and corrugations middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 60
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 73
Table 53 Optimum dimensions of the broadband circular waveguide feed 74
Table 54 Performance of the designed broadband circular waveguide feed 81
-1-
I Introduction
The horns and waveguides are known for their high efficiency and
structural simplicity They are popular choices for feeding for reflectors in
high-gain antenna applications such as satellite and point-to-point microwave
communication links The theory of reflector antenna was developed in the
1940s and has been used to calculate the radiation patterns of various
reflector structures[1]
The basic structure of a prime-focus reflector antenna consists of a
parabolic reflecting surface a feed and its support The placement of the feed
is such that its phase center is at the focal point of the parabolic reflecting
surface The feed is often a circular waveguide because of its symmetric
radiation pattern with low back radiation and low cross polarization The
circular waveguide feed must have a small diameter to reduce the aperture
blockage of the reflector antenna[3]
A radiation pattern with a good circular symmetry in the main beam can
be found from circular waveguide feeds with dominant TE11 mode excitation
The radiation patterns depends on the diameter and wall thickness of the
waveguide[4] A coaxial probe can be inserted into a short-circuited circular
waveguide in the form of a coaxial-to-waveguide transition The diameter of
the circular waveguide is chosen such that only the dominant mode
propagates
When the waveguide dimension does not provide a circular symmteric
-2-
pattern a choke or multiple chokes around the aperture wall can be
employed to equalize radiation patterns and keep the back radiation in low
level If chokes are not enough for the suppression of the back radiation
corrugations on the outer surface of the feed is one way to reduce the back
radiation
In this thesis a broadband circular waveguide feed is developed for
prime-focus reflector antenna application After investigating the radiation
properties of simple circular and square waveguides methods are investigated
for bandwidth enhancement back radiation suppression and beamwidth
equalization in the circular waveguide feed
The first type of the circular waveguide feed consists of a probe-fed
circular waveguide a single quarter-wave choke on the aperture wall and a
dielectric-ring beamwidth equalizer Due to the simple feeding method the
first feed operates over 171-197GHz(141) which is not broadband in the
strict sense of the word
The second feed consists of a coaxial-to-rectangular waveguide transition a
rectangular-to-circular waveguide transition a circular waveguide section four
quarter-wave chokes on the aperture wall and four quarter-wave corrugations
on the feeds outer surface Due to the complicated feeding method the
second feed operates over 10-18GHz(571)
This thesis is arranged as follows Chapter I gives an introduction to the
thesis related works and objectives are stated Chapter II describes the
structure and excitation of the circular and square waveguide and the
operation of the coaxial-to-waveguide transitions Chapter III describes a
compact feed horn design and its fabrication and measurement Chapter IV
-3-
presents dielectric rod feed and its simulated performances Chapter V gives
design and optimization of feed for parabolic reflector antenna In this
chapter includes the detailed information of design procedures and operating
principle also the simulated and measured performances are provided Finally
conclusion is given in the Chapter VI
-4-
II Analysis of Circular and Square Waveguide Feeds
21 Circular Waveguide Radiator
Before design a complicated circular waveguide feed it is helpful to
investigate the impedance and radiation properties of a circular waveguide
open end
The circular waveguide is a cylindrical hollow metallic pipe with a uniform
circular section of radius a Circular waveguides are normally designed to
operate only with the dominant mode The dominant mode in a waveguide is
the mode having the lowest cutoff frequency given by equation (21)
(21)
where
(22)
and a is the waveguide radius The following chart[2] and table show the
cutoff frequencies of various modes in a circular waveguide
-5-
Modes c al11TEc cf f
TE11 341259 100000
TM01 261274 130613
TE21 205720 165885TE01 163979 208111
TM11 163979 208111TE31 149557 228180
TM21 122345 278932TE41 118159 288813
TE12 117852 289566
TM02 113824 299813TE02 0897986 380027
The recommended frequency range of the commercial circular waveguide is
given by the following equation This assumes that the TM01 mode is not
generated or suppressed if generated
11 21 11TE TE TE115 095 158 32 bandwidthc c cf f f fpound pound = reg (23)
Fig 21 shows the geometry of a circular waveguide with a diameter of 2a
When 2a is 2053mm the cutoff frequency of the TE11 mode is 857GHz
According to (23) the useful operating frequency range is from
986-1354GHz
Fig 22 shows the reflection of this waveguide excited with the dominant
TE11 mode The waveguide length l is 60mm The reflection occurs at the
open end of the circular waveguide The reflection coefficient is less than
-15dB over 10-18GHz
-6-
Fig 21 Geometry of a circular waveguide open end radiator
Fig 23 shows a 2D gain pattern of this waveguide antenna The
waveguide antenna has a gain of 80dB 99dB and 115dB at 10GHz
14GHz and 18GHz respectively Fig 24 shows the E- and H-plane patterns
of the circular waveguide antenna Table 21 summarizes the properties of a
circular waveguide antenna
Fig 22 Reflection coefficient of a circular waveguide open end radiator
-7-
(a)
(b)
Fig 23 2D radiation pattern of the circular waveguide open end radiator
at (a)10GHz (b) 14GHz and (c) 18GHz
-8-
(c)
Fig 23 continued
-9-
(a)
(b)
(c)
Fig 24 E-plane and H-plane patterns of the circular waveguide open end
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-10-
Table 21 Properties of a circular waveguide open end radiator of diameter
2053mm
Frequency(GHz)-10dB Beamwith(deg) Front-to-Back
Ratio(dB)E plane H plane
10 67 73 12
14 58 60 18
18 41 50 21
In a circular waveguide radiatoλr a good pattern symmetry and low back
radiation is obtained at 14GHz where 2aλ = 096
22 Square Waveguide Radiator
A square waveguide is often used as a dual-polarized feed To operate the
cutoff frequency of the dominant mode a square-waveguide wall width a
must be greater than one half of a wavelength The modes with cutoff
frequencies equal to or smaller than the operational frequency can exist inside
the waveguide wall The lower cutoff frequency and cutoff wavelength for
square waveguide is determined by the following equations
TE
(24)
TE
(25)
The next higher-order mode is TE11 mode with the cutoff wavelength
given by
-11-
TE
(26)
Similar to the circular waveguide the recommended operating frequency range
of a square waveguide is given by
TEleleTE
TErarr bandwidth (27)
Fig 25 shows the geometry of a square waveguide with a dimension of a
When a is 157mm the cutoff frequency is 95GHz The recommended
operating frequency of this waveguide is from 109GHz to 155GHz
Fig 26 shows the reflection of this waveguide excited with the dominant
TE10 mode The reflection coefficient is less than -15dB over 10-20GHz
Fig 25 Geometry of a square waveguide open end radiator
Fig 27 and shows the 2D radiation pattern of a square waveguide antenna
excited with the dominant TE10 mode The antenna has a gain of 73dB
85dB and 102dB at 10GHz 14GHz and 18GHz respectively Fig 28
shows the E- and H-plane radiation patterns of a square waveguide radiator
Table 22 summarizes the properties of a square waveguide open end radiator
-12-
Fig 26 Reflection coefficient of a square waveguide open end radiator
(a)
Fig 27 2D radiation patterns of a square waveguide radiator
at (a) 10GHz (b) 14GHz and (c) 18GHz
-13-
(b)
(c)
Fig 27 continued
-14-
(a)
(b)
(c)
Fig 28 E-plane and H-plane patterns of square waveguide open radiator
at (a) 10GHz(b) 14GHz and (c) 18GHz
-15-
Table 22 Properties of a square waveguide open end radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 69 71 11
14 47 60 25
18 58 62 16
The radiation pattern symmetry and back radiation performance of the
square waveguide are inferior to those of a circular waveguide
23 Probe-Fed Circular Waveguide Radiator
In Section 21 the radiation properties of a TE11-mode excited waveguide
is investigated In this section a circular waveguide fed by a coaxial probe
shown in Fig 29 is studied
The coaxial probes diameter is 127mm With the Teflon dielectric the
50-ohm coaxial lines outer conductor has a diameter of 41mm For a
circular waveguide the wave impedance of the TE11 mode is given by
∙ (28)
where λg is the guided wavelength given by
(29)
-16-
(a) (b)
Fig 29 Probe-fed circular waveguide radiator (a) Front view and (b) side
view
The combination of the probe length and the probe position from the
shorted wall enables a good impedance matching The probe distance sp from
the back short is close to a quarter wavelength at the design frequency
The designed feed has the following dimension d = 2053mm lp = 42
mm sp = 534mm wall thickness = 05mm and feed length = 400mm
Fig 210 shows the reflection coefficient of the designed probe-fed
circular waveguide radiator The reflection coefficient is less than -10dB over
138-187GHz Fig 211 and 212 shows the E-plane and H-plane radiation
patterns and 2D radiation patterns of the coaxial-to-circular waveguide
transition The radiation patterns symmetry distorted because of the high order
modes The coaxial-to-circular waveguide transition has 73dB 84dB and
79dB gain at 10GHz 14GHz and 18GHz frequencies respectively Table 23
shows the properties of the coaxial-to-circular waveguide transition
-17-
Fig 210 Reflection coefficient of the probe-fed circular waveguide radiator
(a)
Fig 211 2D radiation pattern of the probe-fed circular waveguide radiator
at (a) 10GHz (b) 14GHz and (c) 18GHz
-18-
(b)
(c)
Fig 211 continued
-19-
(a)
(b)
(c)
Fig 212 E- and H-plane patterns of the probe-fed circular waveguide
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-20-
Table 23 Properties of the probe-fed circular waveguide radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 73 70 1414 83 57 17
18 60 52 30
When a circular waveguide radiator is fed by a coaxial probe its radiation
properties are not good due to the excitation of higher-order modes
Therefore a probe-fed circular waveguide radiator can be used as a feed only
over a narrow frequency range
24 Probe-Fed Square Waveguide Radiator
In this section a probe-fed square waveguide radiator is investigated Fig
213 shows a coaxial probe-fed square waveguide radiator The designed
radiator has the following dimension a = b = 157mm lp = 35 mm sp =
50 mm wall thickness = 05mm and feed length = 40mm
(a) (b)
Fig 213 Probe-fed square waveguide radiator (a) Front view and (b) side
view
-21-
Fig 214 shows the 2D radiation patterns of the radiator at 10GHz
14GHz and 18GHz Fig 215 shows E- and H-plane patterns of the radiator
Fig 216 shows the reflection coefficient of the probe-fed square waveguide
radiator The reflection coefficient is less than -10dB over 13-20GHz Table
24 summarizes the properties of the probe-fed square waveguide radiator
(a)
Fig 214 2D radiation patterns of the probe-fed square waveguide radiator at
(a) 10GHz (b) 14GHz and (c) 18GHz
-22-
(b)
(c)
Fig 214 continued
-23-
(a)
(b)
(c)
Fig 216 E-plane and H-plane patterns of the probe-fed square waveguide
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-24-
Fig 216 Reflection coefficient of the probe-fed square waveguide radiator
Table 24 Properties of the probe-fed square waveguide radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 73 71 12
14 85 63 1418 27 65 28
When a square waveguide radiator is fed by a coaxial probe its radiation
properties are not good due to the excitation of higher-order modes as in the
case of the probe-fed circular waveguide radiator A probe-fed square
waveguide radiator can be used as a feed only over a narrow frequency
range
-25-
III Design of Compact Circular Waveguide Feeds
In this chapter the feed design is presented for a prime-focus reflector
antenna The prime-focus paraboloid reflector is one of the most commonly
used high-gain antenna It has been used in earth-station antennas and radio
telescopes It consists of a paraboloid reflector with a feed system at its focal
point
The feed should radiate a low level of cross-polar power over the
operating frequency These conditions not easy to achieve and most prime
focus feeds are compromises The shape and characteristic of the radiation
pattern of the feed are the most important parameter because these will
directly influence the fields which are directed at a reflector[6] Other
electrical factors which relevant to the choice of a feed are the cross-polar
level the gain efficiency the bandwidth and impedance matching
31 Narrow-Band Circular Waveguide Feed
Fig 31 shows the proposed narrow-band circular waveguide feed and its
design variables The feed consists of a circular waveguide open end excited
by a TE11 dominant mode A quarter wave choke is applied along the
circular aperture of the waveguide to equalize E- and H-plane radiation
patterns and to suppress the back radiation A dielectric ring is used to
control the radiation pattern and change the power distribution over the
aperture The control of the amplitude over the aperture are essential to the
design of symmetric radiation pattern The material used for dielectric loading
-26-
is the monocast(MC) nylon with a dielectric constant of 30 The feed is
designed to operate over 171-197GHz
(a)
(b)
Fig 31 Narrow-band circular waveguide feed (a) CAD model and (b) a
cross sectional view
The impedance matching is achieved by a proper combination of the probe
height lp and its distance sp from the waveguide shorted end Here the
-27-
circular waveguide is terminated with an open end with a wall thickness of
2mm radiating into the free space
Fig 32 shows the effect of the probe length lp and the probe distance sp
on the reflection coefficient The best performance is obtained when lp =
363mm and sp = 616mm The feeds reflection coefficient is less than -10dB
over 170-195GHz
(a)
(b)
Fig 32 Effect of the (a) the probe length lp and (b) the probe
distance sp on the reflection coefficient
-28-
Fig 33 shows the effect of the choke depth The E-plane pattern is more
sensitive to the choke depth than the H-plane pattern The choke depth has a
strong influence on the reflection coefficient when it is 360mm By properly
choosing the choke depth we can equalize the E- and H-plane patterns The
optimum value of the choke depth is 410mm which is 0249λ0 at 1825GHz
The choke slot width tch in the range of 06-12mm has almost no effect
on the H-plane pattern and the reflection coefficient For the E-plane pattern
tch of 12mm has some effect on the E-plane radiation pattern as shown in
Fig 34
Fig 35 shows the feed performance versus the dielectric ring length We
observe in Fig 35 that the dielectric length ld has an optimum value of
1168mm which does no effect on the H-plane pattern and tha the value of
1048mm has some effect on the E-plane pattern and the reflection
coefficient
Fig 36 shows E-plane and H-plane patterns and the reflection coefficient
versus the dielectric thickness With the optimum value of the dielectric
thickness t obtained from the Fig 36 is 155mm The larger values of td has
much stronger effects on the E-plane pattern and the reflection coefficient
The H-plane pattern is not sensitive to the dielectric ring thickness
-29-
(a)
(b)
(c)
Fig 33 Feed performance versus the choke depth (a) E-plane pattern
(b) H-plane pattern and (c) reflection coefficient
-30-
(a)
(b)
(c)
Fig 34 Feed performance versus the choke slot width (a) E-plane pattern
(b) H-plane pattern and (c) reflection coefficient
-31-
(a)
(b)
(c)
Fig 35 Feed performance versus the dielectric ring length (a) E-plane
pattern (b) H-plane pattern and (c) reflection coefficient
-32-
(a)
(b)
(c)
Fig 36 Feed performance versus the dielectric ring thickness (a) E-plane
pattern(b) H-plane pattern and (c) reflection coefficient
-33-
From the above parametric analysis an optimum feed design is obtained
The result is shown in Table 31 Fig 37 shows the 2D gain patterns of
designed feed The antenna has a gain of 903dB 933dB and 956dB at
171GHz 1825GHz and 19GHz respectively
Fig 38 shows E- and H-plane radiation patterns of the designed feed The
feed has E- and H-plane 10-dB beamwidths of 60 and 59 degrees at 17GHz
The feed has a front-to-back ration of 1900dB 2490dB and 2200dB at
171GHz 1825GHz and 19GHz respectively Table 32 summarizes the
performance of the designed narrow-band circular waveguide feed
The designed feed has a greatly improved performance over that of a
simple coax-fed feed described in Section 23
Table 31 Dimensions of the designed narrow-band circular feed
Parameter Designation Value(mm)
a Waveguide inside radius 640
l Feed length 2890
lp Probe length 363
sp Probe position from the back short 616
din Probe diameter 127
dout Diameter of coaxial cables outer conductor 400
t Thickness of choked wall 050
tch Choke slot width 100
lch Choke depth 410
ld Dielectric ring length 1168
td Dielectric ring thickness 155
d1 Waveguide outside diameter 1680
-34-
(a)
(b)
Fig 37 2D gain patterns of the narrow-band circular waveguide feed at
(a) 17GHz (b) 1825GHz and (c) 19GHz
-35-
(c)
Fig 37 continued
-36-
(a)
(b)
(c)
Fig 38 E- and H-plane patterns of the narrow-band circular waveguide feed
at (a) 10GHz (b) 1825GHz and (c) 195GHz
-37-
Frequency(GHz)
Gain(dB)
E-H-plane10-dB beamwidths
(deg)
Front-to-back ratio(dB)
Phase centerlocation
(From feeds aperture plane
toward reflector)
(mm)
1700 903 6059 20 062
1825 933 6060 25 004
1900 956 5759 22 007
Table 32 Performance of the narrow-band circular waveguide feed
The designed narrow-band feed is fabricated and its performance is
measured and compared with the simulation results The designed feed is
fabricated in a numerically-controlled machining center The fabricated antenna
is shown in Fig 39
Fig 39 Photograph of the fabricated feed
-38-
Fig 310 shows a comparison of the measured and simulated reflection
coefficients The measured reflection coefficient is less than -10dB over
171-197GHz The agreement between simulated and measured results are
good
Fig 311 shows the E- and H-plane patterns of the fabricated feed at
187GHz The feed has 90dB gain simulation and measurement results are in
good agreement
The fabricated antennarsquos 10dB beamwidth is 60 degrees in both E and H
planes at 187GHz The front-to-back ratio is 21dB
Fig 310 Reflection coefficient of the fabricated feed
-39-
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Fee
d H
orn
Gain
- d
B
Angle - degree
(a)
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Feed H
orn
Gain
- d
B
Angle - degree
(b)
Fig 311 Gain patterns of the fabricated feed at 187 GHz (a) E-plane and
(b) H-plane
-40-
IV Design of Circular Waveguide Feeds Loaded with a
Dielectric Rod
In this section circular waveguide feeds loaded with a dielectric rod feed
are investigated A comprehensive discussion of the circular waveguide loaded
with a dielectric rod is given by Kumar[7] Inserting a dielectric material
inside the circular waveguide improves the E- and H-plane pattern symmetry
In general dielectric-loaded circular waveguide feeds show good performance
only over a narrow bandwidth
Fig 41 shows the geometry of a circular waveguide loaded with a
dielectric rod The waveguide length is 400mm and the wall thickness is
05mm The dielectric rods diameter is 207mm The dielectric rod is
extended 05 wavelength beyond the waveguide open end The dielectric
constant εr is changed and the feeds performance is observed
Fig 41 Geometry of a circular waveguide loaded with a uniform dielectric
rod
-41-
Fig 42 is the radiation pattern of the feed with εr = 25 and L = 05λ0 at
9GHz E- and H-plane 10-dB beamwidths are 810 and 807 degrees
respectively The front-to-back ratio is 18dB The antenna gain is 71dB
(a)
(b)
Fig 42 Radiation pattern at 9GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 05λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-42-
Fig 43 shows the radiation pattern of the feed with εr = 21 at 10GHz
E- and H-plane 10-dB beamwidths are 70 and 71 degrees respectively The
front-to-back ratio is 19dB The antenna gain is 83dB
(a)
(b)
Fig 43 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 21 and L = 05λ0 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-43-
Fig 44 shows the radiation pattern of the feed with εr = 30 at 8GHz
E- and H-plane 10-dB beamwidths are 83 and 824 degrees respectively The
front-to-back ratio is 17dB The antenna gain is 73dB
(a)
(b)
Fig 44 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 30 and L = 05λ0 at 8GHz (a) 2D radiation pattern
and (b) E- and H-plane patterns
-44-
Fig 45 shows the radiation pattern of the feed with εr = 50 at 18GHz
E- and H-plane 10-dB beamwidths are 56 and 54 degrees respectively The
front-to-back ratio is 27dB The antenna gain is 105dB The feed has a good
pattern symmetry and low back radiation
(a)
(b)
Fig 45 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 50 and L = 05λ0 at 18GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-45-
Fig 46 is the radiation pattern of the feed with εr = 25 and L = 10λ0 at
10GHz E- and H-plane 10-dB beamwidths are 50 and 48 degrees
respectively The front-to-back ratio is 16dB The antenna gain is 105dB
(a)
(b)
Fig 46 Radiation pattern at 10GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 10λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-46-
Fig 47 shows the geometry of a circular waveguide with a tapered
dielectric rod The designed feed has the following dimension L = 1λ0 d =
1λ0 and εr =25 at 10GHz The waveguide length is 40mm and the wall
thickness is 05mm
L
Dielectricd3
Fig 47 Geometry of a circular waveguide loaded with a tapered dielectric
rod
Fig 48 shows the radiatio pattern of the designed feed E- and H-plane
10-dB beamwidths are 575 and 564 degrees respectively The front-to-back
ratio is 377dB The antenna gain is 94dB The designed feed has an
excellent beamwidth symmetry and a very low back radiation
-47-
(a)
(b)
Fig 48 Radiation pattern of a circular waveguide loaded with a tapered
dielectric rod with L = 1λ0 d = 1λ0 and εr =25 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-48-
Fig 49 shows the geometry of a spherical ended dielectric rod feed
diameter of 06λ0 at 10GHz with a dielectric constant of 25 and L= 03λ0
Fig 410 shows the radiation patterns of the designed feed E- and H-plane
10-dB beamwidths are both 63 degrees The front-to-back ratio is 24dB The
antenna gain is 864dB
Fig 49 Geometry of a circular waveguide loaded with a spherical ended
dielectric rod
-49-
(a)
(b)
Fig 410 Radiation pattern of a circular waveguide loaded wht a spherical
ended dielectric rod with d = 06λ0 L = 03λ0 and εr =25 at 10GHz (a) 3D
radiation pattern and (b) E- and H-plane patterns
-50-
V Design of a Broadband Circular Waveguide Feed
In this chapter the design of a broadband circular waveguide feed is
presented At microwave frequencies the feed is often a circular waveguide
with chokes and corrugations around the aperture Chokes and corrugations
equalize E- and H-plane patterns and reduce the back radiation
The proposed feed is designed to operate over 10-18GHz The design starts
with the optimization of the coaxial-to-rectangular waveguide adapter
employed for good mode purity over a broad frequency range Next a
rectangular-to-circular waveguide transition is optimized Finally chokes and
corrugations are designed for improved pattern symmetry and low back
radiation
The proposed feed structure is shown in Fig 51 The feed consist of the
following parts a coaxial-to-rectangular waveguide adapter a rectangular-to-
circular waveguide transition a circular waveguide section four quarter-wave
chokes around the feeds aperture and four corrugations on the feeds outer
surface
The computer simulation shows the above arrangement offers good radiation
patterns over a broad frequency range The broadband operation is obtained
by exciting the TE11 mode in the circular waveguide using the TE10 mode of
the rectangular waveguide which is in turn excited by a coaxial probe
-51-
Chokes
Coaxial-to-waveguide transition
Circular wavguide
Corrugations
Mode transition
(a)
(b)
Fig 51 Structure of the proposed broadband circular waveguide feed
(a) CAD model and (b) cross-sectional view
For the coaxial-to-rectangular waveguide adapter an SMA connector with
the probe diameter of 127 mm is employed The coaxial probe inserted into
the waveguide energizes the feed and excites the dominant TE10 mode in
-52-
the rectangular waveguide The impedance matching is achieved by adjusting
the probe distance sp from the back short and the probe length lp
(a)
(b)
Fig 52 Reflection coefficient of the coaxial-to-rectangular adapter versus
(a) probe length lp and (b) the probe position sp
Fig 52 shows the reflection coefficient versus the various values of probe
lengths lp and probe positions sp The probe length lp is adjusted to obtain
antenna impedance matching and the probe distance sp is adjusted to obtain a
-53-
desired resonant frequency
Next a transition between rectangular and circular waveguide is designed
The transition section converts the TE10 mode in the rectangular waveguide to
TE11 mode in the circular waveguide and vice versa The transition is built
in a form of a taper for easy fabrication[22]
(a)
(b)
Fig 53 Structure of the rectangular-to-circular waveguide transition
(a) 3D view and (b) cross sectional view
The dimensions of the final optimized transition are as follows The length
of the rectangular waveguide section is 143mm The rectangular waveguides
width a and height b are 207mm and 857mm respectively The length of
the circular waveguide section is 143mm The inside diameter of the circular
-54-
waveguide is 207mm(097 wavelength at 14GHz) The length of transition
region ltr is 4465mm(approximately equal to 2λ0 at 14GHz) Fig 54 shows
the field distribution inside the mode converter
(a)
(b)
Fig 54 Field distribution inside the mode converter at
(a) 10GHz (b) 14GHz and (c) 18GHz
-55-
(c)
Fig 54 continued
Finally multiple chokes are investigated Figs 55 56 and 57 show the
feed performance without chokes The reflection coefficient is less than -10dB
over 10-19GHz The antenna has a gain of 921dB to 1189dB over
10-19GHz
Fig 55 Reflection coefficient of the broadband circular waveguide feed
without chokes and corrugations
-56-
(a)
(b)
(c)
Fig 56 E- and H-plane patterns of the broadband circular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-57-
(d)
(e)
Fig 56 continued
-58-
(a)
(b)
Fig 57 2D radiation patterns of the broadband cicular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-59-
(c)
(d)
Fig 57 continued
-60-
(e)
Fig 57 continued
To achieve equal beamwidths in E and H planes over a wide frequency
range chokes and corrugations are employed Table51 summarizes the
performance of a feed without chokes and corrugations
Table 51 Performance of the broadband circular waveguide feed without
chokes and corrugations
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
1000 940 6061 15
1200 972 6159 17
1400 920 5957 21
1600 1070 4751 29
1800 1188 5352 21
-61-
Four quarter-wavelength chokes are introduced in the feed design which
has a slot depth of 75mm and slot width of 09mm The choke slot spacing
is 18mm The choke design is investigated by applying the choke one by
one and the effect on the E- and H-plane patterns are observed as illustrated
in Figs 58 and 59 The use of chokes makes the E-plane pattern narrower
The H-plane pattern is not affected Chokes increase the gain slightly and
reduce back radiation
(a)
(b)
Fig 58 Effect of chokes on the E-plane pattern of the broadband circular
waveguide feed at (a) 10GHz(b) 12GHz (c) 14GHz (d) 16GHz and (e)
18GHz
-62-
(c)
(d)
(e)
Fig 58 continued
-63-
(a)
(b)
(c)
Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-64-
(d)
(e)
Fig 59 continued
-65-
Fig 510 shows the feed performance versus the choke depth When the
choke depth is varied from 535mm to 95mm the E- and H-plane patterns
are strongly affected The optimum value of choke depth is 75mm(035λ0 at
14GHz) which gives equal E- and H-plane radiation patterns and leads to
low back radiation
Fig 511 shows the feed performance versus the choke slot width tch The
choke slot width is varied from 09mm to 21mm Radiation patterns and
reflection coefficients are not sensitive to the choke slot width The final
choke slot width is selected to be 09mm considering the feed diameter
minimization and the manufacturability The overall diameter of the proposed
feed is 369mm which is increased from the 207mm of the waveguide
inside diameter due to the use of four chokes
-66-
(a)
(b)
(c)
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection coefficient
-67-
(a)
(b)
(c)
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and (c)
reflection coefficient
-68-
Next we investigated corrugations placed on the outer wall of the feed
Four corrugations applied to the outer surface of the circular waveguide The
corrugation depth is 465mm(0215λ0 at 14GHz) The primary purpose of
using corrugations is to further reduce the back radiation Increasing the
number of corrugations beyond four has little effect in reducing the back
radiation
Figs 512 and 513 show the effect of corrugations on the E- and H-plane
patterns Fig 514 shows the parametric study of the corrugation depth lcor
The corrugation depth is varied from 40mm and 645mm The optimum
value of the corrugation depth is found to be 465mm
-69-
(a)
(b)
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern at (a) 12GHz and (b) 14GHz
-70-
(a)
(b)
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern at (a) 12GHz and (b) 14GHz
-71-
(a)
(b)
(c)
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection coefficient
-72-
The phase center location is important in placing the feed in a reflector
antenna[8] The phase center variation with frequency should be small Fig
515 shows the effect of chokes and corrugations on the phase center The
curve with circle corresponds to the case without chokes and corrugations
The phase center varies from -326mm and -190mm away from the feeds
aperture plane It means the phase center is located inside the waveguide
The curve with triangles corresponds to the case with chokes The curve with
squares to the case with chokes and corrugations The phase center varies
from 0mm to -302mm
From Fig 515 we can observed that phase center variation reduced by the
corrugation and three cases phase center calculated in φ=450 plane
parameter sweep values are given in Table 52
10 12 14 16 181
0
-1
-2
-3
-4
-5
-6
Pha
se c
ente
r (m
m)
Frequency (GHz)
choke+corrugatuion without choke corrugation with choke
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
-73-
Frequency
(GHz)
Phase center from the aperture plane
(mm)
Without
chokes and
corrugations
With
chokes
With chokes
and
corrugations
1000 -326 062 000
1100 -187 030 -002
1200 -563 -208 -065
1300 -296 -154 -202
1400 -319 -314 -302
1500 -201 -203 -241
1600 -242 -233 -207
1700 -208 -208 -186
1800 -190 -157 -132
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
Based on the foregoing parametric studies optimum dimensions of the
broadband circular waveguide feed are obtained as shown in Table 53
-74-
Table 53 Optimum dimensions of the broadband circular waveguide feed
Parameter Designation Value (mm)
2a Waveguide inside diameter 2070
d Waveguide outside diameter 3690
lcrLength of the circular waveguide section 1430
m Distance between the aperture plane and the first corrugation 950
xDistance from the last corrugation to the end of the cylindrical outer surface
550
ltrLength of the rectangular-to-circularwaveguide transition 4465
lrcLength of the rectangular waveguide section 1430
tch Choke slot width 090
lch Choke depth 750
t Choke metal width 090
lcor Corrugation depth 465
tcor Corrugation metal width 100
s Corrugation slot width 10
lp Probe length 530
sp Probe position from the back short 530
din Probe diameter 127
b Inside height of the rectangular waveguide 857
tw Waveguide wall thickness 500
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-viii-
Fig 520 Photograph of the fabricated broadband circular waveguide feed 82
Fig 521 Reflection coefficient of the fabricated broadband circular
waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 82
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 84
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 84
-ix-
List of Tables
Table 21 Properties of a circular waveguide open end radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 10
Table 22 Properties of a square waveguide open end radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 15
Table 23 Properties of the probe-fed circular waveguide radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 20
Table 24 Properties of the probe-fed square waveguide radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 24
Table 31 Dimensions of the designed narrow-band circular feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 33
Table 32 Performance of the narrow-band circular waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 37
Table 51 Performance of the broadband circular waveguide feed without
chokes and corrugations middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 60
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 73
Table 53 Optimum dimensions of the broadband circular waveguide feed 74
Table 54 Performance of the designed broadband circular waveguide feed 81
-1-
I Introduction
The horns and waveguides are known for their high efficiency and
structural simplicity They are popular choices for feeding for reflectors in
high-gain antenna applications such as satellite and point-to-point microwave
communication links The theory of reflector antenna was developed in the
1940s and has been used to calculate the radiation patterns of various
reflector structures[1]
The basic structure of a prime-focus reflector antenna consists of a
parabolic reflecting surface a feed and its support The placement of the feed
is such that its phase center is at the focal point of the parabolic reflecting
surface The feed is often a circular waveguide because of its symmetric
radiation pattern with low back radiation and low cross polarization The
circular waveguide feed must have a small diameter to reduce the aperture
blockage of the reflector antenna[3]
A radiation pattern with a good circular symmetry in the main beam can
be found from circular waveguide feeds with dominant TE11 mode excitation
The radiation patterns depends on the diameter and wall thickness of the
waveguide[4] A coaxial probe can be inserted into a short-circuited circular
waveguide in the form of a coaxial-to-waveguide transition The diameter of
the circular waveguide is chosen such that only the dominant mode
propagates
When the waveguide dimension does not provide a circular symmteric
-2-
pattern a choke or multiple chokes around the aperture wall can be
employed to equalize radiation patterns and keep the back radiation in low
level If chokes are not enough for the suppression of the back radiation
corrugations on the outer surface of the feed is one way to reduce the back
radiation
In this thesis a broadband circular waveguide feed is developed for
prime-focus reflector antenna application After investigating the radiation
properties of simple circular and square waveguides methods are investigated
for bandwidth enhancement back radiation suppression and beamwidth
equalization in the circular waveguide feed
The first type of the circular waveguide feed consists of a probe-fed
circular waveguide a single quarter-wave choke on the aperture wall and a
dielectric-ring beamwidth equalizer Due to the simple feeding method the
first feed operates over 171-197GHz(141) which is not broadband in the
strict sense of the word
The second feed consists of a coaxial-to-rectangular waveguide transition a
rectangular-to-circular waveguide transition a circular waveguide section four
quarter-wave chokes on the aperture wall and four quarter-wave corrugations
on the feeds outer surface Due to the complicated feeding method the
second feed operates over 10-18GHz(571)
This thesis is arranged as follows Chapter I gives an introduction to the
thesis related works and objectives are stated Chapter II describes the
structure and excitation of the circular and square waveguide and the
operation of the coaxial-to-waveguide transitions Chapter III describes a
compact feed horn design and its fabrication and measurement Chapter IV
-3-
presents dielectric rod feed and its simulated performances Chapter V gives
design and optimization of feed for parabolic reflector antenna In this
chapter includes the detailed information of design procedures and operating
principle also the simulated and measured performances are provided Finally
conclusion is given in the Chapter VI
-4-
II Analysis of Circular and Square Waveguide Feeds
21 Circular Waveguide Radiator
Before design a complicated circular waveguide feed it is helpful to
investigate the impedance and radiation properties of a circular waveguide
open end
The circular waveguide is a cylindrical hollow metallic pipe with a uniform
circular section of radius a Circular waveguides are normally designed to
operate only with the dominant mode The dominant mode in a waveguide is
the mode having the lowest cutoff frequency given by equation (21)
(21)
where
(22)
and a is the waveguide radius The following chart[2] and table show the
cutoff frequencies of various modes in a circular waveguide
-5-
Modes c al11TEc cf f
TE11 341259 100000
TM01 261274 130613
TE21 205720 165885TE01 163979 208111
TM11 163979 208111TE31 149557 228180
TM21 122345 278932TE41 118159 288813
TE12 117852 289566
TM02 113824 299813TE02 0897986 380027
The recommended frequency range of the commercial circular waveguide is
given by the following equation This assumes that the TM01 mode is not
generated or suppressed if generated
11 21 11TE TE TE115 095 158 32 bandwidthc c cf f f fpound pound = reg (23)
Fig 21 shows the geometry of a circular waveguide with a diameter of 2a
When 2a is 2053mm the cutoff frequency of the TE11 mode is 857GHz
According to (23) the useful operating frequency range is from
986-1354GHz
Fig 22 shows the reflection of this waveguide excited with the dominant
TE11 mode The waveguide length l is 60mm The reflection occurs at the
open end of the circular waveguide The reflection coefficient is less than
-15dB over 10-18GHz
-6-
Fig 21 Geometry of a circular waveguide open end radiator
Fig 23 shows a 2D gain pattern of this waveguide antenna The
waveguide antenna has a gain of 80dB 99dB and 115dB at 10GHz
14GHz and 18GHz respectively Fig 24 shows the E- and H-plane patterns
of the circular waveguide antenna Table 21 summarizes the properties of a
circular waveguide antenna
Fig 22 Reflection coefficient of a circular waveguide open end radiator
-7-
(a)
(b)
Fig 23 2D radiation pattern of the circular waveguide open end radiator
at (a)10GHz (b) 14GHz and (c) 18GHz
-8-
(c)
Fig 23 continued
-9-
(a)
(b)
(c)
Fig 24 E-plane and H-plane patterns of the circular waveguide open end
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-10-
Table 21 Properties of a circular waveguide open end radiator of diameter
2053mm
Frequency(GHz)-10dB Beamwith(deg) Front-to-Back
Ratio(dB)E plane H plane
10 67 73 12
14 58 60 18
18 41 50 21
In a circular waveguide radiatoλr a good pattern symmetry and low back
radiation is obtained at 14GHz where 2aλ = 096
22 Square Waveguide Radiator
A square waveguide is often used as a dual-polarized feed To operate the
cutoff frequency of the dominant mode a square-waveguide wall width a
must be greater than one half of a wavelength The modes with cutoff
frequencies equal to or smaller than the operational frequency can exist inside
the waveguide wall The lower cutoff frequency and cutoff wavelength for
square waveguide is determined by the following equations
TE
(24)
TE
(25)
The next higher-order mode is TE11 mode with the cutoff wavelength
given by
-11-
TE
(26)
Similar to the circular waveguide the recommended operating frequency range
of a square waveguide is given by
TEleleTE
TErarr bandwidth (27)
Fig 25 shows the geometry of a square waveguide with a dimension of a
When a is 157mm the cutoff frequency is 95GHz The recommended
operating frequency of this waveguide is from 109GHz to 155GHz
Fig 26 shows the reflection of this waveguide excited with the dominant
TE10 mode The reflection coefficient is less than -15dB over 10-20GHz
Fig 25 Geometry of a square waveguide open end radiator
Fig 27 and shows the 2D radiation pattern of a square waveguide antenna
excited with the dominant TE10 mode The antenna has a gain of 73dB
85dB and 102dB at 10GHz 14GHz and 18GHz respectively Fig 28
shows the E- and H-plane radiation patterns of a square waveguide radiator
Table 22 summarizes the properties of a square waveguide open end radiator
-12-
Fig 26 Reflection coefficient of a square waveguide open end radiator
(a)
Fig 27 2D radiation patterns of a square waveguide radiator
at (a) 10GHz (b) 14GHz and (c) 18GHz
-13-
(b)
(c)
Fig 27 continued
-14-
(a)
(b)
(c)
Fig 28 E-plane and H-plane patterns of square waveguide open radiator
at (a) 10GHz(b) 14GHz and (c) 18GHz
-15-
Table 22 Properties of a square waveguide open end radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 69 71 11
14 47 60 25
18 58 62 16
The radiation pattern symmetry and back radiation performance of the
square waveguide are inferior to those of a circular waveguide
23 Probe-Fed Circular Waveguide Radiator
In Section 21 the radiation properties of a TE11-mode excited waveguide
is investigated In this section a circular waveguide fed by a coaxial probe
shown in Fig 29 is studied
The coaxial probes diameter is 127mm With the Teflon dielectric the
50-ohm coaxial lines outer conductor has a diameter of 41mm For a
circular waveguide the wave impedance of the TE11 mode is given by
∙ (28)
where λg is the guided wavelength given by
(29)
-16-
(a) (b)
Fig 29 Probe-fed circular waveguide radiator (a) Front view and (b) side
view
The combination of the probe length and the probe position from the
shorted wall enables a good impedance matching The probe distance sp from
the back short is close to a quarter wavelength at the design frequency
The designed feed has the following dimension d = 2053mm lp = 42
mm sp = 534mm wall thickness = 05mm and feed length = 400mm
Fig 210 shows the reflection coefficient of the designed probe-fed
circular waveguide radiator The reflection coefficient is less than -10dB over
138-187GHz Fig 211 and 212 shows the E-plane and H-plane radiation
patterns and 2D radiation patterns of the coaxial-to-circular waveguide
transition The radiation patterns symmetry distorted because of the high order
modes The coaxial-to-circular waveguide transition has 73dB 84dB and
79dB gain at 10GHz 14GHz and 18GHz frequencies respectively Table 23
shows the properties of the coaxial-to-circular waveguide transition
-17-
Fig 210 Reflection coefficient of the probe-fed circular waveguide radiator
(a)
Fig 211 2D radiation pattern of the probe-fed circular waveguide radiator
at (a) 10GHz (b) 14GHz and (c) 18GHz
-18-
(b)
(c)
Fig 211 continued
-19-
(a)
(b)
(c)
Fig 212 E- and H-plane patterns of the probe-fed circular waveguide
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-20-
Table 23 Properties of the probe-fed circular waveguide radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 73 70 1414 83 57 17
18 60 52 30
When a circular waveguide radiator is fed by a coaxial probe its radiation
properties are not good due to the excitation of higher-order modes
Therefore a probe-fed circular waveguide radiator can be used as a feed only
over a narrow frequency range
24 Probe-Fed Square Waveguide Radiator
In this section a probe-fed square waveguide radiator is investigated Fig
213 shows a coaxial probe-fed square waveguide radiator The designed
radiator has the following dimension a = b = 157mm lp = 35 mm sp =
50 mm wall thickness = 05mm and feed length = 40mm
(a) (b)
Fig 213 Probe-fed square waveguide radiator (a) Front view and (b) side
view
-21-
Fig 214 shows the 2D radiation patterns of the radiator at 10GHz
14GHz and 18GHz Fig 215 shows E- and H-plane patterns of the radiator
Fig 216 shows the reflection coefficient of the probe-fed square waveguide
radiator The reflection coefficient is less than -10dB over 13-20GHz Table
24 summarizes the properties of the probe-fed square waveguide radiator
(a)
Fig 214 2D radiation patterns of the probe-fed square waveguide radiator at
(a) 10GHz (b) 14GHz and (c) 18GHz
-22-
(b)
(c)
Fig 214 continued
-23-
(a)
(b)
(c)
Fig 216 E-plane and H-plane patterns of the probe-fed square waveguide
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-24-
Fig 216 Reflection coefficient of the probe-fed square waveguide radiator
Table 24 Properties of the probe-fed square waveguide radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 73 71 12
14 85 63 1418 27 65 28
When a square waveguide radiator is fed by a coaxial probe its radiation
properties are not good due to the excitation of higher-order modes as in the
case of the probe-fed circular waveguide radiator A probe-fed square
waveguide radiator can be used as a feed only over a narrow frequency
range
-25-
III Design of Compact Circular Waveguide Feeds
In this chapter the feed design is presented for a prime-focus reflector
antenna The prime-focus paraboloid reflector is one of the most commonly
used high-gain antenna It has been used in earth-station antennas and radio
telescopes It consists of a paraboloid reflector with a feed system at its focal
point
The feed should radiate a low level of cross-polar power over the
operating frequency These conditions not easy to achieve and most prime
focus feeds are compromises The shape and characteristic of the radiation
pattern of the feed are the most important parameter because these will
directly influence the fields which are directed at a reflector[6] Other
electrical factors which relevant to the choice of a feed are the cross-polar
level the gain efficiency the bandwidth and impedance matching
31 Narrow-Band Circular Waveguide Feed
Fig 31 shows the proposed narrow-band circular waveguide feed and its
design variables The feed consists of a circular waveguide open end excited
by a TE11 dominant mode A quarter wave choke is applied along the
circular aperture of the waveguide to equalize E- and H-plane radiation
patterns and to suppress the back radiation A dielectric ring is used to
control the radiation pattern and change the power distribution over the
aperture The control of the amplitude over the aperture are essential to the
design of symmetric radiation pattern The material used for dielectric loading
-26-
is the monocast(MC) nylon with a dielectric constant of 30 The feed is
designed to operate over 171-197GHz
(a)
(b)
Fig 31 Narrow-band circular waveguide feed (a) CAD model and (b) a
cross sectional view
The impedance matching is achieved by a proper combination of the probe
height lp and its distance sp from the waveguide shorted end Here the
-27-
circular waveguide is terminated with an open end with a wall thickness of
2mm radiating into the free space
Fig 32 shows the effect of the probe length lp and the probe distance sp
on the reflection coefficient The best performance is obtained when lp =
363mm and sp = 616mm The feeds reflection coefficient is less than -10dB
over 170-195GHz
(a)
(b)
Fig 32 Effect of the (a) the probe length lp and (b) the probe
distance sp on the reflection coefficient
-28-
Fig 33 shows the effect of the choke depth The E-plane pattern is more
sensitive to the choke depth than the H-plane pattern The choke depth has a
strong influence on the reflection coefficient when it is 360mm By properly
choosing the choke depth we can equalize the E- and H-plane patterns The
optimum value of the choke depth is 410mm which is 0249λ0 at 1825GHz
The choke slot width tch in the range of 06-12mm has almost no effect
on the H-plane pattern and the reflection coefficient For the E-plane pattern
tch of 12mm has some effect on the E-plane radiation pattern as shown in
Fig 34
Fig 35 shows the feed performance versus the dielectric ring length We
observe in Fig 35 that the dielectric length ld has an optimum value of
1168mm which does no effect on the H-plane pattern and tha the value of
1048mm has some effect on the E-plane pattern and the reflection
coefficient
Fig 36 shows E-plane and H-plane patterns and the reflection coefficient
versus the dielectric thickness With the optimum value of the dielectric
thickness t obtained from the Fig 36 is 155mm The larger values of td has
much stronger effects on the E-plane pattern and the reflection coefficient
The H-plane pattern is not sensitive to the dielectric ring thickness
-29-
(a)
(b)
(c)
Fig 33 Feed performance versus the choke depth (a) E-plane pattern
(b) H-plane pattern and (c) reflection coefficient
-30-
(a)
(b)
(c)
Fig 34 Feed performance versus the choke slot width (a) E-plane pattern
(b) H-plane pattern and (c) reflection coefficient
-31-
(a)
(b)
(c)
Fig 35 Feed performance versus the dielectric ring length (a) E-plane
pattern (b) H-plane pattern and (c) reflection coefficient
-32-
(a)
(b)
(c)
Fig 36 Feed performance versus the dielectric ring thickness (a) E-plane
pattern(b) H-plane pattern and (c) reflection coefficient
-33-
From the above parametric analysis an optimum feed design is obtained
The result is shown in Table 31 Fig 37 shows the 2D gain patterns of
designed feed The antenna has a gain of 903dB 933dB and 956dB at
171GHz 1825GHz and 19GHz respectively
Fig 38 shows E- and H-plane radiation patterns of the designed feed The
feed has E- and H-plane 10-dB beamwidths of 60 and 59 degrees at 17GHz
The feed has a front-to-back ration of 1900dB 2490dB and 2200dB at
171GHz 1825GHz and 19GHz respectively Table 32 summarizes the
performance of the designed narrow-band circular waveguide feed
The designed feed has a greatly improved performance over that of a
simple coax-fed feed described in Section 23
Table 31 Dimensions of the designed narrow-band circular feed
Parameter Designation Value(mm)
a Waveguide inside radius 640
l Feed length 2890
lp Probe length 363
sp Probe position from the back short 616
din Probe diameter 127
dout Diameter of coaxial cables outer conductor 400
t Thickness of choked wall 050
tch Choke slot width 100
lch Choke depth 410
ld Dielectric ring length 1168
td Dielectric ring thickness 155
d1 Waveguide outside diameter 1680
-34-
(a)
(b)
Fig 37 2D gain patterns of the narrow-band circular waveguide feed at
(a) 17GHz (b) 1825GHz and (c) 19GHz
-35-
(c)
Fig 37 continued
-36-
(a)
(b)
(c)
Fig 38 E- and H-plane patterns of the narrow-band circular waveguide feed
at (a) 10GHz (b) 1825GHz and (c) 195GHz
-37-
Frequency(GHz)
Gain(dB)
E-H-plane10-dB beamwidths
(deg)
Front-to-back ratio(dB)
Phase centerlocation
(From feeds aperture plane
toward reflector)
(mm)
1700 903 6059 20 062
1825 933 6060 25 004
1900 956 5759 22 007
Table 32 Performance of the narrow-band circular waveguide feed
The designed narrow-band feed is fabricated and its performance is
measured and compared with the simulation results The designed feed is
fabricated in a numerically-controlled machining center The fabricated antenna
is shown in Fig 39
Fig 39 Photograph of the fabricated feed
-38-
Fig 310 shows a comparison of the measured and simulated reflection
coefficients The measured reflection coefficient is less than -10dB over
171-197GHz The agreement between simulated and measured results are
good
Fig 311 shows the E- and H-plane patterns of the fabricated feed at
187GHz The feed has 90dB gain simulation and measurement results are in
good agreement
The fabricated antennarsquos 10dB beamwidth is 60 degrees in both E and H
planes at 187GHz The front-to-back ratio is 21dB
Fig 310 Reflection coefficient of the fabricated feed
-39-
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Fee
d H
orn
Gain
- d
B
Angle - degree
(a)
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Feed H
orn
Gain
- d
B
Angle - degree
(b)
Fig 311 Gain patterns of the fabricated feed at 187 GHz (a) E-plane and
(b) H-plane
-40-
IV Design of Circular Waveguide Feeds Loaded with a
Dielectric Rod
In this section circular waveguide feeds loaded with a dielectric rod feed
are investigated A comprehensive discussion of the circular waveguide loaded
with a dielectric rod is given by Kumar[7] Inserting a dielectric material
inside the circular waveguide improves the E- and H-plane pattern symmetry
In general dielectric-loaded circular waveguide feeds show good performance
only over a narrow bandwidth
Fig 41 shows the geometry of a circular waveguide loaded with a
dielectric rod The waveguide length is 400mm and the wall thickness is
05mm The dielectric rods diameter is 207mm The dielectric rod is
extended 05 wavelength beyond the waveguide open end The dielectric
constant εr is changed and the feeds performance is observed
Fig 41 Geometry of a circular waveguide loaded with a uniform dielectric
rod
-41-
Fig 42 is the radiation pattern of the feed with εr = 25 and L = 05λ0 at
9GHz E- and H-plane 10-dB beamwidths are 810 and 807 degrees
respectively The front-to-back ratio is 18dB The antenna gain is 71dB
(a)
(b)
Fig 42 Radiation pattern at 9GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 05λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-42-
Fig 43 shows the radiation pattern of the feed with εr = 21 at 10GHz
E- and H-plane 10-dB beamwidths are 70 and 71 degrees respectively The
front-to-back ratio is 19dB The antenna gain is 83dB
(a)
(b)
Fig 43 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 21 and L = 05λ0 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-43-
Fig 44 shows the radiation pattern of the feed with εr = 30 at 8GHz
E- and H-plane 10-dB beamwidths are 83 and 824 degrees respectively The
front-to-back ratio is 17dB The antenna gain is 73dB
(a)
(b)
Fig 44 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 30 and L = 05λ0 at 8GHz (a) 2D radiation pattern
and (b) E- and H-plane patterns
-44-
Fig 45 shows the radiation pattern of the feed with εr = 50 at 18GHz
E- and H-plane 10-dB beamwidths are 56 and 54 degrees respectively The
front-to-back ratio is 27dB The antenna gain is 105dB The feed has a good
pattern symmetry and low back radiation
(a)
(b)
Fig 45 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 50 and L = 05λ0 at 18GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-45-
Fig 46 is the radiation pattern of the feed with εr = 25 and L = 10λ0 at
10GHz E- and H-plane 10-dB beamwidths are 50 and 48 degrees
respectively The front-to-back ratio is 16dB The antenna gain is 105dB
(a)
(b)
Fig 46 Radiation pattern at 10GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 10λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-46-
Fig 47 shows the geometry of a circular waveguide with a tapered
dielectric rod The designed feed has the following dimension L = 1λ0 d =
1λ0 and εr =25 at 10GHz The waveguide length is 40mm and the wall
thickness is 05mm
L
Dielectricd3
Fig 47 Geometry of a circular waveguide loaded with a tapered dielectric
rod
Fig 48 shows the radiatio pattern of the designed feed E- and H-plane
10-dB beamwidths are 575 and 564 degrees respectively The front-to-back
ratio is 377dB The antenna gain is 94dB The designed feed has an
excellent beamwidth symmetry and a very low back radiation
-47-
(a)
(b)
Fig 48 Radiation pattern of a circular waveguide loaded with a tapered
dielectric rod with L = 1λ0 d = 1λ0 and εr =25 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-48-
Fig 49 shows the geometry of a spherical ended dielectric rod feed
diameter of 06λ0 at 10GHz with a dielectric constant of 25 and L= 03λ0
Fig 410 shows the radiation patterns of the designed feed E- and H-plane
10-dB beamwidths are both 63 degrees The front-to-back ratio is 24dB The
antenna gain is 864dB
Fig 49 Geometry of a circular waveguide loaded with a spherical ended
dielectric rod
-49-
(a)
(b)
Fig 410 Radiation pattern of a circular waveguide loaded wht a spherical
ended dielectric rod with d = 06λ0 L = 03λ0 and εr =25 at 10GHz (a) 3D
radiation pattern and (b) E- and H-plane patterns
-50-
V Design of a Broadband Circular Waveguide Feed
In this chapter the design of a broadband circular waveguide feed is
presented At microwave frequencies the feed is often a circular waveguide
with chokes and corrugations around the aperture Chokes and corrugations
equalize E- and H-plane patterns and reduce the back radiation
The proposed feed is designed to operate over 10-18GHz The design starts
with the optimization of the coaxial-to-rectangular waveguide adapter
employed for good mode purity over a broad frequency range Next a
rectangular-to-circular waveguide transition is optimized Finally chokes and
corrugations are designed for improved pattern symmetry and low back
radiation
The proposed feed structure is shown in Fig 51 The feed consist of the
following parts a coaxial-to-rectangular waveguide adapter a rectangular-to-
circular waveguide transition a circular waveguide section four quarter-wave
chokes around the feeds aperture and four corrugations on the feeds outer
surface
The computer simulation shows the above arrangement offers good radiation
patterns over a broad frequency range The broadband operation is obtained
by exciting the TE11 mode in the circular waveguide using the TE10 mode of
the rectangular waveguide which is in turn excited by a coaxial probe
-51-
Chokes
Coaxial-to-waveguide transition
Circular wavguide
Corrugations
Mode transition
(a)
(b)
Fig 51 Structure of the proposed broadband circular waveguide feed
(a) CAD model and (b) cross-sectional view
For the coaxial-to-rectangular waveguide adapter an SMA connector with
the probe diameter of 127 mm is employed The coaxial probe inserted into
the waveguide energizes the feed and excites the dominant TE10 mode in
-52-
the rectangular waveguide The impedance matching is achieved by adjusting
the probe distance sp from the back short and the probe length lp
(a)
(b)
Fig 52 Reflection coefficient of the coaxial-to-rectangular adapter versus
(a) probe length lp and (b) the probe position sp
Fig 52 shows the reflection coefficient versus the various values of probe
lengths lp and probe positions sp The probe length lp is adjusted to obtain
antenna impedance matching and the probe distance sp is adjusted to obtain a
-53-
desired resonant frequency
Next a transition between rectangular and circular waveguide is designed
The transition section converts the TE10 mode in the rectangular waveguide to
TE11 mode in the circular waveguide and vice versa The transition is built
in a form of a taper for easy fabrication[22]
(a)
(b)
Fig 53 Structure of the rectangular-to-circular waveguide transition
(a) 3D view and (b) cross sectional view
The dimensions of the final optimized transition are as follows The length
of the rectangular waveguide section is 143mm The rectangular waveguides
width a and height b are 207mm and 857mm respectively The length of
the circular waveguide section is 143mm The inside diameter of the circular
-54-
waveguide is 207mm(097 wavelength at 14GHz) The length of transition
region ltr is 4465mm(approximately equal to 2λ0 at 14GHz) Fig 54 shows
the field distribution inside the mode converter
(a)
(b)
Fig 54 Field distribution inside the mode converter at
(a) 10GHz (b) 14GHz and (c) 18GHz
-55-
(c)
Fig 54 continued
Finally multiple chokes are investigated Figs 55 56 and 57 show the
feed performance without chokes The reflection coefficient is less than -10dB
over 10-19GHz The antenna has a gain of 921dB to 1189dB over
10-19GHz
Fig 55 Reflection coefficient of the broadband circular waveguide feed
without chokes and corrugations
-56-
(a)
(b)
(c)
Fig 56 E- and H-plane patterns of the broadband circular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-57-
(d)
(e)
Fig 56 continued
-58-
(a)
(b)
Fig 57 2D radiation patterns of the broadband cicular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-59-
(c)
(d)
Fig 57 continued
-60-
(e)
Fig 57 continued
To achieve equal beamwidths in E and H planes over a wide frequency
range chokes and corrugations are employed Table51 summarizes the
performance of a feed without chokes and corrugations
Table 51 Performance of the broadband circular waveguide feed without
chokes and corrugations
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
1000 940 6061 15
1200 972 6159 17
1400 920 5957 21
1600 1070 4751 29
1800 1188 5352 21
-61-
Four quarter-wavelength chokes are introduced in the feed design which
has a slot depth of 75mm and slot width of 09mm The choke slot spacing
is 18mm The choke design is investigated by applying the choke one by
one and the effect on the E- and H-plane patterns are observed as illustrated
in Figs 58 and 59 The use of chokes makes the E-plane pattern narrower
The H-plane pattern is not affected Chokes increase the gain slightly and
reduce back radiation
(a)
(b)
Fig 58 Effect of chokes on the E-plane pattern of the broadband circular
waveguide feed at (a) 10GHz(b) 12GHz (c) 14GHz (d) 16GHz and (e)
18GHz
-62-
(c)
(d)
(e)
Fig 58 continued
-63-
(a)
(b)
(c)
Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-64-
(d)
(e)
Fig 59 continued
-65-
Fig 510 shows the feed performance versus the choke depth When the
choke depth is varied from 535mm to 95mm the E- and H-plane patterns
are strongly affected The optimum value of choke depth is 75mm(035λ0 at
14GHz) which gives equal E- and H-plane radiation patterns and leads to
low back radiation
Fig 511 shows the feed performance versus the choke slot width tch The
choke slot width is varied from 09mm to 21mm Radiation patterns and
reflection coefficients are not sensitive to the choke slot width The final
choke slot width is selected to be 09mm considering the feed diameter
minimization and the manufacturability The overall diameter of the proposed
feed is 369mm which is increased from the 207mm of the waveguide
inside diameter due to the use of four chokes
-66-
(a)
(b)
(c)
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection coefficient
-67-
(a)
(b)
(c)
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and (c)
reflection coefficient
-68-
Next we investigated corrugations placed on the outer wall of the feed
Four corrugations applied to the outer surface of the circular waveguide The
corrugation depth is 465mm(0215λ0 at 14GHz) The primary purpose of
using corrugations is to further reduce the back radiation Increasing the
number of corrugations beyond four has little effect in reducing the back
radiation
Figs 512 and 513 show the effect of corrugations on the E- and H-plane
patterns Fig 514 shows the parametric study of the corrugation depth lcor
The corrugation depth is varied from 40mm and 645mm The optimum
value of the corrugation depth is found to be 465mm
-69-
(a)
(b)
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern at (a) 12GHz and (b) 14GHz
-70-
(a)
(b)
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern at (a) 12GHz and (b) 14GHz
-71-
(a)
(b)
(c)
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection coefficient
-72-
The phase center location is important in placing the feed in a reflector
antenna[8] The phase center variation with frequency should be small Fig
515 shows the effect of chokes and corrugations on the phase center The
curve with circle corresponds to the case without chokes and corrugations
The phase center varies from -326mm and -190mm away from the feeds
aperture plane It means the phase center is located inside the waveguide
The curve with triangles corresponds to the case with chokes The curve with
squares to the case with chokes and corrugations The phase center varies
from 0mm to -302mm
From Fig 515 we can observed that phase center variation reduced by the
corrugation and three cases phase center calculated in φ=450 plane
parameter sweep values are given in Table 52
10 12 14 16 181
0
-1
-2
-3
-4
-5
-6
Pha
se c
ente
r (m
m)
Frequency (GHz)
choke+corrugatuion without choke corrugation with choke
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
-73-
Frequency
(GHz)
Phase center from the aperture plane
(mm)
Without
chokes and
corrugations
With
chokes
With chokes
and
corrugations
1000 -326 062 000
1100 -187 030 -002
1200 -563 -208 -065
1300 -296 -154 -202
1400 -319 -314 -302
1500 -201 -203 -241
1600 -242 -233 -207
1700 -208 -208 -186
1800 -190 -157 -132
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
Based on the foregoing parametric studies optimum dimensions of the
broadband circular waveguide feed are obtained as shown in Table 53
-74-
Table 53 Optimum dimensions of the broadband circular waveguide feed
Parameter Designation Value (mm)
2a Waveguide inside diameter 2070
d Waveguide outside diameter 3690
lcrLength of the circular waveguide section 1430
m Distance between the aperture plane and the first corrugation 950
xDistance from the last corrugation to the end of the cylindrical outer surface
550
ltrLength of the rectangular-to-circularwaveguide transition 4465
lrcLength of the rectangular waveguide section 1430
tch Choke slot width 090
lch Choke depth 750
t Choke metal width 090
lcor Corrugation depth 465
tcor Corrugation metal width 100
s Corrugation slot width 10
lp Probe length 530
sp Probe position from the back short 530
din Probe diameter 127
b Inside height of the rectangular waveguide 857
tw Waveguide wall thickness 500
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-ix-
List of Tables
Table 21 Properties of a circular waveguide open end radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 10
Table 22 Properties of a square waveguide open end radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 15
Table 23 Properties of the probe-fed circular waveguide radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 20
Table 24 Properties of the probe-fed square waveguide radiator middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 24
Table 31 Dimensions of the designed narrow-band circular feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 33
Table 32 Performance of the narrow-band circular waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 37
Table 51 Performance of the broadband circular waveguide feed without
chokes and corrugations middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 60
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot 73
Table 53 Optimum dimensions of the broadband circular waveguide feed 74
Table 54 Performance of the designed broadband circular waveguide feed 81
-1-
I Introduction
The horns and waveguides are known for their high efficiency and
structural simplicity They are popular choices for feeding for reflectors in
high-gain antenna applications such as satellite and point-to-point microwave
communication links The theory of reflector antenna was developed in the
1940s and has been used to calculate the radiation patterns of various
reflector structures[1]
The basic structure of a prime-focus reflector antenna consists of a
parabolic reflecting surface a feed and its support The placement of the feed
is such that its phase center is at the focal point of the parabolic reflecting
surface The feed is often a circular waveguide because of its symmetric
radiation pattern with low back radiation and low cross polarization The
circular waveguide feed must have a small diameter to reduce the aperture
blockage of the reflector antenna[3]
A radiation pattern with a good circular symmetry in the main beam can
be found from circular waveguide feeds with dominant TE11 mode excitation
The radiation patterns depends on the diameter and wall thickness of the
waveguide[4] A coaxial probe can be inserted into a short-circuited circular
waveguide in the form of a coaxial-to-waveguide transition The diameter of
the circular waveguide is chosen such that only the dominant mode
propagates
When the waveguide dimension does not provide a circular symmteric
-2-
pattern a choke or multiple chokes around the aperture wall can be
employed to equalize radiation patterns and keep the back radiation in low
level If chokes are not enough for the suppression of the back radiation
corrugations on the outer surface of the feed is one way to reduce the back
radiation
In this thesis a broadband circular waveguide feed is developed for
prime-focus reflector antenna application After investigating the radiation
properties of simple circular and square waveguides methods are investigated
for bandwidth enhancement back radiation suppression and beamwidth
equalization in the circular waveguide feed
The first type of the circular waveguide feed consists of a probe-fed
circular waveguide a single quarter-wave choke on the aperture wall and a
dielectric-ring beamwidth equalizer Due to the simple feeding method the
first feed operates over 171-197GHz(141) which is not broadband in the
strict sense of the word
The second feed consists of a coaxial-to-rectangular waveguide transition a
rectangular-to-circular waveguide transition a circular waveguide section four
quarter-wave chokes on the aperture wall and four quarter-wave corrugations
on the feeds outer surface Due to the complicated feeding method the
second feed operates over 10-18GHz(571)
This thesis is arranged as follows Chapter I gives an introduction to the
thesis related works and objectives are stated Chapter II describes the
structure and excitation of the circular and square waveguide and the
operation of the coaxial-to-waveguide transitions Chapter III describes a
compact feed horn design and its fabrication and measurement Chapter IV
-3-
presents dielectric rod feed and its simulated performances Chapter V gives
design and optimization of feed for parabolic reflector antenna In this
chapter includes the detailed information of design procedures and operating
principle also the simulated and measured performances are provided Finally
conclusion is given in the Chapter VI
-4-
II Analysis of Circular and Square Waveguide Feeds
21 Circular Waveguide Radiator
Before design a complicated circular waveguide feed it is helpful to
investigate the impedance and radiation properties of a circular waveguide
open end
The circular waveguide is a cylindrical hollow metallic pipe with a uniform
circular section of radius a Circular waveguides are normally designed to
operate only with the dominant mode The dominant mode in a waveguide is
the mode having the lowest cutoff frequency given by equation (21)
(21)
where
(22)
and a is the waveguide radius The following chart[2] and table show the
cutoff frequencies of various modes in a circular waveguide
-5-
Modes c al11TEc cf f
TE11 341259 100000
TM01 261274 130613
TE21 205720 165885TE01 163979 208111
TM11 163979 208111TE31 149557 228180
TM21 122345 278932TE41 118159 288813
TE12 117852 289566
TM02 113824 299813TE02 0897986 380027
The recommended frequency range of the commercial circular waveguide is
given by the following equation This assumes that the TM01 mode is not
generated or suppressed if generated
11 21 11TE TE TE115 095 158 32 bandwidthc c cf f f fpound pound = reg (23)
Fig 21 shows the geometry of a circular waveguide with a diameter of 2a
When 2a is 2053mm the cutoff frequency of the TE11 mode is 857GHz
According to (23) the useful operating frequency range is from
986-1354GHz
Fig 22 shows the reflection of this waveguide excited with the dominant
TE11 mode The waveguide length l is 60mm The reflection occurs at the
open end of the circular waveguide The reflection coefficient is less than
-15dB over 10-18GHz
-6-
Fig 21 Geometry of a circular waveguide open end radiator
Fig 23 shows a 2D gain pattern of this waveguide antenna The
waveguide antenna has a gain of 80dB 99dB and 115dB at 10GHz
14GHz and 18GHz respectively Fig 24 shows the E- and H-plane patterns
of the circular waveguide antenna Table 21 summarizes the properties of a
circular waveguide antenna
Fig 22 Reflection coefficient of a circular waveguide open end radiator
-7-
(a)
(b)
Fig 23 2D radiation pattern of the circular waveguide open end radiator
at (a)10GHz (b) 14GHz and (c) 18GHz
-8-
(c)
Fig 23 continued
-9-
(a)
(b)
(c)
Fig 24 E-plane and H-plane patterns of the circular waveguide open end
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-10-
Table 21 Properties of a circular waveguide open end radiator of diameter
2053mm
Frequency(GHz)-10dB Beamwith(deg) Front-to-Back
Ratio(dB)E plane H plane
10 67 73 12
14 58 60 18
18 41 50 21
In a circular waveguide radiatoλr a good pattern symmetry and low back
radiation is obtained at 14GHz where 2aλ = 096
22 Square Waveguide Radiator
A square waveguide is often used as a dual-polarized feed To operate the
cutoff frequency of the dominant mode a square-waveguide wall width a
must be greater than one half of a wavelength The modes with cutoff
frequencies equal to or smaller than the operational frequency can exist inside
the waveguide wall The lower cutoff frequency and cutoff wavelength for
square waveguide is determined by the following equations
TE
(24)
TE
(25)
The next higher-order mode is TE11 mode with the cutoff wavelength
given by
-11-
TE
(26)
Similar to the circular waveguide the recommended operating frequency range
of a square waveguide is given by
TEleleTE
TErarr bandwidth (27)
Fig 25 shows the geometry of a square waveguide with a dimension of a
When a is 157mm the cutoff frequency is 95GHz The recommended
operating frequency of this waveguide is from 109GHz to 155GHz
Fig 26 shows the reflection of this waveguide excited with the dominant
TE10 mode The reflection coefficient is less than -15dB over 10-20GHz
Fig 25 Geometry of a square waveguide open end radiator
Fig 27 and shows the 2D radiation pattern of a square waveguide antenna
excited with the dominant TE10 mode The antenna has a gain of 73dB
85dB and 102dB at 10GHz 14GHz and 18GHz respectively Fig 28
shows the E- and H-plane radiation patterns of a square waveguide radiator
Table 22 summarizes the properties of a square waveguide open end radiator
-12-
Fig 26 Reflection coefficient of a square waveguide open end radiator
(a)
Fig 27 2D radiation patterns of a square waveguide radiator
at (a) 10GHz (b) 14GHz and (c) 18GHz
-13-
(b)
(c)
Fig 27 continued
-14-
(a)
(b)
(c)
Fig 28 E-plane and H-plane patterns of square waveguide open radiator
at (a) 10GHz(b) 14GHz and (c) 18GHz
-15-
Table 22 Properties of a square waveguide open end radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 69 71 11
14 47 60 25
18 58 62 16
The radiation pattern symmetry and back radiation performance of the
square waveguide are inferior to those of a circular waveguide
23 Probe-Fed Circular Waveguide Radiator
In Section 21 the radiation properties of a TE11-mode excited waveguide
is investigated In this section a circular waveguide fed by a coaxial probe
shown in Fig 29 is studied
The coaxial probes diameter is 127mm With the Teflon dielectric the
50-ohm coaxial lines outer conductor has a diameter of 41mm For a
circular waveguide the wave impedance of the TE11 mode is given by
∙ (28)
where λg is the guided wavelength given by
(29)
-16-
(a) (b)
Fig 29 Probe-fed circular waveguide radiator (a) Front view and (b) side
view
The combination of the probe length and the probe position from the
shorted wall enables a good impedance matching The probe distance sp from
the back short is close to a quarter wavelength at the design frequency
The designed feed has the following dimension d = 2053mm lp = 42
mm sp = 534mm wall thickness = 05mm and feed length = 400mm
Fig 210 shows the reflection coefficient of the designed probe-fed
circular waveguide radiator The reflection coefficient is less than -10dB over
138-187GHz Fig 211 and 212 shows the E-plane and H-plane radiation
patterns and 2D radiation patterns of the coaxial-to-circular waveguide
transition The radiation patterns symmetry distorted because of the high order
modes The coaxial-to-circular waveguide transition has 73dB 84dB and
79dB gain at 10GHz 14GHz and 18GHz frequencies respectively Table 23
shows the properties of the coaxial-to-circular waveguide transition
-17-
Fig 210 Reflection coefficient of the probe-fed circular waveguide radiator
(a)
Fig 211 2D radiation pattern of the probe-fed circular waveguide radiator
at (a) 10GHz (b) 14GHz and (c) 18GHz
-18-
(b)
(c)
Fig 211 continued
-19-
(a)
(b)
(c)
Fig 212 E- and H-plane patterns of the probe-fed circular waveguide
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-20-
Table 23 Properties of the probe-fed circular waveguide radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 73 70 1414 83 57 17
18 60 52 30
When a circular waveguide radiator is fed by a coaxial probe its radiation
properties are not good due to the excitation of higher-order modes
Therefore a probe-fed circular waveguide radiator can be used as a feed only
over a narrow frequency range
24 Probe-Fed Square Waveguide Radiator
In this section a probe-fed square waveguide radiator is investigated Fig
213 shows a coaxial probe-fed square waveguide radiator The designed
radiator has the following dimension a = b = 157mm lp = 35 mm sp =
50 mm wall thickness = 05mm and feed length = 40mm
(a) (b)
Fig 213 Probe-fed square waveguide radiator (a) Front view and (b) side
view
-21-
Fig 214 shows the 2D radiation patterns of the radiator at 10GHz
14GHz and 18GHz Fig 215 shows E- and H-plane patterns of the radiator
Fig 216 shows the reflection coefficient of the probe-fed square waveguide
radiator The reflection coefficient is less than -10dB over 13-20GHz Table
24 summarizes the properties of the probe-fed square waveguide radiator
(a)
Fig 214 2D radiation patterns of the probe-fed square waveguide radiator at
(a) 10GHz (b) 14GHz and (c) 18GHz
-22-
(b)
(c)
Fig 214 continued
-23-
(a)
(b)
(c)
Fig 216 E-plane and H-plane patterns of the probe-fed square waveguide
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-24-
Fig 216 Reflection coefficient of the probe-fed square waveguide radiator
Table 24 Properties of the probe-fed square waveguide radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 73 71 12
14 85 63 1418 27 65 28
When a square waveguide radiator is fed by a coaxial probe its radiation
properties are not good due to the excitation of higher-order modes as in the
case of the probe-fed circular waveguide radiator A probe-fed square
waveguide radiator can be used as a feed only over a narrow frequency
range
-25-
III Design of Compact Circular Waveguide Feeds
In this chapter the feed design is presented for a prime-focus reflector
antenna The prime-focus paraboloid reflector is one of the most commonly
used high-gain antenna It has been used in earth-station antennas and radio
telescopes It consists of a paraboloid reflector with a feed system at its focal
point
The feed should radiate a low level of cross-polar power over the
operating frequency These conditions not easy to achieve and most prime
focus feeds are compromises The shape and characteristic of the radiation
pattern of the feed are the most important parameter because these will
directly influence the fields which are directed at a reflector[6] Other
electrical factors which relevant to the choice of a feed are the cross-polar
level the gain efficiency the bandwidth and impedance matching
31 Narrow-Band Circular Waveguide Feed
Fig 31 shows the proposed narrow-band circular waveguide feed and its
design variables The feed consists of a circular waveguide open end excited
by a TE11 dominant mode A quarter wave choke is applied along the
circular aperture of the waveguide to equalize E- and H-plane radiation
patterns and to suppress the back radiation A dielectric ring is used to
control the radiation pattern and change the power distribution over the
aperture The control of the amplitude over the aperture are essential to the
design of symmetric radiation pattern The material used for dielectric loading
-26-
is the monocast(MC) nylon with a dielectric constant of 30 The feed is
designed to operate over 171-197GHz
(a)
(b)
Fig 31 Narrow-band circular waveguide feed (a) CAD model and (b) a
cross sectional view
The impedance matching is achieved by a proper combination of the probe
height lp and its distance sp from the waveguide shorted end Here the
-27-
circular waveguide is terminated with an open end with a wall thickness of
2mm radiating into the free space
Fig 32 shows the effect of the probe length lp and the probe distance sp
on the reflection coefficient The best performance is obtained when lp =
363mm and sp = 616mm The feeds reflection coefficient is less than -10dB
over 170-195GHz
(a)
(b)
Fig 32 Effect of the (a) the probe length lp and (b) the probe
distance sp on the reflection coefficient
-28-
Fig 33 shows the effect of the choke depth The E-plane pattern is more
sensitive to the choke depth than the H-plane pattern The choke depth has a
strong influence on the reflection coefficient when it is 360mm By properly
choosing the choke depth we can equalize the E- and H-plane patterns The
optimum value of the choke depth is 410mm which is 0249λ0 at 1825GHz
The choke slot width tch in the range of 06-12mm has almost no effect
on the H-plane pattern and the reflection coefficient For the E-plane pattern
tch of 12mm has some effect on the E-plane radiation pattern as shown in
Fig 34
Fig 35 shows the feed performance versus the dielectric ring length We
observe in Fig 35 that the dielectric length ld has an optimum value of
1168mm which does no effect on the H-plane pattern and tha the value of
1048mm has some effect on the E-plane pattern and the reflection
coefficient
Fig 36 shows E-plane and H-plane patterns and the reflection coefficient
versus the dielectric thickness With the optimum value of the dielectric
thickness t obtained from the Fig 36 is 155mm The larger values of td has
much stronger effects on the E-plane pattern and the reflection coefficient
The H-plane pattern is not sensitive to the dielectric ring thickness
-29-
(a)
(b)
(c)
Fig 33 Feed performance versus the choke depth (a) E-plane pattern
(b) H-plane pattern and (c) reflection coefficient
-30-
(a)
(b)
(c)
Fig 34 Feed performance versus the choke slot width (a) E-plane pattern
(b) H-plane pattern and (c) reflection coefficient
-31-
(a)
(b)
(c)
Fig 35 Feed performance versus the dielectric ring length (a) E-plane
pattern (b) H-plane pattern and (c) reflection coefficient
-32-
(a)
(b)
(c)
Fig 36 Feed performance versus the dielectric ring thickness (a) E-plane
pattern(b) H-plane pattern and (c) reflection coefficient
-33-
From the above parametric analysis an optimum feed design is obtained
The result is shown in Table 31 Fig 37 shows the 2D gain patterns of
designed feed The antenna has a gain of 903dB 933dB and 956dB at
171GHz 1825GHz and 19GHz respectively
Fig 38 shows E- and H-plane radiation patterns of the designed feed The
feed has E- and H-plane 10-dB beamwidths of 60 and 59 degrees at 17GHz
The feed has a front-to-back ration of 1900dB 2490dB and 2200dB at
171GHz 1825GHz and 19GHz respectively Table 32 summarizes the
performance of the designed narrow-band circular waveguide feed
The designed feed has a greatly improved performance over that of a
simple coax-fed feed described in Section 23
Table 31 Dimensions of the designed narrow-band circular feed
Parameter Designation Value(mm)
a Waveguide inside radius 640
l Feed length 2890
lp Probe length 363
sp Probe position from the back short 616
din Probe diameter 127
dout Diameter of coaxial cables outer conductor 400
t Thickness of choked wall 050
tch Choke slot width 100
lch Choke depth 410
ld Dielectric ring length 1168
td Dielectric ring thickness 155
d1 Waveguide outside diameter 1680
-34-
(a)
(b)
Fig 37 2D gain patterns of the narrow-band circular waveguide feed at
(a) 17GHz (b) 1825GHz and (c) 19GHz
-35-
(c)
Fig 37 continued
-36-
(a)
(b)
(c)
Fig 38 E- and H-plane patterns of the narrow-band circular waveguide feed
at (a) 10GHz (b) 1825GHz and (c) 195GHz
-37-
Frequency(GHz)
Gain(dB)
E-H-plane10-dB beamwidths
(deg)
Front-to-back ratio(dB)
Phase centerlocation
(From feeds aperture plane
toward reflector)
(mm)
1700 903 6059 20 062
1825 933 6060 25 004
1900 956 5759 22 007
Table 32 Performance of the narrow-band circular waveguide feed
The designed narrow-band feed is fabricated and its performance is
measured and compared with the simulation results The designed feed is
fabricated in a numerically-controlled machining center The fabricated antenna
is shown in Fig 39
Fig 39 Photograph of the fabricated feed
-38-
Fig 310 shows a comparison of the measured and simulated reflection
coefficients The measured reflection coefficient is less than -10dB over
171-197GHz The agreement between simulated and measured results are
good
Fig 311 shows the E- and H-plane patterns of the fabricated feed at
187GHz The feed has 90dB gain simulation and measurement results are in
good agreement
The fabricated antennarsquos 10dB beamwidth is 60 degrees in both E and H
planes at 187GHz The front-to-back ratio is 21dB
Fig 310 Reflection coefficient of the fabricated feed
-39-
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Fee
d H
orn
Gain
- d
B
Angle - degree
(a)
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Feed H
orn
Gain
- d
B
Angle - degree
(b)
Fig 311 Gain patterns of the fabricated feed at 187 GHz (a) E-plane and
(b) H-plane
-40-
IV Design of Circular Waveguide Feeds Loaded with a
Dielectric Rod
In this section circular waveguide feeds loaded with a dielectric rod feed
are investigated A comprehensive discussion of the circular waveguide loaded
with a dielectric rod is given by Kumar[7] Inserting a dielectric material
inside the circular waveguide improves the E- and H-plane pattern symmetry
In general dielectric-loaded circular waveguide feeds show good performance
only over a narrow bandwidth
Fig 41 shows the geometry of a circular waveguide loaded with a
dielectric rod The waveguide length is 400mm and the wall thickness is
05mm The dielectric rods diameter is 207mm The dielectric rod is
extended 05 wavelength beyond the waveguide open end The dielectric
constant εr is changed and the feeds performance is observed
Fig 41 Geometry of a circular waveguide loaded with a uniform dielectric
rod
-41-
Fig 42 is the radiation pattern of the feed with εr = 25 and L = 05λ0 at
9GHz E- and H-plane 10-dB beamwidths are 810 and 807 degrees
respectively The front-to-back ratio is 18dB The antenna gain is 71dB
(a)
(b)
Fig 42 Radiation pattern at 9GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 05λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-42-
Fig 43 shows the radiation pattern of the feed with εr = 21 at 10GHz
E- and H-plane 10-dB beamwidths are 70 and 71 degrees respectively The
front-to-back ratio is 19dB The antenna gain is 83dB
(a)
(b)
Fig 43 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 21 and L = 05λ0 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-43-
Fig 44 shows the radiation pattern of the feed with εr = 30 at 8GHz
E- and H-plane 10-dB beamwidths are 83 and 824 degrees respectively The
front-to-back ratio is 17dB The antenna gain is 73dB
(a)
(b)
Fig 44 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 30 and L = 05λ0 at 8GHz (a) 2D radiation pattern
and (b) E- and H-plane patterns
-44-
Fig 45 shows the radiation pattern of the feed with εr = 50 at 18GHz
E- and H-plane 10-dB beamwidths are 56 and 54 degrees respectively The
front-to-back ratio is 27dB The antenna gain is 105dB The feed has a good
pattern symmetry and low back radiation
(a)
(b)
Fig 45 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 50 and L = 05λ0 at 18GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-45-
Fig 46 is the radiation pattern of the feed with εr = 25 and L = 10λ0 at
10GHz E- and H-plane 10-dB beamwidths are 50 and 48 degrees
respectively The front-to-back ratio is 16dB The antenna gain is 105dB
(a)
(b)
Fig 46 Radiation pattern at 10GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 10λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-46-
Fig 47 shows the geometry of a circular waveguide with a tapered
dielectric rod The designed feed has the following dimension L = 1λ0 d =
1λ0 and εr =25 at 10GHz The waveguide length is 40mm and the wall
thickness is 05mm
L
Dielectricd3
Fig 47 Geometry of a circular waveguide loaded with a tapered dielectric
rod
Fig 48 shows the radiatio pattern of the designed feed E- and H-plane
10-dB beamwidths are 575 and 564 degrees respectively The front-to-back
ratio is 377dB The antenna gain is 94dB The designed feed has an
excellent beamwidth symmetry and a very low back radiation
-47-
(a)
(b)
Fig 48 Radiation pattern of a circular waveguide loaded with a tapered
dielectric rod with L = 1λ0 d = 1λ0 and εr =25 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-48-
Fig 49 shows the geometry of a spherical ended dielectric rod feed
diameter of 06λ0 at 10GHz with a dielectric constant of 25 and L= 03λ0
Fig 410 shows the radiation patterns of the designed feed E- and H-plane
10-dB beamwidths are both 63 degrees The front-to-back ratio is 24dB The
antenna gain is 864dB
Fig 49 Geometry of a circular waveguide loaded with a spherical ended
dielectric rod
-49-
(a)
(b)
Fig 410 Radiation pattern of a circular waveguide loaded wht a spherical
ended dielectric rod with d = 06λ0 L = 03λ0 and εr =25 at 10GHz (a) 3D
radiation pattern and (b) E- and H-plane patterns
-50-
V Design of a Broadband Circular Waveguide Feed
In this chapter the design of a broadband circular waveguide feed is
presented At microwave frequencies the feed is often a circular waveguide
with chokes and corrugations around the aperture Chokes and corrugations
equalize E- and H-plane patterns and reduce the back radiation
The proposed feed is designed to operate over 10-18GHz The design starts
with the optimization of the coaxial-to-rectangular waveguide adapter
employed for good mode purity over a broad frequency range Next a
rectangular-to-circular waveguide transition is optimized Finally chokes and
corrugations are designed for improved pattern symmetry and low back
radiation
The proposed feed structure is shown in Fig 51 The feed consist of the
following parts a coaxial-to-rectangular waveguide adapter a rectangular-to-
circular waveguide transition a circular waveguide section four quarter-wave
chokes around the feeds aperture and four corrugations on the feeds outer
surface
The computer simulation shows the above arrangement offers good radiation
patterns over a broad frequency range The broadband operation is obtained
by exciting the TE11 mode in the circular waveguide using the TE10 mode of
the rectangular waveguide which is in turn excited by a coaxial probe
-51-
Chokes
Coaxial-to-waveguide transition
Circular wavguide
Corrugations
Mode transition
(a)
(b)
Fig 51 Structure of the proposed broadband circular waveguide feed
(a) CAD model and (b) cross-sectional view
For the coaxial-to-rectangular waveguide adapter an SMA connector with
the probe diameter of 127 mm is employed The coaxial probe inserted into
the waveguide energizes the feed and excites the dominant TE10 mode in
-52-
the rectangular waveguide The impedance matching is achieved by adjusting
the probe distance sp from the back short and the probe length lp
(a)
(b)
Fig 52 Reflection coefficient of the coaxial-to-rectangular adapter versus
(a) probe length lp and (b) the probe position sp
Fig 52 shows the reflection coefficient versus the various values of probe
lengths lp and probe positions sp The probe length lp is adjusted to obtain
antenna impedance matching and the probe distance sp is adjusted to obtain a
-53-
desired resonant frequency
Next a transition between rectangular and circular waveguide is designed
The transition section converts the TE10 mode in the rectangular waveguide to
TE11 mode in the circular waveguide and vice versa The transition is built
in a form of a taper for easy fabrication[22]
(a)
(b)
Fig 53 Structure of the rectangular-to-circular waveguide transition
(a) 3D view and (b) cross sectional view
The dimensions of the final optimized transition are as follows The length
of the rectangular waveguide section is 143mm The rectangular waveguides
width a and height b are 207mm and 857mm respectively The length of
the circular waveguide section is 143mm The inside diameter of the circular
-54-
waveguide is 207mm(097 wavelength at 14GHz) The length of transition
region ltr is 4465mm(approximately equal to 2λ0 at 14GHz) Fig 54 shows
the field distribution inside the mode converter
(a)
(b)
Fig 54 Field distribution inside the mode converter at
(a) 10GHz (b) 14GHz and (c) 18GHz
-55-
(c)
Fig 54 continued
Finally multiple chokes are investigated Figs 55 56 and 57 show the
feed performance without chokes The reflection coefficient is less than -10dB
over 10-19GHz The antenna has a gain of 921dB to 1189dB over
10-19GHz
Fig 55 Reflection coefficient of the broadband circular waveguide feed
without chokes and corrugations
-56-
(a)
(b)
(c)
Fig 56 E- and H-plane patterns of the broadband circular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-57-
(d)
(e)
Fig 56 continued
-58-
(a)
(b)
Fig 57 2D radiation patterns of the broadband cicular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-59-
(c)
(d)
Fig 57 continued
-60-
(e)
Fig 57 continued
To achieve equal beamwidths in E and H planes over a wide frequency
range chokes and corrugations are employed Table51 summarizes the
performance of a feed without chokes and corrugations
Table 51 Performance of the broadband circular waveguide feed without
chokes and corrugations
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
1000 940 6061 15
1200 972 6159 17
1400 920 5957 21
1600 1070 4751 29
1800 1188 5352 21
-61-
Four quarter-wavelength chokes are introduced in the feed design which
has a slot depth of 75mm and slot width of 09mm The choke slot spacing
is 18mm The choke design is investigated by applying the choke one by
one and the effect on the E- and H-plane patterns are observed as illustrated
in Figs 58 and 59 The use of chokes makes the E-plane pattern narrower
The H-plane pattern is not affected Chokes increase the gain slightly and
reduce back radiation
(a)
(b)
Fig 58 Effect of chokes on the E-plane pattern of the broadband circular
waveguide feed at (a) 10GHz(b) 12GHz (c) 14GHz (d) 16GHz and (e)
18GHz
-62-
(c)
(d)
(e)
Fig 58 continued
-63-
(a)
(b)
(c)
Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-64-
(d)
(e)
Fig 59 continued
-65-
Fig 510 shows the feed performance versus the choke depth When the
choke depth is varied from 535mm to 95mm the E- and H-plane patterns
are strongly affected The optimum value of choke depth is 75mm(035λ0 at
14GHz) which gives equal E- and H-plane radiation patterns and leads to
low back radiation
Fig 511 shows the feed performance versus the choke slot width tch The
choke slot width is varied from 09mm to 21mm Radiation patterns and
reflection coefficients are not sensitive to the choke slot width The final
choke slot width is selected to be 09mm considering the feed diameter
minimization and the manufacturability The overall diameter of the proposed
feed is 369mm which is increased from the 207mm of the waveguide
inside diameter due to the use of four chokes
-66-
(a)
(b)
(c)
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection coefficient
-67-
(a)
(b)
(c)
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and (c)
reflection coefficient
-68-
Next we investigated corrugations placed on the outer wall of the feed
Four corrugations applied to the outer surface of the circular waveguide The
corrugation depth is 465mm(0215λ0 at 14GHz) The primary purpose of
using corrugations is to further reduce the back radiation Increasing the
number of corrugations beyond four has little effect in reducing the back
radiation
Figs 512 and 513 show the effect of corrugations on the E- and H-plane
patterns Fig 514 shows the parametric study of the corrugation depth lcor
The corrugation depth is varied from 40mm and 645mm The optimum
value of the corrugation depth is found to be 465mm
-69-
(a)
(b)
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern at (a) 12GHz and (b) 14GHz
-70-
(a)
(b)
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern at (a) 12GHz and (b) 14GHz
-71-
(a)
(b)
(c)
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection coefficient
-72-
The phase center location is important in placing the feed in a reflector
antenna[8] The phase center variation with frequency should be small Fig
515 shows the effect of chokes and corrugations on the phase center The
curve with circle corresponds to the case without chokes and corrugations
The phase center varies from -326mm and -190mm away from the feeds
aperture plane It means the phase center is located inside the waveguide
The curve with triangles corresponds to the case with chokes The curve with
squares to the case with chokes and corrugations The phase center varies
from 0mm to -302mm
From Fig 515 we can observed that phase center variation reduced by the
corrugation and three cases phase center calculated in φ=450 plane
parameter sweep values are given in Table 52
10 12 14 16 181
0
-1
-2
-3
-4
-5
-6
Pha
se c
ente
r (m
m)
Frequency (GHz)
choke+corrugatuion without choke corrugation with choke
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
-73-
Frequency
(GHz)
Phase center from the aperture plane
(mm)
Without
chokes and
corrugations
With
chokes
With chokes
and
corrugations
1000 -326 062 000
1100 -187 030 -002
1200 -563 -208 -065
1300 -296 -154 -202
1400 -319 -314 -302
1500 -201 -203 -241
1600 -242 -233 -207
1700 -208 -208 -186
1800 -190 -157 -132
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
Based on the foregoing parametric studies optimum dimensions of the
broadband circular waveguide feed are obtained as shown in Table 53
-74-
Table 53 Optimum dimensions of the broadband circular waveguide feed
Parameter Designation Value (mm)
2a Waveguide inside diameter 2070
d Waveguide outside diameter 3690
lcrLength of the circular waveguide section 1430
m Distance between the aperture plane and the first corrugation 950
xDistance from the last corrugation to the end of the cylindrical outer surface
550
ltrLength of the rectangular-to-circularwaveguide transition 4465
lrcLength of the rectangular waveguide section 1430
tch Choke slot width 090
lch Choke depth 750
t Choke metal width 090
lcor Corrugation depth 465
tcor Corrugation metal width 100
s Corrugation slot width 10
lp Probe length 530
sp Probe position from the back short 530
din Probe diameter 127
b Inside height of the rectangular waveguide 857
tw Waveguide wall thickness 500
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-1-
I Introduction
The horns and waveguides are known for their high efficiency and
structural simplicity They are popular choices for feeding for reflectors in
high-gain antenna applications such as satellite and point-to-point microwave
communication links The theory of reflector antenna was developed in the
1940s and has been used to calculate the radiation patterns of various
reflector structures[1]
The basic structure of a prime-focus reflector antenna consists of a
parabolic reflecting surface a feed and its support The placement of the feed
is such that its phase center is at the focal point of the parabolic reflecting
surface The feed is often a circular waveguide because of its symmetric
radiation pattern with low back radiation and low cross polarization The
circular waveguide feed must have a small diameter to reduce the aperture
blockage of the reflector antenna[3]
A radiation pattern with a good circular symmetry in the main beam can
be found from circular waveguide feeds with dominant TE11 mode excitation
The radiation patterns depends on the diameter and wall thickness of the
waveguide[4] A coaxial probe can be inserted into a short-circuited circular
waveguide in the form of a coaxial-to-waveguide transition The diameter of
the circular waveguide is chosen such that only the dominant mode
propagates
When the waveguide dimension does not provide a circular symmteric
-2-
pattern a choke or multiple chokes around the aperture wall can be
employed to equalize radiation patterns and keep the back radiation in low
level If chokes are not enough for the suppression of the back radiation
corrugations on the outer surface of the feed is one way to reduce the back
radiation
In this thesis a broadband circular waveguide feed is developed for
prime-focus reflector antenna application After investigating the radiation
properties of simple circular and square waveguides methods are investigated
for bandwidth enhancement back radiation suppression and beamwidth
equalization in the circular waveguide feed
The first type of the circular waveguide feed consists of a probe-fed
circular waveguide a single quarter-wave choke on the aperture wall and a
dielectric-ring beamwidth equalizer Due to the simple feeding method the
first feed operates over 171-197GHz(141) which is not broadband in the
strict sense of the word
The second feed consists of a coaxial-to-rectangular waveguide transition a
rectangular-to-circular waveguide transition a circular waveguide section four
quarter-wave chokes on the aperture wall and four quarter-wave corrugations
on the feeds outer surface Due to the complicated feeding method the
second feed operates over 10-18GHz(571)
This thesis is arranged as follows Chapter I gives an introduction to the
thesis related works and objectives are stated Chapter II describes the
structure and excitation of the circular and square waveguide and the
operation of the coaxial-to-waveguide transitions Chapter III describes a
compact feed horn design and its fabrication and measurement Chapter IV
-3-
presents dielectric rod feed and its simulated performances Chapter V gives
design and optimization of feed for parabolic reflector antenna In this
chapter includes the detailed information of design procedures and operating
principle also the simulated and measured performances are provided Finally
conclusion is given in the Chapter VI
-4-
II Analysis of Circular and Square Waveguide Feeds
21 Circular Waveguide Radiator
Before design a complicated circular waveguide feed it is helpful to
investigate the impedance and radiation properties of a circular waveguide
open end
The circular waveguide is a cylindrical hollow metallic pipe with a uniform
circular section of radius a Circular waveguides are normally designed to
operate only with the dominant mode The dominant mode in a waveguide is
the mode having the lowest cutoff frequency given by equation (21)
(21)
where
(22)
and a is the waveguide radius The following chart[2] and table show the
cutoff frequencies of various modes in a circular waveguide
-5-
Modes c al11TEc cf f
TE11 341259 100000
TM01 261274 130613
TE21 205720 165885TE01 163979 208111
TM11 163979 208111TE31 149557 228180
TM21 122345 278932TE41 118159 288813
TE12 117852 289566
TM02 113824 299813TE02 0897986 380027
The recommended frequency range of the commercial circular waveguide is
given by the following equation This assumes that the TM01 mode is not
generated or suppressed if generated
11 21 11TE TE TE115 095 158 32 bandwidthc c cf f f fpound pound = reg (23)
Fig 21 shows the geometry of a circular waveguide with a diameter of 2a
When 2a is 2053mm the cutoff frequency of the TE11 mode is 857GHz
According to (23) the useful operating frequency range is from
986-1354GHz
Fig 22 shows the reflection of this waveguide excited with the dominant
TE11 mode The waveguide length l is 60mm The reflection occurs at the
open end of the circular waveguide The reflection coefficient is less than
-15dB over 10-18GHz
-6-
Fig 21 Geometry of a circular waveguide open end radiator
Fig 23 shows a 2D gain pattern of this waveguide antenna The
waveguide antenna has a gain of 80dB 99dB and 115dB at 10GHz
14GHz and 18GHz respectively Fig 24 shows the E- and H-plane patterns
of the circular waveguide antenna Table 21 summarizes the properties of a
circular waveguide antenna
Fig 22 Reflection coefficient of a circular waveguide open end radiator
-7-
(a)
(b)
Fig 23 2D radiation pattern of the circular waveguide open end radiator
at (a)10GHz (b) 14GHz and (c) 18GHz
-8-
(c)
Fig 23 continued
-9-
(a)
(b)
(c)
Fig 24 E-plane and H-plane patterns of the circular waveguide open end
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-10-
Table 21 Properties of a circular waveguide open end radiator of diameter
2053mm
Frequency(GHz)-10dB Beamwith(deg) Front-to-Back
Ratio(dB)E plane H plane
10 67 73 12
14 58 60 18
18 41 50 21
In a circular waveguide radiatoλr a good pattern symmetry and low back
radiation is obtained at 14GHz where 2aλ = 096
22 Square Waveguide Radiator
A square waveguide is often used as a dual-polarized feed To operate the
cutoff frequency of the dominant mode a square-waveguide wall width a
must be greater than one half of a wavelength The modes with cutoff
frequencies equal to or smaller than the operational frequency can exist inside
the waveguide wall The lower cutoff frequency and cutoff wavelength for
square waveguide is determined by the following equations
TE
(24)
TE
(25)
The next higher-order mode is TE11 mode with the cutoff wavelength
given by
-11-
TE
(26)
Similar to the circular waveguide the recommended operating frequency range
of a square waveguide is given by
TEleleTE
TErarr bandwidth (27)
Fig 25 shows the geometry of a square waveguide with a dimension of a
When a is 157mm the cutoff frequency is 95GHz The recommended
operating frequency of this waveguide is from 109GHz to 155GHz
Fig 26 shows the reflection of this waveguide excited with the dominant
TE10 mode The reflection coefficient is less than -15dB over 10-20GHz
Fig 25 Geometry of a square waveguide open end radiator
Fig 27 and shows the 2D radiation pattern of a square waveguide antenna
excited with the dominant TE10 mode The antenna has a gain of 73dB
85dB and 102dB at 10GHz 14GHz and 18GHz respectively Fig 28
shows the E- and H-plane radiation patterns of a square waveguide radiator
Table 22 summarizes the properties of a square waveguide open end radiator
-12-
Fig 26 Reflection coefficient of a square waveguide open end radiator
(a)
Fig 27 2D radiation patterns of a square waveguide radiator
at (a) 10GHz (b) 14GHz and (c) 18GHz
-13-
(b)
(c)
Fig 27 continued
-14-
(a)
(b)
(c)
Fig 28 E-plane and H-plane patterns of square waveguide open radiator
at (a) 10GHz(b) 14GHz and (c) 18GHz
-15-
Table 22 Properties of a square waveguide open end radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 69 71 11
14 47 60 25
18 58 62 16
The radiation pattern symmetry and back radiation performance of the
square waveguide are inferior to those of a circular waveguide
23 Probe-Fed Circular Waveguide Radiator
In Section 21 the radiation properties of a TE11-mode excited waveguide
is investigated In this section a circular waveguide fed by a coaxial probe
shown in Fig 29 is studied
The coaxial probes diameter is 127mm With the Teflon dielectric the
50-ohm coaxial lines outer conductor has a diameter of 41mm For a
circular waveguide the wave impedance of the TE11 mode is given by
∙ (28)
where λg is the guided wavelength given by
(29)
-16-
(a) (b)
Fig 29 Probe-fed circular waveguide radiator (a) Front view and (b) side
view
The combination of the probe length and the probe position from the
shorted wall enables a good impedance matching The probe distance sp from
the back short is close to a quarter wavelength at the design frequency
The designed feed has the following dimension d = 2053mm lp = 42
mm sp = 534mm wall thickness = 05mm and feed length = 400mm
Fig 210 shows the reflection coefficient of the designed probe-fed
circular waveguide radiator The reflection coefficient is less than -10dB over
138-187GHz Fig 211 and 212 shows the E-plane and H-plane radiation
patterns and 2D radiation patterns of the coaxial-to-circular waveguide
transition The radiation patterns symmetry distorted because of the high order
modes The coaxial-to-circular waveguide transition has 73dB 84dB and
79dB gain at 10GHz 14GHz and 18GHz frequencies respectively Table 23
shows the properties of the coaxial-to-circular waveguide transition
-17-
Fig 210 Reflection coefficient of the probe-fed circular waveguide radiator
(a)
Fig 211 2D radiation pattern of the probe-fed circular waveguide radiator
at (a) 10GHz (b) 14GHz and (c) 18GHz
-18-
(b)
(c)
Fig 211 continued
-19-
(a)
(b)
(c)
Fig 212 E- and H-plane patterns of the probe-fed circular waveguide
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-20-
Table 23 Properties of the probe-fed circular waveguide radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 73 70 1414 83 57 17
18 60 52 30
When a circular waveguide radiator is fed by a coaxial probe its radiation
properties are not good due to the excitation of higher-order modes
Therefore a probe-fed circular waveguide radiator can be used as a feed only
over a narrow frequency range
24 Probe-Fed Square Waveguide Radiator
In this section a probe-fed square waveguide radiator is investigated Fig
213 shows a coaxial probe-fed square waveguide radiator The designed
radiator has the following dimension a = b = 157mm lp = 35 mm sp =
50 mm wall thickness = 05mm and feed length = 40mm
(a) (b)
Fig 213 Probe-fed square waveguide radiator (a) Front view and (b) side
view
-21-
Fig 214 shows the 2D radiation patterns of the radiator at 10GHz
14GHz and 18GHz Fig 215 shows E- and H-plane patterns of the radiator
Fig 216 shows the reflection coefficient of the probe-fed square waveguide
radiator The reflection coefficient is less than -10dB over 13-20GHz Table
24 summarizes the properties of the probe-fed square waveguide radiator
(a)
Fig 214 2D radiation patterns of the probe-fed square waveguide radiator at
(a) 10GHz (b) 14GHz and (c) 18GHz
-22-
(b)
(c)
Fig 214 continued
-23-
(a)
(b)
(c)
Fig 216 E-plane and H-plane patterns of the probe-fed square waveguide
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-24-
Fig 216 Reflection coefficient of the probe-fed square waveguide radiator
Table 24 Properties of the probe-fed square waveguide radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 73 71 12
14 85 63 1418 27 65 28
When a square waveguide radiator is fed by a coaxial probe its radiation
properties are not good due to the excitation of higher-order modes as in the
case of the probe-fed circular waveguide radiator A probe-fed square
waveguide radiator can be used as a feed only over a narrow frequency
range
-25-
III Design of Compact Circular Waveguide Feeds
In this chapter the feed design is presented for a prime-focus reflector
antenna The prime-focus paraboloid reflector is one of the most commonly
used high-gain antenna It has been used in earth-station antennas and radio
telescopes It consists of a paraboloid reflector with a feed system at its focal
point
The feed should radiate a low level of cross-polar power over the
operating frequency These conditions not easy to achieve and most prime
focus feeds are compromises The shape and characteristic of the radiation
pattern of the feed are the most important parameter because these will
directly influence the fields which are directed at a reflector[6] Other
electrical factors which relevant to the choice of a feed are the cross-polar
level the gain efficiency the bandwidth and impedance matching
31 Narrow-Band Circular Waveguide Feed
Fig 31 shows the proposed narrow-band circular waveguide feed and its
design variables The feed consists of a circular waveguide open end excited
by a TE11 dominant mode A quarter wave choke is applied along the
circular aperture of the waveguide to equalize E- and H-plane radiation
patterns and to suppress the back radiation A dielectric ring is used to
control the radiation pattern and change the power distribution over the
aperture The control of the amplitude over the aperture are essential to the
design of symmetric radiation pattern The material used for dielectric loading
-26-
is the monocast(MC) nylon with a dielectric constant of 30 The feed is
designed to operate over 171-197GHz
(a)
(b)
Fig 31 Narrow-band circular waveguide feed (a) CAD model and (b) a
cross sectional view
The impedance matching is achieved by a proper combination of the probe
height lp and its distance sp from the waveguide shorted end Here the
-27-
circular waveguide is terminated with an open end with a wall thickness of
2mm radiating into the free space
Fig 32 shows the effect of the probe length lp and the probe distance sp
on the reflection coefficient The best performance is obtained when lp =
363mm and sp = 616mm The feeds reflection coefficient is less than -10dB
over 170-195GHz
(a)
(b)
Fig 32 Effect of the (a) the probe length lp and (b) the probe
distance sp on the reflection coefficient
-28-
Fig 33 shows the effect of the choke depth The E-plane pattern is more
sensitive to the choke depth than the H-plane pattern The choke depth has a
strong influence on the reflection coefficient when it is 360mm By properly
choosing the choke depth we can equalize the E- and H-plane patterns The
optimum value of the choke depth is 410mm which is 0249λ0 at 1825GHz
The choke slot width tch in the range of 06-12mm has almost no effect
on the H-plane pattern and the reflection coefficient For the E-plane pattern
tch of 12mm has some effect on the E-plane radiation pattern as shown in
Fig 34
Fig 35 shows the feed performance versus the dielectric ring length We
observe in Fig 35 that the dielectric length ld has an optimum value of
1168mm which does no effect on the H-plane pattern and tha the value of
1048mm has some effect on the E-plane pattern and the reflection
coefficient
Fig 36 shows E-plane and H-plane patterns and the reflection coefficient
versus the dielectric thickness With the optimum value of the dielectric
thickness t obtained from the Fig 36 is 155mm The larger values of td has
much stronger effects on the E-plane pattern and the reflection coefficient
The H-plane pattern is not sensitive to the dielectric ring thickness
-29-
(a)
(b)
(c)
Fig 33 Feed performance versus the choke depth (a) E-plane pattern
(b) H-plane pattern and (c) reflection coefficient
-30-
(a)
(b)
(c)
Fig 34 Feed performance versus the choke slot width (a) E-plane pattern
(b) H-plane pattern and (c) reflection coefficient
-31-
(a)
(b)
(c)
Fig 35 Feed performance versus the dielectric ring length (a) E-plane
pattern (b) H-plane pattern and (c) reflection coefficient
-32-
(a)
(b)
(c)
Fig 36 Feed performance versus the dielectric ring thickness (a) E-plane
pattern(b) H-plane pattern and (c) reflection coefficient
-33-
From the above parametric analysis an optimum feed design is obtained
The result is shown in Table 31 Fig 37 shows the 2D gain patterns of
designed feed The antenna has a gain of 903dB 933dB and 956dB at
171GHz 1825GHz and 19GHz respectively
Fig 38 shows E- and H-plane radiation patterns of the designed feed The
feed has E- and H-plane 10-dB beamwidths of 60 and 59 degrees at 17GHz
The feed has a front-to-back ration of 1900dB 2490dB and 2200dB at
171GHz 1825GHz and 19GHz respectively Table 32 summarizes the
performance of the designed narrow-band circular waveguide feed
The designed feed has a greatly improved performance over that of a
simple coax-fed feed described in Section 23
Table 31 Dimensions of the designed narrow-band circular feed
Parameter Designation Value(mm)
a Waveguide inside radius 640
l Feed length 2890
lp Probe length 363
sp Probe position from the back short 616
din Probe diameter 127
dout Diameter of coaxial cables outer conductor 400
t Thickness of choked wall 050
tch Choke slot width 100
lch Choke depth 410
ld Dielectric ring length 1168
td Dielectric ring thickness 155
d1 Waveguide outside diameter 1680
-34-
(a)
(b)
Fig 37 2D gain patterns of the narrow-band circular waveguide feed at
(a) 17GHz (b) 1825GHz and (c) 19GHz
-35-
(c)
Fig 37 continued
-36-
(a)
(b)
(c)
Fig 38 E- and H-plane patterns of the narrow-band circular waveguide feed
at (a) 10GHz (b) 1825GHz and (c) 195GHz
-37-
Frequency(GHz)
Gain(dB)
E-H-plane10-dB beamwidths
(deg)
Front-to-back ratio(dB)
Phase centerlocation
(From feeds aperture plane
toward reflector)
(mm)
1700 903 6059 20 062
1825 933 6060 25 004
1900 956 5759 22 007
Table 32 Performance of the narrow-band circular waveguide feed
The designed narrow-band feed is fabricated and its performance is
measured and compared with the simulation results The designed feed is
fabricated in a numerically-controlled machining center The fabricated antenna
is shown in Fig 39
Fig 39 Photograph of the fabricated feed
-38-
Fig 310 shows a comparison of the measured and simulated reflection
coefficients The measured reflection coefficient is less than -10dB over
171-197GHz The agreement between simulated and measured results are
good
Fig 311 shows the E- and H-plane patterns of the fabricated feed at
187GHz The feed has 90dB gain simulation and measurement results are in
good agreement
The fabricated antennarsquos 10dB beamwidth is 60 degrees in both E and H
planes at 187GHz The front-to-back ratio is 21dB
Fig 310 Reflection coefficient of the fabricated feed
-39-
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Fee
d H
orn
Gain
- d
B
Angle - degree
(a)
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Feed H
orn
Gain
- d
B
Angle - degree
(b)
Fig 311 Gain patterns of the fabricated feed at 187 GHz (a) E-plane and
(b) H-plane
-40-
IV Design of Circular Waveguide Feeds Loaded with a
Dielectric Rod
In this section circular waveguide feeds loaded with a dielectric rod feed
are investigated A comprehensive discussion of the circular waveguide loaded
with a dielectric rod is given by Kumar[7] Inserting a dielectric material
inside the circular waveguide improves the E- and H-plane pattern symmetry
In general dielectric-loaded circular waveguide feeds show good performance
only over a narrow bandwidth
Fig 41 shows the geometry of a circular waveguide loaded with a
dielectric rod The waveguide length is 400mm and the wall thickness is
05mm The dielectric rods diameter is 207mm The dielectric rod is
extended 05 wavelength beyond the waveguide open end The dielectric
constant εr is changed and the feeds performance is observed
Fig 41 Geometry of a circular waveguide loaded with a uniform dielectric
rod
-41-
Fig 42 is the radiation pattern of the feed with εr = 25 and L = 05λ0 at
9GHz E- and H-plane 10-dB beamwidths are 810 and 807 degrees
respectively The front-to-back ratio is 18dB The antenna gain is 71dB
(a)
(b)
Fig 42 Radiation pattern at 9GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 05λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-42-
Fig 43 shows the radiation pattern of the feed with εr = 21 at 10GHz
E- and H-plane 10-dB beamwidths are 70 and 71 degrees respectively The
front-to-back ratio is 19dB The antenna gain is 83dB
(a)
(b)
Fig 43 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 21 and L = 05λ0 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-43-
Fig 44 shows the radiation pattern of the feed with εr = 30 at 8GHz
E- and H-plane 10-dB beamwidths are 83 and 824 degrees respectively The
front-to-back ratio is 17dB The antenna gain is 73dB
(a)
(b)
Fig 44 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 30 and L = 05λ0 at 8GHz (a) 2D radiation pattern
and (b) E- and H-plane patterns
-44-
Fig 45 shows the radiation pattern of the feed with εr = 50 at 18GHz
E- and H-plane 10-dB beamwidths are 56 and 54 degrees respectively The
front-to-back ratio is 27dB The antenna gain is 105dB The feed has a good
pattern symmetry and low back radiation
(a)
(b)
Fig 45 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 50 and L = 05λ0 at 18GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-45-
Fig 46 is the radiation pattern of the feed with εr = 25 and L = 10λ0 at
10GHz E- and H-plane 10-dB beamwidths are 50 and 48 degrees
respectively The front-to-back ratio is 16dB The antenna gain is 105dB
(a)
(b)
Fig 46 Radiation pattern at 10GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 10λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-46-
Fig 47 shows the geometry of a circular waveguide with a tapered
dielectric rod The designed feed has the following dimension L = 1λ0 d =
1λ0 and εr =25 at 10GHz The waveguide length is 40mm and the wall
thickness is 05mm
L
Dielectricd3
Fig 47 Geometry of a circular waveguide loaded with a tapered dielectric
rod
Fig 48 shows the radiatio pattern of the designed feed E- and H-plane
10-dB beamwidths are 575 and 564 degrees respectively The front-to-back
ratio is 377dB The antenna gain is 94dB The designed feed has an
excellent beamwidth symmetry and a very low back radiation
-47-
(a)
(b)
Fig 48 Radiation pattern of a circular waveguide loaded with a tapered
dielectric rod with L = 1λ0 d = 1λ0 and εr =25 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-48-
Fig 49 shows the geometry of a spherical ended dielectric rod feed
diameter of 06λ0 at 10GHz with a dielectric constant of 25 and L= 03λ0
Fig 410 shows the radiation patterns of the designed feed E- and H-plane
10-dB beamwidths are both 63 degrees The front-to-back ratio is 24dB The
antenna gain is 864dB
Fig 49 Geometry of a circular waveguide loaded with a spherical ended
dielectric rod
-49-
(a)
(b)
Fig 410 Radiation pattern of a circular waveguide loaded wht a spherical
ended dielectric rod with d = 06λ0 L = 03λ0 and εr =25 at 10GHz (a) 3D
radiation pattern and (b) E- and H-plane patterns
-50-
V Design of a Broadband Circular Waveguide Feed
In this chapter the design of a broadband circular waveguide feed is
presented At microwave frequencies the feed is often a circular waveguide
with chokes and corrugations around the aperture Chokes and corrugations
equalize E- and H-plane patterns and reduce the back radiation
The proposed feed is designed to operate over 10-18GHz The design starts
with the optimization of the coaxial-to-rectangular waveguide adapter
employed for good mode purity over a broad frequency range Next a
rectangular-to-circular waveguide transition is optimized Finally chokes and
corrugations are designed for improved pattern symmetry and low back
radiation
The proposed feed structure is shown in Fig 51 The feed consist of the
following parts a coaxial-to-rectangular waveguide adapter a rectangular-to-
circular waveguide transition a circular waveguide section four quarter-wave
chokes around the feeds aperture and four corrugations on the feeds outer
surface
The computer simulation shows the above arrangement offers good radiation
patterns over a broad frequency range The broadband operation is obtained
by exciting the TE11 mode in the circular waveguide using the TE10 mode of
the rectangular waveguide which is in turn excited by a coaxial probe
-51-
Chokes
Coaxial-to-waveguide transition
Circular wavguide
Corrugations
Mode transition
(a)
(b)
Fig 51 Structure of the proposed broadband circular waveguide feed
(a) CAD model and (b) cross-sectional view
For the coaxial-to-rectangular waveguide adapter an SMA connector with
the probe diameter of 127 mm is employed The coaxial probe inserted into
the waveguide energizes the feed and excites the dominant TE10 mode in
-52-
the rectangular waveguide The impedance matching is achieved by adjusting
the probe distance sp from the back short and the probe length lp
(a)
(b)
Fig 52 Reflection coefficient of the coaxial-to-rectangular adapter versus
(a) probe length lp and (b) the probe position sp
Fig 52 shows the reflection coefficient versus the various values of probe
lengths lp and probe positions sp The probe length lp is adjusted to obtain
antenna impedance matching and the probe distance sp is adjusted to obtain a
-53-
desired resonant frequency
Next a transition between rectangular and circular waveguide is designed
The transition section converts the TE10 mode in the rectangular waveguide to
TE11 mode in the circular waveguide and vice versa The transition is built
in a form of a taper for easy fabrication[22]
(a)
(b)
Fig 53 Structure of the rectangular-to-circular waveguide transition
(a) 3D view and (b) cross sectional view
The dimensions of the final optimized transition are as follows The length
of the rectangular waveguide section is 143mm The rectangular waveguides
width a and height b are 207mm and 857mm respectively The length of
the circular waveguide section is 143mm The inside diameter of the circular
-54-
waveguide is 207mm(097 wavelength at 14GHz) The length of transition
region ltr is 4465mm(approximately equal to 2λ0 at 14GHz) Fig 54 shows
the field distribution inside the mode converter
(a)
(b)
Fig 54 Field distribution inside the mode converter at
(a) 10GHz (b) 14GHz and (c) 18GHz
-55-
(c)
Fig 54 continued
Finally multiple chokes are investigated Figs 55 56 and 57 show the
feed performance without chokes The reflection coefficient is less than -10dB
over 10-19GHz The antenna has a gain of 921dB to 1189dB over
10-19GHz
Fig 55 Reflection coefficient of the broadband circular waveguide feed
without chokes and corrugations
-56-
(a)
(b)
(c)
Fig 56 E- and H-plane patterns of the broadband circular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-57-
(d)
(e)
Fig 56 continued
-58-
(a)
(b)
Fig 57 2D radiation patterns of the broadband cicular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-59-
(c)
(d)
Fig 57 continued
-60-
(e)
Fig 57 continued
To achieve equal beamwidths in E and H planes over a wide frequency
range chokes and corrugations are employed Table51 summarizes the
performance of a feed without chokes and corrugations
Table 51 Performance of the broadband circular waveguide feed without
chokes and corrugations
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
1000 940 6061 15
1200 972 6159 17
1400 920 5957 21
1600 1070 4751 29
1800 1188 5352 21
-61-
Four quarter-wavelength chokes are introduced in the feed design which
has a slot depth of 75mm and slot width of 09mm The choke slot spacing
is 18mm The choke design is investigated by applying the choke one by
one and the effect on the E- and H-plane patterns are observed as illustrated
in Figs 58 and 59 The use of chokes makes the E-plane pattern narrower
The H-plane pattern is not affected Chokes increase the gain slightly and
reduce back radiation
(a)
(b)
Fig 58 Effect of chokes on the E-plane pattern of the broadband circular
waveguide feed at (a) 10GHz(b) 12GHz (c) 14GHz (d) 16GHz and (e)
18GHz
-62-
(c)
(d)
(e)
Fig 58 continued
-63-
(a)
(b)
(c)
Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-64-
(d)
(e)
Fig 59 continued
-65-
Fig 510 shows the feed performance versus the choke depth When the
choke depth is varied from 535mm to 95mm the E- and H-plane patterns
are strongly affected The optimum value of choke depth is 75mm(035λ0 at
14GHz) which gives equal E- and H-plane radiation patterns and leads to
low back radiation
Fig 511 shows the feed performance versus the choke slot width tch The
choke slot width is varied from 09mm to 21mm Radiation patterns and
reflection coefficients are not sensitive to the choke slot width The final
choke slot width is selected to be 09mm considering the feed diameter
minimization and the manufacturability The overall diameter of the proposed
feed is 369mm which is increased from the 207mm of the waveguide
inside diameter due to the use of four chokes
-66-
(a)
(b)
(c)
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection coefficient
-67-
(a)
(b)
(c)
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and (c)
reflection coefficient
-68-
Next we investigated corrugations placed on the outer wall of the feed
Four corrugations applied to the outer surface of the circular waveguide The
corrugation depth is 465mm(0215λ0 at 14GHz) The primary purpose of
using corrugations is to further reduce the back radiation Increasing the
number of corrugations beyond four has little effect in reducing the back
radiation
Figs 512 and 513 show the effect of corrugations on the E- and H-plane
patterns Fig 514 shows the parametric study of the corrugation depth lcor
The corrugation depth is varied from 40mm and 645mm The optimum
value of the corrugation depth is found to be 465mm
-69-
(a)
(b)
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern at (a) 12GHz and (b) 14GHz
-70-
(a)
(b)
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern at (a) 12GHz and (b) 14GHz
-71-
(a)
(b)
(c)
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection coefficient
-72-
The phase center location is important in placing the feed in a reflector
antenna[8] The phase center variation with frequency should be small Fig
515 shows the effect of chokes and corrugations on the phase center The
curve with circle corresponds to the case without chokes and corrugations
The phase center varies from -326mm and -190mm away from the feeds
aperture plane It means the phase center is located inside the waveguide
The curve with triangles corresponds to the case with chokes The curve with
squares to the case with chokes and corrugations The phase center varies
from 0mm to -302mm
From Fig 515 we can observed that phase center variation reduced by the
corrugation and three cases phase center calculated in φ=450 plane
parameter sweep values are given in Table 52
10 12 14 16 181
0
-1
-2
-3
-4
-5
-6
Pha
se c
ente
r (m
m)
Frequency (GHz)
choke+corrugatuion without choke corrugation with choke
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
-73-
Frequency
(GHz)
Phase center from the aperture plane
(mm)
Without
chokes and
corrugations
With
chokes
With chokes
and
corrugations
1000 -326 062 000
1100 -187 030 -002
1200 -563 -208 -065
1300 -296 -154 -202
1400 -319 -314 -302
1500 -201 -203 -241
1600 -242 -233 -207
1700 -208 -208 -186
1800 -190 -157 -132
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
Based on the foregoing parametric studies optimum dimensions of the
broadband circular waveguide feed are obtained as shown in Table 53
-74-
Table 53 Optimum dimensions of the broadband circular waveguide feed
Parameter Designation Value (mm)
2a Waveguide inside diameter 2070
d Waveguide outside diameter 3690
lcrLength of the circular waveguide section 1430
m Distance between the aperture plane and the first corrugation 950
xDistance from the last corrugation to the end of the cylindrical outer surface
550
ltrLength of the rectangular-to-circularwaveguide transition 4465
lrcLength of the rectangular waveguide section 1430
tch Choke slot width 090
lch Choke depth 750
t Choke metal width 090
lcor Corrugation depth 465
tcor Corrugation metal width 100
s Corrugation slot width 10
lp Probe length 530
sp Probe position from the back short 530
din Probe diameter 127
b Inside height of the rectangular waveguide 857
tw Waveguide wall thickness 500
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-2-
pattern a choke or multiple chokes around the aperture wall can be
employed to equalize radiation patterns and keep the back radiation in low
level If chokes are not enough for the suppression of the back radiation
corrugations on the outer surface of the feed is one way to reduce the back
radiation
In this thesis a broadband circular waveguide feed is developed for
prime-focus reflector antenna application After investigating the radiation
properties of simple circular and square waveguides methods are investigated
for bandwidth enhancement back radiation suppression and beamwidth
equalization in the circular waveguide feed
The first type of the circular waveguide feed consists of a probe-fed
circular waveguide a single quarter-wave choke on the aperture wall and a
dielectric-ring beamwidth equalizer Due to the simple feeding method the
first feed operates over 171-197GHz(141) which is not broadband in the
strict sense of the word
The second feed consists of a coaxial-to-rectangular waveguide transition a
rectangular-to-circular waveguide transition a circular waveguide section four
quarter-wave chokes on the aperture wall and four quarter-wave corrugations
on the feeds outer surface Due to the complicated feeding method the
second feed operates over 10-18GHz(571)
This thesis is arranged as follows Chapter I gives an introduction to the
thesis related works and objectives are stated Chapter II describes the
structure and excitation of the circular and square waveguide and the
operation of the coaxial-to-waveguide transitions Chapter III describes a
compact feed horn design and its fabrication and measurement Chapter IV
-3-
presents dielectric rod feed and its simulated performances Chapter V gives
design and optimization of feed for parabolic reflector antenna In this
chapter includes the detailed information of design procedures and operating
principle also the simulated and measured performances are provided Finally
conclusion is given in the Chapter VI
-4-
II Analysis of Circular and Square Waveguide Feeds
21 Circular Waveguide Radiator
Before design a complicated circular waveguide feed it is helpful to
investigate the impedance and radiation properties of a circular waveguide
open end
The circular waveguide is a cylindrical hollow metallic pipe with a uniform
circular section of radius a Circular waveguides are normally designed to
operate only with the dominant mode The dominant mode in a waveguide is
the mode having the lowest cutoff frequency given by equation (21)
(21)
where
(22)
and a is the waveguide radius The following chart[2] and table show the
cutoff frequencies of various modes in a circular waveguide
-5-
Modes c al11TEc cf f
TE11 341259 100000
TM01 261274 130613
TE21 205720 165885TE01 163979 208111
TM11 163979 208111TE31 149557 228180
TM21 122345 278932TE41 118159 288813
TE12 117852 289566
TM02 113824 299813TE02 0897986 380027
The recommended frequency range of the commercial circular waveguide is
given by the following equation This assumes that the TM01 mode is not
generated or suppressed if generated
11 21 11TE TE TE115 095 158 32 bandwidthc c cf f f fpound pound = reg (23)
Fig 21 shows the geometry of a circular waveguide with a diameter of 2a
When 2a is 2053mm the cutoff frequency of the TE11 mode is 857GHz
According to (23) the useful operating frequency range is from
986-1354GHz
Fig 22 shows the reflection of this waveguide excited with the dominant
TE11 mode The waveguide length l is 60mm The reflection occurs at the
open end of the circular waveguide The reflection coefficient is less than
-15dB over 10-18GHz
-6-
Fig 21 Geometry of a circular waveguide open end radiator
Fig 23 shows a 2D gain pattern of this waveguide antenna The
waveguide antenna has a gain of 80dB 99dB and 115dB at 10GHz
14GHz and 18GHz respectively Fig 24 shows the E- and H-plane patterns
of the circular waveguide antenna Table 21 summarizes the properties of a
circular waveguide antenna
Fig 22 Reflection coefficient of a circular waveguide open end radiator
-7-
(a)
(b)
Fig 23 2D radiation pattern of the circular waveguide open end radiator
at (a)10GHz (b) 14GHz and (c) 18GHz
-8-
(c)
Fig 23 continued
-9-
(a)
(b)
(c)
Fig 24 E-plane and H-plane patterns of the circular waveguide open end
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-10-
Table 21 Properties of a circular waveguide open end radiator of diameter
2053mm
Frequency(GHz)-10dB Beamwith(deg) Front-to-Back
Ratio(dB)E plane H plane
10 67 73 12
14 58 60 18
18 41 50 21
In a circular waveguide radiatoλr a good pattern symmetry and low back
radiation is obtained at 14GHz where 2aλ = 096
22 Square Waveguide Radiator
A square waveguide is often used as a dual-polarized feed To operate the
cutoff frequency of the dominant mode a square-waveguide wall width a
must be greater than one half of a wavelength The modes with cutoff
frequencies equal to or smaller than the operational frequency can exist inside
the waveguide wall The lower cutoff frequency and cutoff wavelength for
square waveguide is determined by the following equations
TE
(24)
TE
(25)
The next higher-order mode is TE11 mode with the cutoff wavelength
given by
-11-
TE
(26)
Similar to the circular waveguide the recommended operating frequency range
of a square waveguide is given by
TEleleTE
TErarr bandwidth (27)
Fig 25 shows the geometry of a square waveguide with a dimension of a
When a is 157mm the cutoff frequency is 95GHz The recommended
operating frequency of this waveguide is from 109GHz to 155GHz
Fig 26 shows the reflection of this waveguide excited with the dominant
TE10 mode The reflection coefficient is less than -15dB over 10-20GHz
Fig 25 Geometry of a square waveguide open end radiator
Fig 27 and shows the 2D radiation pattern of a square waveguide antenna
excited with the dominant TE10 mode The antenna has a gain of 73dB
85dB and 102dB at 10GHz 14GHz and 18GHz respectively Fig 28
shows the E- and H-plane radiation patterns of a square waveguide radiator
Table 22 summarizes the properties of a square waveguide open end radiator
-12-
Fig 26 Reflection coefficient of a square waveguide open end radiator
(a)
Fig 27 2D radiation patterns of a square waveguide radiator
at (a) 10GHz (b) 14GHz and (c) 18GHz
-13-
(b)
(c)
Fig 27 continued
-14-
(a)
(b)
(c)
Fig 28 E-plane and H-plane patterns of square waveguide open radiator
at (a) 10GHz(b) 14GHz and (c) 18GHz
-15-
Table 22 Properties of a square waveguide open end radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 69 71 11
14 47 60 25
18 58 62 16
The radiation pattern symmetry and back radiation performance of the
square waveguide are inferior to those of a circular waveguide
23 Probe-Fed Circular Waveguide Radiator
In Section 21 the radiation properties of a TE11-mode excited waveguide
is investigated In this section a circular waveguide fed by a coaxial probe
shown in Fig 29 is studied
The coaxial probes diameter is 127mm With the Teflon dielectric the
50-ohm coaxial lines outer conductor has a diameter of 41mm For a
circular waveguide the wave impedance of the TE11 mode is given by
∙ (28)
where λg is the guided wavelength given by
(29)
-16-
(a) (b)
Fig 29 Probe-fed circular waveguide radiator (a) Front view and (b) side
view
The combination of the probe length and the probe position from the
shorted wall enables a good impedance matching The probe distance sp from
the back short is close to a quarter wavelength at the design frequency
The designed feed has the following dimension d = 2053mm lp = 42
mm sp = 534mm wall thickness = 05mm and feed length = 400mm
Fig 210 shows the reflection coefficient of the designed probe-fed
circular waveguide radiator The reflection coefficient is less than -10dB over
138-187GHz Fig 211 and 212 shows the E-plane and H-plane radiation
patterns and 2D radiation patterns of the coaxial-to-circular waveguide
transition The radiation patterns symmetry distorted because of the high order
modes The coaxial-to-circular waveguide transition has 73dB 84dB and
79dB gain at 10GHz 14GHz and 18GHz frequencies respectively Table 23
shows the properties of the coaxial-to-circular waveguide transition
-17-
Fig 210 Reflection coefficient of the probe-fed circular waveguide radiator
(a)
Fig 211 2D radiation pattern of the probe-fed circular waveguide radiator
at (a) 10GHz (b) 14GHz and (c) 18GHz
-18-
(b)
(c)
Fig 211 continued
-19-
(a)
(b)
(c)
Fig 212 E- and H-plane patterns of the probe-fed circular waveguide
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-20-
Table 23 Properties of the probe-fed circular waveguide radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 73 70 1414 83 57 17
18 60 52 30
When a circular waveguide radiator is fed by a coaxial probe its radiation
properties are not good due to the excitation of higher-order modes
Therefore a probe-fed circular waveguide radiator can be used as a feed only
over a narrow frequency range
24 Probe-Fed Square Waveguide Radiator
In this section a probe-fed square waveguide radiator is investigated Fig
213 shows a coaxial probe-fed square waveguide radiator The designed
radiator has the following dimension a = b = 157mm lp = 35 mm sp =
50 mm wall thickness = 05mm and feed length = 40mm
(a) (b)
Fig 213 Probe-fed square waveguide radiator (a) Front view and (b) side
view
-21-
Fig 214 shows the 2D radiation patterns of the radiator at 10GHz
14GHz and 18GHz Fig 215 shows E- and H-plane patterns of the radiator
Fig 216 shows the reflection coefficient of the probe-fed square waveguide
radiator The reflection coefficient is less than -10dB over 13-20GHz Table
24 summarizes the properties of the probe-fed square waveguide radiator
(a)
Fig 214 2D radiation patterns of the probe-fed square waveguide radiator at
(a) 10GHz (b) 14GHz and (c) 18GHz
-22-
(b)
(c)
Fig 214 continued
-23-
(a)
(b)
(c)
Fig 216 E-plane and H-plane patterns of the probe-fed square waveguide
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-24-
Fig 216 Reflection coefficient of the probe-fed square waveguide radiator
Table 24 Properties of the probe-fed square waveguide radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 73 71 12
14 85 63 1418 27 65 28
When a square waveguide radiator is fed by a coaxial probe its radiation
properties are not good due to the excitation of higher-order modes as in the
case of the probe-fed circular waveguide radiator A probe-fed square
waveguide radiator can be used as a feed only over a narrow frequency
range
-25-
III Design of Compact Circular Waveguide Feeds
In this chapter the feed design is presented for a prime-focus reflector
antenna The prime-focus paraboloid reflector is one of the most commonly
used high-gain antenna It has been used in earth-station antennas and radio
telescopes It consists of a paraboloid reflector with a feed system at its focal
point
The feed should radiate a low level of cross-polar power over the
operating frequency These conditions not easy to achieve and most prime
focus feeds are compromises The shape and characteristic of the radiation
pattern of the feed are the most important parameter because these will
directly influence the fields which are directed at a reflector[6] Other
electrical factors which relevant to the choice of a feed are the cross-polar
level the gain efficiency the bandwidth and impedance matching
31 Narrow-Band Circular Waveguide Feed
Fig 31 shows the proposed narrow-band circular waveguide feed and its
design variables The feed consists of a circular waveguide open end excited
by a TE11 dominant mode A quarter wave choke is applied along the
circular aperture of the waveguide to equalize E- and H-plane radiation
patterns and to suppress the back radiation A dielectric ring is used to
control the radiation pattern and change the power distribution over the
aperture The control of the amplitude over the aperture are essential to the
design of symmetric radiation pattern The material used for dielectric loading
-26-
is the monocast(MC) nylon with a dielectric constant of 30 The feed is
designed to operate over 171-197GHz
(a)
(b)
Fig 31 Narrow-band circular waveguide feed (a) CAD model and (b) a
cross sectional view
The impedance matching is achieved by a proper combination of the probe
height lp and its distance sp from the waveguide shorted end Here the
-27-
circular waveguide is terminated with an open end with a wall thickness of
2mm radiating into the free space
Fig 32 shows the effect of the probe length lp and the probe distance sp
on the reflection coefficient The best performance is obtained when lp =
363mm and sp = 616mm The feeds reflection coefficient is less than -10dB
over 170-195GHz
(a)
(b)
Fig 32 Effect of the (a) the probe length lp and (b) the probe
distance sp on the reflection coefficient
-28-
Fig 33 shows the effect of the choke depth The E-plane pattern is more
sensitive to the choke depth than the H-plane pattern The choke depth has a
strong influence on the reflection coefficient when it is 360mm By properly
choosing the choke depth we can equalize the E- and H-plane patterns The
optimum value of the choke depth is 410mm which is 0249λ0 at 1825GHz
The choke slot width tch in the range of 06-12mm has almost no effect
on the H-plane pattern and the reflection coefficient For the E-plane pattern
tch of 12mm has some effect on the E-plane radiation pattern as shown in
Fig 34
Fig 35 shows the feed performance versus the dielectric ring length We
observe in Fig 35 that the dielectric length ld has an optimum value of
1168mm which does no effect on the H-plane pattern and tha the value of
1048mm has some effect on the E-plane pattern and the reflection
coefficient
Fig 36 shows E-plane and H-plane patterns and the reflection coefficient
versus the dielectric thickness With the optimum value of the dielectric
thickness t obtained from the Fig 36 is 155mm The larger values of td has
much stronger effects on the E-plane pattern and the reflection coefficient
The H-plane pattern is not sensitive to the dielectric ring thickness
-29-
(a)
(b)
(c)
Fig 33 Feed performance versus the choke depth (a) E-plane pattern
(b) H-plane pattern and (c) reflection coefficient
-30-
(a)
(b)
(c)
Fig 34 Feed performance versus the choke slot width (a) E-plane pattern
(b) H-plane pattern and (c) reflection coefficient
-31-
(a)
(b)
(c)
Fig 35 Feed performance versus the dielectric ring length (a) E-plane
pattern (b) H-plane pattern and (c) reflection coefficient
-32-
(a)
(b)
(c)
Fig 36 Feed performance versus the dielectric ring thickness (a) E-plane
pattern(b) H-plane pattern and (c) reflection coefficient
-33-
From the above parametric analysis an optimum feed design is obtained
The result is shown in Table 31 Fig 37 shows the 2D gain patterns of
designed feed The antenna has a gain of 903dB 933dB and 956dB at
171GHz 1825GHz and 19GHz respectively
Fig 38 shows E- and H-plane radiation patterns of the designed feed The
feed has E- and H-plane 10-dB beamwidths of 60 and 59 degrees at 17GHz
The feed has a front-to-back ration of 1900dB 2490dB and 2200dB at
171GHz 1825GHz and 19GHz respectively Table 32 summarizes the
performance of the designed narrow-band circular waveguide feed
The designed feed has a greatly improved performance over that of a
simple coax-fed feed described in Section 23
Table 31 Dimensions of the designed narrow-band circular feed
Parameter Designation Value(mm)
a Waveguide inside radius 640
l Feed length 2890
lp Probe length 363
sp Probe position from the back short 616
din Probe diameter 127
dout Diameter of coaxial cables outer conductor 400
t Thickness of choked wall 050
tch Choke slot width 100
lch Choke depth 410
ld Dielectric ring length 1168
td Dielectric ring thickness 155
d1 Waveguide outside diameter 1680
-34-
(a)
(b)
Fig 37 2D gain patterns of the narrow-band circular waveguide feed at
(a) 17GHz (b) 1825GHz and (c) 19GHz
-35-
(c)
Fig 37 continued
-36-
(a)
(b)
(c)
Fig 38 E- and H-plane patterns of the narrow-band circular waveguide feed
at (a) 10GHz (b) 1825GHz and (c) 195GHz
-37-
Frequency(GHz)
Gain(dB)
E-H-plane10-dB beamwidths
(deg)
Front-to-back ratio(dB)
Phase centerlocation
(From feeds aperture plane
toward reflector)
(mm)
1700 903 6059 20 062
1825 933 6060 25 004
1900 956 5759 22 007
Table 32 Performance of the narrow-band circular waveguide feed
The designed narrow-band feed is fabricated and its performance is
measured and compared with the simulation results The designed feed is
fabricated in a numerically-controlled machining center The fabricated antenna
is shown in Fig 39
Fig 39 Photograph of the fabricated feed
-38-
Fig 310 shows a comparison of the measured and simulated reflection
coefficients The measured reflection coefficient is less than -10dB over
171-197GHz The agreement between simulated and measured results are
good
Fig 311 shows the E- and H-plane patterns of the fabricated feed at
187GHz The feed has 90dB gain simulation and measurement results are in
good agreement
The fabricated antennarsquos 10dB beamwidth is 60 degrees in both E and H
planes at 187GHz The front-to-back ratio is 21dB
Fig 310 Reflection coefficient of the fabricated feed
-39-
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Fee
d H
orn
Gain
- d
B
Angle - degree
(a)
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Feed H
orn
Gain
- d
B
Angle - degree
(b)
Fig 311 Gain patterns of the fabricated feed at 187 GHz (a) E-plane and
(b) H-plane
-40-
IV Design of Circular Waveguide Feeds Loaded with a
Dielectric Rod
In this section circular waveguide feeds loaded with a dielectric rod feed
are investigated A comprehensive discussion of the circular waveguide loaded
with a dielectric rod is given by Kumar[7] Inserting a dielectric material
inside the circular waveguide improves the E- and H-plane pattern symmetry
In general dielectric-loaded circular waveguide feeds show good performance
only over a narrow bandwidth
Fig 41 shows the geometry of a circular waveguide loaded with a
dielectric rod The waveguide length is 400mm and the wall thickness is
05mm The dielectric rods diameter is 207mm The dielectric rod is
extended 05 wavelength beyond the waveguide open end The dielectric
constant εr is changed and the feeds performance is observed
Fig 41 Geometry of a circular waveguide loaded with a uniform dielectric
rod
-41-
Fig 42 is the radiation pattern of the feed with εr = 25 and L = 05λ0 at
9GHz E- and H-plane 10-dB beamwidths are 810 and 807 degrees
respectively The front-to-back ratio is 18dB The antenna gain is 71dB
(a)
(b)
Fig 42 Radiation pattern at 9GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 05λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-42-
Fig 43 shows the radiation pattern of the feed with εr = 21 at 10GHz
E- and H-plane 10-dB beamwidths are 70 and 71 degrees respectively The
front-to-back ratio is 19dB The antenna gain is 83dB
(a)
(b)
Fig 43 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 21 and L = 05λ0 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-43-
Fig 44 shows the radiation pattern of the feed with εr = 30 at 8GHz
E- and H-plane 10-dB beamwidths are 83 and 824 degrees respectively The
front-to-back ratio is 17dB The antenna gain is 73dB
(a)
(b)
Fig 44 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 30 and L = 05λ0 at 8GHz (a) 2D radiation pattern
and (b) E- and H-plane patterns
-44-
Fig 45 shows the radiation pattern of the feed with εr = 50 at 18GHz
E- and H-plane 10-dB beamwidths are 56 and 54 degrees respectively The
front-to-back ratio is 27dB The antenna gain is 105dB The feed has a good
pattern symmetry and low back radiation
(a)
(b)
Fig 45 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 50 and L = 05λ0 at 18GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-45-
Fig 46 is the radiation pattern of the feed with εr = 25 and L = 10λ0 at
10GHz E- and H-plane 10-dB beamwidths are 50 and 48 degrees
respectively The front-to-back ratio is 16dB The antenna gain is 105dB
(a)
(b)
Fig 46 Radiation pattern at 10GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 10λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-46-
Fig 47 shows the geometry of a circular waveguide with a tapered
dielectric rod The designed feed has the following dimension L = 1λ0 d =
1λ0 and εr =25 at 10GHz The waveguide length is 40mm and the wall
thickness is 05mm
L
Dielectricd3
Fig 47 Geometry of a circular waveguide loaded with a tapered dielectric
rod
Fig 48 shows the radiatio pattern of the designed feed E- and H-plane
10-dB beamwidths are 575 and 564 degrees respectively The front-to-back
ratio is 377dB The antenna gain is 94dB The designed feed has an
excellent beamwidth symmetry and a very low back radiation
-47-
(a)
(b)
Fig 48 Radiation pattern of a circular waveguide loaded with a tapered
dielectric rod with L = 1λ0 d = 1λ0 and εr =25 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-48-
Fig 49 shows the geometry of a spherical ended dielectric rod feed
diameter of 06λ0 at 10GHz with a dielectric constant of 25 and L= 03λ0
Fig 410 shows the radiation patterns of the designed feed E- and H-plane
10-dB beamwidths are both 63 degrees The front-to-back ratio is 24dB The
antenna gain is 864dB
Fig 49 Geometry of a circular waveguide loaded with a spherical ended
dielectric rod
-49-
(a)
(b)
Fig 410 Radiation pattern of a circular waveguide loaded wht a spherical
ended dielectric rod with d = 06λ0 L = 03λ0 and εr =25 at 10GHz (a) 3D
radiation pattern and (b) E- and H-plane patterns
-50-
V Design of a Broadband Circular Waveguide Feed
In this chapter the design of a broadband circular waveguide feed is
presented At microwave frequencies the feed is often a circular waveguide
with chokes and corrugations around the aperture Chokes and corrugations
equalize E- and H-plane patterns and reduce the back radiation
The proposed feed is designed to operate over 10-18GHz The design starts
with the optimization of the coaxial-to-rectangular waveguide adapter
employed for good mode purity over a broad frequency range Next a
rectangular-to-circular waveguide transition is optimized Finally chokes and
corrugations are designed for improved pattern symmetry and low back
radiation
The proposed feed structure is shown in Fig 51 The feed consist of the
following parts a coaxial-to-rectangular waveguide adapter a rectangular-to-
circular waveguide transition a circular waveguide section four quarter-wave
chokes around the feeds aperture and four corrugations on the feeds outer
surface
The computer simulation shows the above arrangement offers good radiation
patterns over a broad frequency range The broadband operation is obtained
by exciting the TE11 mode in the circular waveguide using the TE10 mode of
the rectangular waveguide which is in turn excited by a coaxial probe
-51-
Chokes
Coaxial-to-waveguide transition
Circular wavguide
Corrugations
Mode transition
(a)
(b)
Fig 51 Structure of the proposed broadband circular waveguide feed
(a) CAD model and (b) cross-sectional view
For the coaxial-to-rectangular waveguide adapter an SMA connector with
the probe diameter of 127 mm is employed The coaxial probe inserted into
the waveguide energizes the feed and excites the dominant TE10 mode in
-52-
the rectangular waveguide The impedance matching is achieved by adjusting
the probe distance sp from the back short and the probe length lp
(a)
(b)
Fig 52 Reflection coefficient of the coaxial-to-rectangular adapter versus
(a) probe length lp and (b) the probe position sp
Fig 52 shows the reflection coefficient versus the various values of probe
lengths lp and probe positions sp The probe length lp is adjusted to obtain
antenna impedance matching and the probe distance sp is adjusted to obtain a
-53-
desired resonant frequency
Next a transition between rectangular and circular waveguide is designed
The transition section converts the TE10 mode in the rectangular waveguide to
TE11 mode in the circular waveguide and vice versa The transition is built
in a form of a taper for easy fabrication[22]
(a)
(b)
Fig 53 Structure of the rectangular-to-circular waveguide transition
(a) 3D view and (b) cross sectional view
The dimensions of the final optimized transition are as follows The length
of the rectangular waveguide section is 143mm The rectangular waveguides
width a and height b are 207mm and 857mm respectively The length of
the circular waveguide section is 143mm The inside diameter of the circular
-54-
waveguide is 207mm(097 wavelength at 14GHz) The length of transition
region ltr is 4465mm(approximately equal to 2λ0 at 14GHz) Fig 54 shows
the field distribution inside the mode converter
(a)
(b)
Fig 54 Field distribution inside the mode converter at
(a) 10GHz (b) 14GHz and (c) 18GHz
-55-
(c)
Fig 54 continued
Finally multiple chokes are investigated Figs 55 56 and 57 show the
feed performance without chokes The reflection coefficient is less than -10dB
over 10-19GHz The antenna has a gain of 921dB to 1189dB over
10-19GHz
Fig 55 Reflection coefficient of the broadband circular waveguide feed
without chokes and corrugations
-56-
(a)
(b)
(c)
Fig 56 E- and H-plane patterns of the broadband circular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-57-
(d)
(e)
Fig 56 continued
-58-
(a)
(b)
Fig 57 2D radiation patterns of the broadband cicular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-59-
(c)
(d)
Fig 57 continued
-60-
(e)
Fig 57 continued
To achieve equal beamwidths in E and H planes over a wide frequency
range chokes and corrugations are employed Table51 summarizes the
performance of a feed without chokes and corrugations
Table 51 Performance of the broadband circular waveguide feed without
chokes and corrugations
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
1000 940 6061 15
1200 972 6159 17
1400 920 5957 21
1600 1070 4751 29
1800 1188 5352 21
-61-
Four quarter-wavelength chokes are introduced in the feed design which
has a slot depth of 75mm and slot width of 09mm The choke slot spacing
is 18mm The choke design is investigated by applying the choke one by
one and the effect on the E- and H-plane patterns are observed as illustrated
in Figs 58 and 59 The use of chokes makes the E-plane pattern narrower
The H-plane pattern is not affected Chokes increase the gain slightly and
reduce back radiation
(a)
(b)
Fig 58 Effect of chokes on the E-plane pattern of the broadband circular
waveguide feed at (a) 10GHz(b) 12GHz (c) 14GHz (d) 16GHz and (e)
18GHz
-62-
(c)
(d)
(e)
Fig 58 continued
-63-
(a)
(b)
(c)
Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-64-
(d)
(e)
Fig 59 continued
-65-
Fig 510 shows the feed performance versus the choke depth When the
choke depth is varied from 535mm to 95mm the E- and H-plane patterns
are strongly affected The optimum value of choke depth is 75mm(035λ0 at
14GHz) which gives equal E- and H-plane radiation patterns and leads to
low back radiation
Fig 511 shows the feed performance versus the choke slot width tch The
choke slot width is varied from 09mm to 21mm Radiation patterns and
reflection coefficients are not sensitive to the choke slot width The final
choke slot width is selected to be 09mm considering the feed diameter
minimization and the manufacturability The overall diameter of the proposed
feed is 369mm which is increased from the 207mm of the waveguide
inside diameter due to the use of four chokes
-66-
(a)
(b)
(c)
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection coefficient
-67-
(a)
(b)
(c)
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and (c)
reflection coefficient
-68-
Next we investigated corrugations placed on the outer wall of the feed
Four corrugations applied to the outer surface of the circular waveguide The
corrugation depth is 465mm(0215λ0 at 14GHz) The primary purpose of
using corrugations is to further reduce the back radiation Increasing the
number of corrugations beyond four has little effect in reducing the back
radiation
Figs 512 and 513 show the effect of corrugations on the E- and H-plane
patterns Fig 514 shows the parametric study of the corrugation depth lcor
The corrugation depth is varied from 40mm and 645mm The optimum
value of the corrugation depth is found to be 465mm
-69-
(a)
(b)
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern at (a) 12GHz and (b) 14GHz
-70-
(a)
(b)
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern at (a) 12GHz and (b) 14GHz
-71-
(a)
(b)
(c)
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection coefficient
-72-
The phase center location is important in placing the feed in a reflector
antenna[8] The phase center variation with frequency should be small Fig
515 shows the effect of chokes and corrugations on the phase center The
curve with circle corresponds to the case without chokes and corrugations
The phase center varies from -326mm and -190mm away from the feeds
aperture plane It means the phase center is located inside the waveguide
The curve with triangles corresponds to the case with chokes The curve with
squares to the case with chokes and corrugations The phase center varies
from 0mm to -302mm
From Fig 515 we can observed that phase center variation reduced by the
corrugation and three cases phase center calculated in φ=450 plane
parameter sweep values are given in Table 52
10 12 14 16 181
0
-1
-2
-3
-4
-5
-6
Pha
se c
ente
r (m
m)
Frequency (GHz)
choke+corrugatuion without choke corrugation with choke
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
-73-
Frequency
(GHz)
Phase center from the aperture plane
(mm)
Without
chokes and
corrugations
With
chokes
With chokes
and
corrugations
1000 -326 062 000
1100 -187 030 -002
1200 -563 -208 -065
1300 -296 -154 -202
1400 -319 -314 -302
1500 -201 -203 -241
1600 -242 -233 -207
1700 -208 -208 -186
1800 -190 -157 -132
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
Based on the foregoing parametric studies optimum dimensions of the
broadband circular waveguide feed are obtained as shown in Table 53
-74-
Table 53 Optimum dimensions of the broadband circular waveguide feed
Parameter Designation Value (mm)
2a Waveguide inside diameter 2070
d Waveguide outside diameter 3690
lcrLength of the circular waveguide section 1430
m Distance between the aperture plane and the first corrugation 950
xDistance from the last corrugation to the end of the cylindrical outer surface
550
ltrLength of the rectangular-to-circularwaveguide transition 4465
lrcLength of the rectangular waveguide section 1430
tch Choke slot width 090
lch Choke depth 750
t Choke metal width 090
lcor Corrugation depth 465
tcor Corrugation metal width 100
s Corrugation slot width 10
lp Probe length 530
sp Probe position from the back short 530
din Probe diameter 127
b Inside height of the rectangular waveguide 857
tw Waveguide wall thickness 500
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-3-
presents dielectric rod feed and its simulated performances Chapter V gives
design and optimization of feed for parabolic reflector antenna In this
chapter includes the detailed information of design procedures and operating
principle also the simulated and measured performances are provided Finally
conclusion is given in the Chapter VI
-4-
II Analysis of Circular and Square Waveguide Feeds
21 Circular Waveguide Radiator
Before design a complicated circular waveguide feed it is helpful to
investigate the impedance and radiation properties of a circular waveguide
open end
The circular waveguide is a cylindrical hollow metallic pipe with a uniform
circular section of radius a Circular waveguides are normally designed to
operate only with the dominant mode The dominant mode in a waveguide is
the mode having the lowest cutoff frequency given by equation (21)
(21)
where
(22)
and a is the waveguide radius The following chart[2] and table show the
cutoff frequencies of various modes in a circular waveguide
-5-
Modes c al11TEc cf f
TE11 341259 100000
TM01 261274 130613
TE21 205720 165885TE01 163979 208111
TM11 163979 208111TE31 149557 228180
TM21 122345 278932TE41 118159 288813
TE12 117852 289566
TM02 113824 299813TE02 0897986 380027
The recommended frequency range of the commercial circular waveguide is
given by the following equation This assumes that the TM01 mode is not
generated or suppressed if generated
11 21 11TE TE TE115 095 158 32 bandwidthc c cf f f fpound pound = reg (23)
Fig 21 shows the geometry of a circular waveguide with a diameter of 2a
When 2a is 2053mm the cutoff frequency of the TE11 mode is 857GHz
According to (23) the useful operating frequency range is from
986-1354GHz
Fig 22 shows the reflection of this waveguide excited with the dominant
TE11 mode The waveguide length l is 60mm The reflection occurs at the
open end of the circular waveguide The reflection coefficient is less than
-15dB over 10-18GHz
-6-
Fig 21 Geometry of a circular waveguide open end radiator
Fig 23 shows a 2D gain pattern of this waveguide antenna The
waveguide antenna has a gain of 80dB 99dB and 115dB at 10GHz
14GHz and 18GHz respectively Fig 24 shows the E- and H-plane patterns
of the circular waveguide antenna Table 21 summarizes the properties of a
circular waveguide antenna
Fig 22 Reflection coefficient of a circular waveguide open end radiator
-7-
(a)
(b)
Fig 23 2D radiation pattern of the circular waveguide open end radiator
at (a)10GHz (b) 14GHz and (c) 18GHz
-8-
(c)
Fig 23 continued
-9-
(a)
(b)
(c)
Fig 24 E-plane and H-plane patterns of the circular waveguide open end
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-10-
Table 21 Properties of a circular waveguide open end radiator of diameter
2053mm
Frequency(GHz)-10dB Beamwith(deg) Front-to-Back
Ratio(dB)E plane H plane
10 67 73 12
14 58 60 18
18 41 50 21
In a circular waveguide radiatoλr a good pattern symmetry and low back
radiation is obtained at 14GHz where 2aλ = 096
22 Square Waveguide Radiator
A square waveguide is often used as a dual-polarized feed To operate the
cutoff frequency of the dominant mode a square-waveguide wall width a
must be greater than one half of a wavelength The modes with cutoff
frequencies equal to or smaller than the operational frequency can exist inside
the waveguide wall The lower cutoff frequency and cutoff wavelength for
square waveguide is determined by the following equations
TE
(24)
TE
(25)
The next higher-order mode is TE11 mode with the cutoff wavelength
given by
-11-
TE
(26)
Similar to the circular waveguide the recommended operating frequency range
of a square waveguide is given by
TEleleTE
TErarr bandwidth (27)
Fig 25 shows the geometry of a square waveguide with a dimension of a
When a is 157mm the cutoff frequency is 95GHz The recommended
operating frequency of this waveguide is from 109GHz to 155GHz
Fig 26 shows the reflection of this waveguide excited with the dominant
TE10 mode The reflection coefficient is less than -15dB over 10-20GHz
Fig 25 Geometry of a square waveguide open end radiator
Fig 27 and shows the 2D radiation pattern of a square waveguide antenna
excited with the dominant TE10 mode The antenna has a gain of 73dB
85dB and 102dB at 10GHz 14GHz and 18GHz respectively Fig 28
shows the E- and H-plane radiation patterns of a square waveguide radiator
Table 22 summarizes the properties of a square waveguide open end radiator
-12-
Fig 26 Reflection coefficient of a square waveguide open end radiator
(a)
Fig 27 2D radiation patterns of a square waveguide radiator
at (a) 10GHz (b) 14GHz and (c) 18GHz
-13-
(b)
(c)
Fig 27 continued
-14-
(a)
(b)
(c)
Fig 28 E-plane and H-plane patterns of square waveguide open radiator
at (a) 10GHz(b) 14GHz and (c) 18GHz
-15-
Table 22 Properties of a square waveguide open end radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 69 71 11
14 47 60 25
18 58 62 16
The radiation pattern symmetry and back radiation performance of the
square waveguide are inferior to those of a circular waveguide
23 Probe-Fed Circular Waveguide Radiator
In Section 21 the radiation properties of a TE11-mode excited waveguide
is investigated In this section a circular waveguide fed by a coaxial probe
shown in Fig 29 is studied
The coaxial probes diameter is 127mm With the Teflon dielectric the
50-ohm coaxial lines outer conductor has a diameter of 41mm For a
circular waveguide the wave impedance of the TE11 mode is given by
∙ (28)
where λg is the guided wavelength given by
(29)
-16-
(a) (b)
Fig 29 Probe-fed circular waveguide radiator (a) Front view and (b) side
view
The combination of the probe length and the probe position from the
shorted wall enables a good impedance matching The probe distance sp from
the back short is close to a quarter wavelength at the design frequency
The designed feed has the following dimension d = 2053mm lp = 42
mm sp = 534mm wall thickness = 05mm and feed length = 400mm
Fig 210 shows the reflection coefficient of the designed probe-fed
circular waveguide radiator The reflection coefficient is less than -10dB over
138-187GHz Fig 211 and 212 shows the E-plane and H-plane radiation
patterns and 2D radiation patterns of the coaxial-to-circular waveguide
transition The radiation patterns symmetry distorted because of the high order
modes The coaxial-to-circular waveguide transition has 73dB 84dB and
79dB gain at 10GHz 14GHz and 18GHz frequencies respectively Table 23
shows the properties of the coaxial-to-circular waveguide transition
-17-
Fig 210 Reflection coefficient of the probe-fed circular waveguide radiator
(a)
Fig 211 2D radiation pattern of the probe-fed circular waveguide radiator
at (a) 10GHz (b) 14GHz and (c) 18GHz
-18-
(b)
(c)
Fig 211 continued
-19-
(a)
(b)
(c)
Fig 212 E- and H-plane patterns of the probe-fed circular waveguide
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-20-
Table 23 Properties of the probe-fed circular waveguide radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 73 70 1414 83 57 17
18 60 52 30
When a circular waveguide radiator is fed by a coaxial probe its radiation
properties are not good due to the excitation of higher-order modes
Therefore a probe-fed circular waveguide radiator can be used as a feed only
over a narrow frequency range
24 Probe-Fed Square Waveguide Radiator
In this section a probe-fed square waveguide radiator is investigated Fig
213 shows a coaxial probe-fed square waveguide radiator The designed
radiator has the following dimension a = b = 157mm lp = 35 mm sp =
50 mm wall thickness = 05mm and feed length = 40mm
(a) (b)
Fig 213 Probe-fed square waveguide radiator (a) Front view and (b) side
view
-21-
Fig 214 shows the 2D radiation patterns of the radiator at 10GHz
14GHz and 18GHz Fig 215 shows E- and H-plane patterns of the radiator
Fig 216 shows the reflection coefficient of the probe-fed square waveguide
radiator The reflection coefficient is less than -10dB over 13-20GHz Table
24 summarizes the properties of the probe-fed square waveguide radiator
(a)
Fig 214 2D radiation patterns of the probe-fed square waveguide radiator at
(a) 10GHz (b) 14GHz and (c) 18GHz
-22-
(b)
(c)
Fig 214 continued
-23-
(a)
(b)
(c)
Fig 216 E-plane and H-plane patterns of the probe-fed square waveguide
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-24-
Fig 216 Reflection coefficient of the probe-fed square waveguide radiator
Table 24 Properties of the probe-fed square waveguide radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 73 71 12
14 85 63 1418 27 65 28
When a square waveguide radiator is fed by a coaxial probe its radiation
properties are not good due to the excitation of higher-order modes as in the
case of the probe-fed circular waveguide radiator A probe-fed square
waveguide radiator can be used as a feed only over a narrow frequency
range
-25-
III Design of Compact Circular Waveguide Feeds
In this chapter the feed design is presented for a prime-focus reflector
antenna The prime-focus paraboloid reflector is one of the most commonly
used high-gain antenna It has been used in earth-station antennas and radio
telescopes It consists of a paraboloid reflector with a feed system at its focal
point
The feed should radiate a low level of cross-polar power over the
operating frequency These conditions not easy to achieve and most prime
focus feeds are compromises The shape and characteristic of the radiation
pattern of the feed are the most important parameter because these will
directly influence the fields which are directed at a reflector[6] Other
electrical factors which relevant to the choice of a feed are the cross-polar
level the gain efficiency the bandwidth and impedance matching
31 Narrow-Band Circular Waveguide Feed
Fig 31 shows the proposed narrow-band circular waveguide feed and its
design variables The feed consists of a circular waveguide open end excited
by a TE11 dominant mode A quarter wave choke is applied along the
circular aperture of the waveguide to equalize E- and H-plane radiation
patterns and to suppress the back radiation A dielectric ring is used to
control the radiation pattern and change the power distribution over the
aperture The control of the amplitude over the aperture are essential to the
design of symmetric radiation pattern The material used for dielectric loading
-26-
is the monocast(MC) nylon with a dielectric constant of 30 The feed is
designed to operate over 171-197GHz
(a)
(b)
Fig 31 Narrow-band circular waveguide feed (a) CAD model and (b) a
cross sectional view
The impedance matching is achieved by a proper combination of the probe
height lp and its distance sp from the waveguide shorted end Here the
-27-
circular waveguide is terminated with an open end with a wall thickness of
2mm radiating into the free space
Fig 32 shows the effect of the probe length lp and the probe distance sp
on the reflection coefficient The best performance is obtained when lp =
363mm and sp = 616mm The feeds reflection coefficient is less than -10dB
over 170-195GHz
(a)
(b)
Fig 32 Effect of the (a) the probe length lp and (b) the probe
distance sp on the reflection coefficient
-28-
Fig 33 shows the effect of the choke depth The E-plane pattern is more
sensitive to the choke depth than the H-plane pattern The choke depth has a
strong influence on the reflection coefficient when it is 360mm By properly
choosing the choke depth we can equalize the E- and H-plane patterns The
optimum value of the choke depth is 410mm which is 0249λ0 at 1825GHz
The choke slot width tch in the range of 06-12mm has almost no effect
on the H-plane pattern and the reflection coefficient For the E-plane pattern
tch of 12mm has some effect on the E-plane radiation pattern as shown in
Fig 34
Fig 35 shows the feed performance versus the dielectric ring length We
observe in Fig 35 that the dielectric length ld has an optimum value of
1168mm which does no effect on the H-plane pattern and tha the value of
1048mm has some effect on the E-plane pattern and the reflection
coefficient
Fig 36 shows E-plane and H-plane patterns and the reflection coefficient
versus the dielectric thickness With the optimum value of the dielectric
thickness t obtained from the Fig 36 is 155mm The larger values of td has
much stronger effects on the E-plane pattern and the reflection coefficient
The H-plane pattern is not sensitive to the dielectric ring thickness
-29-
(a)
(b)
(c)
Fig 33 Feed performance versus the choke depth (a) E-plane pattern
(b) H-plane pattern and (c) reflection coefficient
-30-
(a)
(b)
(c)
Fig 34 Feed performance versus the choke slot width (a) E-plane pattern
(b) H-plane pattern and (c) reflection coefficient
-31-
(a)
(b)
(c)
Fig 35 Feed performance versus the dielectric ring length (a) E-plane
pattern (b) H-plane pattern and (c) reflection coefficient
-32-
(a)
(b)
(c)
Fig 36 Feed performance versus the dielectric ring thickness (a) E-plane
pattern(b) H-plane pattern and (c) reflection coefficient
-33-
From the above parametric analysis an optimum feed design is obtained
The result is shown in Table 31 Fig 37 shows the 2D gain patterns of
designed feed The antenna has a gain of 903dB 933dB and 956dB at
171GHz 1825GHz and 19GHz respectively
Fig 38 shows E- and H-plane radiation patterns of the designed feed The
feed has E- and H-plane 10-dB beamwidths of 60 and 59 degrees at 17GHz
The feed has a front-to-back ration of 1900dB 2490dB and 2200dB at
171GHz 1825GHz and 19GHz respectively Table 32 summarizes the
performance of the designed narrow-band circular waveguide feed
The designed feed has a greatly improved performance over that of a
simple coax-fed feed described in Section 23
Table 31 Dimensions of the designed narrow-band circular feed
Parameter Designation Value(mm)
a Waveguide inside radius 640
l Feed length 2890
lp Probe length 363
sp Probe position from the back short 616
din Probe diameter 127
dout Diameter of coaxial cables outer conductor 400
t Thickness of choked wall 050
tch Choke slot width 100
lch Choke depth 410
ld Dielectric ring length 1168
td Dielectric ring thickness 155
d1 Waveguide outside diameter 1680
-34-
(a)
(b)
Fig 37 2D gain patterns of the narrow-band circular waveguide feed at
(a) 17GHz (b) 1825GHz and (c) 19GHz
-35-
(c)
Fig 37 continued
-36-
(a)
(b)
(c)
Fig 38 E- and H-plane patterns of the narrow-band circular waveguide feed
at (a) 10GHz (b) 1825GHz and (c) 195GHz
-37-
Frequency(GHz)
Gain(dB)
E-H-plane10-dB beamwidths
(deg)
Front-to-back ratio(dB)
Phase centerlocation
(From feeds aperture plane
toward reflector)
(mm)
1700 903 6059 20 062
1825 933 6060 25 004
1900 956 5759 22 007
Table 32 Performance of the narrow-band circular waveguide feed
The designed narrow-band feed is fabricated and its performance is
measured and compared with the simulation results The designed feed is
fabricated in a numerically-controlled machining center The fabricated antenna
is shown in Fig 39
Fig 39 Photograph of the fabricated feed
-38-
Fig 310 shows a comparison of the measured and simulated reflection
coefficients The measured reflection coefficient is less than -10dB over
171-197GHz The agreement between simulated and measured results are
good
Fig 311 shows the E- and H-plane patterns of the fabricated feed at
187GHz The feed has 90dB gain simulation and measurement results are in
good agreement
The fabricated antennarsquos 10dB beamwidth is 60 degrees in both E and H
planes at 187GHz The front-to-back ratio is 21dB
Fig 310 Reflection coefficient of the fabricated feed
-39-
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Fee
d H
orn
Gain
- d
B
Angle - degree
(a)
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Feed H
orn
Gain
- d
B
Angle - degree
(b)
Fig 311 Gain patterns of the fabricated feed at 187 GHz (a) E-plane and
(b) H-plane
-40-
IV Design of Circular Waveguide Feeds Loaded with a
Dielectric Rod
In this section circular waveguide feeds loaded with a dielectric rod feed
are investigated A comprehensive discussion of the circular waveguide loaded
with a dielectric rod is given by Kumar[7] Inserting a dielectric material
inside the circular waveguide improves the E- and H-plane pattern symmetry
In general dielectric-loaded circular waveguide feeds show good performance
only over a narrow bandwidth
Fig 41 shows the geometry of a circular waveguide loaded with a
dielectric rod The waveguide length is 400mm and the wall thickness is
05mm The dielectric rods diameter is 207mm The dielectric rod is
extended 05 wavelength beyond the waveguide open end The dielectric
constant εr is changed and the feeds performance is observed
Fig 41 Geometry of a circular waveguide loaded with a uniform dielectric
rod
-41-
Fig 42 is the radiation pattern of the feed with εr = 25 and L = 05λ0 at
9GHz E- and H-plane 10-dB beamwidths are 810 and 807 degrees
respectively The front-to-back ratio is 18dB The antenna gain is 71dB
(a)
(b)
Fig 42 Radiation pattern at 9GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 05λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-42-
Fig 43 shows the radiation pattern of the feed with εr = 21 at 10GHz
E- and H-plane 10-dB beamwidths are 70 and 71 degrees respectively The
front-to-back ratio is 19dB The antenna gain is 83dB
(a)
(b)
Fig 43 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 21 and L = 05λ0 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-43-
Fig 44 shows the radiation pattern of the feed with εr = 30 at 8GHz
E- and H-plane 10-dB beamwidths are 83 and 824 degrees respectively The
front-to-back ratio is 17dB The antenna gain is 73dB
(a)
(b)
Fig 44 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 30 and L = 05λ0 at 8GHz (a) 2D radiation pattern
and (b) E- and H-plane patterns
-44-
Fig 45 shows the radiation pattern of the feed with εr = 50 at 18GHz
E- and H-plane 10-dB beamwidths are 56 and 54 degrees respectively The
front-to-back ratio is 27dB The antenna gain is 105dB The feed has a good
pattern symmetry and low back radiation
(a)
(b)
Fig 45 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 50 and L = 05λ0 at 18GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-45-
Fig 46 is the radiation pattern of the feed with εr = 25 and L = 10λ0 at
10GHz E- and H-plane 10-dB beamwidths are 50 and 48 degrees
respectively The front-to-back ratio is 16dB The antenna gain is 105dB
(a)
(b)
Fig 46 Radiation pattern at 10GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 10λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-46-
Fig 47 shows the geometry of a circular waveguide with a tapered
dielectric rod The designed feed has the following dimension L = 1λ0 d =
1λ0 and εr =25 at 10GHz The waveguide length is 40mm and the wall
thickness is 05mm
L
Dielectricd3
Fig 47 Geometry of a circular waveguide loaded with a tapered dielectric
rod
Fig 48 shows the radiatio pattern of the designed feed E- and H-plane
10-dB beamwidths are 575 and 564 degrees respectively The front-to-back
ratio is 377dB The antenna gain is 94dB The designed feed has an
excellent beamwidth symmetry and a very low back radiation
-47-
(a)
(b)
Fig 48 Radiation pattern of a circular waveguide loaded with a tapered
dielectric rod with L = 1λ0 d = 1λ0 and εr =25 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-48-
Fig 49 shows the geometry of a spherical ended dielectric rod feed
diameter of 06λ0 at 10GHz with a dielectric constant of 25 and L= 03λ0
Fig 410 shows the radiation patterns of the designed feed E- and H-plane
10-dB beamwidths are both 63 degrees The front-to-back ratio is 24dB The
antenna gain is 864dB
Fig 49 Geometry of a circular waveguide loaded with a spherical ended
dielectric rod
-49-
(a)
(b)
Fig 410 Radiation pattern of a circular waveguide loaded wht a spherical
ended dielectric rod with d = 06λ0 L = 03λ0 and εr =25 at 10GHz (a) 3D
radiation pattern and (b) E- and H-plane patterns
-50-
V Design of a Broadband Circular Waveguide Feed
In this chapter the design of a broadband circular waveguide feed is
presented At microwave frequencies the feed is often a circular waveguide
with chokes and corrugations around the aperture Chokes and corrugations
equalize E- and H-plane patterns and reduce the back radiation
The proposed feed is designed to operate over 10-18GHz The design starts
with the optimization of the coaxial-to-rectangular waveguide adapter
employed for good mode purity over a broad frequency range Next a
rectangular-to-circular waveguide transition is optimized Finally chokes and
corrugations are designed for improved pattern symmetry and low back
radiation
The proposed feed structure is shown in Fig 51 The feed consist of the
following parts a coaxial-to-rectangular waveguide adapter a rectangular-to-
circular waveguide transition a circular waveguide section four quarter-wave
chokes around the feeds aperture and four corrugations on the feeds outer
surface
The computer simulation shows the above arrangement offers good radiation
patterns over a broad frequency range The broadband operation is obtained
by exciting the TE11 mode in the circular waveguide using the TE10 mode of
the rectangular waveguide which is in turn excited by a coaxial probe
-51-
Chokes
Coaxial-to-waveguide transition
Circular wavguide
Corrugations
Mode transition
(a)
(b)
Fig 51 Structure of the proposed broadband circular waveguide feed
(a) CAD model and (b) cross-sectional view
For the coaxial-to-rectangular waveguide adapter an SMA connector with
the probe diameter of 127 mm is employed The coaxial probe inserted into
the waveguide energizes the feed and excites the dominant TE10 mode in
-52-
the rectangular waveguide The impedance matching is achieved by adjusting
the probe distance sp from the back short and the probe length lp
(a)
(b)
Fig 52 Reflection coefficient of the coaxial-to-rectangular adapter versus
(a) probe length lp and (b) the probe position sp
Fig 52 shows the reflection coefficient versus the various values of probe
lengths lp and probe positions sp The probe length lp is adjusted to obtain
antenna impedance matching and the probe distance sp is adjusted to obtain a
-53-
desired resonant frequency
Next a transition between rectangular and circular waveguide is designed
The transition section converts the TE10 mode in the rectangular waveguide to
TE11 mode in the circular waveguide and vice versa The transition is built
in a form of a taper for easy fabrication[22]
(a)
(b)
Fig 53 Structure of the rectangular-to-circular waveguide transition
(a) 3D view and (b) cross sectional view
The dimensions of the final optimized transition are as follows The length
of the rectangular waveguide section is 143mm The rectangular waveguides
width a and height b are 207mm and 857mm respectively The length of
the circular waveguide section is 143mm The inside diameter of the circular
-54-
waveguide is 207mm(097 wavelength at 14GHz) The length of transition
region ltr is 4465mm(approximately equal to 2λ0 at 14GHz) Fig 54 shows
the field distribution inside the mode converter
(a)
(b)
Fig 54 Field distribution inside the mode converter at
(a) 10GHz (b) 14GHz and (c) 18GHz
-55-
(c)
Fig 54 continued
Finally multiple chokes are investigated Figs 55 56 and 57 show the
feed performance without chokes The reflection coefficient is less than -10dB
over 10-19GHz The antenna has a gain of 921dB to 1189dB over
10-19GHz
Fig 55 Reflection coefficient of the broadband circular waveguide feed
without chokes and corrugations
-56-
(a)
(b)
(c)
Fig 56 E- and H-plane patterns of the broadband circular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-57-
(d)
(e)
Fig 56 continued
-58-
(a)
(b)
Fig 57 2D radiation patterns of the broadband cicular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-59-
(c)
(d)
Fig 57 continued
-60-
(e)
Fig 57 continued
To achieve equal beamwidths in E and H planes over a wide frequency
range chokes and corrugations are employed Table51 summarizes the
performance of a feed without chokes and corrugations
Table 51 Performance of the broadband circular waveguide feed without
chokes and corrugations
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
1000 940 6061 15
1200 972 6159 17
1400 920 5957 21
1600 1070 4751 29
1800 1188 5352 21
-61-
Four quarter-wavelength chokes are introduced in the feed design which
has a slot depth of 75mm and slot width of 09mm The choke slot spacing
is 18mm The choke design is investigated by applying the choke one by
one and the effect on the E- and H-plane patterns are observed as illustrated
in Figs 58 and 59 The use of chokes makes the E-plane pattern narrower
The H-plane pattern is not affected Chokes increase the gain slightly and
reduce back radiation
(a)
(b)
Fig 58 Effect of chokes on the E-plane pattern of the broadband circular
waveguide feed at (a) 10GHz(b) 12GHz (c) 14GHz (d) 16GHz and (e)
18GHz
-62-
(c)
(d)
(e)
Fig 58 continued
-63-
(a)
(b)
(c)
Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-64-
(d)
(e)
Fig 59 continued
-65-
Fig 510 shows the feed performance versus the choke depth When the
choke depth is varied from 535mm to 95mm the E- and H-plane patterns
are strongly affected The optimum value of choke depth is 75mm(035λ0 at
14GHz) which gives equal E- and H-plane radiation patterns and leads to
low back radiation
Fig 511 shows the feed performance versus the choke slot width tch The
choke slot width is varied from 09mm to 21mm Radiation patterns and
reflection coefficients are not sensitive to the choke slot width The final
choke slot width is selected to be 09mm considering the feed diameter
minimization and the manufacturability The overall diameter of the proposed
feed is 369mm which is increased from the 207mm of the waveguide
inside diameter due to the use of four chokes
-66-
(a)
(b)
(c)
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection coefficient
-67-
(a)
(b)
(c)
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and (c)
reflection coefficient
-68-
Next we investigated corrugations placed on the outer wall of the feed
Four corrugations applied to the outer surface of the circular waveguide The
corrugation depth is 465mm(0215λ0 at 14GHz) The primary purpose of
using corrugations is to further reduce the back radiation Increasing the
number of corrugations beyond four has little effect in reducing the back
radiation
Figs 512 and 513 show the effect of corrugations on the E- and H-plane
patterns Fig 514 shows the parametric study of the corrugation depth lcor
The corrugation depth is varied from 40mm and 645mm The optimum
value of the corrugation depth is found to be 465mm
-69-
(a)
(b)
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern at (a) 12GHz and (b) 14GHz
-70-
(a)
(b)
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern at (a) 12GHz and (b) 14GHz
-71-
(a)
(b)
(c)
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection coefficient
-72-
The phase center location is important in placing the feed in a reflector
antenna[8] The phase center variation with frequency should be small Fig
515 shows the effect of chokes and corrugations on the phase center The
curve with circle corresponds to the case without chokes and corrugations
The phase center varies from -326mm and -190mm away from the feeds
aperture plane It means the phase center is located inside the waveguide
The curve with triangles corresponds to the case with chokes The curve with
squares to the case with chokes and corrugations The phase center varies
from 0mm to -302mm
From Fig 515 we can observed that phase center variation reduced by the
corrugation and three cases phase center calculated in φ=450 plane
parameter sweep values are given in Table 52
10 12 14 16 181
0
-1
-2
-3
-4
-5
-6
Pha
se c
ente
r (m
m)
Frequency (GHz)
choke+corrugatuion without choke corrugation with choke
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
-73-
Frequency
(GHz)
Phase center from the aperture plane
(mm)
Without
chokes and
corrugations
With
chokes
With chokes
and
corrugations
1000 -326 062 000
1100 -187 030 -002
1200 -563 -208 -065
1300 -296 -154 -202
1400 -319 -314 -302
1500 -201 -203 -241
1600 -242 -233 -207
1700 -208 -208 -186
1800 -190 -157 -132
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
Based on the foregoing parametric studies optimum dimensions of the
broadband circular waveguide feed are obtained as shown in Table 53
-74-
Table 53 Optimum dimensions of the broadband circular waveguide feed
Parameter Designation Value (mm)
2a Waveguide inside diameter 2070
d Waveguide outside diameter 3690
lcrLength of the circular waveguide section 1430
m Distance between the aperture plane and the first corrugation 950
xDistance from the last corrugation to the end of the cylindrical outer surface
550
ltrLength of the rectangular-to-circularwaveguide transition 4465
lrcLength of the rectangular waveguide section 1430
tch Choke slot width 090
lch Choke depth 750
t Choke metal width 090
lcor Corrugation depth 465
tcor Corrugation metal width 100
s Corrugation slot width 10
lp Probe length 530
sp Probe position from the back short 530
din Probe diameter 127
b Inside height of the rectangular waveguide 857
tw Waveguide wall thickness 500
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-4-
II Analysis of Circular and Square Waveguide Feeds
21 Circular Waveguide Radiator
Before design a complicated circular waveguide feed it is helpful to
investigate the impedance and radiation properties of a circular waveguide
open end
The circular waveguide is a cylindrical hollow metallic pipe with a uniform
circular section of radius a Circular waveguides are normally designed to
operate only with the dominant mode The dominant mode in a waveguide is
the mode having the lowest cutoff frequency given by equation (21)
(21)
where
(22)
and a is the waveguide radius The following chart[2] and table show the
cutoff frequencies of various modes in a circular waveguide
-5-
Modes c al11TEc cf f
TE11 341259 100000
TM01 261274 130613
TE21 205720 165885TE01 163979 208111
TM11 163979 208111TE31 149557 228180
TM21 122345 278932TE41 118159 288813
TE12 117852 289566
TM02 113824 299813TE02 0897986 380027
The recommended frequency range of the commercial circular waveguide is
given by the following equation This assumes that the TM01 mode is not
generated or suppressed if generated
11 21 11TE TE TE115 095 158 32 bandwidthc c cf f f fpound pound = reg (23)
Fig 21 shows the geometry of a circular waveguide with a diameter of 2a
When 2a is 2053mm the cutoff frequency of the TE11 mode is 857GHz
According to (23) the useful operating frequency range is from
986-1354GHz
Fig 22 shows the reflection of this waveguide excited with the dominant
TE11 mode The waveguide length l is 60mm The reflection occurs at the
open end of the circular waveguide The reflection coefficient is less than
-15dB over 10-18GHz
-6-
Fig 21 Geometry of a circular waveguide open end radiator
Fig 23 shows a 2D gain pattern of this waveguide antenna The
waveguide antenna has a gain of 80dB 99dB and 115dB at 10GHz
14GHz and 18GHz respectively Fig 24 shows the E- and H-plane patterns
of the circular waveguide antenna Table 21 summarizes the properties of a
circular waveguide antenna
Fig 22 Reflection coefficient of a circular waveguide open end radiator
-7-
(a)
(b)
Fig 23 2D radiation pattern of the circular waveguide open end radiator
at (a)10GHz (b) 14GHz and (c) 18GHz
-8-
(c)
Fig 23 continued
-9-
(a)
(b)
(c)
Fig 24 E-plane and H-plane patterns of the circular waveguide open end
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-10-
Table 21 Properties of a circular waveguide open end radiator of diameter
2053mm
Frequency(GHz)-10dB Beamwith(deg) Front-to-Back
Ratio(dB)E plane H plane
10 67 73 12
14 58 60 18
18 41 50 21
In a circular waveguide radiatoλr a good pattern symmetry and low back
radiation is obtained at 14GHz where 2aλ = 096
22 Square Waveguide Radiator
A square waveguide is often used as a dual-polarized feed To operate the
cutoff frequency of the dominant mode a square-waveguide wall width a
must be greater than one half of a wavelength The modes with cutoff
frequencies equal to or smaller than the operational frequency can exist inside
the waveguide wall The lower cutoff frequency and cutoff wavelength for
square waveguide is determined by the following equations
TE
(24)
TE
(25)
The next higher-order mode is TE11 mode with the cutoff wavelength
given by
-11-
TE
(26)
Similar to the circular waveguide the recommended operating frequency range
of a square waveguide is given by
TEleleTE
TErarr bandwidth (27)
Fig 25 shows the geometry of a square waveguide with a dimension of a
When a is 157mm the cutoff frequency is 95GHz The recommended
operating frequency of this waveguide is from 109GHz to 155GHz
Fig 26 shows the reflection of this waveguide excited with the dominant
TE10 mode The reflection coefficient is less than -15dB over 10-20GHz
Fig 25 Geometry of a square waveguide open end radiator
Fig 27 and shows the 2D radiation pattern of a square waveguide antenna
excited with the dominant TE10 mode The antenna has a gain of 73dB
85dB and 102dB at 10GHz 14GHz and 18GHz respectively Fig 28
shows the E- and H-plane radiation patterns of a square waveguide radiator
Table 22 summarizes the properties of a square waveguide open end radiator
-12-
Fig 26 Reflection coefficient of a square waveguide open end radiator
(a)
Fig 27 2D radiation patterns of a square waveguide radiator
at (a) 10GHz (b) 14GHz and (c) 18GHz
-13-
(b)
(c)
Fig 27 continued
-14-
(a)
(b)
(c)
Fig 28 E-plane and H-plane patterns of square waveguide open radiator
at (a) 10GHz(b) 14GHz and (c) 18GHz
-15-
Table 22 Properties of a square waveguide open end radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 69 71 11
14 47 60 25
18 58 62 16
The radiation pattern symmetry and back radiation performance of the
square waveguide are inferior to those of a circular waveguide
23 Probe-Fed Circular Waveguide Radiator
In Section 21 the radiation properties of a TE11-mode excited waveguide
is investigated In this section a circular waveguide fed by a coaxial probe
shown in Fig 29 is studied
The coaxial probes diameter is 127mm With the Teflon dielectric the
50-ohm coaxial lines outer conductor has a diameter of 41mm For a
circular waveguide the wave impedance of the TE11 mode is given by
∙ (28)
where λg is the guided wavelength given by
(29)
-16-
(a) (b)
Fig 29 Probe-fed circular waveguide radiator (a) Front view and (b) side
view
The combination of the probe length and the probe position from the
shorted wall enables a good impedance matching The probe distance sp from
the back short is close to a quarter wavelength at the design frequency
The designed feed has the following dimension d = 2053mm lp = 42
mm sp = 534mm wall thickness = 05mm and feed length = 400mm
Fig 210 shows the reflection coefficient of the designed probe-fed
circular waveguide radiator The reflection coefficient is less than -10dB over
138-187GHz Fig 211 and 212 shows the E-plane and H-plane radiation
patterns and 2D radiation patterns of the coaxial-to-circular waveguide
transition The radiation patterns symmetry distorted because of the high order
modes The coaxial-to-circular waveguide transition has 73dB 84dB and
79dB gain at 10GHz 14GHz and 18GHz frequencies respectively Table 23
shows the properties of the coaxial-to-circular waveguide transition
-17-
Fig 210 Reflection coefficient of the probe-fed circular waveguide radiator
(a)
Fig 211 2D radiation pattern of the probe-fed circular waveguide radiator
at (a) 10GHz (b) 14GHz and (c) 18GHz
-18-
(b)
(c)
Fig 211 continued
-19-
(a)
(b)
(c)
Fig 212 E- and H-plane patterns of the probe-fed circular waveguide
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-20-
Table 23 Properties of the probe-fed circular waveguide radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 73 70 1414 83 57 17
18 60 52 30
When a circular waveguide radiator is fed by a coaxial probe its radiation
properties are not good due to the excitation of higher-order modes
Therefore a probe-fed circular waveguide radiator can be used as a feed only
over a narrow frequency range
24 Probe-Fed Square Waveguide Radiator
In this section a probe-fed square waveguide radiator is investigated Fig
213 shows a coaxial probe-fed square waveguide radiator The designed
radiator has the following dimension a = b = 157mm lp = 35 mm sp =
50 mm wall thickness = 05mm and feed length = 40mm
(a) (b)
Fig 213 Probe-fed square waveguide radiator (a) Front view and (b) side
view
-21-
Fig 214 shows the 2D radiation patterns of the radiator at 10GHz
14GHz and 18GHz Fig 215 shows E- and H-plane patterns of the radiator
Fig 216 shows the reflection coefficient of the probe-fed square waveguide
radiator The reflection coefficient is less than -10dB over 13-20GHz Table
24 summarizes the properties of the probe-fed square waveguide radiator
(a)
Fig 214 2D radiation patterns of the probe-fed square waveguide radiator at
(a) 10GHz (b) 14GHz and (c) 18GHz
-22-
(b)
(c)
Fig 214 continued
-23-
(a)
(b)
(c)
Fig 216 E-plane and H-plane patterns of the probe-fed square waveguide
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-24-
Fig 216 Reflection coefficient of the probe-fed square waveguide radiator
Table 24 Properties of the probe-fed square waveguide radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 73 71 12
14 85 63 1418 27 65 28
When a square waveguide radiator is fed by a coaxial probe its radiation
properties are not good due to the excitation of higher-order modes as in the
case of the probe-fed circular waveguide radiator A probe-fed square
waveguide radiator can be used as a feed only over a narrow frequency
range
-25-
III Design of Compact Circular Waveguide Feeds
In this chapter the feed design is presented for a prime-focus reflector
antenna The prime-focus paraboloid reflector is one of the most commonly
used high-gain antenna It has been used in earth-station antennas and radio
telescopes It consists of a paraboloid reflector with a feed system at its focal
point
The feed should radiate a low level of cross-polar power over the
operating frequency These conditions not easy to achieve and most prime
focus feeds are compromises The shape and characteristic of the radiation
pattern of the feed are the most important parameter because these will
directly influence the fields which are directed at a reflector[6] Other
electrical factors which relevant to the choice of a feed are the cross-polar
level the gain efficiency the bandwidth and impedance matching
31 Narrow-Band Circular Waveguide Feed
Fig 31 shows the proposed narrow-band circular waveguide feed and its
design variables The feed consists of a circular waveguide open end excited
by a TE11 dominant mode A quarter wave choke is applied along the
circular aperture of the waveguide to equalize E- and H-plane radiation
patterns and to suppress the back radiation A dielectric ring is used to
control the radiation pattern and change the power distribution over the
aperture The control of the amplitude over the aperture are essential to the
design of symmetric radiation pattern The material used for dielectric loading
-26-
is the monocast(MC) nylon with a dielectric constant of 30 The feed is
designed to operate over 171-197GHz
(a)
(b)
Fig 31 Narrow-band circular waveguide feed (a) CAD model and (b) a
cross sectional view
The impedance matching is achieved by a proper combination of the probe
height lp and its distance sp from the waveguide shorted end Here the
-27-
circular waveguide is terminated with an open end with a wall thickness of
2mm radiating into the free space
Fig 32 shows the effect of the probe length lp and the probe distance sp
on the reflection coefficient The best performance is obtained when lp =
363mm and sp = 616mm The feeds reflection coefficient is less than -10dB
over 170-195GHz
(a)
(b)
Fig 32 Effect of the (a) the probe length lp and (b) the probe
distance sp on the reflection coefficient
-28-
Fig 33 shows the effect of the choke depth The E-plane pattern is more
sensitive to the choke depth than the H-plane pattern The choke depth has a
strong influence on the reflection coefficient when it is 360mm By properly
choosing the choke depth we can equalize the E- and H-plane patterns The
optimum value of the choke depth is 410mm which is 0249λ0 at 1825GHz
The choke slot width tch in the range of 06-12mm has almost no effect
on the H-plane pattern and the reflection coefficient For the E-plane pattern
tch of 12mm has some effect on the E-plane radiation pattern as shown in
Fig 34
Fig 35 shows the feed performance versus the dielectric ring length We
observe in Fig 35 that the dielectric length ld has an optimum value of
1168mm which does no effect on the H-plane pattern and tha the value of
1048mm has some effect on the E-plane pattern and the reflection
coefficient
Fig 36 shows E-plane and H-plane patterns and the reflection coefficient
versus the dielectric thickness With the optimum value of the dielectric
thickness t obtained from the Fig 36 is 155mm The larger values of td has
much stronger effects on the E-plane pattern and the reflection coefficient
The H-plane pattern is not sensitive to the dielectric ring thickness
-29-
(a)
(b)
(c)
Fig 33 Feed performance versus the choke depth (a) E-plane pattern
(b) H-plane pattern and (c) reflection coefficient
-30-
(a)
(b)
(c)
Fig 34 Feed performance versus the choke slot width (a) E-plane pattern
(b) H-plane pattern and (c) reflection coefficient
-31-
(a)
(b)
(c)
Fig 35 Feed performance versus the dielectric ring length (a) E-plane
pattern (b) H-plane pattern and (c) reflection coefficient
-32-
(a)
(b)
(c)
Fig 36 Feed performance versus the dielectric ring thickness (a) E-plane
pattern(b) H-plane pattern and (c) reflection coefficient
-33-
From the above parametric analysis an optimum feed design is obtained
The result is shown in Table 31 Fig 37 shows the 2D gain patterns of
designed feed The antenna has a gain of 903dB 933dB and 956dB at
171GHz 1825GHz and 19GHz respectively
Fig 38 shows E- and H-plane radiation patterns of the designed feed The
feed has E- and H-plane 10-dB beamwidths of 60 and 59 degrees at 17GHz
The feed has a front-to-back ration of 1900dB 2490dB and 2200dB at
171GHz 1825GHz and 19GHz respectively Table 32 summarizes the
performance of the designed narrow-band circular waveguide feed
The designed feed has a greatly improved performance over that of a
simple coax-fed feed described in Section 23
Table 31 Dimensions of the designed narrow-band circular feed
Parameter Designation Value(mm)
a Waveguide inside radius 640
l Feed length 2890
lp Probe length 363
sp Probe position from the back short 616
din Probe diameter 127
dout Diameter of coaxial cables outer conductor 400
t Thickness of choked wall 050
tch Choke slot width 100
lch Choke depth 410
ld Dielectric ring length 1168
td Dielectric ring thickness 155
d1 Waveguide outside diameter 1680
-34-
(a)
(b)
Fig 37 2D gain patterns of the narrow-band circular waveguide feed at
(a) 17GHz (b) 1825GHz and (c) 19GHz
-35-
(c)
Fig 37 continued
-36-
(a)
(b)
(c)
Fig 38 E- and H-plane patterns of the narrow-band circular waveguide feed
at (a) 10GHz (b) 1825GHz and (c) 195GHz
-37-
Frequency(GHz)
Gain(dB)
E-H-plane10-dB beamwidths
(deg)
Front-to-back ratio(dB)
Phase centerlocation
(From feeds aperture plane
toward reflector)
(mm)
1700 903 6059 20 062
1825 933 6060 25 004
1900 956 5759 22 007
Table 32 Performance of the narrow-band circular waveguide feed
The designed narrow-band feed is fabricated and its performance is
measured and compared with the simulation results The designed feed is
fabricated in a numerically-controlled machining center The fabricated antenna
is shown in Fig 39
Fig 39 Photograph of the fabricated feed
-38-
Fig 310 shows a comparison of the measured and simulated reflection
coefficients The measured reflection coefficient is less than -10dB over
171-197GHz The agreement between simulated and measured results are
good
Fig 311 shows the E- and H-plane patterns of the fabricated feed at
187GHz The feed has 90dB gain simulation and measurement results are in
good agreement
The fabricated antennarsquos 10dB beamwidth is 60 degrees in both E and H
planes at 187GHz The front-to-back ratio is 21dB
Fig 310 Reflection coefficient of the fabricated feed
-39-
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Fee
d H
orn
Gain
- d
B
Angle - degree
(a)
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Feed H
orn
Gain
- d
B
Angle - degree
(b)
Fig 311 Gain patterns of the fabricated feed at 187 GHz (a) E-plane and
(b) H-plane
-40-
IV Design of Circular Waveguide Feeds Loaded with a
Dielectric Rod
In this section circular waveguide feeds loaded with a dielectric rod feed
are investigated A comprehensive discussion of the circular waveguide loaded
with a dielectric rod is given by Kumar[7] Inserting a dielectric material
inside the circular waveguide improves the E- and H-plane pattern symmetry
In general dielectric-loaded circular waveguide feeds show good performance
only over a narrow bandwidth
Fig 41 shows the geometry of a circular waveguide loaded with a
dielectric rod The waveguide length is 400mm and the wall thickness is
05mm The dielectric rods diameter is 207mm The dielectric rod is
extended 05 wavelength beyond the waveguide open end The dielectric
constant εr is changed and the feeds performance is observed
Fig 41 Geometry of a circular waveguide loaded with a uniform dielectric
rod
-41-
Fig 42 is the radiation pattern of the feed with εr = 25 and L = 05λ0 at
9GHz E- and H-plane 10-dB beamwidths are 810 and 807 degrees
respectively The front-to-back ratio is 18dB The antenna gain is 71dB
(a)
(b)
Fig 42 Radiation pattern at 9GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 05λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-42-
Fig 43 shows the radiation pattern of the feed with εr = 21 at 10GHz
E- and H-plane 10-dB beamwidths are 70 and 71 degrees respectively The
front-to-back ratio is 19dB The antenna gain is 83dB
(a)
(b)
Fig 43 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 21 and L = 05λ0 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-43-
Fig 44 shows the radiation pattern of the feed with εr = 30 at 8GHz
E- and H-plane 10-dB beamwidths are 83 and 824 degrees respectively The
front-to-back ratio is 17dB The antenna gain is 73dB
(a)
(b)
Fig 44 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 30 and L = 05λ0 at 8GHz (a) 2D radiation pattern
and (b) E- and H-plane patterns
-44-
Fig 45 shows the radiation pattern of the feed with εr = 50 at 18GHz
E- and H-plane 10-dB beamwidths are 56 and 54 degrees respectively The
front-to-back ratio is 27dB The antenna gain is 105dB The feed has a good
pattern symmetry and low back radiation
(a)
(b)
Fig 45 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 50 and L = 05λ0 at 18GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-45-
Fig 46 is the radiation pattern of the feed with εr = 25 and L = 10λ0 at
10GHz E- and H-plane 10-dB beamwidths are 50 and 48 degrees
respectively The front-to-back ratio is 16dB The antenna gain is 105dB
(a)
(b)
Fig 46 Radiation pattern at 10GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 10λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-46-
Fig 47 shows the geometry of a circular waveguide with a tapered
dielectric rod The designed feed has the following dimension L = 1λ0 d =
1λ0 and εr =25 at 10GHz The waveguide length is 40mm and the wall
thickness is 05mm
L
Dielectricd3
Fig 47 Geometry of a circular waveguide loaded with a tapered dielectric
rod
Fig 48 shows the radiatio pattern of the designed feed E- and H-plane
10-dB beamwidths are 575 and 564 degrees respectively The front-to-back
ratio is 377dB The antenna gain is 94dB The designed feed has an
excellent beamwidth symmetry and a very low back radiation
-47-
(a)
(b)
Fig 48 Radiation pattern of a circular waveguide loaded with a tapered
dielectric rod with L = 1λ0 d = 1λ0 and εr =25 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-48-
Fig 49 shows the geometry of a spherical ended dielectric rod feed
diameter of 06λ0 at 10GHz with a dielectric constant of 25 and L= 03λ0
Fig 410 shows the radiation patterns of the designed feed E- and H-plane
10-dB beamwidths are both 63 degrees The front-to-back ratio is 24dB The
antenna gain is 864dB
Fig 49 Geometry of a circular waveguide loaded with a spherical ended
dielectric rod
-49-
(a)
(b)
Fig 410 Radiation pattern of a circular waveguide loaded wht a spherical
ended dielectric rod with d = 06λ0 L = 03λ0 and εr =25 at 10GHz (a) 3D
radiation pattern and (b) E- and H-plane patterns
-50-
V Design of a Broadband Circular Waveguide Feed
In this chapter the design of a broadband circular waveguide feed is
presented At microwave frequencies the feed is often a circular waveguide
with chokes and corrugations around the aperture Chokes and corrugations
equalize E- and H-plane patterns and reduce the back radiation
The proposed feed is designed to operate over 10-18GHz The design starts
with the optimization of the coaxial-to-rectangular waveguide adapter
employed for good mode purity over a broad frequency range Next a
rectangular-to-circular waveguide transition is optimized Finally chokes and
corrugations are designed for improved pattern symmetry and low back
radiation
The proposed feed structure is shown in Fig 51 The feed consist of the
following parts a coaxial-to-rectangular waveguide adapter a rectangular-to-
circular waveguide transition a circular waveguide section four quarter-wave
chokes around the feeds aperture and four corrugations on the feeds outer
surface
The computer simulation shows the above arrangement offers good radiation
patterns over a broad frequency range The broadband operation is obtained
by exciting the TE11 mode in the circular waveguide using the TE10 mode of
the rectangular waveguide which is in turn excited by a coaxial probe
-51-
Chokes
Coaxial-to-waveguide transition
Circular wavguide
Corrugations
Mode transition
(a)
(b)
Fig 51 Structure of the proposed broadband circular waveguide feed
(a) CAD model and (b) cross-sectional view
For the coaxial-to-rectangular waveguide adapter an SMA connector with
the probe diameter of 127 mm is employed The coaxial probe inserted into
the waveguide energizes the feed and excites the dominant TE10 mode in
-52-
the rectangular waveguide The impedance matching is achieved by adjusting
the probe distance sp from the back short and the probe length lp
(a)
(b)
Fig 52 Reflection coefficient of the coaxial-to-rectangular adapter versus
(a) probe length lp and (b) the probe position sp
Fig 52 shows the reflection coefficient versus the various values of probe
lengths lp and probe positions sp The probe length lp is adjusted to obtain
antenna impedance matching and the probe distance sp is adjusted to obtain a
-53-
desired resonant frequency
Next a transition between rectangular and circular waveguide is designed
The transition section converts the TE10 mode in the rectangular waveguide to
TE11 mode in the circular waveguide and vice versa The transition is built
in a form of a taper for easy fabrication[22]
(a)
(b)
Fig 53 Structure of the rectangular-to-circular waveguide transition
(a) 3D view and (b) cross sectional view
The dimensions of the final optimized transition are as follows The length
of the rectangular waveguide section is 143mm The rectangular waveguides
width a and height b are 207mm and 857mm respectively The length of
the circular waveguide section is 143mm The inside diameter of the circular
-54-
waveguide is 207mm(097 wavelength at 14GHz) The length of transition
region ltr is 4465mm(approximately equal to 2λ0 at 14GHz) Fig 54 shows
the field distribution inside the mode converter
(a)
(b)
Fig 54 Field distribution inside the mode converter at
(a) 10GHz (b) 14GHz and (c) 18GHz
-55-
(c)
Fig 54 continued
Finally multiple chokes are investigated Figs 55 56 and 57 show the
feed performance without chokes The reflection coefficient is less than -10dB
over 10-19GHz The antenna has a gain of 921dB to 1189dB over
10-19GHz
Fig 55 Reflection coefficient of the broadband circular waveguide feed
without chokes and corrugations
-56-
(a)
(b)
(c)
Fig 56 E- and H-plane patterns of the broadband circular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-57-
(d)
(e)
Fig 56 continued
-58-
(a)
(b)
Fig 57 2D radiation patterns of the broadband cicular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-59-
(c)
(d)
Fig 57 continued
-60-
(e)
Fig 57 continued
To achieve equal beamwidths in E and H planes over a wide frequency
range chokes and corrugations are employed Table51 summarizes the
performance of a feed without chokes and corrugations
Table 51 Performance of the broadband circular waveguide feed without
chokes and corrugations
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
1000 940 6061 15
1200 972 6159 17
1400 920 5957 21
1600 1070 4751 29
1800 1188 5352 21
-61-
Four quarter-wavelength chokes are introduced in the feed design which
has a slot depth of 75mm and slot width of 09mm The choke slot spacing
is 18mm The choke design is investigated by applying the choke one by
one and the effect on the E- and H-plane patterns are observed as illustrated
in Figs 58 and 59 The use of chokes makes the E-plane pattern narrower
The H-plane pattern is not affected Chokes increase the gain slightly and
reduce back radiation
(a)
(b)
Fig 58 Effect of chokes on the E-plane pattern of the broadband circular
waveguide feed at (a) 10GHz(b) 12GHz (c) 14GHz (d) 16GHz and (e)
18GHz
-62-
(c)
(d)
(e)
Fig 58 continued
-63-
(a)
(b)
(c)
Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-64-
(d)
(e)
Fig 59 continued
-65-
Fig 510 shows the feed performance versus the choke depth When the
choke depth is varied from 535mm to 95mm the E- and H-plane patterns
are strongly affected The optimum value of choke depth is 75mm(035λ0 at
14GHz) which gives equal E- and H-plane radiation patterns and leads to
low back radiation
Fig 511 shows the feed performance versus the choke slot width tch The
choke slot width is varied from 09mm to 21mm Radiation patterns and
reflection coefficients are not sensitive to the choke slot width The final
choke slot width is selected to be 09mm considering the feed diameter
minimization and the manufacturability The overall diameter of the proposed
feed is 369mm which is increased from the 207mm of the waveguide
inside diameter due to the use of four chokes
-66-
(a)
(b)
(c)
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection coefficient
-67-
(a)
(b)
(c)
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and (c)
reflection coefficient
-68-
Next we investigated corrugations placed on the outer wall of the feed
Four corrugations applied to the outer surface of the circular waveguide The
corrugation depth is 465mm(0215λ0 at 14GHz) The primary purpose of
using corrugations is to further reduce the back radiation Increasing the
number of corrugations beyond four has little effect in reducing the back
radiation
Figs 512 and 513 show the effect of corrugations on the E- and H-plane
patterns Fig 514 shows the parametric study of the corrugation depth lcor
The corrugation depth is varied from 40mm and 645mm The optimum
value of the corrugation depth is found to be 465mm
-69-
(a)
(b)
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern at (a) 12GHz and (b) 14GHz
-70-
(a)
(b)
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern at (a) 12GHz and (b) 14GHz
-71-
(a)
(b)
(c)
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection coefficient
-72-
The phase center location is important in placing the feed in a reflector
antenna[8] The phase center variation with frequency should be small Fig
515 shows the effect of chokes and corrugations on the phase center The
curve with circle corresponds to the case without chokes and corrugations
The phase center varies from -326mm and -190mm away from the feeds
aperture plane It means the phase center is located inside the waveguide
The curve with triangles corresponds to the case with chokes The curve with
squares to the case with chokes and corrugations The phase center varies
from 0mm to -302mm
From Fig 515 we can observed that phase center variation reduced by the
corrugation and three cases phase center calculated in φ=450 plane
parameter sweep values are given in Table 52
10 12 14 16 181
0
-1
-2
-3
-4
-5
-6
Pha
se c
ente
r (m
m)
Frequency (GHz)
choke+corrugatuion without choke corrugation with choke
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
-73-
Frequency
(GHz)
Phase center from the aperture plane
(mm)
Without
chokes and
corrugations
With
chokes
With chokes
and
corrugations
1000 -326 062 000
1100 -187 030 -002
1200 -563 -208 -065
1300 -296 -154 -202
1400 -319 -314 -302
1500 -201 -203 -241
1600 -242 -233 -207
1700 -208 -208 -186
1800 -190 -157 -132
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
Based on the foregoing parametric studies optimum dimensions of the
broadband circular waveguide feed are obtained as shown in Table 53
-74-
Table 53 Optimum dimensions of the broadband circular waveguide feed
Parameter Designation Value (mm)
2a Waveguide inside diameter 2070
d Waveguide outside diameter 3690
lcrLength of the circular waveguide section 1430
m Distance between the aperture plane and the first corrugation 950
xDistance from the last corrugation to the end of the cylindrical outer surface
550
ltrLength of the rectangular-to-circularwaveguide transition 4465
lrcLength of the rectangular waveguide section 1430
tch Choke slot width 090
lch Choke depth 750
t Choke metal width 090
lcor Corrugation depth 465
tcor Corrugation metal width 100
s Corrugation slot width 10
lp Probe length 530
sp Probe position from the back short 530
din Probe diameter 127
b Inside height of the rectangular waveguide 857
tw Waveguide wall thickness 500
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-5-
Modes c al11TEc cf f
TE11 341259 100000
TM01 261274 130613
TE21 205720 165885TE01 163979 208111
TM11 163979 208111TE31 149557 228180
TM21 122345 278932TE41 118159 288813
TE12 117852 289566
TM02 113824 299813TE02 0897986 380027
The recommended frequency range of the commercial circular waveguide is
given by the following equation This assumes that the TM01 mode is not
generated or suppressed if generated
11 21 11TE TE TE115 095 158 32 bandwidthc c cf f f fpound pound = reg (23)
Fig 21 shows the geometry of a circular waveguide with a diameter of 2a
When 2a is 2053mm the cutoff frequency of the TE11 mode is 857GHz
According to (23) the useful operating frequency range is from
986-1354GHz
Fig 22 shows the reflection of this waveguide excited with the dominant
TE11 mode The waveguide length l is 60mm The reflection occurs at the
open end of the circular waveguide The reflection coefficient is less than
-15dB over 10-18GHz
-6-
Fig 21 Geometry of a circular waveguide open end radiator
Fig 23 shows a 2D gain pattern of this waveguide antenna The
waveguide antenna has a gain of 80dB 99dB and 115dB at 10GHz
14GHz and 18GHz respectively Fig 24 shows the E- and H-plane patterns
of the circular waveguide antenna Table 21 summarizes the properties of a
circular waveguide antenna
Fig 22 Reflection coefficient of a circular waveguide open end radiator
-7-
(a)
(b)
Fig 23 2D radiation pattern of the circular waveguide open end radiator
at (a)10GHz (b) 14GHz and (c) 18GHz
-8-
(c)
Fig 23 continued
-9-
(a)
(b)
(c)
Fig 24 E-plane and H-plane patterns of the circular waveguide open end
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-10-
Table 21 Properties of a circular waveguide open end radiator of diameter
2053mm
Frequency(GHz)-10dB Beamwith(deg) Front-to-Back
Ratio(dB)E plane H plane
10 67 73 12
14 58 60 18
18 41 50 21
In a circular waveguide radiatoλr a good pattern symmetry and low back
radiation is obtained at 14GHz where 2aλ = 096
22 Square Waveguide Radiator
A square waveguide is often used as a dual-polarized feed To operate the
cutoff frequency of the dominant mode a square-waveguide wall width a
must be greater than one half of a wavelength The modes with cutoff
frequencies equal to or smaller than the operational frequency can exist inside
the waveguide wall The lower cutoff frequency and cutoff wavelength for
square waveguide is determined by the following equations
TE
(24)
TE
(25)
The next higher-order mode is TE11 mode with the cutoff wavelength
given by
-11-
TE
(26)
Similar to the circular waveguide the recommended operating frequency range
of a square waveguide is given by
TEleleTE
TErarr bandwidth (27)
Fig 25 shows the geometry of a square waveguide with a dimension of a
When a is 157mm the cutoff frequency is 95GHz The recommended
operating frequency of this waveguide is from 109GHz to 155GHz
Fig 26 shows the reflection of this waveguide excited with the dominant
TE10 mode The reflection coefficient is less than -15dB over 10-20GHz
Fig 25 Geometry of a square waveguide open end radiator
Fig 27 and shows the 2D radiation pattern of a square waveguide antenna
excited with the dominant TE10 mode The antenna has a gain of 73dB
85dB and 102dB at 10GHz 14GHz and 18GHz respectively Fig 28
shows the E- and H-plane radiation patterns of a square waveguide radiator
Table 22 summarizes the properties of a square waveguide open end radiator
-12-
Fig 26 Reflection coefficient of a square waveguide open end radiator
(a)
Fig 27 2D radiation patterns of a square waveguide radiator
at (a) 10GHz (b) 14GHz and (c) 18GHz
-13-
(b)
(c)
Fig 27 continued
-14-
(a)
(b)
(c)
Fig 28 E-plane and H-plane patterns of square waveguide open radiator
at (a) 10GHz(b) 14GHz and (c) 18GHz
-15-
Table 22 Properties of a square waveguide open end radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 69 71 11
14 47 60 25
18 58 62 16
The radiation pattern symmetry and back radiation performance of the
square waveguide are inferior to those of a circular waveguide
23 Probe-Fed Circular Waveguide Radiator
In Section 21 the radiation properties of a TE11-mode excited waveguide
is investigated In this section a circular waveguide fed by a coaxial probe
shown in Fig 29 is studied
The coaxial probes diameter is 127mm With the Teflon dielectric the
50-ohm coaxial lines outer conductor has a diameter of 41mm For a
circular waveguide the wave impedance of the TE11 mode is given by
∙ (28)
where λg is the guided wavelength given by
(29)
-16-
(a) (b)
Fig 29 Probe-fed circular waveguide radiator (a) Front view and (b) side
view
The combination of the probe length and the probe position from the
shorted wall enables a good impedance matching The probe distance sp from
the back short is close to a quarter wavelength at the design frequency
The designed feed has the following dimension d = 2053mm lp = 42
mm sp = 534mm wall thickness = 05mm and feed length = 400mm
Fig 210 shows the reflection coefficient of the designed probe-fed
circular waveguide radiator The reflection coefficient is less than -10dB over
138-187GHz Fig 211 and 212 shows the E-plane and H-plane radiation
patterns and 2D radiation patterns of the coaxial-to-circular waveguide
transition The radiation patterns symmetry distorted because of the high order
modes The coaxial-to-circular waveguide transition has 73dB 84dB and
79dB gain at 10GHz 14GHz and 18GHz frequencies respectively Table 23
shows the properties of the coaxial-to-circular waveguide transition
-17-
Fig 210 Reflection coefficient of the probe-fed circular waveguide radiator
(a)
Fig 211 2D radiation pattern of the probe-fed circular waveguide radiator
at (a) 10GHz (b) 14GHz and (c) 18GHz
-18-
(b)
(c)
Fig 211 continued
-19-
(a)
(b)
(c)
Fig 212 E- and H-plane patterns of the probe-fed circular waveguide
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-20-
Table 23 Properties of the probe-fed circular waveguide radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 73 70 1414 83 57 17
18 60 52 30
When a circular waveguide radiator is fed by a coaxial probe its radiation
properties are not good due to the excitation of higher-order modes
Therefore a probe-fed circular waveguide radiator can be used as a feed only
over a narrow frequency range
24 Probe-Fed Square Waveguide Radiator
In this section a probe-fed square waveguide radiator is investigated Fig
213 shows a coaxial probe-fed square waveguide radiator The designed
radiator has the following dimension a = b = 157mm lp = 35 mm sp =
50 mm wall thickness = 05mm and feed length = 40mm
(a) (b)
Fig 213 Probe-fed square waveguide radiator (a) Front view and (b) side
view
-21-
Fig 214 shows the 2D radiation patterns of the radiator at 10GHz
14GHz and 18GHz Fig 215 shows E- and H-plane patterns of the radiator
Fig 216 shows the reflection coefficient of the probe-fed square waveguide
radiator The reflection coefficient is less than -10dB over 13-20GHz Table
24 summarizes the properties of the probe-fed square waveguide radiator
(a)
Fig 214 2D radiation patterns of the probe-fed square waveguide radiator at
(a) 10GHz (b) 14GHz and (c) 18GHz
-22-
(b)
(c)
Fig 214 continued
-23-
(a)
(b)
(c)
Fig 216 E-plane and H-plane patterns of the probe-fed square waveguide
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-24-
Fig 216 Reflection coefficient of the probe-fed square waveguide radiator
Table 24 Properties of the probe-fed square waveguide radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 73 71 12
14 85 63 1418 27 65 28
When a square waveguide radiator is fed by a coaxial probe its radiation
properties are not good due to the excitation of higher-order modes as in the
case of the probe-fed circular waveguide radiator A probe-fed square
waveguide radiator can be used as a feed only over a narrow frequency
range
-25-
III Design of Compact Circular Waveguide Feeds
In this chapter the feed design is presented for a prime-focus reflector
antenna The prime-focus paraboloid reflector is one of the most commonly
used high-gain antenna It has been used in earth-station antennas and radio
telescopes It consists of a paraboloid reflector with a feed system at its focal
point
The feed should radiate a low level of cross-polar power over the
operating frequency These conditions not easy to achieve and most prime
focus feeds are compromises The shape and characteristic of the radiation
pattern of the feed are the most important parameter because these will
directly influence the fields which are directed at a reflector[6] Other
electrical factors which relevant to the choice of a feed are the cross-polar
level the gain efficiency the bandwidth and impedance matching
31 Narrow-Band Circular Waveguide Feed
Fig 31 shows the proposed narrow-band circular waveguide feed and its
design variables The feed consists of a circular waveguide open end excited
by a TE11 dominant mode A quarter wave choke is applied along the
circular aperture of the waveguide to equalize E- and H-plane radiation
patterns and to suppress the back radiation A dielectric ring is used to
control the radiation pattern and change the power distribution over the
aperture The control of the amplitude over the aperture are essential to the
design of symmetric radiation pattern The material used for dielectric loading
-26-
is the monocast(MC) nylon with a dielectric constant of 30 The feed is
designed to operate over 171-197GHz
(a)
(b)
Fig 31 Narrow-band circular waveguide feed (a) CAD model and (b) a
cross sectional view
The impedance matching is achieved by a proper combination of the probe
height lp and its distance sp from the waveguide shorted end Here the
-27-
circular waveguide is terminated with an open end with a wall thickness of
2mm radiating into the free space
Fig 32 shows the effect of the probe length lp and the probe distance sp
on the reflection coefficient The best performance is obtained when lp =
363mm and sp = 616mm The feeds reflection coefficient is less than -10dB
over 170-195GHz
(a)
(b)
Fig 32 Effect of the (a) the probe length lp and (b) the probe
distance sp on the reflection coefficient
-28-
Fig 33 shows the effect of the choke depth The E-plane pattern is more
sensitive to the choke depth than the H-plane pattern The choke depth has a
strong influence on the reflection coefficient when it is 360mm By properly
choosing the choke depth we can equalize the E- and H-plane patterns The
optimum value of the choke depth is 410mm which is 0249λ0 at 1825GHz
The choke slot width tch in the range of 06-12mm has almost no effect
on the H-plane pattern and the reflection coefficient For the E-plane pattern
tch of 12mm has some effect on the E-plane radiation pattern as shown in
Fig 34
Fig 35 shows the feed performance versus the dielectric ring length We
observe in Fig 35 that the dielectric length ld has an optimum value of
1168mm which does no effect on the H-plane pattern and tha the value of
1048mm has some effect on the E-plane pattern and the reflection
coefficient
Fig 36 shows E-plane and H-plane patterns and the reflection coefficient
versus the dielectric thickness With the optimum value of the dielectric
thickness t obtained from the Fig 36 is 155mm The larger values of td has
much stronger effects on the E-plane pattern and the reflection coefficient
The H-plane pattern is not sensitive to the dielectric ring thickness
-29-
(a)
(b)
(c)
Fig 33 Feed performance versus the choke depth (a) E-plane pattern
(b) H-plane pattern and (c) reflection coefficient
-30-
(a)
(b)
(c)
Fig 34 Feed performance versus the choke slot width (a) E-plane pattern
(b) H-plane pattern and (c) reflection coefficient
-31-
(a)
(b)
(c)
Fig 35 Feed performance versus the dielectric ring length (a) E-plane
pattern (b) H-plane pattern and (c) reflection coefficient
-32-
(a)
(b)
(c)
Fig 36 Feed performance versus the dielectric ring thickness (a) E-plane
pattern(b) H-plane pattern and (c) reflection coefficient
-33-
From the above parametric analysis an optimum feed design is obtained
The result is shown in Table 31 Fig 37 shows the 2D gain patterns of
designed feed The antenna has a gain of 903dB 933dB and 956dB at
171GHz 1825GHz and 19GHz respectively
Fig 38 shows E- and H-plane radiation patterns of the designed feed The
feed has E- and H-plane 10-dB beamwidths of 60 and 59 degrees at 17GHz
The feed has a front-to-back ration of 1900dB 2490dB and 2200dB at
171GHz 1825GHz and 19GHz respectively Table 32 summarizes the
performance of the designed narrow-band circular waveguide feed
The designed feed has a greatly improved performance over that of a
simple coax-fed feed described in Section 23
Table 31 Dimensions of the designed narrow-band circular feed
Parameter Designation Value(mm)
a Waveguide inside radius 640
l Feed length 2890
lp Probe length 363
sp Probe position from the back short 616
din Probe diameter 127
dout Diameter of coaxial cables outer conductor 400
t Thickness of choked wall 050
tch Choke slot width 100
lch Choke depth 410
ld Dielectric ring length 1168
td Dielectric ring thickness 155
d1 Waveguide outside diameter 1680
-34-
(a)
(b)
Fig 37 2D gain patterns of the narrow-band circular waveguide feed at
(a) 17GHz (b) 1825GHz and (c) 19GHz
-35-
(c)
Fig 37 continued
-36-
(a)
(b)
(c)
Fig 38 E- and H-plane patterns of the narrow-band circular waveguide feed
at (a) 10GHz (b) 1825GHz and (c) 195GHz
-37-
Frequency(GHz)
Gain(dB)
E-H-plane10-dB beamwidths
(deg)
Front-to-back ratio(dB)
Phase centerlocation
(From feeds aperture plane
toward reflector)
(mm)
1700 903 6059 20 062
1825 933 6060 25 004
1900 956 5759 22 007
Table 32 Performance of the narrow-band circular waveguide feed
The designed narrow-band feed is fabricated and its performance is
measured and compared with the simulation results The designed feed is
fabricated in a numerically-controlled machining center The fabricated antenna
is shown in Fig 39
Fig 39 Photograph of the fabricated feed
-38-
Fig 310 shows a comparison of the measured and simulated reflection
coefficients The measured reflection coefficient is less than -10dB over
171-197GHz The agreement between simulated and measured results are
good
Fig 311 shows the E- and H-plane patterns of the fabricated feed at
187GHz The feed has 90dB gain simulation and measurement results are in
good agreement
The fabricated antennarsquos 10dB beamwidth is 60 degrees in both E and H
planes at 187GHz The front-to-back ratio is 21dB
Fig 310 Reflection coefficient of the fabricated feed
-39-
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Fee
d H
orn
Gain
- d
B
Angle - degree
(a)
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Feed H
orn
Gain
- d
B
Angle - degree
(b)
Fig 311 Gain patterns of the fabricated feed at 187 GHz (a) E-plane and
(b) H-plane
-40-
IV Design of Circular Waveguide Feeds Loaded with a
Dielectric Rod
In this section circular waveguide feeds loaded with a dielectric rod feed
are investigated A comprehensive discussion of the circular waveguide loaded
with a dielectric rod is given by Kumar[7] Inserting a dielectric material
inside the circular waveguide improves the E- and H-plane pattern symmetry
In general dielectric-loaded circular waveguide feeds show good performance
only over a narrow bandwidth
Fig 41 shows the geometry of a circular waveguide loaded with a
dielectric rod The waveguide length is 400mm and the wall thickness is
05mm The dielectric rods diameter is 207mm The dielectric rod is
extended 05 wavelength beyond the waveguide open end The dielectric
constant εr is changed and the feeds performance is observed
Fig 41 Geometry of a circular waveguide loaded with a uniform dielectric
rod
-41-
Fig 42 is the radiation pattern of the feed with εr = 25 and L = 05λ0 at
9GHz E- and H-plane 10-dB beamwidths are 810 and 807 degrees
respectively The front-to-back ratio is 18dB The antenna gain is 71dB
(a)
(b)
Fig 42 Radiation pattern at 9GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 05λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-42-
Fig 43 shows the radiation pattern of the feed with εr = 21 at 10GHz
E- and H-plane 10-dB beamwidths are 70 and 71 degrees respectively The
front-to-back ratio is 19dB The antenna gain is 83dB
(a)
(b)
Fig 43 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 21 and L = 05λ0 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-43-
Fig 44 shows the radiation pattern of the feed with εr = 30 at 8GHz
E- and H-plane 10-dB beamwidths are 83 and 824 degrees respectively The
front-to-back ratio is 17dB The antenna gain is 73dB
(a)
(b)
Fig 44 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 30 and L = 05λ0 at 8GHz (a) 2D radiation pattern
and (b) E- and H-plane patterns
-44-
Fig 45 shows the radiation pattern of the feed with εr = 50 at 18GHz
E- and H-plane 10-dB beamwidths are 56 and 54 degrees respectively The
front-to-back ratio is 27dB The antenna gain is 105dB The feed has a good
pattern symmetry and low back radiation
(a)
(b)
Fig 45 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 50 and L = 05λ0 at 18GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-45-
Fig 46 is the radiation pattern of the feed with εr = 25 and L = 10λ0 at
10GHz E- and H-plane 10-dB beamwidths are 50 and 48 degrees
respectively The front-to-back ratio is 16dB The antenna gain is 105dB
(a)
(b)
Fig 46 Radiation pattern at 10GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 10λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-46-
Fig 47 shows the geometry of a circular waveguide with a tapered
dielectric rod The designed feed has the following dimension L = 1λ0 d =
1λ0 and εr =25 at 10GHz The waveguide length is 40mm and the wall
thickness is 05mm
L
Dielectricd3
Fig 47 Geometry of a circular waveguide loaded with a tapered dielectric
rod
Fig 48 shows the radiatio pattern of the designed feed E- and H-plane
10-dB beamwidths are 575 and 564 degrees respectively The front-to-back
ratio is 377dB The antenna gain is 94dB The designed feed has an
excellent beamwidth symmetry and a very low back radiation
-47-
(a)
(b)
Fig 48 Radiation pattern of a circular waveguide loaded with a tapered
dielectric rod with L = 1λ0 d = 1λ0 and εr =25 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-48-
Fig 49 shows the geometry of a spherical ended dielectric rod feed
diameter of 06λ0 at 10GHz with a dielectric constant of 25 and L= 03λ0
Fig 410 shows the radiation patterns of the designed feed E- and H-plane
10-dB beamwidths are both 63 degrees The front-to-back ratio is 24dB The
antenna gain is 864dB
Fig 49 Geometry of a circular waveguide loaded with a spherical ended
dielectric rod
-49-
(a)
(b)
Fig 410 Radiation pattern of a circular waveguide loaded wht a spherical
ended dielectric rod with d = 06λ0 L = 03λ0 and εr =25 at 10GHz (a) 3D
radiation pattern and (b) E- and H-plane patterns
-50-
V Design of a Broadband Circular Waveguide Feed
In this chapter the design of a broadband circular waveguide feed is
presented At microwave frequencies the feed is often a circular waveguide
with chokes and corrugations around the aperture Chokes and corrugations
equalize E- and H-plane patterns and reduce the back radiation
The proposed feed is designed to operate over 10-18GHz The design starts
with the optimization of the coaxial-to-rectangular waveguide adapter
employed for good mode purity over a broad frequency range Next a
rectangular-to-circular waveguide transition is optimized Finally chokes and
corrugations are designed for improved pattern symmetry and low back
radiation
The proposed feed structure is shown in Fig 51 The feed consist of the
following parts a coaxial-to-rectangular waveguide adapter a rectangular-to-
circular waveguide transition a circular waveguide section four quarter-wave
chokes around the feeds aperture and four corrugations on the feeds outer
surface
The computer simulation shows the above arrangement offers good radiation
patterns over a broad frequency range The broadband operation is obtained
by exciting the TE11 mode in the circular waveguide using the TE10 mode of
the rectangular waveguide which is in turn excited by a coaxial probe
-51-
Chokes
Coaxial-to-waveguide transition
Circular wavguide
Corrugations
Mode transition
(a)
(b)
Fig 51 Structure of the proposed broadband circular waveguide feed
(a) CAD model and (b) cross-sectional view
For the coaxial-to-rectangular waveguide adapter an SMA connector with
the probe diameter of 127 mm is employed The coaxial probe inserted into
the waveguide energizes the feed and excites the dominant TE10 mode in
-52-
the rectangular waveguide The impedance matching is achieved by adjusting
the probe distance sp from the back short and the probe length lp
(a)
(b)
Fig 52 Reflection coefficient of the coaxial-to-rectangular adapter versus
(a) probe length lp and (b) the probe position sp
Fig 52 shows the reflection coefficient versus the various values of probe
lengths lp and probe positions sp The probe length lp is adjusted to obtain
antenna impedance matching and the probe distance sp is adjusted to obtain a
-53-
desired resonant frequency
Next a transition between rectangular and circular waveguide is designed
The transition section converts the TE10 mode in the rectangular waveguide to
TE11 mode in the circular waveguide and vice versa The transition is built
in a form of a taper for easy fabrication[22]
(a)
(b)
Fig 53 Structure of the rectangular-to-circular waveguide transition
(a) 3D view and (b) cross sectional view
The dimensions of the final optimized transition are as follows The length
of the rectangular waveguide section is 143mm The rectangular waveguides
width a and height b are 207mm and 857mm respectively The length of
the circular waveguide section is 143mm The inside diameter of the circular
-54-
waveguide is 207mm(097 wavelength at 14GHz) The length of transition
region ltr is 4465mm(approximately equal to 2λ0 at 14GHz) Fig 54 shows
the field distribution inside the mode converter
(a)
(b)
Fig 54 Field distribution inside the mode converter at
(a) 10GHz (b) 14GHz and (c) 18GHz
-55-
(c)
Fig 54 continued
Finally multiple chokes are investigated Figs 55 56 and 57 show the
feed performance without chokes The reflection coefficient is less than -10dB
over 10-19GHz The antenna has a gain of 921dB to 1189dB over
10-19GHz
Fig 55 Reflection coefficient of the broadband circular waveguide feed
without chokes and corrugations
-56-
(a)
(b)
(c)
Fig 56 E- and H-plane patterns of the broadband circular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-57-
(d)
(e)
Fig 56 continued
-58-
(a)
(b)
Fig 57 2D radiation patterns of the broadband cicular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-59-
(c)
(d)
Fig 57 continued
-60-
(e)
Fig 57 continued
To achieve equal beamwidths in E and H planes over a wide frequency
range chokes and corrugations are employed Table51 summarizes the
performance of a feed without chokes and corrugations
Table 51 Performance of the broadband circular waveguide feed without
chokes and corrugations
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
1000 940 6061 15
1200 972 6159 17
1400 920 5957 21
1600 1070 4751 29
1800 1188 5352 21
-61-
Four quarter-wavelength chokes are introduced in the feed design which
has a slot depth of 75mm and slot width of 09mm The choke slot spacing
is 18mm The choke design is investigated by applying the choke one by
one and the effect on the E- and H-plane patterns are observed as illustrated
in Figs 58 and 59 The use of chokes makes the E-plane pattern narrower
The H-plane pattern is not affected Chokes increase the gain slightly and
reduce back radiation
(a)
(b)
Fig 58 Effect of chokes on the E-plane pattern of the broadband circular
waveguide feed at (a) 10GHz(b) 12GHz (c) 14GHz (d) 16GHz and (e)
18GHz
-62-
(c)
(d)
(e)
Fig 58 continued
-63-
(a)
(b)
(c)
Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-64-
(d)
(e)
Fig 59 continued
-65-
Fig 510 shows the feed performance versus the choke depth When the
choke depth is varied from 535mm to 95mm the E- and H-plane patterns
are strongly affected The optimum value of choke depth is 75mm(035λ0 at
14GHz) which gives equal E- and H-plane radiation patterns and leads to
low back radiation
Fig 511 shows the feed performance versus the choke slot width tch The
choke slot width is varied from 09mm to 21mm Radiation patterns and
reflection coefficients are not sensitive to the choke slot width The final
choke slot width is selected to be 09mm considering the feed diameter
minimization and the manufacturability The overall diameter of the proposed
feed is 369mm which is increased from the 207mm of the waveguide
inside diameter due to the use of four chokes
-66-
(a)
(b)
(c)
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection coefficient
-67-
(a)
(b)
(c)
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and (c)
reflection coefficient
-68-
Next we investigated corrugations placed on the outer wall of the feed
Four corrugations applied to the outer surface of the circular waveguide The
corrugation depth is 465mm(0215λ0 at 14GHz) The primary purpose of
using corrugations is to further reduce the back radiation Increasing the
number of corrugations beyond four has little effect in reducing the back
radiation
Figs 512 and 513 show the effect of corrugations on the E- and H-plane
patterns Fig 514 shows the parametric study of the corrugation depth lcor
The corrugation depth is varied from 40mm and 645mm The optimum
value of the corrugation depth is found to be 465mm
-69-
(a)
(b)
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern at (a) 12GHz and (b) 14GHz
-70-
(a)
(b)
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern at (a) 12GHz and (b) 14GHz
-71-
(a)
(b)
(c)
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection coefficient
-72-
The phase center location is important in placing the feed in a reflector
antenna[8] The phase center variation with frequency should be small Fig
515 shows the effect of chokes and corrugations on the phase center The
curve with circle corresponds to the case without chokes and corrugations
The phase center varies from -326mm and -190mm away from the feeds
aperture plane It means the phase center is located inside the waveguide
The curve with triangles corresponds to the case with chokes The curve with
squares to the case with chokes and corrugations The phase center varies
from 0mm to -302mm
From Fig 515 we can observed that phase center variation reduced by the
corrugation and three cases phase center calculated in φ=450 plane
parameter sweep values are given in Table 52
10 12 14 16 181
0
-1
-2
-3
-4
-5
-6
Pha
se c
ente
r (m
m)
Frequency (GHz)
choke+corrugatuion without choke corrugation with choke
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
-73-
Frequency
(GHz)
Phase center from the aperture plane
(mm)
Without
chokes and
corrugations
With
chokes
With chokes
and
corrugations
1000 -326 062 000
1100 -187 030 -002
1200 -563 -208 -065
1300 -296 -154 -202
1400 -319 -314 -302
1500 -201 -203 -241
1600 -242 -233 -207
1700 -208 -208 -186
1800 -190 -157 -132
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
Based on the foregoing parametric studies optimum dimensions of the
broadband circular waveguide feed are obtained as shown in Table 53
-74-
Table 53 Optimum dimensions of the broadband circular waveguide feed
Parameter Designation Value (mm)
2a Waveguide inside diameter 2070
d Waveguide outside diameter 3690
lcrLength of the circular waveguide section 1430
m Distance between the aperture plane and the first corrugation 950
xDistance from the last corrugation to the end of the cylindrical outer surface
550
ltrLength of the rectangular-to-circularwaveguide transition 4465
lrcLength of the rectangular waveguide section 1430
tch Choke slot width 090
lch Choke depth 750
t Choke metal width 090
lcor Corrugation depth 465
tcor Corrugation metal width 100
s Corrugation slot width 10
lp Probe length 530
sp Probe position from the back short 530
din Probe diameter 127
b Inside height of the rectangular waveguide 857
tw Waveguide wall thickness 500
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-6-
Fig 21 Geometry of a circular waveguide open end radiator
Fig 23 shows a 2D gain pattern of this waveguide antenna The
waveguide antenna has a gain of 80dB 99dB and 115dB at 10GHz
14GHz and 18GHz respectively Fig 24 shows the E- and H-plane patterns
of the circular waveguide antenna Table 21 summarizes the properties of a
circular waveguide antenna
Fig 22 Reflection coefficient of a circular waveguide open end radiator
-7-
(a)
(b)
Fig 23 2D radiation pattern of the circular waveguide open end radiator
at (a)10GHz (b) 14GHz and (c) 18GHz
-8-
(c)
Fig 23 continued
-9-
(a)
(b)
(c)
Fig 24 E-plane and H-plane patterns of the circular waveguide open end
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-10-
Table 21 Properties of a circular waveguide open end radiator of diameter
2053mm
Frequency(GHz)-10dB Beamwith(deg) Front-to-Back
Ratio(dB)E plane H plane
10 67 73 12
14 58 60 18
18 41 50 21
In a circular waveguide radiatoλr a good pattern symmetry and low back
radiation is obtained at 14GHz where 2aλ = 096
22 Square Waveguide Radiator
A square waveguide is often used as a dual-polarized feed To operate the
cutoff frequency of the dominant mode a square-waveguide wall width a
must be greater than one half of a wavelength The modes with cutoff
frequencies equal to or smaller than the operational frequency can exist inside
the waveguide wall The lower cutoff frequency and cutoff wavelength for
square waveguide is determined by the following equations
TE
(24)
TE
(25)
The next higher-order mode is TE11 mode with the cutoff wavelength
given by
-11-
TE
(26)
Similar to the circular waveguide the recommended operating frequency range
of a square waveguide is given by
TEleleTE
TErarr bandwidth (27)
Fig 25 shows the geometry of a square waveguide with a dimension of a
When a is 157mm the cutoff frequency is 95GHz The recommended
operating frequency of this waveguide is from 109GHz to 155GHz
Fig 26 shows the reflection of this waveguide excited with the dominant
TE10 mode The reflection coefficient is less than -15dB over 10-20GHz
Fig 25 Geometry of a square waveguide open end radiator
Fig 27 and shows the 2D radiation pattern of a square waveguide antenna
excited with the dominant TE10 mode The antenna has a gain of 73dB
85dB and 102dB at 10GHz 14GHz and 18GHz respectively Fig 28
shows the E- and H-plane radiation patterns of a square waveguide radiator
Table 22 summarizes the properties of a square waveguide open end radiator
-12-
Fig 26 Reflection coefficient of a square waveguide open end radiator
(a)
Fig 27 2D radiation patterns of a square waveguide radiator
at (a) 10GHz (b) 14GHz and (c) 18GHz
-13-
(b)
(c)
Fig 27 continued
-14-
(a)
(b)
(c)
Fig 28 E-plane and H-plane patterns of square waveguide open radiator
at (a) 10GHz(b) 14GHz and (c) 18GHz
-15-
Table 22 Properties of a square waveguide open end radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 69 71 11
14 47 60 25
18 58 62 16
The radiation pattern symmetry and back radiation performance of the
square waveguide are inferior to those of a circular waveguide
23 Probe-Fed Circular Waveguide Radiator
In Section 21 the radiation properties of a TE11-mode excited waveguide
is investigated In this section a circular waveguide fed by a coaxial probe
shown in Fig 29 is studied
The coaxial probes diameter is 127mm With the Teflon dielectric the
50-ohm coaxial lines outer conductor has a diameter of 41mm For a
circular waveguide the wave impedance of the TE11 mode is given by
∙ (28)
where λg is the guided wavelength given by
(29)
-16-
(a) (b)
Fig 29 Probe-fed circular waveguide radiator (a) Front view and (b) side
view
The combination of the probe length and the probe position from the
shorted wall enables a good impedance matching The probe distance sp from
the back short is close to a quarter wavelength at the design frequency
The designed feed has the following dimension d = 2053mm lp = 42
mm sp = 534mm wall thickness = 05mm and feed length = 400mm
Fig 210 shows the reflection coefficient of the designed probe-fed
circular waveguide radiator The reflection coefficient is less than -10dB over
138-187GHz Fig 211 and 212 shows the E-plane and H-plane radiation
patterns and 2D radiation patterns of the coaxial-to-circular waveguide
transition The radiation patterns symmetry distorted because of the high order
modes The coaxial-to-circular waveguide transition has 73dB 84dB and
79dB gain at 10GHz 14GHz and 18GHz frequencies respectively Table 23
shows the properties of the coaxial-to-circular waveguide transition
-17-
Fig 210 Reflection coefficient of the probe-fed circular waveguide radiator
(a)
Fig 211 2D radiation pattern of the probe-fed circular waveguide radiator
at (a) 10GHz (b) 14GHz and (c) 18GHz
-18-
(b)
(c)
Fig 211 continued
-19-
(a)
(b)
(c)
Fig 212 E- and H-plane patterns of the probe-fed circular waveguide
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-20-
Table 23 Properties of the probe-fed circular waveguide radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 73 70 1414 83 57 17
18 60 52 30
When a circular waveguide radiator is fed by a coaxial probe its radiation
properties are not good due to the excitation of higher-order modes
Therefore a probe-fed circular waveguide radiator can be used as a feed only
over a narrow frequency range
24 Probe-Fed Square Waveguide Radiator
In this section a probe-fed square waveguide radiator is investigated Fig
213 shows a coaxial probe-fed square waveguide radiator The designed
radiator has the following dimension a = b = 157mm lp = 35 mm sp =
50 mm wall thickness = 05mm and feed length = 40mm
(a) (b)
Fig 213 Probe-fed square waveguide radiator (a) Front view and (b) side
view
-21-
Fig 214 shows the 2D radiation patterns of the radiator at 10GHz
14GHz and 18GHz Fig 215 shows E- and H-plane patterns of the radiator
Fig 216 shows the reflection coefficient of the probe-fed square waveguide
radiator The reflection coefficient is less than -10dB over 13-20GHz Table
24 summarizes the properties of the probe-fed square waveguide radiator
(a)
Fig 214 2D radiation patterns of the probe-fed square waveguide radiator at
(a) 10GHz (b) 14GHz and (c) 18GHz
-22-
(b)
(c)
Fig 214 continued
-23-
(a)
(b)
(c)
Fig 216 E-plane and H-plane patterns of the probe-fed square waveguide
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-24-
Fig 216 Reflection coefficient of the probe-fed square waveguide radiator
Table 24 Properties of the probe-fed square waveguide radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 73 71 12
14 85 63 1418 27 65 28
When a square waveguide radiator is fed by a coaxial probe its radiation
properties are not good due to the excitation of higher-order modes as in the
case of the probe-fed circular waveguide radiator A probe-fed square
waveguide radiator can be used as a feed only over a narrow frequency
range
-25-
III Design of Compact Circular Waveguide Feeds
In this chapter the feed design is presented for a prime-focus reflector
antenna The prime-focus paraboloid reflector is one of the most commonly
used high-gain antenna It has been used in earth-station antennas and radio
telescopes It consists of a paraboloid reflector with a feed system at its focal
point
The feed should radiate a low level of cross-polar power over the
operating frequency These conditions not easy to achieve and most prime
focus feeds are compromises The shape and characteristic of the radiation
pattern of the feed are the most important parameter because these will
directly influence the fields which are directed at a reflector[6] Other
electrical factors which relevant to the choice of a feed are the cross-polar
level the gain efficiency the bandwidth and impedance matching
31 Narrow-Band Circular Waveguide Feed
Fig 31 shows the proposed narrow-band circular waveguide feed and its
design variables The feed consists of a circular waveguide open end excited
by a TE11 dominant mode A quarter wave choke is applied along the
circular aperture of the waveguide to equalize E- and H-plane radiation
patterns and to suppress the back radiation A dielectric ring is used to
control the radiation pattern and change the power distribution over the
aperture The control of the amplitude over the aperture are essential to the
design of symmetric radiation pattern The material used for dielectric loading
-26-
is the monocast(MC) nylon with a dielectric constant of 30 The feed is
designed to operate over 171-197GHz
(a)
(b)
Fig 31 Narrow-band circular waveguide feed (a) CAD model and (b) a
cross sectional view
The impedance matching is achieved by a proper combination of the probe
height lp and its distance sp from the waveguide shorted end Here the
-27-
circular waveguide is terminated with an open end with a wall thickness of
2mm radiating into the free space
Fig 32 shows the effect of the probe length lp and the probe distance sp
on the reflection coefficient The best performance is obtained when lp =
363mm and sp = 616mm The feeds reflection coefficient is less than -10dB
over 170-195GHz
(a)
(b)
Fig 32 Effect of the (a) the probe length lp and (b) the probe
distance sp on the reflection coefficient
-28-
Fig 33 shows the effect of the choke depth The E-plane pattern is more
sensitive to the choke depth than the H-plane pattern The choke depth has a
strong influence on the reflection coefficient when it is 360mm By properly
choosing the choke depth we can equalize the E- and H-plane patterns The
optimum value of the choke depth is 410mm which is 0249λ0 at 1825GHz
The choke slot width tch in the range of 06-12mm has almost no effect
on the H-plane pattern and the reflection coefficient For the E-plane pattern
tch of 12mm has some effect on the E-plane radiation pattern as shown in
Fig 34
Fig 35 shows the feed performance versus the dielectric ring length We
observe in Fig 35 that the dielectric length ld has an optimum value of
1168mm which does no effect on the H-plane pattern and tha the value of
1048mm has some effect on the E-plane pattern and the reflection
coefficient
Fig 36 shows E-plane and H-plane patterns and the reflection coefficient
versus the dielectric thickness With the optimum value of the dielectric
thickness t obtained from the Fig 36 is 155mm The larger values of td has
much stronger effects on the E-plane pattern and the reflection coefficient
The H-plane pattern is not sensitive to the dielectric ring thickness
-29-
(a)
(b)
(c)
Fig 33 Feed performance versus the choke depth (a) E-plane pattern
(b) H-plane pattern and (c) reflection coefficient
-30-
(a)
(b)
(c)
Fig 34 Feed performance versus the choke slot width (a) E-plane pattern
(b) H-plane pattern and (c) reflection coefficient
-31-
(a)
(b)
(c)
Fig 35 Feed performance versus the dielectric ring length (a) E-plane
pattern (b) H-plane pattern and (c) reflection coefficient
-32-
(a)
(b)
(c)
Fig 36 Feed performance versus the dielectric ring thickness (a) E-plane
pattern(b) H-plane pattern and (c) reflection coefficient
-33-
From the above parametric analysis an optimum feed design is obtained
The result is shown in Table 31 Fig 37 shows the 2D gain patterns of
designed feed The antenna has a gain of 903dB 933dB and 956dB at
171GHz 1825GHz and 19GHz respectively
Fig 38 shows E- and H-plane radiation patterns of the designed feed The
feed has E- and H-plane 10-dB beamwidths of 60 and 59 degrees at 17GHz
The feed has a front-to-back ration of 1900dB 2490dB and 2200dB at
171GHz 1825GHz and 19GHz respectively Table 32 summarizes the
performance of the designed narrow-band circular waveguide feed
The designed feed has a greatly improved performance over that of a
simple coax-fed feed described in Section 23
Table 31 Dimensions of the designed narrow-band circular feed
Parameter Designation Value(mm)
a Waveguide inside radius 640
l Feed length 2890
lp Probe length 363
sp Probe position from the back short 616
din Probe diameter 127
dout Diameter of coaxial cables outer conductor 400
t Thickness of choked wall 050
tch Choke slot width 100
lch Choke depth 410
ld Dielectric ring length 1168
td Dielectric ring thickness 155
d1 Waveguide outside diameter 1680
-34-
(a)
(b)
Fig 37 2D gain patterns of the narrow-band circular waveguide feed at
(a) 17GHz (b) 1825GHz and (c) 19GHz
-35-
(c)
Fig 37 continued
-36-
(a)
(b)
(c)
Fig 38 E- and H-plane patterns of the narrow-band circular waveguide feed
at (a) 10GHz (b) 1825GHz and (c) 195GHz
-37-
Frequency(GHz)
Gain(dB)
E-H-plane10-dB beamwidths
(deg)
Front-to-back ratio(dB)
Phase centerlocation
(From feeds aperture plane
toward reflector)
(mm)
1700 903 6059 20 062
1825 933 6060 25 004
1900 956 5759 22 007
Table 32 Performance of the narrow-band circular waveguide feed
The designed narrow-band feed is fabricated and its performance is
measured and compared with the simulation results The designed feed is
fabricated in a numerically-controlled machining center The fabricated antenna
is shown in Fig 39
Fig 39 Photograph of the fabricated feed
-38-
Fig 310 shows a comparison of the measured and simulated reflection
coefficients The measured reflection coefficient is less than -10dB over
171-197GHz The agreement between simulated and measured results are
good
Fig 311 shows the E- and H-plane patterns of the fabricated feed at
187GHz The feed has 90dB gain simulation and measurement results are in
good agreement
The fabricated antennarsquos 10dB beamwidth is 60 degrees in both E and H
planes at 187GHz The front-to-back ratio is 21dB
Fig 310 Reflection coefficient of the fabricated feed
-39-
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Fee
d H
orn
Gain
- d
B
Angle - degree
(a)
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Feed H
orn
Gain
- d
B
Angle - degree
(b)
Fig 311 Gain patterns of the fabricated feed at 187 GHz (a) E-plane and
(b) H-plane
-40-
IV Design of Circular Waveguide Feeds Loaded with a
Dielectric Rod
In this section circular waveguide feeds loaded with a dielectric rod feed
are investigated A comprehensive discussion of the circular waveguide loaded
with a dielectric rod is given by Kumar[7] Inserting a dielectric material
inside the circular waveguide improves the E- and H-plane pattern symmetry
In general dielectric-loaded circular waveguide feeds show good performance
only over a narrow bandwidth
Fig 41 shows the geometry of a circular waveguide loaded with a
dielectric rod The waveguide length is 400mm and the wall thickness is
05mm The dielectric rods diameter is 207mm The dielectric rod is
extended 05 wavelength beyond the waveguide open end The dielectric
constant εr is changed and the feeds performance is observed
Fig 41 Geometry of a circular waveguide loaded with a uniform dielectric
rod
-41-
Fig 42 is the radiation pattern of the feed with εr = 25 and L = 05λ0 at
9GHz E- and H-plane 10-dB beamwidths are 810 and 807 degrees
respectively The front-to-back ratio is 18dB The antenna gain is 71dB
(a)
(b)
Fig 42 Radiation pattern at 9GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 05λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-42-
Fig 43 shows the radiation pattern of the feed with εr = 21 at 10GHz
E- and H-plane 10-dB beamwidths are 70 and 71 degrees respectively The
front-to-back ratio is 19dB The antenna gain is 83dB
(a)
(b)
Fig 43 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 21 and L = 05λ0 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-43-
Fig 44 shows the radiation pattern of the feed with εr = 30 at 8GHz
E- and H-plane 10-dB beamwidths are 83 and 824 degrees respectively The
front-to-back ratio is 17dB The antenna gain is 73dB
(a)
(b)
Fig 44 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 30 and L = 05λ0 at 8GHz (a) 2D radiation pattern
and (b) E- and H-plane patterns
-44-
Fig 45 shows the radiation pattern of the feed with εr = 50 at 18GHz
E- and H-plane 10-dB beamwidths are 56 and 54 degrees respectively The
front-to-back ratio is 27dB The antenna gain is 105dB The feed has a good
pattern symmetry and low back radiation
(a)
(b)
Fig 45 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 50 and L = 05λ0 at 18GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-45-
Fig 46 is the radiation pattern of the feed with εr = 25 and L = 10λ0 at
10GHz E- and H-plane 10-dB beamwidths are 50 and 48 degrees
respectively The front-to-back ratio is 16dB The antenna gain is 105dB
(a)
(b)
Fig 46 Radiation pattern at 10GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 10λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-46-
Fig 47 shows the geometry of a circular waveguide with a tapered
dielectric rod The designed feed has the following dimension L = 1λ0 d =
1λ0 and εr =25 at 10GHz The waveguide length is 40mm and the wall
thickness is 05mm
L
Dielectricd3
Fig 47 Geometry of a circular waveguide loaded with a tapered dielectric
rod
Fig 48 shows the radiatio pattern of the designed feed E- and H-plane
10-dB beamwidths are 575 and 564 degrees respectively The front-to-back
ratio is 377dB The antenna gain is 94dB The designed feed has an
excellent beamwidth symmetry and a very low back radiation
-47-
(a)
(b)
Fig 48 Radiation pattern of a circular waveguide loaded with a tapered
dielectric rod with L = 1λ0 d = 1λ0 and εr =25 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-48-
Fig 49 shows the geometry of a spherical ended dielectric rod feed
diameter of 06λ0 at 10GHz with a dielectric constant of 25 and L= 03λ0
Fig 410 shows the radiation patterns of the designed feed E- and H-plane
10-dB beamwidths are both 63 degrees The front-to-back ratio is 24dB The
antenna gain is 864dB
Fig 49 Geometry of a circular waveguide loaded with a spherical ended
dielectric rod
-49-
(a)
(b)
Fig 410 Radiation pattern of a circular waveguide loaded wht a spherical
ended dielectric rod with d = 06λ0 L = 03λ0 and εr =25 at 10GHz (a) 3D
radiation pattern and (b) E- and H-plane patterns
-50-
V Design of a Broadband Circular Waveguide Feed
In this chapter the design of a broadband circular waveguide feed is
presented At microwave frequencies the feed is often a circular waveguide
with chokes and corrugations around the aperture Chokes and corrugations
equalize E- and H-plane patterns and reduce the back radiation
The proposed feed is designed to operate over 10-18GHz The design starts
with the optimization of the coaxial-to-rectangular waveguide adapter
employed for good mode purity over a broad frequency range Next a
rectangular-to-circular waveguide transition is optimized Finally chokes and
corrugations are designed for improved pattern symmetry and low back
radiation
The proposed feed structure is shown in Fig 51 The feed consist of the
following parts a coaxial-to-rectangular waveguide adapter a rectangular-to-
circular waveguide transition a circular waveguide section four quarter-wave
chokes around the feeds aperture and four corrugations on the feeds outer
surface
The computer simulation shows the above arrangement offers good radiation
patterns over a broad frequency range The broadband operation is obtained
by exciting the TE11 mode in the circular waveguide using the TE10 mode of
the rectangular waveguide which is in turn excited by a coaxial probe
-51-
Chokes
Coaxial-to-waveguide transition
Circular wavguide
Corrugations
Mode transition
(a)
(b)
Fig 51 Structure of the proposed broadband circular waveguide feed
(a) CAD model and (b) cross-sectional view
For the coaxial-to-rectangular waveguide adapter an SMA connector with
the probe diameter of 127 mm is employed The coaxial probe inserted into
the waveguide energizes the feed and excites the dominant TE10 mode in
-52-
the rectangular waveguide The impedance matching is achieved by adjusting
the probe distance sp from the back short and the probe length lp
(a)
(b)
Fig 52 Reflection coefficient of the coaxial-to-rectangular adapter versus
(a) probe length lp and (b) the probe position sp
Fig 52 shows the reflection coefficient versus the various values of probe
lengths lp and probe positions sp The probe length lp is adjusted to obtain
antenna impedance matching and the probe distance sp is adjusted to obtain a
-53-
desired resonant frequency
Next a transition between rectangular and circular waveguide is designed
The transition section converts the TE10 mode in the rectangular waveguide to
TE11 mode in the circular waveguide and vice versa The transition is built
in a form of a taper for easy fabrication[22]
(a)
(b)
Fig 53 Structure of the rectangular-to-circular waveguide transition
(a) 3D view and (b) cross sectional view
The dimensions of the final optimized transition are as follows The length
of the rectangular waveguide section is 143mm The rectangular waveguides
width a and height b are 207mm and 857mm respectively The length of
the circular waveguide section is 143mm The inside diameter of the circular
-54-
waveguide is 207mm(097 wavelength at 14GHz) The length of transition
region ltr is 4465mm(approximately equal to 2λ0 at 14GHz) Fig 54 shows
the field distribution inside the mode converter
(a)
(b)
Fig 54 Field distribution inside the mode converter at
(a) 10GHz (b) 14GHz and (c) 18GHz
-55-
(c)
Fig 54 continued
Finally multiple chokes are investigated Figs 55 56 and 57 show the
feed performance without chokes The reflection coefficient is less than -10dB
over 10-19GHz The antenna has a gain of 921dB to 1189dB over
10-19GHz
Fig 55 Reflection coefficient of the broadband circular waveguide feed
without chokes and corrugations
-56-
(a)
(b)
(c)
Fig 56 E- and H-plane patterns of the broadband circular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-57-
(d)
(e)
Fig 56 continued
-58-
(a)
(b)
Fig 57 2D radiation patterns of the broadband cicular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-59-
(c)
(d)
Fig 57 continued
-60-
(e)
Fig 57 continued
To achieve equal beamwidths in E and H planes over a wide frequency
range chokes and corrugations are employed Table51 summarizes the
performance of a feed without chokes and corrugations
Table 51 Performance of the broadband circular waveguide feed without
chokes and corrugations
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
1000 940 6061 15
1200 972 6159 17
1400 920 5957 21
1600 1070 4751 29
1800 1188 5352 21
-61-
Four quarter-wavelength chokes are introduced in the feed design which
has a slot depth of 75mm and slot width of 09mm The choke slot spacing
is 18mm The choke design is investigated by applying the choke one by
one and the effect on the E- and H-plane patterns are observed as illustrated
in Figs 58 and 59 The use of chokes makes the E-plane pattern narrower
The H-plane pattern is not affected Chokes increase the gain slightly and
reduce back radiation
(a)
(b)
Fig 58 Effect of chokes on the E-plane pattern of the broadband circular
waveguide feed at (a) 10GHz(b) 12GHz (c) 14GHz (d) 16GHz and (e)
18GHz
-62-
(c)
(d)
(e)
Fig 58 continued
-63-
(a)
(b)
(c)
Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-64-
(d)
(e)
Fig 59 continued
-65-
Fig 510 shows the feed performance versus the choke depth When the
choke depth is varied from 535mm to 95mm the E- and H-plane patterns
are strongly affected The optimum value of choke depth is 75mm(035λ0 at
14GHz) which gives equal E- and H-plane radiation patterns and leads to
low back radiation
Fig 511 shows the feed performance versus the choke slot width tch The
choke slot width is varied from 09mm to 21mm Radiation patterns and
reflection coefficients are not sensitive to the choke slot width The final
choke slot width is selected to be 09mm considering the feed diameter
minimization and the manufacturability The overall diameter of the proposed
feed is 369mm which is increased from the 207mm of the waveguide
inside diameter due to the use of four chokes
-66-
(a)
(b)
(c)
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection coefficient
-67-
(a)
(b)
(c)
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and (c)
reflection coefficient
-68-
Next we investigated corrugations placed on the outer wall of the feed
Four corrugations applied to the outer surface of the circular waveguide The
corrugation depth is 465mm(0215λ0 at 14GHz) The primary purpose of
using corrugations is to further reduce the back radiation Increasing the
number of corrugations beyond four has little effect in reducing the back
radiation
Figs 512 and 513 show the effect of corrugations on the E- and H-plane
patterns Fig 514 shows the parametric study of the corrugation depth lcor
The corrugation depth is varied from 40mm and 645mm The optimum
value of the corrugation depth is found to be 465mm
-69-
(a)
(b)
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern at (a) 12GHz and (b) 14GHz
-70-
(a)
(b)
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern at (a) 12GHz and (b) 14GHz
-71-
(a)
(b)
(c)
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection coefficient
-72-
The phase center location is important in placing the feed in a reflector
antenna[8] The phase center variation with frequency should be small Fig
515 shows the effect of chokes and corrugations on the phase center The
curve with circle corresponds to the case without chokes and corrugations
The phase center varies from -326mm and -190mm away from the feeds
aperture plane It means the phase center is located inside the waveguide
The curve with triangles corresponds to the case with chokes The curve with
squares to the case with chokes and corrugations The phase center varies
from 0mm to -302mm
From Fig 515 we can observed that phase center variation reduced by the
corrugation and three cases phase center calculated in φ=450 plane
parameter sweep values are given in Table 52
10 12 14 16 181
0
-1
-2
-3
-4
-5
-6
Pha
se c
ente
r (m
m)
Frequency (GHz)
choke+corrugatuion without choke corrugation with choke
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
-73-
Frequency
(GHz)
Phase center from the aperture plane
(mm)
Without
chokes and
corrugations
With
chokes
With chokes
and
corrugations
1000 -326 062 000
1100 -187 030 -002
1200 -563 -208 -065
1300 -296 -154 -202
1400 -319 -314 -302
1500 -201 -203 -241
1600 -242 -233 -207
1700 -208 -208 -186
1800 -190 -157 -132
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
Based on the foregoing parametric studies optimum dimensions of the
broadband circular waveguide feed are obtained as shown in Table 53
-74-
Table 53 Optimum dimensions of the broadband circular waveguide feed
Parameter Designation Value (mm)
2a Waveguide inside diameter 2070
d Waveguide outside diameter 3690
lcrLength of the circular waveguide section 1430
m Distance between the aperture plane and the first corrugation 950
xDistance from the last corrugation to the end of the cylindrical outer surface
550
ltrLength of the rectangular-to-circularwaveguide transition 4465
lrcLength of the rectangular waveguide section 1430
tch Choke slot width 090
lch Choke depth 750
t Choke metal width 090
lcor Corrugation depth 465
tcor Corrugation metal width 100
s Corrugation slot width 10
lp Probe length 530
sp Probe position from the back short 530
din Probe diameter 127
b Inside height of the rectangular waveguide 857
tw Waveguide wall thickness 500
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-7-
(a)
(b)
Fig 23 2D radiation pattern of the circular waveguide open end radiator
at (a)10GHz (b) 14GHz and (c) 18GHz
-8-
(c)
Fig 23 continued
-9-
(a)
(b)
(c)
Fig 24 E-plane and H-plane patterns of the circular waveguide open end
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-10-
Table 21 Properties of a circular waveguide open end radiator of diameter
2053mm
Frequency(GHz)-10dB Beamwith(deg) Front-to-Back
Ratio(dB)E plane H plane
10 67 73 12
14 58 60 18
18 41 50 21
In a circular waveguide radiatoλr a good pattern symmetry and low back
radiation is obtained at 14GHz where 2aλ = 096
22 Square Waveguide Radiator
A square waveguide is often used as a dual-polarized feed To operate the
cutoff frequency of the dominant mode a square-waveguide wall width a
must be greater than one half of a wavelength The modes with cutoff
frequencies equal to or smaller than the operational frequency can exist inside
the waveguide wall The lower cutoff frequency and cutoff wavelength for
square waveguide is determined by the following equations
TE
(24)
TE
(25)
The next higher-order mode is TE11 mode with the cutoff wavelength
given by
-11-
TE
(26)
Similar to the circular waveguide the recommended operating frequency range
of a square waveguide is given by
TEleleTE
TErarr bandwidth (27)
Fig 25 shows the geometry of a square waveguide with a dimension of a
When a is 157mm the cutoff frequency is 95GHz The recommended
operating frequency of this waveguide is from 109GHz to 155GHz
Fig 26 shows the reflection of this waveguide excited with the dominant
TE10 mode The reflection coefficient is less than -15dB over 10-20GHz
Fig 25 Geometry of a square waveguide open end radiator
Fig 27 and shows the 2D radiation pattern of a square waveguide antenna
excited with the dominant TE10 mode The antenna has a gain of 73dB
85dB and 102dB at 10GHz 14GHz and 18GHz respectively Fig 28
shows the E- and H-plane radiation patterns of a square waveguide radiator
Table 22 summarizes the properties of a square waveguide open end radiator
-12-
Fig 26 Reflection coefficient of a square waveguide open end radiator
(a)
Fig 27 2D radiation patterns of a square waveguide radiator
at (a) 10GHz (b) 14GHz and (c) 18GHz
-13-
(b)
(c)
Fig 27 continued
-14-
(a)
(b)
(c)
Fig 28 E-plane and H-plane patterns of square waveguide open radiator
at (a) 10GHz(b) 14GHz and (c) 18GHz
-15-
Table 22 Properties of a square waveguide open end radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 69 71 11
14 47 60 25
18 58 62 16
The radiation pattern symmetry and back radiation performance of the
square waveguide are inferior to those of a circular waveguide
23 Probe-Fed Circular Waveguide Radiator
In Section 21 the radiation properties of a TE11-mode excited waveguide
is investigated In this section a circular waveguide fed by a coaxial probe
shown in Fig 29 is studied
The coaxial probes diameter is 127mm With the Teflon dielectric the
50-ohm coaxial lines outer conductor has a diameter of 41mm For a
circular waveguide the wave impedance of the TE11 mode is given by
∙ (28)
where λg is the guided wavelength given by
(29)
-16-
(a) (b)
Fig 29 Probe-fed circular waveguide radiator (a) Front view and (b) side
view
The combination of the probe length and the probe position from the
shorted wall enables a good impedance matching The probe distance sp from
the back short is close to a quarter wavelength at the design frequency
The designed feed has the following dimension d = 2053mm lp = 42
mm sp = 534mm wall thickness = 05mm and feed length = 400mm
Fig 210 shows the reflection coefficient of the designed probe-fed
circular waveguide radiator The reflection coefficient is less than -10dB over
138-187GHz Fig 211 and 212 shows the E-plane and H-plane radiation
patterns and 2D radiation patterns of the coaxial-to-circular waveguide
transition The radiation patterns symmetry distorted because of the high order
modes The coaxial-to-circular waveguide transition has 73dB 84dB and
79dB gain at 10GHz 14GHz and 18GHz frequencies respectively Table 23
shows the properties of the coaxial-to-circular waveguide transition
-17-
Fig 210 Reflection coefficient of the probe-fed circular waveguide radiator
(a)
Fig 211 2D radiation pattern of the probe-fed circular waveguide radiator
at (a) 10GHz (b) 14GHz and (c) 18GHz
-18-
(b)
(c)
Fig 211 continued
-19-
(a)
(b)
(c)
Fig 212 E- and H-plane patterns of the probe-fed circular waveguide
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-20-
Table 23 Properties of the probe-fed circular waveguide radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 73 70 1414 83 57 17
18 60 52 30
When a circular waveguide radiator is fed by a coaxial probe its radiation
properties are not good due to the excitation of higher-order modes
Therefore a probe-fed circular waveguide radiator can be used as a feed only
over a narrow frequency range
24 Probe-Fed Square Waveguide Radiator
In this section a probe-fed square waveguide radiator is investigated Fig
213 shows a coaxial probe-fed square waveguide radiator The designed
radiator has the following dimension a = b = 157mm lp = 35 mm sp =
50 mm wall thickness = 05mm and feed length = 40mm
(a) (b)
Fig 213 Probe-fed square waveguide radiator (a) Front view and (b) side
view
-21-
Fig 214 shows the 2D radiation patterns of the radiator at 10GHz
14GHz and 18GHz Fig 215 shows E- and H-plane patterns of the radiator
Fig 216 shows the reflection coefficient of the probe-fed square waveguide
radiator The reflection coefficient is less than -10dB over 13-20GHz Table
24 summarizes the properties of the probe-fed square waveguide radiator
(a)
Fig 214 2D radiation patterns of the probe-fed square waveguide radiator at
(a) 10GHz (b) 14GHz and (c) 18GHz
-22-
(b)
(c)
Fig 214 continued
-23-
(a)
(b)
(c)
Fig 216 E-plane and H-plane patterns of the probe-fed square waveguide
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-24-
Fig 216 Reflection coefficient of the probe-fed square waveguide radiator
Table 24 Properties of the probe-fed square waveguide radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 73 71 12
14 85 63 1418 27 65 28
When a square waveguide radiator is fed by a coaxial probe its radiation
properties are not good due to the excitation of higher-order modes as in the
case of the probe-fed circular waveguide radiator A probe-fed square
waveguide radiator can be used as a feed only over a narrow frequency
range
-25-
III Design of Compact Circular Waveguide Feeds
In this chapter the feed design is presented for a prime-focus reflector
antenna The prime-focus paraboloid reflector is one of the most commonly
used high-gain antenna It has been used in earth-station antennas and radio
telescopes It consists of a paraboloid reflector with a feed system at its focal
point
The feed should radiate a low level of cross-polar power over the
operating frequency These conditions not easy to achieve and most prime
focus feeds are compromises The shape and characteristic of the radiation
pattern of the feed are the most important parameter because these will
directly influence the fields which are directed at a reflector[6] Other
electrical factors which relevant to the choice of a feed are the cross-polar
level the gain efficiency the bandwidth and impedance matching
31 Narrow-Band Circular Waveguide Feed
Fig 31 shows the proposed narrow-band circular waveguide feed and its
design variables The feed consists of a circular waveguide open end excited
by a TE11 dominant mode A quarter wave choke is applied along the
circular aperture of the waveguide to equalize E- and H-plane radiation
patterns and to suppress the back radiation A dielectric ring is used to
control the radiation pattern and change the power distribution over the
aperture The control of the amplitude over the aperture are essential to the
design of symmetric radiation pattern The material used for dielectric loading
-26-
is the monocast(MC) nylon with a dielectric constant of 30 The feed is
designed to operate over 171-197GHz
(a)
(b)
Fig 31 Narrow-band circular waveguide feed (a) CAD model and (b) a
cross sectional view
The impedance matching is achieved by a proper combination of the probe
height lp and its distance sp from the waveguide shorted end Here the
-27-
circular waveguide is terminated with an open end with a wall thickness of
2mm radiating into the free space
Fig 32 shows the effect of the probe length lp and the probe distance sp
on the reflection coefficient The best performance is obtained when lp =
363mm and sp = 616mm The feeds reflection coefficient is less than -10dB
over 170-195GHz
(a)
(b)
Fig 32 Effect of the (a) the probe length lp and (b) the probe
distance sp on the reflection coefficient
-28-
Fig 33 shows the effect of the choke depth The E-plane pattern is more
sensitive to the choke depth than the H-plane pattern The choke depth has a
strong influence on the reflection coefficient when it is 360mm By properly
choosing the choke depth we can equalize the E- and H-plane patterns The
optimum value of the choke depth is 410mm which is 0249λ0 at 1825GHz
The choke slot width tch in the range of 06-12mm has almost no effect
on the H-plane pattern and the reflection coefficient For the E-plane pattern
tch of 12mm has some effect on the E-plane radiation pattern as shown in
Fig 34
Fig 35 shows the feed performance versus the dielectric ring length We
observe in Fig 35 that the dielectric length ld has an optimum value of
1168mm which does no effect on the H-plane pattern and tha the value of
1048mm has some effect on the E-plane pattern and the reflection
coefficient
Fig 36 shows E-plane and H-plane patterns and the reflection coefficient
versus the dielectric thickness With the optimum value of the dielectric
thickness t obtained from the Fig 36 is 155mm The larger values of td has
much stronger effects on the E-plane pattern and the reflection coefficient
The H-plane pattern is not sensitive to the dielectric ring thickness
-29-
(a)
(b)
(c)
Fig 33 Feed performance versus the choke depth (a) E-plane pattern
(b) H-plane pattern and (c) reflection coefficient
-30-
(a)
(b)
(c)
Fig 34 Feed performance versus the choke slot width (a) E-plane pattern
(b) H-plane pattern and (c) reflection coefficient
-31-
(a)
(b)
(c)
Fig 35 Feed performance versus the dielectric ring length (a) E-plane
pattern (b) H-plane pattern and (c) reflection coefficient
-32-
(a)
(b)
(c)
Fig 36 Feed performance versus the dielectric ring thickness (a) E-plane
pattern(b) H-plane pattern and (c) reflection coefficient
-33-
From the above parametric analysis an optimum feed design is obtained
The result is shown in Table 31 Fig 37 shows the 2D gain patterns of
designed feed The antenna has a gain of 903dB 933dB and 956dB at
171GHz 1825GHz and 19GHz respectively
Fig 38 shows E- and H-plane radiation patterns of the designed feed The
feed has E- and H-plane 10-dB beamwidths of 60 and 59 degrees at 17GHz
The feed has a front-to-back ration of 1900dB 2490dB and 2200dB at
171GHz 1825GHz and 19GHz respectively Table 32 summarizes the
performance of the designed narrow-band circular waveguide feed
The designed feed has a greatly improved performance over that of a
simple coax-fed feed described in Section 23
Table 31 Dimensions of the designed narrow-band circular feed
Parameter Designation Value(mm)
a Waveguide inside radius 640
l Feed length 2890
lp Probe length 363
sp Probe position from the back short 616
din Probe diameter 127
dout Diameter of coaxial cables outer conductor 400
t Thickness of choked wall 050
tch Choke slot width 100
lch Choke depth 410
ld Dielectric ring length 1168
td Dielectric ring thickness 155
d1 Waveguide outside diameter 1680
-34-
(a)
(b)
Fig 37 2D gain patterns of the narrow-band circular waveguide feed at
(a) 17GHz (b) 1825GHz and (c) 19GHz
-35-
(c)
Fig 37 continued
-36-
(a)
(b)
(c)
Fig 38 E- and H-plane patterns of the narrow-band circular waveguide feed
at (a) 10GHz (b) 1825GHz and (c) 195GHz
-37-
Frequency(GHz)
Gain(dB)
E-H-plane10-dB beamwidths
(deg)
Front-to-back ratio(dB)
Phase centerlocation
(From feeds aperture plane
toward reflector)
(mm)
1700 903 6059 20 062
1825 933 6060 25 004
1900 956 5759 22 007
Table 32 Performance of the narrow-band circular waveguide feed
The designed narrow-band feed is fabricated and its performance is
measured and compared with the simulation results The designed feed is
fabricated in a numerically-controlled machining center The fabricated antenna
is shown in Fig 39
Fig 39 Photograph of the fabricated feed
-38-
Fig 310 shows a comparison of the measured and simulated reflection
coefficients The measured reflection coefficient is less than -10dB over
171-197GHz The agreement between simulated and measured results are
good
Fig 311 shows the E- and H-plane patterns of the fabricated feed at
187GHz The feed has 90dB gain simulation and measurement results are in
good agreement
The fabricated antennarsquos 10dB beamwidth is 60 degrees in both E and H
planes at 187GHz The front-to-back ratio is 21dB
Fig 310 Reflection coefficient of the fabricated feed
-39-
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Fee
d H
orn
Gain
- d
B
Angle - degree
(a)
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Feed H
orn
Gain
- d
B
Angle - degree
(b)
Fig 311 Gain patterns of the fabricated feed at 187 GHz (a) E-plane and
(b) H-plane
-40-
IV Design of Circular Waveguide Feeds Loaded with a
Dielectric Rod
In this section circular waveguide feeds loaded with a dielectric rod feed
are investigated A comprehensive discussion of the circular waveguide loaded
with a dielectric rod is given by Kumar[7] Inserting a dielectric material
inside the circular waveguide improves the E- and H-plane pattern symmetry
In general dielectric-loaded circular waveguide feeds show good performance
only over a narrow bandwidth
Fig 41 shows the geometry of a circular waveguide loaded with a
dielectric rod The waveguide length is 400mm and the wall thickness is
05mm The dielectric rods diameter is 207mm The dielectric rod is
extended 05 wavelength beyond the waveguide open end The dielectric
constant εr is changed and the feeds performance is observed
Fig 41 Geometry of a circular waveguide loaded with a uniform dielectric
rod
-41-
Fig 42 is the radiation pattern of the feed with εr = 25 and L = 05λ0 at
9GHz E- and H-plane 10-dB beamwidths are 810 and 807 degrees
respectively The front-to-back ratio is 18dB The antenna gain is 71dB
(a)
(b)
Fig 42 Radiation pattern at 9GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 05λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-42-
Fig 43 shows the radiation pattern of the feed with εr = 21 at 10GHz
E- and H-plane 10-dB beamwidths are 70 and 71 degrees respectively The
front-to-back ratio is 19dB The antenna gain is 83dB
(a)
(b)
Fig 43 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 21 and L = 05λ0 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-43-
Fig 44 shows the radiation pattern of the feed with εr = 30 at 8GHz
E- and H-plane 10-dB beamwidths are 83 and 824 degrees respectively The
front-to-back ratio is 17dB The antenna gain is 73dB
(a)
(b)
Fig 44 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 30 and L = 05λ0 at 8GHz (a) 2D radiation pattern
and (b) E- and H-plane patterns
-44-
Fig 45 shows the radiation pattern of the feed with εr = 50 at 18GHz
E- and H-plane 10-dB beamwidths are 56 and 54 degrees respectively The
front-to-back ratio is 27dB The antenna gain is 105dB The feed has a good
pattern symmetry and low back radiation
(a)
(b)
Fig 45 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 50 and L = 05λ0 at 18GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-45-
Fig 46 is the radiation pattern of the feed with εr = 25 and L = 10λ0 at
10GHz E- and H-plane 10-dB beamwidths are 50 and 48 degrees
respectively The front-to-back ratio is 16dB The antenna gain is 105dB
(a)
(b)
Fig 46 Radiation pattern at 10GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 10λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-46-
Fig 47 shows the geometry of a circular waveguide with a tapered
dielectric rod The designed feed has the following dimension L = 1λ0 d =
1λ0 and εr =25 at 10GHz The waveguide length is 40mm and the wall
thickness is 05mm
L
Dielectricd3
Fig 47 Geometry of a circular waveguide loaded with a tapered dielectric
rod
Fig 48 shows the radiatio pattern of the designed feed E- and H-plane
10-dB beamwidths are 575 and 564 degrees respectively The front-to-back
ratio is 377dB The antenna gain is 94dB The designed feed has an
excellent beamwidth symmetry and a very low back radiation
-47-
(a)
(b)
Fig 48 Radiation pattern of a circular waveguide loaded with a tapered
dielectric rod with L = 1λ0 d = 1λ0 and εr =25 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-48-
Fig 49 shows the geometry of a spherical ended dielectric rod feed
diameter of 06λ0 at 10GHz with a dielectric constant of 25 and L= 03λ0
Fig 410 shows the radiation patterns of the designed feed E- and H-plane
10-dB beamwidths are both 63 degrees The front-to-back ratio is 24dB The
antenna gain is 864dB
Fig 49 Geometry of a circular waveguide loaded with a spherical ended
dielectric rod
-49-
(a)
(b)
Fig 410 Radiation pattern of a circular waveguide loaded wht a spherical
ended dielectric rod with d = 06λ0 L = 03λ0 and εr =25 at 10GHz (a) 3D
radiation pattern and (b) E- and H-plane patterns
-50-
V Design of a Broadband Circular Waveguide Feed
In this chapter the design of a broadband circular waveguide feed is
presented At microwave frequencies the feed is often a circular waveguide
with chokes and corrugations around the aperture Chokes and corrugations
equalize E- and H-plane patterns and reduce the back radiation
The proposed feed is designed to operate over 10-18GHz The design starts
with the optimization of the coaxial-to-rectangular waveguide adapter
employed for good mode purity over a broad frequency range Next a
rectangular-to-circular waveguide transition is optimized Finally chokes and
corrugations are designed for improved pattern symmetry and low back
radiation
The proposed feed structure is shown in Fig 51 The feed consist of the
following parts a coaxial-to-rectangular waveguide adapter a rectangular-to-
circular waveguide transition a circular waveguide section four quarter-wave
chokes around the feeds aperture and four corrugations on the feeds outer
surface
The computer simulation shows the above arrangement offers good radiation
patterns over a broad frequency range The broadband operation is obtained
by exciting the TE11 mode in the circular waveguide using the TE10 mode of
the rectangular waveguide which is in turn excited by a coaxial probe
-51-
Chokes
Coaxial-to-waveguide transition
Circular wavguide
Corrugations
Mode transition
(a)
(b)
Fig 51 Structure of the proposed broadband circular waveguide feed
(a) CAD model and (b) cross-sectional view
For the coaxial-to-rectangular waveguide adapter an SMA connector with
the probe diameter of 127 mm is employed The coaxial probe inserted into
the waveguide energizes the feed and excites the dominant TE10 mode in
-52-
the rectangular waveguide The impedance matching is achieved by adjusting
the probe distance sp from the back short and the probe length lp
(a)
(b)
Fig 52 Reflection coefficient of the coaxial-to-rectangular adapter versus
(a) probe length lp and (b) the probe position sp
Fig 52 shows the reflection coefficient versus the various values of probe
lengths lp and probe positions sp The probe length lp is adjusted to obtain
antenna impedance matching and the probe distance sp is adjusted to obtain a
-53-
desired resonant frequency
Next a transition between rectangular and circular waveguide is designed
The transition section converts the TE10 mode in the rectangular waveguide to
TE11 mode in the circular waveguide and vice versa The transition is built
in a form of a taper for easy fabrication[22]
(a)
(b)
Fig 53 Structure of the rectangular-to-circular waveguide transition
(a) 3D view and (b) cross sectional view
The dimensions of the final optimized transition are as follows The length
of the rectangular waveguide section is 143mm The rectangular waveguides
width a and height b are 207mm and 857mm respectively The length of
the circular waveguide section is 143mm The inside diameter of the circular
-54-
waveguide is 207mm(097 wavelength at 14GHz) The length of transition
region ltr is 4465mm(approximately equal to 2λ0 at 14GHz) Fig 54 shows
the field distribution inside the mode converter
(a)
(b)
Fig 54 Field distribution inside the mode converter at
(a) 10GHz (b) 14GHz and (c) 18GHz
-55-
(c)
Fig 54 continued
Finally multiple chokes are investigated Figs 55 56 and 57 show the
feed performance without chokes The reflection coefficient is less than -10dB
over 10-19GHz The antenna has a gain of 921dB to 1189dB over
10-19GHz
Fig 55 Reflection coefficient of the broadband circular waveguide feed
without chokes and corrugations
-56-
(a)
(b)
(c)
Fig 56 E- and H-plane patterns of the broadband circular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-57-
(d)
(e)
Fig 56 continued
-58-
(a)
(b)
Fig 57 2D radiation patterns of the broadband cicular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-59-
(c)
(d)
Fig 57 continued
-60-
(e)
Fig 57 continued
To achieve equal beamwidths in E and H planes over a wide frequency
range chokes and corrugations are employed Table51 summarizes the
performance of a feed without chokes and corrugations
Table 51 Performance of the broadband circular waveguide feed without
chokes and corrugations
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
1000 940 6061 15
1200 972 6159 17
1400 920 5957 21
1600 1070 4751 29
1800 1188 5352 21
-61-
Four quarter-wavelength chokes are introduced in the feed design which
has a slot depth of 75mm and slot width of 09mm The choke slot spacing
is 18mm The choke design is investigated by applying the choke one by
one and the effect on the E- and H-plane patterns are observed as illustrated
in Figs 58 and 59 The use of chokes makes the E-plane pattern narrower
The H-plane pattern is not affected Chokes increase the gain slightly and
reduce back radiation
(a)
(b)
Fig 58 Effect of chokes on the E-plane pattern of the broadband circular
waveguide feed at (a) 10GHz(b) 12GHz (c) 14GHz (d) 16GHz and (e)
18GHz
-62-
(c)
(d)
(e)
Fig 58 continued
-63-
(a)
(b)
(c)
Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-64-
(d)
(e)
Fig 59 continued
-65-
Fig 510 shows the feed performance versus the choke depth When the
choke depth is varied from 535mm to 95mm the E- and H-plane patterns
are strongly affected The optimum value of choke depth is 75mm(035λ0 at
14GHz) which gives equal E- and H-plane radiation patterns and leads to
low back radiation
Fig 511 shows the feed performance versus the choke slot width tch The
choke slot width is varied from 09mm to 21mm Radiation patterns and
reflection coefficients are not sensitive to the choke slot width The final
choke slot width is selected to be 09mm considering the feed diameter
minimization and the manufacturability The overall diameter of the proposed
feed is 369mm which is increased from the 207mm of the waveguide
inside diameter due to the use of four chokes
-66-
(a)
(b)
(c)
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection coefficient
-67-
(a)
(b)
(c)
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and (c)
reflection coefficient
-68-
Next we investigated corrugations placed on the outer wall of the feed
Four corrugations applied to the outer surface of the circular waveguide The
corrugation depth is 465mm(0215λ0 at 14GHz) The primary purpose of
using corrugations is to further reduce the back radiation Increasing the
number of corrugations beyond four has little effect in reducing the back
radiation
Figs 512 and 513 show the effect of corrugations on the E- and H-plane
patterns Fig 514 shows the parametric study of the corrugation depth lcor
The corrugation depth is varied from 40mm and 645mm The optimum
value of the corrugation depth is found to be 465mm
-69-
(a)
(b)
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern at (a) 12GHz and (b) 14GHz
-70-
(a)
(b)
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern at (a) 12GHz and (b) 14GHz
-71-
(a)
(b)
(c)
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection coefficient
-72-
The phase center location is important in placing the feed in a reflector
antenna[8] The phase center variation with frequency should be small Fig
515 shows the effect of chokes and corrugations on the phase center The
curve with circle corresponds to the case without chokes and corrugations
The phase center varies from -326mm and -190mm away from the feeds
aperture plane It means the phase center is located inside the waveguide
The curve with triangles corresponds to the case with chokes The curve with
squares to the case with chokes and corrugations The phase center varies
from 0mm to -302mm
From Fig 515 we can observed that phase center variation reduced by the
corrugation and three cases phase center calculated in φ=450 plane
parameter sweep values are given in Table 52
10 12 14 16 181
0
-1
-2
-3
-4
-5
-6
Pha
se c
ente
r (m
m)
Frequency (GHz)
choke+corrugatuion without choke corrugation with choke
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
-73-
Frequency
(GHz)
Phase center from the aperture plane
(mm)
Without
chokes and
corrugations
With
chokes
With chokes
and
corrugations
1000 -326 062 000
1100 -187 030 -002
1200 -563 -208 -065
1300 -296 -154 -202
1400 -319 -314 -302
1500 -201 -203 -241
1600 -242 -233 -207
1700 -208 -208 -186
1800 -190 -157 -132
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
Based on the foregoing parametric studies optimum dimensions of the
broadband circular waveguide feed are obtained as shown in Table 53
-74-
Table 53 Optimum dimensions of the broadband circular waveguide feed
Parameter Designation Value (mm)
2a Waveguide inside diameter 2070
d Waveguide outside diameter 3690
lcrLength of the circular waveguide section 1430
m Distance between the aperture plane and the first corrugation 950
xDistance from the last corrugation to the end of the cylindrical outer surface
550
ltrLength of the rectangular-to-circularwaveguide transition 4465
lrcLength of the rectangular waveguide section 1430
tch Choke slot width 090
lch Choke depth 750
t Choke metal width 090
lcor Corrugation depth 465
tcor Corrugation metal width 100
s Corrugation slot width 10
lp Probe length 530
sp Probe position from the back short 530
din Probe diameter 127
b Inside height of the rectangular waveguide 857
tw Waveguide wall thickness 500
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-8-
(c)
Fig 23 continued
-9-
(a)
(b)
(c)
Fig 24 E-plane and H-plane patterns of the circular waveguide open end
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-10-
Table 21 Properties of a circular waveguide open end radiator of diameter
2053mm
Frequency(GHz)-10dB Beamwith(deg) Front-to-Back
Ratio(dB)E plane H plane
10 67 73 12
14 58 60 18
18 41 50 21
In a circular waveguide radiatoλr a good pattern symmetry and low back
radiation is obtained at 14GHz where 2aλ = 096
22 Square Waveguide Radiator
A square waveguide is often used as a dual-polarized feed To operate the
cutoff frequency of the dominant mode a square-waveguide wall width a
must be greater than one half of a wavelength The modes with cutoff
frequencies equal to or smaller than the operational frequency can exist inside
the waveguide wall The lower cutoff frequency and cutoff wavelength for
square waveguide is determined by the following equations
TE
(24)
TE
(25)
The next higher-order mode is TE11 mode with the cutoff wavelength
given by
-11-
TE
(26)
Similar to the circular waveguide the recommended operating frequency range
of a square waveguide is given by
TEleleTE
TErarr bandwidth (27)
Fig 25 shows the geometry of a square waveguide with a dimension of a
When a is 157mm the cutoff frequency is 95GHz The recommended
operating frequency of this waveguide is from 109GHz to 155GHz
Fig 26 shows the reflection of this waveguide excited with the dominant
TE10 mode The reflection coefficient is less than -15dB over 10-20GHz
Fig 25 Geometry of a square waveguide open end radiator
Fig 27 and shows the 2D radiation pattern of a square waveguide antenna
excited with the dominant TE10 mode The antenna has a gain of 73dB
85dB and 102dB at 10GHz 14GHz and 18GHz respectively Fig 28
shows the E- and H-plane radiation patterns of a square waveguide radiator
Table 22 summarizes the properties of a square waveguide open end radiator
-12-
Fig 26 Reflection coefficient of a square waveguide open end radiator
(a)
Fig 27 2D radiation patterns of a square waveguide radiator
at (a) 10GHz (b) 14GHz and (c) 18GHz
-13-
(b)
(c)
Fig 27 continued
-14-
(a)
(b)
(c)
Fig 28 E-plane and H-plane patterns of square waveguide open radiator
at (a) 10GHz(b) 14GHz and (c) 18GHz
-15-
Table 22 Properties of a square waveguide open end radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 69 71 11
14 47 60 25
18 58 62 16
The radiation pattern symmetry and back radiation performance of the
square waveguide are inferior to those of a circular waveguide
23 Probe-Fed Circular Waveguide Radiator
In Section 21 the radiation properties of a TE11-mode excited waveguide
is investigated In this section a circular waveguide fed by a coaxial probe
shown in Fig 29 is studied
The coaxial probes diameter is 127mm With the Teflon dielectric the
50-ohm coaxial lines outer conductor has a diameter of 41mm For a
circular waveguide the wave impedance of the TE11 mode is given by
∙ (28)
where λg is the guided wavelength given by
(29)
-16-
(a) (b)
Fig 29 Probe-fed circular waveguide radiator (a) Front view and (b) side
view
The combination of the probe length and the probe position from the
shorted wall enables a good impedance matching The probe distance sp from
the back short is close to a quarter wavelength at the design frequency
The designed feed has the following dimension d = 2053mm lp = 42
mm sp = 534mm wall thickness = 05mm and feed length = 400mm
Fig 210 shows the reflection coefficient of the designed probe-fed
circular waveguide radiator The reflection coefficient is less than -10dB over
138-187GHz Fig 211 and 212 shows the E-plane and H-plane radiation
patterns and 2D radiation patterns of the coaxial-to-circular waveguide
transition The radiation patterns symmetry distorted because of the high order
modes The coaxial-to-circular waveguide transition has 73dB 84dB and
79dB gain at 10GHz 14GHz and 18GHz frequencies respectively Table 23
shows the properties of the coaxial-to-circular waveguide transition
-17-
Fig 210 Reflection coefficient of the probe-fed circular waveguide radiator
(a)
Fig 211 2D radiation pattern of the probe-fed circular waveguide radiator
at (a) 10GHz (b) 14GHz and (c) 18GHz
-18-
(b)
(c)
Fig 211 continued
-19-
(a)
(b)
(c)
Fig 212 E- and H-plane patterns of the probe-fed circular waveguide
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-20-
Table 23 Properties of the probe-fed circular waveguide radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 73 70 1414 83 57 17
18 60 52 30
When a circular waveguide radiator is fed by a coaxial probe its radiation
properties are not good due to the excitation of higher-order modes
Therefore a probe-fed circular waveguide radiator can be used as a feed only
over a narrow frequency range
24 Probe-Fed Square Waveguide Radiator
In this section a probe-fed square waveguide radiator is investigated Fig
213 shows a coaxial probe-fed square waveguide radiator The designed
radiator has the following dimension a = b = 157mm lp = 35 mm sp =
50 mm wall thickness = 05mm and feed length = 40mm
(a) (b)
Fig 213 Probe-fed square waveguide radiator (a) Front view and (b) side
view
-21-
Fig 214 shows the 2D radiation patterns of the radiator at 10GHz
14GHz and 18GHz Fig 215 shows E- and H-plane patterns of the radiator
Fig 216 shows the reflection coefficient of the probe-fed square waveguide
radiator The reflection coefficient is less than -10dB over 13-20GHz Table
24 summarizes the properties of the probe-fed square waveguide radiator
(a)
Fig 214 2D radiation patterns of the probe-fed square waveguide radiator at
(a) 10GHz (b) 14GHz and (c) 18GHz
-22-
(b)
(c)
Fig 214 continued
-23-
(a)
(b)
(c)
Fig 216 E-plane and H-plane patterns of the probe-fed square waveguide
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-24-
Fig 216 Reflection coefficient of the probe-fed square waveguide radiator
Table 24 Properties of the probe-fed square waveguide radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 73 71 12
14 85 63 1418 27 65 28
When a square waveguide radiator is fed by a coaxial probe its radiation
properties are not good due to the excitation of higher-order modes as in the
case of the probe-fed circular waveguide radiator A probe-fed square
waveguide radiator can be used as a feed only over a narrow frequency
range
-25-
III Design of Compact Circular Waveguide Feeds
In this chapter the feed design is presented for a prime-focus reflector
antenna The prime-focus paraboloid reflector is one of the most commonly
used high-gain antenna It has been used in earth-station antennas and radio
telescopes It consists of a paraboloid reflector with a feed system at its focal
point
The feed should radiate a low level of cross-polar power over the
operating frequency These conditions not easy to achieve and most prime
focus feeds are compromises The shape and characteristic of the radiation
pattern of the feed are the most important parameter because these will
directly influence the fields which are directed at a reflector[6] Other
electrical factors which relevant to the choice of a feed are the cross-polar
level the gain efficiency the bandwidth and impedance matching
31 Narrow-Band Circular Waveguide Feed
Fig 31 shows the proposed narrow-band circular waveguide feed and its
design variables The feed consists of a circular waveguide open end excited
by a TE11 dominant mode A quarter wave choke is applied along the
circular aperture of the waveguide to equalize E- and H-plane radiation
patterns and to suppress the back radiation A dielectric ring is used to
control the radiation pattern and change the power distribution over the
aperture The control of the amplitude over the aperture are essential to the
design of symmetric radiation pattern The material used for dielectric loading
-26-
is the monocast(MC) nylon with a dielectric constant of 30 The feed is
designed to operate over 171-197GHz
(a)
(b)
Fig 31 Narrow-band circular waveguide feed (a) CAD model and (b) a
cross sectional view
The impedance matching is achieved by a proper combination of the probe
height lp and its distance sp from the waveguide shorted end Here the
-27-
circular waveguide is terminated with an open end with a wall thickness of
2mm radiating into the free space
Fig 32 shows the effect of the probe length lp and the probe distance sp
on the reflection coefficient The best performance is obtained when lp =
363mm and sp = 616mm The feeds reflection coefficient is less than -10dB
over 170-195GHz
(a)
(b)
Fig 32 Effect of the (a) the probe length lp and (b) the probe
distance sp on the reflection coefficient
-28-
Fig 33 shows the effect of the choke depth The E-plane pattern is more
sensitive to the choke depth than the H-plane pattern The choke depth has a
strong influence on the reflection coefficient when it is 360mm By properly
choosing the choke depth we can equalize the E- and H-plane patterns The
optimum value of the choke depth is 410mm which is 0249λ0 at 1825GHz
The choke slot width tch in the range of 06-12mm has almost no effect
on the H-plane pattern and the reflection coefficient For the E-plane pattern
tch of 12mm has some effect on the E-plane radiation pattern as shown in
Fig 34
Fig 35 shows the feed performance versus the dielectric ring length We
observe in Fig 35 that the dielectric length ld has an optimum value of
1168mm which does no effect on the H-plane pattern and tha the value of
1048mm has some effect on the E-plane pattern and the reflection
coefficient
Fig 36 shows E-plane and H-plane patterns and the reflection coefficient
versus the dielectric thickness With the optimum value of the dielectric
thickness t obtained from the Fig 36 is 155mm The larger values of td has
much stronger effects on the E-plane pattern and the reflection coefficient
The H-plane pattern is not sensitive to the dielectric ring thickness
-29-
(a)
(b)
(c)
Fig 33 Feed performance versus the choke depth (a) E-plane pattern
(b) H-plane pattern and (c) reflection coefficient
-30-
(a)
(b)
(c)
Fig 34 Feed performance versus the choke slot width (a) E-plane pattern
(b) H-plane pattern and (c) reflection coefficient
-31-
(a)
(b)
(c)
Fig 35 Feed performance versus the dielectric ring length (a) E-plane
pattern (b) H-plane pattern and (c) reflection coefficient
-32-
(a)
(b)
(c)
Fig 36 Feed performance versus the dielectric ring thickness (a) E-plane
pattern(b) H-plane pattern and (c) reflection coefficient
-33-
From the above parametric analysis an optimum feed design is obtained
The result is shown in Table 31 Fig 37 shows the 2D gain patterns of
designed feed The antenna has a gain of 903dB 933dB and 956dB at
171GHz 1825GHz and 19GHz respectively
Fig 38 shows E- and H-plane radiation patterns of the designed feed The
feed has E- and H-plane 10-dB beamwidths of 60 and 59 degrees at 17GHz
The feed has a front-to-back ration of 1900dB 2490dB and 2200dB at
171GHz 1825GHz and 19GHz respectively Table 32 summarizes the
performance of the designed narrow-band circular waveguide feed
The designed feed has a greatly improved performance over that of a
simple coax-fed feed described in Section 23
Table 31 Dimensions of the designed narrow-band circular feed
Parameter Designation Value(mm)
a Waveguide inside radius 640
l Feed length 2890
lp Probe length 363
sp Probe position from the back short 616
din Probe diameter 127
dout Diameter of coaxial cables outer conductor 400
t Thickness of choked wall 050
tch Choke slot width 100
lch Choke depth 410
ld Dielectric ring length 1168
td Dielectric ring thickness 155
d1 Waveguide outside diameter 1680
-34-
(a)
(b)
Fig 37 2D gain patterns of the narrow-band circular waveguide feed at
(a) 17GHz (b) 1825GHz and (c) 19GHz
-35-
(c)
Fig 37 continued
-36-
(a)
(b)
(c)
Fig 38 E- and H-plane patterns of the narrow-band circular waveguide feed
at (a) 10GHz (b) 1825GHz and (c) 195GHz
-37-
Frequency(GHz)
Gain(dB)
E-H-plane10-dB beamwidths
(deg)
Front-to-back ratio(dB)
Phase centerlocation
(From feeds aperture plane
toward reflector)
(mm)
1700 903 6059 20 062
1825 933 6060 25 004
1900 956 5759 22 007
Table 32 Performance of the narrow-band circular waveguide feed
The designed narrow-band feed is fabricated and its performance is
measured and compared with the simulation results The designed feed is
fabricated in a numerically-controlled machining center The fabricated antenna
is shown in Fig 39
Fig 39 Photograph of the fabricated feed
-38-
Fig 310 shows a comparison of the measured and simulated reflection
coefficients The measured reflection coefficient is less than -10dB over
171-197GHz The agreement between simulated and measured results are
good
Fig 311 shows the E- and H-plane patterns of the fabricated feed at
187GHz The feed has 90dB gain simulation and measurement results are in
good agreement
The fabricated antennarsquos 10dB beamwidth is 60 degrees in both E and H
planes at 187GHz The front-to-back ratio is 21dB
Fig 310 Reflection coefficient of the fabricated feed
-39-
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Fee
d H
orn
Gain
- d
B
Angle - degree
(a)
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Feed H
orn
Gain
- d
B
Angle - degree
(b)
Fig 311 Gain patterns of the fabricated feed at 187 GHz (a) E-plane and
(b) H-plane
-40-
IV Design of Circular Waveguide Feeds Loaded with a
Dielectric Rod
In this section circular waveguide feeds loaded with a dielectric rod feed
are investigated A comprehensive discussion of the circular waveguide loaded
with a dielectric rod is given by Kumar[7] Inserting a dielectric material
inside the circular waveguide improves the E- and H-plane pattern symmetry
In general dielectric-loaded circular waveguide feeds show good performance
only over a narrow bandwidth
Fig 41 shows the geometry of a circular waveguide loaded with a
dielectric rod The waveguide length is 400mm and the wall thickness is
05mm The dielectric rods diameter is 207mm The dielectric rod is
extended 05 wavelength beyond the waveguide open end The dielectric
constant εr is changed and the feeds performance is observed
Fig 41 Geometry of a circular waveguide loaded with a uniform dielectric
rod
-41-
Fig 42 is the radiation pattern of the feed with εr = 25 and L = 05λ0 at
9GHz E- and H-plane 10-dB beamwidths are 810 and 807 degrees
respectively The front-to-back ratio is 18dB The antenna gain is 71dB
(a)
(b)
Fig 42 Radiation pattern at 9GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 05λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-42-
Fig 43 shows the radiation pattern of the feed with εr = 21 at 10GHz
E- and H-plane 10-dB beamwidths are 70 and 71 degrees respectively The
front-to-back ratio is 19dB The antenna gain is 83dB
(a)
(b)
Fig 43 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 21 and L = 05λ0 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-43-
Fig 44 shows the radiation pattern of the feed with εr = 30 at 8GHz
E- and H-plane 10-dB beamwidths are 83 and 824 degrees respectively The
front-to-back ratio is 17dB The antenna gain is 73dB
(a)
(b)
Fig 44 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 30 and L = 05λ0 at 8GHz (a) 2D radiation pattern
and (b) E- and H-plane patterns
-44-
Fig 45 shows the radiation pattern of the feed with εr = 50 at 18GHz
E- and H-plane 10-dB beamwidths are 56 and 54 degrees respectively The
front-to-back ratio is 27dB The antenna gain is 105dB The feed has a good
pattern symmetry and low back radiation
(a)
(b)
Fig 45 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 50 and L = 05λ0 at 18GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-45-
Fig 46 is the radiation pattern of the feed with εr = 25 and L = 10λ0 at
10GHz E- and H-plane 10-dB beamwidths are 50 and 48 degrees
respectively The front-to-back ratio is 16dB The antenna gain is 105dB
(a)
(b)
Fig 46 Radiation pattern at 10GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 10λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-46-
Fig 47 shows the geometry of a circular waveguide with a tapered
dielectric rod The designed feed has the following dimension L = 1λ0 d =
1λ0 and εr =25 at 10GHz The waveguide length is 40mm and the wall
thickness is 05mm
L
Dielectricd3
Fig 47 Geometry of a circular waveguide loaded with a tapered dielectric
rod
Fig 48 shows the radiatio pattern of the designed feed E- and H-plane
10-dB beamwidths are 575 and 564 degrees respectively The front-to-back
ratio is 377dB The antenna gain is 94dB The designed feed has an
excellent beamwidth symmetry and a very low back radiation
-47-
(a)
(b)
Fig 48 Radiation pattern of a circular waveguide loaded with a tapered
dielectric rod with L = 1λ0 d = 1λ0 and εr =25 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-48-
Fig 49 shows the geometry of a spherical ended dielectric rod feed
diameter of 06λ0 at 10GHz with a dielectric constant of 25 and L= 03λ0
Fig 410 shows the radiation patterns of the designed feed E- and H-plane
10-dB beamwidths are both 63 degrees The front-to-back ratio is 24dB The
antenna gain is 864dB
Fig 49 Geometry of a circular waveguide loaded with a spherical ended
dielectric rod
-49-
(a)
(b)
Fig 410 Radiation pattern of a circular waveguide loaded wht a spherical
ended dielectric rod with d = 06λ0 L = 03λ0 and εr =25 at 10GHz (a) 3D
radiation pattern and (b) E- and H-plane patterns
-50-
V Design of a Broadband Circular Waveguide Feed
In this chapter the design of a broadband circular waveguide feed is
presented At microwave frequencies the feed is often a circular waveguide
with chokes and corrugations around the aperture Chokes and corrugations
equalize E- and H-plane patterns and reduce the back radiation
The proposed feed is designed to operate over 10-18GHz The design starts
with the optimization of the coaxial-to-rectangular waveguide adapter
employed for good mode purity over a broad frequency range Next a
rectangular-to-circular waveguide transition is optimized Finally chokes and
corrugations are designed for improved pattern symmetry and low back
radiation
The proposed feed structure is shown in Fig 51 The feed consist of the
following parts a coaxial-to-rectangular waveguide adapter a rectangular-to-
circular waveguide transition a circular waveguide section four quarter-wave
chokes around the feeds aperture and four corrugations on the feeds outer
surface
The computer simulation shows the above arrangement offers good radiation
patterns over a broad frequency range The broadband operation is obtained
by exciting the TE11 mode in the circular waveguide using the TE10 mode of
the rectangular waveguide which is in turn excited by a coaxial probe
-51-
Chokes
Coaxial-to-waveguide transition
Circular wavguide
Corrugations
Mode transition
(a)
(b)
Fig 51 Structure of the proposed broadband circular waveguide feed
(a) CAD model and (b) cross-sectional view
For the coaxial-to-rectangular waveguide adapter an SMA connector with
the probe diameter of 127 mm is employed The coaxial probe inserted into
the waveguide energizes the feed and excites the dominant TE10 mode in
-52-
the rectangular waveguide The impedance matching is achieved by adjusting
the probe distance sp from the back short and the probe length lp
(a)
(b)
Fig 52 Reflection coefficient of the coaxial-to-rectangular adapter versus
(a) probe length lp and (b) the probe position sp
Fig 52 shows the reflection coefficient versus the various values of probe
lengths lp and probe positions sp The probe length lp is adjusted to obtain
antenna impedance matching and the probe distance sp is adjusted to obtain a
-53-
desired resonant frequency
Next a transition between rectangular and circular waveguide is designed
The transition section converts the TE10 mode in the rectangular waveguide to
TE11 mode in the circular waveguide and vice versa The transition is built
in a form of a taper for easy fabrication[22]
(a)
(b)
Fig 53 Structure of the rectangular-to-circular waveguide transition
(a) 3D view and (b) cross sectional view
The dimensions of the final optimized transition are as follows The length
of the rectangular waveguide section is 143mm The rectangular waveguides
width a and height b are 207mm and 857mm respectively The length of
the circular waveguide section is 143mm The inside diameter of the circular
-54-
waveguide is 207mm(097 wavelength at 14GHz) The length of transition
region ltr is 4465mm(approximately equal to 2λ0 at 14GHz) Fig 54 shows
the field distribution inside the mode converter
(a)
(b)
Fig 54 Field distribution inside the mode converter at
(a) 10GHz (b) 14GHz and (c) 18GHz
-55-
(c)
Fig 54 continued
Finally multiple chokes are investigated Figs 55 56 and 57 show the
feed performance without chokes The reflection coefficient is less than -10dB
over 10-19GHz The antenna has a gain of 921dB to 1189dB over
10-19GHz
Fig 55 Reflection coefficient of the broadband circular waveguide feed
without chokes and corrugations
-56-
(a)
(b)
(c)
Fig 56 E- and H-plane patterns of the broadband circular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-57-
(d)
(e)
Fig 56 continued
-58-
(a)
(b)
Fig 57 2D radiation patterns of the broadband cicular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-59-
(c)
(d)
Fig 57 continued
-60-
(e)
Fig 57 continued
To achieve equal beamwidths in E and H planes over a wide frequency
range chokes and corrugations are employed Table51 summarizes the
performance of a feed without chokes and corrugations
Table 51 Performance of the broadband circular waveguide feed without
chokes and corrugations
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
1000 940 6061 15
1200 972 6159 17
1400 920 5957 21
1600 1070 4751 29
1800 1188 5352 21
-61-
Four quarter-wavelength chokes are introduced in the feed design which
has a slot depth of 75mm and slot width of 09mm The choke slot spacing
is 18mm The choke design is investigated by applying the choke one by
one and the effect on the E- and H-plane patterns are observed as illustrated
in Figs 58 and 59 The use of chokes makes the E-plane pattern narrower
The H-plane pattern is not affected Chokes increase the gain slightly and
reduce back radiation
(a)
(b)
Fig 58 Effect of chokes on the E-plane pattern of the broadband circular
waveguide feed at (a) 10GHz(b) 12GHz (c) 14GHz (d) 16GHz and (e)
18GHz
-62-
(c)
(d)
(e)
Fig 58 continued
-63-
(a)
(b)
(c)
Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-64-
(d)
(e)
Fig 59 continued
-65-
Fig 510 shows the feed performance versus the choke depth When the
choke depth is varied from 535mm to 95mm the E- and H-plane patterns
are strongly affected The optimum value of choke depth is 75mm(035λ0 at
14GHz) which gives equal E- and H-plane radiation patterns and leads to
low back radiation
Fig 511 shows the feed performance versus the choke slot width tch The
choke slot width is varied from 09mm to 21mm Radiation patterns and
reflection coefficients are not sensitive to the choke slot width The final
choke slot width is selected to be 09mm considering the feed diameter
minimization and the manufacturability The overall diameter of the proposed
feed is 369mm which is increased from the 207mm of the waveguide
inside diameter due to the use of four chokes
-66-
(a)
(b)
(c)
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection coefficient
-67-
(a)
(b)
(c)
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and (c)
reflection coefficient
-68-
Next we investigated corrugations placed on the outer wall of the feed
Four corrugations applied to the outer surface of the circular waveguide The
corrugation depth is 465mm(0215λ0 at 14GHz) The primary purpose of
using corrugations is to further reduce the back radiation Increasing the
number of corrugations beyond four has little effect in reducing the back
radiation
Figs 512 and 513 show the effect of corrugations on the E- and H-plane
patterns Fig 514 shows the parametric study of the corrugation depth lcor
The corrugation depth is varied from 40mm and 645mm The optimum
value of the corrugation depth is found to be 465mm
-69-
(a)
(b)
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern at (a) 12GHz and (b) 14GHz
-70-
(a)
(b)
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern at (a) 12GHz and (b) 14GHz
-71-
(a)
(b)
(c)
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection coefficient
-72-
The phase center location is important in placing the feed in a reflector
antenna[8] The phase center variation with frequency should be small Fig
515 shows the effect of chokes and corrugations on the phase center The
curve with circle corresponds to the case without chokes and corrugations
The phase center varies from -326mm and -190mm away from the feeds
aperture plane It means the phase center is located inside the waveguide
The curve with triangles corresponds to the case with chokes The curve with
squares to the case with chokes and corrugations The phase center varies
from 0mm to -302mm
From Fig 515 we can observed that phase center variation reduced by the
corrugation and three cases phase center calculated in φ=450 plane
parameter sweep values are given in Table 52
10 12 14 16 181
0
-1
-2
-3
-4
-5
-6
Pha
se c
ente
r (m
m)
Frequency (GHz)
choke+corrugatuion without choke corrugation with choke
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
-73-
Frequency
(GHz)
Phase center from the aperture plane
(mm)
Without
chokes and
corrugations
With
chokes
With chokes
and
corrugations
1000 -326 062 000
1100 -187 030 -002
1200 -563 -208 -065
1300 -296 -154 -202
1400 -319 -314 -302
1500 -201 -203 -241
1600 -242 -233 -207
1700 -208 -208 -186
1800 -190 -157 -132
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
Based on the foregoing parametric studies optimum dimensions of the
broadband circular waveguide feed are obtained as shown in Table 53
-74-
Table 53 Optimum dimensions of the broadband circular waveguide feed
Parameter Designation Value (mm)
2a Waveguide inside diameter 2070
d Waveguide outside diameter 3690
lcrLength of the circular waveguide section 1430
m Distance between the aperture plane and the first corrugation 950
xDistance from the last corrugation to the end of the cylindrical outer surface
550
ltrLength of the rectangular-to-circularwaveguide transition 4465
lrcLength of the rectangular waveguide section 1430
tch Choke slot width 090
lch Choke depth 750
t Choke metal width 090
lcor Corrugation depth 465
tcor Corrugation metal width 100
s Corrugation slot width 10
lp Probe length 530
sp Probe position from the back short 530
din Probe diameter 127
b Inside height of the rectangular waveguide 857
tw Waveguide wall thickness 500
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-9-
(a)
(b)
(c)
Fig 24 E-plane and H-plane patterns of the circular waveguide open end
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-10-
Table 21 Properties of a circular waveguide open end radiator of diameter
2053mm
Frequency(GHz)-10dB Beamwith(deg) Front-to-Back
Ratio(dB)E plane H plane
10 67 73 12
14 58 60 18
18 41 50 21
In a circular waveguide radiatoλr a good pattern symmetry and low back
radiation is obtained at 14GHz where 2aλ = 096
22 Square Waveguide Radiator
A square waveguide is often used as a dual-polarized feed To operate the
cutoff frequency of the dominant mode a square-waveguide wall width a
must be greater than one half of a wavelength The modes with cutoff
frequencies equal to or smaller than the operational frequency can exist inside
the waveguide wall The lower cutoff frequency and cutoff wavelength for
square waveguide is determined by the following equations
TE
(24)
TE
(25)
The next higher-order mode is TE11 mode with the cutoff wavelength
given by
-11-
TE
(26)
Similar to the circular waveguide the recommended operating frequency range
of a square waveguide is given by
TEleleTE
TErarr bandwidth (27)
Fig 25 shows the geometry of a square waveguide with a dimension of a
When a is 157mm the cutoff frequency is 95GHz The recommended
operating frequency of this waveguide is from 109GHz to 155GHz
Fig 26 shows the reflection of this waveguide excited with the dominant
TE10 mode The reflection coefficient is less than -15dB over 10-20GHz
Fig 25 Geometry of a square waveguide open end radiator
Fig 27 and shows the 2D radiation pattern of a square waveguide antenna
excited with the dominant TE10 mode The antenna has a gain of 73dB
85dB and 102dB at 10GHz 14GHz and 18GHz respectively Fig 28
shows the E- and H-plane radiation patterns of a square waveguide radiator
Table 22 summarizes the properties of a square waveguide open end radiator
-12-
Fig 26 Reflection coefficient of a square waveguide open end radiator
(a)
Fig 27 2D radiation patterns of a square waveguide radiator
at (a) 10GHz (b) 14GHz and (c) 18GHz
-13-
(b)
(c)
Fig 27 continued
-14-
(a)
(b)
(c)
Fig 28 E-plane and H-plane patterns of square waveguide open radiator
at (a) 10GHz(b) 14GHz and (c) 18GHz
-15-
Table 22 Properties of a square waveguide open end radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 69 71 11
14 47 60 25
18 58 62 16
The radiation pattern symmetry and back radiation performance of the
square waveguide are inferior to those of a circular waveguide
23 Probe-Fed Circular Waveguide Radiator
In Section 21 the radiation properties of a TE11-mode excited waveguide
is investigated In this section a circular waveguide fed by a coaxial probe
shown in Fig 29 is studied
The coaxial probes diameter is 127mm With the Teflon dielectric the
50-ohm coaxial lines outer conductor has a diameter of 41mm For a
circular waveguide the wave impedance of the TE11 mode is given by
∙ (28)
where λg is the guided wavelength given by
(29)
-16-
(a) (b)
Fig 29 Probe-fed circular waveguide radiator (a) Front view and (b) side
view
The combination of the probe length and the probe position from the
shorted wall enables a good impedance matching The probe distance sp from
the back short is close to a quarter wavelength at the design frequency
The designed feed has the following dimension d = 2053mm lp = 42
mm sp = 534mm wall thickness = 05mm and feed length = 400mm
Fig 210 shows the reflection coefficient of the designed probe-fed
circular waveguide radiator The reflection coefficient is less than -10dB over
138-187GHz Fig 211 and 212 shows the E-plane and H-plane radiation
patterns and 2D radiation patterns of the coaxial-to-circular waveguide
transition The radiation patterns symmetry distorted because of the high order
modes The coaxial-to-circular waveguide transition has 73dB 84dB and
79dB gain at 10GHz 14GHz and 18GHz frequencies respectively Table 23
shows the properties of the coaxial-to-circular waveguide transition
-17-
Fig 210 Reflection coefficient of the probe-fed circular waveguide radiator
(a)
Fig 211 2D radiation pattern of the probe-fed circular waveguide radiator
at (a) 10GHz (b) 14GHz and (c) 18GHz
-18-
(b)
(c)
Fig 211 continued
-19-
(a)
(b)
(c)
Fig 212 E- and H-plane patterns of the probe-fed circular waveguide
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-20-
Table 23 Properties of the probe-fed circular waveguide radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 73 70 1414 83 57 17
18 60 52 30
When a circular waveguide radiator is fed by a coaxial probe its radiation
properties are not good due to the excitation of higher-order modes
Therefore a probe-fed circular waveguide radiator can be used as a feed only
over a narrow frequency range
24 Probe-Fed Square Waveguide Radiator
In this section a probe-fed square waveguide radiator is investigated Fig
213 shows a coaxial probe-fed square waveguide radiator The designed
radiator has the following dimension a = b = 157mm lp = 35 mm sp =
50 mm wall thickness = 05mm and feed length = 40mm
(a) (b)
Fig 213 Probe-fed square waveguide radiator (a) Front view and (b) side
view
-21-
Fig 214 shows the 2D radiation patterns of the radiator at 10GHz
14GHz and 18GHz Fig 215 shows E- and H-plane patterns of the radiator
Fig 216 shows the reflection coefficient of the probe-fed square waveguide
radiator The reflection coefficient is less than -10dB over 13-20GHz Table
24 summarizes the properties of the probe-fed square waveguide radiator
(a)
Fig 214 2D radiation patterns of the probe-fed square waveguide radiator at
(a) 10GHz (b) 14GHz and (c) 18GHz
-22-
(b)
(c)
Fig 214 continued
-23-
(a)
(b)
(c)
Fig 216 E-plane and H-plane patterns of the probe-fed square waveguide
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-24-
Fig 216 Reflection coefficient of the probe-fed square waveguide radiator
Table 24 Properties of the probe-fed square waveguide radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 73 71 12
14 85 63 1418 27 65 28
When a square waveguide radiator is fed by a coaxial probe its radiation
properties are not good due to the excitation of higher-order modes as in the
case of the probe-fed circular waveguide radiator A probe-fed square
waveguide radiator can be used as a feed only over a narrow frequency
range
-25-
III Design of Compact Circular Waveguide Feeds
In this chapter the feed design is presented for a prime-focus reflector
antenna The prime-focus paraboloid reflector is one of the most commonly
used high-gain antenna It has been used in earth-station antennas and radio
telescopes It consists of a paraboloid reflector with a feed system at its focal
point
The feed should radiate a low level of cross-polar power over the
operating frequency These conditions not easy to achieve and most prime
focus feeds are compromises The shape and characteristic of the radiation
pattern of the feed are the most important parameter because these will
directly influence the fields which are directed at a reflector[6] Other
electrical factors which relevant to the choice of a feed are the cross-polar
level the gain efficiency the bandwidth and impedance matching
31 Narrow-Band Circular Waveguide Feed
Fig 31 shows the proposed narrow-band circular waveguide feed and its
design variables The feed consists of a circular waveguide open end excited
by a TE11 dominant mode A quarter wave choke is applied along the
circular aperture of the waveguide to equalize E- and H-plane radiation
patterns and to suppress the back radiation A dielectric ring is used to
control the radiation pattern and change the power distribution over the
aperture The control of the amplitude over the aperture are essential to the
design of symmetric radiation pattern The material used for dielectric loading
-26-
is the monocast(MC) nylon with a dielectric constant of 30 The feed is
designed to operate over 171-197GHz
(a)
(b)
Fig 31 Narrow-band circular waveguide feed (a) CAD model and (b) a
cross sectional view
The impedance matching is achieved by a proper combination of the probe
height lp and its distance sp from the waveguide shorted end Here the
-27-
circular waveguide is terminated with an open end with a wall thickness of
2mm radiating into the free space
Fig 32 shows the effect of the probe length lp and the probe distance sp
on the reflection coefficient The best performance is obtained when lp =
363mm and sp = 616mm The feeds reflection coefficient is less than -10dB
over 170-195GHz
(a)
(b)
Fig 32 Effect of the (a) the probe length lp and (b) the probe
distance sp on the reflection coefficient
-28-
Fig 33 shows the effect of the choke depth The E-plane pattern is more
sensitive to the choke depth than the H-plane pattern The choke depth has a
strong influence on the reflection coefficient when it is 360mm By properly
choosing the choke depth we can equalize the E- and H-plane patterns The
optimum value of the choke depth is 410mm which is 0249λ0 at 1825GHz
The choke slot width tch in the range of 06-12mm has almost no effect
on the H-plane pattern and the reflection coefficient For the E-plane pattern
tch of 12mm has some effect on the E-plane radiation pattern as shown in
Fig 34
Fig 35 shows the feed performance versus the dielectric ring length We
observe in Fig 35 that the dielectric length ld has an optimum value of
1168mm which does no effect on the H-plane pattern and tha the value of
1048mm has some effect on the E-plane pattern and the reflection
coefficient
Fig 36 shows E-plane and H-plane patterns and the reflection coefficient
versus the dielectric thickness With the optimum value of the dielectric
thickness t obtained from the Fig 36 is 155mm The larger values of td has
much stronger effects on the E-plane pattern and the reflection coefficient
The H-plane pattern is not sensitive to the dielectric ring thickness
-29-
(a)
(b)
(c)
Fig 33 Feed performance versus the choke depth (a) E-plane pattern
(b) H-plane pattern and (c) reflection coefficient
-30-
(a)
(b)
(c)
Fig 34 Feed performance versus the choke slot width (a) E-plane pattern
(b) H-plane pattern and (c) reflection coefficient
-31-
(a)
(b)
(c)
Fig 35 Feed performance versus the dielectric ring length (a) E-plane
pattern (b) H-plane pattern and (c) reflection coefficient
-32-
(a)
(b)
(c)
Fig 36 Feed performance versus the dielectric ring thickness (a) E-plane
pattern(b) H-plane pattern and (c) reflection coefficient
-33-
From the above parametric analysis an optimum feed design is obtained
The result is shown in Table 31 Fig 37 shows the 2D gain patterns of
designed feed The antenna has a gain of 903dB 933dB and 956dB at
171GHz 1825GHz and 19GHz respectively
Fig 38 shows E- and H-plane radiation patterns of the designed feed The
feed has E- and H-plane 10-dB beamwidths of 60 and 59 degrees at 17GHz
The feed has a front-to-back ration of 1900dB 2490dB and 2200dB at
171GHz 1825GHz and 19GHz respectively Table 32 summarizes the
performance of the designed narrow-band circular waveguide feed
The designed feed has a greatly improved performance over that of a
simple coax-fed feed described in Section 23
Table 31 Dimensions of the designed narrow-band circular feed
Parameter Designation Value(mm)
a Waveguide inside radius 640
l Feed length 2890
lp Probe length 363
sp Probe position from the back short 616
din Probe diameter 127
dout Diameter of coaxial cables outer conductor 400
t Thickness of choked wall 050
tch Choke slot width 100
lch Choke depth 410
ld Dielectric ring length 1168
td Dielectric ring thickness 155
d1 Waveguide outside diameter 1680
-34-
(a)
(b)
Fig 37 2D gain patterns of the narrow-band circular waveguide feed at
(a) 17GHz (b) 1825GHz and (c) 19GHz
-35-
(c)
Fig 37 continued
-36-
(a)
(b)
(c)
Fig 38 E- and H-plane patterns of the narrow-band circular waveguide feed
at (a) 10GHz (b) 1825GHz and (c) 195GHz
-37-
Frequency(GHz)
Gain(dB)
E-H-plane10-dB beamwidths
(deg)
Front-to-back ratio(dB)
Phase centerlocation
(From feeds aperture plane
toward reflector)
(mm)
1700 903 6059 20 062
1825 933 6060 25 004
1900 956 5759 22 007
Table 32 Performance of the narrow-band circular waveguide feed
The designed narrow-band feed is fabricated and its performance is
measured and compared with the simulation results The designed feed is
fabricated in a numerically-controlled machining center The fabricated antenna
is shown in Fig 39
Fig 39 Photograph of the fabricated feed
-38-
Fig 310 shows a comparison of the measured and simulated reflection
coefficients The measured reflection coefficient is less than -10dB over
171-197GHz The agreement between simulated and measured results are
good
Fig 311 shows the E- and H-plane patterns of the fabricated feed at
187GHz The feed has 90dB gain simulation and measurement results are in
good agreement
The fabricated antennarsquos 10dB beamwidth is 60 degrees in both E and H
planes at 187GHz The front-to-back ratio is 21dB
Fig 310 Reflection coefficient of the fabricated feed
-39-
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Fee
d H
orn
Gain
- d
B
Angle - degree
(a)
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Feed H
orn
Gain
- d
B
Angle - degree
(b)
Fig 311 Gain patterns of the fabricated feed at 187 GHz (a) E-plane and
(b) H-plane
-40-
IV Design of Circular Waveguide Feeds Loaded with a
Dielectric Rod
In this section circular waveguide feeds loaded with a dielectric rod feed
are investigated A comprehensive discussion of the circular waveguide loaded
with a dielectric rod is given by Kumar[7] Inserting a dielectric material
inside the circular waveguide improves the E- and H-plane pattern symmetry
In general dielectric-loaded circular waveguide feeds show good performance
only over a narrow bandwidth
Fig 41 shows the geometry of a circular waveguide loaded with a
dielectric rod The waveguide length is 400mm and the wall thickness is
05mm The dielectric rods diameter is 207mm The dielectric rod is
extended 05 wavelength beyond the waveguide open end The dielectric
constant εr is changed and the feeds performance is observed
Fig 41 Geometry of a circular waveguide loaded with a uniform dielectric
rod
-41-
Fig 42 is the radiation pattern of the feed with εr = 25 and L = 05λ0 at
9GHz E- and H-plane 10-dB beamwidths are 810 and 807 degrees
respectively The front-to-back ratio is 18dB The antenna gain is 71dB
(a)
(b)
Fig 42 Radiation pattern at 9GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 05λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-42-
Fig 43 shows the radiation pattern of the feed with εr = 21 at 10GHz
E- and H-plane 10-dB beamwidths are 70 and 71 degrees respectively The
front-to-back ratio is 19dB The antenna gain is 83dB
(a)
(b)
Fig 43 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 21 and L = 05λ0 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-43-
Fig 44 shows the radiation pattern of the feed with εr = 30 at 8GHz
E- and H-plane 10-dB beamwidths are 83 and 824 degrees respectively The
front-to-back ratio is 17dB The antenna gain is 73dB
(a)
(b)
Fig 44 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 30 and L = 05λ0 at 8GHz (a) 2D radiation pattern
and (b) E- and H-plane patterns
-44-
Fig 45 shows the radiation pattern of the feed with εr = 50 at 18GHz
E- and H-plane 10-dB beamwidths are 56 and 54 degrees respectively The
front-to-back ratio is 27dB The antenna gain is 105dB The feed has a good
pattern symmetry and low back radiation
(a)
(b)
Fig 45 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 50 and L = 05λ0 at 18GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-45-
Fig 46 is the radiation pattern of the feed with εr = 25 and L = 10λ0 at
10GHz E- and H-plane 10-dB beamwidths are 50 and 48 degrees
respectively The front-to-back ratio is 16dB The antenna gain is 105dB
(a)
(b)
Fig 46 Radiation pattern at 10GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 10λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-46-
Fig 47 shows the geometry of a circular waveguide with a tapered
dielectric rod The designed feed has the following dimension L = 1λ0 d =
1λ0 and εr =25 at 10GHz The waveguide length is 40mm and the wall
thickness is 05mm
L
Dielectricd3
Fig 47 Geometry of a circular waveguide loaded with a tapered dielectric
rod
Fig 48 shows the radiatio pattern of the designed feed E- and H-plane
10-dB beamwidths are 575 and 564 degrees respectively The front-to-back
ratio is 377dB The antenna gain is 94dB The designed feed has an
excellent beamwidth symmetry and a very low back radiation
-47-
(a)
(b)
Fig 48 Radiation pattern of a circular waveguide loaded with a tapered
dielectric rod with L = 1λ0 d = 1λ0 and εr =25 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-48-
Fig 49 shows the geometry of a spherical ended dielectric rod feed
diameter of 06λ0 at 10GHz with a dielectric constant of 25 and L= 03λ0
Fig 410 shows the radiation patterns of the designed feed E- and H-plane
10-dB beamwidths are both 63 degrees The front-to-back ratio is 24dB The
antenna gain is 864dB
Fig 49 Geometry of a circular waveguide loaded with a spherical ended
dielectric rod
-49-
(a)
(b)
Fig 410 Radiation pattern of a circular waveguide loaded wht a spherical
ended dielectric rod with d = 06λ0 L = 03λ0 and εr =25 at 10GHz (a) 3D
radiation pattern and (b) E- and H-plane patterns
-50-
V Design of a Broadband Circular Waveguide Feed
In this chapter the design of a broadband circular waveguide feed is
presented At microwave frequencies the feed is often a circular waveguide
with chokes and corrugations around the aperture Chokes and corrugations
equalize E- and H-plane patterns and reduce the back radiation
The proposed feed is designed to operate over 10-18GHz The design starts
with the optimization of the coaxial-to-rectangular waveguide adapter
employed for good mode purity over a broad frequency range Next a
rectangular-to-circular waveguide transition is optimized Finally chokes and
corrugations are designed for improved pattern symmetry and low back
radiation
The proposed feed structure is shown in Fig 51 The feed consist of the
following parts a coaxial-to-rectangular waveguide adapter a rectangular-to-
circular waveguide transition a circular waveguide section four quarter-wave
chokes around the feeds aperture and four corrugations on the feeds outer
surface
The computer simulation shows the above arrangement offers good radiation
patterns over a broad frequency range The broadband operation is obtained
by exciting the TE11 mode in the circular waveguide using the TE10 mode of
the rectangular waveguide which is in turn excited by a coaxial probe
-51-
Chokes
Coaxial-to-waveguide transition
Circular wavguide
Corrugations
Mode transition
(a)
(b)
Fig 51 Structure of the proposed broadband circular waveguide feed
(a) CAD model and (b) cross-sectional view
For the coaxial-to-rectangular waveguide adapter an SMA connector with
the probe diameter of 127 mm is employed The coaxial probe inserted into
the waveguide energizes the feed and excites the dominant TE10 mode in
-52-
the rectangular waveguide The impedance matching is achieved by adjusting
the probe distance sp from the back short and the probe length lp
(a)
(b)
Fig 52 Reflection coefficient of the coaxial-to-rectangular adapter versus
(a) probe length lp and (b) the probe position sp
Fig 52 shows the reflection coefficient versus the various values of probe
lengths lp and probe positions sp The probe length lp is adjusted to obtain
antenna impedance matching and the probe distance sp is adjusted to obtain a
-53-
desired resonant frequency
Next a transition between rectangular and circular waveguide is designed
The transition section converts the TE10 mode in the rectangular waveguide to
TE11 mode in the circular waveguide and vice versa The transition is built
in a form of a taper for easy fabrication[22]
(a)
(b)
Fig 53 Structure of the rectangular-to-circular waveguide transition
(a) 3D view and (b) cross sectional view
The dimensions of the final optimized transition are as follows The length
of the rectangular waveguide section is 143mm The rectangular waveguides
width a and height b are 207mm and 857mm respectively The length of
the circular waveguide section is 143mm The inside diameter of the circular
-54-
waveguide is 207mm(097 wavelength at 14GHz) The length of transition
region ltr is 4465mm(approximately equal to 2λ0 at 14GHz) Fig 54 shows
the field distribution inside the mode converter
(a)
(b)
Fig 54 Field distribution inside the mode converter at
(a) 10GHz (b) 14GHz and (c) 18GHz
-55-
(c)
Fig 54 continued
Finally multiple chokes are investigated Figs 55 56 and 57 show the
feed performance without chokes The reflection coefficient is less than -10dB
over 10-19GHz The antenna has a gain of 921dB to 1189dB over
10-19GHz
Fig 55 Reflection coefficient of the broadband circular waveguide feed
without chokes and corrugations
-56-
(a)
(b)
(c)
Fig 56 E- and H-plane patterns of the broadband circular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-57-
(d)
(e)
Fig 56 continued
-58-
(a)
(b)
Fig 57 2D radiation patterns of the broadband cicular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-59-
(c)
(d)
Fig 57 continued
-60-
(e)
Fig 57 continued
To achieve equal beamwidths in E and H planes over a wide frequency
range chokes and corrugations are employed Table51 summarizes the
performance of a feed without chokes and corrugations
Table 51 Performance of the broadband circular waveguide feed without
chokes and corrugations
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
1000 940 6061 15
1200 972 6159 17
1400 920 5957 21
1600 1070 4751 29
1800 1188 5352 21
-61-
Four quarter-wavelength chokes are introduced in the feed design which
has a slot depth of 75mm and slot width of 09mm The choke slot spacing
is 18mm The choke design is investigated by applying the choke one by
one and the effect on the E- and H-plane patterns are observed as illustrated
in Figs 58 and 59 The use of chokes makes the E-plane pattern narrower
The H-plane pattern is not affected Chokes increase the gain slightly and
reduce back radiation
(a)
(b)
Fig 58 Effect of chokes on the E-plane pattern of the broadband circular
waveguide feed at (a) 10GHz(b) 12GHz (c) 14GHz (d) 16GHz and (e)
18GHz
-62-
(c)
(d)
(e)
Fig 58 continued
-63-
(a)
(b)
(c)
Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-64-
(d)
(e)
Fig 59 continued
-65-
Fig 510 shows the feed performance versus the choke depth When the
choke depth is varied from 535mm to 95mm the E- and H-plane patterns
are strongly affected The optimum value of choke depth is 75mm(035λ0 at
14GHz) which gives equal E- and H-plane radiation patterns and leads to
low back radiation
Fig 511 shows the feed performance versus the choke slot width tch The
choke slot width is varied from 09mm to 21mm Radiation patterns and
reflection coefficients are not sensitive to the choke slot width The final
choke slot width is selected to be 09mm considering the feed diameter
minimization and the manufacturability The overall diameter of the proposed
feed is 369mm which is increased from the 207mm of the waveguide
inside diameter due to the use of four chokes
-66-
(a)
(b)
(c)
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection coefficient
-67-
(a)
(b)
(c)
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and (c)
reflection coefficient
-68-
Next we investigated corrugations placed on the outer wall of the feed
Four corrugations applied to the outer surface of the circular waveguide The
corrugation depth is 465mm(0215λ0 at 14GHz) The primary purpose of
using corrugations is to further reduce the back radiation Increasing the
number of corrugations beyond four has little effect in reducing the back
radiation
Figs 512 and 513 show the effect of corrugations on the E- and H-plane
patterns Fig 514 shows the parametric study of the corrugation depth lcor
The corrugation depth is varied from 40mm and 645mm The optimum
value of the corrugation depth is found to be 465mm
-69-
(a)
(b)
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern at (a) 12GHz and (b) 14GHz
-70-
(a)
(b)
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern at (a) 12GHz and (b) 14GHz
-71-
(a)
(b)
(c)
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection coefficient
-72-
The phase center location is important in placing the feed in a reflector
antenna[8] The phase center variation with frequency should be small Fig
515 shows the effect of chokes and corrugations on the phase center The
curve with circle corresponds to the case without chokes and corrugations
The phase center varies from -326mm and -190mm away from the feeds
aperture plane It means the phase center is located inside the waveguide
The curve with triangles corresponds to the case with chokes The curve with
squares to the case with chokes and corrugations The phase center varies
from 0mm to -302mm
From Fig 515 we can observed that phase center variation reduced by the
corrugation and three cases phase center calculated in φ=450 plane
parameter sweep values are given in Table 52
10 12 14 16 181
0
-1
-2
-3
-4
-5
-6
Pha
se c
ente
r (m
m)
Frequency (GHz)
choke+corrugatuion without choke corrugation with choke
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
-73-
Frequency
(GHz)
Phase center from the aperture plane
(mm)
Without
chokes and
corrugations
With
chokes
With chokes
and
corrugations
1000 -326 062 000
1100 -187 030 -002
1200 -563 -208 -065
1300 -296 -154 -202
1400 -319 -314 -302
1500 -201 -203 -241
1600 -242 -233 -207
1700 -208 -208 -186
1800 -190 -157 -132
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
Based on the foregoing parametric studies optimum dimensions of the
broadband circular waveguide feed are obtained as shown in Table 53
-74-
Table 53 Optimum dimensions of the broadband circular waveguide feed
Parameter Designation Value (mm)
2a Waveguide inside diameter 2070
d Waveguide outside diameter 3690
lcrLength of the circular waveguide section 1430
m Distance between the aperture plane and the first corrugation 950
xDistance from the last corrugation to the end of the cylindrical outer surface
550
ltrLength of the rectangular-to-circularwaveguide transition 4465
lrcLength of the rectangular waveguide section 1430
tch Choke slot width 090
lch Choke depth 750
t Choke metal width 090
lcor Corrugation depth 465
tcor Corrugation metal width 100
s Corrugation slot width 10
lp Probe length 530
sp Probe position from the back short 530
din Probe diameter 127
b Inside height of the rectangular waveguide 857
tw Waveguide wall thickness 500
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-10-
Table 21 Properties of a circular waveguide open end radiator of diameter
2053mm
Frequency(GHz)-10dB Beamwith(deg) Front-to-Back
Ratio(dB)E plane H plane
10 67 73 12
14 58 60 18
18 41 50 21
In a circular waveguide radiatoλr a good pattern symmetry and low back
radiation is obtained at 14GHz where 2aλ = 096
22 Square Waveguide Radiator
A square waveguide is often used as a dual-polarized feed To operate the
cutoff frequency of the dominant mode a square-waveguide wall width a
must be greater than one half of a wavelength The modes with cutoff
frequencies equal to or smaller than the operational frequency can exist inside
the waveguide wall The lower cutoff frequency and cutoff wavelength for
square waveguide is determined by the following equations
TE
(24)
TE
(25)
The next higher-order mode is TE11 mode with the cutoff wavelength
given by
-11-
TE
(26)
Similar to the circular waveguide the recommended operating frequency range
of a square waveguide is given by
TEleleTE
TErarr bandwidth (27)
Fig 25 shows the geometry of a square waveguide with a dimension of a
When a is 157mm the cutoff frequency is 95GHz The recommended
operating frequency of this waveguide is from 109GHz to 155GHz
Fig 26 shows the reflection of this waveguide excited with the dominant
TE10 mode The reflection coefficient is less than -15dB over 10-20GHz
Fig 25 Geometry of a square waveguide open end radiator
Fig 27 and shows the 2D radiation pattern of a square waveguide antenna
excited with the dominant TE10 mode The antenna has a gain of 73dB
85dB and 102dB at 10GHz 14GHz and 18GHz respectively Fig 28
shows the E- and H-plane radiation patterns of a square waveguide radiator
Table 22 summarizes the properties of a square waveguide open end radiator
-12-
Fig 26 Reflection coefficient of a square waveguide open end radiator
(a)
Fig 27 2D radiation patterns of a square waveguide radiator
at (a) 10GHz (b) 14GHz and (c) 18GHz
-13-
(b)
(c)
Fig 27 continued
-14-
(a)
(b)
(c)
Fig 28 E-plane and H-plane patterns of square waveguide open radiator
at (a) 10GHz(b) 14GHz and (c) 18GHz
-15-
Table 22 Properties of a square waveguide open end radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 69 71 11
14 47 60 25
18 58 62 16
The radiation pattern symmetry and back radiation performance of the
square waveguide are inferior to those of a circular waveguide
23 Probe-Fed Circular Waveguide Radiator
In Section 21 the radiation properties of a TE11-mode excited waveguide
is investigated In this section a circular waveguide fed by a coaxial probe
shown in Fig 29 is studied
The coaxial probes diameter is 127mm With the Teflon dielectric the
50-ohm coaxial lines outer conductor has a diameter of 41mm For a
circular waveguide the wave impedance of the TE11 mode is given by
∙ (28)
where λg is the guided wavelength given by
(29)
-16-
(a) (b)
Fig 29 Probe-fed circular waveguide radiator (a) Front view and (b) side
view
The combination of the probe length and the probe position from the
shorted wall enables a good impedance matching The probe distance sp from
the back short is close to a quarter wavelength at the design frequency
The designed feed has the following dimension d = 2053mm lp = 42
mm sp = 534mm wall thickness = 05mm and feed length = 400mm
Fig 210 shows the reflection coefficient of the designed probe-fed
circular waveguide radiator The reflection coefficient is less than -10dB over
138-187GHz Fig 211 and 212 shows the E-plane and H-plane radiation
patterns and 2D radiation patterns of the coaxial-to-circular waveguide
transition The radiation patterns symmetry distorted because of the high order
modes The coaxial-to-circular waveguide transition has 73dB 84dB and
79dB gain at 10GHz 14GHz and 18GHz frequencies respectively Table 23
shows the properties of the coaxial-to-circular waveguide transition
-17-
Fig 210 Reflection coefficient of the probe-fed circular waveguide radiator
(a)
Fig 211 2D radiation pattern of the probe-fed circular waveguide radiator
at (a) 10GHz (b) 14GHz and (c) 18GHz
-18-
(b)
(c)
Fig 211 continued
-19-
(a)
(b)
(c)
Fig 212 E- and H-plane patterns of the probe-fed circular waveguide
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-20-
Table 23 Properties of the probe-fed circular waveguide radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 73 70 1414 83 57 17
18 60 52 30
When a circular waveguide radiator is fed by a coaxial probe its radiation
properties are not good due to the excitation of higher-order modes
Therefore a probe-fed circular waveguide radiator can be used as a feed only
over a narrow frequency range
24 Probe-Fed Square Waveguide Radiator
In this section a probe-fed square waveguide radiator is investigated Fig
213 shows a coaxial probe-fed square waveguide radiator The designed
radiator has the following dimension a = b = 157mm lp = 35 mm sp =
50 mm wall thickness = 05mm and feed length = 40mm
(a) (b)
Fig 213 Probe-fed square waveguide radiator (a) Front view and (b) side
view
-21-
Fig 214 shows the 2D radiation patterns of the radiator at 10GHz
14GHz and 18GHz Fig 215 shows E- and H-plane patterns of the radiator
Fig 216 shows the reflection coefficient of the probe-fed square waveguide
radiator The reflection coefficient is less than -10dB over 13-20GHz Table
24 summarizes the properties of the probe-fed square waveguide radiator
(a)
Fig 214 2D radiation patterns of the probe-fed square waveguide radiator at
(a) 10GHz (b) 14GHz and (c) 18GHz
-22-
(b)
(c)
Fig 214 continued
-23-
(a)
(b)
(c)
Fig 216 E-plane and H-plane patterns of the probe-fed square waveguide
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-24-
Fig 216 Reflection coefficient of the probe-fed square waveguide radiator
Table 24 Properties of the probe-fed square waveguide radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 73 71 12
14 85 63 1418 27 65 28
When a square waveguide radiator is fed by a coaxial probe its radiation
properties are not good due to the excitation of higher-order modes as in the
case of the probe-fed circular waveguide radiator A probe-fed square
waveguide radiator can be used as a feed only over a narrow frequency
range
-25-
III Design of Compact Circular Waveguide Feeds
In this chapter the feed design is presented for a prime-focus reflector
antenna The prime-focus paraboloid reflector is one of the most commonly
used high-gain antenna It has been used in earth-station antennas and radio
telescopes It consists of a paraboloid reflector with a feed system at its focal
point
The feed should radiate a low level of cross-polar power over the
operating frequency These conditions not easy to achieve and most prime
focus feeds are compromises The shape and characteristic of the radiation
pattern of the feed are the most important parameter because these will
directly influence the fields which are directed at a reflector[6] Other
electrical factors which relevant to the choice of a feed are the cross-polar
level the gain efficiency the bandwidth and impedance matching
31 Narrow-Band Circular Waveguide Feed
Fig 31 shows the proposed narrow-band circular waveguide feed and its
design variables The feed consists of a circular waveguide open end excited
by a TE11 dominant mode A quarter wave choke is applied along the
circular aperture of the waveguide to equalize E- and H-plane radiation
patterns and to suppress the back radiation A dielectric ring is used to
control the radiation pattern and change the power distribution over the
aperture The control of the amplitude over the aperture are essential to the
design of symmetric radiation pattern The material used for dielectric loading
-26-
is the monocast(MC) nylon with a dielectric constant of 30 The feed is
designed to operate over 171-197GHz
(a)
(b)
Fig 31 Narrow-band circular waveguide feed (a) CAD model and (b) a
cross sectional view
The impedance matching is achieved by a proper combination of the probe
height lp and its distance sp from the waveguide shorted end Here the
-27-
circular waveguide is terminated with an open end with a wall thickness of
2mm radiating into the free space
Fig 32 shows the effect of the probe length lp and the probe distance sp
on the reflection coefficient The best performance is obtained when lp =
363mm and sp = 616mm The feeds reflection coefficient is less than -10dB
over 170-195GHz
(a)
(b)
Fig 32 Effect of the (a) the probe length lp and (b) the probe
distance sp on the reflection coefficient
-28-
Fig 33 shows the effect of the choke depth The E-plane pattern is more
sensitive to the choke depth than the H-plane pattern The choke depth has a
strong influence on the reflection coefficient when it is 360mm By properly
choosing the choke depth we can equalize the E- and H-plane patterns The
optimum value of the choke depth is 410mm which is 0249λ0 at 1825GHz
The choke slot width tch in the range of 06-12mm has almost no effect
on the H-plane pattern and the reflection coefficient For the E-plane pattern
tch of 12mm has some effect on the E-plane radiation pattern as shown in
Fig 34
Fig 35 shows the feed performance versus the dielectric ring length We
observe in Fig 35 that the dielectric length ld has an optimum value of
1168mm which does no effect on the H-plane pattern and tha the value of
1048mm has some effect on the E-plane pattern and the reflection
coefficient
Fig 36 shows E-plane and H-plane patterns and the reflection coefficient
versus the dielectric thickness With the optimum value of the dielectric
thickness t obtained from the Fig 36 is 155mm The larger values of td has
much stronger effects on the E-plane pattern and the reflection coefficient
The H-plane pattern is not sensitive to the dielectric ring thickness
-29-
(a)
(b)
(c)
Fig 33 Feed performance versus the choke depth (a) E-plane pattern
(b) H-plane pattern and (c) reflection coefficient
-30-
(a)
(b)
(c)
Fig 34 Feed performance versus the choke slot width (a) E-plane pattern
(b) H-plane pattern and (c) reflection coefficient
-31-
(a)
(b)
(c)
Fig 35 Feed performance versus the dielectric ring length (a) E-plane
pattern (b) H-plane pattern and (c) reflection coefficient
-32-
(a)
(b)
(c)
Fig 36 Feed performance versus the dielectric ring thickness (a) E-plane
pattern(b) H-plane pattern and (c) reflection coefficient
-33-
From the above parametric analysis an optimum feed design is obtained
The result is shown in Table 31 Fig 37 shows the 2D gain patterns of
designed feed The antenna has a gain of 903dB 933dB and 956dB at
171GHz 1825GHz and 19GHz respectively
Fig 38 shows E- and H-plane radiation patterns of the designed feed The
feed has E- and H-plane 10-dB beamwidths of 60 and 59 degrees at 17GHz
The feed has a front-to-back ration of 1900dB 2490dB and 2200dB at
171GHz 1825GHz and 19GHz respectively Table 32 summarizes the
performance of the designed narrow-band circular waveguide feed
The designed feed has a greatly improved performance over that of a
simple coax-fed feed described in Section 23
Table 31 Dimensions of the designed narrow-band circular feed
Parameter Designation Value(mm)
a Waveguide inside radius 640
l Feed length 2890
lp Probe length 363
sp Probe position from the back short 616
din Probe diameter 127
dout Diameter of coaxial cables outer conductor 400
t Thickness of choked wall 050
tch Choke slot width 100
lch Choke depth 410
ld Dielectric ring length 1168
td Dielectric ring thickness 155
d1 Waveguide outside diameter 1680
-34-
(a)
(b)
Fig 37 2D gain patterns of the narrow-band circular waveguide feed at
(a) 17GHz (b) 1825GHz and (c) 19GHz
-35-
(c)
Fig 37 continued
-36-
(a)
(b)
(c)
Fig 38 E- and H-plane patterns of the narrow-band circular waveguide feed
at (a) 10GHz (b) 1825GHz and (c) 195GHz
-37-
Frequency(GHz)
Gain(dB)
E-H-plane10-dB beamwidths
(deg)
Front-to-back ratio(dB)
Phase centerlocation
(From feeds aperture plane
toward reflector)
(mm)
1700 903 6059 20 062
1825 933 6060 25 004
1900 956 5759 22 007
Table 32 Performance of the narrow-band circular waveguide feed
The designed narrow-band feed is fabricated and its performance is
measured and compared with the simulation results The designed feed is
fabricated in a numerically-controlled machining center The fabricated antenna
is shown in Fig 39
Fig 39 Photograph of the fabricated feed
-38-
Fig 310 shows a comparison of the measured and simulated reflection
coefficients The measured reflection coefficient is less than -10dB over
171-197GHz The agreement between simulated and measured results are
good
Fig 311 shows the E- and H-plane patterns of the fabricated feed at
187GHz The feed has 90dB gain simulation and measurement results are in
good agreement
The fabricated antennarsquos 10dB beamwidth is 60 degrees in both E and H
planes at 187GHz The front-to-back ratio is 21dB
Fig 310 Reflection coefficient of the fabricated feed
-39-
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Fee
d H
orn
Gain
- d
B
Angle - degree
(a)
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Feed H
orn
Gain
- d
B
Angle - degree
(b)
Fig 311 Gain patterns of the fabricated feed at 187 GHz (a) E-plane and
(b) H-plane
-40-
IV Design of Circular Waveguide Feeds Loaded with a
Dielectric Rod
In this section circular waveguide feeds loaded with a dielectric rod feed
are investigated A comprehensive discussion of the circular waveguide loaded
with a dielectric rod is given by Kumar[7] Inserting a dielectric material
inside the circular waveguide improves the E- and H-plane pattern symmetry
In general dielectric-loaded circular waveguide feeds show good performance
only over a narrow bandwidth
Fig 41 shows the geometry of a circular waveguide loaded with a
dielectric rod The waveguide length is 400mm and the wall thickness is
05mm The dielectric rods diameter is 207mm The dielectric rod is
extended 05 wavelength beyond the waveguide open end The dielectric
constant εr is changed and the feeds performance is observed
Fig 41 Geometry of a circular waveguide loaded with a uniform dielectric
rod
-41-
Fig 42 is the radiation pattern of the feed with εr = 25 and L = 05λ0 at
9GHz E- and H-plane 10-dB beamwidths are 810 and 807 degrees
respectively The front-to-back ratio is 18dB The antenna gain is 71dB
(a)
(b)
Fig 42 Radiation pattern at 9GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 05λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-42-
Fig 43 shows the radiation pattern of the feed with εr = 21 at 10GHz
E- and H-plane 10-dB beamwidths are 70 and 71 degrees respectively The
front-to-back ratio is 19dB The antenna gain is 83dB
(a)
(b)
Fig 43 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 21 and L = 05λ0 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-43-
Fig 44 shows the radiation pattern of the feed with εr = 30 at 8GHz
E- and H-plane 10-dB beamwidths are 83 and 824 degrees respectively The
front-to-back ratio is 17dB The antenna gain is 73dB
(a)
(b)
Fig 44 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 30 and L = 05λ0 at 8GHz (a) 2D radiation pattern
and (b) E- and H-plane patterns
-44-
Fig 45 shows the radiation pattern of the feed with εr = 50 at 18GHz
E- and H-plane 10-dB beamwidths are 56 and 54 degrees respectively The
front-to-back ratio is 27dB The antenna gain is 105dB The feed has a good
pattern symmetry and low back radiation
(a)
(b)
Fig 45 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 50 and L = 05λ0 at 18GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-45-
Fig 46 is the radiation pattern of the feed with εr = 25 and L = 10λ0 at
10GHz E- and H-plane 10-dB beamwidths are 50 and 48 degrees
respectively The front-to-back ratio is 16dB The antenna gain is 105dB
(a)
(b)
Fig 46 Radiation pattern at 10GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 10λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-46-
Fig 47 shows the geometry of a circular waveguide with a tapered
dielectric rod The designed feed has the following dimension L = 1λ0 d =
1λ0 and εr =25 at 10GHz The waveguide length is 40mm and the wall
thickness is 05mm
L
Dielectricd3
Fig 47 Geometry of a circular waveguide loaded with a tapered dielectric
rod
Fig 48 shows the radiatio pattern of the designed feed E- and H-plane
10-dB beamwidths are 575 and 564 degrees respectively The front-to-back
ratio is 377dB The antenna gain is 94dB The designed feed has an
excellent beamwidth symmetry and a very low back radiation
-47-
(a)
(b)
Fig 48 Radiation pattern of a circular waveguide loaded with a tapered
dielectric rod with L = 1λ0 d = 1λ0 and εr =25 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-48-
Fig 49 shows the geometry of a spherical ended dielectric rod feed
diameter of 06λ0 at 10GHz with a dielectric constant of 25 and L= 03λ0
Fig 410 shows the radiation patterns of the designed feed E- and H-plane
10-dB beamwidths are both 63 degrees The front-to-back ratio is 24dB The
antenna gain is 864dB
Fig 49 Geometry of a circular waveguide loaded with a spherical ended
dielectric rod
-49-
(a)
(b)
Fig 410 Radiation pattern of a circular waveguide loaded wht a spherical
ended dielectric rod with d = 06λ0 L = 03λ0 and εr =25 at 10GHz (a) 3D
radiation pattern and (b) E- and H-plane patterns
-50-
V Design of a Broadband Circular Waveguide Feed
In this chapter the design of a broadband circular waveguide feed is
presented At microwave frequencies the feed is often a circular waveguide
with chokes and corrugations around the aperture Chokes and corrugations
equalize E- and H-plane patterns and reduce the back radiation
The proposed feed is designed to operate over 10-18GHz The design starts
with the optimization of the coaxial-to-rectangular waveguide adapter
employed for good mode purity over a broad frequency range Next a
rectangular-to-circular waveguide transition is optimized Finally chokes and
corrugations are designed for improved pattern symmetry and low back
radiation
The proposed feed structure is shown in Fig 51 The feed consist of the
following parts a coaxial-to-rectangular waveguide adapter a rectangular-to-
circular waveguide transition a circular waveguide section four quarter-wave
chokes around the feeds aperture and four corrugations on the feeds outer
surface
The computer simulation shows the above arrangement offers good radiation
patterns over a broad frequency range The broadband operation is obtained
by exciting the TE11 mode in the circular waveguide using the TE10 mode of
the rectangular waveguide which is in turn excited by a coaxial probe
-51-
Chokes
Coaxial-to-waveguide transition
Circular wavguide
Corrugations
Mode transition
(a)
(b)
Fig 51 Structure of the proposed broadband circular waveguide feed
(a) CAD model and (b) cross-sectional view
For the coaxial-to-rectangular waveguide adapter an SMA connector with
the probe diameter of 127 mm is employed The coaxial probe inserted into
the waveguide energizes the feed and excites the dominant TE10 mode in
-52-
the rectangular waveguide The impedance matching is achieved by adjusting
the probe distance sp from the back short and the probe length lp
(a)
(b)
Fig 52 Reflection coefficient of the coaxial-to-rectangular adapter versus
(a) probe length lp and (b) the probe position sp
Fig 52 shows the reflection coefficient versus the various values of probe
lengths lp and probe positions sp The probe length lp is adjusted to obtain
antenna impedance matching and the probe distance sp is adjusted to obtain a
-53-
desired resonant frequency
Next a transition between rectangular and circular waveguide is designed
The transition section converts the TE10 mode in the rectangular waveguide to
TE11 mode in the circular waveguide and vice versa The transition is built
in a form of a taper for easy fabrication[22]
(a)
(b)
Fig 53 Structure of the rectangular-to-circular waveguide transition
(a) 3D view and (b) cross sectional view
The dimensions of the final optimized transition are as follows The length
of the rectangular waveguide section is 143mm The rectangular waveguides
width a and height b are 207mm and 857mm respectively The length of
the circular waveguide section is 143mm The inside diameter of the circular
-54-
waveguide is 207mm(097 wavelength at 14GHz) The length of transition
region ltr is 4465mm(approximately equal to 2λ0 at 14GHz) Fig 54 shows
the field distribution inside the mode converter
(a)
(b)
Fig 54 Field distribution inside the mode converter at
(a) 10GHz (b) 14GHz and (c) 18GHz
-55-
(c)
Fig 54 continued
Finally multiple chokes are investigated Figs 55 56 and 57 show the
feed performance without chokes The reflection coefficient is less than -10dB
over 10-19GHz The antenna has a gain of 921dB to 1189dB over
10-19GHz
Fig 55 Reflection coefficient of the broadband circular waveguide feed
without chokes and corrugations
-56-
(a)
(b)
(c)
Fig 56 E- and H-plane patterns of the broadband circular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-57-
(d)
(e)
Fig 56 continued
-58-
(a)
(b)
Fig 57 2D radiation patterns of the broadband cicular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-59-
(c)
(d)
Fig 57 continued
-60-
(e)
Fig 57 continued
To achieve equal beamwidths in E and H planes over a wide frequency
range chokes and corrugations are employed Table51 summarizes the
performance of a feed without chokes and corrugations
Table 51 Performance of the broadband circular waveguide feed without
chokes and corrugations
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
1000 940 6061 15
1200 972 6159 17
1400 920 5957 21
1600 1070 4751 29
1800 1188 5352 21
-61-
Four quarter-wavelength chokes are introduced in the feed design which
has a slot depth of 75mm and slot width of 09mm The choke slot spacing
is 18mm The choke design is investigated by applying the choke one by
one and the effect on the E- and H-plane patterns are observed as illustrated
in Figs 58 and 59 The use of chokes makes the E-plane pattern narrower
The H-plane pattern is not affected Chokes increase the gain slightly and
reduce back radiation
(a)
(b)
Fig 58 Effect of chokes on the E-plane pattern of the broadband circular
waveguide feed at (a) 10GHz(b) 12GHz (c) 14GHz (d) 16GHz and (e)
18GHz
-62-
(c)
(d)
(e)
Fig 58 continued
-63-
(a)
(b)
(c)
Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-64-
(d)
(e)
Fig 59 continued
-65-
Fig 510 shows the feed performance versus the choke depth When the
choke depth is varied from 535mm to 95mm the E- and H-plane patterns
are strongly affected The optimum value of choke depth is 75mm(035λ0 at
14GHz) which gives equal E- and H-plane radiation patterns and leads to
low back radiation
Fig 511 shows the feed performance versus the choke slot width tch The
choke slot width is varied from 09mm to 21mm Radiation patterns and
reflection coefficients are not sensitive to the choke slot width The final
choke slot width is selected to be 09mm considering the feed diameter
minimization and the manufacturability The overall diameter of the proposed
feed is 369mm which is increased from the 207mm of the waveguide
inside diameter due to the use of four chokes
-66-
(a)
(b)
(c)
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection coefficient
-67-
(a)
(b)
(c)
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and (c)
reflection coefficient
-68-
Next we investigated corrugations placed on the outer wall of the feed
Four corrugations applied to the outer surface of the circular waveguide The
corrugation depth is 465mm(0215λ0 at 14GHz) The primary purpose of
using corrugations is to further reduce the back radiation Increasing the
number of corrugations beyond four has little effect in reducing the back
radiation
Figs 512 and 513 show the effect of corrugations on the E- and H-plane
patterns Fig 514 shows the parametric study of the corrugation depth lcor
The corrugation depth is varied from 40mm and 645mm The optimum
value of the corrugation depth is found to be 465mm
-69-
(a)
(b)
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern at (a) 12GHz and (b) 14GHz
-70-
(a)
(b)
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern at (a) 12GHz and (b) 14GHz
-71-
(a)
(b)
(c)
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection coefficient
-72-
The phase center location is important in placing the feed in a reflector
antenna[8] The phase center variation with frequency should be small Fig
515 shows the effect of chokes and corrugations on the phase center The
curve with circle corresponds to the case without chokes and corrugations
The phase center varies from -326mm and -190mm away from the feeds
aperture plane It means the phase center is located inside the waveguide
The curve with triangles corresponds to the case with chokes The curve with
squares to the case with chokes and corrugations The phase center varies
from 0mm to -302mm
From Fig 515 we can observed that phase center variation reduced by the
corrugation and three cases phase center calculated in φ=450 plane
parameter sweep values are given in Table 52
10 12 14 16 181
0
-1
-2
-3
-4
-5
-6
Pha
se c
ente
r (m
m)
Frequency (GHz)
choke+corrugatuion without choke corrugation with choke
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
-73-
Frequency
(GHz)
Phase center from the aperture plane
(mm)
Without
chokes and
corrugations
With
chokes
With chokes
and
corrugations
1000 -326 062 000
1100 -187 030 -002
1200 -563 -208 -065
1300 -296 -154 -202
1400 -319 -314 -302
1500 -201 -203 -241
1600 -242 -233 -207
1700 -208 -208 -186
1800 -190 -157 -132
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
Based on the foregoing parametric studies optimum dimensions of the
broadband circular waveguide feed are obtained as shown in Table 53
-74-
Table 53 Optimum dimensions of the broadband circular waveguide feed
Parameter Designation Value (mm)
2a Waveguide inside diameter 2070
d Waveguide outside diameter 3690
lcrLength of the circular waveguide section 1430
m Distance between the aperture plane and the first corrugation 950
xDistance from the last corrugation to the end of the cylindrical outer surface
550
ltrLength of the rectangular-to-circularwaveguide transition 4465
lrcLength of the rectangular waveguide section 1430
tch Choke slot width 090
lch Choke depth 750
t Choke metal width 090
lcor Corrugation depth 465
tcor Corrugation metal width 100
s Corrugation slot width 10
lp Probe length 530
sp Probe position from the back short 530
din Probe diameter 127
b Inside height of the rectangular waveguide 857
tw Waveguide wall thickness 500
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-11-
TE
(26)
Similar to the circular waveguide the recommended operating frequency range
of a square waveguide is given by
TEleleTE
TErarr bandwidth (27)
Fig 25 shows the geometry of a square waveguide with a dimension of a
When a is 157mm the cutoff frequency is 95GHz The recommended
operating frequency of this waveguide is from 109GHz to 155GHz
Fig 26 shows the reflection of this waveguide excited with the dominant
TE10 mode The reflection coefficient is less than -15dB over 10-20GHz
Fig 25 Geometry of a square waveguide open end radiator
Fig 27 and shows the 2D radiation pattern of a square waveguide antenna
excited with the dominant TE10 mode The antenna has a gain of 73dB
85dB and 102dB at 10GHz 14GHz and 18GHz respectively Fig 28
shows the E- and H-plane radiation patterns of a square waveguide radiator
Table 22 summarizes the properties of a square waveguide open end radiator
-12-
Fig 26 Reflection coefficient of a square waveguide open end radiator
(a)
Fig 27 2D radiation patterns of a square waveguide radiator
at (a) 10GHz (b) 14GHz and (c) 18GHz
-13-
(b)
(c)
Fig 27 continued
-14-
(a)
(b)
(c)
Fig 28 E-plane and H-plane patterns of square waveguide open radiator
at (a) 10GHz(b) 14GHz and (c) 18GHz
-15-
Table 22 Properties of a square waveguide open end radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 69 71 11
14 47 60 25
18 58 62 16
The radiation pattern symmetry and back radiation performance of the
square waveguide are inferior to those of a circular waveguide
23 Probe-Fed Circular Waveguide Radiator
In Section 21 the radiation properties of a TE11-mode excited waveguide
is investigated In this section a circular waveguide fed by a coaxial probe
shown in Fig 29 is studied
The coaxial probes diameter is 127mm With the Teflon dielectric the
50-ohm coaxial lines outer conductor has a diameter of 41mm For a
circular waveguide the wave impedance of the TE11 mode is given by
∙ (28)
where λg is the guided wavelength given by
(29)
-16-
(a) (b)
Fig 29 Probe-fed circular waveguide radiator (a) Front view and (b) side
view
The combination of the probe length and the probe position from the
shorted wall enables a good impedance matching The probe distance sp from
the back short is close to a quarter wavelength at the design frequency
The designed feed has the following dimension d = 2053mm lp = 42
mm sp = 534mm wall thickness = 05mm and feed length = 400mm
Fig 210 shows the reflection coefficient of the designed probe-fed
circular waveguide radiator The reflection coefficient is less than -10dB over
138-187GHz Fig 211 and 212 shows the E-plane and H-plane radiation
patterns and 2D radiation patterns of the coaxial-to-circular waveguide
transition The radiation patterns symmetry distorted because of the high order
modes The coaxial-to-circular waveguide transition has 73dB 84dB and
79dB gain at 10GHz 14GHz and 18GHz frequencies respectively Table 23
shows the properties of the coaxial-to-circular waveguide transition
-17-
Fig 210 Reflection coefficient of the probe-fed circular waveguide radiator
(a)
Fig 211 2D radiation pattern of the probe-fed circular waveguide radiator
at (a) 10GHz (b) 14GHz and (c) 18GHz
-18-
(b)
(c)
Fig 211 continued
-19-
(a)
(b)
(c)
Fig 212 E- and H-plane patterns of the probe-fed circular waveguide
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-20-
Table 23 Properties of the probe-fed circular waveguide radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 73 70 1414 83 57 17
18 60 52 30
When a circular waveguide radiator is fed by a coaxial probe its radiation
properties are not good due to the excitation of higher-order modes
Therefore a probe-fed circular waveguide radiator can be used as a feed only
over a narrow frequency range
24 Probe-Fed Square Waveguide Radiator
In this section a probe-fed square waveguide radiator is investigated Fig
213 shows a coaxial probe-fed square waveguide radiator The designed
radiator has the following dimension a = b = 157mm lp = 35 mm sp =
50 mm wall thickness = 05mm and feed length = 40mm
(a) (b)
Fig 213 Probe-fed square waveguide radiator (a) Front view and (b) side
view
-21-
Fig 214 shows the 2D radiation patterns of the radiator at 10GHz
14GHz and 18GHz Fig 215 shows E- and H-plane patterns of the radiator
Fig 216 shows the reflection coefficient of the probe-fed square waveguide
radiator The reflection coefficient is less than -10dB over 13-20GHz Table
24 summarizes the properties of the probe-fed square waveguide radiator
(a)
Fig 214 2D radiation patterns of the probe-fed square waveguide radiator at
(a) 10GHz (b) 14GHz and (c) 18GHz
-22-
(b)
(c)
Fig 214 continued
-23-
(a)
(b)
(c)
Fig 216 E-plane and H-plane patterns of the probe-fed square waveguide
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-24-
Fig 216 Reflection coefficient of the probe-fed square waveguide radiator
Table 24 Properties of the probe-fed square waveguide radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 73 71 12
14 85 63 1418 27 65 28
When a square waveguide radiator is fed by a coaxial probe its radiation
properties are not good due to the excitation of higher-order modes as in the
case of the probe-fed circular waveguide radiator A probe-fed square
waveguide radiator can be used as a feed only over a narrow frequency
range
-25-
III Design of Compact Circular Waveguide Feeds
In this chapter the feed design is presented for a prime-focus reflector
antenna The prime-focus paraboloid reflector is one of the most commonly
used high-gain antenna It has been used in earth-station antennas and radio
telescopes It consists of a paraboloid reflector with a feed system at its focal
point
The feed should radiate a low level of cross-polar power over the
operating frequency These conditions not easy to achieve and most prime
focus feeds are compromises The shape and characteristic of the radiation
pattern of the feed are the most important parameter because these will
directly influence the fields which are directed at a reflector[6] Other
electrical factors which relevant to the choice of a feed are the cross-polar
level the gain efficiency the bandwidth and impedance matching
31 Narrow-Band Circular Waveguide Feed
Fig 31 shows the proposed narrow-band circular waveguide feed and its
design variables The feed consists of a circular waveguide open end excited
by a TE11 dominant mode A quarter wave choke is applied along the
circular aperture of the waveguide to equalize E- and H-plane radiation
patterns and to suppress the back radiation A dielectric ring is used to
control the radiation pattern and change the power distribution over the
aperture The control of the amplitude over the aperture are essential to the
design of symmetric radiation pattern The material used for dielectric loading
-26-
is the monocast(MC) nylon with a dielectric constant of 30 The feed is
designed to operate over 171-197GHz
(a)
(b)
Fig 31 Narrow-band circular waveguide feed (a) CAD model and (b) a
cross sectional view
The impedance matching is achieved by a proper combination of the probe
height lp and its distance sp from the waveguide shorted end Here the
-27-
circular waveguide is terminated with an open end with a wall thickness of
2mm radiating into the free space
Fig 32 shows the effect of the probe length lp and the probe distance sp
on the reflection coefficient The best performance is obtained when lp =
363mm and sp = 616mm The feeds reflection coefficient is less than -10dB
over 170-195GHz
(a)
(b)
Fig 32 Effect of the (a) the probe length lp and (b) the probe
distance sp on the reflection coefficient
-28-
Fig 33 shows the effect of the choke depth The E-plane pattern is more
sensitive to the choke depth than the H-plane pattern The choke depth has a
strong influence on the reflection coefficient when it is 360mm By properly
choosing the choke depth we can equalize the E- and H-plane patterns The
optimum value of the choke depth is 410mm which is 0249λ0 at 1825GHz
The choke slot width tch in the range of 06-12mm has almost no effect
on the H-plane pattern and the reflection coefficient For the E-plane pattern
tch of 12mm has some effect on the E-plane radiation pattern as shown in
Fig 34
Fig 35 shows the feed performance versus the dielectric ring length We
observe in Fig 35 that the dielectric length ld has an optimum value of
1168mm which does no effect on the H-plane pattern and tha the value of
1048mm has some effect on the E-plane pattern and the reflection
coefficient
Fig 36 shows E-plane and H-plane patterns and the reflection coefficient
versus the dielectric thickness With the optimum value of the dielectric
thickness t obtained from the Fig 36 is 155mm The larger values of td has
much stronger effects on the E-plane pattern and the reflection coefficient
The H-plane pattern is not sensitive to the dielectric ring thickness
-29-
(a)
(b)
(c)
Fig 33 Feed performance versus the choke depth (a) E-plane pattern
(b) H-plane pattern and (c) reflection coefficient
-30-
(a)
(b)
(c)
Fig 34 Feed performance versus the choke slot width (a) E-plane pattern
(b) H-plane pattern and (c) reflection coefficient
-31-
(a)
(b)
(c)
Fig 35 Feed performance versus the dielectric ring length (a) E-plane
pattern (b) H-plane pattern and (c) reflection coefficient
-32-
(a)
(b)
(c)
Fig 36 Feed performance versus the dielectric ring thickness (a) E-plane
pattern(b) H-plane pattern and (c) reflection coefficient
-33-
From the above parametric analysis an optimum feed design is obtained
The result is shown in Table 31 Fig 37 shows the 2D gain patterns of
designed feed The antenna has a gain of 903dB 933dB and 956dB at
171GHz 1825GHz and 19GHz respectively
Fig 38 shows E- and H-plane radiation patterns of the designed feed The
feed has E- and H-plane 10-dB beamwidths of 60 and 59 degrees at 17GHz
The feed has a front-to-back ration of 1900dB 2490dB and 2200dB at
171GHz 1825GHz and 19GHz respectively Table 32 summarizes the
performance of the designed narrow-band circular waveguide feed
The designed feed has a greatly improved performance over that of a
simple coax-fed feed described in Section 23
Table 31 Dimensions of the designed narrow-band circular feed
Parameter Designation Value(mm)
a Waveguide inside radius 640
l Feed length 2890
lp Probe length 363
sp Probe position from the back short 616
din Probe diameter 127
dout Diameter of coaxial cables outer conductor 400
t Thickness of choked wall 050
tch Choke slot width 100
lch Choke depth 410
ld Dielectric ring length 1168
td Dielectric ring thickness 155
d1 Waveguide outside diameter 1680
-34-
(a)
(b)
Fig 37 2D gain patterns of the narrow-band circular waveguide feed at
(a) 17GHz (b) 1825GHz and (c) 19GHz
-35-
(c)
Fig 37 continued
-36-
(a)
(b)
(c)
Fig 38 E- and H-plane patterns of the narrow-band circular waveguide feed
at (a) 10GHz (b) 1825GHz and (c) 195GHz
-37-
Frequency(GHz)
Gain(dB)
E-H-plane10-dB beamwidths
(deg)
Front-to-back ratio(dB)
Phase centerlocation
(From feeds aperture plane
toward reflector)
(mm)
1700 903 6059 20 062
1825 933 6060 25 004
1900 956 5759 22 007
Table 32 Performance of the narrow-band circular waveguide feed
The designed narrow-band feed is fabricated and its performance is
measured and compared with the simulation results The designed feed is
fabricated in a numerically-controlled machining center The fabricated antenna
is shown in Fig 39
Fig 39 Photograph of the fabricated feed
-38-
Fig 310 shows a comparison of the measured and simulated reflection
coefficients The measured reflection coefficient is less than -10dB over
171-197GHz The agreement between simulated and measured results are
good
Fig 311 shows the E- and H-plane patterns of the fabricated feed at
187GHz The feed has 90dB gain simulation and measurement results are in
good agreement
The fabricated antennarsquos 10dB beamwidth is 60 degrees in both E and H
planes at 187GHz The front-to-back ratio is 21dB
Fig 310 Reflection coefficient of the fabricated feed
-39-
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Fee
d H
orn
Gain
- d
B
Angle - degree
(a)
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Feed H
orn
Gain
- d
B
Angle - degree
(b)
Fig 311 Gain patterns of the fabricated feed at 187 GHz (a) E-plane and
(b) H-plane
-40-
IV Design of Circular Waveguide Feeds Loaded with a
Dielectric Rod
In this section circular waveguide feeds loaded with a dielectric rod feed
are investigated A comprehensive discussion of the circular waveguide loaded
with a dielectric rod is given by Kumar[7] Inserting a dielectric material
inside the circular waveguide improves the E- and H-plane pattern symmetry
In general dielectric-loaded circular waveguide feeds show good performance
only over a narrow bandwidth
Fig 41 shows the geometry of a circular waveguide loaded with a
dielectric rod The waveguide length is 400mm and the wall thickness is
05mm The dielectric rods diameter is 207mm The dielectric rod is
extended 05 wavelength beyond the waveguide open end The dielectric
constant εr is changed and the feeds performance is observed
Fig 41 Geometry of a circular waveguide loaded with a uniform dielectric
rod
-41-
Fig 42 is the radiation pattern of the feed with εr = 25 and L = 05λ0 at
9GHz E- and H-plane 10-dB beamwidths are 810 and 807 degrees
respectively The front-to-back ratio is 18dB The antenna gain is 71dB
(a)
(b)
Fig 42 Radiation pattern at 9GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 05λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-42-
Fig 43 shows the radiation pattern of the feed with εr = 21 at 10GHz
E- and H-plane 10-dB beamwidths are 70 and 71 degrees respectively The
front-to-back ratio is 19dB The antenna gain is 83dB
(a)
(b)
Fig 43 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 21 and L = 05λ0 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-43-
Fig 44 shows the radiation pattern of the feed with εr = 30 at 8GHz
E- and H-plane 10-dB beamwidths are 83 and 824 degrees respectively The
front-to-back ratio is 17dB The antenna gain is 73dB
(a)
(b)
Fig 44 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 30 and L = 05λ0 at 8GHz (a) 2D radiation pattern
and (b) E- and H-plane patterns
-44-
Fig 45 shows the radiation pattern of the feed with εr = 50 at 18GHz
E- and H-plane 10-dB beamwidths are 56 and 54 degrees respectively The
front-to-back ratio is 27dB The antenna gain is 105dB The feed has a good
pattern symmetry and low back radiation
(a)
(b)
Fig 45 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 50 and L = 05λ0 at 18GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-45-
Fig 46 is the radiation pattern of the feed with εr = 25 and L = 10λ0 at
10GHz E- and H-plane 10-dB beamwidths are 50 and 48 degrees
respectively The front-to-back ratio is 16dB The antenna gain is 105dB
(a)
(b)
Fig 46 Radiation pattern at 10GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 10λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-46-
Fig 47 shows the geometry of a circular waveguide with a tapered
dielectric rod The designed feed has the following dimension L = 1λ0 d =
1λ0 and εr =25 at 10GHz The waveguide length is 40mm and the wall
thickness is 05mm
L
Dielectricd3
Fig 47 Geometry of a circular waveguide loaded with a tapered dielectric
rod
Fig 48 shows the radiatio pattern of the designed feed E- and H-plane
10-dB beamwidths are 575 and 564 degrees respectively The front-to-back
ratio is 377dB The antenna gain is 94dB The designed feed has an
excellent beamwidth symmetry and a very low back radiation
-47-
(a)
(b)
Fig 48 Radiation pattern of a circular waveguide loaded with a tapered
dielectric rod with L = 1λ0 d = 1λ0 and εr =25 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-48-
Fig 49 shows the geometry of a spherical ended dielectric rod feed
diameter of 06λ0 at 10GHz with a dielectric constant of 25 and L= 03λ0
Fig 410 shows the radiation patterns of the designed feed E- and H-plane
10-dB beamwidths are both 63 degrees The front-to-back ratio is 24dB The
antenna gain is 864dB
Fig 49 Geometry of a circular waveguide loaded with a spherical ended
dielectric rod
-49-
(a)
(b)
Fig 410 Radiation pattern of a circular waveguide loaded wht a spherical
ended dielectric rod with d = 06λ0 L = 03λ0 and εr =25 at 10GHz (a) 3D
radiation pattern and (b) E- and H-plane patterns
-50-
V Design of a Broadband Circular Waveguide Feed
In this chapter the design of a broadband circular waveguide feed is
presented At microwave frequencies the feed is often a circular waveguide
with chokes and corrugations around the aperture Chokes and corrugations
equalize E- and H-plane patterns and reduce the back radiation
The proposed feed is designed to operate over 10-18GHz The design starts
with the optimization of the coaxial-to-rectangular waveguide adapter
employed for good mode purity over a broad frequency range Next a
rectangular-to-circular waveguide transition is optimized Finally chokes and
corrugations are designed for improved pattern symmetry and low back
radiation
The proposed feed structure is shown in Fig 51 The feed consist of the
following parts a coaxial-to-rectangular waveguide adapter a rectangular-to-
circular waveguide transition a circular waveguide section four quarter-wave
chokes around the feeds aperture and four corrugations on the feeds outer
surface
The computer simulation shows the above arrangement offers good radiation
patterns over a broad frequency range The broadband operation is obtained
by exciting the TE11 mode in the circular waveguide using the TE10 mode of
the rectangular waveguide which is in turn excited by a coaxial probe
-51-
Chokes
Coaxial-to-waveguide transition
Circular wavguide
Corrugations
Mode transition
(a)
(b)
Fig 51 Structure of the proposed broadband circular waveguide feed
(a) CAD model and (b) cross-sectional view
For the coaxial-to-rectangular waveguide adapter an SMA connector with
the probe diameter of 127 mm is employed The coaxial probe inserted into
the waveguide energizes the feed and excites the dominant TE10 mode in
-52-
the rectangular waveguide The impedance matching is achieved by adjusting
the probe distance sp from the back short and the probe length lp
(a)
(b)
Fig 52 Reflection coefficient of the coaxial-to-rectangular adapter versus
(a) probe length lp and (b) the probe position sp
Fig 52 shows the reflection coefficient versus the various values of probe
lengths lp and probe positions sp The probe length lp is adjusted to obtain
antenna impedance matching and the probe distance sp is adjusted to obtain a
-53-
desired resonant frequency
Next a transition between rectangular and circular waveguide is designed
The transition section converts the TE10 mode in the rectangular waveguide to
TE11 mode in the circular waveguide and vice versa The transition is built
in a form of a taper for easy fabrication[22]
(a)
(b)
Fig 53 Structure of the rectangular-to-circular waveguide transition
(a) 3D view and (b) cross sectional view
The dimensions of the final optimized transition are as follows The length
of the rectangular waveguide section is 143mm The rectangular waveguides
width a and height b are 207mm and 857mm respectively The length of
the circular waveguide section is 143mm The inside diameter of the circular
-54-
waveguide is 207mm(097 wavelength at 14GHz) The length of transition
region ltr is 4465mm(approximately equal to 2λ0 at 14GHz) Fig 54 shows
the field distribution inside the mode converter
(a)
(b)
Fig 54 Field distribution inside the mode converter at
(a) 10GHz (b) 14GHz and (c) 18GHz
-55-
(c)
Fig 54 continued
Finally multiple chokes are investigated Figs 55 56 and 57 show the
feed performance without chokes The reflection coefficient is less than -10dB
over 10-19GHz The antenna has a gain of 921dB to 1189dB over
10-19GHz
Fig 55 Reflection coefficient of the broadband circular waveguide feed
without chokes and corrugations
-56-
(a)
(b)
(c)
Fig 56 E- and H-plane patterns of the broadband circular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-57-
(d)
(e)
Fig 56 continued
-58-
(a)
(b)
Fig 57 2D radiation patterns of the broadband cicular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-59-
(c)
(d)
Fig 57 continued
-60-
(e)
Fig 57 continued
To achieve equal beamwidths in E and H planes over a wide frequency
range chokes and corrugations are employed Table51 summarizes the
performance of a feed without chokes and corrugations
Table 51 Performance of the broadband circular waveguide feed without
chokes and corrugations
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
1000 940 6061 15
1200 972 6159 17
1400 920 5957 21
1600 1070 4751 29
1800 1188 5352 21
-61-
Four quarter-wavelength chokes are introduced in the feed design which
has a slot depth of 75mm and slot width of 09mm The choke slot spacing
is 18mm The choke design is investigated by applying the choke one by
one and the effect on the E- and H-plane patterns are observed as illustrated
in Figs 58 and 59 The use of chokes makes the E-plane pattern narrower
The H-plane pattern is not affected Chokes increase the gain slightly and
reduce back radiation
(a)
(b)
Fig 58 Effect of chokes on the E-plane pattern of the broadband circular
waveguide feed at (a) 10GHz(b) 12GHz (c) 14GHz (d) 16GHz and (e)
18GHz
-62-
(c)
(d)
(e)
Fig 58 continued
-63-
(a)
(b)
(c)
Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-64-
(d)
(e)
Fig 59 continued
-65-
Fig 510 shows the feed performance versus the choke depth When the
choke depth is varied from 535mm to 95mm the E- and H-plane patterns
are strongly affected The optimum value of choke depth is 75mm(035λ0 at
14GHz) which gives equal E- and H-plane radiation patterns and leads to
low back radiation
Fig 511 shows the feed performance versus the choke slot width tch The
choke slot width is varied from 09mm to 21mm Radiation patterns and
reflection coefficients are not sensitive to the choke slot width The final
choke slot width is selected to be 09mm considering the feed diameter
minimization and the manufacturability The overall diameter of the proposed
feed is 369mm which is increased from the 207mm of the waveguide
inside diameter due to the use of four chokes
-66-
(a)
(b)
(c)
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection coefficient
-67-
(a)
(b)
(c)
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and (c)
reflection coefficient
-68-
Next we investigated corrugations placed on the outer wall of the feed
Four corrugations applied to the outer surface of the circular waveguide The
corrugation depth is 465mm(0215λ0 at 14GHz) The primary purpose of
using corrugations is to further reduce the back radiation Increasing the
number of corrugations beyond four has little effect in reducing the back
radiation
Figs 512 and 513 show the effect of corrugations on the E- and H-plane
patterns Fig 514 shows the parametric study of the corrugation depth lcor
The corrugation depth is varied from 40mm and 645mm The optimum
value of the corrugation depth is found to be 465mm
-69-
(a)
(b)
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern at (a) 12GHz and (b) 14GHz
-70-
(a)
(b)
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern at (a) 12GHz and (b) 14GHz
-71-
(a)
(b)
(c)
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection coefficient
-72-
The phase center location is important in placing the feed in a reflector
antenna[8] The phase center variation with frequency should be small Fig
515 shows the effect of chokes and corrugations on the phase center The
curve with circle corresponds to the case without chokes and corrugations
The phase center varies from -326mm and -190mm away from the feeds
aperture plane It means the phase center is located inside the waveguide
The curve with triangles corresponds to the case with chokes The curve with
squares to the case with chokes and corrugations The phase center varies
from 0mm to -302mm
From Fig 515 we can observed that phase center variation reduced by the
corrugation and three cases phase center calculated in φ=450 plane
parameter sweep values are given in Table 52
10 12 14 16 181
0
-1
-2
-3
-4
-5
-6
Pha
se c
ente
r (m
m)
Frequency (GHz)
choke+corrugatuion without choke corrugation with choke
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
-73-
Frequency
(GHz)
Phase center from the aperture plane
(mm)
Without
chokes and
corrugations
With
chokes
With chokes
and
corrugations
1000 -326 062 000
1100 -187 030 -002
1200 -563 -208 -065
1300 -296 -154 -202
1400 -319 -314 -302
1500 -201 -203 -241
1600 -242 -233 -207
1700 -208 -208 -186
1800 -190 -157 -132
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
Based on the foregoing parametric studies optimum dimensions of the
broadband circular waveguide feed are obtained as shown in Table 53
-74-
Table 53 Optimum dimensions of the broadband circular waveguide feed
Parameter Designation Value (mm)
2a Waveguide inside diameter 2070
d Waveguide outside diameter 3690
lcrLength of the circular waveguide section 1430
m Distance between the aperture plane and the first corrugation 950
xDistance from the last corrugation to the end of the cylindrical outer surface
550
ltrLength of the rectangular-to-circularwaveguide transition 4465
lrcLength of the rectangular waveguide section 1430
tch Choke slot width 090
lch Choke depth 750
t Choke metal width 090
lcor Corrugation depth 465
tcor Corrugation metal width 100
s Corrugation slot width 10
lp Probe length 530
sp Probe position from the back short 530
din Probe diameter 127
b Inside height of the rectangular waveguide 857
tw Waveguide wall thickness 500
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-12-
Fig 26 Reflection coefficient of a square waveguide open end radiator
(a)
Fig 27 2D radiation patterns of a square waveguide radiator
at (a) 10GHz (b) 14GHz and (c) 18GHz
-13-
(b)
(c)
Fig 27 continued
-14-
(a)
(b)
(c)
Fig 28 E-plane and H-plane patterns of square waveguide open radiator
at (a) 10GHz(b) 14GHz and (c) 18GHz
-15-
Table 22 Properties of a square waveguide open end radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 69 71 11
14 47 60 25
18 58 62 16
The radiation pattern symmetry and back radiation performance of the
square waveguide are inferior to those of a circular waveguide
23 Probe-Fed Circular Waveguide Radiator
In Section 21 the radiation properties of a TE11-mode excited waveguide
is investigated In this section a circular waveguide fed by a coaxial probe
shown in Fig 29 is studied
The coaxial probes diameter is 127mm With the Teflon dielectric the
50-ohm coaxial lines outer conductor has a diameter of 41mm For a
circular waveguide the wave impedance of the TE11 mode is given by
∙ (28)
where λg is the guided wavelength given by
(29)
-16-
(a) (b)
Fig 29 Probe-fed circular waveguide radiator (a) Front view and (b) side
view
The combination of the probe length and the probe position from the
shorted wall enables a good impedance matching The probe distance sp from
the back short is close to a quarter wavelength at the design frequency
The designed feed has the following dimension d = 2053mm lp = 42
mm sp = 534mm wall thickness = 05mm and feed length = 400mm
Fig 210 shows the reflection coefficient of the designed probe-fed
circular waveguide radiator The reflection coefficient is less than -10dB over
138-187GHz Fig 211 and 212 shows the E-plane and H-plane radiation
patterns and 2D radiation patterns of the coaxial-to-circular waveguide
transition The radiation patterns symmetry distorted because of the high order
modes The coaxial-to-circular waveguide transition has 73dB 84dB and
79dB gain at 10GHz 14GHz and 18GHz frequencies respectively Table 23
shows the properties of the coaxial-to-circular waveguide transition
-17-
Fig 210 Reflection coefficient of the probe-fed circular waveguide radiator
(a)
Fig 211 2D radiation pattern of the probe-fed circular waveguide radiator
at (a) 10GHz (b) 14GHz and (c) 18GHz
-18-
(b)
(c)
Fig 211 continued
-19-
(a)
(b)
(c)
Fig 212 E- and H-plane patterns of the probe-fed circular waveguide
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-20-
Table 23 Properties of the probe-fed circular waveguide radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 73 70 1414 83 57 17
18 60 52 30
When a circular waveguide radiator is fed by a coaxial probe its radiation
properties are not good due to the excitation of higher-order modes
Therefore a probe-fed circular waveguide radiator can be used as a feed only
over a narrow frequency range
24 Probe-Fed Square Waveguide Radiator
In this section a probe-fed square waveguide radiator is investigated Fig
213 shows a coaxial probe-fed square waveguide radiator The designed
radiator has the following dimension a = b = 157mm lp = 35 mm sp =
50 mm wall thickness = 05mm and feed length = 40mm
(a) (b)
Fig 213 Probe-fed square waveguide radiator (a) Front view and (b) side
view
-21-
Fig 214 shows the 2D radiation patterns of the radiator at 10GHz
14GHz and 18GHz Fig 215 shows E- and H-plane patterns of the radiator
Fig 216 shows the reflection coefficient of the probe-fed square waveguide
radiator The reflection coefficient is less than -10dB over 13-20GHz Table
24 summarizes the properties of the probe-fed square waveguide radiator
(a)
Fig 214 2D radiation patterns of the probe-fed square waveguide radiator at
(a) 10GHz (b) 14GHz and (c) 18GHz
-22-
(b)
(c)
Fig 214 continued
-23-
(a)
(b)
(c)
Fig 216 E-plane and H-plane patterns of the probe-fed square waveguide
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-24-
Fig 216 Reflection coefficient of the probe-fed square waveguide radiator
Table 24 Properties of the probe-fed square waveguide radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 73 71 12
14 85 63 1418 27 65 28
When a square waveguide radiator is fed by a coaxial probe its radiation
properties are not good due to the excitation of higher-order modes as in the
case of the probe-fed circular waveguide radiator A probe-fed square
waveguide radiator can be used as a feed only over a narrow frequency
range
-25-
III Design of Compact Circular Waveguide Feeds
In this chapter the feed design is presented for a prime-focus reflector
antenna The prime-focus paraboloid reflector is one of the most commonly
used high-gain antenna It has been used in earth-station antennas and radio
telescopes It consists of a paraboloid reflector with a feed system at its focal
point
The feed should radiate a low level of cross-polar power over the
operating frequency These conditions not easy to achieve and most prime
focus feeds are compromises The shape and characteristic of the radiation
pattern of the feed are the most important parameter because these will
directly influence the fields which are directed at a reflector[6] Other
electrical factors which relevant to the choice of a feed are the cross-polar
level the gain efficiency the bandwidth and impedance matching
31 Narrow-Band Circular Waveguide Feed
Fig 31 shows the proposed narrow-band circular waveguide feed and its
design variables The feed consists of a circular waveguide open end excited
by a TE11 dominant mode A quarter wave choke is applied along the
circular aperture of the waveguide to equalize E- and H-plane radiation
patterns and to suppress the back radiation A dielectric ring is used to
control the radiation pattern and change the power distribution over the
aperture The control of the amplitude over the aperture are essential to the
design of symmetric radiation pattern The material used for dielectric loading
-26-
is the monocast(MC) nylon with a dielectric constant of 30 The feed is
designed to operate over 171-197GHz
(a)
(b)
Fig 31 Narrow-band circular waveguide feed (a) CAD model and (b) a
cross sectional view
The impedance matching is achieved by a proper combination of the probe
height lp and its distance sp from the waveguide shorted end Here the
-27-
circular waveguide is terminated with an open end with a wall thickness of
2mm radiating into the free space
Fig 32 shows the effect of the probe length lp and the probe distance sp
on the reflection coefficient The best performance is obtained when lp =
363mm and sp = 616mm The feeds reflection coefficient is less than -10dB
over 170-195GHz
(a)
(b)
Fig 32 Effect of the (a) the probe length lp and (b) the probe
distance sp on the reflection coefficient
-28-
Fig 33 shows the effect of the choke depth The E-plane pattern is more
sensitive to the choke depth than the H-plane pattern The choke depth has a
strong influence on the reflection coefficient when it is 360mm By properly
choosing the choke depth we can equalize the E- and H-plane patterns The
optimum value of the choke depth is 410mm which is 0249λ0 at 1825GHz
The choke slot width tch in the range of 06-12mm has almost no effect
on the H-plane pattern and the reflection coefficient For the E-plane pattern
tch of 12mm has some effect on the E-plane radiation pattern as shown in
Fig 34
Fig 35 shows the feed performance versus the dielectric ring length We
observe in Fig 35 that the dielectric length ld has an optimum value of
1168mm which does no effect on the H-plane pattern and tha the value of
1048mm has some effect on the E-plane pattern and the reflection
coefficient
Fig 36 shows E-plane and H-plane patterns and the reflection coefficient
versus the dielectric thickness With the optimum value of the dielectric
thickness t obtained from the Fig 36 is 155mm The larger values of td has
much stronger effects on the E-plane pattern and the reflection coefficient
The H-plane pattern is not sensitive to the dielectric ring thickness
-29-
(a)
(b)
(c)
Fig 33 Feed performance versus the choke depth (a) E-plane pattern
(b) H-plane pattern and (c) reflection coefficient
-30-
(a)
(b)
(c)
Fig 34 Feed performance versus the choke slot width (a) E-plane pattern
(b) H-plane pattern and (c) reflection coefficient
-31-
(a)
(b)
(c)
Fig 35 Feed performance versus the dielectric ring length (a) E-plane
pattern (b) H-plane pattern and (c) reflection coefficient
-32-
(a)
(b)
(c)
Fig 36 Feed performance versus the dielectric ring thickness (a) E-plane
pattern(b) H-plane pattern and (c) reflection coefficient
-33-
From the above parametric analysis an optimum feed design is obtained
The result is shown in Table 31 Fig 37 shows the 2D gain patterns of
designed feed The antenna has a gain of 903dB 933dB and 956dB at
171GHz 1825GHz and 19GHz respectively
Fig 38 shows E- and H-plane radiation patterns of the designed feed The
feed has E- and H-plane 10-dB beamwidths of 60 and 59 degrees at 17GHz
The feed has a front-to-back ration of 1900dB 2490dB and 2200dB at
171GHz 1825GHz and 19GHz respectively Table 32 summarizes the
performance of the designed narrow-band circular waveguide feed
The designed feed has a greatly improved performance over that of a
simple coax-fed feed described in Section 23
Table 31 Dimensions of the designed narrow-band circular feed
Parameter Designation Value(mm)
a Waveguide inside radius 640
l Feed length 2890
lp Probe length 363
sp Probe position from the back short 616
din Probe diameter 127
dout Diameter of coaxial cables outer conductor 400
t Thickness of choked wall 050
tch Choke slot width 100
lch Choke depth 410
ld Dielectric ring length 1168
td Dielectric ring thickness 155
d1 Waveguide outside diameter 1680
-34-
(a)
(b)
Fig 37 2D gain patterns of the narrow-band circular waveguide feed at
(a) 17GHz (b) 1825GHz and (c) 19GHz
-35-
(c)
Fig 37 continued
-36-
(a)
(b)
(c)
Fig 38 E- and H-plane patterns of the narrow-band circular waveguide feed
at (a) 10GHz (b) 1825GHz and (c) 195GHz
-37-
Frequency(GHz)
Gain(dB)
E-H-plane10-dB beamwidths
(deg)
Front-to-back ratio(dB)
Phase centerlocation
(From feeds aperture plane
toward reflector)
(mm)
1700 903 6059 20 062
1825 933 6060 25 004
1900 956 5759 22 007
Table 32 Performance of the narrow-band circular waveguide feed
The designed narrow-band feed is fabricated and its performance is
measured and compared with the simulation results The designed feed is
fabricated in a numerically-controlled machining center The fabricated antenna
is shown in Fig 39
Fig 39 Photograph of the fabricated feed
-38-
Fig 310 shows a comparison of the measured and simulated reflection
coefficients The measured reflection coefficient is less than -10dB over
171-197GHz The agreement between simulated and measured results are
good
Fig 311 shows the E- and H-plane patterns of the fabricated feed at
187GHz The feed has 90dB gain simulation and measurement results are in
good agreement
The fabricated antennarsquos 10dB beamwidth is 60 degrees in both E and H
planes at 187GHz The front-to-back ratio is 21dB
Fig 310 Reflection coefficient of the fabricated feed
-39-
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Fee
d H
orn
Gain
- d
B
Angle - degree
(a)
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Feed H
orn
Gain
- d
B
Angle - degree
(b)
Fig 311 Gain patterns of the fabricated feed at 187 GHz (a) E-plane and
(b) H-plane
-40-
IV Design of Circular Waveguide Feeds Loaded with a
Dielectric Rod
In this section circular waveguide feeds loaded with a dielectric rod feed
are investigated A comprehensive discussion of the circular waveguide loaded
with a dielectric rod is given by Kumar[7] Inserting a dielectric material
inside the circular waveguide improves the E- and H-plane pattern symmetry
In general dielectric-loaded circular waveguide feeds show good performance
only over a narrow bandwidth
Fig 41 shows the geometry of a circular waveguide loaded with a
dielectric rod The waveguide length is 400mm and the wall thickness is
05mm The dielectric rods diameter is 207mm The dielectric rod is
extended 05 wavelength beyond the waveguide open end The dielectric
constant εr is changed and the feeds performance is observed
Fig 41 Geometry of a circular waveguide loaded with a uniform dielectric
rod
-41-
Fig 42 is the radiation pattern of the feed with εr = 25 and L = 05λ0 at
9GHz E- and H-plane 10-dB beamwidths are 810 and 807 degrees
respectively The front-to-back ratio is 18dB The antenna gain is 71dB
(a)
(b)
Fig 42 Radiation pattern at 9GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 05λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-42-
Fig 43 shows the radiation pattern of the feed with εr = 21 at 10GHz
E- and H-plane 10-dB beamwidths are 70 and 71 degrees respectively The
front-to-back ratio is 19dB The antenna gain is 83dB
(a)
(b)
Fig 43 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 21 and L = 05λ0 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-43-
Fig 44 shows the radiation pattern of the feed with εr = 30 at 8GHz
E- and H-plane 10-dB beamwidths are 83 and 824 degrees respectively The
front-to-back ratio is 17dB The antenna gain is 73dB
(a)
(b)
Fig 44 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 30 and L = 05λ0 at 8GHz (a) 2D radiation pattern
and (b) E- and H-plane patterns
-44-
Fig 45 shows the radiation pattern of the feed with εr = 50 at 18GHz
E- and H-plane 10-dB beamwidths are 56 and 54 degrees respectively The
front-to-back ratio is 27dB The antenna gain is 105dB The feed has a good
pattern symmetry and low back radiation
(a)
(b)
Fig 45 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 50 and L = 05λ0 at 18GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-45-
Fig 46 is the radiation pattern of the feed with εr = 25 and L = 10λ0 at
10GHz E- and H-plane 10-dB beamwidths are 50 and 48 degrees
respectively The front-to-back ratio is 16dB The antenna gain is 105dB
(a)
(b)
Fig 46 Radiation pattern at 10GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 10λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-46-
Fig 47 shows the geometry of a circular waveguide with a tapered
dielectric rod The designed feed has the following dimension L = 1λ0 d =
1λ0 and εr =25 at 10GHz The waveguide length is 40mm and the wall
thickness is 05mm
L
Dielectricd3
Fig 47 Geometry of a circular waveguide loaded with a tapered dielectric
rod
Fig 48 shows the radiatio pattern of the designed feed E- and H-plane
10-dB beamwidths are 575 and 564 degrees respectively The front-to-back
ratio is 377dB The antenna gain is 94dB The designed feed has an
excellent beamwidth symmetry and a very low back radiation
-47-
(a)
(b)
Fig 48 Radiation pattern of a circular waveguide loaded with a tapered
dielectric rod with L = 1λ0 d = 1λ0 and εr =25 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-48-
Fig 49 shows the geometry of a spherical ended dielectric rod feed
diameter of 06λ0 at 10GHz with a dielectric constant of 25 and L= 03λ0
Fig 410 shows the radiation patterns of the designed feed E- and H-plane
10-dB beamwidths are both 63 degrees The front-to-back ratio is 24dB The
antenna gain is 864dB
Fig 49 Geometry of a circular waveguide loaded with a spherical ended
dielectric rod
-49-
(a)
(b)
Fig 410 Radiation pattern of a circular waveguide loaded wht a spherical
ended dielectric rod with d = 06λ0 L = 03λ0 and εr =25 at 10GHz (a) 3D
radiation pattern and (b) E- and H-plane patterns
-50-
V Design of a Broadband Circular Waveguide Feed
In this chapter the design of a broadband circular waveguide feed is
presented At microwave frequencies the feed is often a circular waveguide
with chokes and corrugations around the aperture Chokes and corrugations
equalize E- and H-plane patterns and reduce the back radiation
The proposed feed is designed to operate over 10-18GHz The design starts
with the optimization of the coaxial-to-rectangular waveguide adapter
employed for good mode purity over a broad frequency range Next a
rectangular-to-circular waveguide transition is optimized Finally chokes and
corrugations are designed for improved pattern symmetry and low back
radiation
The proposed feed structure is shown in Fig 51 The feed consist of the
following parts a coaxial-to-rectangular waveguide adapter a rectangular-to-
circular waveguide transition a circular waveguide section four quarter-wave
chokes around the feeds aperture and four corrugations on the feeds outer
surface
The computer simulation shows the above arrangement offers good radiation
patterns over a broad frequency range The broadband operation is obtained
by exciting the TE11 mode in the circular waveguide using the TE10 mode of
the rectangular waveguide which is in turn excited by a coaxial probe
-51-
Chokes
Coaxial-to-waveguide transition
Circular wavguide
Corrugations
Mode transition
(a)
(b)
Fig 51 Structure of the proposed broadband circular waveguide feed
(a) CAD model and (b) cross-sectional view
For the coaxial-to-rectangular waveguide adapter an SMA connector with
the probe diameter of 127 mm is employed The coaxial probe inserted into
the waveguide energizes the feed and excites the dominant TE10 mode in
-52-
the rectangular waveguide The impedance matching is achieved by adjusting
the probe distance sp from the back short and the probe length lp
(a)
(b)
Fig 52 Reflection coefficient of the coaxial-to-rectangular adapter versus
(a) probe length lp and (b) the probe position sp
Fig 52 shows the reflection coefficient versus the various values of probe
lengths lp and probe positions sp The probe length lp is adjusted to obtain
antenna impedance matching and the probe distance sp is adjusted to obtain a
-53-
desired resonant frequency
Next a transition between rectangular and circular waveguide is designed
The transition section converts the TE10 mode in the rectangular waveguide to
TE11 mode in the circular waveguide and vice versa The transition is built
in a form of a taper for easy fabrication[22]
(a)
(b)
Fig 53 Structure of the rectangular-to-circular waveguide transition
(a) 3D view and (b) cross sectional view
The dimensions of the final optimized transition are as follows The length
of the rectangular waveguide section is 143mm The rectangular waveguides
width a and height b are 207mm and 857mm respectively The length of
the circular waveguide section is 143mm The inside diameter of the circular
-54-
waveguide is 207mm(097 wavelength at 14GHz) The length of transition
region ltr is 4465mm(approximately equal to 2λ0 at 14GHz) Fig 54 shows
the field distribution inside the mode converter
(a)
(b)
Fig 54 Field distribution inside the mode converter at
(a) 10GHz (b) 14GHz and (c) 18GHz
-55-
(c)
Fig 54 continued
Finally multiple chokes are investigated Figs 55 56 and 57 show the
feed performance without chokes The reflection coefficient is less than -10dB
over 10-19GHz The antenna has a gain of 921dB to 1189dB over
10-19GHz
Fig 55 Reflection coefficient of the broadband circular waveguide feed
without chokes and corrugations
-56-
(a)
(b)
(c)
Fig 56 E- and H-plane patterns of the broadband circular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-57-
(d)
(e)
Fig 56 continued
-58-
(a)
(b)
Fig 57 2D radiation patterns of the broadband cicular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-59-
(c)
(d)
Fig 57 continued
-60-
(e)
Fig 57 continued
To achieve equal beamwidths in E and H planes over a wide frequency
range chokes and corrugations are employed Table51 summarizes the
performance of a feed without chokes and corrugations
Table 51 Performance of the broadband circular waveguide feed without
chokes and corrugations
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
1000 940 6061 15
1200 972 6159 17
1400 920 5957 21
1600 1070 4751 29
1800 1188 5352 21
-61-
Four quarter-wavelength chokes are introduced in the feed design which
has a slot depth of 75mm and slot width of 09mm The choke slot spacing
is 18mm The choke design is investigated by applying the choke one by
one and the effect on the E- and H-plane patterns are observed as illustrated
in Figs 58 and 59 The use of chokes makes the E-plane pattern narrower
The H-plane pattern is not affected Chokes increase the gain slightly and
reduce back radiation
(a)
(b)
Fig 58 Effect of chokes on the E-plane pattern of the broadband circular
waveguide feed at (a) 10GHz(b) 12GHz (c) 14GHz (d) 16GHz and (e)
18GHz
-62-
(c)
(d)
(e)
Fig 58 continued
-63-
(a)
(b)
(c)
Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-64-
(d)
(e)
Fig 59 continued
-65-
Fig 510 shows the feed performance versus the choke depth When the
choke depth is varied from 535mm to 95mm the E- and H-plane patterns
are strongly affected The optimum value of choke depth is 75mm(035λ0 at
14GHz) which gives equal E- and H-plane radiation patterns and leads to
low back radiation
Fig 511 shows the feed performance versus the choke slot width tch The
choke slot width is varied from 09mm to 21mm Radiation patterns and
reflection coefficients are not sensitive to the choke slot width The final
choke slot width is selected to be 09mm considering the feed diameter
minimization and the manufacturability The overall diameter of the proposed
feed is 369mm which is increased from the 207mm of the waveguide
inside diameter due to the use of four chokes
-66-
(a)
(b)
(c)
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection coefficient
-67-
(a)
(b)
(c)
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and (c)
reflection coefficient
-68-
Next we investigated corrugations placed on the outer wall of the feed
Four corrugations applied to the outer surface of the circular waveguide The
corrugation depth is 465mm(0215λ0 at 14GHz) The primary purpose of
using corrugations is to further reduce the back radiation Increasing the
number of corrugations beyond four has little effect in reducing the back
radiation
Figs 512 and 513 show the effect of corrugations on the E- and H-plane
patterns Fig 514 shows the parametric study of the corrugation depth lcor
The corrugation depth is varied from 40mm and 645mm The optimum
value of the corrugation depth is found to be 465mm
-69-
(a)
(b)
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern at (a) 12GHz and (b) 14GHz
-70-
(a)
(b)
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern at (a) 12GHz and (b) 14GHz
-71-
(a)
(b)
(c)
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection coefficient
-72-
The phase center location is important in placing the feed in a reflector
antenna[8] The phase center variation with frequency should be small Fig
515 shows the effect of chokes and corrugations on the phase center The
curve with circle corresponds to the case without chokes and corrugations
The phase center varies from -326mm and -190mm away from the feeds
aperture plane It means the phase center is located inside the waveguide
The curve with triangles corresponds to the case with chokes The curve with
squares to the case with chokes and corrugations The phase center varies
from 0mm to -302mm
From Fig 515 we can observed that phase center variation reduced by the
corrugation and three cases phase center calculated in φ=450 plane
parameter sweep values are given in Table 52
10 12 14 16 181
0
-1
-2
-3
-4
-5
-6
Pha
se c
ente
r (m
m)
Frequency (GHz)
choke+corrugatuion without choke corrugation with choke
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
-73-
Frequency
(GHz)
Phase center from the aperture plane
(mm)
Without
chokes and
corrugations
With
chokes
With chokes
and
corrugations
1000 -326 062 000
1100 -187 030 -002
1200 -563 -208 -065
1300 -296 -154 -202
1400 -319 -314 -302
1500 -201 -203 -241
1600 -242 -233 -207
1700 -208 -208 -186
1800 -190 -157 -132
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
Based on the foregoing parametric studies optimum dimensions of the
broadband circular waveguide feed are obtained as shown in Table 53
-74-
Table 53 Optimum dimensions of the broadband circular waveguide feed
Parameter Designation Value (mm)
2a Waveguide inside diameter 2070
d Waveguide outside diameter 3690
lcrLength of the circular waveguide section 1430
m Distance between the aperture plane and the first corrugation 950
xDistance from the last corrugation to the end of the cylindrical outer surface
550
ltrLength of the rectangular-to-circularwaveguide transition 4465
lrcLength of the rectangular waveguide section 1430
tch Choke slot width 090
lch Choke depth 750
t Choke metal width 090
lcor Corrugation depth 465
tcor Corrugation metal width 100
s Corrugation slot width 10
lp Probe length 530
sp Probe position from the back short 530
din Probe diameter 127
b Inside height of the rectangular waveguide 857
tw Waveguide wall thickness 500
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-13-
(b)
(c)
Fig 27 continued
-14-
(a)
(b)
(c)
Fig 28 E-plane and H-plane patterns of square waveguide open radiator
at (a) 10GHz(b) 14GHz and (c) 18GHz
-15-
Table 22 Properties of a square waveguide open end radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 69 71 11
14 47 60 25
18 58 62 16
The radiation pattern symmetry and back radiation performance of the
square waveguide are inferior to those of a circular waveguide
23 Probe-Fed Circular Waveguide Radiator
In Section 21 the radiation properties of a TE11-mode excited waveguide
is investigated In this section a circular waveguide fed by a coaxial probe
shown in Fig 29 is studied
The coaxial probes diameter is 127mm With the Teflon dielectric the
50-ohm coaxial lines outer conductor has a diameter of 41mm For a
circular waveguide the wave impedance of the TE11 mode is given by
∙ (28)
where λg is the guided wavelength given by
(29)
-16-
(a) (b)
Fig 29 Probe-fed circular waveguide radiator (a) Front view and (b) side
view
The combination of the probe length and the probe position from the
shorted wall enables a good impedance matching The probe distance sp from
the back short is close to a quarter wavelength at the design frequency
The designed feed has the following dimension d = 2053mm lp = 42
mm sp = 534mm wall thickness = 05mm and feed length = 400mm
Fig 210 shows the reflection coefficient of the designed probe-fed
circular waveguide radiator The reflection coefficient is less than -10dB over
138-187GHz Fig 211 and 212 shows the E-plane and H-plane radiation
patterns and 2D radiation patterns of the coaxial-to-circular waveguide
transition The radiation patterns symmetry distorted because of the high order
modes The coaxial-to-circular waveguide transition has 73dB 84dB and
79dB gain at 10GHz 14GHz and 18GHz frequencies respectively Table 23
shows the properties of the coaxial-to-circular waveguide transition
-17-
Fig 210 Reflection coefficient of the probe-fed circular waveguide radiator
(a)
Fig 211 2D radiation pattern of the probe-fed circular waveguide radiator
at (a) 10GHz (b) 14GHz and (c) 18GHz
-18-
(b)
(c)
Fig 211 continued
-19-
(a)
(b)
(c)
Fig 212 E- and H-plane patterns of the probe-fed circular waveguide
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-20-
Table 23 Properties of the probe-fed circular waveguide radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 73 70 1414 83 57 17
18 60 52 30
When a circular waveguide radiator is fed by a coaxial probe its radiation
properties are not good due to the excitation of higher-order modes
Therefore a probe-fed circular waveguide radiator can be used as a feed only
over a narrow frequency range
24 Probe-Fed Square Waveguide Radiator
In this section a probe-fed square waveguide radiator is investigated Fig
213 shows a coaxial probe-fed square waveguide radiator The designed
radiator has the following dimension a = b = 157mm lp = 35 mm sp =
50 mm wall thickness = 05mm and feed length = 40mm
(a) (b)
Fig 213 Probe-fed square waveguide radiator (a) Front view and (b) side
view
-21-
Fig 214 shows the 2D radiation patterns of the radiator at 10GHz
14GHz and 18GHz Fig 215 shows E- and H-plane patterns of the radiator
Fig 216 shows the reflection coefficient of the probe-fed square waveguide
radiator The reflection coefficient is less than -10dB over 13-20GHz Table
24 summarizes the properties of the probe-fed square waveguide radiator
(a)
Fig 214 2D radiation patterns of the probe-fed square waveguide radiator at
(a) 10GHz (b) 14GHz and (c) 18GHz
-22-
(b)
(c)
Fig 214 continued
-23-
(a)
(b)
(c)
Fig 216 E-plane and H-plane patterns of the probe-fed square waveguide
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-24-
Fig 216 Reflection coefficient of the probe-fed square waveguide radiator
Table 24 Properties of the probe-fed square waveguide radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 73 71 12
14 85 63 1418 27 65 28
When a square waveguide radiator is fed by a coaxial probe its radiation
properties are not good due to the excitation of higher-order modes as in the
case of the probe-fed circular waveguide radiator A probe-fed square
waveguide radiator can be used as a feed only over a narrow frequency
range
-25-
III Design of Compact Circular Waveguide Feeds
In this chapter the feed design is presented for a prime-focus reflector
antenna The prime-focus paraboloid reflector is one of the most commonly
used high-gain antenna It has been used in earth-station antennas and radio
telescopes It consists of a paraboloid reflector with a feed system at its focal
point
The feed should radiate a low level of cross-polar power over the
operating frequency These conditions not easy to achieve and most prime
focus feeds are compromises The shape and characteristic of the radiation
pattern of the feed are the most important parameter because these will
directly influence the fields which are directed at a reflector[6] Other
electrical factors which relevant to the choice of a feed are the cross-polar
level the gain efficiency the bandwidth and impedance matching
31 Narrow-Band Circular Waveguide Feed
Fig 31 shows the proposed narrow-band circular waveguide feed and its
design variables The feed consists of a circular waveguide open end excited
by a TE11 dominant mode A quarter wave choke is applied along the
circular aperture of the waveguide to equalize E- and H-plane radiation
patterns and to suppress the back radiation A dielectric ring is used to
control the radiation pattern and change the power distribution over the
aperture The control of the amplitude over the aperture are essential to the
design of symmetric radiation pattern The material used for dielectric loading
-26-
is the monocast(MC) nylon with a dielectric constant of 30 The feed is
designed to operate over 171-197GHz
(a)
(b)
Fig 31 Narrow-band circular waveguide feed (a) CAD model and (b) a
cross sectional view
The impedance matching is achieved by a proper combination of the probe
height lp and its distance sp from the waveguide shorted end Here the
-27-
circular waveguide is terminated with an open end with a wall thickness of
2mm radiating into the free space
Fig 32 shows the effect of the probe length lp and the probe distance sp
on the reflection coefficient The best performance is obtained when lp =
363mm and sp = 616mm The feeds reflection coefficient is less than -10dB
over 170-195GHz
(a)
(b)
Fig 32 Effect of the (a) the probe length lp and (b) the probe
distance sp on the reflection coefficient
-28-
Fig 33 shows the effect of the choke depth The E-plane pattern is more
sensitive to the choke depth than the H-plane pattern The choke depth has a
strong influence on the reflection coefficient when it is 360mm By properly
choosing the choke depth we can equalize the E- and H-plane patterns The
optimum value of the choke depth is 410mm which is 0249λ0 at 1825GHz
The choke slot width tch in the range of 06-12mm has almost no effect
on the H-plane pattern and the reflection coefficient For the E-plane pattern
tch of 12mm has some effect on the E-plane radiation pattern as shown in
Fig 34
Fig 35 shows the feed performance versus the dielectric ring length We
observe in Fig 35 that the dielectric length ld has an optimum value of
1168mm which does no effect on the H-plane pattern and tha the value of
1048mm has some effect on the E-plane pattern and the reflection
coefficient
Fig 36 shows E-plane and H-plane patterns and the reflection coefficient
versus the dielectric thickness With the optimum value of the dielectric
thickness t obtained from the Fig 36 is 155mm The larger values of td has
much stronger effects on the E-plane pattern and the reflection coefficient
The H-plane pattern is not sensitive to the dielectric ring thickness
-29-
(a)
(b)
(c)
Fig 33 Feed performance versus the choke depth (a) E-plane pattern
(b) H-plane pattern and (c) reflection coefficient
-30-
(a)
(b)
(c)
Fig 34 Feed performance versus the choke slot width (a) E-plane pattern
(b) H-plane pattern and (c) reflection coefficient
-31-
(a)
(b)
(c)
Fig 35 Feed performance versus the dielectric ring length (a) E-plane
pattern (b) H-plane pattern and (c) reflection coefficient
-32-
(a)
(b)
(c)
Fig 36 Feed performance versus the dielectric ring thickness (a) E-plane
pattern(b) H-plane pattern and (c) reflection coefficient
-33-
From the above parametric analysis an optimum feed design is obtained
The result is shown in Table 31 Fig 37 shows the 2D gain patterns of
designed feed The antenna has a gain of 903dB 933dB and 956dB at
171GHz 1825GHz and 19GHz respectively
Fig 38 shows E- and H-plane radiation patterns of the designed feed The
feed has E- and H-plane 10-dB beamwidths of 60 and 59 degrees at 17GHz
The feed has a front-to-back ration of 1900dB 2490dB and 2200dB at
171GHz 1825GHz and 19GHz respectively Table 32 summarizes the
performance of the designed narrow-band circular waveguide feed
The designed feed has a greatly improved performance over that of a
simple coax-fed feed described in Section 23
Table 31 Dimensions of the designed narrow-band circular feed
Parameter Designation Value(mm)
a Waveguide inside radius 640
l Feed length 2890
lp Probe length 363
sp Probe position from the back short 616
din Probe diameter 127
dout Diameter of coaxial cables outer conductor 400
t Thickness of choked wall 050
tch Choke slot width 100
lch Choke depth 410
ld Dielectric ring length 1168
td Dielectric ring thickness 155
d1 Waveguide outside diameter 1680
-34-
(a)
(b)
Fig 37 2D gain patterns of the narrow-band circular waveguide feed at
(a) 17GHz (b) 1825GHz and (c) 19GHz
-35-
(c)
Fig 37 continued
-36-
(a)
(b)
(c)
Fig 38 E- and H-plane patterns of the narrow-band circular waveguide feed
at (a) 10GHz (b) 1825GHz and (c) 195GHz
-37-
Frequency(GHz)
Gain(dB)
E-H-plane10-dB beamwidths
(deg)
Front-to-back ratio(dB)
Phase centerlocation
(From feeds aperture plane
toward reflector)
(mm)
1700 903 6059 20 062
1825 933 6060 25 004
1900 956 5759 22 007
Table 32 Performance of the narrow-band circular waveguide feed
The designed narrow-band feed is fabricated and its performance is
measured and compared with the simulation results The designed feed is
fabricated in a numerically-controlled machining center The fabricated antenna
is shown in Fig 39
Fig 39 Photograph of the fabricated feed
-38-
Fig 310 shows a comparison of the measured and simulated reflection
coefficients The measured reflection coefficient is less than -10dB over
171-197GHz The agreement between simulated and measured results are
good
Fig 311 shows the E- and H-plane patterns of the fabricated feed at
187GHz The feed has 90dB gain simulation and measurement results are in
good agreement
The fabricated antennarsquos 10dB beamwidth is 60 degrees in both E and H
planes at 187GHz The front-to-back ratio is 21dB
Fig 310 Reflection coefficient of the fabricated feed
-39-
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Fee
d H
orn
Gain
- d
B
Angle - degree
(a)
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Feed H
orn
Gain
- d
B
Angle - degree
(b)
Fig 311 Gain patterns of the fabricated feed at 187 GHz (a) E-plane and
(b) H-plane
-40-
IV Design of Circular Waveguide Feeds Loaded with a
Dielectric Rod
In this section circular waveguide feeds loaded with a dielectric rod feed
are investigated A comprehensive discussion of the circular waveguide loaded
with a dielectric rod is given by Kumar[7] Inserting a dielectric material
inside the circular waveguide improves the E- and H-plane pattern symmetry
In general dielectric-loaded circular waveguide feeds show good performance
only over a narrow bandwidth
Fig 41 shows the geometry of a circular waveguide loaded with a
dielectric rod The waveguide length is 400mm and the wall thickness is
05mm The dielectric rods diameter is 207mm The dielectric rod is
extended 05 wavelength beyond the waveguide open end The dielectric
constant εr is changed and the feeds performance is observed
Fig 41 Geometry of a circular waveguide loaded with a uniform dielectric
rod
-41-
Fig 42 is the radiation pattern of the feed with εr = 25 and L = 05λ0 at
9GHz E- and H-plane 10-dB beamwidths are 810 and 807 degrees
respectively The front-to-back ratio is 18dB The antenna gain is 71dB
(a)
(b)
Fig 42 Radiation pattern at 9GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 05λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-42-
Fig 43 shows the radiation pattern of the feed with εr = 21 at 10GHz
E- and H-plane 10-dB beamwidths are 70 and 71 degrees respectively The
front-to-back ratio is 19dB The antenna gain is 83dB
(a)
(b)
Fig 43 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 21 and L = 05λ0 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-43-
Fig 44 shows the radiation pattern of the feed with εr = 30 at 8GHz
E- and H-plane 10-dB beamwidths are 83 and 824 degrees respectively The
front-to-back ratio is 17dB The antenna gain is 73dB
(a)
(b)
Fig 44 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 30 and L = 05λ0 at 8GHz (a) 2D radiation pattern
and (b) E- and H-plane patterns
-44-
Fig 45 shows the radiation pattern of the feed with εr = 50 at 18GHz
E- and H-plane 10-dB beamwidths are 56 and 54 degrees respectively The
front-to-back ratio is 27dB The antenna gain is 105dB The feed has a good
pattern symmetry and low back radiation
(a)
(b)
Fig 45 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 50 and L = 05λ0 at 18GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-45-
Fig 46 is the radiation pattern of the feed with εr = 25 and L = 10λ0 at
10GHz E- and H-plane 10-dB beamwidths are 50 and 48 degrees
respectively The front-to-back ratio is 16dB The antenna gain is 105dB
(a)
(b)
Fig 46 Radiation pattern at 10GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 10λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-46-
Fig 47 shows the geometry of a circular waveguide with a tapered
dielectric rod The designed feed has the following dimension L = 1λ0 d =
1λ0 and εr =25 at 10GHz The waveguide length is 40mm and the wall
thickness is 05mm
L
Dielectricd3
Fig 47 Geometry of a circular waveguide loaded with a tapered dielectric
rod
Fig 48 shows the radiatio pattern of the designed feed E- and H-plane
10-dB beamwidths are 575 and 564 degrees respectively The front-to-back
ratio is 377dB The antenna gain is 94dB The designed feed has an
excellent beamwidth symmetry and a very low back radiation
-47-
(a)
(b)
Fig 48 Radiation pattern of a circular waveguide loaded with a tapered
dielectric rod with L = 1λ0 d = 1λ0 and εr =25 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-48-
Fig 49 shows the geometry of a spherical ended dielectric rod feed
diameter of 06λ0 at 10GHz with a dielectric constant of 25 and L= 03λ0
Fig 410 shows the radiation patterns of the designed feed E- and H-plane
10-dB beamwidths are both 63 degrees The front-to-back ratio is 24dB The
antenna gain is 864dB
Fig 49 Geometry of a circular waveguide loaded with a spherical ended
dielectric rod
-49-
(a)
(b)
Fig 410 Radiation pattern of a circular waveguide loaded wht a spherical
ended dielectric rod with d = 06λ0 L = 03λ0 and εr =25 at 10GHz (a) 3D
radiation pattern and (b) E- and H-plane patterns
-50-
V Design of a Broadband Circular Waveguide Feed
In this chapter the design of a broadband circular waveguide feed is
presented At microwave frequencies the feed is often a circular waveguide
with chokes and corrugations around the aperture Chokes and corrugations
equalize E- and H-plane patterns and reduce the back radiation
The proposed feed is designed to operate over 10-18GHz The design starts
with the optimization of the coaxial-to-rectangular waveguide adapter
employed for good mode purity over a broad frequency range Next a
rectangular-to-circular waveguide transition is optimized Finally chokes and
corrugations are designed for improved pattern symmetry and low back
radiation
The proposed feed structure is shown in Fig 51 The feed consist of the
following parts a coaxial-to-rectangular waveguide adapter a rectangular-to-
circular waveguide transition a circular waveguide section four quarter-wave
chokes around the feeds aperture and four corrugations on the feeds outer
surface
The computer simulation shows the above arrangement offers good radiation
patterns over a broad frequency range The broadband operation is obtained
by exciting the TE11 mode in the circular waveguide using the TE10 mode of
the rectangular waveguide which is in turn excited by a coaxial probe
-51-
Chokes
Coaxial-to-waveguide transition
Circular wavguide
Corrugations
Mode transition
(a)
(b)
Fig 51 Structure of the proposed broadband circular waveguide feed
(a) CAD model and (b) cross-sectional view
For the coaxial-to-rectangular waveguide adapter an SMA connector with
the probe diameter of 127 mm is employed The coaxial probe inserted into
the waveguide energizes the feed and excites the dominant TE10 mode in
-52-
the rectangular waveguide The impedance matching is achieved by adjusting
the probe distance sp from the back short and the probe length lp
(a)
(b)
Fig 52 Reflection coefficient of the coaxial-to-rectangular adapter versus
(a) probe length lp and (b) the probe position sp
Fig 52 shows the reflection coefficient versus the various values of probe
lengths lp and probe positions sp The probe length lp is adjusted to obtain
antenna impedance matching and the probe distance sp is adjusted to obtain a
-53-
desired resonant frequency
Next a transition between rectangular and circular waveguide is designed
The transition section converts the TE10 mode in the rectangular waveguide to
TE11 mode in the circular waveguide and vice versa The transition is built
in a form of a taper for easy fabrication[22]
(a)
(b)
Fig 53 Structure of the rectangular-to-circular waveguide transition
(a) 3D view and (b) cross sectional view
The dimensions of the final optimized transition are as follows The length
of the rectangular waveguide section is 143mm The rectangular waveguides
width a and height b are 207mm and 857mm respectively The length of
the circular waveguide section is 143mm The inside diameter of the circular
-54-
waveguide is 207mm(097 wavelength at 14GHz) The length of transition
region ltr is 4465mm(approximately equal to 2λ0 at 14GHz) Fig 54 shows
the field distribution inside the mode converter
(a)
(b)
Fig 54 Field distribution inside the mode converter at
(a) 10GHz (b) 14GHz and (c) 18GHz
-55-
(c)
Fig 54 continued
Finally multiple chokes are investigated Figs 55 56 and 57 show the
feed performance without chokes The reflection coefficient is less than -10dB
over 10-19GHz The antenna has a gain of 921dB to 1189dB over
10-19GHz
Fig 55 Reflection coefficient of the broadband circular waveguide feed
without chokes and corrugations
-56-
(a)
(b)
(c)
Fig 56 E- and H-plane patterns of the broadband circular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-57-
(d)
(e)
Fig 56 continued
-58-
(a)
(b)
Fig 57 2D radiation patterns of the broadband cicular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-59-
(c)
(d)
Fig 57 continued
-60-
(e)
Fig 57 continued
To achieve equal beamwidths in E and H planes over a wide frequency
range chokes and corrugations are employed Table51 summarizes the
performance of a feed without chokes and corrugations
Table 51 Performance of the broadband circular waveguide feed without
chokes and corrugations
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
1000 940 6061 15
1200 972 6159 17
1400 920 5957 21
1600 1070 4751 29
1800 1188 5352 21
-61-
Four quarter-wavelength chokes are introduced in the feed design which
has a slot depth of 75mm and slot width of 09mm The choke slot spacing
is 18mm The choke design is investigated by applying the choke one by
one and the effect on the E- and H-plane patterns are observed as illustrated
in Figs 58 and 59 The use of chokes makes the E-plane pattern narrower
The H-plane pattern is not affected Chokes increase the gain slightly and
reduce back radiation
(a)
(b)
Fig 58 Effect of chokes on the E-plane pattern of the broadband circular
waveguide feed at (a) 10GHz(b) 12GHz (c) 14GHz (d) 16GHz and (e)
18GHz
-62-
(c)
(d)
(e)
Fig 58 continued
-63-
(a)
(b)
(c)
Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-64-
(d)
(e)
Fig 59 continued
-65-
Fig 510 shows the feed performance versus the choke depth When the
choke depth is varied from 535mm to 95mm the E- and H-plane patterns
are strongly affected The optimum value of choke depth is 75mm(035λ0 at
14GHz) which gives equal E- and H-plane radiation patterns and leads to
low back radiation
Fig 511 shows the feed performance versus the choke slot width tch The
choke slot width is varied from 09mm to 21mm Radiation patterns and
reflection coefficients are not sensitive to the choke slot width The final
choke slot width is selected to be 09mm considering the feed diameter
minimization and the manufacturability The overall diameter of the proposed
feed is 369mm which is increased from the 207mm of the waveguide
inside diameter due to the use of four chokes
-66-
(a)
(b)
(c)
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection coefficient
-67-
(a)
(b)
(c)
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and (c)
reflection coefficient
-68-
Next we investigated corrugations placed on the outer wall of the feed
Four corrugations applied to the outer surface of the circular waveguide The
corrugation depth is 465mm(0215λ0 at 14GHz) The primary purpose of
using corrugations is to further reduce the back radiation Increasing the
number of corrugations beyond four has little effect in reducing the back
radiation
Figs 512 and 513 show the effect of corrugations on the E- and H-plane
patterns Fig 514 shows the parametric study of the corrugation depth lcor
The corrugation depth is varied from 40mm and 645mm The optimum
value of the corrugation depth is found to be 465mm
-69-
(a)
(b)
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern at (a) 12GHz and (b) 14GHz
-70-
(a)
(b)
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern at (a) 12GHz and (b) 14GHz
-71-
(a)
(b)
(c)
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection coefficient
-72-
The phase center location is important in placing the feed in a reflector
antenna[8] The phase center variation with frequency should be small Fig
515 shows the effect of chokes and corrugations on the phase center The
curve with circle corresponds to the case without chokes and corrugations
The phase center varies from -326mm and -190mm away from the feeds
aperture plane It means the phase center is located inside the waveguide
The curve with triangles corresponds to the case with chokes The curve with
squares to the case with chokes and corrugations The phase center varies
from 0mm to -302mm
From Fig 515 we can observed that phase center variation reduced by the
corrugation and three cases phase center calculated in φ=450 plane
parameter sweep values are given in Table 52
10 12 14 16 181
0
-1
-2
-3
-4
-5
-6
Pha
se c
ente
r (m
m)
Frequency (GHz)
choke+corrugatuion without choke corrugation with choke
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
-73-
Frequency
(GHz)
Phase center from the aperture plane
(mm)
Without
chokes and
corrugations
With
chokes
With chokes
and
corrugations
1000 -326 062 000
1100 -187 030 -002
1200 -563 -208 -065
1300 -296 -154 -202
1400 -319 -314 -302
1500 -201 -203 -241
1600 -242 -233 -207
1700 -208 -208 -186
1800 -190 -157 -132
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
Based on the foregoing parametric studies optimum dimensions of the
broadband circular waveguide feed are obtained as shown in Table 53
-74-
Table 53 Optimum dimensions of the broadband circular waveguide feed
Parameter Designation Value (mm)
2a Waveguide inside diameter 2070
d Waveguide outside diameter 3690
lcrLength of the circular waveguide section 1430
m Distance between the aperture plane and the first corrugation 950
xDistance from the last corrugation to the end of the cylindrical outer surface
550
ltrLength of the rectangular-to-circularwaveguide transition 4465
lrcLength of the rectangular waveguide section 1430
tch Choke slot width 090
lch Choke depth 750
t Choke metal width 090
lcor Corrugation depth 465
tcor Corrugation metal width 100
s Corrugation slot width 10
lp Probe length 530
sp Probe position from the back short 530
din Probe diameter 127
b Inside height of the rectangular waveguide 857
tw Waveguide wall thickness 500
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-14-
(a)
(b)
(c)
Fig 28 E-plane and H-plane patterns of square waveguide open radiator
at (a) 10GHz(b) 14GHz and (c) 18GHz
-15-
Table 22 Properties of a square waveguide open end radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 69 71 11
14 47 60 25
18 58 62 16
The radiation pattern symmetry and back radiation performance of the
square waveguide are inferior to those of a circular waveguide
23 Probe-Fed Circular Waveguide Radiator
In Section 21 the radiation properties of a TE11-mode excited waveguide
is investigated In this section a circular waveguide fed by a coaxial probe
shown in Fig 29 is studied
The coaxial probes diameter is 127mm With the Teflon dielectric the
50-ohm coaxial lines outer conductor has a diameter of 41mm For a
circular waveguide the wave impedance of the TE11 mode is given by
∙ (28)
where λg is the guided wavelength given by
(29)
-16-
(a) (b)
Fig 29 Probe-fed circular waveguide radiator (a) Front view and (b) side
view
The combination of the probe length and the probe position from the
shorted wall enables a good impedance matching The probe distance sp from
the back short is close to a quarter wavelength at the design frequency
The designed feed has the following dimension d = 2053mm lp = 42
mm sp = 534mm wall thickness = 05mm and feed length = 400mm
Fig 210 shows the reflection coefficient of the designed probe-fed
circular waveguide radiator The reflection coefficient is less than -10dB over
138-187GHz Fig 211 and 212 shows the E-plane and H-plane radiation
patterns and 2D radiation patterns of the coaxial-to-circular waveguide
transition The radiation patterns symmetry distorted because of the high order
modes The coaxial-to-circular waveguide transition has 73dB 84dB and
79dB gain at 10GHz 14GHz and 18GHz frequencies respectively Table 23
shows the properties of the coaxial-to-circular waveguide transition
-17-
Fig 210 Reflection coefficient of the probe-fed circular waveguide radiator
(a)
Fig 211 2D radiation pattern of the probe-fed circular waveguide radiator
at (a) 10GHz (b) 14GHz and (c) 18GHz
-18-
(b)
(c)
Fig 211 continued
-19-
(a)
(b)
(c)
Fig 212 E- and H-plane patterns of the probe-fed circular waveguide
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-20-
Table 23 Properties of the probe-fed circular waveguide radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 73 70 1414 83 57 17
18 60 52 30
When a circular waveguide radiator is fed by a coaxial probe its radiation
properties are not good due to the excitation of higher-order modes
Therefore a probe-fed circular waveguide radiator can be used as a feed only
over a narrow frequency range
24 Probe-Fed Square Waveguide Radiator
In this section a probe-fed square waveguide radiator is investigated Fig
213 shows a coaxial probe-fed square waveguide radiator The designed
radiator has the following dimension a = b = 157mm lp = 35 mm sp =
50 mm wall thickness = 05mm and feed length = 40mm
(a) (b)
Fig 213 Probe-fed square waveguide radiator (a) Front view and (b) side
view
-21-
Fig 214 shows the 2D radiation patterns of the radiator at 10GHz
14GHz and 18GHz Fig 215 shows E- and H-plane patterns of the radiator
Fig 216 shows the reflection coefficient of the probe-fed square waveguide
radiator The reflection coefficient is less than -10dB over 13-20GHz Table
24 summarizes the properties of the probe-fed square waveguide radiator
(a)
Fig 214 2D radiation patterns of the probe-fed square waveguide radiator at
(a) 10GHz (b) 14GHz and (c) 18GHz
-22-
(b)
(c)
Fig 214 continued
-23-
(a)
(b)
(c)
Fig 216 E-plane and H-plane patterns of the probe-fed square waveguide
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-24-
Fig 216 Reflection coefficient of the probe-fed square waveguide radiator
Table 24 Properties of the probe-fed square waveguide radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 73 71 12
14 85 63 1418 27 65 28
When a square waveguide radiator is fed by a coaxial probe its radiation
properties are not good due to the excitation of higher-order modes as in the
case of the probe-fed circular waveguide radiator A probe-fed square
waveguide radiator can be used as a feed only over a narrow frequency
range
-25-
III Design of Compact Circular Waveguide Feeds
In this chapter the feed design is presented for a prime-focus reflector
antenna The prime-focus paraboloid reflector is one of the most commonly
used high-gain antenna It has been used in earth-station antennas and radio
telescopes It consists of a paraboloid reflector with a feed system at its focal
point
The feed should radiate a low level of cross-polar power over the
operating frequency These conditions not easy to achieve and most prime
focus feeds are compromises The shape and characteristic of the radiation
pattern of the feed are the most important parameter because these will
directly influence the fields which are directed at a reflector[6] Other
electrical factors which relevant to the choice of a feed are the cross-polar
level the gain efficiency the bandwidth and impedance matching
31 Narrow-Band Circular Waveguide Feed
Fig 31 shows the proposed narrow-band circular waveguide feed and its
design variables The feed consists of a circular waveguide open end excited
by a TE11 dominant mode A quarter wave choke is applied along the
circular aperture of the waveguide to equalize E- and H-plane radiation
patterns and to suppress the back radiation A dielectric ring is used to
control the radiation pattern and change the power distribution over the
aperture The control of the amplitude over the aperture are essential to the
design of symmetric radiation pattern The material used for dielectric loading
-26-
is the monocast(MC) nylon with a dielectric constant of 30 The feed is
designed to operate over 171-197GHz
(a)
(b)
Fig 31 Narrow-band circular waveguide feed (a) CAD model and (b) a
cross sectional view
The impedance matching is achieved by a proper combination of the probe
height lp and its distance sp from the waveguide shorted end Here the
-27-
circular waveguide is terminated with an open end with a wall thickness of
2mm radiating into the free space
Fig 32 shows the effect of the probe length lp and the probe distance sp
on the reflection coefficient The best performance is obtained when lp =
363mm and sp = 616mm The feeds reflection coefficient is less than -10dB
over 170-195GHz
(a)
(b)
Fig 32 Effect of the (a) the probe length lp and (b) the probe
distance sp on the reflection coefficient
-28-
Fig 33 shows the effect of the choke depth The E-plane pattern is more
sensitive to the choke depth than the H-plane pattern The choke depth has a
strong influence on the reflection coefficient when it is 360mm By properly
choosing the choke depth we can equalize the E- and H-plane patterns The
optimum value of the choke depth is 410mm which is 0249λ0 at 1825GHz
The choke slot width tch in the range of 06-12mm has almost no effect
on the H-plane pattern and the reflection coefficient For the E-plane pattern
tch of 12mm has some effect on the E-plane radiation pattern as shown in
Fig 34
Fig 35 shows the feed performance versus the dielectric ring length We
observe in Fig 35 that the dielectric length ld has an optimum value of
1168mm which does no effect on the H-plane pattern and tha the value of
1048mm has some effect on the E-plane pattern and the reflection
coefficient
Fig 36 shows E-plane and H-plane patterns and the reflection coefficient
versus the dielectric thickness With the optimum value of the dielectric
thickness t obtained from the Fig 36 is 155mm The larger values of td has
much stronger effects on the E-plane pattern and the reflection coefficient
The H-plane pattern is not sensitive to the dielectric ring thickness
-29-
(a)
(b)
(c)
Fig 33 Feed performance versus the choke depth (a) E-plane pattern
(b) H-plane pattern and (c) reflection coefficient
-30-
(a)
(b)
(c)
Fig 34 Feed performance versus the choke slot width (a) E-plane pattern
(b) H-plane pattern and (c) reflection coefficient
-31-
(a)
(b)
(c)
Fig 35 Feed performance versus the dielectric ring length (a) E-plane
pattern (b) H-plane pattern and (c) reflection coefficient
-32-
(a)
(b)
(c)
Fig 36 Feed performance versus the dielectric ring thickness (a) E-plane
pattern(b) H-plane pattern and (c) reflection coefficient
-33-
From the above parametric analysis an optimum feed design is obtained
The result is shown in Table 31 Fig 37 shows the 2D gain patterns of
designed feed The antenna has a gain of 903dB 933dB and 956dB at
171GHz 1825GHz and 19GHz respectively
Fig 38 shows E- and H-plane radiation patterns of the designed feed The
feed has E- and H-plane 10-dB beamwidths of 60 and 59 degrees at 17GHz
The feed has a front-to-back ration of 1900dB 2490dB and 2200dB at
171GHz 1825GHz and 19GHz respectively Table 32 summarizes the
performance of the designed narrow-band circular waveguide feed
The designed feed has a greatly improved performance over that of a
simple coax-fed feed described in Section 23
Table 31 Dimensions of the designed narrow-band circular feed
Parameter Designation Value(mm)
a Waveguide inside radius 640
l Feed length 2890
lp Probe length 363
sp Probe position from the back short 616
din Probe diameter 127
dout Diameter of coaxial cables outer conductor 400
t Thickness of choked wall 050
tch Choke slot width 100
lch Choke depth 410
ld Dielectric ring length 1168
td Dielectric ring thickness 155
d1 Waveguide outside diameter 1680
-34-
(a)
(b)
Fig 37 2D gain patterns of the narrow-band circular waveguide feed at
(a) 17GHz (b) 1825GHz and (c) 19GHz
-35-
(c)
Fig 37 continued
-36-
(a)
(b)
(c)
Fig 38 E- and H-plane patterns of the narrow-band circular waveguide feed
at (a) 10GHz (b) 1825GHz and (c) 195GHz
-37-
Frequency(GHz)
Gain(dB)
E-H-plane10-dB beamwidths
(deg)
Front-to-back ratio(dB)
Phase centerlocation
(From feeds aperture plane
toward reflector)
(mm)
1700 903 6059 20 062
1825 933 6060 25 004
1900 956 5759 22 007
Table 32 Performance of the narrow-band circular waveguide feed
The designed narrow-band feed is fabricated and its performance is
measured and compared with the simulation results The designed feed is
fabricated in a numerically-controlled machining center The fabricated antenna
is shown in Fig 39
Fig 39 Photograph of the fabricated feed
-38-
Fig 310 shows a comparison of the measured and simulated reflection
coefficients The measured reflection coefficient is less than -10dB over
171-197GHz The agreement between simulated and measured results are
good
Fig 311 shows the E- and H-plane patterns of the fabricated feed at
187GHz The feed has 90dB gain simulation and measurement results are in
good agreement
The fabricated antennarsquos 10dB beamwidth is 60 degrees in both E and H
planes at 187GHz The front-to-back ratio is 21dB
Fig 310 Reflection coefficient of the fabricated feed
-39-
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Fee
d H
orn
Gain
- d
B
Angle - degree
(a)
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Feed H
orn
Gain
- d
B
Angle - degree
(b)
Fig 311 Gain patterns of the fabricated feed at 187 GHz (a) E-plane and
(b) H-plane
-40-
IV Design of Circular Waveguide Feeds Loaded with a
Dielectric Rod
In this section circular waveguide feeds loaded with a dielectric rod feed
are investigated A comprehensive discussion of the circular waveguide loaded
with a dielectric rod is given by Kumar[7] Inserting a dielectric material
inside the circular waveguide improves the E- and H-plane pattern symmetry
In general dielectric-loaded circular waveguide feeds show good performance
only over a narrow bandwidth
Fig 41 shows the geometry of a circular waveguide loaded with a
dielectric rod The waveguide length is 400mm and the wall thickness is
05mm The dielectric rods diameter is 207mm The dielectric rod is
extended 05 wavelength beyond the waveguide open end The dielectric
constant εr is changed and the feeds performance is observed
Fig 41 Geometry of a circular waveguide loaded with a uniform dielectric
rod
-41-
Fig 42 is the radiation pattern of the feed with εr = 25 and L = 05λ0 at
9GHz E- and H-plane 10-dB beamwidths are 810 and 807 degrees
respectively The front-to-back ratio is 18dB The antenna gain is 71dB
(a)
(b)
Fig 42 Radiation pattern at 9GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 05λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-42-
Fig 43 shows the radiation pattern of the feed with εr = 21 at 10GHz
E- and H-plane 10-dB beamwidths are 70 and 71 degrees respectively The
front-to-back ratio is 19dB The antenna gain is 83dB
(a)
(b)
Fig 43 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 21 and L = 05λ0 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-43-
Fig 44 shows the radiation pattern of the feed with εr = 30 at 8GHz
E- and H-plane 10-dB beamwidths are 83 and 824 degrees respectively The
front-to-back ratio is 17dB The antenna gain is 73dB
(a)
(b)
Fig 44 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 30 and L = 05λ0 at 8GHz (a) 2D radiation pattern
and (b) E- and H-plane patterns
-44-
Fig 45 shows the radiation pattern of the feed with εr = 50 at 18GHz
E- and H-plane 10-dB beamwidths are 56 and 54 degrees respectively The
front-to-back ratio is 27dB The antenna gain is 105dB The feed has a good
pattern symmetry and low back radiation
(a)
(b)
Fig 45 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 50 and L = 05λ0 at 18GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-45-
Fig 46 is the radiation pattern of the feed with εr = 25 and L = 10λ0 at
10GHz E- and H-plane 10-dB beamwidths are 50 and 48 degrees
respectively The front-to-back ratio is 16dB The antenna gain is 105dB
(a)
(b)
Fig 46 Radiation pattern at 10GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 10λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-46-
Fig 47 shows the geometry of a circular waveguide with a tapered
dielectric rod The designed feed has the following dimension L = 1λ0 d =
1λ0 and εr =25 at 10GHz The waveguide length is 40mm and the wall
thickness is 05mm
L
Dielectricd3
Fig 47 Geometry of a circular waveguide loaded with a tapered dielectric
rod
Fig 48 shows the radiatio pattern of the designed feed E- and H-plane
10-dB beamwidths are 575 and 564 degrees respectively The front-to-back
ratio is 377dB The antenna gain is 94dB The designed feed has an
excellent beamwidth symmetry and a very low back radiation
-47-
(a)
(b)
Fig 48 Radiation pattern of a circular waveguide loaded with a tapered
dielectric rod with L = 1λ0 d = 1λ0 and εr =25 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-48-
Fig 49 shows the geometry of a spherical ended dielectric rod feed
diameter of 06λ0 at 10GHz with a dielectric constant of 25 and L= 03λ0
Fig 410 shows the radiation patterns of the designed feed E- and H-plane
10-dB beamwidths are both 63 degrees The front-to-back ratio is 24dB The
antenna gain is 864dB
Fig 49 Geometry of a circular waveguide loaded with a spherical ended
dielectric rod
-49-
(a)
(b)
Fig 410 Radiation pattern of a circular waveguide loaded wht a spherical
ended dielectric rod with d = 06λ0 L = 03λ0 and εr =25 at 10GHz (a) 3D
radiation pattern and (b) E- and H-plane patterns
-50-
V Design of a Broadband Circular Waveguide Feed
In this chapter the design of a broadband circular waveguide feed is
presented At microwave frequencies the feed is often a circular waveguide
with chokes and corrugations around the aperture Chokes and corrugations
equalize E- and H-plane patterns and reduce the back radiation
The proposed feed is designed to operate over 10-18GHz The design starts
with the optimization of the coaxial-to-rectangular waveguide adapter
employed for good mode purity over a broad frequency range Next a
rectangular-to-circular waveguide transition is optimized Finally chokes and
corrugations are designed for improved pattern symmetry and low back
radiation
The proposed feed structure is shown in Fig 51 The feed consist of the
following parts a coaxial-to-rectangular waveguide adapter a rectangular-to-
circular waveguide transition a circular waveguide section four quarter-wave
chokes around the feeds aperture and four corrugations on the feeds outer
surface
The computer simulation shows the above arrangement offers good radiation
patterns over a broad frequency range The broadband operation is obtained
by exciting the TE11 mode in the circular waveguide using the TE10 mode of
the rectangular waveguide which is in turn excited by a coaxial probe
-51-
Chokes
Coaxial-to-waveguide transition
Circular wavguide
Corrugations
Mode transition
(a)
(b)
Fig 51 Structure of the proposed broadband circular waveguide feed
(a) CAD model and (b) cross-sectional view
For the coaxial-to-rectangular waveguide adapter an SMA connector with
the probe diameter of 127 mm is employed The coaxial probe inserted into
the waveguide energizes the feed and excites the dominant TE10 mode in
-52-
the rectangular waveguide The impedance matching is achieved by adjusting
the probe distance sp from the back short and the probe length lp
(a)
(b)
Fig 52 Reflection coefficient of the coaxial-to-rectangular adapter versus
(a) probe length lp and (b) the probe position sp
Fig 52 shows the reflection coefficient versus the various values of probe
lengths lp and probe positions sp The probe length lp is adjusted to obtain
antenna impedance matching and the probe distance sp is adjusted to obtain a
-53-
desired resonant frequency
Next a transition between rectangular and circular waveguide is designed
The transition section converts the TE10 mode in the rectangular waveguide to
TE11 mode in the circular waveguide and vice versa The transition is built
in a form of a taper for easy fabrication[22]
(a)
(b)
Fig 53 Structure of the rectangular-to-circular waveguide transition
(a) 3D view and (b) cross sectional view
The dimensions of the final optimized transition are as follows The length
of the rectangular waveguide section is 143mm The rectangular waveguides
width a and height b are 207mm and 857mm respectively The length of
the circular waveguide section is 143mm The inside diameter of the circular
-54-
waveguide is 207mm(097 wavelength at 14GHz) The length of transition
region ltr is 4465mm(approximately equal to 2λ0 at 14GHz) Fig 54 shows
the field distribution inside the mode converter
(a)
(b)
Fig 54 Field distribution inside the mode converter at
(a) 10GHz (b) 14GHz and (c) 18GHz
-55-
(c)
Fig 54 continued
Finally multiple chokes are investigated Figs 55 56 and 57 show the
feed performance without chokes The reflection coefficient is less than -10dB
over 10-19GHz The antenna has a gain of 921dB to 1189dB over
10-19GHz
Fig 55 Reflection coefficient of the broadband circular waveguide feed
without chokes and corrugations
-56-
(a)
(b)
(c)
Fig 56 E- and H-plane patterns of the broadband circular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-57-
(d)
(e)
Fig 56 continued
-58-
(a)
(b)
Fig 57 2D radiation patterns of the broadband cicular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-59-
(c)
(d)
Fig 57 continued
-60-
(e)
Fig 57 continued
To achieve equal beamwidths in E and H planes over a wide frequency
range chokes and corrugations are employed Table51 summarizes the
performance of a feed without chokes and corrugations
Table 51 Performance of the broadband circular waveguide feed without
chokes and corrugations
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
1000 940 6061 15
1200 972 6159 17
1400 920 5957 21
1600 1070 4751 29
1800 1188 5352 21
-61-
Four quarter-wavelength chokes are introduced in the feed design which
has a slot depth of 75mm and slot width of 09mm The choke slot spacing
is 18mm The choke design is investigated by applying the choke one by
one and the effect on the E- and H-plane patterns are observed as illustrated
in Figs 58 and 59 The use of chokes makes the E-plane pattern narrower
The H-plane pattern is not affected Chokes increase the gain slightly and
reduce back radiation
(a)
(b)
Fig 58 Effect of chokes on the E-plane pattern of the broadband circular
waveguide feed at (a) 10GHz(b) 12GHz (c) 14GHz (d) 16GHz and (e)
18GHz
-62-
(c)
(d)
(e)
Fig 58 continued
-63-
(a)
(b)
(c)
Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-64-
(d)
(e)
Fig 59 continued
-65-
Fig 510 shows the feed performance versus the choke depth When the
choke depth is varied from 535mm to 95mm the E- and H-plane patterns
are strongly affected The optimum value of choke depth is 75mm(035λ0 at
14GHz) which gives equal E- and H-plane radiation patterns and leads to
low back radiation
Fig 511 shows the feed performance versus the choke slot width tch The
choke slot width is varied from 09mm to 21mm Radiation patterns and
reflection coefficients are not sensitive to the choke slot width The final
choke slot width is selected to be 09mm considering the feed diameter
minimization and the manufacturability The overall diameter of the proposed
feed is 369mm which is increased from the 207mm of the waveguide
inside diameter due to the use of four chokes
-66-
(a)
(b)
(c)
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection coefficient
-67-
(a)
(b)
(c)
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and (c)
reflection coefficient
-68-
Next we investigated corrugations placed on the outer wall of the feed
Four corrugations applied to the outer surface of the circular waveguide The
corrugation depth is 465mm(0215λ0 at 14GHz) The primary purpose of
using corrugations is to further reduce the back radiation Increasing the
number of corrugations beyond four has little effect in reducing the back
radiation
Figs 512 and 513 show the effect of corrugations on the E- and H-plane
patterns Fig 514 shows the parametric study of the corrugation depth lcor
The corrugation depth is varied from 40mm and 645mm The optimum
value of the corrugation depth is found to be 465mm
-69-
(a)
(b)
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern at (a) 12GHz and (b) 14GHz
-70-
(a)
(b)
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern at (a) 12GHz and (b) 14GHz
-71-
(a)
(b)
(c)
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection coefficient
-72-
The phase center location is important in placing the feed in a reflector
antenna[8] The phase center variation with frequency should be small Fig
515 shows the effect of chokes and corrugations on the phase center The
curve with circle corresponds to the case without chokes and corrugations
The phase center varies from -326mm and -190mm away from the feeds
aperture plane It means the phase center is located inside the waveguide
The curve with triangles corresponds to the case with chokes The curve with
squares to the case with chokes and corrugations The phase center varies
from 0mm to -302mm
From Fig 515 we can observed that phase center variation reduced by the
corrugation and three cases phase center calculated in φ=450 plane
parameter sweep values are given in Table 52
10 12 14 16 181
0
-1
-2
-3
-4
-5
-6
Pha
se c
ente
r (m
m)
Frequency (GHz)
choke+corrugatuion without choke corrugation with choke
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
-73-
Frequency
(GHz)
Phase center from the aperture plane
(mm)
Without
chokes and
corrugations
With
chokes
With chokes
and
corrugations
1000 -326 062 000
1100 -187 030 -002
1200 -563 -208 -065
1300 -296 -154 -202
1400 -319 -314 -302
1500 -201 -203 -241
1600 -242 -233 -207
1700 -208 -208 -186
1800 -190 -157 -132
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
Based on the foregoing parametric studies optimum dimensions of the
broadband circular waveguide feed are obtained as shown in Table 53
-74-
Table 53 Optimum dimensions of the broadband circular waveguide feed
Parameter Designation Value (mm)
2a Waveguide inside diameter 2070
d Waveguide outside diameter 3690
lcrLength of the circular waveguide section 1430
m Distance between the aperture plane and the first corrugation 950
xDistance from the last corrugation to the end of the cylindrical outer surface
550
ltrLength of the rectangular-to-circularwaveguide transition 4465
lrcLength of the rectangular waveguide section 1430
tch Choke slot width 090
lch Choke depth 750
t Choke metal width 090
lcor Corrugation depth 465
tcor Corrugation metal width 100
s Corrugation slot width 10
lp Probe length 530
sp Probe position from the back short 530
din Probe diameter 127
b Inside height of the rectangular waveguide 857
tw Waveguide wall thickness 500
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-15-
Table 22 Properties of a square waveguide open end radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 69 71 11
14 47 60 25
18 58 62 16
The radiation pattern symmetry and back radiation performance of the
square waveguide are inferior to those of a circular waveguide
23 Probe-Fed Circular Waveguide Radiator
In Section 21 the radiation properties of a TE11-mode excited waveguide
is investigated In this section a circular waveguide fed by a coaxial probe
shown in Fig 29 is studied
The coaxial probes diameter is 127mm With the Teflon dielectric the
50-ohm coaxial lines outer conductor has a diameter of 41mm For a
circular waveguide the wave impedance of the TE11 mode is given by
∙ (28)
where λg is the guided wavelength given by
(29)
-16-
(a) (b)
Fig 29 Probe-fed circular waveguide radiator (a) Front view and (b) side
view
The combination of the probe length and the probe position from the
shorted wall enables a good impedance matching The probe distance sp from
the back short is close to a quarter wavelength at the design frequency
The designed feed has the following dimension d = 2053mm lp = 42
mm sp = 534mm wall thickness = 05mm and feed length = 400mm
Fig 210 shows the reflection coefficient of the designed probe-fed
circular waveguide radiator The reflection coefficient is less than -10dB over
138-187GHz Fig 211 and 212 shows the E-plane and H-plane radiation
patterns and 2D radiation patterns of the coaxial-to-circular waveguide
transition The radiation patterns symmetry distorted because of the high order
modes The coaxial-to-circular waveguide transition has 73dB 84dB and
79dB gain at 10GHz 14GHz and 18GHz frequencies respectively Table 23
shows the properties of the coaxial-to-circular waveguide transition
-17-
Fig 210 Reflection coefficient of the probe-fed circular waveguide radiator
(a)
Fig 211 2D radiation pattern of the probe-fed circular waveguide radiator
at (a) 10GHz (b) 14GHz and (c) 18GHz
-18-
(b)
(c)
Fig 211 continued
-19-
(a)
(b)
(c)
Fig 212 E- and H-plane patterns of the probe-fed circular waveguide
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-20-
Table 23 Properties of the probe-fed circular waveguide radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 73 70 1414 83 57 17
18 60 52 30
When a circular waveguide radiator is fed by a coaxial probe its radiation
properties are not good due to the excitation of higher-order modes
Therefore a probe-fed circular waveguide radiator can be used as a feed only
over a narrow frequency range
24 Probe-Fed Square Waveguide Radiator
In this section a probe-fed square waveguide radiator is investigated Fig
213 shows a coaxial probe-fed square waveguide radiator The designed
radiator has the following dimension a = b = 157mm lp = 35 mm sp =
50 mm wall thickness = 05mm and feed length = 40mm
(a) (b)
Fig 213 Probe-fed square waveguide radiator (a) Front view and (b) side
view
-21-
Fig 214 shows the 2D radiation patterns of the radiator at 10GHz
14GHz and 18GHz Fig 215 shows E- and H-plane patterns of the radiator
Fig 216 shows the reflection coefficient of the probe-fed square waveguide
radiator The reflection coefficient is less than -10dB over 13-20GHz Table
24 summarizes the properties of the probe-fed square waveguide radiator
(a)
Fig 214 2D radiation patterns of the probe-fed square waveguide radiator at
(a) 10GHz (b) 14GHz and (c) 18GHz
-22-
(b)
(c)
Fig 214 continued
-23-
(a)
(b)
(c)
Fig 216 E-plane and H-plane patterns of the probe-fed square waveguide
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-24-
Fig 216 Reflection coefficient of the probe-fed square waveguide radiator
Table 24 Properties of the probe-fed square waveguide radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 73 71 12
14 85 63 1418 27 65 28
When a square waveguide radiator is fed by a coaxial probe its radiation
properties are not good due to the excitation of higher-order modes as in the
case of the probe-fed circular waveguide radiator A probe-fed square
waveguide radiator can be used as a feed only over a narrow frequency
range
-25-
III Design of Compact Circular Waveguide Feeds
In this chapter the feed design is presented for a prime-focus reflector
antenna The prime-focus paraboloid reflector is one of the most commonly
used high-gain antenna It has been used in earth-station antennas and radio
telescopes It consists of a paraboloid reflector with a feed system at its focal
point
The feed should radiate a low level of cross-polar power over the
operating frequency These conditions not easy to achieve and most prime
focus feeds are compromises The shape and characteristic of the radiation
pattern of the feed are the most important parameter because these will
directly influence the fields which are directed at a reflector[6] Other
electrical factors which relevant to the choice of a feed are the cross-polar
level the gain efficiency the bandwidth and impedance matching
31 Narrow-Band Circular Waveguide Feed
Fig 31 shows the proposed narrow-band circular waveguide feed and its
design variables The feed consists of a circular waveguide open end excited
by a TE11 dominant mode A quarter wave choke is applied along the
circular aperture of the waveguide to equalize E- and H-plane radiation
patterns and to suppress the back radiation A dielectric ring is used to
control the radiation pattern and change the power distribution over the
aperture The control of the amplitude over the aperture are essential to the
design of symmetric radiation pattern The material used for dielectric loading
-26-
is the monocast(MC) nylon with a dielectric constant of 30 The feed is
designed to operate over 171-197GHz
(a)
(b)
Fig 31 Narrow-band circular waveguide feed (a) CAD model and (b) a
cross sectional view
The impedance matching is achieved by a proper combination of the probe
height lp and its distance sp from the waveguide shorted end Here the
-27-
circular waveguide is terminated with an open end with a wall thickness of
2mm radiating into the free space
Fig 32 shows the effect of the probe length lp and the probe distance sp
on the reflection coefficient The best performance is obtained when lp =
363mm and sp = 616mm The feeds reflection coefficient is less than -10dB
over 170-195GHz
(a)
(b)
Fig 32 Effect of the (a) the probe length lp and (b) the probe
distance sp on the reflection coefficient
-28-
Fig 33 shows the effect of the choke depth The E-plane pattern is more
sensitive to the choke depth than the H-plane pattern The choke depth has a
strong influence on the reflection coefficient when it is 360mm By properly
choosing the choke depth we can equalize the E- and H-plane patterns The
optimum value of the choke depth is 410mm which is 0249λ0 at 1825GHz
The choke slot width tch in the range of 06-12mm has almost no effect
on the H-plane pattern and the reflection coefficient For the E-plane pattern
tch of 12mm has some effect on the E-plane radiation pattern as shown in
Fig 34
Fig 35 shows the feed performance versus the dielectric ring length We
observe in Fig 35 that the dielectric length ld has an optimum value of
1168mm which does no effect on the H-plane pattern and tha the value of
1048mm has some effect on the E-plane pattern and the reflection
coefficient
Fig 36 shows E-plane and H-plane patterns and the reflection coefficient
versus the dielectric thickness With the optimum value of the dielectric
thickness t obtained from the Fig 36 is 155mm The larger values of td has
much stronger effects on the E-plane pattern and the reflection coefficient
The H-plane pattern is not sensitive to the dielectric ring thickness
-29-
(a)
(b)
(c)
Fig 33 Feed performance versus the choke depth (a) E-plane pattern
(b) H-plane pattern and (c) reflection coefficient
-30-
(a)
(b)
(c)
Fig 34 Feed performance versus the choke slot width (a) E-plane pattern
(b) H-plane pattern and (c) reflection coefficient
-31-
(a)
(b)
(c)
Fig 35 Feed performance versus the dielectric ring length (a) E-plane
pattern (b) H-plane pattern and (c) reflection coefficient
-32-
(a)
(b)
(c)
Fig 36 Feed performance versus the dielectric ring thickness (a) E-plane
pattern(b) H-plane pattern and (c) reflection coefficient
-33-
From the above parametric analysis an optimum feed design is obtained
The result is shown in Table 31 Fig 37 shows the 2D gain patterns of
designed feed The antenna has a gain of 903dB 933dB and 956dB at
171GHz 1825GHz and 19GHz respectively
Fig 38 shows E- and H-plane radiation patterns of the designed feed The
feed has E- and H-plane 10-dB beamwidths of 60 and 59 degrees at 17GHz
The feed has a front-to-back ration of 1900dB 2490dB and 2200dB at
171GHz 1825GHz and 19GHz respectively Table 32 summarizes the
performance of the designed narrow-band circular waveguide feed
The designed feed has a greatly improved performance over that of a
simple coax-fed feed described in Section 23
Table 31 Dimensions of the designed narrow-band circular feed
Parameter Designation Value(mm)
a Waveguide inside radius 640
l Feed length 2890
lp Probe length 363
sp Probe position from the back short 616
din Probe diameter 127
dout Diameter of coaxial cables outer conductor 400
t Thickness of choked wall 050
tch Choke slot width 100
lch Choke depth 410
ld Dielectric ring length 1168
td Dielectric ring thickness 155
d1 Waveguide outside diameter 1680
-34-
(a)
(b)
Fig 37 2D gain patterns of the narrow-band circular waveguide feed at
(a) 17GHz (b) 1825GHz and (c) 19GHz
-35-
(c)
Fig 37 continued
-36-
(a)
(b)
(c)
Fig 38 E- and H-plane patterns of the narrow-band circular waveguide feed
at (a) 10GHz (b) 1825GHz and (c) 195GHz
-37-
Frequency(GHz)
Gain(dB)
E-H-plane10-dB beamwidths
(deg)
Front-to-back ratio(dB)
Phase centerlocation
(From feeds aperture plane
toward reflector)
(mm)
1700 903 6059 20 062
1825 933 6060 25 004
1900 956 5759 22 007
Table 32 Performance of the narrow-band circular waveguide feed
The designed narrow-band feed is fabricated and its performance is
measured and compared with the simulation results The designed feed is
fabricated in a numerically-controlled machining center The fabricated antenna
is shown in Fig 39
Fig 39 Photograph of the fabricated feed
-38-
Fig 310 shows a comparison of the measured and simulated reflection
coefficients The measured reflection coefficient is less than -10dB over
171-197GHz The agreement between simulated and measured results are
good
Fig 311 shows the E- and H-plane patterns of the fabricated feed at
187GHz The feed has 90dB gain simulation and measurement results are in
good agreement
The fabricated antennarsquos 10dB beamwidth is 60 degrees in both E and H
planes at 187GHz The front-to-back ratio is 21dB
Fig 310 Reflection coefficient of the fabricated feed
-39-
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Fee
d H
orn
Gain
- d
B
Angle - degree
(a)
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Feed H
orn
Gain
- d
B
Angle - degree
(b)
Fig 311 Gain patterns of the fabricated feed at 187 GHz (a) E-plane and
(b) H-plane
-40-
IV Design of Circular Waveguide Feeds Loaded with a
Dielectric Rod
In this section circular waveguide feeds loaded with a dielectric rod feed
are investigated A comprehensive discussion of the circular waveguide loaded
with a dielectric rod is given by Kumar[7] Inserting a dielectric material
inside the circular waveguide improves the E- and H-plane pattern symmetry
In general dielectric-loaded circular waveguide feeds show good performance
only over a narrow bandwidth
Fig 41 shows the geometry of a circular waveguide loaded with a
dielectric rod The waveguide length is 400mm and the wall thickness is
05mm The dielectric rods diameter is 207mm The dielectric rod is
extended 05 wavelength beyond the waveguide open end The dielectric
constant εr is changed and the feeds performance is observed
Fig 41 Geometry of a circular waveguide loaded with a uniform dielectric
rod
-41-
Fig 42 is the radiation pattern of the feed with εr = 25 and L = 05λ0 at
9GHz E- and H-plane 10-dB beamwidths are 810 and 807 degrees
respectively The front-to-back ratio is 18dB The antenna gain is 71dB
(a)
(b)
Fig 42 Radiation pattern at 9GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 05λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-42-
Fig 43 shows the radiation pattern of the feed with εr = 21 at 10GHz
E- and H-plane 10-dB beamwidths are 70 and 71 degrees respectively The
front-to-back ratio is 19dB The antenna gain is 83dB
(a)
(b)
Fig 43 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 21 and L = 05λ0 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-43-
Fig 44 shows the radiation pattern of the feed with εr = 30 at 8GHz
E- and H-plane 10-dB beamwidths are 83 and 824 degrees respectively The
front-to-back ratio is 17dB The antenna gain is 73dB
(a)
(b)
Fig 44 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 30 and L = 05λ0 at 8GHz (a) 2D radiation pattern
and (b) E- and H-plane patterns
-44-
Fig 45 shows the radiation pattern of the feed with εr = 50 at 18GHz
E- and H-plane 10-dB beamwidths are 56 and 54 degrees respectively The
front-to-back ratio is 27dB The antenna gain is 105dB The feed has a good
pattern symmetry and low back radiation
(a)
(b)
Fig 45 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 50 and L = 05λ0 at 18GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-45-
Fig 46 is the radiation pattern of the feed with εr = 25 and L = 10λ0 at
10GHz E- and H-plane 10-dB beamwidths are 50 and 48 degrees
respectively The front-to-back ratio is 16dB The antenna gain is 105dB
(a)
(b)
Fig 46 Radiation pattern at 10GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 10λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-46-
Fig 47 shows the geometry of a circular waveguide with a tapered
dielectric rod The designed feed has the following dimension L = 1λ0 d =
1λ0 and εr =25 at 10GHz The waveguide length is 40mm and the wall
thickness is 05mm
L
Dielectricd3
Fig 47 Geometry of a circular waveguide loaded with a tapered dielectric
rod
Fig 48 shows the radiatio pattern of the designed feed E- and H-plane
10-dB beamwidths are 575 and 564 degrees respectively The front-to-back
ratio is 377dB The antenna gain is 94dB The designed feed has an
excellent beamwidth symmetry and a very low back radiation
-47-
(a)
(b)
Fig 48 Radiation pattern of a circular waveguide loaded with a tapered
dielectric rod with L = 1λ0 d = 1λ0 and εr =25 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-48-
Fig 49 shows the geometry of a spherical ended dielectric rod feed
diameter of 06λ0 at 10GHz with a dielectric constant of 25 and L= 03λ0
Fig 410 shows the radiation patterns of the designed feed E- and H-plane
10-dB beamwidths are both 63 degrees The front-to-back ratio is 24dB The
antenna gain is 864dB
Fig 49 Geometry of a circular waveguide loaded with a spherical ended
dielectric rod
-49-
(a)
(b)
Fig 410 Radiation pattern of a circular waveguide loaded wht a spherical
ended dielectric rod with d = 06λ0 L = 03λ0 and εr =25 at 10GHz (a) 3D
radiation pattern and (b) E- and H-plane patterns
-50-
V Design of a Broadband Circular Waveguide Feed
In this chapter the design of a broadband circular waveguide feed is
presented At microwave frequencies the feed is often a circular waveguide
with chokes and corrugations around the aperture Chokes and corrugations
equalize E- and H-plane patterns and reduce the back radiation
The proposed feed is designed to operate over 10-18GHz The design starts
with the optimization of the coaxial-to-rectangular waveguide adapter
employed for good mode purity over a broad frequency range Next a
rectangular-to-circular waveguide transition is optimized Finally chokes and
corrugations are designed for improved pattern symmetry and low back
radiation
The proposed feed structure is shown in Fig 51 The feed consist of the
following parts a coaxial-to-rectangular waveguide adapter a rectangular-to-
circular waveguide transition a circular waveguide section four quarter-wave
chokes around the feeds aperture and four corrugations on the feeds outer
surface
The computer simulation shows the above arrangement offers good radiation
patterns over a broad frequency range The broadband operation is obtained
by exciting the TE11 mode in the circular waveguide using the TE10 mode of
the rectangular waveguide which is in turn excited by a coaxial probe
-51-
Chokes
Coaxial-to-waveguide transition
Circular wavguide
Corrugations
Mode transition
(a)
(b)
Fig 51 Structure of the proposed broadband circular waveguide feed
(a) CAD model and (b) cross-sectional view
For the coaxial-to-rectangular waveguide adapter an SMA connector with
the probe diameter of 127 mm is employed The coaxial probe inserted into
the waveguide energizes the feed and excites the dominant TE10 mode in
-52-
the rectangular waveguide The impedance matching is achieved by adjusting
the probe distance sp from the back short and the probe length lp
(a)
(b)
Fig 52 Reflection coefficient of the coaxial-to-rectangular adapter versus
(a) probe length lp and (b) the probe position sp
Fig 52 shows the reflection coefficient versus the various values of probe
lengths lp and probe positions sp The probe length lp is adjusted to obtain
antenna impedance matching and the probe distance sp is adjusted to obtain a
-53-
desired resonant frequency
Next a transition between rectangular and circular waveguide is designed
The transition section converts the TE10 mode in the rectangular waveguide to
TE11 mode in the circular waveguide and vice versa The transition is built
in a form of a taper for easy fabrication[22]
(a)
(b)
Fig 53 Structure of the rectangular-to-circular waveguide transition
(a) 3D view and (b) cross sectional view
The dimensions of the final optimized transition are as follows The length
of the rectangular waveguide section is 143mm The rectangular waveguides
width a and height b are 207mm and 857mm respectively The length of
the circular waveguide section is 143mm The inside diameter of the circular
-54-
waveguide is 207mm(097 wavelength at 14GHz) The length of transition
region ltr is 4465mm(approximately equal to 2λ0 at 14GHz) Fig 54 shows
the field distribution inside the mode converter
(a)
(b)
Fig 54 Field distribution inside the mode converter at
(a) 10GHz (b) 14GHz and (c) 18GHz
-55-
(c)
Fig 54 continued
Finally multiple chokes are investigated Figs 55 56 and 57 show the
feed performance without chokes The reflection coefficient is less than -10dB
over 10-19GHz The antenna has a gain of 921dB to 1189dB over
10-19GHz
Fig 55 Reflection coefficient of the broadband circular waveguide feed
without chokes and corrugations
-56-
(a)
(b)
(c)
Fig 56 E- and H-plane patterns of the broadband circular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-57-
(d)
(e)
Fig 56 continued
-58-
(a)
(b)
Fig 57 2D radiation patterns of the broadband cicular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-59-
(c)
(d)
Fig 57 continued
-60-
(e)
Fig 57 continued
To achieve equal beamwidths in E and H planes over a wide frequency
range chokes and corrugations are employed Table51 summarizes the
performance of a feed without chokes and corrugations
Table 51 Performance of the broadband circular waveguide feed without
chokes and corrugations
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
1000 940 6061 15
1200 972 6159 17
1400 920 5957 21
1600 1070 4751 29
1800 1188 5352 21
-61-
Four quarter-wavelength chokes are introduced in the feed design which
has a slot depth of 75mm and slot width of 09mm The choke slot spacing
is 18mm The choke design is investigated by applying the choke one by
one and the effect on the E- and H-plane patterns are observed as illustrated
in Figs 58 and 59 The use of chokes makes the E-plane pattern narrower
The H-plane pattern is not affected Chokes increase the gain slightly and
reduce back radiation
(a)
(b)
Fig 58 Effect of chokes on the E-plane pattern of the broadband circular
waveguide feed at (a) 10GHz(b) 12GHz (c) 14GHz (d) 16GHz and (e)
18GHz
-62-
(c)
(d)
(e)
Fig 58 continued
-63-
(a)
(b)
(c)
Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-64-
(d)
(e)
Fig 59 continued
-65-
Fig 510 shows the feed performance versus the choke depth When the
choke depth is varied from 535mm to 95mm the E- and H-plane patterns
are strongly affected The optimum value of choke depth is 75mm(035λ0 at
14GHz) which gives equal E- and H-plane radiation patterns and leads to
low back radiation
Fig 511 shows the feed performance versus the choke slot width tch The
choke slot width is varied from 09mm to 21mm Radiation patterns and
reflection coefficients are not sensitive to the choke slot width The final
choke slot width is selected to be 09mm considering the feed diameter
minimization and the manufacturability The overall diameter of the proposed
feed is 369mm which is increased from the 207mm of the waveguide
inside diameter due to the use of four chokes
-66-
(a)
(b)
(c)
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection coefficient
-67-
(a)
(b)
(c)
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and (c)
reflection coefficient
-68-
Next we investigated corrugations placed on the outer wall of the feed
Four corrugations applied to the outer surface of the circular waveguide The
corrugation depth is 465mm(0215λ0 at 14GHz) The primary purpose of
using corrugations is to further reduce the back radiation Increasing the
number of corrugations beyond four has little effect in reducing the back
radiation
Figs 512 and 513 show the effect of corrugations on the E- and H-plane
patterns Fig 514 shows the parametric study of the corrugation depth lcor
The corrugation depth is varied from 40mm and 645mm The optimum
value of the corrugation depth is found to be 465mm
-69-
(a)
(b)
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern at (a) 12GHz and (b) 14GHz
-70-
(a)
(b)
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern at (a) 12GHz and (b) 14GHz
-71-
(a)
(b)
(c)
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection coefficient
-72-
The phase center location is important in placing the feed in a reflector
antenna[8] The phase center variation with frequency should be small Fig
515 shows the effect of chokes and corrugations on the phase center The
curve with circle corresponds to the case without chokes and corrugations
The phase center varies from -326mm and -190mm away from the feeds
aperture plane It means the phase center is located inside the waveguide
The curve with triangles corresponds to the case with chokes The curve with
squares to the case with chokes and corrugations The phase center varies
from 0mm to -302mm
From Fig 515 we can observed that phase center variation reduced by the
corrugation and three cases phase center calculated in φ=450 plane
parameter sweep values are given in Table 52
10 12 14 16 181
0
-1
-2
-3
-4
-5
-6
Pha
se c
ente
r (m
m)
Frequency (GHz)
choke+corrugatuion without choke corrugation with choke
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
-73-
Frequency
(GHz)
Phase center from the aperture plane
(mm)
Without
chokes and
corrugations
With
chokes
With chokes
and
corrugations
1000 -326 062 000
1100 -187 030 -002
1200 -563 -208 -065
1300 -296 -154 -202
1400 -319 -314 -302
1500 -201 -203 -241
1600 -242 -233 -207
1700 -208 -208 -186
1800 -190 -157 -132
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
Based on the foregoing parametric studies optimum dimensions of the
broadband circular waveguide feed are obtained as shown in Table 53
-74-
Table 53 Optimum dimensions of the broadband circular waveguide feed
Parameter Designation Value (mm)
2a Waveguide inside diameter 2070
d Waveguide outside diameter 3690
lcrLength of the circular waveguide section 1430
m Distance between the aperture plane and the first corrugation 950
xDistance from the last corrugation to the end of the cylindrical outer surface
550
ltrLength of the rectangular-to-circularwaveguide transition 4465
lrcLength of the rectangular waveguide section 1430
tch Choke slot width 090
lch Choke depth 750
t Choke metal width 090
lcor Corrugation depth 465
tcor Corrugation metal width 100
s Corrugation slot width 10
lp Probe length 530
sp Probe position from the back short 530
din Probe diameter 127
b Inside height of the rectangular waveguide 857
tw Waveguide wall thickness 500
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-16-
(a) (b)
Fig 29 Probe-fed circular waveguide radiator (a) Front view and (b) side
view
The combination of the probe length and the probe position from the
shorted wall enables a good impedance matching The probe distance sp from
the back short is close to a quarter wavelength at the design frequency
The designed feed has the following dimension d = 2053mm lp = 42
mm sp = 534mm wall thickness = 05mm and feed length = 400mm
Fig 210 shows the reflection coefficient of the designed probe-fed
circular waveguide radiator The reflection coefficient is less than -10dB over
138-187GHz Fig 211 and 212 shows the E-plane and H-plane radiation
patterns and 2D radiation patterns of the coaxial-to-circular waveguide
transition The radiation patterns symmetry distorted because of the high order
modes The coaxial-to-circular waveguide transition has 73dB 84dB and
79dB gain at 10GHz 14GHz and 18GHz frequencies respectively Table 23
shows the properties of the coaxial-to-circular waveguide transition
-17-
Fig 210 Reflection coefficient of the probe-fed circular waveguide radiator
(a)
Fig 211 2D radiation pattern of the probe-fed circular waveguide radiator
at (a) 10GHz (b) 14GHz and (c) 18GHz
-18-
(b)
(c)
Fig 211 continued
-19-
(a)
(b)
(c)
Fig 212 E- and H-plane patterns of the probe-fed circular waveguide
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-20-
Table 23 Properties of the probe-fed circular waveguide radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 73 70 1414 83 57 17
18 60 52 30
When a circular waveguide radiator is fed by a coaxial probe its radiation
properties are not good due to the excitation of higher-order modes
Therefore a probe-fed circular waveguide radiator can be used as a feed only
over a narrow frequency range
24 Probe-Fed Square Waveguide Radiator
In this section a probe-fed square waveguide radiator is investigated Fig
213 shows a coaxial probe-fed square waveguide radiator The designed
radiator has the following dimension a = b = 157mm lp = 35 mm sp =
50 mm wall thickness = 05mm and feed length = 40mm
(a) (b)
Fig 213 Probe-fed square waveguide radiator (a) Front view and (b) side
view
-21-
Fig 214 shows the 2D radiation patterns of the radiator at 10GHz
14GHz and 18GHz Fig 215 shows E- and H-plane patterns of the radiator
Fig 216 shows the reflection coefficient of the probe-fed square waveguide
radiator The reflection coefficient is less than -10dB over 13-20GHz Table
24 summarizes the properties of the probe-fed square waveguide radiator
(a)
Fig 214 2D radiation patterns of the probe-fed square waveguide radiator at
(a) 10GHz (b) 14GHz and (c) 18GHz
-22-
(b)
(c)
Fig 214 continued
-23-
(a)
(b)
(c)
Fig 216 E-plane and H-plane patterns of the probe-fed square waveguide
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-24-
Fig 216 Reflection coefficient of the probe-fed square waveguide radiator
Table 24 Properties of the probe-fed square waveguide radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 73 71 12
14 85 63 1418 27 65 28
When a square waveguide radiator is fed by a coaxial probe its radiation
properties are not good due to the excitation of higher-order modes as in the
case of the probe-fed circular waveguide radiator A probe-fed square
waveguide radiator can be used as a feed only over a narrow frequency
range
-25-
III Design of Compact Circular Waveguide Feeds
In this chapter the feed design is presented for a prime-focus reflector
antenna The prime-focus paraboloid reflector is one of the most commonly
used high-gain antenna It has been used in earth-station antennas and radio
telescopes It consists of a paraboloid reflector with a feed system at its focal
point
The feed should radiate a low level of cross-polar power over the
operating frequency These conditions not easy to achieve and most prime
focus feeds are compromises The shape and characteristic of the radiation
pattern of the feed are the most important parameter because these will
directly influence the fields which are directed at a reflector[6] Other
electrical factors which relevant to the choice of a feed are the cross-polar
level the gain efficiency the bandwidth and impedance matching
31 Narrow-Band Circular Waveguide Feed
Fig 31 shows the proposed narrow-band circular waveguide feed and its
design variables The feed consists of a circular waveguide open end excited
by a TE11 dominant mode A quarter wave choke is applied along the
circular aperture of the waveguide to equalize E- and H-plane radiation
patterns and to suppress the back radiation A dielectric ring is used to
control the radiation pattern and change the power distribution over the
aperture The control of the amplitude over the aperture are essential to the
design of symmetric radiation pattern The material used for dielectric loading
-26-
is the monocast(MC) nylon with a dielectric constant of 30 The feed is
designed to operate over 171-197GHz
(a)
(b)
Fig 31 Narrow-band circular waveguide feed (a) CAD model and (b) a
cross sectional view
The impedance matching is achieved by a proper combination of the probe
height lp and its distance sp from the waveguide shorted end Here the
-27-
circular waveguide is terminated with an open end with a wall thickness of
2mm radiating into the free space
Fig 32 shows the effect of the probe length lp and the probe distance sp
on the reflection coefficient The best performance is obtained when lp =
363mm and sp = 616mm The feeds reflection coefficient is less than -10dB
over 170-195GHz
(a)
(b)
Fig 32 Effect of the (a) the probe length lp and (b) the probe
distance sp on the reflection coefficient
-28-
Fig 33 shows the effect of the choke depth The E-plane pattern is more
sensitive to the choke depth than the H-plane pattern The choke depth has a
strong influence on the reflection coefficient when it is 360mm By properly
choosing the choke depth we can equalize the E- and H-plane patterns The
optimum value of the choke depth is 410mm which is 0249λ0 at 1825GHz
The choke slot width tch in the range of 06-12mm has almost no effect
on the H-plane pattern and the reflection coefficient For the E-plane pattern
tch of 12mm has some effect on the E-plane radiation pattern as shown in
Fig 34
Fig 35 shows the feed performance versus the dielectric ring length We
observe in Fig 35 that the dielectric length ld has an optimum value of
1168mm which does no effect on the H-plane pattern and tha the value of
1048mm has some effect on the E-plane pattern and the reflection
coefficient
Fig 36 shows E-plane and H-plane patterns and the reflection coefficient
versus the dielectric thickness With the optimum value of the dielectric
thickness t obtained from the Fig 36 is 155mm The larger values of td has
much stronger effects on the E-plane pattern and the reflection coefficient
The H-plane pattern is not sensitive to the dielectric ring thickness
-29-
(a)
(b)
(c)
Fig 33 Feed performance versus the choke depth (a) E-plane pattern
(b) H-plane pattern and (c) reflection coefficient
-30-
(a)
(b)
(c)
Fig 34 Feed performance versus the choke slot width (a) E-plane pattern
(b) H-plane pattern and (c) reflection coefficient
-31-
(a)
(b)
(c)
Fig 35 Feed performance versus the dielectric ring length (a) E-plane
pattern (b) H-plane pattern and (c) reflection coefficient
-32-
(a)
(b)
(c)
Fig 36 Feed performance versus the dielectric ring thickness (a) E-plane
pattern(b) H-plane pattern and (c) reflection coefficient
-33-
From the above parametric analysis an optimum feed design is obtained
The result is shown in Table 31 Fig 37 shows the 2D gain patterns of
designed feed The antenna has a gain of 903dB 933dB and 956dB at
171GHz 1825GHz and 19GHz respectively
Fig 38 shows E- and H-plane radiation patterns of the designed feed The
feed has E- and H-plane 10-dB beamwidths of 60 and 59 degrees at 17GHz
The feed has a front-to-back ration of 1900dB 2490dB and 2200dB at
171GHz 1825GHz and 19GHz respectively Table 32 summarizes the
performance of the designed narrow-band circular waveguide feed
The designed feed has a greatly improved performance over that of a
simple coax-fed feed described in Section 23
Table 31 Dimensions of the designed narrow-band circular feed
Parameter Designation Value(mm)
a Waveguide inside radius 640
l Feed length 2890
lp Probe length 363
sp Probe position from the back short 616
din Probe diameter 127
dout Diameter of coaxial cables outer conductor 400
t Thickness of choked wall 050
tch Choke slot width 100
lch Choke depth 410
ld Dielectric ring length 1168
td Dielectric ring thickness 155
d1 Waveguide outside diameter 1680
-34-
(a)
(b)
Fig 37 2D gain patterns of the narrow-band circular waveguide feed at
(a) 17GHz (b) 1825GHz and (c) 19GHz
-35-
(c)
Fig 37 continued
-36-
(a)
(b)
(c)
Fig 38 E- and H-plane patterns of the narrow-band circular waveguide feed
at (a) 10GHz (b) 1825GHz and (c) 195GHz
-37-
Frequency(GHz)
Gain(dB)
E-H-plane10-dB beamwidths
(deg)
Front-to-back ratio(dB)
Phase centerlocation
(From feeds aperture plane
toward reflector)
(mm)
1700 903 6059 20 062
1825 933 6060 25 004
1900 956 5759 22 007
Table 32 Performance of the narrow-band circular waveguide feed
The designed narrow-band feed is fabricated and its performance is
measured and compared with the simulation results The designed feed is
fabricated in a numerically-controlled machining center The fabricated antenna
is shown in Fig 39
Fig 39 Photograph of the fabricated feed
-38-
Fig 310 shows a comparison of the measured and simulated reflection
coefficients The measured reflection coefficient is less than -10dB over
171-197GHz The agreement between simulated and measured results are
good
Fig 311 shows the E- and H-plane patterns of the fabricated feed at
187GHz The feed has 90dB gain simulation and measurement results are in
good agreement
The fabricated antennarsquos 10dB beamwidth is 60 degrees in both E and H
planes at 187GHz The front-to-back ratio is 21dB
Fig 310 Reflection coefficient of the fabricated feed
-39-
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Fee
d H
orn
Gain
- d
B
Angle - degree
(a)
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Feed H
orn
Gain
- d
B
Angle - degree
(b)
Fig 311 Gain patterns of the fabricated feed at 187 GHz (a) E-plane and
(b) H-plane
-40-
IV Design of Circular Waveguide Feeds Loaded with a
Dielectric Rod
In this section circular waveguide feeds loaded with a dielectric rod feed
are investigated A comprehensive discussion of the circular waveguide loaded
with a dielectric rod is given by Kumar[7] Inserting a dielectric material
inside the circular waveguide improves the E- and H-plane pattern symmetry
In general dielectric-loaded circular waveguide feeds show good performance
only over a narrow bandwidth
Fig 41 shows the geometry of a circular waveguide loaded with a
dielectric rod The waveguide length is 400mm and the wall thickness is
05mm The dielectric rods diameter is 207mm The dielectric rod is
extended 05 wavelength beyond the waveguide open end The dielectric
constant εr is changed and the feeds performance is observed
Fig 41 Geometry of a circular waveguide loaded with a uniform dielectric
rod
-41-
Fig 42 is the radiation pattern of the feed with εr = 25 and L = 05λ0 at
9GHz E- and H-plane 10-dB beamwidths are 810 and 807 degrees
respectively The front-to-back ratio is 18dB The antenna gain is 71dB
(a)
(b)
Fig 42 Radiation pattern at 9GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 05λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-42-
Fig 43 shows the radiation pattern of the feed with εr = 21 at 10GHz
E- and H-plane 10-dB beamwidths are 70 and 71 degrees respectively The
front-to-back ratio is 19dB The antenna gain is 83dB
(a)
(b)
Fig 43 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 21 and L = 05λ0 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-43-
Fig 44 shows the radiation pattern of the feed with εr = 30 at 8GHz
E- and H-plane 10-dB beamwidths are 83 and 824 degrees respectively The
front-to-back ratio is 17dB The antenna gain is 73dB
(a)
(b)
Fig 44 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 30 and L = 05λ0 at 8GHz (a) 2D radiation pattern
and (b) E- and H-plane patterns
-44-
Fig 45 shows the radiation pattern of the feed with εr = 50 at 18GHz
E- and H-plane 10-dB beamwidths are 56 and 54 degrees respectively The
front-to-back ratio is 27dB The antenna gain is 105dB The feed has a good
pattern symmetry and low back radiation
(a)
(b)
Fig 45 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 50 and L = 05λ0 at 18GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-45-
Fig 46 is the radiation pattern of the feed with εr = 25 and L = 10λ0 at
10GHz E- and H-plane 10-dB beamwidths are 50 and 48 degrees
respectively The front-to-back ratio is 16dB The antenna gain is 105dB
(a)
(b)
Fig 46 Radiation pattern at 10GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 10λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-46-
Fig 47 shows the geometry of a circular waveguide with a tapered
dielectric rod The designed feed has the following dimension L = 1λ0 d =
1λ0 and εr =25 at 10GHz The waveguide length is 40mm and the wall
thickness is 05mm
L
Dielectricd3
Fig 47 Geometry of a circular waveguide loaded with a tapered dielectric
rod
Fig 48 shows the radiatio pattern of the designed feed E- and H-plane
10-dB beamwidths are 575 and 564 degrees respectively The front-to-back
ratio is 377dB The antenna gain is 94dB The designed feed has an
excellent beamwidth symmetry and a very low back radiation
-47-
(a)
(b)
Fig 48 Radiation pattern of a circular waveguide loaded with a tapered
dielectric rod with L = 1λ0 d = 1λ0 and εr =25 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-48-
Fig 49 shows the geometry of a spherical ended dielectric rod feed
diameter of 06λ0 at 10GHz with a dielectric constant of 25 and L= 03λ0
Fig 410 shows the radiation patterns of the designed feed E- and H-plane
10-dB beamwidths are both 63 degrees The front-to-back ratio is 24dB The
antenna gain is 864dB
Fig 49 Geometry of a circular waveguide loaded with a spherical ended
dielectric rod
-49-
(a)
(b)
Fig 410 Radiation pattern of a circular waveguide loaded wht a spherical
ended dielectric rod with d = 06λ0 L = 03λ0 and εr =25 at 10GHz (a) 3D
radiation pattern and (b) E- and H-plane patterns
-50-
V Design of a Broadband Circular Waveguide Feed
In this chapter the design of a broadband circular waveguide feed is
presented At microwave frequencies the feed is often a circular waveguide
with chokes and corrugations around the aperture Chokes and corrugations
equalize E- and H-plane patterns and reduce the back radiation
The proposed feed is designed to operate over 10-18GHz The design starts
with the optimization of the coaxial-to-rectangular waveguide adapter
employed for good mode purity over a broad frequency range Next a
rectangular-to-circular waveguide transition is optimized Finally chokes and
corrugations are designed for improved pattern symmetry and low back
radiation
The proposed feed structure is shown in Fig 51 The feed consist of the
following parts a coaxial-to-rectangular waveguide adapter a rectangular-to-
circular waveguide transition a circular waveguide section four quarter-wave
chokes around the feeds aperture and four corrugations on the feeds outer
surface
The computer simulation shows the above arrangement offers good radiation
patterns over a broad frequency range The broadband operation is obtained
by exciting the TE11 mode in the circular waveguide using the TE10 mode of
the rectangular waveguide which is in turn excited by a coaxial probe
-51-
Chokes
Coaxial-to-waveguide transition
Circular wavguide
Corrugations
Mode transition
(a)
(b)
Fig 51 Structure of the proposed broadband circular waveguide feed
(a) CAD model and (b) cross-sectional view
For the coaxial-to-rectangular waveguide adapter an SMA connector with
the probe diameter of 127 mm is employed The coaxial probe inserted into
the waveguide energizes the feed and excites the dominant TE10 mode in
-52-
the rectangular waveguide The impedance matching is achieved by adjusting
the probe distance sp from the back short and the probe length lp
(a)
(b)
Fig 52 Reflection coefficient of the coaxial-to-rectangular adapter versus
(a) probe length lp and (b) the probe position sp
Fig 52 shows the reflection coefficient versus the various values of probe
lengths lp and probe positions sp The probe length lp is adjusted to obtain
antenna impedance matching and the probe distance sp is adjusted to obtain a
-53-
desired resonant frequency
Next a transition between rectangular and circular waveguide is designed
The transition section converts the TE10 mode in the rectangular waveguide to
TE11 mode in the circular waveguide and vice versa The transition is built
in a form of a taper for easy fabrication[22]
(a)
(b)
Fig 53 Structure of the rectangular-to-circular waveguide transition
(a) 3D view and (b) cross sectional view
The dimensions of the final optimized transition are as follows The length
of the rectangular waveguide section is 143mm The rectangular waveguides
width a and height b are 207mm and 857mm respectively The length of
the circular waveguide section is 143mm The inside diameter of the circular
-54-
waveguide is 207mm(097 wavelength at 14GHz) The length of transition
region ltr is 4465mm(approximately equal to 2λ0 at 14GHz) Fig 54 shows
the field distribution inside the mode converter
(a)
(b)
Fig 54 Field distribution inside the mode converter at
(a) 10GHz (b) 14GHz and (c) 18GHz
-55-
(c)
Fig 54 continued
Finally multiple chokes are investigated Figs 55 56 and 57 show the
feed performance without chokes The reflection coefficient is less than -10dB
over 10-19GHz The antenna has a gain of 921dB to 1189dB over
10-19GHz
Fig 55 Reflection coefficient of the broadband circular waveguide feed
without chokes and corrugations
-56-
(a)
(b)
(c)
Fig 56 E- and H-plane patterns of the broadband circular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-57-
(d)
(e)
Fig 56 continued
-58-
(a)
(b)
Fig 57 2D radiation patterns of the broadband cicular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-59-
(c)
(d)
Fig 57 continued
-60-
(e)
Fig 57 continued
To achieve equal beamwidths in E and H planes over a wide frequency
range chokes and corrugations are employed Table51 summarizes the
performance of a feed without chokes and corrugations
Table 51 Performance of the broadband circular waveguide feed without
chokes and corrugations
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
1000 940 6061 15
1200 972 6159 17
1400 920 5957 21
1600 1070 4751 29
1800 1188 5352 21
-61-
Four quarter-wavelength chokes are introduced in the feed design which
has a slot depth of 75mm and slot width of 09mm The choke slot spacing
is 18mm The choke design is investigated by applying the choke one by
one and the effect on the E- and H-plane patterns are observed as illustrated
in Figs 58 and 59 The use of chokes makes the E-plane pattern narrower
The H-plane pattern is not affected Chokes increase the gain slightly and
reduce back radiation
(a)
(b)
Fig 58 Effect of chokes on the E-plane pattern of the broadband circular
waveguide feed at (a) 10GHz(b) 12GHz (c) 14GHz (d) 16GHz and (e)
18GHz
-62-
(c)
(d)
(e)
Fig 58 continued
-63-
(a)
(b)
(c)
Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-64-
(d)
(e)
Fig 59 continued
-65-
Fig 510 shows the feed performance versus the choke depth When the
choke depth is varied from 535mm to 95mm the E- and H-plane patterns
are strongly affected The optimum value of choke depth is 75mm(035λ0 at
14GHz) which gives equal E- and H-plane radiation patterns and leads to
low back radiation
Fig 511 shows the feed performance versus the choke slot width tch The
choke slot width is varied from 09mm to 21mm Radiation patterns and
reflection coefficients are not sensitive to the choke slot width The final
choke slot width is selected to be 09mm considering the feed diameter
minimization and the manufacturability The overall diameter of the proposed
feed is 369mm which is increased from the 207mm of the waveguide
inside diameter due to the use of four chokes
-66-
(a)
(b)
(c)
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection coefficient
-67-
(a)
(b)
(c)
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and (c)
reflection coefficient
-68-
Next we investigated corrugations placed on the outer wall of the feed
Four corrugations applied to the outer surface of the circular waveguide The
corrugation depth is 465mm(0215λ0 at 14GHz) The primary purpose of
using corrugations is to further reduce the back radiation Increasing the
number of corrugations beyond four has little effect in reducing the back
radiation
Figs 512 and 513 show the effect of corrugations on the E- and H-plane
patterns Fig 514 shows the parametric study of the corrugation depth lcor
The corrugation depth is varied from 40mm and 645mm The optimum
value of the corrugation depth is found to be 465mm
-69-
(a)
(b)
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern at (a) 12GHz and (b) 14GHz
-70-
(a)
(b)
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern at (a) 12GHz and (b) 14GHz
-71-
(a)
(b)
(c)
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection coefficient
-72-
The phase center location is important in placing the feed in a reflector
antenna[8] The phase center variation with frequency should be small Fig
515 shows the effect of chokes and corrugations on the phase center The
curve with circle corresponds to the case without chokes and corrugations
The phase center varies from -326mm and -190mm away from the feeds
aperture plane It means the phase center is located inside the waveguide
The curve with triangles corresponds to the case with chokes The curve with
squares to the case with chokes and corrugations The phase center varies
from 0mm to -302mm
From Fig 515 we can observed that phase center variation reduced by the
corrugation and three cases phase center calculated in φ=450 plane
parameter sweep values are given in Table 52
10 12 14 16 181
0
-1
-2
-3
-4
-5
-6
Pha
se c
ente
r (m
m)
Frequency (GHz)
choke+corrugatuion without choke corrugation with choke
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
-73-
Frequency
(GHz)
Phase center from the aperture plane
(mm)
Without
chokes and
corrugations
With
chokes
With chokes
and
corrugations
1000 -326 062 000
1100 -187 030 -002
1200 -563 -208 -065
1300 -296 -154 -202
1400 -319 -314 -302
1500 -201 -203 -241
1600 -242 -233 -207
1700 -208 -208 -186
1800 -190 -157 -132
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
Based on the foregoing parametric studies optimum dimensions of the
broadband circular waveguide feed are obtained as shown in Table 53
-74-
Table 53 Optimum dimensions of the broadband circular waveguide feed
Parameter Designation Value (mm)
2a Waveguide inside diameter 2070
d Waveguide outside diameter 3690
lcrLength of the circular waveguide section 1430
m Distance between the aperture plane and the first corrugation 950
xDistance from the last corrugation to the end of the cylindrical outer surface
550
ltrLength of the rectangular-to-circularwaveguide transition 4465
lrcLength of the rectangular waveguide section 1430
tch Choke slot width 090
lch Choke depth 750
t Choke metal width 090
lcor Corrugation depth 465
tcor Corrugation metal width 100
s Corrugation slot width 10
lp Probe length 530
sp Probe position from the back short 530
din Probe diameter 127
b Inside height of the rectangular waveguide 857
tw Waveguide wall thickness 500
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-17-
Fig 210 Reflection coefficient of the probe-fed circular waveguide radiator
(a)
Fig 211 2D radiation pattern of the probe-fed circular waveguide radiator
at (a) 10GHz (b) 14GHz and (c) 18GHz
-18-
(b)
(c)
Fig 211 continued
-19-
(a)
(b)
(c)
Fig 212 E- and H-plane patterns of the probe-fed circular waveguide
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-20-
Table 23 Properties of the probe-fed circular waveguide radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 73 70 1414 83 57 17
18 60 52 30
When a circular waveguide radiator is fed by a coaxial probe its radiation
properties are not good due to the excitation of higher-order modes
Therefore a probe-fed circular waveguide radiator can be used as a feed only
over a narrow frequency range
24 Probe-Fed Square Waveguide Radiator
In this section a probe-fed square waveguide radiator is investigated Fig
213 shows a coaxial probe-fed square waveguide radiator The designed
radiator has the following dimension a = b = 157mm lp = 35 mm sp =
50 mm wall thickness = 05mm and feed length = 40mm
(a) (b)
Fig 213 Probe-fed square waveguide radiator (a) Front view and (b) side
view
-21-
Fig 214 shows the 2D radiation patterns of the radiator at 10GHz
14GHz and 18GHz Fig 215 shows E- and H-plane patterns of the radiator
Fig 216 shows the reflection coefficient of the probe-fed square waveguide
radiator The reflection coefficient is less than -10dB over 13-20GHz Table
24 summarizes the properties of the probe-fed square waveguide radiator
(a)
Fig 214 2D radiation patterns of the probe-fed square waveguide radiator at
(a) 10GHz (b) 14GHz and (c) 18GHz
-22-
(b)
(c)
Fig 214 continued
-23-
(a)
(b)
(c)
Fig 216 E-plane and H-plane patterns of the probe-fed square waveguide
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-24-
Fig 216 Reflection coefficient of the probe-fed square waveguide radiator
Table 24 Properties of the probe-fed square waveguide radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 73 71 12
14 85 63 1418 27 65 28
When a square waveguide radiator is fed by a coaxial probe its radiation
properties are not good due to the excitation of higher-order modes as in the
case of the probe-fed circular waveguide radiator A probe-fed square
waveguide radiator can be used as a feed only over a narrow frequency
range
-25-
III Design of Compact Circular Waveguide Feeds
In this chapter the feed design is presented for a prime-focus reflector
antenna The prime-focus paraboloid reflector is one of the most commonly
used high-gain antenna It has been used in earth-station antennas and radio
telescopes It consists of a paraboloid reflector with a feed system at its focal
point
The feed should radiate a low level of cross-polar power over the
operating frequency These conditions not easy to achieve and most prime
focus feeds are compromises The shape and characteristic of the radiation
pattern of the feed are the most important parameter because these will
directly influence the fields which are directed at a reflector[6] Other
electrical factors which relevant to the choice of a feed are the cross-polar
level the gain efficiency the bandwidth and impedance matching
31 Narrow-Band Circular Waveguide Feed
Fig 31 shows the proposed narrow-band circular waveguide feed and its
design variables The feed consists of a circular waveguide open end excited
by a TE11 dominant mode A quarter wave choke is applied along the
circular aperture of the waveguide to equalize E- and H-plane radiation
patterns and to suppress the back radiation A dielectric ring is used to
control the radiation pattern and change the power distribution over the
aperture The control of the amplitude over the aperture are essential to the
design of symmetric radiation pattern The material used for dielectric loading
-26-
is the monocast(MC) nylon with a dielectric constant of 30 The feed is
designed to operate over 171-197GHz
(a)
(b)
Fig 31 Narrow-band circular waveguide feed (a) CAD model and (b) a
cross sectional view
The impedance matching is achieved by a proper combination of the probe
height lp and its distance sp from the waveguide shorted end Here the
-27-
circular waveguide is terminated with an open end with a wall thickness of
2mm radiating into the free space
Fig 32 shows the effect of the probe length lp and the probe distance sp
on the reflection coefficient The best performance is obtained when lp =
363mm and sp = 616mm The feeds reflection coefficient is less than -10dB
over 170-195GHz
(a)
(b)
Fig 32 Effect of the (a) the probe length lp and (b) the probe
distance sp on the reflection coefficient
-28-
Fig 33 shows the effect of the choke depth The E-plane pattern is more
sensitive to the choke depth than the H-plane pattern The choke depth has a
strong influence on the reflection coefficient when it is 360mm By properly
choosing the choke depth we can equalize the E- and H-plane patterns The
optimum value of the choke depth is 410mm which is 0249λ0 at 1825GHz
The choke slot width tch in the range of 06-12mm has almost no effect
on the H-plane pattern and the reflection coefficient For the E-plane pattern
tch of 12mm has some effect on the E-plane radiation pattern as shown in
Fig 34
Fig 35 shows the feed performance versus the dielectric ring length We
observe in Fig 35 that the dielectric length ld has an optimum value of
1168mm which does no effect on the H-plane pattern and tha the value of
1048mm has some effect on the E-plane pattern and the reflection
coefficient
Fig 36 shows E-plane and H-plane patterns and the reflection coefficient
versus the dielectric thickness With the optimum value of the dielectric
thickness t obtained from the Fig 36 is 155mm The larger values of td has
much stronger effects on the E-plane pattern and the reflection coefficient
The H-plane pattern is not sensitive to the dielectric ring thickness
-29-
(a)
(b)
(c)
Fig 33 Feed performance versus the choke depth (a) E-plane pattern
(b) H-plane pattern and (c) reflection coefficient
-30-
(a)
(b)
(c)
Fig 34 Feed performance versus the choke slot width (a) E-plane pattern
(b) H-plane pattern and (c) reflection coefficient
-31-
(a)
(b)
(c)
Fig 35 Feed performance versus the dielectric ring length (a) E-plane
pattern (b) H-plane pattern and (c) reflection coefficient
-32-
(a)
(b)
(c)
Fig 36 Feed performance versus the dielectric ring thickness (a) E-plane
pattern(b) H-plane pattern and (c) reflection coefficient
-33-
From the above parametric analysis an optimum feed design is obtained
The result is shown in Table 31 Fig 37 shows the 2D gain patterns of
designed feed The antenna has a gain of 903dB 933dB and 956dB at
171GHz 1825GHz and 19GHz respectively
Fig 38 shows E- and H-plane radiation patterns of the designed feed The
feed has E- and H-plane 10-dB beamwidths of 60 and 59 degrees at 17GHz
The feed has a front-to-back ration of 1900dB 2490dB and 2200dB at
171GHz 1825GHz and 19GHz respectively Table 32 summarizes the
performance of the designed narrow-band circular waveguide feed
The designed feed has a greatly improved performance over that of a
simple coax-fed feed described in Section 23
Table 31 Dimensions of the designed narrow-band circular feed
Parameter Designation Value(mm)
a Waveguide inside radius 640
l Feed length 2890
lp Probe length 363
sp Probe position from the back short 616
din Probe diameter 127
dout Diameter of coaxial cables outer conductor 400
t Thickness of choked wall 050
tch Choke slot width 100
lch Choke depth 410
ld Dielectric ring length 1168
td Dielectric ring thickness 155
d1 Waveguide outside diameter 1680
-34-
(a)
(b)
Fig 37 2D gain patterns of the narrow-band circular waveguide feed at
(a) 17GHz (b) 1825GHz and (c) 19GHz
-35-
(c)
Fig 37 continued
-36-
(a)
(b)
(c)
Fig 38 E- and H-plane patterns of the narrow-band circular waveguide feed
at (a) 10GHz (b) 1825GHz and (c) 195GHz
-37-
Frequency(GHz)
Gain(dB)
E-H-plane10-dB beamwidths
(deg)
Front-to-back ratio(dB)
Phase centerlocation
(From feeds aperture plane
toward reflector)
(mm)
1700 903 6059 20 062
1825 933 6060 25 004
1900 956 5759 22 007
Table 32 Performance of the narrow-band circular waveguide feed
The designed narrow-band feed is fabricated and its performance is
measured and compared with the simulation results The designed feed is
fabricated in a numerically-controlled machining center The fabricated antenna
is shown in Fig 39
Fig 39 Photograph of the fabricated feed
-38-
Fig 310 shows a comparison of the measured and simulated reflection
coefficients The measured reflection coefficient is less than -10dB over
171-197GHz The agreement between simulated and measured results are
good
Fig 311 shows the E- and H-plane patterns of the fabricated feed at
187GHz The feed has 90dB gain simulation and measurement results are in
good agreement
The fabricated antennarsquos 10dB beamwidth is 60 degrees in both E and H
planes at 187GHz The front-to-back ratio is 21dB
Fig 310 Reflection coefficient of the fabricated feed
-39-
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Fee
d H
orn
Gain
- d
B
Angle - degree
(a)
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Feed H
orn
Gain
- d
B
Angle - degree
(b)
Fig 311 Gain patterns of the fabricated feed at 187 GHz (a) E-plane and
(b) H-plane
-40-
IV Design of Circular Waveguide Feeds Loaded with a
Dielectric Rod
In this section circular waveguide feeds loaded with a dielectric rod feed
are investigated A comprehensive discussion of the circular waveguide loaded
with a dielectric rod is given by Kumar[7] Inserting a dielectric material
inside the circular waveguide improves the E- and H-plane pattern symmetry
In general dielectric-loaded circular waveguide feeds show good performance
only over a narrow bandwidth
Fig 41 shows the geometry of a circular waveguide loaded with a
dielectric rod The waveguide length is 400mm and the wall thickness is
05mm The dielectric rods diameter is 207mm The dielectric rod is
extended 05 wavelength beyond the waveguide open end The dielectric
constant εr is changed and the feeds performance is observed
Fig 41 Geometry of a circular waveguide loaded with a uniform dielectric
rod
-41-
Fig 42 is the radiation pattern of the feed with εr = 25 and L = 05λ0 at
9GHz E- and H-plane 10-dB beamwidths are 810 and 807 degrees
respectively The front-to-back ratio is 18dB The antenna gain is 71dB
(a)
(b)
Fig 42 Radiation pattern at 9GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 05λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-42-
Fig 43 shows the radiation pattern of the feed with εr = 21 at 10GHz
E- and H-plane 10-dB beamwidths are 70 and 71 degrees respectively The
front-to-back ratio is 19dB The antenna gain is 83dB
(a)
(b)
Fig 43 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 21 and L = 05λ0 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-43-
Fig 44 shows the radiation pattern of the feed with εr = 30 at 8GHz
E- and H-plane 10-dB beamwidths are 83 and 824 degrees respectively The
front-to-back ratio is 17dB The antenna gain is 73dB
(a)
(b)
Fig 44 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 30 and L = 05λ0 at 8GHz (a) 2D radiation pattern
and (b) E- and H-plane patterns
-44-
Fig 45 shows the radiation pattern of the feed with εr = 50 at 18GHz
E- and H-plane 10-dB beamwidths are 56 and 54 degrees respectively The
front-to-back ratio is 27dB The antenna gain is 105dB The feed has a good
pattern symmetry and low back radiation
(a)
(b)
Fig 45 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 50 and L = 05λ0 at 18GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-45-
Fig 46 is the radiation pattern of the feed with εr = 25 and L = 10λ0 at
10GHz E- and H-plane 10-dB beamwidths are 50 and 48 degrees
respectively The front-to-back ratio is 16dB The antenna gain is 105dB
(a)
(b)
Fig 46 Radiation pattern at 10GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 10λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-46-
Fig 47 shows the geometry of a circular waveguide with a tapered
dielectric rod The designed feed has the following dimension L = 1λ0 d =
1λ0 and εr =25 at 10GHz The waveguide length is 40mm and the wall
thickness is 05mm
L
Dielectricd3
Fig 47 Geometry of a circular waveguide loaded with a tapered dielectric
rod
Fig 48 shows the radiatio pattern of the designed feed E- and H-plane
10-dB beamwidths are 575 and 564 degrees respectively The front-to-back
ratio is 377dB The antenna gain is 94dB The designed feed has an
excellent beamwidth symmetry and a very low back radiation
-47-
(a)
(b)
Fig 48 Radiation pattern of a circular waveguide loaded with a tapered
dielectric rod with L = 1λ0 d = 1λ0 and εr =25 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-48-
Fig 49 shows the geometry of a spherical ended dielectric rod feed
diameter of 06λ0 at 10GHz with a dielectric constant of 25 and L= 03λ0
Fig 410 shows the radiation patterns of the designed feed E- and H-plane
10-dB beamwidths are both 63 degrees The front-to-back ratio is 24dB The
antenna gain is 864dB
Fig 49 Geometry of a circular waveguide loaded with a spherical ended
dielectric rod
-49-
(a)
(b)
Fig 410 Radiation pattern of a circular waveguide loaded wht a spherical
ended dielectric rod with d = 06λ0 L = 03λ0 and εr =25 at 10GHz (a) 3D
radiation pattern and (b) E- and H-plane patterns
-50-
V Design of a Broadband Circular Waveguide Feed
In this chapter the design of a broadband circular waveguide feed is
presented At microwave frequencies the feed is often a circular waveguide
with chokes and corrugations around the aperture Chokes and corrugations
equalize E- and H-plane patterns and reduce the back radiation
The proposed feed is designed to operate over 10-18GHz The design starts
with the optimization of the coaxial-to-rectangular waveguide adapter
employed for good mode purity over a broad frequency range Next a
rectangular-to-circular waveguide transition is optimized Finally chokes and
corrugations are designed for improved pattern symmetry and low back
radiation
The proposed feed structure is shown in Fig 51 The feed consist of the
following parts a coaxial-to-rectangular waveguide adapter a rectangular-to-
circular waveguide transition a circular waveguide section four quarter-wave
chokes around the feeds aperture and four corrugations on the feeds outer
surface
The computer simulation shows the above arrangement offers good radiation
patterns over a broad frequency range The broadband operation is obtained
by exciting the TE11 mode in the circular waveguide using the TE10 mode of
the rectangular waveguide which is in turn excited by a coaxial probe
-51-
Chokes
Coaxial-to-waveguide transition
Circular wavguide
Corrugations
Mode transition
(a)
(b)
Fig 51 Structure of the proposed broadband circular waveguide feed
(a) CAD model and (b) cross-sectional view
For the coaxial-to-rectangular waveguide adapter an SMA connector with
the probe diameter of 127 mm is employed The coaxial probe inserted into
the waveguide energizes the feed and excites the dominant TE10 mode in
-52-
the rectangular waveguide The impedance matching is achieved by adjusting
the probe distance sp from the back short and the probe length lp
(a)
(b)
Fig 52 Reflection coefficient of the coaxial-to-rectangular adapter versus
(a) probe length lp and (b) the probe position sp
Fig 52 shows the reflection coefficient versus the various values of probe
lengths lp and probe positions sp The probe length lp is adjusted to obtain
antenna impedance matching and the probe distance sp is adjusted to obtain a
-53-
desired resonant frequency
Next a transition between rectangular and circular waveguide is designed
The transition section converts the TE10 mode in the rectangular waveguide to
TE11 mode in the circular waveguide and vice versa The transition is built
in a form of a taper for easy fabrication[22]
(a)
(b)
Fig 53 Structure of the rectangular-to-circular waveguide transition
(a) 3D view and (b) cross sectional view
The dimensions of the final optimized transition are as follows The length
of the rectangular waveguide section is 143mm The rectangular waveguides
width a and height b are 207mm and 857mm respectively The length of
the circular waveguide section is 143mm The inside diameter of the circular
-54-
waveguide is 207mm(097 wavelength at 14GHz) The length of transition
region ltr is 4465mm(approximately equal to 2λ0 at 14GHz) Fig 54 shows
the field distribution inside the mode converter
(a)
(b)
Fig 54 Field distribution inside the mode converter at
(a) 10GHz (b) 14GHz and (c) 18GHz
-55-
(c)
Fig 54 continued
Finally multiple chokes are investigated Figs 55 56 and 57 show the
feed performance without chokes The reflection coefficient is less than -10dB
over 10-19GHz The antenna has a gain of 921dB to 1189dB over
10-19GHz
Fig 55 Reflection coefficient of the broadband circular waveguide feed
without chokes and corrugations
-56-
(a)
(b)
(c)
Fig 56 E- and H-plane patterns of the broadband circular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-57-
(d)
(e)
Fig 56 continued
-58-
(a)
(b)
Fig 57 2D radiation patterns of the broadband cicular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-59-
(c)
(d)
Fig 57 continued
-60-
(e)
Fig 57 continued
To achieve equal beamwidths in E and H planes over a wide frequency
range chokes and corrugations are employed Table51 summarizes the
performance of a feed without chokes and corrugations
Table 51 Performance of the broadband circular waveguide feed without
chokes and corrugations
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
1000 940 6061 15
1200 972 6159 17
1400 920 5957 21
1600 1070 4751 29
1800 1188 5352 21
-61-
Four quarter-wavelength chokes are introduced in the feed design which
has a slot depth of 75mm and slot width of 09mm The choke slot spacing
is 18mm The choke design is investigated by applying the choke one by
one and the effect on the E- and H-plane patterns are observed as illustrated
in Figs 58 and 59 The use of chokes makes the E-plane pattern narrower
The H-plane pattern is not affected Chokes increase the gain slightly and
reduce back radiation
(a)
(b)
Fig 58 Effect of chokes on the E-plane pattern of the broadband circular
waveguide feed at (a) 10GHz(b) 12GHz (c) 14GHz (d) 16GHz and (e)
18GHz
-62-
(c)
(d)
(e)
Fig 58 continued
-63-
(a)
(b)
(c)
Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-64-
(d)
(e)
Fig 59 continued
-65-
Fig 510 shows the feed performance versus the choke depth When the
choke depth is varied from 535mm to 95mm the E- and H-plane patterns
are strongly affected The optimum value of choke depth is 75mm(035λ0 at
14GHz) which gives equal E- and H-plane radiation patterns and leads to
low back radiation
Fig 511 shows the feed performance versus the choke slot width tch The
choke slot width is varied from 09mm to 21mm Radiation patterns and
reflection coefficients are not sensitive to the choke slot width The final
choke slot width is selected to be 09mm considering the feed diameter
minimization and the manufacturability The overall diameter of the proposed
feed is 369mm which is increased from the 207mm of the waveguide
inside diameter due to the use of four chokes
-66-
(a)
(b)
(c)
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection coefficient
-67-
(a)
(b)
(c)
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and (c)
reflection coefficient
-68-
Next we investigated corrugations placed on the outer wall of the feed
Four corrugations applied to the outer surface of the circular waveguide The
corrugation depth is 465mm(0215λ0 at 14GHz) The primary purpose of
using corrugations is to further reduce the back radiation Increasing the
number of corrugations beyond four has little effect in reducing the back
radiation
Figs 512 and 513 show the effect of corrugations on the E- and H-plane
patterns Fig 514 shows the parametric study of the corrugation depth lcor
The corrugation depth is varied from 40mm and 645mm The optimum
value of the corrugation depth is found to be 465mm
-69-
(a)
(b)
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern at (a) 12GHz and (b) 14GHz
-70-
(a)
(b)
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern at (a) 12GHz and (b) 14GHz
-71-
(a)
(b)
(c)
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection coefficient
-72-
The phase center location is important in placing the feed in a reflector
antenna[8] The phase center variation with frequency should be small Fig
515 shows the effect of chokes and corrugations on the phase center The
curve with circle corresponds to the case without chokes and corrugations
The phase center varies from -326mm and -190mm away from the feeds
aperture plane It means the phase center is located inside the waveguide
The curve with triangles corresponds to the case with chokes The curve with
squares to the case with chokes and corrugations The phase center varies
from 0mm to -302mm
From Fig 515 we can observed that phase center variation reduced by the
corrugation and three cases phase center calculated in φ=450 plane
parameter sweep values are given in Table 52
10 12 14 16 181
0
-1
-2
-3
-4
-5
-6
Pha
se c
ente
r (m
m)
Frequency (GHz)
choke+corrugatuion without choke corrugation with choke
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
-73-
Frequency
(GHz)
Phase center from the aperture plane
(mm)
Without
chokes and
corrugations
With
chokes
With chokes
and
corrugations
1000 -326 062 000
1100 -187 030 -002
1200 -563 -208 -065
1300 -296 -154 -202
1400 -319 -314 -302
1500 -201 -203 -241
1600 -242 -233 -207
1700 -208 -208 -186
1800 -190 -157 -132
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
Based on the foregoing parametric studies optimum dimensions of the
broadband circular waveguide feed are obtained as shown in Table 53
-74-
Table 53 Optimum dimensions of the broadband circular waveguide feed
Parameter Designation Value (mm)
2a Waveguide inside diameter 2070
d Waveguide outside diameter 3690
lcrLength of the circular waveguide section 1430
m Distance between the aperture plane and the first corrugation 950
xDistance from the last corrugation to the end of the cylindrical outer surface
550
ltrLength of the rectangular-to-circularwaveguide transition 4465
lrcLength of the rectangular waveguide section 1430
tch Choke slot width 090
lch Choke depth 750
t Choke metal width 090
lcor Corrugation depth 465
tcor Corrugation metal width 100
s Corrugation slot width 10
lp Probe length 530
sp Probe position from the back short 530
din Probe diameter 127
b Inside height of the rectangular waveguide 857
tw Waveguide wall thickness 500
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-18-
(b)
(c)
Fig 211 continued
-19-
(a)
(b)
(c)
Fig 212 E- and H-plane patterns of the probe-fed circular waveguide
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-20-
Table 23 Properties of the probe-fed circular waveguide radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 73 70 1414 83 57 17
18 60 52 30
When a circular waveguide radiator is fed by a coaxial probe its radiation
properties are not good due to the excitation of higher-order modes
Therefore a probe-fed circular waveguide radiator can be used as a feed only
over a narrow frequency range
24 Probe-Fed Square Waveguide Radiator
In this section a probe-fed square waveguide radiator is investigated Fig
213 shows a coaxial probe-fed square waveguide radiator The designed
radiator has the following dimension a = b = 157mm lp = 35 mm sp =
50 mm wall thickness = 05mm and feed length = 40mm
(a) (b)
Fig 213 Probe-fed square waveguide radiator (a) Front view and (b) side
view
-21-
Fig 214 shows the 2D radiation patterns of the radiator at 10GHz
14GHz and 18GHz Fig 215 shows E- and H-plane patterns of the radiator
Fig 216 shows the reflection coefficient of the probe-fed square waveguide
radiator The reflection coefficient is less than -10dB over 13-20GHz Table
24 summarizes the properties of the probe-fed square waveguide radiator
(a)
Fig 214 2D radiation patterns of the probe-fed square waveguide radiator at
(a) 10GHz (b) 14GHz and (c) 18GHz
-22-
(b)
(c)
Fig 214 continued
-23-
(a)
(b)
(c)
Fig 216 E-plane and H-plane patterns of the probe-fed square waveguide
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-24-
Fig 216 Reflection coefficient of the probe-fed square waveguide radiator
Table 24 Properties of the probe-fed square waveguide radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 73 71 12
14 85 63 1418 27 65 28
When a square waveguide radiator is fed by a coaxial probe its radiation
properties are not good due to the excitation of higher-order modes as in the
case of the probe-fed circular waveguide radiator A probe-fed square
waveguide radiator can be used as a feed only over a narrow frequency
range
-25-
III Design of Compact Circular Waveguide Feeds
In this chapter the feed design is presented for a prime-focus reflector
antenna The prime-focus paraboloid reflector is one of the most commonly
used high-gain antenna It has been used in earth-station antennas and radio
telescopes It consists of a paraboloid reflector with a feed system at its focal
point
The feed should radiate a low level of cross-polar power over the
operating frequency These conditions not easy to achieve and most prime
focus feeds are compromises The shape and characteristic of the radiation
pattern of the feed are the most important parameter because these will
directly influence the fields which are directed at a reflector[6] Other
electrical factors which relevant to the choice of a feed are the cross-polar
level the gain efficiency the bandwidth and impedance matching
31 Narrow-Band Circular Waveguide Feed
Fig 31 shows the proposed narrow-band circular waveguide feed and its
design variables The feed consists of a circular waveguide open end excited
by a TE11 dominant mode A quarter wave choke is applied along the
circular aperture of the waveguide to equalize E- and H-plane radiation
patterns and to suppress the back radiation A dielectric ring is used to
control the radiation pattern and change the power distribution over the
aperture The control of the amplitude over the aperture are essential to the
design of symmetric radiation pattern The material used for dielectric loading
-26-
is the monocast(MC) nylon with a dielectric constant of 30 The feed is
designed to operate over 171-197GHz
(a)
(b)
Fig 31 Narrow-band circular waveguide feed (a) CAD model and (b) a
cross sectional view
The impedance matching is achieved by a proper combination of the probe
height lp and its distance sp from the waveguide shorted end Here the
-27-
circular waveguide is terminated with an open end with a wall thickness of
2mm radiating into the free space
Fig 32 shows the effect of the probe length lp and the probe distance sp
on the reflection coefficient The best performance is obtained when lp =
363mm and sp = 616mm The feeds reflection coefficient is less than -10dB
over 170-195GHz
(a)
(b)
Fig 32 Effect of the (a) the probe length lp and (b) the probe
distance sp on the reflection coefficient
-28-
Fig 33 shows the effect of the choke depth The E-plane pattern is more
sensitive to the choke depth than the H-plane pattern The choke depth has a
strong influence on the reflection coefficient when it is 360mm By properly
choosing the choke depth we can equalize the E- and H-plane patterns The
optimum value of the choke depth is 410mm which is 0249λ0 at 1825GHz
The choke slot width tch in the range of 06-12mm has almost no effect
on the H-plane pattern and the reflection coefficient For the E-plane pattern
tch of 12mm has some effect on the E-plane radiation pattern as shown in
Fig 34
Fig 35 shows the feed performance versus the dielectric ring length We
observe in Fig 35 that the dielectric length ld has an optimum value of
1168mm which does no effect on the H-plane pattern and tha the value of
1048mm has some effect on the E-plane pattern and the reflection
coefficient
Fig 36 shows E-plane and H-plane patterns and the reflection coefficient
versus the dielectric thickness With the optimum value of the dielectric
thickness t obtained from the Fig 36 is 155mm The larger values of td has
much stronger effects on the E-plane pattern and the reflection coefficient
The H-plane pattern is not sensitive to the dielectric ring thickness
-29-
(a)
(b)
(c)
Fig 33 Feed performance versus the choke depth (a) E-plane pattern
(b) H-plane pattern and (c) reflection coefficient
-30-
(a)
(b)
(c)
Fig 34 Feed performance versus the choke slot width (a) E-plane pattern
(b) H-plane pattern and (c) reflection coefficient
-31-
(a)
(b)
(c)
Fig 35 Feed performance versus the dielectric ring length (a) E-plane
pattern (b) H-plane pattern and (c) reflection coefficient
-32-
(a)
(b)
(c)
Fig 36 Feed performance versus the dielectric ring thickness (a) E-plane
pattern(b) H-plane pattern and (c) reflection coefficient
-33-
From the above parametric analysis an optimum feed design is obtained
The result is shown in Table 31 Fig 37 shows the 2D gain patterns of
designed feed The antenna has a gain of 903dB 933dB and 956dB at
171GHz 1825GHz and 19GHz respectively
Fig 38 shows E- and H-plane radiation patterns of the designed feed The
feed has E- and H-plane 10-dB beamwidths of 60 and 59 degrees at 17GHz
The feed has a front-to-back ration of 1900dB 2490dB and 2200dB at
171GHz 1825GHz and 19GHz respectively Table 32 summarizes the
performance of the designed narrow-band circular waveguide feed
The designed feed has a greatly improved performance over that of a
simple coax-fed feed described in Section 23
Table 31 Dimensions of the designed narrow-band circular feed
Parameter Designation Value(mm)
a Waveguide inside radius 640
l Feed length 2890
lp Probe length 363
sp Probe position from the back short 616
din Probe diameter 127
dout Diameter of coaxial cables outer conductor 400
t Thickness of choked wall 050
tch Choke slot width 100
lch Choke depth 410
ld Dielectric ring length 1168
td Dielectric ring thickness 155
d1 Waveguide outside diameter 1680
-34-
(a)
(b)
Fig 37 2D gain patterns of the narrow-band circular waveguide feed at
(a) 17GHz (b) 1825GHz and (c) 19GHz
-35-
(c)
Fig 37 continued
-36-
(a)
(b)
(c)
Fig 38 E- and H-plane patterns of the narrow-band circular waveguide feed
at (a) 10GHz (b) 1825GHz and (c) 195GHz
-37-
Frequency(GHz)
Gain(dB)
E-H-plane10-dB beamwidths
(deg)
Front-to-back ratio(dB)
Phase centerlocation
(From feeds aperture plane
toward reflector)
(mm)
1700 903 6059 20 062
1825 933 6060 25 004
1900 956 5759 22 007
Table 32 Performance of the narrow-band circular waveguide feed
The designed narrow-band feed is fabricated and its performance is
measured and compared with the simulation results The designed feed is
fabricated in a numerically-controlled machining center The fabricated antenna
is shown in Fig 39
Fig 39 Photograph of the fabricated feed
-38-
Fig 310 shows a comparison of the measured and simulated reflection
coefficients The measured reflection coefficient is less than -10dB over
171-197GHz The agreement between simulated and measured results are
good
Fig 311 shows the E- and H-plane patterns of the fabricated feed at
187GHz The feed has 90dB gain simulation and measurement results are in
good agreement
The fabricated antennarsquos 10dB beamwidth is 60 degrees in both E and H
planes at 187GHz The front-to-back ratio is 21dB
Fig 310 Reflection coefficient of the fabricated feed
-39-
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Fee
d H
orn
Gain
- d
B
Angle - degree
(a)
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Feed H
orn
Gain
- d
B
Angle - degree
(b)
Fig 311 Gain patterns of the fabricated feed at 187 GHz (a) E-plane and
(b) H-plane
-40-
IV Design of Circular Waveguide Feeds Loaded with a
Dielectric Rod
In this section circular waveguide feeds loaded with a dielectric rod feed
are investigated A comprehensive discussion of the circular waveguide loaded
with a dielectric rod is given by Kumar[7] Inserting a dielectric material
inside the circular waveguide improves the E- and H-plane pattern symmetry
In general dielectric-loaded circular waveguide feeds show good performance
only over a narrow bandwidth
Fig 41 shows the geometry of a circular waveguide loaded with a
dielectric rod The waveguide length is 400mm and the wall thickness is
05mm The dielectric rods diameter is 207mm The dielectric rod is
extended 05 wavelength beyond the waveguide open end The dielectric
constant εr is changed and the feeds performance is observed
Fig 41 Geometry of a circular waveguide loaded with a uniform dielectric
rod
-41-
Fig 42 is the radiation pattern of the feed with εr = 25 and L = 05λ0 at
9GHz E- and H-plane 10-dB beamwidths are 810 and 807 degrees
respectively The front-to-back ratio is 18dB The antenna gain is 71dB
(a)
(b)
Fig 42 Radiation pattern at 9GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 05λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-42-
Fig 43 shows the radiation pattern of the feed with εr = 21 at 10GHz
E- and H-plane 10-dB beamwidths are 70 and 71 degrees respectively The
front-to-back ratio is 19dB The antenna gain is 83dB
(a)
(b)
Fig 43 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 21 and L = 05λ0 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-43-
Fig 44 shows the radiation pattern of the feed with εr = 30 at 8GHz
E- and H-plane 10-dB beamwidths are 83 and 824 degrees respectively The
front-to-back ratio is 17dB The antenna gain is 73dB
(a)
(b)
Fig 44 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 30 and L = 05λ0 at 8GHz (a) 2D radiation pattern
and (b) E- and H-plane patterns
-44-
Fig 45 shows the radiation pattern of the feed with εr = 50 at 18GHz
E- and H-plane 10-dB beamwidths are 56 and 54 degrees respectively The
front-to-back ratio is 27dB The antenna gain is 105dB The feed has a good
pattern symmetry and low back radiation
(a)
(b)
Fig 45 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 50 and L = 05λ0 at 18GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-45-
Fig 46 is the radiation pattern of the feed with εr = 25 and L = 10λ0 at
10GHz E- and H-plane 10-dB beamwidths are 50 and 48 degrees
respectively The front-to-back ratio is 16dB The antenna gain is 105dB
(a)
(b)
Fig 46 Radiation pattern at 10GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 10λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-46-
Fig 47 shows the geometry of a circular waveguide with a tapered
dielectric rod The designed feed has the following dimension L = 1λ0 d =
1λ0 and εr =25 at 10GHz The waveguide length is 40mm and the wall
thickness is 05mm
L
Dielectricd3
Fig 47 Geometry of a circular waveguide loaded with a tapered dielectric
rod
Fig 48 shows the radiatio pattern of the designed feed E- and H-plane
10-dB beamwidths are 575 and 564 degrees respectively The front-to-back
ratio is 377dB The antenna gain is 94dB The designed feed has an
excellent beamwidth symmetry and a very low back radiation
-47-
(a)
(b)
Fig 48 Radiation pattern of a circular waveguide loaded with a tapered
dielectric rod with L = 1λ0 d = 1λ0 and εr =25 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-48-
Fig 49 shows the geometry of a spherical ended dielectric rod feed
diameter of 06λ0 at 10GHz with a dielectric constant of 25 and L= 03λ0
Fig 410 shows the radiation patterns of the designed feed E- and H-plane
10-dB beamwidths are both 63 degrees The front-to-back ratio is 24dB The
antenna gain is 864dB
Fig 49 Geometry of a circular waveguide loaded with a spherical ended
dielectric rod
-49-
(a)
(b)
Fig 410 Radiation pattern of a circular waveguide loaded wht a spherical
ended dielectric rod with d = 06λ0 L = 03λ0 and εr =25 at 10GHz (a) 3D
radiation pattern and (b) E- and H-plane patterns
-50-
V Design of a Broadband Circular Waveguide Feed
In this chapter the design of a broadband circular waveguide feed is
presented At microwave frequencies the feed is often a circular waveguide
with chokes and corrugations around the aperture Chokes and corrugations
equalize E- and H-plane patterns and reduce the back radiation
The proposed feed is designed to operate over 10-18GHz The design starts
with the optimization of the coaxial-to-rectangular waveguide adapter
employed for good mode purity over a broad frequency range Next a
rectangular-to-circular waveguide transition is optimized Finally chokes and
corrugations are designed for improved pattern symmetry and low back
radiation
The proposed feed structure is shown in Fig 51 The feed consist of the
following parts a coaxial-to-rectangular waveguide adapter a rectangular-to-
circular waveguide transition a circular waveguide section four quarter-wave
chokes around the feeds aperture and four corrugations on the feeds outer
surface
The computer simulation shows the above arrangement offers good radiation
patterns over a broad frequency range The broadband operation is obtained
by exciting the TE11 mode in the circular waveguide using the TE10 mode of
the rectangular waveguide which is in turn excited by a coaxial probe
-51-
Chokes
Coaxial-to-waveguide transition
Circular wavguide
Corrugations
Mode transition
(a)
(b)
Fig 51 Structure of the proposed broadband circular waveguide feed
(a) CAD model and (b) cross-sectional view
For the coaxial-to-rectangular waveguide adapter an SMA connector with
the probe diameter of 127 mm is employed The coaxial probe inserted into
the waveguide energizes the feed and excites the dominant TE10 mode in
-52-
the rectangular waveguide The impedance matching is achieved by adjusting
the probe distance sp from the back short and the probe length lp
(a)
(b)
Fig 52 Reflection coefficient of the coaxial-to-rectangular adapter versus
(a) probe length lp and (b) the probe position sp
Fig 52 shows the reflection coefficient versus the various values of probe
lengths lp and probe positions sp The probe length lp is adjusted to obtain
antenna impedance matching and the probe distance sp is adjusted to obtain a
-53-
desired resonant frequency
Next a transition between rectangular and circular waveguide is designed
The transition section converts the TE10 mode in the rectangular waveguide to
TE11 mode in the circular waveguide and vice versa The transition is built
in a form of a taper for easy fabrication[22]
(a)
(b)
Fig 53 Structure of the rectangular-to-circular waveguide transition
(a) 3D view and (b) cross sectional view
The dimensions of the final optimized transition are as follows The length
of the rectangular waveguide section is 143mm The rectangular waveguides
width a and height b are 207mm and 857mm respectively The length of
the circular waveguide section is 143mm The inside diameter of the circular
-54-
waveguide is 207mm(097 wavelength at 14GHz) The length of transition
region ltr is 4465mm(approximately equal to 2λ0 at 14GHz) Fig 54 shows
the field distribution inside the mode converter
(a)
(b)
Fig 54 Field distribution inside the mode converter at
(a) 10GHz (b) 14GHz and (c) 18GHz
-55-
(c)
Fig 54 continued
Finally multiple chokes are investigated Figs 55 56 and 57 show the
feed performance without chokes The reflection coefficient is less than -10dB
over 10-19GHz The antenna has a gain of 921dB to 1189dB over
10-19GHz
Fig 55 Reflection coefficient of the broadband circular waveguide feed
without chokes and corrugations
-56-
(a)
(b)
(c)
Fig 56 E- and H-plane patterns of the broadband circular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-57-
(d)
(e)
Fig 56 continued
-58-
(a)
(b)
Fig 57 2D radiation patterns of the broadband cicular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-59-
(c)
(d)
Fig 57 continued
-60-
(e)
Fig 57 continued
To achieve equal beamwidths in E and H planes over a wide frequency
range chokes and corrugations are employed Table51 summarizes the
performance of a feed without chokes and corrugations
Table 51 Performance of the broadband circular waveguide feed without
chokes and corrugations
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
1000 940 6061 15
1200 972 6159 17
1400 920 5957 21
1600 1070 4751 29
1800 1188 5352 21
-61-
Four quarter-wavelength chokes are introduced in the feed design which
has a slot depth of 75mm and slot width of 09mm The choke slot spacing
is 18mm The choke design is investigated by applying the choke one by
one and the effect on the E- and H-plane patterns are observed as illustrated
in Figs 58 and 59 The use of chokes makes the E-plane pattern narrower
The H-plane pattern is not affected Chokes increase the gain slightly and
reduce back radiation
(a)
(b)
Fig 58 Effect of chokes on the E-plane pattern of the broadband circular
waveguide feed at (a) 10GHz(b) 12GHz (c) 14GHz (d) 16GHz and (e)
18GHz
-62-
(c)
(d)
(e)
Fig 58 continued
-63-
(a)
(b)
(c)
Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-64-
(d)
(e)
Fig 59 continued
-65-
Fig 510 shows the feed performance versus the choke depth When the
choke depth is varied from 535mm to 95mm the E- and H-plane patterns
are strongly affected The optimum value of choke depth is 75mm(035λ0 at
14GHz) which gives equal E- and H-plane radiation patterns and leads to
low back radiation
Fig 511 shows the feed performance versus the choke slot width tch The
choke slot width is varied from 09mm to 21mm Radiation patterns and
reflection coefficients are not sensitive to the choke slot width The final
choke slot width is selected to be 09mm considering the feed diameter
minimization and the manufacturability The overall diameter of the proposed
feed is 369mm which is increased from the 207mm of the waveguide
inside diameter due to the use of four chokes
-66-
(a)
(b)
(c)
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection coefficient
-67-
(a)
(b)
(c)
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and (c)
reflection coefficient
-68-
Next we investigated corrugations placed on the outer wall of the feed
Four corrugations applied to the outer surface of the circular waveguide The
corrugation depth is 465mm(0215λ0 at 14GHz) The primary purpose of
using corrugations is to further reduce the back radiation Increasing the
number of corrugations beyond four has little effect in reducing the back
radiation
Figs 512 and 513 show the effect of corrugations on the E- and H-plane
patterns Fig 514 shows the parametric study of the corrugation depth lcor
The corrugation depth is varied from 40mm and 645mm The optimum
value of the corrugation depth is found to be 465mm
-69-
(a)
(b)
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern at (a) 12GHz and (b) 14GHz
-70-
(a)
(b)
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern at (a) 12GHz and (b) 14GHz
-71-
(a)
(b)
(c)
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection coefficient
-72-
The phase center location is important in placing the feed in a reflector
antenna[8] The phase center variation with frequency should be small Fig
515 shows the effect of chokes and corrugations on the phase center The
curve with circle corresponds to the case without chokes and corrugations
The phase center varies from -326mm and -190mm away from the feeds
aperture plane It means the phase center is located inside the waveguide
The curve with triangles corresponds to the case with chokes The curve with
squares to the case with chokes and corrugations The phase center varies
from 0mm to -302mm
From Fig 515 we can observed that phase center variation reduced by the
corrugation and three cases phase center calculated in φ=450 plane
parameter sweep values are given in Table 52
10 12 14 16 181
0
-1
-2
-3
-4
-5
-6
Pha
se c
ente
r (m
m)
Frequency (GHz)
choke+corrugatuion without choke corrugation with choke
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
-73-
Frequency
(GHz)
Phase center from the aperture plane
(mm)
Without
chokes and
corrugations
With
chokes
With chokes
and
corrugations
1000 -326 062 000
1100 -187 030 -002
1200 -563 -208 -065
1300 -296 -154 -202
1400 -319 -314 -302
1500 -201 -203 -241
1600 -242 -233 -207
1700 -208 -208 -186
1800 -190 -157 -132
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
Based on the foregoing parametric studies optimum dimensions of the
broadband circular waveguide feed are obtained as shown in Table 53
-74-
Table 53 Optimum dimensions of the broadband circular waveguide feed
Parameter Designation Value (mm)
2a Waveguide inside diameter 2070
d Waveguide outside diameter 3690
lcrLength of the circular waveguide section 1430
m Distance between the aperture plane and the first corrugation 950
xDistance from the last corrugation to the end of the cylindrical outer surface
550
ltrLength of the rectangular-to-circularwaveguide transition 4465
lrcLength of the rectangular waveguide section 1430
tch Choke slot width 090
lch Choke depth 750
t Choke metal width 090
lcor Corrugation depth 465
tcor Corrugation metal width 100
s Corrugation slot width 10
lp Probe length 530
sp Probe position from the back short 530
din Probe diameter 127
b Inside height of the rectangular waveguide 857
tw Waveguide wall thickness 500
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-19-
(a)
(b)
(c)
Fig 212 E- and H-plane patterns of the probe-fed circular waveguide
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-20-
Table 23 Properties of the probe-fed circular waveguide radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 73 70 1414 83 57 17
18 60 52 30
When a circular waveguide radiator is fed by a coaxial probe its radiation
properties are not good due to the excitation of higher-order modes
Therefore a probe-fed circular waveguide radiator can be used as a feed only
over a narrow frequency range
24 Probe-Fed Square Waveguide Radiator
In this section a probe-fed square waveguide radiator is investigated Fig
213 shows a coaxial probe-fed square waveguide radiator The designed
radiator has the following dimension a = b = 157mm lp = 35 mm sp =
50 mm wall thickness = 05mm and feed length = 40mm
(a) (b)
Fig 213 Probe-fed square waveguide radiator (a) Front view and (b) side
view
-21-
Fig 214 shows the 2D radiation patterns of the radiator at 10GHz
14GHz and 18GHz Fig 215 shows E- and H-plane patterns of the radiator
Fig 216 shows the reflection coefficient of the probe-fed square waveguide
radiator The reflection coefficient is less than -10dB over 13-20GHz Table
24 summarizes the properties of the probe-fed square waveguide radiator
(a)
Fig 214 2D radiation patterns of the probe-fed square waveguide radiator at
(a) 10GHz (b) 14GHz and (c) 18GHz
-22-
(b)
(c)
Fig 214 continued
-23-
(a)
(b)
(c)
Fig 216 E-plane and H-plane patterns of the probe-fed square waveguide
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-24-
Fig 216 Reflection coefficient of the probe-fed square waveguide radiator
Table 24 Properties of the probe-fed square waveguide radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 73 71 12
14 85 63 1418 27 65 28
When a square waveguide radiator is fed by a coaxial probe its radiation
properties are not good due to the excitation of higher-order modes as in the
case of the probe-fed circular waveguide radiator A probe-fed square
waveguide radiator can be used as a feed only over a narrow frequency
range
-25-
III Design of Compact Circular Waveguide Feeds
In this chapter the feed design is presented for a prime-focus reflector
antenna The prime-focus paraboloid reflector is one of the most commonly
used high-gain antenna It has been used in earth-station antennas and radio
telescopes It consists of a paraboloid reflector with a feed system at its focal
point
The feed should radiate a low level of cross-polar power over the
operating frequency These conditions not easy to achieve and most prime
focus feeds are compromises The shape and characteristic of the radiation
pattern of the feed are the most important parameter because these will
directly influence the fields which are directed at a reflector[6] Other
electrical factors which relevant to the choice of a feed are the cross-polar
level the gain efficiency the bandwidth and impedance matching
31 Narrow-Band Circular Waveguide Feed
Fig 31 shows the proposed narrow-band circular waveguide feed and its
design variables The feed consists of a circular waveguide open end excited
by a TE11 dominant mode A quarter wave choke is applied along the
circular aperture of the waveguide to equalize E- and H-plane radiation
patterns and to suppress the back radiation A dielectric ring is used to
control the radiation pattern and change the power distribution over the
aperture The control of the amplitude over the aperture are essential to the
design of symmetric radiation pattern The material used for dielectric loading
-26-
is the monocast(MC) nylon with a dielectric constant of 30 The feed is
designed to operate over 171-197GHz
(a)
(b)
Fig 31 Narrow-band circular waveguide feed (a) CAD model and (b) a
cross sectional view
The impedance matching is achieved by a proper combination of the probe
height lp and its distance sp from the waveguide shorted end Here the
-27-
circular waveguide is terminated with an open end with a wall thickness of
2mm radiating into the free space
Fig 32 shows the effect of the probe length lp and the probe distance sp
on the reflection coefficient The best performance is obtained when lp =
363mm and sp = 616mm The feeds reflection coefficient is less than -10dB
over 170-195GHz
(a)
(b)
Fig 32 Effect of the (a) the probe length lp and (b) the probe
distance sp on the reflection coefficient
-28-
Fig 33 shows the effect of the choke depth The E-plane pattern is more
sensitive to the choke depth than the H-plane pattern The choke depth has a
strong influence on the reflection coefficient when it is 360mm By properly
choosing the choke depth we can equalize the E- and H-plane patterns The
optimum value of the choke depth is 410mm which is 0249λ0 at 1825GHz
The choke slot width tch in the range of 06-12mm has almost no effect
on the H-plane pattern and the reflection coefficient For the E-plane pattern
tch of 12mm has some effect on the E-plane radiation pattern as shown in
Fig 34
Fig 35 shows the feed performance versus the dielectric ring length We
observe in Fig 35 that the dielectric length ld has an optimum value of
1168mm which does no effect on the H-plane pattern and tha the value of
1048mm has some effect on the E-plane pattern and the reflection
coefficient
Fig 36 shows E-plane and H-plane patterns and the reflection coefficient
versus the dielectric thickness With the optimum value of the dielectric
thickness t obtained from the Fig 36 is 155mm The larger values of td has
much stronger effects on the E-plane pattern and the reflection coefficient
The H-plane pattern is not sensitive to the dielectric ring thickness
-29-
(a)
(b)
(c)
Fig 33 Feed performance versus the choke depth (a) E-plane pattern
(b) H-plane pattern and (c) reflection coefficient
-30-
(a)
(b)
(c)
Fig 34 Feed performance versus the choke slot width (a) E-plane pattern
(b) H-plane pattern and (c) reflection coefficient
-31-
(a)
(b)
(c)
Fig 35 Feed performance versus the dielectric ring length (a) E-plane
pattern (b) H-plane pattern and (c) reflection coefficient
-32-
(a)
(b)
(c)
Fig 36 Feed performance versus the dielectric ring thickness (a) E-plane
pattern(b) H-plane pattern and (c) reflection coefficient
-33-
From the above parametric analysis an optimum feed design is obtained
The result is shown in Table 31 Fig 37 shows the 2D gain patterns of
designed feed The antenna has a gain of 903dB 933dB and 956dB at
171GHz 1825GHz and 19GHz respectively
Fig 38 shows E- and H-plane radiation patterns of the designed feed The
feed has E- and H-plane 10-dB beamwidths of 60 and 59 degrees at 17GHz
The feed has a front-to-back ration of 1900dB 2490dB and 2200dB at
171GHz 1825GHz and 19GHz respectively Table 32 summarizes the
performance of the designed narrow-band circular waveguide feed
The designed feed has a greatly improved performance over that of a
simple coax-fed feed described in Section 23
Table 31 Dimensions of the designed narrow-band circular feed
Parameter Designation Value(mm)
a Waveguide inside radius 640
l Feed length 2890
lp Probe length 363
sp Probe position from the back short 616
din Probe diameter 127
dout Diameter of coaxial cables outer conductor 400
t Thickness of choked wall 050
tch Choke slot width 100
lch Choke depth 410
ld Dielectric ring length 1168
td Dielectric ring thickness 155
d1 Waveguide outside diameter 1680
-34-
(a)
(b)
Fig 37 2D gain patterns of the narrow-band circular waveguide feed at
(a) 17GHz (b) 1825GHz and (c) 19GHz
-35-
(c)
Fig 37 continued
-36-
(a)
(b)
(c)
Fig 38 E- and H-plane patterns of the narrow-band circular waveguide feed
at (a) 10GHz (b) 1825GHz and (c) 195GHz
-37-
Frequency(GHz)
Gain(dB)
E-H-plane10-dB beamwidths
(deg)
Front-to-back ratio(dB)
Phase centerlocation
(From feeds aperture plane
toward reflector)
(mm)
1700 903 6059 20 062
1825 933 6060 25 004
1900 956 5759 22 007
Table 32 Performance of the narrow-band circular waveguide feed
The designed narrow-band feed is fabricated and its performance is
measured and compared with the simulation results The designed feed is
fabricated in a numerically-controlled machining center The fabricated antenna
is shown in Fig 39
Fig 39 Photograph of the fabricated feed
-38-
Fig 310 shows a comparison of the measured and simulated reflection
coefficients The measured reflection coefficient is less than -10dB over
171-197GHz The agreement between simulated and measured results are
good
Fig 311 shows the E- and H-plane patterns of the fabricated feed at
187GHz The feed has 90dB gain simulation and measurement results are in
good agreement
The fabricated antennarsquos 10dB beamwidth is 60 degrees in both E and H
planes at 187GHz The front-to-back ratio is 21dB
Fig 310 Reflection coefficient of the fabricated feed
-39-
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Fee
d H
orn
Gain
- d
B
Angle - degree
(a)
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Feed H
orn
Gain
- d
B
Angle - degree
(b)
Fig 311 Gain patterns of the fabricated feed at 187 GHz (a) E-plane and
(b) H-plane
-40-
IV Design of Circular Waveguide Feeds Loaded with a
Dielectric Rod
In this section circular waveguide feeds loaded with a dielectric rod feed
are investigated A comprehensive discussion of the circular waveguide loaded
with a dielectric rod is given by Kumar[7] Inserting a dielectric material
inside the circular waveguide improves the E- and H-plane pattern symmetry
In general dielectric-loaded circular waveguide feeds show good performance
only over a narrow bandwidth
Fig 41 shows the geometry of a circular waveguide loaded with a
dielectric rod The waveguide length is 400mm and the wall thickness is
05mm The dielectric rods diameter is 207mm The dielectric rod is
extended 05 wavelength beyond the waveguide open end The dielectric
constant εr is changed and the feeds performance is observed
Fig 41 Geometry of a circular waveguide loaded with a uniform dielectric
rod
-41-
Fig 42 is the radiation pattern of the feed with εr = 25 and L = 05λ0 at
9GHz E- and H-plane 10-dB beamwidths are 810 and 807 degrees
respectively The front-to-back ratio is 18dB The antenna gain is 71dB
(a)
(b)
Fig 42 Radiation pattern at 9GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 05λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-42-
Fig 43 shows the radiation pattern of the feed with εr = 21 at 10GHz
E- and H-plane 10-dB beamwidths are 70 and 71 degrees respectively The
front-to-back ratio is 19dB The antenna gain is 83dB
(a)
(b)
Fig 43 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 21 and L = 05λ0 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-43-
Fig 44 shows the radiation pattern of the feed with εr = 30 at 8GHz
E- and H-plane 10-dB beamwidths are 83 and 824 degrees respectively The
front-to-back ratio is 17dB The antenna gain is 73dB
(a)
(b)
Fig 44 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 30 and L = 05λ0 at 8GHz (a) 2D radiation pattern
and (b) E- and H-plane patterns
-44-
Fig 45 shows the radiation pattern of the feed with εr = 50 at 18GHz
E- and H-plane 10-dB beamwidths are 56 and 54 degrees respectively The
front-to-back ratio is 27dB The antenna gain is 105dB The feed has a good
pattern symmetry and low back radiation
(a)
(b)
Fig 45 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 50 and L = 05λ0 at 18GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-45-
Fig 46 is the radiation pattern of the feed with εr = 25 and L = 10λ0 at
10GHz E- and H-plane 10-dB beamwidths are 50 and 48 degrees
respectively The front-to-back ratio is 16dB The antenna gain is 105dB
(a)
(b)
Fig 46 Radiation pattern at 10GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 10λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-46-
Fig 47 shows the geometry of a circular waveguide with a tapered
dielectric rod The designed feed has the following dimension L = 1λ0 d =
1λ0 and εr =25 at 10GHz The waveguide length is 40mm and the wall
thickness is 05mm
L
Dielectricd3
Fig 47 Geometry of a circular waveguide loaded with a tapered dielectric
rod
Fig 48 shows the radiatio pattern of the designed feed E- and H-plane
10-dB beamwidths are 575 and 564 degrees respectively The front-to-back
ratio is 377dB The antenna gain is 94dB The designed feed has an
excellent beamwidth symmetry and a very low back radiation
-47-
(a)
(b)
Fig 48 Radiation pattern of a circular waveguide loaded with a tapered
dielectric rod with L = 1λ0 d = 1λ0 and εr =25 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-48-
Fig 49 shows the geometry of a spherical ended dielectric rod feed
diameter of 06λ0 at 10GHz with a dielectric constant of 25 and L= 03λ0
Fig 410 shows the radiation patterns of the designed feed E- and H-plane
10-dB beamwidths are both 63 degrees The front-to-back ratio is 24dB The
antenna gain is 864dB
Fig 49 Geometry of a circular waveguide loaded with a spherical ended
dielectric rod
-49-
(a)
(b)
Fig 410 Radiation pattern of a circular waveguide loaded wht a spherical
ended dielectric rod with d = 06λ0 L = 03λ0 and εr =25 at 10GHz (a) 3D
radiation pattern and (b) E- and H-plane patterns
-50-
V Design of a Broadband Circular Waveguide Feed
In this chapter the design of a broadband circular waveguide feed is
presented At microwave frequencies the feed is often a circular waveguide
with chokes and corrugations around the aperture Chokes and corrugations
equalize E- and H-plane patterns and reduce the back radiation
The proposed feed is designed to operate over 10-18GHz The design starts
with the optimization of the coaxial-to-rectangular waveguide adapter
employed for good mode purity over a broad frequency range Next a
rectangular-to-circular waveguide transition is optimized Finally chokes and
corrugations are designed for improved pattern symmetry and low back
radiation
The proposed feed structure is shown in Fig 51 The feed consist of the
following parts a coaxial-to-rectangular waveguide adapter a rectangular-to-
circular waveguide transition a circular waveguide section four quarter-wave
chokes around the feeds aperture and four corrugations on the feeds outer
surface
The computer simulation shows the above arrangement offers good radiation
patterns over a broad frequency range The broadband operation is obtained
by exciting the TE11 mode in the circular waveguide using the TE10 mode of
the rectangular waveguide which is in turn excited by a coaxial probe
-51-
Chokes
Coaxial-to-waveguide transition
Circular wavguide
Corrugations
Mode transition
(a)
(b)
Fig 51 Structure of the proposed broadband circular waveguide feed
(a) CAD model and (b) cross-sectional view
For the coaxial-to-rectangular waveguide adapter an SMA connector with
the probe diameter of 127 mm is employed The coaxial probe inserted into
the waveguide energizes the feed and excites the dominant TE10 mode in
-52-
the rectangular waveguide The impedance matching is achieved by adjusting
the probe distance sp from the back short and the probe length lp
(a)
(b)
Fig 52 Reflection coefficient of the coaxial-to-rectangular adapter versus
(a) probe length lp and (b) the probe position sp
Fig 52 shows the reflection coefficient versus the various values of probe
lengths lp and probe positions sp The probe length lp is adjusted to obtain
antenna impedance matching and the probe distance sp is adjusted to obtain a
-53-
desired resonant frequency
Next a transition between rectangular and circular waveguide is designed
The transition section converts the TE10 mode in the rectangular waveguide to
TE11 mode in the circular waveguide and vice versa The transition is built
in a form of a taper for easy fabrication[22]
(a)
(b)
Fig 53 Structure of the rectangular-to-circular waveguide transition
(a) 3D view and (b) cross sectional view
The dimensions of the final optimized transition are as follows The length
of the rectangular waveguide section is 143mm The rectangular waveguides
width a and height b are 207mm and 857mm respectively The length of
the circular waveguide section is 143mm The inside diameter of the circular
-54-
waveguide is 207mm(097 wavelength at 14GHz) The length of transition
region ltr is 4465mm(approximately equal to 2λ0 at 14GHz) Fig 54 shows
the field distribution inside the mode converter
(a)
(b)
Fig 54 Field distribution inside the mode converter at
(a) 10GHz (b) 14GHz and (c) 18GHz
-55-
(c)
Fig 54 continued
Finally multiple chokes are investigated Figs 55 56 and 57 show the
feed performance without chokes The reflection coefficient is less than -10dB
over 10-19GHz The antenna has a gain of 921dB to 1189dB over
10-19GHz
Fig 55 Reflection coefficient of the broadband circular waveguide feed
without chokes and corrugations
-56-
(a)
(b)
(c)
Fig 56 E- and H-plane patterns of the broadband circular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-57-
(d)
(e)
Fig 56 continued
-58-
(a)
(b)
Fig 57 2D radiation patterns of the broadband cicular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-59-
(c)
(d)
Fig 57 continued
-60-
(e)
Fig 57 continued
To achieve equal beamwidths in E and H planes over a wide frequency
range chokes and corrugations are employed Table51 summarizes the
performance of a feed without chokes and corrugations
Table 51 Performance of the broadband circular waveguide feed without
chokes and corrugations
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
1000 940 6061 15
1200 972 6159 17
1400 920 5957 21
1600 1070 4751 29
1800 1188 5352 21
-61-
Four quarter-wavelength chokes are introduced in the feed design which
has a slot depth of 75mm and slot width of 09mm The choke slot spacing
is 18mm The choke design is investigated by applying the choke one by
one and the effect on the E- and H-plane patterns are observed as illustrated
in Figs 58 and 59 The use of chokes makes the E-plane pattern narrower
The H-plane pattern is not affected Chokes increase the gain slightly and
reduce back radiation
(a)
(b)
Fig 58 Effect of chokes on the E-plane pattern of the broadband circular
waveguide feed at (a) 10GHz(b) 12GHz (c) 14GHz (d) 16GHz and (e)
18GHz
-62-
(c)
(d)
(e)
Fig 58 continued
-63-
(a)
(b)
(c)
Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-64-
(d)
(e)
Fig 59 continued
-65-
Fig 510 shows the feed performance versus the choke depth When the
choke depth is varied from 535mm to 95mm the E- and H-plane patterns
are strongly affected The optimum value of choke depth is 75mm(035λ0 at
14GHz) which gives equal E- and H-plane radiation patterns and leads to
low back radiation
Fig 511 shows the feed performance versus the choke slot width tch The
choke slot width is varied from 09mm to 21mm Radiation patterns and
reflection coefficients are not sensitive to the choke slot width The final
choke slot width is selected to be 09mm considering the feed diameter
minimization and the manufacturability The overall diameter of the proposed
feed is 369mm which is increased from the 207mm of the waveguide
inside diameter due to the use of four chokes
-66-
(a)
(b)
(c)
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection coefficient
-67-
(a)
(b)
(c)
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and (c)
reflection coefficient
-68-
Next we investigated corrugations placed on the outer wall of the feed
Four corrugations applied to the outer surface of the circular waveguide The
corrugation depth is 465mm(0215λ0 at 14GHz) The primary purpose of
using corrugations is to further reduce the back radiation Increasing the
number of corrugations beyond four has little effect in reducing the back
radiation
Figs 512 and 513 show the effect of corrugations on the E- and H-plane
patterns Fig 514 shows the parametric study of the corrugation depth lcor
The corrugation depth is varied from 40mm and 645mm The optimum
value of the corrugation depth is found to be 465mm
-69-
(a)
(b)
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern at (a) 12GHz and (b) 14GHz
-70-
(a)
(b)
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern at (a) 12GHz and (b) 14GHz
-71-
(a)
(b)
(c)
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection coefficient
-72-
The phase center location is important in placing the feed in a reflector
antenna[8] The phase center variation with frequency should be small Fig
515 shows the effect of chokes and corrugations on the phase center The
curve with circle corresponds to the case without chokes and corrugations
The phase center varies from -326mm and -190mm away from the feeds
aperture plane It means the phase center is located inside the waveguide
The curve with triangles corresponds to the case with chokes The curve with
squares to the case with chokes and corrugations The phase center varies
from 0mm to -302mm
From Fig 515 we can observed that phase center variation reduced by the
corrugation and three cases phase center calculated in φ=450 plane
parameter sweep values are given in Table 52
10 12 14 16 181
0
-1
-2
-3
-4
-5
-6
Pha
se c
ente
r (m
m)
Frequency (GHz)
choke+corrugatuion without choke corrugation with choke
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
-73-
Frequency
(GHz)
Phase center from the aperture plane
(mm)
Without
chokes and
corrugations
With
chokes
With chokes
and
corrugations
1000 -326 062 000
1100 -187 030 -002
1200 -563 -208 -065
1300 -296 -154 -202
1400 -319 -314 -302
1500 -201 -203 -241
1600 -242 -233 -207
1700 -208 -208 -186
1800 -190 -157 -132
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
Based on the foregoing parametric studies optimum dimensions of the
broadband circular waveguide feed are obtained as shown in Table 53
-74-
Table 53 Optimum dimensions of the broadband circular waveguide feed
Parameter Designation Value (mm)
2a Waveguide inside diameter 2070
d Waveguide outside diameter 3690
lcrLength of the circular waveguide section 1430
m Distance between the aperture plane and the first corrugation 950
xDistance from the last corrugation to the end of the cylindrical outer surface
550
ltrLength of the rectangular-to-circularwaveguide transition 4465
lrcLength of the rectangular waveguide section 1430
tch Choke slot width 090
lch Choke depth 750
t Choke metal width 090
lcor Corrugation depth 465
tcor Corrugation metal width 100
s Corrugation slot width 10
lp Probe length 530
sp Probe position from the back short 530
din Probe diameter 127
b Inside height of the rectangular waveguide 857
tw Waveguide wall thickness 500
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-20-
Table 23 Properties of the probe-fed circular waveguide radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 73 70 1414 83 57 17
18 60 52 30
When a circular waveguide radiator is fed by a coaxial probe its radiation
properties are not good due to the excitation of higher-order modes
Therefore a probe-fed circular waveguide radiator can be used as a feed only
over a narrow frequency range
24 Probe-Fed Square Waveguide Radiator
In this section a probe-fed square waveguide radiator is investigated Fig
213 shows a coaxial probe-fed square waveguide radiator The designed
radiator has the following dimension a = b = 157mm lp = 35 mm sp =
50 mm wall thickness = 05mm and feed length = 40mm
(a) (b)
Fig 213 Probe-fed square waveguide radiator (a) Front view and (b) side
view
-21-
Fig 214 shows the 2D radiation patterns of the radiator at 10GHz
14GHz and 18GHz Fig 215 shows E- and H-plane patterns of the radiator
Fig 216 shows the reflection coefficient of the probe-fed square waveguide
radiator The reflection coefficient is less than -10dB over 13-20GHz Table
24 summarizes the properties of the probe-fed square waveguide radiator
(a)
Fig 214 2D radiation patterns of the probe-fed square waveguide radiator at
(a) 10GHz (b) 14GHz and (c) 18GHz
-22-
(b)
(c)
Fig 214 continued
-23-
(a)
(b)
(c)
Fig 216 E-plane and H-plane patterns of the probe-fed square waveguide
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-24-
Fig 216 Reflection coefficient of the probe-fed square waveguide radiator
Table 24 Properties of the probe-fed square waveguide radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 73 71 12
14 85 63 1418 27 65 28
When a square waveguide radiator is fed by a coaxial probe its radiation
properties are not good due to the excitation of higher-order modes as in the
case of the probe-fed circular waveguide radiator A probe-fed square
waveguide radiator can be used as a feed only over a narrow frequency
range
-25-
III Design of Compact Circular Waveguide Feeds
In this chapter the feed design is presented for a prime-focus reflector
antenna The prime-focus paraboloid reflector is one of the most commonly
used high-gain antenna It has been used in earth-station antennas and radio
telescopes It consists of a paraboloid reflector with a feed system at its focal
point
The feed should radiate a low level of cross-polar power over the
operating frequency These conditions not easy to achieve and most prime
focus feeds are compromises The shape and characteristic of the radiation
pattern of the feed are the most important parameter because these will
directly influence the fields which are directed at a reflector[6] Other
electrical factors which relevant to the choice of a feed are the cross-polar
level the gain efficiency the bandwidth and impedance matching
31 Narrow-Band Circular Waveguide Feed
Fig 31 shows the proposed narrow-band circular waveguide feed and its
design variables The feed consists of a circular waveguide open end excited
by a TE11 dominant mode A quarter wave choke is applied along the
circular aperture of the waveguide to equalize E- and H-plane radiation
patterns and to suppress the back radiation A dielectric ring is used to
control the radiation pattern and change the power distribution over the
aperture The control of the amplitude over the aperture are essential to the
design of symmetric radiation pattern The material used for dielectric loading
-26-
is the monocast(MC) nylon with a dielectric constant of 30 The feed is
designed to operate over 171-197GHz
(a)
(b)
Fig 31 Narrow-band circular waveguide feed (a) CAD model and (b) a
cross sectional view
The impedance matching is achieved by a proper combination of the probe
height lp and its distance sp from the waveguide shorted end Here the
-27-
circular waveguide is terminated with an open end with a wall thickness of
2mm radiating into the free space
Fig 32 shows the effect of the probe length lp and the probe distance sp
on the reflection coefficient The best performance is obtained when lp =
363mm and sp = 616mm The feeds reflection coefficient is less than -10dB
over 170-195GHz
(a)
(b)
Fig 32 Effect of the (a) the probe length lp and (b) the probe
distance sp on the reflection coefficient
-28-
Fig 33 shows the effect of the choke depth The E-plane pattern is more
sensitive to the choke depth than the H-plane pattern The choke depth has a
strong influence on the reflection coefficient when it is 360mm By properly
choosing the choke depth we can equalize the E- and H-plane patterns The
optimum value of the choke depth is 410mm which is 0249λ0 at 1825GHz
The choke slot width tch in the range of 06-12mm has almost no effect
on the H-plane pattern and the reflection coefficient For the E-plane pattern
tch of 12mm has some effect on the E-plane radiation pattern as shown in
Fig 34
Fig 35 shows the feed performance versus the dielectric ring length We
observe in Fig 35 that the dielectric length ld has an optimum value of
1168mm which does no effect on the H-plane pattern and tha the value of
1048mm has some effect on the E-plane pattern and the reflection
coefficient
Fig 36 shows E-plane and H-plane patterns and the reflection coefficient
versus the dielectric thickness With the optimum value of the dielectric
thickness t obtained from the Fig 36 is 155mm The larger values of td has
much stronger effects on the E-plane pattern and the reflection coefficient
The H-plane pattern is not sensitive to the dielectric ring thickness
-29-
(a)
(b)
(c)
Fig 33 Feed performance versus the choke depth (a) E-plane pattern
(b) H-plane pattern and (c) reflection coefficient
-30-
(a)
(b)
(c)
Fig 34 Feed performance versus the choke slot width (a) E-plane pattern
(b) H-plane pattern and (c) reflection coefficient
-31-
(a)
(b)
(c)
Fig 35 Feed performance versus the dielectric ring length (a) E-plane
pattern (b) H-plane pattern and (c) reflection coefficient
-32-
(a)
(b)
(c)
Fig 36 Feed performance versus the dielectric ring thickness (a) E-plane
pattern(b) H-plane pattern and (c) reflection coefficient
-33-
From the above parametric analysis an optimum feed design is obtained
The result is shown in Table 31 Fig 37 shows the 2D gain patterns of
designed feed The antenna has a gain of 903dB 933dB and 956dB at
171GHz 1825GHz and 19GHz respectively
Fig 38 shows E- and H-plane radiation patterns of the designed feed The
feed has E- and H-plane 10-dB beamwidths of 60 and 59 degrees at 17GHz
The feed has a front-to-back ration of 1900dB 2490dB and 2200dB at
171GHz 1825GHz and 19GHz respectively Table 32 summarizes the
performance of the designed narrow-band circular waveguide feed
The designed feed has a greatly improved performance over that of a
simple coax-fed feed described in Section 23
Table 31 Dimensions of the designed narrow-band circular feed
Parameter Designation Value(mm)
a Waveguide inside radius 640
l Feed length 2890
lp Probe length 363
sp Probe position from the back short 616
din Probe diameter 127
dout Diameter of coaxial cables outer conductor 400
t Thickness of choked wall 050
tch Choke slot width 100
lch Choke depth 410
ld Dielectric ring length 1168
td Dielectric ring thickness 155
d1 Waveguide outside diameter 1680
-34-
(a)
(b)
Fig 37 2D gain patterns of the narrow-band circular waveguide feed at
(a) 17GHz (b) 1825GHz and (c) 19GHz
-35-
(c)
Fig 37 continued
-36-
(a)
(b)
(c)
Fig 38 E- and H-plane patterns of the narrow-band circular waveguide feed
at (a) 10GHz (b) 1825GHz and (c) 195GHz
-37-
Frequency(GHz)
Gain(dB)
E-H-plane10-dB beamwidths
(deg)
Front-to-back ratio(dB)
Phase centerlocation
(From feeds aperture plane
toward reflector)
(mm)
1700 903 6059 20 062
1825 933 6060 25 004
1900 956 5759 22 007
Table 32 Performance of the narrow-band circular waveguide feed
The designed narrow-band feed is fabricated and its performance is
measured and compared with the simulation results The designed feed is
fabricated in a numerically-controlled machining center The fabricated antenna
is shown in Fig 39
Fig 39 Photograph of the fabricated feed
-38-
Fig 310 shows a comparison of the measured and simulated reflection
coefficients The measured reflection coefficient is less than -10dB over
171-197GHz The agreement between simulated and measured results are
good
Fig 311 shows the E- and H-plane patterns of the fabricated feed at
187GHz The feed has 90dB gain simulation and measurement results are in
good agreement
The fabricated antennarsquos 10dB beamwidth is 60 degrees in both E and H
planes at 187GHz The front-to-back ratio is 21dB
Fig 310 Reflection coefficient of the fabricated feed
-39-
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Fee
d H
orn
Gain
- d
B
Angle - degree
(a)
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Feed H
orn
Gain
- d
B
Angle - degree
(b)
Fig 311 Gain patterns of the fabricated feed at 187 GHz (a) E-plane and
(b) H-plane
-40-
IV Design of Circular Waveguide Feeds Loaded with a
Dielectric Rod
In this section circular waveguide feeds loaded with a dielectric rod feed
are investigated A comprehensive discussion of the circular waveguide loaded
with a dielectric rod is given by Kumar[7] Inserting a dielectric material
inside the circular waveguide improves the E- and H-plane pattern symmetry
In general dielectric-loaded circular waveguide feeds show good performance
only over a narrow bandwidth
Fig 41 shows the geometry of a circular waveguide loaded with a
dielectric rod The waveguide length is 400mm and the wall thickness is
05mm The dielectric rods diameter is 207mm The dielectric rod is
extended 05 wavelength beyond the waveguide open end The dielectric
constant εr is changed and the feeds performance is observed
Fig 41 Geometry of a circular waveguide loaded with a uniform dielectric
rod
-41-
Fig 42 is the radiation pattern of the feed with εr = 25 and L = 05λ0 at
9GHz E- and H-plane 10-dB beamwidths are 810 and 807 degrees
respectively The front-to-back ratio is 18dB The antenna gain is 71dB
(a)
(b)
Fig 42 Radiation pattern at 9GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 05λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-42-
Fig 43 shows the radiation pattern of the feed with εr = 21 at 10GHz
E- and H-plane 10-dB beamwidths are 70 and 71 degrees respectively The
front-to-back ratio is 19dB The antenna gain is 83dB
(a)
(b)
Fig 43 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 21 and L = 05λ0 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-43-
Fig 44 shows the radiation pattern of the feed with εr = 30 at 8GHz
E- and H-plane 10-dB beamwidths are 83 and 824 degrees respectively The
front-to-back ratio is 17dB The antenna gain is 73dB
(a)
(b)
Fig 44 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 30 and L = 05λ0 at 8GHz (a) 2D radiation pattern
and (b) E- and H-plane patterns
-44-
Fig 45 shows the radiation pattern of the feed with εr = 50 at 18GHz
E- and H-plane 10-dB beamwidths are 56 and 54 degrees respectively The
front-to-back ratio is 27dB The antenna gain is 105dB The feed has a good
pattern symmetry and low back radiation
(a)
(b)
Fig 45 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 50 and L = 05λ0 at 18GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-45-
Fig 46 is the radiation pattern of the feed with εr = 25 and L = 10λ0 at
10GHz E- and H-plane 10-dB beamwidths are 50 and 48 degrees
respectively The front-to-back ratio is 16dB The antenna gain is 105dB
(a)
(b)
Fig 46 Radiation pattern at 10GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 10λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-46-
Fig 47 shows the geometry of a circular waveguide with a tapered
dielectric rod The designed feed has the following dimension L = 1λ0 d =
1λ0 and εr =25 at 10GHz The waveguide length is 40mm and the wall
thickness is 05mm
L
Dielectricd3
Fig 47 Geometry of a circular waveguide loaded with a tapered dielectric
rod
Fig 48 shows the radiatio pattern of the designed feed E- and H-plane
10-dB beamwidths are 575 and 564 degrees respectively The front-to-back
ratio is 377dB The antenna gain is 94dB The designed feed has an
excellent beamwidth symmetry and a very low back radiation
-47-
(a)
(b)
Fig 48 Radiation pattern of a circular waveguide loaded with a tapered
dielectric rod with L = 1λ0 d = 1λ0 and εr =25 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-48-
Fig 49 shows the geometry of a spherical ended dielectric rod feed
diameter of 06λ0 at 10GHz with a dielectric constant of 25 and L= 03λ0
Fig 410 shows the radiation patterns of the designed feed E- and H-plane
10-dB beamwidths are both 63 degrees The front-to-back ratio is 24dB The
antenna gain is 864dB
Fig 49 Geometry of a circular waveguide loaded with a spherical ended
dielectric rod
-49-
(a)
(b)
Fig 410 Radiation pattern of a circular waveguide loaded wht a spherical
ended dielectric rod with d = 06λ0 L = 03λ0 and εr =25 at 10GHz (a) 3D
radiation pattern and (b) E- and H-plane patterns
-50-
V Design of a Broadband Circular Waveguide Feed
In this chapter the design of a broadband circular waveguide feed is
presented At microwave frequencies the feed is often a circular waveguide
with chokes and corrugations around the aperture Chokes and corrugations
equalize E- and H-plane patterns and reduce the back radiation
The proposed feed is designed to operate over 10-18GHz The design starts
with the optimization of the coaxial-to-rectangular waveguide adapter
employed for good mode purity over a broad frequency range Next a
rectangular-to-circular waveguide transition is optimized Finally chokes and
corrugations are designed for improved pattern symmetry and low back
radiation
The proposed feed structure is shown in Fig 51 The feed consist of the
following parts a coaxial-to-rectangular waveguide adapter a rectangular-to-
circular waveguide transition a circular waveguide section four quarter-wave
chokes around the feeds aperture and four corrugations on the feeds outer
surface
The computer simulation shows the above arrangement offers good radiation
patterns over a broad frequency range The broadband operation is obtained
by exciting the TE11 mode in the circular waveguide using the TE10 mode of
the rectangular waveguide which is in turn excited by a coaxial probe
-51-
Chokes
Coaxial-to-waveguide transition
Circular wavguide
Corrugations
Mode transition
(a)
(b)
Fig 51 Structure of the proposed broadband circular waveguide feed
(a) CAD model and (b) cross-sectional view
For the coaxial-to-rectangular waveguide adapter an SMA connector with
the probe diameter of 127 mm is employed The coaxial probe inserted into
the waveguide energizes the feed and excites the dominant TE10 mode in
-52-
the rectangular waveguide The impedance matching is achieved by adjusting
the probe distance sp from the back short and the probe length lp
(a)
(b)
Fig 52 Reflection coefficient of the coaxial-to-rectangular adapter versus
(a) probe length lp and (b) the probe position sp
Fig 52 shows the reflection coefficient versus the various values of probe
lengths lp and probe positions sp The probe length lp is adjusted to obtain
antenna impedance matching and the probe distance sp is adjusted to obtain a
-53-
desired resonant frequency
Next a transition between rectangular and circular waveguide is designed
The transition section converts the TE10 mode in the rectangular waveguide to
TE11 mode in the circular waveguide and vice versa The transition is built
in a form of a taper for easy fabrication[22]
(a)
(b)
Fig 53 Structure of the rectangular-to-circular waveguide transition
(a) 3D view and (b) cross sectional view
The dimensions of the final optimized transition are as follows The length
of the rectangular waveguide section is 143mm The rectangular waveguides
width a and height b are 207mm and 857mm respectively The length of
the circular waveguide section is 143mm The inside diameter of the circular
-54-
waveguide is 207mm(097 wavelength at 14GHz) The length of transition
region ltr is 4465mm(approximately equal to 2λ0 at 14GHz) Fig 54 shows
the field distribution inside the mode converter
(a)
(b)
Fig 54 Field distribution inside the mode converter at
(a) 10GHz (b) 14GHz and (c) 18GHz
-55-
(c)
Fig 54 continued
Finally multiple chokes are investigated Figs 55 56 and 57 show the
feed performance without chokes The reflection coefficient is less than -10dB
over 10-19GHz The antenna has a gain of 921dB to 1189dB over
10-19GHz
Fig 55 Reflection coefficient of the broadband circular waveguide feed
without chokes and corrugations
-56-
(a)
(b)
(c)
Fig 56 E- and H-plane patterns of the broadband circular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-57-
(d)
(e)
Fig 56 continued
-58-
(a)
(b)
Fig 57 2D radiation patterns of the broadband cicular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-59-
(c)
(d)
Fig 57 continued
-60-
(e)
Fig 57 continued
To achieve equal beamwidths in E and H planes over a wide frequency
range chokes and corrugations are employed Table51 summarizes the
performance of a feed without chokes and corrugations
Table 51 Performance of the broadband circular waveguide feed without
chokes and corrugations
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
1000 940 6061 15
1200 972 6159 17
1400 920 5957 21
1600 1070 4751 29
1800 1188 5352 21
-61-
Four quarter-wavelength chokes are introduced in the feed design which
has a slot depth of 75mm and slot width of 09mm The choke slot spacing
is 18mm The choke design is investigated by applying the choke one by
one and the effect on the E- and H-plane patterns are observed as illustrated
in Figs 58 and 59 The use of chokes makes the E-plane pattern narrower
The H-plane pattern is not affected Chokes increase the gain slightly and
reduce back radiation
(a)
(b)
Fig 58 Effect of chokes on the E-plane pattern of the broadband circular
waveguide feed at (a) 10GHz(b) 12GHz (c) 14GHz (d) 16GHz and (e)
18GHz
-62-
(c)
(d)
(e)
Fig 58 continued
-63-
(a)
(b)
(c)
Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-64-
(d)
(e)
Fig 59 continued
-65-
Fig 510 shows the feed performance versus the choke depth When the
choke depth is varied from 535mm to 95mm the E- and H-plane patterns
are strongly affected The optimum value of choke depth is 75mm(035λ0 at
14GHz) which gives equal E- and H-plane radiation patterns and leads to
low back radiation
Fig 511 shows the feed performance versus the choke slot width tch The
choke slot width is varied from 09mm to 21mm Radiation patterns and
reflection coefficients are not sensitive to the choke slot width The final
choke slot width is selected to be 09mm considering the feed diameter
minimization and the manufacturability The overall diameter of the proposed
feed is 369mm which is increased from the 207mm of the waveguide
inside diameter due to the use of four chokes
-66-
(a)
(b)
(c)
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection coefficient
-67-
(a)
(b)
(c)
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and (c)
reflection coefficient
-68-
Next we investigated corrugations placed on the outer wall of the feed
Four corrugations applied to the outer surface of the circular waveguide The
corrugation depth is 465mm(0215λ0 at 14GHz) The primary purpose of
using corrugations is to further reduce the back radiation Increasing the
number of corrugations beyond four has little effect in reducing the back
radiation
Figs 512 and 513 show the effect of corrugations on the E- and H-plane
patterns Fig 514 shows the parametric study of the corrugation depth lcor
The corrugation depth is varied from 40mm and 645mm The optimum
value of the corrugation depth is found to be 465mm
-69-
(a)
(b)
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern at (a) 12GHz and (b) 14GHz
-70-
(a)
(b)
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern at (a) 12GHz and (b) 14GHz
-71-
(a)
(b)
(c)
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection coefficient
-72-
The phase center location is important in placing the feed in a reflector
antenna[8] The phase center variation with frequency should be small Fig
515 shows the effect of chokes and corrugations on the phase center The
curve with circle corresponds to the case without chokes and corrugations
The phase center varies from -326mm and -190mm away from the feeds
aperture plane It means the phase center is located inside the waveguide
The curve with triangles corresponds to the case with chokes The curve with
squares to the case with chokes and corrugations The phase center varies
from 0mm to -302mm
From Fig 515 we can observed that phase center variation reduced by the
corrugation and three cases phase center calculated in φ=450 plane
parameter sweep values are given in Table 52
10 12 14 16 181
0
-1
-2
-3
-4
-5
-6
Pha
se c
ente
r (m
m)
Frequency (GHz)
choke+corrugatuion without choke corrugation with choke
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
-73-
Frequency
(GHz)
Phase center from the aperture plane
(mm)
Without
chokes and
corrugations
With
chokes
With chokes
and
corrugations
1000 -326 062 000
1100 -187 030 -002
1200 -563 -208 -065
1300 -296 -154 -202
1400 -319 -314 -302
1500 -201 -203 -241
1600 -242 -233 -207
1700 -208 -208 -186
1800 -190 -157 -132
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
Based on the foregoing parametric studies optimum dimensions of the
broadband circular waveguide feed are obtained as shown in Table 53
-74-
Table 53 Optimum dimensions of the broadband circular waveguide feed
Parameter Designation Value (mm)
2a Waveguide inside diameter 2070
d Waveguide outside diameter 3690
lcrLength of the circular waveguide section 1430
m Distance between the aperture plane and the first corrugation 950
xDistance from the last corrugation to the end of the cylindrical outer surface
550
ltrLength of the rectangular-to-circularwaveguide transition 4465
lrcLength of the rectangular waveguide section 1430
tch Choke slot width 090
lch Choke depth 750
t Choke metal width 090
lcor Corrugation depth 465
tcor Corrugation metal width 100
s Corrugation slot width 10
lp Probe length 530
sp Probe position from the back short 530
din Probe diameter 127
b Inside height of the rectangular waveguide 857
tw Waveguide wall thickness 500
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-21-
Fig 214 shows the 2D radiation patterns of the radiator at 10GHz
14GHz and 18GHz Fig 215 shows E- and H-plane patterns of the radiator
Fig 216 shows the reflection coefficient of the probe-fed square waveguide
radiator The reflection coefficient is less than -10dB over 13-20GHz Table
24 summarizes the properties of the probe-fed square waveguide radiator
(a)
Fig 214 2D radiation patterns of the probe-fed square waveguide radiator at
(a) 10GHz (b) 14GHz and (c) 18GHz
-22-
(b)
(c)
Fig 214 continued
-23-
(a)
(b)
(c)
Fig 216 E-plane and H-plane patterns of the probe-fed square waveguide
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-24-
Fig 216 Reflection coefficient of the probe-fed square waveguide radiator
Table 24 Properties of the probe-fed square waveguide radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 73 71 12
14 85 63 1418 27 65 28
When a square waveguide radiator is fed by a coaxial probe its radiation
properties are not good due to the excitation of higher-order modes as in the
case of the probe-fed circular waveguide radiator A probe-fed square
waveguide radiator can be used as a feed only over a narrow frequency
range
-25-
III Design of Compact Circular Waveguide Feeds
In this chapter the feed design is presented for a prime-focus reflector
antenna The prime-focus paraboloid reflector is one of the most commonly
used high-gain antenna It has been used in earth-station antennas and radio
telescopes It consists of a paraboloid reflector with a feed system at its focal
point
The feed should radiate a low level of cross-polar power over the
operating frequency These conditions not easy to achieve and most prime
focus feeds are compromises The shape and characteristic of the radiation
pattern of the feed are the most important parameter because these will
directly influence the fields which are directed at a reflector[6] Other
electrical factors which relevant to the choice of a feed are the cross-polar
level the gain efficiency the bandwidth and impedance matching
31 Narrow-Band Circular Waveguide Feed
Fig 31 shows the proposed narrow-band circular waveguide feed and its
design variables The feed consists of a circular waveguide open end excited
by a TE11 dominant mode A quarter wave choke is applied along the
circular aperture of the waveguide to equalize E- and H-plane radiation
patterns and to suppress the back radiation A dielectric ring is used to
control the radiation pattern and change the power distribution over the
aperture The control of the amplitude over the aperture are essential to the
design of symmetric radiation pattern The material used for dielectric loading
-26-
is the monocast(MC) nylon with a dielectric constant of 30 The feed is
designed to operate over 171-197GHz
(a)
(b)
Fig 31 Narrow-band circular waveguide feed (a) CAD model and (b) a
cross sectional view
The impedance matching is achieved by a proper combination of the probe
height lp and its distance sp from the waveguide shorted end Here the
-27-
circular waveguide is terminated with an open end with a wall thickness of
2mm radiating into the free space
Fig 32 shows the effect of the probe length lp and the probe distance sp
on the reflection coefficient The best performance is obtained when lp =
363mm and sp = 616mm The feeds reflection coefficient is less than -10dB
over 170-195GHz
(a)
(b)
Fig 32 Effect of the (a) the probe length lp and (b) the probe
distance sp on the reflection coefficient
-28-
Fig 33 shows the effect of the choke depth The E-plane pattern is more
sensitive to the choke depth than the H-plane pattern The choke depth has a
strong influence on the reflection coefficient when it is 360mm By properly
choosing the choke depth we can equalize the E- and H-plane patterns The
optimum value of the choke depth is 410mm which is 0249λ0 at 1825GHz
The choke slot width tch in the range of 06-12mm has almost no effect
on the H-plane pattern and the reflection coefficient For the E-plane pattern
tch of 12mm has some effect on the E-plane radiation pattern as shown in
Fig 34
Fig 35 shows the feed performance versus the dielectric ring length We
observe in Fig 35 that the dielectric length ld has an optimum value of
1168mm which does no effect on the H-plane pattern and tha the value of
1048mm has some effect on the E-plane pattern and the reflection
coefficient
Fig 36 shows E-plane and H-plane patterns and the reflection coefficient
versus the dielectric thickness With the optimum value of the dielectric
thickness t obtained from the Fig 36 is 155mm The larger values of td has
much stronger effects on the E-plane pattern and the reflection coefficient
The H-plane pattern is not sensitive to the dielectric ring thickness
-29-
(a)
(b)
(c)
Fig 33 Feed performance versus the choke depth (a) E-plane pattern
(b) H-plane pattern and (c) reflection coefficient
-30-
(a)
(b)
(c)
Fig 34 Feed performance versus the choke slot width (a) E-plane pattern
(b) H-plane pattern and (c) reflection coefficient
-31-
(a)
(b)
(c)
Fig 35 Feed performance versus the dielectric ring length (a) E-plane
pattern (b) H-plane pattern and (c) reflection coefficient
-32-
(a)
(b)
(c)
Fig 36 Feed performance versus the dielectric ring thickness (a) E-plane
pattern(b) H-plane pattern and (c) reflection coefficient
-33-
From the above parametric analysis an optimum feed design is obtained
The result is shown in Table 31 Fig 37 shows the 2D gain patterns of
designed feed The antenna has a gain of 903dB 933dB and 956dB at
171GHz 1825GHz and 19GHz respectively
Fig 38 shows E- and H-plane radiation patterns of the designed feed The
feed has E- and H-plane 10-dB beamwidths of 60 and 59 degrees at 17GHz
The feed has a front-to-back ration of 1900dB 2490dB and 2200dB at
171GHz 1825GHz and 19GHz respectively Table 32 summarizes the
performance of the designed narrow-band circular waveguide feed
The designed feed has a greatly improved performance over that of a
simple coax-fed feed described in Section 23
Table 31 Dimensions of the designed narrow-band circular feed
Parameter Designation Value(mm)
a Waveguide inside radius 640
l Feed length 2890
lp Probe length 363
sp Probe position from the back short 616
din Probe diameter 127
dout Diameter of coaxial cables outer conductor 400
t Thickness of choked wall 050
tch Choke slot width 100
lch Choke depth 410
ld Dielectric ring length 1168
td Dielectric ring thickness 155
d1 Waveguide outside diameter 1680
-34-
(a)
(b)
Fig 37 2D gain patterns of the narrow-band circular waveguide feed at
(a) 17GHz (b) 1825GHz and (c) 19GHz
-35-
(c)
Fig 37 continued
-36-
(a)
(b)
(c)
Fig 38 E- and H-plane patterns of the narrow-band circular waveguide feed
at (a) 10GHz (b) 1825GHz and (c) 195GHz
-37-
Frequency(GHz)
Gain(dB)
E-H-plane10-dB beamwidths
(deg)
Front-to-back ratio(dB)
Phase centerlocation
(From feeds aperture plane
toward reflector)
(mm)
1700 903 6059 20 062
1825 933 6060 25 004
1900 956 5759 22 007
Table 32 Performance of the narrow-band circular waveguide feed
The designed narrow-band feed is fabricated and its performance is
measured and compared with the simulation results The designed feed is
fabricated in a numerically-controlled machining center The fabricated antenna
is shown in Fig 39
Fig 39 Photograph of the fabricated feed
-38-
Fig 310 shows a comparison of the measured and simulated reflection
coefficients The measured reflection coefficient is less than -10dB over
171-197GHz The agreement between simulated and measured results are
good
Fig 311 shows the E- and H-plane patterns of the fabricated feed at
187GHz The feed has 90dB gain simulation and measurement results are in
good agreement
The fabricated antennarsquos 10dB beamwidth is 60 degrees in both E and H
planes at 187GHz The front-to-back ratio is 21dB
Fig 310 Reflection coefficient of the fabricated feed
-39-
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Fee
d H
orn
Gain
- d
B
Angle - degree
(a)
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Feed H
orn
Gain
- d
B
Angle - degree
(b)
Fig 311 Gain patterns of the fabricated feed at 187 GHz (a) E-plane and
(b) H-plane
-40-
IV Design of Circular Waveguide Feeds Loaded with a
Dielectric Rod
In this section circular waveguide feeds loaded with a dielectric rod feed
are investigated A comprehensive discussion of the circular waveguide loaded
with a dielectric rod is given by Kumar[7] Inserting a dielectric material
inside the circular waveguide improves the E- and H-plane pattern symmetry
In general dielectric-loaded circular waveguide feeds show good performance
only over a narrow bandwidth
Fig 41 shows the geometry of a circular waveguide loaded with a
dielectric rod The waveguide length is 400mm and the wall thickness is
05mm The dielectric rods diameter is 207mm The dielectric rod is
extended 05 wavelength beyond the waveguide open end The dielectric
constant εr is changed and the feeds performance is observed
Fig 41 Geometry of a circular waveguide loaded with a uniform dielectric
rod
-41-
Fig 42 is the radiation pattern of the feed with εr = 25 and L = 05λ0 at
9GHz E- and H-plane 10-dB beamwidths are 810 and 807 degrees
respectively The front-to-back ratio is 18dB The antenna gain is 71dB
(a)
(b)
Fig 42 Radiation pattern at 9GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 05λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-42-
Fig 43 shows the radiation pattern of the feed with εr = 21 at 10GHz
E- and H-plane 10-dB beamwidths are 70 and 71 degrees respectively The
front-to-back ratio is 19dB The antenna gain is 83dB
(a)
(b)
Fig 43 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 21 and L = 05λ0 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-43-
Fig 44 shows the radiation pattern of the feed with εr = 30 at 8GHz
E- and H-plane 10-dB beamwidths are 83 and 824 degrees respectively The
front-to-back ratio is 17dB The antenna gain is 73dB
(a)
(b)
Fig 44 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 30 and L = 05λ0 at 8GHz (a) 2D radiation pattern
and (b) E- and H-plane patterns
-44-
Fig 45 shows the radiation pattern of the feed with εr = 50 at 18GHz
E- and H-plane 10-dB beamwidths are 56 and 54 degrees respectively The
front-to-back ratio is 27dB The antenna gain is 105dB The feed has a good
pattern symmetry and low back radiation
(a)
(b)
Fig 45 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 50 and L = 05λ0 at 18GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-45-
Fig 46 is the radiation pattern of the feed with εr = 25 and L = 10λ0 at
10GHz E- and H-plane 10-dB beamwidths are 50 and 48 degrees
respectively The front-to-back ratio is 16dB The antenna gain is 105dB
(a)
(b)
Fig 46 Radiation pattern at 10GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 10λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-46-
Fig 47 shows the geometry of a circular waveguide with a tapered
dielectric rod The designed feed has the following dimension L = 1λ0 d =
1λ0 and εr =25 at 10GHz The waveguide length is 40mm and the wall
thickness is 05mm
L
Dielectricd3
Fig 47 Geometry of a circular waveguide loaded with a tapered dielectric
rod
Fig 48 shows the radiatio pattern of the designed feed E- and H-plane
10-dB beamwidths are 575 and 564 degrees respectively The front-to-back
ratio is 377dB The antenna gain is 94dB The designed feed has an
excellent beamwidth symmetry and a very low back radiation
-47-
(a)
(b)
Fig 48 Radiation pattern of a circular waveguide loaded with a tapered
dielectric rod with L = 1λ0 d = 1λ0 and εr =25 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-48-
Fig 49 shows the geometry of a spherical ended dielectric rod feed
diameter of 06λ0 at 10GHz with a dielectric constant of 25 and L= 03λ0
Fig 410 shows the radiation patterns of the designed feed E- and H-plane
10-dB beamwidths are both 63 degrees The front-to-back ratio is 24dB The
antenna gain is 864dB
Fig 49 Geometry of a circular waveguide loaded with a spherical ended
dielectric rod
-49-
(a)
(b)
Fig 410 Radiation pattern of a circular waveguide loaded wht a spherical
ended dielectric rod with d = 06λ0 L = 03λ0 and εr =25 at 10GHz (a) 3D
radiation pattern and (b) E- and H-plane patterns
-50-
V Design of a Broadband Circular Waveguide Feed
In this chapter the design of a broadband circular waveguide feed is
presented At microwave frequencies the feed is often a circular waveguide
with chokes and corrugations around the aperture Chokes and corrugations
equalize E- and H-plane patterns and reduce the back radiation
The proposed feed is designed to operate over 10-18GHz The design starts
with the optimization of the coaxial-to-rectangular waveguide adapter
employed for good mode purity over a broad frequency range Next a
rectangular-to-circular waveguide transition is optimized Finally chokes and
corrugations are designed for improved pattern symmetry and low back
radiation
The proposed feed structure is shown in Fig 51 The feed consist of the
following parts a coaxial-to-rectangular waveguide adapter a rectangular-to-
circular waveguide transition a circular waveguide section four quarter-wave
chokes around the feeds aperture and four corrugations on the feeds outer
surface
The computer simulation shows the above arrangement offers good radiation
patterns over a broad frequency range The broadband operation is obtained
by exciting the TE11 mode in the circular waveguide using the TE10 mode of
the rectangular waveguide which is in turn excited by a coaxial probe
-51-
Chokes
Coaxial-to-waveguide transition
Circular wavguide
Corrugations
Mode transition
(a)
(b)
Fig 51 Structure of the proposed broadband circular waveguide feed
(a) CAD model and (b) cross-sectional view
For the coaxial-to-rectangular waveguide adapter an SMA connector with
the probe diameter of 127 mm is employed The coaxial probe inserted into
the waveguide energizes the feed and excites the dominant TE10 mode in
-52-
the rectangular waveguide The impedance matching is achieved by adjusting
the probe distance sp from the back short and the probe length lp
(a)
(b)
Fig 52 Reflection coefficient of the coaxial-to-rectangular adapter versus
(a) probe length lp and (b) the probe position sp
Fig 52 shows the reflection coefficient versus the various values of probe
lengths lp and probe positions sp The probe length lp is adjusted to obtain
antenna impedance matching and the probe distance sp is adjusted to obtain a
-53-
desired resonant frequency
Next a transition between rectangular and circular waveguide is designed
The transition section converts the TE10 mode in the rectangular waveguide to
TE11 mode in the circular waveguide and vice versa The transition is built
in a form of a taper for easy fabrication[22]
(a)
(b)
Fig 53 Structure of the rectangular-to-circular waveguide transition
(a) 3D view and (b) cross sectional view
The dimensions of the final optimized transition are as follows The length
of the rectangular waveguide section is 143mm The rectangular waveguides
width a and height b are 207mm and 857mm respectively The length of
the circular waveguide section is 143mm The inside diameter of the circular
-54-
waveguide is 207mm(097 wavelength at 14GHz) The length of transition
region ltr is 4465mm(approximately equal to 2λ0 at 14GHz) Fig 54 shows
the field distribution inside the mode converter
(a)
(b)
Fig 54 Field distribution inside the mode converter at
(a) 10GHz (b) 14GHz and (c) 18GHz
-55-
(c)
Fig 54 continued
Finally multiple chokes are investigated Figs 55 56 and 57 show the
feed performance without chokes The reflection coefficient is less than -10dB
over 10-19GHz The antenna has a gain of 921dB to 1189dB over
10-19GHz
Fig 55 Reflection coefficient of the broadband circular waveguide feed
without chokes and corrugations
-56-
(a)
(b)
(c)
Fig 56 E- and H-plane patterns of the broadband circular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-57-
(d)
(e)
Fig 56 continued
-58-
(a)
(b)
Fig 57 2D radiation patterns of the broadband cicular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-59-
(c)
(d)
Fig 57 continued
-60-
(e)
Fig 57 continued
To achieve equal beamwidths in E and H planes over a wide frequency
range chokes and corrugations are employed Table51 summarizes the
performance of a feed without chokes and corrugations
Table 51 Performance of the broadband circular waveguide feed without
chokes and corrugations
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
1000 940 6061 15
1200 972 6159 17
1400 920 5957 21
1600 1070 4751 29
1800 1188 5352 21
-61-
Four quarter-wavelength chokes are introduced in the feed design which
has a slot depth of 75mm and slot width of 09mm The choke slot spacing
is 18mm The choke design is investigated by applying the choke one by
one and the effect on the E- and H-plane patterns are observed as illustrated
in Figs 58 and 59 The use of chokes makes the E-plane pattern narrower
The H-plane pattern is not affected Chokes increase the gain slightly and
reduce back radiation
(a)
(b)
Fig 58 Effect of chokes on the E-plane pattern of the broadband circular
waveguide feed at (a) 10GHz(b) 12GHz (c) 14GHz (d) 16GHz and (e)
18GHz
-62-
(c)
(d)
(e)
Fig 58 continued
-63-
(a)
(b)
(c)
Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-64-
(d)
(e)
Fig 59 continued
-65-
Fig 510 shows the feed performance versus the choke depth When the
choke depth is varied from 535mm to 95mm the E- and H-plane patterns
are strongly affected The optimum value of choke depth is 75mm(035λ0 at
14GHz) which gives equal E- and H-plane radiation patterns and leads to
low back radiation
Fig 511 shows the feed performance versus the choke slot width tch The
choke slot width is varied from 09mm to 21mm Radiation patterns and
reflection coefficients are not sensitive to the choke slot width The final
choke slot width is selected to be 09mm considering the feed diameter
minimization and the manufacturability The overall diameter of the proposed
feed is 369mm which is increased from the 207mm of the waveguide
inside diameter due to the use of four chokes
-66-
(a)
(b)
(c)
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection coefficient
-67-
(a)
(b)
(c)
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and (c)
reflection coefficient
-68-
Next we investigated corrugations placed on the outer wall of the feed
Four corrugations applied to the outer surface of the circular waveguide The
corrugation depth is 465mm(0215λ0 at 14GHz) The primary purpose of
using corrugations is to further reduce the back radiation Increasing the
number of corrugations beyond four has little effect in reducing the back
radiation
Figs 512 and 513 show the effect of corrugations on the E- and H-plane
patterns Fig 514 shows the parametric study of the corrugation depth lcor
The corrugation depth is varied from 40mm and 645mm The optimum
value of the corrugation depth is found to be 465mm
-69-
(a)
(b)
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern at (a) 12GHz and (b) 14GHz
-70-
(a)
(b)
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern at (a) 12GHz and (b) 14GHz
-71-
(a)
(b)
(c)
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection coefficient
-72-
The phase center location is important in placing the feed in a reflector
antenna[8] The phase center variation with frequency should be small Fig
515 shows the effect of chokes and corrugations on the phase center The
curve with circle corresponds to the case without chokes and corrugations
The phase center varies from -326mm and -190mm away from the feeds
aperture plane It means the phase center is located inside the waveguide
The curve with triangles corresponds to the case with chokes The curve with
squares to the case with chokes and corrugations The phase center varies
from 0mm to -302mm
From Fig 515 we can observed that phase center variation reduced by the
corrugation and three cases phase center calculated in φ=450 plane
parameter sweep values are given in Table 52
10 12 14 16 181
0
-1
-2
-3
-4
-5
-6
Pha
se c
ente
r (m
m)
Frequency (GHz)
choke+corrugatuion without choke corrugation with choke
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
-73-
Frequency
(GHz)
Phase center from the aperture plane
(mm)
Without
chokes and
corrugations
With
chokes
With chokes
and
corrugations
1000 -326 062 000
1100 -187 030 -002
1200 -563 -208 -065
1300 -296 -154 -202
1400 -319 -314 -302
1500 -201 -203 -241
1600 -242 -233 -207
1700 -208 -208 -186
1800 -190 -157 -132
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
Based on the foregoing parametric studies optimum dimensions of the
broadband circular waveguide feed are obtained as shown in Table 53
-74-
Table 53 Optimum dimensions of the broadband circular waveguide feed
Parameter Designation Value (mm)
2a Waveguide inside diameter 2070
d Waveguide outside diameter 3690
lcrLength of the circular waveguide section 1430
m Distance between the aperture plane and the first corrugation 950
xDistance from the last corrugation to the end of the cylindrical outer surface
550
ltrLength of the rectangular-to-circularwaveguide transition 4465
lrcLength of the rectangular waveguide section 1430
tch Choke slot width 090
lch Choke depth 750
t Choke metal width 090
lcor Corrugation depth 465
tcor Corrugation metal width 100
s Corrugation slot width 10
lp Probe length 530
sp Probe position from the back short 530
din Probe diameter 127
b Inside height of the rectangular waveguide 857
tw Waveguide wall thickness 500
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-22-
(b)
(c)
Fig 214 continued
-23-
(a)
(b)
(c)
Fig 216 E-plane and H-plane patterns of the probe-fed square waveguide
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-24-
Fig 216 Reflection coefficient of the probe-fed square waveguide radiator
Table 24 Properties of the probe-fed square waveguide radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 73 71 12
14 85 63 1418 27 65 28
When a square waveguide radiator is fed by a coaxial probe its radiation
properties are not good due to the excitation of higher-order modes as in the
case of the probe-fed circular waveguide radiator A probe-fed square
waveguide radiator can be used as a feed only over a narrow frequency
range
-25-
III Design of Compact Circular Waveguide Feeds
In this chapter the feed design is presented for a prime-focus reflector
antenna The prime-focus paraboloid reflector is one of the most commonly
used high-gain antenna It has been used in earth-station antennas and radio
telescopes It consists of a paraboloid reflector with a feed system at its focal
point
The feed should radiate a low level of cross-polar power over the
operating frequency These conditions not easy to achieve and most prime
focus feeds are compromises The shape and characteristic of the radiation
pattern of the feed are the most important parameter because these will
directly influence the fields which are directed at a reflector[6] Other
electrical factors which relevant to the choice of a feed are the cross-polar
level the gain efficiency the bandwidth and impedance matching
31 Narrow-Band Circular Waveguide Feed
Fig 31 shows the proposed narrow-band circular waveguide feed and its
design variables The feed consists of a circular waveguide open end excited
by a TE11 dominant mode A quarter wave choke is applied along the
circular aperture of the waveguide to equalize E- and H-plane radiation
patterns and to suppress the back radiation A dielectric ring is used to
control the radiation pattern and change the power distribution over the
aperture The control of the amplitude over the aperture are essential to the
design of symmetric radiation pattern The material used for dielectric loading
-26-
is the monocast(MC) nylon with a dielectric constant of 30 The feed is
designed to operate over 171-197GHz
(a)
(b)
Fig 31 Narrow-band circular waveguide feed (a) CAD model and (b) a
cross sectional view
The impedance matching is achieved by a proper combination of the probe
height lp and its distance sp from the waveguide shorted end Here the
-27-
circular waveguide is terminated with an open end with a wall thickness of
2mm radiating into the free space
Fig 32 shows the effect of the probe length lp and the probe distance sp
on the reflection coefficient The best performance is obtained when lp =
363mm and sp = 616mm The feeds reflection coefficient is less than -10dB
over 170-195GHz
(a)
(b)
Fig 32 Effect of the (a) the probe length lp and (b) the probe
distance sp on the reflection coefficient
-28-
Fig 33 shows the effect of the choke depth The E-plane pattern is more
sensitive to the choke depth than the H-plane pattern The choke depth has a
strong influence on the reflection coefficient when it is 360mm By properly
choosing the choke depth we can equalize the E- and H-plane patterns The
optimum value of the choke depth is 410mm which is 0249λ0 at 1825GHz
The choke slot width tch in the range of 06-12mm has almost no effect
on the H-plane pattern and the reflection coefficient For the E-plane pattern
tch of 12mm has some effect on the E-plane radiation pattern as shown in
Fig 34
Fig 35 shows the feed performance versus the dielectric ring length We
observe in Fig 35 that the dielectric length ld has an optimum value of
1168mm which does no effect on the H-plane pattern and tha the value of
1048mm has some effect on the E-plane pattern and the reflection
coefficient
Fig 36 shows E-plane and H-plane patterns and the reflection coefficient
versus the dielectric thickness With the optimum value of the dielectric
thickness t obtained from the Fig 36 is 155mm The larger values of td has
much stronger effects on the E-plane pattern and the reflection coefficient
The H-plane pattern is not sensitive to the dielectric ring thickness
-29-
(a)
(b)
(c)
Fig 33 Feed performance versus the choke depth (a) E-plane pattern
(b) H-plane pattern and (c) reflection coefficient
-30-
(a)
(b)
(c)
Fig 34 Feed performance versus the choke slot width (a) E-plane pattern
(b) H-plane pattern and (c) reflection coefficient
-31-
(a)
(b)
(c)
Fig 35 Feed performance versus the dielectric ring length (a) E-plane
pattern (b) H-plane pattern and (c) reflection coefficient
-32-
(a)
(b)
(c)
Fig 36 Feed performance versus the dielectric ring thickness (a) E-plane
pattern(b) H-plane pattern and (c) reflection coefficient
-33-
From the above parametric analysis an optimum feed design is obtained
The result is shown in Table 31 Fig 37 shows the 2D gain patterns of
designed feed The antenna has a gain of 903dB 933dB and 956dB at
171GHz 1825GHz and 19GHz respectively
Fig 38 shows E- and H-plane radiation patterns of the designed feed The
feed has E- and H-plane 10-dB beamwidths of 60 and 59 degrees at 17GHz
The feed has a front-to-back ration of 1900dB 2490dB and 2200dB at
171GHz 1825GHz and 19GHz respectively Table 32 summarizes the
performance of the designed narrow-band circular waveguide feed
The designed feed has a greatly improved performance over that of a
simple coax-fed feed described in Section 23
Table 31 Dimensions of the designed narrow-band circular feed
Parameter Designation Value(mm)
a Waveguide inside radius 640
l Feed length 2890
lp Probe length 363
sp Probe position from the back short 616
din Probe diameter 127
dout Diameter of coaxial cables outer conductor 400
t Thickness of choked wall 050
tch Choke slot width 100
lch Choke depth 410
ld Dielectric ring length 1168
td Dielectric ring thickness 155
d1 Waveguide outside diameter 1680
-34-
(a)
(b)
Fig 37 2D gain patterns of the narrow-band circular waveguide feed at
(a) 17GHz (b) 1825GHz and (c) 19GHz
-35-
(c)
Fig 37 continued
-36-
(a)
(b)
(c)
Fig 38 E- and H-plane patterns of the narrow-band circular waveguide feed
at (a) 10GHz (b) 1825GHz and (c) 195GHz
-37-
Frequency(GHz)
Gain(dB)
E-H-plane10-dB beamwidths
(deg)
Front-to-back ratio(dB)
Phase centerlocation
(From feeds aperture plane
toward reflector)
(mm)
1700 903 6059 20 062
1825 933 6060 25 004
1900 956 5759 22 007
Table 32 Performance of the narrow-band circular waveguide feed
The designed narrow-band feed is fabricated and its performance is
measured and compared with the simulation results The designed feed is
fabricated in a numerically-controlled machining center The fabricated antenna
is shown in Fig 39
Fig 39 Photograph of the fabricated feed
-38-
Fig 310 shows a comparison of the measured and simulated reflection
coefficients The measured reflection coefficient is less than -10dB over
171-197GHz The agreement between simulated and measured results are
good
Fig 311 shows the E- and H-plane patterns of the fabricated feed at
187GHz The feed has 90dB gain simulation and measurement results are in
good agreement
The fabricated antennarsquos 10dB beamwidth is 60 degrees in both E and H
planes at 187GHz The front-to-back ratio is 21dB
Fig 310 Reflection coefficient of the fabricated feed
-39-
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Fee
d H
orn
Gain
- d
B
Angle - degree
(a)
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Feed H
orn
Gain
- d
B
Angle - degree
(b)
Fig 311 Gain patterns of the fabricated feed at 187 GHz (a) E-plane and
(b) H-plane
-40-
IV Design of Circular Waveguide Feeds Loaded with a
Dielectric Rod
In this section circular waveguide feeds loaded with a dielectric rod feed
are investigated A comprehensive discussion of the circular waveguide loaded
with a dielectric rod is given by Kumar[7] Inserting a dielectric material
inside the circular waveguide improves the E- and H-plane pattern symmetry
In general dielectric-loaded circular waveguide feeds show good performance
only over a narrow bandwidth
Fig 41 shows the geometry of a circular waveguide loaded with a
dielectric rod The waveguide length is 400mm and the wall thickness is
05mm The dielectric rods diameter is 207mm The dielectric rod is
extended 05 wavelength beyond the waveguide open end The dielectric
constant εr is changed and the feeds performance is observed
Fig 41 Geometry of a circular waveguide loaded with a uniform dielectric
rod
-41-
Fig 42 is the radiation pattern of the feed with εr = 25 and L = 05λ0 at
9GHz E- and H-plane 10-dB beamwidths are 810 and 807 degrees
respectively The front-to-back ratio is 18dB The antenna gain is 71dB
(a)
(b)
Fig 42 Radiation pattern at 9GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 05λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-42-
Fig 43 shows the radiation pattern of the feed with εr = 21 at 10GHz
E- and H-plane 10-dB beamwidths are 70 and 71 degrees respectively The
front-to-back ratio is 19dB The antenna gain is 83dB
(a)
(b)
Fig 43 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 21 and L = 05λ0 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-43-
Fig 44 shows the radiation pattern of the feed with εr = 30 at 8GHz
E- and H-plane 10-dB beamwidths are 83 and 824 degrees respectively The
front-to-back ratio is 17dB The antenna gain is 73dB
(a)
(b)
Fig 44 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 30 and L = 05λ0 at 8GHz (a) 2D radiation pattern
and (b) E- and H-plane patterns
-44-
Fig 45 shows the radiation pattern of the feed with εr = 50 at 18GHz
E- and H-plane 10-dB beamwidths are 56 and 54 degrees respectively The
front-to-back ratio is 27dB The antenna gain is 105dB The feed has a good
pattern symmetry and low back radiation
(a)
(b)
Fig 45 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 50 and L = 05λ0 at 18GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-45-
Fig 46 is the radiation pattern of the feed with εr = 25 and L = 10λ0 at
10GHz E- and H-plane 10-dB beamwidths are 50 and 48 degrees
respectively The front-to-back ratio is 16dB The antenna gain is 105dB
(a)
(b)
Fig 46 Radiation pattern at 10GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 10λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-46-
Fig 47 shows the geometry of a circular waveguide with a tapered
dielectric rod The designed feed has the following dimension L = 1λ0 d =
1λ0 and εr =25 at 10GHz The waveguide length is 40mm and the wall
thickness is 05mm
L
Dielectricd3
Fig 47 Geometry of a circular waveguide loaded with a tapered dielectric
rod
Fig 48 shows the radiatio pattern of the designed feed E- and H-plane
10-dB beamwidths are 575 and 564 degrees respectively The front-to-back
ratio is 377dB The antenna gain is 94dB The designed feed has an
excellent beamwidth symmetry and a very low back radiation
-47-
(a)
(b)
Fig 48 Radiation pattern of a circular waveguide loaded with a tapered
dielectric rod with L = 1λ0 d = 1λ0 and εr =25 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-48-
Fig 49 shows the geometry of a spherical ended dielectric rod feed
diameter of 06λ0 at 10GHz with a dielectric constant of 25 and L= 03λ0
Fig 410 shows the radiation patterns of the designed feed E- and H-plane
10-dB beamwidths are both 63 degrees The front-to-back ratio is 24dB The
antenna gain is 864dB
Fig 49 Geometry of a circular waveguide loaded with a spherical ended
dielectric rod
-49-
(a)
(b)
Fig 410 Radiation pattern of a circular waveguide loaded wht a spherical
ended dielectric rod with d = 06λ0 L = 03λ0 and εr =25 at 10GHz (a) 3D
radiation pattern and (b) E- and H-plane patterns
-50-
V Design of a Broadband Circular Waveguide Feed
In this chapter the design of a broadband circular waveguide feed is
presented At microwave frequencies the feed is often a circular waveguide
with chokes and corrugations around the aperture Chokes and corrugations
equalize E- and H-plane patterns and reduce the back radiation
The proposed feed is designed to operate over 10-18GHz The design starts
with the optimization of the coaxial-to-rectangular waveguide adapter
employed for good mode purity over a broad frequency range Next a
rectangular-to-circular waveguide transition is optimized Finally chokes and
corrugations are designed for improved pattern symmetry and low back
radiation
The proposed feed structure is shown in Fig 51 The feed consist of the
following parts a coaxial-to-rectangular waveguide adapter a rectangular-to-
circular waveguide transition a circular waveguide section four quarter-wave
chokes around the feeds aperture and four corrugations on the feeds outer
surface
The computer simulation shows the above arrangement offers good radiation
patterns over a broad frequency range The broadband operation is obtained
by exciting the TE11 mode in the circular waveguide using the TE10 mode of
the rectangular waveguide which is in turn excited by a coaxial probe
-51-
Chokes
Coaxial-to-waveguide transition
Circular wavguide
Corrugations
Mode transition
(a)
(b)
Fig 51 Structure of the proposed broadband circular waveguide feed
(a) CAD model and (b) cross-sectional view
For the coaxial-to-rectangular waveguide adapter an SMA connector with
the probe diameter of 127 mm is employed The coaxial probe inserted into
the waveguide energizes the feed and excites the dominant TE10 mode in
-52-
the rectangular waveguide The impedance matching is achieved by adjusting
the probe distance sp from the back short and the probe length lp
(a)
(b)
Fig 52 Reflection coefficient of the coaxial-to-rectangular adapter versus
(a) probe length lp and (b) the probe position sp
Fig 52 shows the reflection coefficient versus the various values of probe
lengths lp and probe positions sp The probe length lp is adjusted to obtain
antenna impedance matching and the probe distance sp is adjusted to obtain a
-53-
desired resonant frequency
Next a transition between rectangular and circular waveguide is designed
The transition section converts the TE10 mode in the rectangular waveguide to
TE11 mode in the circular waveguide and vice versa The transition is built
in a form of a taper for easy fabrication[22]
(a)
(b)
Fig 53 Structure of the rectangular-to-circular waveguide transition
(a) 3D view and (b) cross sectional view
The dimensions of the final optimized transition are as follows The length
of the rectangular waveguide section is 143mm The rectangular waveguides
width a and height b are 207mm and 857mm respectively The length of
the circular waveguide section is 143mm The inside diameter of the circular
-54-
waveguide is 207mm(097 wavelength at 14GHz) The length of transition
region ltr is 4465mm(approximately equal to 2λ0 at 14GHz) Fig 54 shows
the field distribution inside the mode converter
(a)
(b)
Fig 54 Field distribution inside the mode converter at
(a) 10GHz (b) 14GHz and (c) 18GHz
-55-
(c)
Fig 54 continued
Finally multiple chokes are investigated Figs 55 56 and 57 show the
feed performance without chokes The reflection coefficient is less than -10dB
over 10-19GHz The antenna has a gain of 921dB to 1189dB over
10-19GHz
Fig 55 Reflection coefficient of the broadband circular waveguide feed
without chokes and corrugations
-56-
(a)
(b)
(c)
Fig 56 E- and H-plane patterns of the broadband circular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-57-
(d)
(e)
Fig 56 continued
-58-
(a)
(b)
Fig 57 2D radiation patterns of the broadband cicular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-59-
(c)
(d)
Fig 57 continued
-60-
(e)
Fig 57 continued
To achieve equal beamwidths in E and H planes over a wide frequency
range chokes and corrugations are employed Table51 summarizes the
performance of a feed without chokes and corrugations
Table 51 Performance of the broadband circular waveguide feed without
chokes and corrugations
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
1000 940 6061 15
1200 972 6159 17
1400 920 5957 21
1600 1070 4751 29
1800 1188 5352 21
-61-
Four quarter-wavelength chokes are introduced in the feed design which
has a slot depth of 75mm and slot width of 09mm The choke slot spacing
is 18mm The choke design is investigated by applying the choke one by
one and the effect on the E- and H-plane patterns are observed as illustrated
in Figs 58 and 59 The use of chokes makes the E-plane pattern narrower
The H-plane pattern is not affected Chokes increase the gain slightly and
reduce back radiation
(a)
(b)
Fig 58 Effect of chokes on the E-plane pattern of the broadband circular
waveguide feed at (a) 10GHz(b) 12GHz (c) 14GHz (d) 16GHz and (e)
18GHz
-62-
(c)
(d)
(e)
Fig 58 continued
-63-
(a)
(b)
(c)
Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-64-
(d)
(e)
Fig 59 continued
-65-
Fig 510 shows the feed performance versus the choke depth When the
choke depth is varied from 535mm to 95mm the E- and H-plane patterns
are strongly affected The optimum value of choke depth is 75mm(035λ0 at
14GHz) which gives equal E- and H-plane radiation patterns and leads to
low back radiation
Fig 511 shows the feed performance versus the choke slot width tch The
choke slot width is varied from 09mm to 21mm Radiation patterns and
reflection coefficients are not sensitive to the choke slot width The final
choke slot width is selected to be 09mm considering the feed diameter
minimization and the manufacturability The overall diameter of the proposed
feed is 369mm which is increased from the 207mm of the waveguide
inside diameter due to the use of four chokes
-66-
(a)
(b)
(c)
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection coefficient
-67-
(a)
(b)
(c)
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and (c)
reflection coefficient
-68-
Next we investigated corrugations placed on the outer wall of the feed
Four corrugations applied to the outer surface of the circular waveguide The
corrugation depth is 465mm(0215λ0 at 14GHz) The primary purpose of
using corrugations is to further reduce the back radiation Increasing the
number of corrugations beyond four has little effect in reducing the back
radiation
Figs 512 and 513 show the effect of corrugations on the E- and H-plane
patterns Fig 514 shows the parametric study of the corrugation depth lcor
The corrugation depth is varied from 40mm and 645mm The optimum
value of the corrugation depth is found to be 465mm
-69-
(a)
(b)
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern at (a) 12GHz and (b) 14GHz
-70-
(a)
(b)
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern at (a) 12GHz and (b) 14GHz
-71-
(a)
(b)
(c)
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection coefficient
-72-
The phase center location is important in placing the feed in a reflector
antenna[8] The phase center variation with frequency should be small Fig
515 shows the effect of chokes and corrugations on the phase center The
curve with circle corresponds to the case without chokes and corrugations
The phase center varies from -326mm and -190mm away from the feeds
aperture plane It means the phase center is located inside the waveguide
The curve with triangles corresponds to the case with chokes The curve with
squares to the case with chokes and corrugations The phase center varies
from 0mm to -302mm
From Fig 515 we can observed that phase center variation reduced by the
corrugation and three cases phase center calculated in φ=450 plane
parameter sweep values are given in Table 52
10 12 14 16 181
0
-1
-2
-3
-4
-5
-6
Pha
se c
ente
r (m
m)
Frequency (GHz)
choke+corrugatuion without choke corrugation with choke
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
-73-
Frequency
(GHz)
Phase center from the aperture plane
(mm)
Without
chokes and
corrugations
With
chokes
With chokes
and
corrugations
1000 -326 062 000
1100 -187 030 -002
1200 -563 -208 -065
1300 -296 -154 -202
1400 -319 -314 -302
1500 -201 -203 -241
1600 -242 -233 -207
1700 -208 -208 -186
1800 -190 -157 -132
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
Based on the foregoing parametric studies optimum dimensions of the
broadband circular waveguide feed are obtained as shown in Table 53
-74-
Table 53 Optimum dimensions of the broadband circular waveguide feed
Parameter Designation Value (mm)
2a Waveguide inside diameter 2070
d Waveguide outside diameter 3690
lcrLength of the circular waveguide section 1430
m Distance between the aperture plane and the first corrugation 950
xDistance from the last corrugation to the end of the cylindrical outer surface
550
ltrLength of the rectangular-to-circularwaveguide transition 4465
lrcLength of the rectangular waveguide section 1430
tch Choke slot width 090
lch Choke depth 750
t Choke metal width 090
lcor Corrugation depth 465
tcor Corrugation metal width 100
s Corrugation slot width 10
lp Probe length 530
sp Probe position from the back short 530
din Probe diameter 127
b Inside height of the rectangular waveguide 857
tw Waveguide wall thickness 500
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-23-
(a)
(b)
(c)
Fig 216 E-plane and H-plane patterns of the probe-fed square waveguide
radiator at (a) 10GHz (b) 14GHz and (c) 18GHz
-24-
Fig 216 Reflection coefficient of the probe-fed square waveguide radiator
Table 24 Properties of the probe-fed square waveguide radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 73 71 12
14 85 63 1418 27 65 28
When a square waveguide radiator is fed by a coaxial probe its radiation
properties are not good due to the excitation of higher-order modes as in the
case of the probe-fed circular waveguide radiator A probe-fed square
waveguide radiator can be used as a feed only over a narrow frequency
range
-25-
III Design of Compact Circular Waveguide Feeds
In this chapter the feed design is presented for a prime-focus reflector
antenna The prime-focus paraboloid reflector is one of the most commonly
used high-gain antenna It has been used in earth-station antennas and radio
telescopes It consists of a paraboloid reflector with a feed system at its focal
point
The feed should radiate a low level of cross-polar power over the
operating frequency These conditions not easy to achieve and most prime
focus feeds are compromises The shape and characteristic of the radiation
pattern of the feed are the most important parameter because these will
directly influence the fields which are directed at a reflector[6] Other
electrical factors which relevant to the choice of a feed are the cross-polar
level the gain efficiency the bandwidth and impedance matching
31 Narrow-Band Circular Waveguide Feed
Fig 31 shows the proposed narrow-band circular waveguide feed and its
design variables The feed consists of a circular waveguide open end excited
by a TE11 dominant mode A quarter wave choke is applied along the
circular aperture of the waveguide to equalize E- and H-plane radiation
patterns and to suppress the back radiation A dielectric ring is used to
control the radiation pattern and change the power distribution over the
aperture The control of the amplitude over the aperture are essential to the
design of symmetric radiation pattern The material used for dielectric loading
-26-
is the monocast(MC) nylon with a dielectric constant of 30 The feed is
designed to operate over 171-197GHz
(a)
(b)
Fig 31 Narrow-band circular waveguide feed (a) CAD model and (b) a
cross sectional view
The impedance matching is achieved by a proper combination of the probe
height lp and its distance sp from the waveguide shorted end Here the
-27-
circular waveguide is terminated with an open end with a wall thickness of
2mm radiating into the free space
Fig 32 shows the effect of the probe length lp and the probe distance sp
on the reflection coefficient The best performance is obtained when lp =
363mm and sp = 616mm The feeds reflection coefficient is less than -10dB
over 170-195GHz
(a)
(b)
Fig 32 Effect of the (a) the probe length lp and (b) the probe
distance sp on the reflection coefficient
-28-
Fig 33 shows the effect of the choke depth The E-plane pattern is more
sensitive to the choke depth than the H-plane pattern The choke depth has a
strong influence on the reflection coefficient when it is 360mm By properly
choosing the choke depth we can equalize the E- and H-plane patterns The
optimum value of the choke depth is 410mm which is 0249λ0 at 1825GHz
The choke slot width tch in the range of 06-12mm has almost no effect
on the H-plane pattern and the reflection coefficient For the E-plane pattern
tch of 12mm has some effect on the E-plane radiation pattern as shown in
Fig 34
Fig 35 shows the feed performance versus the dielectric ring length We
observe in Fig 35 that the dielectric length ld has an optimum value of
1168mm which does no effect on the H-plane pattern and tha the value of
1048mm has some effect on the E-plane pattern and the reflection
coefficient
Fig 36 shows E-plane and H-plane patterns and the reflection coefficient
versus the dielectric thickness With the optimum value of the dielectric
thickness t obtained from the Fig 36 is 155mm The larger values of td has
much stronger effects on the E-plane pattern and the reflection coefficient
The H-plane pattern is not sensitive to the dielectric ring thickness
-29-
(a)
(b)
(c)
Fig 33 Feed performance versus the choke depth (a) E-plane pattern
(b) H-plane pattern and (c) reflection coefficient
-30-
(a)
(b)
(c)
Fig 34 Feed performance versus the choke slot width (a) E-plane pattern
(b) H-plane pattern and (c) reflection coefficient
-31-
(a)
(b)
(c)
Fig 35 Feed performance versus the dielectric ring length (a) E-plane
pattern (b) H-plane pattern and (c) reflection coefficient
-32-
(a)
(b)
(c)
Fig 36 Feed performance versus the dielectric ring thickness (a) E-plane
pattern(b) H-plane pattern and (c) reflection coefficient
-33-
From the above parametric analysis an optimum feed design is obtained
The result is shown in Table 31 Fig 37 shows the 2D gain patterns of
designed feed The antenna has a gain of 903dB 933dB and 956dB at
171GHz 1825GHz and 19GHz respectively
Fig 38 shows E- and H-plane radiation patterns of the designed feed The
feed has E- and H-plane 10-dB beamwidths of 60 and 59 degrees at 17GHz
The feed has a front-to-back ration of 1900dB 2490dB and 2200dB at
171GHz 1825GHz and 19GHz respectively Table 32 summarizes the
performance of the designed narrow-band circular waveguide feed
The designed feed has a greatly improved performance over that of a
simple coax-fed feed described in Section 23
Table 31 Dimensions of the designed narrow-band circular feed
Parameter Designation Value(mm)
a Waveguide inside radius 640
l Feed length 2890
lp Probe length 363
sp Probe position from the back short 616
din Probe diameter 127
dout Diameter of coaxial cables outer conductor 400
t Thickness of choked wall 050
tch Choke slot width 100
lch Choke depth 410
ld Dielectric ring length 1168
td Dielectric ring thickness 155
d1 Waveguide outside diameter 1680
-34-
(a)
(b)
Fig 37 2D gain patterns of the narrow-band circular waveguide feed at
(a) 17GHz (b) 1825GHz and (c) 19GHz
-35-
(c)
Fig 37 continued
-36-
(a)
(b)
(c)
Fig 38 E- and H-plane patterns of the narrow-band circular waveguide feed
at (a) 10GHz (b) 1825GHz and (c) 195GHz
-37-
Frequency(GHz)
Gain(dB)
E-H-plane10-dB beamwidths
(deg)
Front-to-back ratio(dB)
Phase centerlocation
(From feeds aperture plane
toward reflector)
(mm)
1700 903 6059 20 062
1825 933 6060 25 004
1900 956 5759 22 007
Table 32 Performance of the narrow-band circular waveguide feed
The designed narrow-band feed is fabricated and its performance is
measured and compared with the simulation results The designed feed is
fabricated in a numerically-controlled machining center The fabricated antenna
is shown in Fig 39
Fig 39 Photograph of the fabricated feed
-38-
Fig 310 shows a comparison of the measured and simulated reflection
coefficients The measured reflection coefficient is less than -10dB over
171-197GHz The agreement between simulated and measured results are
good
Fig 311 shows the E- and H-plane patterns of the fabricated feed at
187GHz The feed has 90dB gain simulation and measurement results are in
good agreement
The fabricated antennarsquos 10dB beamwidth is 60 degrees in both E and H
planes at 187GHz The front-to-back ratio is 21dB
Fig 310 Reflection coefficient of the fabricated feed
-39-
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Fee
d H
orn
Gain
- d
B
Angle - degree
(a)
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Feed H
orn
Gain
- d
B
Angle - degree
(b)
Fig 311 Gain patterns of the fabricated feed at 187 GHz (a) E-plane and
(b) H-plane
-40-
IV Design of Circular Waveguide Feeds Loaded with a
Dielectric Rod
In this section circular waveguide feeds loaded with a dielectric rod feed
are investigated A comprehensive discussion of the circular waveguide loaded
with a dielectric rod is given by Kumar[7] Inserting a dielectric material
inside the circular waveguide improves the E- and H-plane pattern symmetry
In general dielectric-loaded circular waveguide feeds show good performance
only over a narrow bandwidth
Fig 41 shows the geometry of a circular waveguide loaded with a
dielectric rod The waveguide length is 400mm and the wall thickness is
05mm The dielectric rods diameter is 207mm The dielectric rod is
extended 05 wavelength beyond the waveguide open end The dielectric
constant εr is changed and the feeds performance is observed
Fig 41 Geometry of a circular waveguide loaded with a uniform dielectric
rod
-41-
Fig 42 is the radiation pattern of the feed with εr = 25 and L = 05λ0 at
9GHz E- and H-plane 10-dB beamwidths are 810 and 807 degrees
respectively The front-to-back ratio is 18dB The antenna gain is 71dB
(a)
(b)
Fig 42 Radiation pattern at 9GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 05λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-42-
Fig 43 shows the radiation pattern of the feed with εr = 21 at 10GHz
E- and H-plane 10-dB beamwidths are 70 and 71 degrees respectively The
front-to-back ratio is 19dB The antenna gain is 83dB
(a)
(b)
Fig 43 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 21 and L = 05λ0 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-43-
Fig 44 shows the radiation pattern of the feed with εr = 30 at 8GHz
E- and H-plane 10-dB beamwidths are 83 and 824 degrees respectively The
front-to-back ratio is 17dB The antenna gain is 73dB
(a)
(b)
Fig 44 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 30 and L = 05λ0 at 8GHz (a) 2D radiation pattern
and (b) E- and H-plane patterns
-44-
Fig 45 shows the radiation pattern of the feed with εr = 50 at 18GHz
E- and H-plane 10-dB beamwidths are 56 and 54 degrees respectively The
front-to-back ratio is 27dB The antenna gain is 105dB The feed has a good
pattern symmetry and low back radiation
(a)
(b)
Fig 45 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 50 and L = 05λ0 at 18GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-45-
Fig 46 is the radiation pattern of the feed with εr = 25 and L = 10λ0 at
10GHz E- and H-plane 10-dB beamwidths are 50 and 48 degrees
respectively The front-to-back ratio is 16dB The antenna gain is 105dB
(a)
(b)
Fig 46 Radiation pattern at 10GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 10λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-46-
Fig 47 shows the geometry of a circular waveguide with a tapered
dielectric rod The designed feed has the following dimension L = 1λ0 d =
1λ0 and εr =25 at 10GHz The waveguide length is 40mm and the wall
thickness is 05mm
L
Dielectricd3
Fig 47 Geometry of a circular waveguide loaded with a tapered dielectric
rod
Fig 48 shows the radiatio pattern of the designed feed E- and H-plane
10-dB beamwidths are 575 and 564 degrees respectively The front-to-back
ratio is 377dB The antenna gain is 94dB The designed feed has an
excellent beamwidth symmetry and a very low back radiation
-47-
(a)
(b)
Fig 48 Radiation pattern of a circular waveguide loaded with a tapered
dielectric rod with L = 1λ0 d = 1λ0 and εr =25 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-48-
Fig 49 shows the geometry of a spherical ended dielectric rod feed
diameter of 06λ0 at 10GHz with a dielectric constant of 25 and L= 03λ0
Fig 410 shows the radiation patterns of the designed feed E- and H-plane
10-dB beamwidths are both 63 degrees The front-to-back ratio is 24dB The
antenna gain is 864dB
Fig 49 Geometry of a circular waveguide loaded with a spherical ended
dielectric rod
-49-
(a)
(b)
Fig 410 Radiation pattern of a circular waveguide loaded wht a spherical
ended dielectric rod with d = 06λ0 L = 03λ0 and εr =25 at 10GHz (a) 3D
radiation pattern and (b) E- and H-plane patterns
-50-
V Design of a Broadband Circular Waveguide Feed
In this chapter the design of a broadband circular waveguide feed is
presented At microwave frequencies the feed is often a circular waveguide
with chokes and corrugations around the aperture Chokes and corrugations
equalize E- and H-plane patterns and reduce the back radiation
The proposed feed is designed to operate over 10-18GHz The design starts
with the optimization of the coaxial-to-rectangular waveguide adapter
employed for good mode purity over a broad frequency range Next a
rectangular-to-circular waveguide transition is optimized Finally chokes and
corrugations are designed for improved pattern symmetry and low back
radiation
The proposed feed structure is shown in Fig 51 The feed consist of the
following parts a coaxial-to-rectangular waveguide adapter a rectangular-to-
circular waveguide transition a circular waveguide section four quarter-wave
chokes around the feeds aperture and four corrugations on the feeds outer
surface
The computer simulation shows the above arrangement offers good radiation
patterns over a broad frequency range The broadband operation is obtained
by exciting the TE11 mode in the circular waveguide using the TE10 mode of
the rectangular waveguide which is in turn excited by a coaxial probe
-51-
Chokes
Coaxial-to-waveguide transition
Circular wavguide
Corrugations
Mode transition
(a)
(b)
Fig 51 Structure of the proposed broadband circular waveguide feed
(a) CAD model and (b) cross-sectional view
For the coaxial-to-rectangular waveguide adapter an SMA connector with
the probe diameter of 127 mm is employed The coaxial probe inserted into
the waveguide energizes the feed and excites the dominant TE10 mode in
-52-
the rectangular waveguide The impedance matching is achieved by adjusting
the probe distance sp from the back short and the probe length lp
(a)
(b)
Fig 52 Reflection coefficient of the coaxial-to-rectangular adapter versus
(a) probe length lp and (b) the probe position sp
Fig 52 shows the reflection coefficient versus the various values of probe
lengths lp and probe positions sp The probe length lp is adjusted to obtain
antenna impedance matching and the probe distance sp is adjusted to obtain a
-53-
desired resonant frequency
Next a transition between rectangular and circular waveguide is designed
The transition section converts the TE10 mode in the rectangular waveguide to
TE11 mode in the circular waveguide and vice versa The transition is built
in a form of a taper for easy fabrication[22]
(a)
(b)
Fig 53 Structure of the rectangular-to-circular waveguide transition
(a) 3D view and (b) cross sectional view
The dimensions of the final optimized transition are as follows The length
of the rectangular waveguide section is 143mm The rectangular waveguides
width a and height b are 207mm and 857mm respectively The length of
the circular waveguide section is 143mm The inside diameter of the circular
-54-
waveguide is 207mm(097 wavelength at 14GHz) The length of transition
region ltr is 4465mm(approximately equal to 2λ0 at 14GHz) Fig 54 shows
the field distribution inside the mode converter
(a)
(b)
Fig 54 Field distribution inside the mode converter at
(a) 10GHz (b) 14GHz and (c) 18GHz
-55-
(c)
Fig 54 continued
Finally multiple chokes are investigated Figs 55 56 and 57 show the
feed performance without chokes The reflection coefficient is less than -10dB
over 10-19GHz The antenna has a gain of 921dB to 1189dB over
10-19GHz
Fig 55 Reflection coefficient of the broadband circular waveguide feed
without chokes and corrugations
-56-
(a)
(b)
(c)
Fig 56 E- and H-plane patterns of the broadband circular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-57-
(d)
(e)
Fig 56 continued
-58-
(a)
(b)
Fig 57 2D radiation patterns of the broadband cicular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-59-
(c)
(d)
Fig 57 continued
-60-
(e)
Fig 57 continued
To achieve equal beamwidths in E and H planes over a wide frequency
range chokes and corrugations are employed Table51 summarizes the
performance of a feed without chokes and corrugations
Table 51 Performance of the broadband circular waveguide feed without
chokes and corrugations
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
1000 940 6061 15
1200 972 6159 17
1400 920 5957 21
1600 1070 4751 29
1800 1188 5352 21
-61-
Four quarter-wavelength chokes are introduced in the feed design which
has a slot depth of 75mm and slot width of 09mm The choke slot spacing
is 18mm The choke design is investigated by applying the choke one by
one and the effect on the E- and H-plane patterns are observed as illustrated
in Figs 58 and 59 The use of chokes makes the E-plane pattern narrower
The H-plane pattern is not affected Chokes increase the gain slightly and
reduce back radiation
(a)
(b)
Fig 58 Effect of chokes on the E-plane pattern of the broadband circular
waveguide feed at (a) 10GHz(b) 12GHz (c) 14GHz (d) 16GHz and (e)
18GHz
-62-
(c)
(d)
(e)
Fig 58 continued
-63-
(a)
(b)
(c)
Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-64-
(d)
(e)
Fig 59 continued
-65-
Fig 510 shows the feed performance versus the choke depth When the
choke depth is varied from 535mm to 95mm the E- and H-plane patterns
are strongly affected The optimum value of choke depth is 75mm(035λ0 at
14GHz) which gives equal E- and H-plane radiation patterns and leads to
low back radiation
Fig 511 shows the feed performance versus the choke slot width tch The
choke slot width is varied from 09mm to 21mm Radiation patterns and
reflection coefficients are not sensitive to the choke slot width The final
choke slot width is selected to be 09mm considering the feed diameter
minimization and the manufacturability The overall diameter of the proposed
feed is 369mm which is increased from the 207mm of the waveguide
inside diameter due to the use of four chokes
-66-
(a)
(b)
(c)
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection coefficient
-67-
(a)
(b)
(c)
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and (c)
reflection coefficient
-68-
Next we investigated corrugations placed on the outer wall of the feed
Four corrugations applied to the outer surface of the circular waveguide The
corrugation depth is 465mm(0215λ0 at 14GHz) The primary purpose of
using corrugations is to further reduce the back radiation Increasing the
number of corrugations beyond four has little effect in reducing the back
radiation
Figs 512 and 513 show the effect of corrugations on the E- and H-plane
patterns Fig 514 shows the parametric study of the corrugation depth lcor
The corrugation depth is varied from 40mm and 645mm The optimum
value of the corrugation depth is found to be 465mm
-69-
(a)
(b)
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern at (a) 12GHz and (b) 14GHz
-70-
(a)
(b)
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern at (a) 12GHz and (b) 14GHz
-71-
(a)
(b)
(c)
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection coefficient
-72-
The phase center location is important in placing the feed in a reflector
antenna[8] The phase center variation with frequency should be small Fig
515 shows the effect of chokes and corrugations on the phase center The
curve with circle corresponds to the case without chokes and corrugations
The phase center varies from -326mm and -190mm away from the feeds
aperture plane It means the phase center is located inside the waveguide
The curve with triangles corresponds to the case with chokes The curve with
squares to the case with chokes and corrugations The phase center varies
from 0mm to -302mm
From Fig 515 we can observed that phase center variation reduced by the
corrugation and three cases phase center calculated in φ=450 plane
parameter sweep values are given in Table 52
10 12 14 16 181
0
-1
-2
-3
-4
-5
-6
Pha
se c
ente
r (m
m)
Frequency (GHz)
choke+corrugatuion without choke corrugation with choke
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
-73-
Frequency
(GHz)
Phase center from the aperture plane
(mm)
Without
chokes and
corrugations
With
chokes
With chokes
and
corrugations
1000 -326 062 000
1100 -187 030 -002
1200 -563 -208 -065
1300 -296 -154 -202
1400 -319 -314 -302
1500 -201 -203 -241
1600 -242 -233 -207
1700 -208 -208 -186
1800 -190 -157 -132
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
Based on the foregoing parametric studies optimum dimensions of the
broadband circular waveguide feed are obtained as shown in Table 53
-74-
Table 53 Optimum dimensions of the broadband circular waveguide feed
Parameter Designation Value (mm)
2a Waveguide inside diameter 2070
d Waveguide outside diameter 3690
lcrLength of the circular waveguide section 1430
m Distance between the aperture plane and the first corrugation 950
xDistance from the last corrugation to the end of the cylindrical outer surface
550
ltrLength of the rectangular-to-circularwaveguide transition 4465
lrcLength of the rectangular waveguide section 1430
tch Choke slot width 090
lch Choke depth 750
t Choke metal width 090
lcor Corrugation depth 465
tcor Corrugation metal width 100
s Corrugation slot width 10
lp Probe length 530
sp Probe position from the back short 530
din Probe diameter 127
b Inside height of the rectangular waveguide 857
tw Waveguide wall thickness 500
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-24-
Fig 216 Reflection coefficient of the probe-fed square waveguide radiator
Table 24 Properties of the probe-fed square waveguide radiator
Frequency(GHz)-10dB beamwidth(deg) Front-to-back
ratio(dB)E plane H plane
10 73 71 12
14 85 63 1418 27 65 28
When a square waveguide radiator is fed by a coaxial probe its radiation
properties are not good due to the excitation of higher-order modes as in the
case of the probe-fed circular waveguide radiator A probe-fed square
waveguide radiator can be used as a feed only over a narrow frequency
range
-25-
III Design of Compact Circular Waveguide Feeds
In this chapter the feed design is presented for a prime-focus reflector
antenna The prime-focus paraboloid reflector is one of the most commonly
used high-gain antenna It has been used in earth-station antennas and radio
telescopes It consists of a paraboloid reflector with a feed system at its focal
point
The feed should radiate a low level of cross-polar power over the
operating frequency These conditions not easy to achieve and most prime
focus feeds are compromises The shape and characteristic of the radiation
pattern of the feed are the most important parameter because these will
directly influence the fields which are directed at a reflector[6] Other
electrical factors which relevant to the choice of a feed are the cross-polar
level the gain efficiency the bandwidth and impedance matching
31 Narrow-Band Circular Waveguide Feed
Fig 31 shows the proposed narrow-band circular waveguide feed and its
design variables The feed consists of a circular waveguide open end excited
by a TE11 dominant mode A quarter wave choke is applied along the
circular aperture of the waveguide to equalize E- and H-plane radiation
patterns and to suppress the back radiation A dielectric ring is used to
control the radiation pattern and change the power distribution over the
aperture The control of the amplitude over the aperture are essential to the
design of symmetric radiation pattern The material used for dielectric loading
-26-
is the monocast(MC) nylon with a dielectric constant of 30 The feed is
designed to operate over 171-197GHz
(a)
(b)
Fig 31 Narrow-band circular waveguide feed (a) CAD model and (b) a
cross sectional view
The impedance matching is achieved by a proper combination of the probe
height lp and its distance sp from the waveguide shorted end Here the
-27-
circular waveguide is terminated with an open end with a wall thickness of
2mm radiating into the free space
Fig 32 shows the effect of the probe length lp and the probe distance sp
on the reflection coefficient The best performance is obtained when lp =
363mm and sp = 616mm The feeds reflection coefficient is less than -10dB
over 170-195GHz
(a)
(b)
Fig 32 Effect of the (a) the probe length lp and (b) the probe
distance sp on the reflection coefficient
-28-
Fig 33 shows the effect of the choke depth The E-plane pattern is more
sensitive to the choke depth than the H-plane pattern The choke depth has a
strong influence on the reflection coefficient when it is 360mm By properly
choosing the choke depth we can equalize the E- and H-plane patterns The
optimum value of the choke depth is 410mm which is 0249λ0 at 1825GHz
The choke slot width tch in the range of 06-12mm has almost no effect
on the H-plane pattern and the reflection coefficient For the E-plane pattern
tch of 12mm has some effect on the E-plane radiation pattern as shown in
Fig 34
Fig 35 shows the feed performance versus the dielectric ring length We
observe in Fig 35 that the dielectric length ld has an optimum value of
1168mm which does no effect on the H-plane pattern and tha the value of
1048mm has some effect on the E-plane pattern and the reflection
coefficient
Fig 36 shows E-plane and H-plane patterns and the reflection coefficient
versus the dielectric thickness With the optimum value of the dielectric
thickness t obtained from the Fig 36 is 155mm The larger values of td has
much stronger effects on the E-plane pattern and the reflection coefficient
The H-plane pattern is not sensitive to the dielectric ring thickness
-29-
(a)
(b)
(c)
Fig 33 Feed performance versus the choke depth (a) E-plane pattern
(b) H-plane pattern and (c) reflection coefficient
-30-
(a)
(b)
(c)
Fig 34 Feed performance versus the choke slot width (a) E-plane pattern
(b) H-plane pattern and (c) reflection coefficient
-31-
(a)
(b)
(c)
Fig 35 Feed performance versus the dielectric ring length (a) E-plane
pattern (b) H-plane pattern and (c) reflection coefficient
-32-
(a)
(b)
(c)
Fig 36 Feed performance versus the dielectric ring thickness (a) E-plane
pattern(b) H-plane pattern and (c) reflection coefficient
-33-
From the above parametric analysis an optimum feed design is obtained
The result is shown in Table 31 Fig 37 shows the 2D gain patterns of
designed feed The antenna has a gain of 903dB 933dB and 956dB at
171GHz 1825GHz and 19GHz respectively
Fig 38 shows E- and H-plane radiation patterns of the designed feed The
feed has E- and H-plane 10-dB beamwidths of 60 and 59 degrees at 17GHz
The feed has a front-to-back ration of 1900dB 2490dB and 2200dB at
171GHz 1825GHz and 19GHz respectively Table 32 summarizes the
performance of the designed narrow-band circular waveguide feed
The designed feed has a greatly improved performance over that of a
simple coax-fed feed described in Section 23
Table 31 Dimensions of the designed narrow-band circular feed
Parameter Designation Value(mm)
a Waveguide inside radius 640
l Feed length 2890
lp Probe length 363
sp Probe position from the back short 616
din Probe diameter 127
dout Diameter of coaxial cables outer conductor 400
t Thickness of choked wall 050
tch Choke slot width 100
lch Choke depth 410
ld Dielectric ring length 1168
td Dielectric ring thickness 155
d1 Waveguide outside diameter 1680
-34-
(a)
(b)
Fig 37 2D gain patterns of the narrow-band circular waveguide feed at
(a) 17GHz (b) 1825GHz and (c) 19GHz
-35-
(c)
Fig 37 continued
-36-
(a)
(b)
(c)
Fig 38 E- and H-plane patterns of the narrow-band circular waveguide feed
at (a) 10GHz (b) 1825GHz and (c) 195GHz
-37-
Frequency(GHz)
Gain(dB)
E-H-plane10-dB beamwidths
(deg)
Front-to-back ratio(dB)
Phase centerlocation
(From feeds aperture plane
toward reflector)
(mm)
1700 903 6059 20 062
1825 933 6060 25 004
1900 956 5759 22 007
Table 32 Performance of the narrow-band circular waveguide feed
The designed narrow-band feed is fabricated and its performance is
measured and compared with the simulation results The designed feed is
fabricated in a numerically-controlled machining center The fabricated antenna
is shown in Fig 39
Fig 39 Photograph of the fabricated feed
-38-
Fig 310 shows a comparison of the measured and simulated reflection
coefficients The measured reflection coefficient is less than -10dB over
171-197GHz The agreement between simulated and measured results are
good
Fig 311 shows the E- and H-plane patterns of the fabricated feed at
187GHz The feed has 90dB gain simulation and measurement results are in
good agreement
The fabricated antennarsquos 10dB beamwidth is 60 degrees in both E and H
planes at 187GHz The front-to-back ratio is 21dB
Fig 310 Reflection coefficient of the fabricated feed
-39-
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Fee
d H
orn
Gain
- d
B
Angle - degree
(a)
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Feed H
orn
Gain
- d
B
Angle - degree
(b)
Fig 311 Gain patterns of the fabricated feed at 187 GHz (a) E-plane and
(b) H-plane
-40-
IV Design of Circular Waveguide Feeds Loaded with a
Dielectric Rod
In this section circular waveguide feeds loaded with a dielectric rod feed
are investigated A comprehensive discussion of the circular waveguide loaded
with a dielectric rod is given by Kumar[7] Inserting a dielectric material
inside the circular waveguide improves the E- and H-plane pattern symmetry
In general dielectric-loaded circular waveguide feeds show good performance
only over a narrow bandwidth
Fig 41 shows the geometry of a circular waveguide loaded with a
dielectric rod The waveguide length is 400mm and the wall thickness is
05mm The dielectric rods diameter is 207mm The dielectric rod is
extended 05 wavelength beyond the waveguide open end The dielectric
constant εr is changed and the feeds performance is observed
Fig 41 Geometry of a circular waveguide loaded with a uniform dielectric
rod
-41-
Fig 42 is the radiation pattern of the feed with εr = 25 and L = 05λ0 at
9GHz E- and H-plane 10-dB beamwidths are 810 and 807 degrees
respectively The front-to-back ratio is 18dB The antenna gain is 71dB
(a)
(b)
Fig 42 Radiation pattern at 9GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 05λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-42-
Fig 43 shows the radiation pattern of the feed with εr = 21 at 10GHz
E- and H-plane 10-dB beamwidths are 70 and 71 degrees respectively The
front-to-back ratio is 19dB The antenna gain is 83dB
(a)
(b)
Fig 43 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 21 and L = 05λ0 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-43-
Fig 44 shows the radiation pattern of the feed with εr = 30 at 8GHz
E- and H-plane 10-dB beamwidths are 83 and 824 degrees respectively The
front-to-back ratio is 17dB The antenna gain is 73dB
(a)
(b)
Fig 44 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 30 and L = 05λ0 at 8GHz (a) 2D radiation pattern
and (b) E- and H-plane patterns
-44-
Fig 45 shows the radiation pattern of the feed with εr = 50 at 18GHz
E- and H-plane 10-dB beamwidths are 56 and 54 degrees respectively The
front-to-back ratio is 27dB The antenna gain is 105dB The feed has a good
pattern symmetry and low back radiation
(a)
(b)
Fig 45 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 50 and L = 05λ0 at 18GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-45-
Fig 46 is the radiation pattern of the feed with εr = 25 and L = 10λ0 at
10GHz E- and H-plane 10-dB beamwidths are 50 and 48 degrees
respectively The front-to-back ratio is 16dB The antenna gain is 105dB
(a)
(b)
Fig 46 Radiation pattern at 10GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 10λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-46-
Fig 47 shows the geometry of a circular waveguide with a tapered
dielectric rod The designed feed has the following dimension L = 1λ0 d =
1λ0 and εr =25 at 10GHz The waveguide length is 40mm and the wall
thickness is 05mm
L
Dielectricd3
Fig 47 Geometry of a circular waveguide loaded with a tapered dielectric
rod
Fig 48 shows the radiatio pattern of the designed feed E- and H-plane
10-dB beamwidths are 575 and 564 degrees respectively The front-to-back
ratio is 377dB The antenna gain is 94dB The designed feed has an
excellent beamwidth symmetry and a very low back radiation
-47-
(a)
(b)
Fig 48 Radiation pattern of a circular waveguide loaded with a tapered
dielectric rod with L = 1λ0 d = 1λ0 and εr =25 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-48-
Fig 49 shows the geometry of a spherical ended dielectric rod feed
diameter of 06λ0 at 10GHz with a dielectric constant of 25 and L= 03λ0
Fig 410 shows the radiation patterns of the designed feed E- and H-plane
10-dB beamwidths are both 63 degrees The front-to-back ratio is 24dB The
antenna gain is 864dB
Fig 49 Geometry of a circular waveguide loaded with a spherical ended
dielectric rod
-49-
(a)
(b)
Fig 410 Radiation pattern of a circular waveguide loaded wht a spherical
ended dielectric rod with d = 06λ0 L = 03λ0 and εr =25 at 10GHz (a) 3D
radiation pattern and (b) E- and H-plane patterns
-50-
V Design of a Broadband Circular Waveguide Feed
In this chapter the design of a broadband circular waveguide feed is
presented At microwave frequencies the feed is often a circular waveguide
with chokes and corrugations around the aperture Chokes and corrugations
equalize E- and H-plane patterns and reduce the back radiation
The proposed feed is designed to operate over 10-18GHz The design starts
with the optimization of the coaxial-to-rectangular waveguide adapter
employed for good mode purity over a broad frequency range Next a
rectangular-to-circular waveguide transition is optimized Finally chokes and
corrugations are designed for improved pattern symmetry and low back
radiation
The proposed feed structure is shown in Fig 51 The feed consist of the
following parts a coaxial-to-rectangular waveguide adapter a rectangular-to-
circular waveguide transition a circular waveguide section four quarter-wave
chokes around the feeds aperture and four corrugations on the feeds outer
surface
The computer simulation shows the above arrangement offers good radiation
patterns over a broad frequency range The broadband operation is obtained
by exciting the TE11 mode in the circular waveguide using the TE10 mode of
the rectangular waveguide which is in turn excited by a coaxial probe
-51-
Chokes
Coaxial-to-waveguide transition
Circular wavguide
Corrugations
Mode transition
(a)
(b)
Fig 51 Structure of the proposed broadband circular waveguide feed
(a) CAD model and (b) cross-sectional view
For the coaxial-to-rectangular waveguide adapter an SMA connector with
the probe diameter of 127 mm is employed The coaxial probe inserted into
the waveguide energizes the feed and excites the dominant TE10 mode in
-52-
the rectangular waveguide The impedance matching is achieved by adjusting
the probe distance sp from the back short and the probe length lp
(a)
(b)
Fig 52 Reflection coefficient of the coaxial-to-rectangular adapter versus
(a) probe length lp and (b) the probe position sp
Fig 52 shows the reflection coefficient versus the various values of probe
lengths lp and probe positions sp The probe length lp is adjusted to obtain
antenna impedance matching and the probe distance sp is adjusted to obtain a
-53-
desired resonant frequency
Next a transition between rectangular and circular waveguide is designed
The transition section converts the TE10 mode in the rectangular waveguide to
TE11 mode in the circular waveguide and vice versa The transition is built
in a form of a taper for easy fabrication[22]
(a)
(b)
Fig 53 Structure of the rectangular-to-circular waveguide transition
(a) 3D view and (b) cross sectional view
The dimensions of the final optimized transition are as follows The length
of the rectangular waveguide section is 143mm The rectangular waveguides
width a and height b are 207mm and 857mm respectively The length of
the circular waveguide section is 143mm The inside diameter of the circular
-54-
waveguide is 207mm(097 wavelength at 14GHz) The length of transition
region ltr is 4465mm(approximately equal to 2λ0 at 14GHz) Fig 54 shows
the field distribution inside the mode converter
(a)
(b)
Fig 54 Field distribution inside the mode converter at
(a) 10GHz (b) 14GHz and (c) 18GHz
-55-
(c)
Fig 54 continued
Finally multiple chokes are investigated Figs 55 56 and 57 show the
feed performance without chokes The reflection coefficient is less than -10dB
over 10-19GHz The antenna has a gain of 921dB to 1189dB over
10-19GHz
Fig 55 Reflection coefficient of the broadband circular waveguide feed
without chokes and corrugations
-56-
(a)
(b)
(c)
Fig 56 E- and H-plane patterns of the broadband circular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-57-
(d)
(e)
Fig 56 continued
-58-
(a)
(b)
Fig 57 2D radiation patterns of the broadband cicular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-59-
(c)
(d)
Fig 57 continued
-60-
(e)
Fig 57 continued
To achieve equal beamwidths in E and H planes over a wide frequency
range chokes and corrugations are employed Table51 summarizes the
performance of a feed without chokes and corrugations
Table 51 Performance of the broadband circular waveguide feed without
chokes and corrugations
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
1000 940 6061 15
1200 972 6159 17
1400 920 5957 21
1600 1070 4751 29
1800 1188 5352 21
-61-
Four quarter-wavelength chokes are introduced in the feed design which
has a slot depth of 75mm and slot width of 09mm The choke slot spacing
is 18mm The choke design is investigated by applying the choke one by
one and the effect on the E- and H-plane patterns are observed as illustrated
in Figs 58 and 59 The use of chokes makes the E-plane pattern narrower
The H-plane pattern is not affected Chokes increase the gain slightly and
reduce back radiation
(a)
(b)
Fig 58 Effect of chokes on the E-plane pattern of the broadband circular
waveguide feed at (a) 10GHz(b) 12GHz (c) 14GHz (d) 16GHz and (e)
18GHz
-62-
(c)
(d)
(e)
Fig 58 continued
-63-
(a)
(b)
(c)
Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-64-
(d)
(e)
Fig 59 continued
-65-
Fig 510 shows the feed performance versus the choke depth When the
choke depth is varied from 535mm to 95mm the E- and H-plane patterns
are strongly affected The optimum value of choke depth is 75mm(035λ0 at
14GHz) which gives equal E- and H-plane radiation patterns and leads to
low back radiation
Fig 511 shows the feed performance versus the choke slot width tch The
choke slot width is varied from 09mm to 21mm Radiation patterns and
reflection coefficients are not sensitive to the choke slot width The final
choke slot width is selected to be 09mm considering the feed diameter
minimization and the manufacturability The overall diameter of the proposed
feed is 369mm which is increased from the 207mm of the waveguide
inside diameter due to the use of four chokes
-66-
(a)
(b)
(c)
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection coefficient
-67-
(a)
(b)
(c)
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and (c)
reflection coefficient
-68-
Next we investigated corrugations placed on the outer wall of the feed
Four corrugations applied to the outer surface of the circular waveguide The
corrugation depth is 465mm(0215λ0 at 14GHz) The primary purpose of
using corrugations is to further reduce the back radiation Increasing the
number of corrugations beyond four has little effect in reducing the back
radiation
Figs 512 and 513 show the effect of corrugations on the E- and H-plane
patterns Fig 514 shows the parametric study of the corrugation depth lcor
The corrugation depth is varied from 40mm and 645mm The optimum
value of the corrugation depth is found to be 465mm
-69-
(a)
(b)
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern at (a) 12GHz and (b) 14GHz
-70-
(a)
(b)
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern at (a) 12GHz and (b) 14GHz
-71-
(a)
(b)
(c)
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection coefficient
-72-
The phase center location is important in placing the feed in a reflector
antenna[8] The phase center variation with frequency should be small Fig
515 shows the effect of chokes and corrugations on the phase center The
curve with circle corresponds to the case without chokes and corrugations
The phase center varies from -326mm and -190mm away from the feeds
aperture plane It means the phase center is located inside the waveguide
The curve with triangles corresponds to the case with chokes The curve with
squares to the case with chokes and corrugations The phase center varies
from 0mm to -302mm
From Fig 515 we can observed that phase center variation reduced by the
corrugation and three cases phase center calculated in φ=450 plane
parameter sweep values are given in Table 52
10 12 14 16 181
0
-1
-2
-3
-4
-5
-6
Pha
se c
ente
r (m
m)
Frequency (GHz)
choke+corrugatuion without choke corrugation with choke
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
-73-
Frequency
(GHz)
Phase center from the aperture plane
(mm)
Without
chokes and
corrugations
With
chokes
With chokes
and
corrugations
1000 -326 062 000
1100 -187 030 -002
1200 -563 -208 -065
1300 -296 -154 -202
1400 -319 -314 -302
1500 -201 -203 -241
1600 -242 -233 -207
1700 -208 -208 -186
1800 -190 -157 -132
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
Based on the foregoing parametric studies optimum dimensions of the
broadband circular waveguide feed are obtained as shown in Table 53
-74-
Table 53 Optimum dimensions of the broadband circular waveguide feed
Parameter Designation Value (mm)
2a Waveguide inside diameter 2070
d Waveguide outside diameter 3690
lcrLength of the circular waveguide section 1430
m Distance between the aperture plane and the first corrugation 950
xDistance from the last corrugation to the end of the cylindrical outer surface
550
ltrLength of the rectangular-to-circularwaveguide transition 4465
lrcLength of the rectangular waveguide section 1430
tch Choke slot width 090
lch Choke depth 750
t Choke metal width 090
lcor Corrugation depth 465
tcor Corrugation metal width 100
s Corrugation slot width 10
lp Probe length 530
sp Probe position from the back short 530
din Probe diameter 127
b Inside height of the rectangular waveguide 857
tw Waveguide wall thickness 500
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-25-
III Design of Compact Circular Waveguide Feeds
In this chapter the feed design is presented for a prime-focus reflector
antenna The prime-focus paraboloid reflector is one of the most commonly
used high-gain antenna It has been used in earth-station antennas and radio
telescopes It consists of a paraboloid reflector with a feed system at its focal
point
The feed should radiate a low level of cross-polar power over the
operating frequency These conditions not easy to achieve and most prime
focus feeds are compromises The shape and characteristic of the radiation
pattern of the feed are the most important parameter because these will
directly influence the fields which are directed at a reflector[6] Other
electrical factors which relevant to the choice of a feed are the cross-polar
level the gain efficiency the bandwidth and impedance matching
31 Narrow-Band Circular Waveguide Feed
Fig 31 shows the proposed narrow-band circular waveguide feed and its
design variables The feed consists of a circular waveguide open end excited
by a TE11 dominant mode A quarter wave choke is applied along the
circular aperture of the waveguide to equalize E- and H-plane radiation
patterns and to suppress the back radiation A dielectric ring is used to
control the radiation pattern and change the power distribution over the
aperture The control of the amplitude over the aperture are essential to the
design of symmetric radiation pattern The material used for dielectric loading
-26-
is the monocast(MC) nylon with a dielectric constant of 30 The feed is
designed to operate over 171-197GHz
(a)
(b)
Fig 31 Narrow-band circular waveguide feed (a) CAD model and (b) a
cross sectional view
The impedance matching is achieved by a proper combination of the probe
height lp and its distance sp from the waveguide shorted end Here the
-27-
circular waveguide is terminated with an open end with a wall thickness of
2mm radiating into the free space
Fig 32 shows the effect of the probe length lp and the probe distance sp
on the reflection coefficient The best performance is obtained when lp =
363mm and sp = 616mm The feeds reflection coefficient is less than -10dB
over 170-195GHz
(a)
(b)
Fig 32 Effect of the (a) the probe length lp and (b) the probe
distance sp on the reflection coefficient
-28-
Fig 33 shows the effect of the choke depth The E-plane pattern is more
sensitive to the choke depth than the H-plane pattern The choke depth has a
strong influence on the reflection coefficient when it is 360mm By properly
choosing the choke depth we can equalize the E- and H-plane patterns The
optimum value of the choke depth is 410mm which is 0249λ0 at 1825GHz
The choke slot width tch in the range of 06-12mm has almost no effect
on the H-plane pattern and the reflection coefficient For the E-plane pattern
tch of 12mm has some effect on the E-plane radiation pattern as shown in
Fig 34
Fig 35 shows the feed performance versus the dielectric ring length We
observe in Fig 35 that the dielectric length ld has an optimum value of
1168mm which does no effect on the H-plane pattern and tha the value of
1048mm has some effect on the E-plane pattern and the reflection
coefficient
Fig 36 shows E-plane and H-plane patterns and the reflection coefficient
versus the dielectric thickness With the optimum value of the dielectric
thickness t obtained from the Fig 36 is 155mm The larger values of td has
much stronger effects on the E-plane pattern and the reflection coefficient
The H-plane pattern is not sensitive to the dielectric ring thickness
-29-
(a)
(b)
(c)
Fig 33 Feed performance versus the choke depth (a) E-plane pattern
(b) H-plane pattern and (c) reflection coefficient
-30-
(a)
(b)
(c)
Fig 34 Feed performance versus the choke slot width (a) E-plane pattern
(b) H-plane pattern and (c) reflection coefficient
-31-
(a)
(b)
(c)
Fig 35 Feed performance versus the dielectric ring length (a) E-plane
pattern (b) H-plane pattern and (c) reflection coefficient
-32-
(a)
(b)
(c)
Fig 36 Feed performance versus the dielectric ring thickness (a) E-plane
pattern(b) H-plane pattern and (c) reflection coefficient
-33-
From the above parametric analysis an optimum feed design is obtained
The result is shown in Table 31 Fig 37 shows the 2D gain patterns of
designed feed The antenna has a gain of 903dB 933dB and 956dB at
171GHz 1825GHz and 19GHz respectively
Fig 38 shows E- and H-plane radiation patterns of the designed feed The
feed has E- and H-plane 10-dB beamwidths of 60 and 59 degrees at 17GHz
The feed has a front-to-back ration of 1900dB 2490dB and 2200dB at
171GHz 1825GHz and 19GHz respectively Table 32 summarizes the
performance of the designed narrow-band circular waveguide feed
The designed feed has a greatly improved performance over that of a
simple coax-fed feed described in Section 23
Table 31 Dimensions of the designed narrow-band circular feed
Parameter Designation Value(mm)
a Waveguide inside radius 640
l Feed length 2890
lp Probe length 363
sp Probe position from the back short 616
din Probe diameter 127
dout Diameter of coaxial cables outer conductor 400
t Thickness of choked wall 050
tch Choke slot width 100
lch Choke depth 410
ld Dielectric ring length 1168
td Dielectric ring thickness 155
d1 Waveguide outside diameter 1680
-34-
(a)
(b)
Fig 37 2D gain patterns of the narrow-band circular waveguide feed at
(a) 17GHz (b) 1825GHz and (c) 19GHz
-35-
(c)
Fig 37 continued
-36-
(a)
(b)
(c)
Fig 38 E- and H-plane patterns of the narrow-band circular waveguide feed
at (a) 10GHz (b) 1825GHz and (c) 195GHz
-37-
Frequency(GHz)
Gain(dB)
E-H-plane10-dB beamwidths
(deg)
Front-to-back ratio(dB)
Phase centerlocation
(From feeds aperture plane
toward reflector)
(mm)
1700 903 6059 20 062
1825 933 6060 25 004
1900 956 5759 22 007
Table 32 Performance of the narrow-band circular waveguide feed
The designed narrow-band feed is fabricated and its performance is
measured and compared with the simulation results The designed feed is
fabricated in a numerically-controlled machining center The fabricated antenna
is shown in Fig 39
Fig 39 Photograph of the fabricated feed
-38-
Fig 310 shows a comparison of the measured and simulated reflection
coefficients The measured reflection coefficient is less than -10dB over
171-197GHz The agreement between simulated and measured results are
good
Fig 311 shows the E- and H-plane patterns of the fabricated feed at
187GHz The feed has 90dB gain simulation and measurement results are in
good agreement
The fabricated antennarsquos 10dB beamwidth is 60 degrees in both E and H
planes at 187GHz The front-to-back ratio is 21dB
Fig 310 Reflection coefficient of the fabricated feed
-39-
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Fee
d H
orn
Gain
- d
B
Angle - degree
(a)
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Feed H
orn
Gain
- d
B
Angle - degree
(b)
Fig 311 Gain patterns of the fabricated feed at 187 GHz (a) E-plane and
(b) H-plane
-40-
IV Design of Circular Waveguide Feeds Loaded with a
Dielectric Rod
In this section circular waveguide feeds loaded with a dielectric rod feed
are investigated A comprehensive discussion of the circular waveguide loaded
with a dielectric rod is given by Kumar[7] Inserting a dielectric material
inside the circular waveguide improves the E- and H-plane pattern symmetry
In general dielectric-loaded circular waveguide feeds show good performance
only over a narrow bandwidth
Fig 41 shows the geometry of a circular waveguide loaded with a
dielectric rod The waveguide length is 400mm and the wall thickness is
05mm The dielectric rods diameter is 207mm The dielectric rod is
extended 05 wavelength beyond the waveguide open end The dielectric
constant εr is changed and the feeds performance is observed
Fig 41 Geometry of a circular waveguide loaded with a uniform dielectric
rod
-41-
Fig 42 is the radiation pattern of the feed with εr = 25 and L = 05λ0 at
9GHz E- and H-plane 10-dB beamwidths are 810 and 807 degrees
respectively The front-to-back ratio is 18dB The antenna gain is 71dB
(a)
(b)
Fig 42 Radiation pattern at 9GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 05λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-42-
Fig 43 shows the radiation pattern of the feed with εr = 21 at 10GHz
E- and H-plane 10-dB beamwidths are 70 and 71 degrees respectively The
front-to-back ratio is 19dB The antenna gain is 83dB
(a)
(b)
Fig 43 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 21 and L = 05λ0 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-43-
Fig 44 shows the radiation pattern of the feed with εr = 30 at 8GHz
E- and H-plane 10-dB beamwidths are 83 and 824 degrees respectively The
front-to-back ratio is 17dB The antenna gain is 73dB
(a)
(b)
Fig 44 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 30 and L = 05λ0 at 8GHz (a) 2D radiation pattern
and (b) E- and H-plane patterns
-44-
Fig 45 shows the radiation pattern of the feed with εr = 50 at 18GHz
E- and H-plane 10-dB beamwidths are 56 and 54 degrees respectively The
front-to-back ratio is 27dB The antenna gain is 105dB The feed has a good
pattern symmetry and low back radiation
(a)
(b)
Fig 45 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 50 and L = 05λ0 at 18GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-45-
Fig 46 is the radiation pattern of the feed with εr = 25 and L = 10λ0 at
10GHz E- and H-plane 10-dB beamwidths are 50 and 48 degrees
respectively The front-to-back ratio is 16dB The antenna gain is 105dB
(a)
(b)
Fig 46 Radiation pattern at 10GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 10λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-46-
Fig 47 shows the geometry of a circular waveguide with a tapered
dielectric rod The designed feed has the following dimension L = 1λ0 d =
1λ0 and εr =25 at 10GHz The waveguide length is 40mm and the wall
thickness is 05mm
L
Dielectricd3
Fig 47 Geometry of a circular waveguide loaded with a tapered dielectric
rod
Fig 48 shows the radiatio pattern of the designed feed E- and H-plane
10-dB beamwidths are 575 and 564 degrees respectively The front-to-back
ratio is 377dB The antenna gain is 94dB The designed feed has an
excellent beamwidth symmetry and a very low back radiation
-47-
(a)
(b)
Fig 48 Radiation pattern of a circular waveguide loaded with a tapered
dielectric rod with L = 1λ0 d = 1λ0 and εr =25 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-48-
Fig 49 shows the geometry of a spherical ended dielectric rod feed
diameter of 06λ0 at 10GHz with a dielectric constant of 25 and L= 03λ0
Fig 410 shows the radiation patterns of the designed feed E- and H-plane
10-dB beamwidths are both 63 degrees The front-to-back ratio is 24dB The
antenna gain is 864dB
Fig 49 Geometry of a circular waveguide loaded with a spherical ended
dielectric rod
-49-
(a)
(b)
Fig 410 Radiation pattern of a circular waveguide loaded wht a spherical
ended dielectric rod with d = 06λ0 L = 03λ0 and εr =25 at 10GHz (a) 3D
radiation pattern and (b) E- and H-plane patterns
-50-
V Design of a Broadband Circular Waveguide Feed
In this chapter the design of a broadband circular waveguide feed is
presented At microwave frequencies the feed is often a circular waveguide
with chokes and corrugations around the aperture Chokes and corrugations
equalize E- and H-plane patterns and reduce the back radiation
The proposed feed is designed to operate over 10-18GHz The design starts
with the optimization of the coaxial-to-rectangular waveguide adapter
employed for good mode purity over a broad frequency range Next a
rectangular-to-circular waveguide transition is optimized Finally chokes and
corrugations are designed for improved pattern symmetry and low back
radiation
The proposed feed structure is shown in Fig 51 The feed consist of the
following parts a coaxial-to-rectangular waveguide adapter a rectangular-to-
circular waveguide transition a circular waveguide section four quarter-wave
chokes around the feeds aperture and four corrugations on the feeds outer
surface
The computer simulation shows the above arrangement offers good radiation
patterns over a broad frequency range The broadband operation is obtained
by exciting the TE11 mode in the circular waveguide using the TE10 mode of
the rectangular waveguide which is in turn excited by a coaxial probe
-51-
Chokes
Coaxial-to-waveguide transition
Circular wavguide
Corrugations
Mode transition
(a)
(b)
Fig 51 Structure of the proposed broadband circular waveguide feed
(a) CAD model and (b) cross-sectional view
For the coaxial-to-rectangular waveguide adapter an SMA connector with
the probe diameter of 127 mm is employed The coaxial probe inserted into
the waveguide energizes the feed and excites the dominant TE10 mode in
-52-
the rectangular waveguide The impedance matching is achieved by adjusting
the probe distance sp from the back short and the probe length lp
(a)
(b)
Fig 52 Reflection coefficient of the coaxial-to-rectangular adapter versus
(a) probe length lp and (b) the probe position sp
Fig 52 shows the reflection coefficient versus the various values of probe
lengths lp and probe positions sp The probe length lp is adjusted to obtain
antenna impedance matching and the probe distance sp is adjusted to obtain a
-53-
desired resonant frequency
Next a transition between rectangular and circular waveguide is designed
The transition section converts the TE10 mode in the rectangular waveguide to
TE11 mode in the circular waveguide and vice versa The transition is built
in a form of a taper for easy fabrication[22]
(a)
(b)
Fig 53 Structure of the rectangular-to-circular waveguide transition
(a) 3D view and (b) cross sectional view
The dimensions of the final optimized transition are as follows The length
of the rectangular waveguide section is 143mm The rectangular waveguides
width a and height b are 207mm and 857mm respectively The length of
the circular waveguide section is 143mm The inside diameter of the circular
-54-
waveguide is 207mm(097 wavelength at 14GHz) The length of transition
region ltr is 4465mm(approximately equal to 2λ0 at 14GHz) Fig 54 shows
the field distribution inside the mode converter
(a)
(b)
Fig 54 Field distribution inside the mode converter at
(a) 10GHz (b) 14GHz and (c) 18GHz
-55-
(c)
Fig 54 continued
Finally multiple chokes are investigated Figs 55 56 and 57 show the
feed performance without chokes The reflection coefficient is less than -10dB
over 10-19GHz The antenna has a gain of 921dB to 1189dB over
10-19GHz
Fig 55 Reflection coefficient of the broadband circular waveguide feed
without chokes and corrugations
-56-
(a)
(b)
(c)
Fig 56 E- and H-plane patterns of the broadband circular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-57-
(d)
(e)
Fig 56 continued
-58-
(a)
(b)
Fig 57 2D radiation patterns of the broadband cicular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-59-
(c)
(d)
Fig 57 continued
-60-
(e)
Fig 57 continued
To achieve equal beamwidths in E and H planes over a wide frequency
range chokes and corrugations are employed Table51 summarizes the
performance of a feed without chokes and corrugations
Table 51 Performance of the broadband circular waveguide feed without
chokes and corrugations
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
1000 940 6061 15
1200 972 6159 17
1400 920 5957 21
1600 1070 4751 29
1800 1188 5352 21
-61-
Four quarter-wavelength chokes are introduced in the feed design which
has a slot depth of 75mm and slot width of 09mm The choke slot spacing
is 18mm The choke design is investigated by applying the choke one by
one and the effect on the E- and H-plane patterns are observed as illustrated
in Figs 58 and 59 The use of chokes makes the E-plane pattern narrower
The H-plane pattern is not affected Chokes increase the gain slightly and
reduce back radiation
(a)
(b)
Fig 58 Effect of chokes on the E-plane pattern of the broadband circular
waveguide feed at (a) 10GHz(b) 12GHz (c) 14GHz (d) 16GHz and (e)
18GHz
-62-
(c)
(d)
(e)
Fig 58 continued
-63-
(a)
(b)
(c)
Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-64-
(d)
(e)
Fig 59 continued
-65-
Fig 510 shows the feed performance versus the choke depth When the
choke depth is varied from 535mm to 95mm the E- and H-plane patterns
are strongly affected The optimum value of choke depth is 75mm(035λ0 at
14GHz) which gives equal E- and H-plane radiation patterns and leads to
low back radiation
Fig 511 shows the feed performance versus the choke slot width tch The
choke slot width is varied from 09mm to 21mm Radiation patterns and
reflection coefficients are not sensitive to the choke slot width The final
choke slot width is selected to be 09mm considering the feed diameter
minimization and the manufacturability The overall diameter of the proposed
feed is 369mm which is increased from the 207mm of the waveguide
inside diameter due to the use of four chokes
-66-
(a)
(b)
(c)
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection coefficient
-67-
(a)
(b)
(c)
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and (c)
reflection coefficient
-68-
Next we investigated corrugations placed on the outer wall of the feed
Four corrugations applied to the outer surface of the circular waveguide The
corrugation depth is 465mm(0215λ0 at 14GHz) The primary purpose of
using corrugations is to further reduce the back radiation Increasing the
number of corrugations beyond four has little effect in reducing the back
radiation
Figs 512 and 513 show the effect of corrugations on the E- and H-plane
patterns Fig 514 shows the parametric study of the corrugation depth lcor
The corrugation depth is varied from 40mm and 645mm The optimum
value of the corrugation depth is found to be 465mm
-69-
(a)
(b)
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern at (a) 12GHz and (b) 14GHz
-70-
(a)
(b)
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern at (a) 12GHz and (b) 14GHz
-71-
(a)
(b)
(c)
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection coefficient
-72-
The phase center location is important in placing the feed in a reflector
antenna[8] The phase center variation with frequency should be small Fig
515 shows the effect of chokes and corrugations on the phase center The
curve with circle corresponds to the case without chokes and corrugations
The phase center varies from -326mm and -190mm away from the feeds
aperture plane It means the phase center is located inside the waveguide
The curve with triangles corresponds to the case with chokes The curve with
squares to the case with chokes and corrugations The phase center varies
from 0mm to -302mm
From Fig 515 we can observed that phase center variation reduced by the
corrugation and three cases phase center calculated in φ=450 plane
parameter sweep values are given in Table 52
10 12 14 16 181
0
-1
-2
-3
-4
-5
-6
Pha
se c
ente
r (m
m)
Frequency (GHz)
choke+corrugatuion without choke corrugation with choke
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
-73-
Frequency
(GHz)
Phase center from the aperture plane
(mm)
Without
chokes and
corrugations
With
chokes
With chokes
and
corrugations
1000 -326 062 000
1100 -187 030 -002
1200 -563 -208 -065
1300 -296 -154 -202
1400 -319 -314 -302
1500 -201 -203 -241
1600 -242 -233 -207
1700 -208 -208 -186
1800 -190 -157 -132
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
Based on the foregoing parametric studies optimum dimensions of the
broadband circular waveguide feed are obtained as shown in Table 53
-74-
Table 53 Optimum dimensions of the broadband circular waveguide feed
Parameter Designation Value (mm)
2a Waveguide inside diameter 2070
d Waveguide outside diameter 3690
lcrLength of the circular waveguide section 1430
m Distance between the aperture plane and the first corrugation 950
xDistance from the last corrugation to the end of the cylindrical outer surface
550
ltrLength of the rectangular-to-circularwaveguide transition 4465
lrcLength of the rectangular waveguide section 1430
tch Choke slot width 090
lch Choke depth 750
t Choke metal width 090
lcor Corrugation depth 465
tcor Corrugation metal width 100
s Corrugation slot width 10
lp Probe length 530
sp Probe position from the back short 530
din Probe diameter 127
b Inside height of the rectangular waveguide 857
tw Waveguide wall thickness 500
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-26-
is the monocast(MC) nylon with a dielectric constant of 30 The feed is
designed to operate over 171-197GHz
(a)
(b)
Fig 31 Narrow-band circular waveguide feed (a) CAD model and (b) a
cross sectional view
The impedance matching is achieved by a proper combination of the probe
height lp and its distance sp from the waveguide shorted end Here the
-27-
circular waveguide is terminated with an open end with a wall thickness of
2mm radiating into the free space
Fig 32 shows the effect of the probe length lp and the probe distance sp
on the reflection coefficient The best performance is obtained when lp =
363mm and sp = 616mm The feeds reflection coefficient is less than -10dB
over 170-195GHz
(a)
(b)
Fig 32 Effect of the (a) the probe length lp and (b) the probe
distance sp on the reflection coefficient
-28-
Fig 33 shows the effect of the choke depth The E-plane pattern is more
sensitive to the choke depth than the H-plane pattern The choke depth has a
strong influence on the reflection coefficient when it is 360mm By properly
choosing the choke depth we can equalize the E- and H-plane patterns The
optimum value of the choke depth is 410mm which is 0249λ0 at 1825GHz
The choke slot width tch in the range of 06-12mm has almost no effect
on the H-plane pattern and the reflection coefficient For the E-plane pattern
tch of 12mm has some effect on the E-plane radiation pattern as shown in
Fig 34
Fig 35 shows the feed performance versus the dielectric ring length We
observe in Fig 35 that the dielectric length ld has an optimum value of
1168mm which does no effect on the H-plane pattern and tha the value of
1048mm has some effect on the E-plane pattern and the reflection
coefficient
Fig 36 shows E-plane and H-plane patterns and the reflection coefficient
versus the dielectric thickness With the optimum value of the dielectric
thickness t obtained from the Fig 36 is 155mm The larger values of td has
much stronger effects on the E-plane pattern and the reflection coefficient
The H-plane pattern is not sensitive to the dielectric ring thickness
-29-
(a)
(b)
(c)
Fig 33 Feed performance versus the choke depth (a) E-plane pattern
(b) H-plane pattern and (c) reflection coefficient
-30-
(a)
(b)
(c)
Fig 34 Feed performance versus the choke slot width (a) E-plane pattern
(b) H-plane pattern and (c) reflection coefficient
-31-
(a)
(b)
(c)
Fig 35 Feed performance versus the dielectric ring length (a) E-plane
pattern (b) H-plane pattern and (c) reflection coefficient
-32-
(a)
(b)
(c)
Fig 36 Feed performance versus the dielectric ring thickness (a) E-plane
pattern(b) H-plane pattern and (c) reflection coefficient
-33-
From the above parametric analysis an optimum feed design is obtained
The result is shown in Table 31 Fig 37 shows the 2D gain patterns of
designed feed The antenna has a gain of 903dB 933dB and 956dB at
171GHz 1825GHz and 19GHz respectively
Fig 38 shows E- and H-plane radiation patterns of the designed feed The
feed has E- and H-plane 10-dB beamwidths of 60 and 59 degrees at 17GHz
The feed has a front-to-back ration of 1900dB 2490dB and 2200dB at
171GHz 1825GHz and 19GHz respectively Table 32 summarizes the
performance of the designed narrow-band circular waveguide feed
The designed feed has a greatly improved performance over that of a
simple coax-fed feed described in Section 23
Table 31 Dimensions of the designed narrow-band circular feed
Parameter Designation Value(mm)
a Waveguide inside radius 640
l Feed length 2890
lp Probe length 363
sp Probe position from the back short 616
din Probe diameter 127
dout Diameter of coaxial cables outer conductor 400
t Thickness of choked wall 050
tch Choke slot width 100
lch Choke depth 410
ld Dielectric ring length 1168
td Dielectric ring thickness 155
d1 Waveguide outside diameter 1680
-34-
(a)
(b)
Fig 37 2D gain patterns of the narrow-band circular waveguide feed at
(a) 17GHz (b) 1825GHz and (c) 19GHz
-35-
(c)
Fig 37 continued
-36-
(a)
(b)
(c)
Fig 38 E- and H-plane patterns of the narrow-band circular waveguide feed
at (a) 10GHz (b) 1825GHz and (c) 195GHz
-37-
Frequency(GHz)
Gain(dB)
E-H-plane10-dB beamwidths
(deg)
Front-to-back ratio(dB)
Phase centerlocation
(From feeds aperture plane
toward reflector)
(mm)
1700 903 6059 20 062
1825 933 6060 25 004
1900 956 5759 22 007
Table 32 Performance of the narrow-band circular waveguide feed
The designed narrow-band feed is fabricated and its performance is
measured and compared with the simulation results The designed feed is
fabricated in a numerically-controlled machining center The fabricated antenna
is shown in Fig 39
Fig 39 Photograph of the fabricated feed
-38-
Fig 310 shows a comparison of the measured and simulated reflection
coefficients The measured reflection coefficient is less than -10dB over
171-197GHz The agreement between simulated and measured results are
good
Fig 311 shows the E- and H-plane patterns of the fabricated feed at
187GHz The feed has 90dB gain simulation and measurement results are in
good agreement
The fabricated antennarsquos 10dB beamwidth is 60 degrees in both E and H
planes at 187GHz The front-to-back ratio is 21dB
Fig 310 Reflection coefficient of the fabricated feed
-39-
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Fee
d H
orn
Gain
- d
B
Angle - degree
(a)
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Feed H
orn
Gain
- d
B
Angle - degree
(b)
Fig 311 Gain patterns of the fabricated feed at 187 GHz (a) E-plane and
(b) H-plane
-40-
IV Design of Circular Waveguide Feeds Loaded with a
Dielectric Rod
In this section circular waveguide feeds loaded with a dielectric rod feed
are investigated A comprehensive discussion of the circular waveguide loaded
with a dielectric rod is given by Kumar[7] Inserting a dielectric material
inside the circular waveguide improves the E- and H-plane pattern symmetry
In general dielectric-loaded circular waveguide feeds show good performance
only over a narrow bandwidth
Fig 41 shows the geometry of a circular waveguide loaded with a
dielectric rod The waveguide length is 400mm and the wall thickness is
05mm The dielectric rods diameter is 207mm The dielectric rod is
extended 05 wavelength beyond the waveguide open end The dielectric
constant εr is changed and the feeds performance is observed
Fig 41 Geometry of a circular waveguide loaded with a uniform dielectric
rod
-41-
Fig 42 is the radiation pattern of the feed with εr = 25 and L = 05λ0 at
9GHz E- and H-plane 10-dB beamwidths are 810 and 807 degrees
respectively The front-to-back ratio is 18dB The antenna gain is 71dB
(a)
(b)
Fig 42 Radiation pattern at 9GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 05λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-42-
Fig 43 shows the radiation pattern of the feed with εr = 21 at 10GHz
E- and H-plane 10-dB beamwidths are 70 and 71 degrees respectively The
front-to-back ratio is 19dB The antenna gain is 83dB
(a)
(b)
Fig 43 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 21 and L = 05λ0 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-43-
Fig 44 shows the radiation pattern of the feed with εr = 30 at 8GHz
E- and H-plane 10-dB beamwidths are 83 and 824 degrees respectively The
front-to-back ratio is 17dB The antenna gain is 73dB
(a)
(b)
Fig 44 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 30 and L = 05λ0 at 8GHz (a) 2D radiation pattern
and (b) E- and H-plane patterns
-44-
Fig 45 shows the radiation pattern of the feed with εr = 50 at 18GHz
E- and H-plane 10-dB beamwidths are 56 and 54 degrees respectively The
front-to-back ratio is 27dB The antenna gain is 105dB The feed has a good
pattern symmetry and low back radiation
(a)
(b)
Fig 45 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 50 and L = 05λ0 at 18GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-45-
Fig 46 is the radiation pattern of the feed with εr = 25 and L = 10λ0 at
10GHz E- and H-plane 10-dB beamwidths are 50 and 48 degrees
respectively The front-to-back ratio is 16dB The antenna gain is 105dB
(a)
(b)
Fig 46 Radiation pattern at 10GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 10λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-46-
Fig 47 shows the geometry of a circular waveguide with a tapered
dielectric rod The designed feed has the following dimension L = 1λ0 d =
1λ0 and εr =25 at 10GHz The waveguide length is 40mm and the wall
thickness is 05mm
L
Dielectricd3
Fig 47 Geometry of a circular waveguide loaded with a tapered dielectric
rod
Fig 48 shows the radiatio pattern of the designed feed E- and H-plane
10-dB beamwidths are 575 and 564 degrees respectively The front-to-back
ratio is 377dB The antenna gain is 94dB The designed feed has an
excellent beamwidth symmetry and a very low back radiation
-47-
(a)
(b)
Fig 48 Radiation pattern of a circular waveguide loaded with a tapered
dielectric rod with L = 1λ0 d = 1λ0 and εr =25 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-48-
Fig 49 shows the geometry of a spherical ended dielectric rod feed
diameter of 06λ0 at 10GHz with a dielectric constant of 25 and L= 03λ0
Fig 410 shows the radiation patterns of the designed feed E- and H-plane
10-dB beamwidths are both 63 degrees The front-to-back ratio is 24dB The
antenna gain is 864dB
Fig 49 Geometry of a circular waveguide loaded with a spherical ended
dielectric rod
-49-
(a)
(b)
Fig 410 Radiation pattern of a circular waveguide loaded wht a spherical
ended dielectric rod with d = 06λ0 L = 03λ0 and εr =25 at 10GHz (a) 3D
radiation pattern and (b) E- and H-plane patterns
-50-
V Design of a Broadband Circular Waveguide Feed
In this chapter the design of a broadband circular waveguide feed is
presented At microwave frequencies the feed is often a circular waveguide
with chokes and corrugations around the aperture Chokes and corrugations
equalize E- and H-plane patterns and reduce the back radiation
The proposed feed is designed to operate over 10-18GHz The design starts
with the optimization of the coaxial-to-rectangular waveguide adapter
employed for good mode purity over a broad frequency range Next a
rectangular-to-circular waveguide transition is optimized Finally chokes and
corrugations are designed for improved pattern symmetry and low back
radiation
The proposed feed structure is shown in Fig 51 The feed consist of the
following parts a coaxial-to-rectangular waveguide adapter a rectangular-to-
circular waveguide transition a circular waveguide section four quarter-wave
chokes around the feeds aperture and four corrugations on the feeds outer
surface
The computer simulation shows the above arrangement offers good radiation
patterns over a broad frequency range The broadband operation is obtained
by exciting the TE11 mode in the circular waveguide using the TE10 mode of
the rectangular waveguide which is in turn excited by a coaxial probe
-51-
Chokes
Coaxial-to-waveguide transition
Circular wavguide
Corrugations
Mode transition
(a)
(b)
Fig 51 Structure of the proposed broadband circular waveguide feed
(a) CAD model and (b) cross-sectional view
For the coaxial-to-rectangular waveguide adapter an SMA connector with
the probe diameter of 127 mm is employed The coaxial probe inserted into
the waveguide energizes the feed and excites the dominant TE10 mode in
-52-
the rectangular waveguide The impedance matching is achieved by adjusting
the probe distance sp from the back short and the probe length lp
(a)
(b)
Fig 52 Reflection coefficient of the coaxial-to-rectangular adapter versus
(a) probe length lp and (b) the probe position sp
Fig 52 shows the reflection coefficient versus the various values of probe
lengths lp and probe positions sp The probe length lp is adjusted to obtain
antenna impedance matching and the probe distance sp is adjusted to obtain a
-53-
desired resonant frequency
Next a transition between rectangular and circular waveguide is designed
The transition section converts the TE10 mode in the rectangular waveguide to
TE11 mode in the circular waveguide and vice versa The transition is built
in a form of a taper for easy fabrication[22]
(a)
(b)
Fig 53 Structure of the rectangular-to-circular waveguide transition
(a) 3D view and (b) cross sectional view
The dimensions of the final optimized transition are as follows The length
of the rectangular waveguide section is 143mm The rectangular waveguides
width a and height b are 207mm and 857mm respectively The length of
the circular waveguide section is 143mm The inside diameter of the circular
-54-
waveguide is 207mm(097 wavelength at 14GHz) The length of transition
region ltr is 4465mm(approximately equal to 2λ0 at 14GHz) Fig 54 shows
the field distribution inside the mode converter
(a)
(b)
Fig 54 Field distribution inside the mode converter at
(a) 10GHz (b) 14GHz and (c) 18GHz
-55-
(c)
Fig 54 continued
Finally multiple chokes are investigated Figs 55 56 and 57 show the
feed performance without chokes The reflection coefficient is less than -10dB
over 10-19GHz The antenna has a gain of 921dB to 1189dB over
10-19GHz
Fig 55 Reflection coefficient of the broadband circular waveguide feed
without chokes and corrugations
-56-
(a)
(b)
(c)
Fig 56 E- and H-plane patterns of the broadband circular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-57-
(d)
(e)
Fig 56 continued
-58-
(a)
(b)
Fig 57 2D radiation patterns of the broadband cicular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-59-
(c)
(d)
Fig 57 continued
-60-
(e)
Fig 57 continued
To achieve equal beamwidths in E and H planes over a wide frequency
range chokes and corrugations are employed Table51 summarizes the
performance of a feed without chokes and corrugations
Table 51 Performance of the broadband circular waveguide feed without
chokes and corrugations
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
1000 940 6061 15
1200 972 6159 17
1400 920 5957 21
1600 1070 4751 29
1800 1188 5352 21
-61-
Four quarter-wavelength chokes are introduced in the feed design which
has a slot depth of 75mm and slot width of 09mm The choke slot spacing
is 18mm The choke design is investigated by applying the choke one by
one and the effect on the E- and H-plane patterns are observed as illustrated
in Figs 58 and 59 The use of chokes makes the E-plane pattern narrower
The H-plane pattern is not affected Chokes increase the gain slightly and
reduce back radiation
(a)
(b)
Fig 58 Effect of chokes on the E-plane pattern of the broadband circular
waveguide feed at (a) 10GHz(b) 12GHz (c) 14GHz (d) 16GHz and (e)
18GHz
-62-
(c)
(d)
(e)
Fig 58 continued
-63-
(a)
(b)
(c)
Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-64-
(d)
(e)
Fig 59 continued
-65-
Fig 510 shows the feed performance versus the choke depth When the
choke depth is varied from 535mm to 95mm the E- and H-plane patterns
are strongly affected The optimum value of choke depth is 75mm(035λ0 at
14GHz) which gives equal E- and H-plane radiation patterns and leads to
low back radiation
Fig 511 shows the feed performance versus the choke slot width tch The
choke slot width is varied from 09mm to 21mm Radiation patterns and
reflection coefficients are not sensitive to the choke slot width The final
choke slot width is selected to be 09mm considering the feed diameter
minimization and the manufacturability The overall diameter of the proposed
feed is 369mm which is increased from the 207mm of the waveguide
inside diameter due to the use of four chokes
-66-
(a)
(b)
(c)
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection coefficient
-67-
(a)
(b)
(c)
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and (c)
reflection coefficient
-68-
Next we investigated corrugations placed on the outer wall of the feed
Four corrugations applied to the outer surface of the circular waveguide The
corrugation depth is 465mm(0215λ0 at 14GHz) The primary purpose of
using corrugations is to further reduce the back radiation Increasing the
number of corrugations beyond four has little effect in reducing the back
radiation
Figs 512 and 513 show the effect of corrugations on the E- and H-plane
patterns Fig 514 shows the parametric study of the corrugation depth lcor
The corrugation depth is varied from 40mm and 645mm The optimum
value of the corrugation depth is found to be 465mm
-69-
(a)
(b)
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern at (a) 12GHz and (b) 14GHz
-70-
(a)
(b)
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern at (a) 12GHz and (b) 14GHz
-71-
(a)
(b)
(c)
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection coefficient
-72-
The phase center location is important in placing the feed in a reflector
antenna[8] The phase center variation with frequency should be small Fig
515 shows the effect of chokes and corrugations on the phase center The
curve with circle corresponds to the case without chokes and corrugations
The phase center varies from -326mm and -190mm away from the feeds
aperture plane It means the phase center is located inside the waveguide
The curve with triangles corresponds to the case with chokes The curve with
squares to the case with chokes and corrugations The phase center varies
from 0mm to -302mm
From Fig 515 we can observed that phase center variation reduced by the
corrugation and three cases phase center calculated in φ=450 plane
parameter sweep values are given in Table 52
10 12 14 16 181
0
-1
-2
-3
-4
-5
-6
Pha
se c
ente
r (m
m)
Frequency (GHz)
choke+corrugatuion without choke corrugation with choke
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
-73-
Frequency
(GHz)
Phase center from the aperture plane
(mm)
Without
chokes and
corrugations
With
chokes
With chokes
and
corrugations
1000 -326 062 000
1100 -187 030 -002
1200 -563 -208 -065
1300 -296 -154 -202
1400 -319 -314 -302
1500 -201 -203 -241
1600 -242 -233 -207
1700 -208 -208 -186
1800 -190 -157 -132
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
Based on the foregoing parametric studies optimum dimensions of the
broadband circular waveguide feed are obtained as shown in Table 53
-74-
Table 53 Optimum dimensions of the broadband circular waveguide feed
Parameter Designation Value (mm)
2a Waveguide inside diameter 2070
d Waveguide outside diameter 3690
lcrLength of the circular waveguide section 1430
m Distance between the aperture plane and the first corrugation 950
xDistance from the last corrugation to the end of the cylindrical outer surface
550
ltrLength of the rectangular-to-circularwaveguide transition 4465
lrcLength of the rectangular waveguide section 1430
tch Choke slot width 090
lch Choke depth 750
t Choke metal width 090
lcor Corrugation depth 465
tcor Corrugation metal width 100
s Corrugation slot width 10
lp Probe length 530
sp Probe position from the back short 530
din Probe diameter 127
b Inside height of the rectangular waveguide 857
tw Waveguide wall thickness 500
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-27-
circular waveguide is terminated with an open end with a wall thickness of
2mm radiating into the free space
Fig 32 shows the effect of the probe length lp and the probe distance sp
on the reflection coefficient The best performance is obtained when lp =
363mm and sp = 616mm The feeds reflection coefficient is less than -10dB
over 170-195GHz
(a)
(b)
Fig 32 Effect of the (a) the probe length lp and (b) the probe
distance sp on the reflection coefficient
-28-
Fig 33 shows the effect of the choke depth The E-plane pattern is more
sensitive to the choke depth than the H-plane pattern The choke depth has a
strong influence on the reflection coefficient when it is 360mm By properly
choosing the choke depth we can equalize the E- and H-plane patterns The
optimum value of the choke depth is 410mm which is 0249λ0 at 1825GHz
The choke slot width tch in the range of 06-12mm has almost no effect
on the H-plane pattern and the reflection coefficient For the E-plane pattern
tch of 12mm has some effect on the E-plane radiation pattern as shown in
Fig 34
Fig 35 shows the feed performance versus the dielectric ring length We
observe in Fig 35 that the dielectric length ld has an optimum value of
1168mm which does no effect on the H-plane pattern and tha the value of
1048mm has some effect on the E-plane pattern and the reflection
coefficient
Fig 36 shows E-plane and H-plane patterns and the reflection coefficient
versus the dielectric thickness With the optimum value of the dielectric
thickness t obtained from the Fig 36 is 155mm The larger values of td has
much stronger effects on the E-plane pattern and the reflection coefficient
The H-plane pattern is not sensitive to the dielectric ring thickness
-29-
(a)
(b)
(c)
Fig 33 Feed performance versus the choke depth (a) E-plane pattern
(b) H-plane pattern and (c) reflection coefficient
-30-
(a)
(b)
(c)
Fig 34 Feed performance versus the choke slot width (a) E-plane pattern
(b) H-plane pattern and (c) reflection coefficient
-31-
(a)
(b)
(c)
Fig 35 Feed performance versus the dielectric ring length (a) E-plane
pattern (b) H-plane pattern and (c) reflection coefficient
-32-
(a)
(b)
(c)
Fig 36 Feed performance versus the dielectric ring thickness (a) E-plane
pattern(b) H-plane pattern and (c) reflection coefficient
-33-
From the above parametric analysis an optimum feed design is obtained
The result is shown in Table 31 Fig 37 shows the 2D gain patterns of
designed feed The antenna has a gain of 903dB 933dB and 956dB at
171GHz 1825GHz and 19GHz respectively
Fig 38 shows E- and H-plane radiation patterns of the designed feed The
feed has E- and H-plane 10-dB beamwidths of 60 and 59 degrees at 17GHz
The feed has a front-to-back ration of 1900dB 2490dB and 2200dB at
171GHz 1825GHz and 19GHz respectively Table 32 summarizes the
performance of the designed narrow-band circular waveguide feed
The designed feed has a greatly improved performance over that of a
simple coax-fed feed described in Section 23
Table 31 Dimensions of the designed narrow-band circular feed
Parameter Designation Value(mm)
a Waveguide inside radius 640
l Feed length 2890
lp Probe length 363
sp Probe position from the back short 616
din Probe diameter 127
dout Diameter of coaxial cables outer conductor 400
t Thickness of choked wall 050
tch Choke slot width 100
lch Choke depth 410
ld Dielectric ring length 1168
td Dielectric ring thickness 155
d1 Waveguide outside diameter 1680
-34-
(a)
(b)
Fig 37 2D gain patterns of the narrow-band circular waveguide feed at
(a) 17GHz (b) 1825GHz and (c) 19GHz
-35-
(c)
Fig 37 continued
-36-
(a)
(b)
(c)
Fig 38 E- and H-plane patterns of the narrow-band circular waveguide feed
at (a) 10GHz (b) 1825GHz and (c) 195GHz
-37-
Frequency(GHz)
Gain(dB)
E-H-plane10-dB beamwidths
(deg)
Front-to-back ratio(dB)
Phase centerlocation
(From feeds aperture plane
toward reflector)
(mm)
1700 903 6059 20 062
1825 933 6060 25 004
1900 956 5759 22 007
Table 32 Performance of the narrow-band circular waveguide feed
The designed narrow-band feed is fabricated and its performance is
measured and compared with the simulation results The designed feed is
fabricated in a numerically-controlled machining center The fabricated antenna
is shown in Fig 39
Fig 39 Photograph of the fabricated feed
-38-
Fig 310 shows a comparison of the measured and simulated reflection
coefficients The measured reflection coefficient is less than -10dB over
171-197GHz The agreement between simulated and measured results are
good
Fig 311 shows the E- and H-plane patterns of the fabricated feed at
187GHz The feed has 90dB gain simulation and measurement results are in
good agreement
The fabricated antennarsquos 10dB beamwidth is 60 degrees in both E and H
planes at 187GHz The front-to-back ratio is 21dB
Fig 310 Reflection coefficient of the fabricated feed
-39-
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Fee
d H
orn
Gain
- d
B
Angle - degree
(a)
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Feed H
orn
Gain
- d
B
Angle - degree
(b)
Fig 311 Gain patterns of the fabricated feed at 187 GHz (a) E-plane and
(b) H-plane
-40-
IV Design of Circular Waveguide Feeds Loaded with a
Dielectric Rod
In this section circular waveguide feeds loaded with a dielectric rod feed
are investigated A comprehensive discussion of the circular waveguide loaded
with a dielectric rod is given by Kumar[7] Inserting a dielectric material
inside the circular waveguide improves the E- and H-plane pattern symmetry
In general dielectric-loaded circular waveguide feeds show good performance
only over a narrow bandwidth
Fig 41 shows the geometry of a circular waveguide loaded with a
dielectric rod The waveguide length is 400mm and the wall thickness is
05mm The dielectric rods diameter is 207mm The dielectric rod is
extended 05 wavelength beyond the waveguide open end The dielectric
constant εr is changed and the feeds performance is observed
Fig 41 Geometry of a circular waveguide loaded with a uniform dielectric
rod
-41-
Fig 42 is the radiation pattern of the feed with εr = 25 and L = 05λ0 at
9GHz E- and H-plane 10-dB beamwidths are 810 and 807 degrees
respectively The front-to-back ratio is 18dB The antenna gain is 71dB
(a)
(b)
Fig 42 Radiation pattern at 9GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 05λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-42-
Fig 43 shows the radiation pattern of the feed with εr = 21 at 10GHz
E- and H-plane 10-dB beamwidths are 70 and 71 degrees respectively The
front-to-back ratio is 19dB The antenna gain is 83dB
(a)
(b)
Fig 43 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 21 and L = 05λ0 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-43-
Fig 44 shows the radiation pattern of the feed with εr = 30 at 8GHz
E- and H-plane 10-dB beamwidths are 83 and 824 degrees respectively The
front-to-back ratio is 17dB The antenna gain is 73dB
(a)
(b)
Fig 44 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 30 and L = 05λ0 at 8GHz (a) 2D radiation pattern
and (b) E- and H-plane patterns
-44-
Fig 45 shows the radiation pattern of the feed with εr = 50 at 18GHz
E- and H-plane 10-dB beamwidths are 56 and 54 degrees respectively The
front-to-back ratio is 27dB The antenna gain is 105dB The feed has a good
pattern symmetry and low back radiation
(a)
(b)
Fig 45 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 50 and L = 05λ0 at 18GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-45-
Fig 46 is the radiation pattern of the feed with εr = 25 and L = 10λ0 at
10GHz E- and H-plane 10-dB beamwidths are 50 and 48 degrees
respectively The front-to-back ratio is 16dB The antenna gain is 105dB
(a)
(b)
Fig 46 Radiation pattern at 10GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 10λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-46-
Fig 47 shows the geometry of a circular waveguide with a tapered
dielectric rod The designed feed has the following dimension L = 1λ0 d =
1λ0 and εr =25 at 10GHz The waveguide length is 40mm and the wall
thickness is 05mm
L
Dielectricd3
Fig 47 Geometry of a circular waveguide loaded with a tapered dielectric
rod
Fig 48 shows the radiatio pattern of the designed feed E- and H-plane
10-dB beamwidths are 575 and 564 degrees respectively The front-to-back
ratio is 377dB The antenna gain is 94dB The designed feed has an
excellent beamwidth symmetry and a very low back radiation
-47-
(a)
(b)
Fig 48 Radiation pattern of a circular waveguide loaded with a tapered
dielectric rod with L = 1λ0 d = 1λ0 and εr =25 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-48-
Fig 49 shows the geometry of a spherical ended dielectric rod feed
diameter of 06λ0 at 10GHz with a dielectric constant of 25 and L= 03λ0
Fig 410 shows the radiation patterns of the designed feed E- and H-plane
10-dB beamwidths are both 63 degrees The front-to-back ratio is 24dB The
antenna gain is 864dB
Fig 49 Geometry of a circular waveguide loaded with a spherical ended
dielectric rod
-49-
(a)
(b)
Fig 410 Radiation pattern of a circular waveguide loaded wht a spherical
ended dielectric rod with d = 06λ0 L = 03λ0 and εr =25 at 10GHz (a) 3D
radiation pattern and (b) E- and H-plane patterns
-50-
V Design of a Broadband Circular Waveguide Feed
In this chapter the design of a broadband circular waveguide feed is
presented At microwave frequencies the feed is often a circular waveguide
with chokes and corrugations around the aperture Chokes and corrugations
equalize E- and H-plane patterns and reduce the back radiation
The proposed feed is designed to operate over 10-18GHz The design starts
with the optimization of the coaxial-to-rectangular waveguide adapter
employed for good mode purity over a broad frequency range Next a
rectangular-to-circular waveguide transition is optimized Finally chokes and
corrugations are designed for improved pattern symmetry and low back
radiation
The proposed feed structure is shown in Fig 51 The feed consist of the
following parts a coaxial-to-rectangular waveguide adapter a rectangular-to-
circular waveguide transition a circular waveguide section four quarter-wave
chokes around the feeds aperture and four corrugations on the feeds outer
surface
The computer simulation shows the above arrangement offers good radiation
patterns over a broad frequency range The broadband operation is obtained
by exciting the TE11 mode in the circular waveguide using the TE10 mode of
the rectangular waveguide which is in turn excited by a coaxial probe
-51-
Chokes
Coaxial-to-waveguide transition
Circular wavguide
Corrugations
Mode transition
(a)
(b)
Fig 51 Structure of the proposed broadband circular waveguide feed
(a) CAD model and (b) cross-sectional view
For the coaxial-to-rectangular waveguide adapter an SMA connector with
the probe diameter of 127 mm is employed The coaxial probe inserted into
the waveguide energizes the feed and excites the dominant TE10 mode in
-52-
the rectangular waveguide The impedance matching is achieved by adjusting
the probe distance sp from the back short and the probe length lp
(a)
(b)
Fig 52 Reflection coefficient of the coaxial-to-rectangular adapter versus
(a) probe length lp and (b) the probe position sp
Fig 52 shows the reflection coefficient versus the various values of probe
lengths lp and probe positions sp The probe length lp is adjusted to obtain
antenna impedance matching and the probe distance sp is adjusted to obtain a
-53-
desired resonant frequency
Next a transition between rectangular and circular waveguide is designed
The transition section converts the TE10 mode in the rectangular waveguide to
TE11 mode in the circular waveguide and vice versa The transition is built
in a form of a taper for easy fabrication[22]
(a)
(b)
Fig 53 Structure of the rectangular-to-circular waveguide transition
(a) 3D view and (b) cross sectional view
The dimensions of the final optimized transition are as follows The length
of the rectangular waveguide section is 143mm The rectangular waveguides
width a and height b are 207mm and 857mm respectively The length of
the circular waveguide section is 143mm The inside diameter of the circular
-54-
waveguide is 207mm(097 wavelength at 14GHz) The length of transition
region ltr is 4465mm(approximately equal to 2λ0 at 14GHz) Fig 54 shows
the field distribution inside the mode converter
(a)
(b)
Fig 54 Field distribution inside the mode converter at
(a) 10GHz (b) 14GHz and (c) 18GHz
-55-
(c)
Fig 54 continued
Finally multiple chokes are investigated Figs 55 56 and 57 show the
feed performance without chokes The reflection coefficient is less than -10dB
over 10-19GHz The antenna has a gain of 921dB to 1189dB over
10-19GHz
Fig 55 Reflection coefficient of the broadband circular waveguide feed
without chokes and corrugations
-56-
(a)
(b)
(c)
Fig 56 E- and H-plane patterns of the broadband circular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-57-
(d)
(e)
Fig 56 continued
-58-
(a)
(b)
Fig 57 2D radiation patterns of the broadband cicular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-59-
(c)
(d)
Fig 57 continued
-60-
(e)
Fig 57 continued
To achieve equal beamwidths in E and H planes over a wide frequency
range chokes and corrugations are employed Table51 summarizes the
performance of a feed without chokes and corrugations
Table 51 Performance of the broadband circular waveguide feed without
chokes and corrugations
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
1000 940 6061 15
1200 972 6159 17
1400 920 5957 21
1600 1070 4751 29
1800 1188 5352 21
-61-
Four quarter-wavelength chokes are introduced in the feed design which
has a slot depth of 75mm and slot width of 09mm The choke slot spacing
is 18mm The choke design is investigated by applying the choke one by
one and the effect on the E- and H-plane patterns are observed as illustrated
in Figs 58 and 59 The use of chokes makes the E-plane pattern narrower
The H-plane pattern is not affected Chokes increase the gain slightly and
reduce back radiation
(a)
(b)
Fig 58 Effect of chokes on the E-plane pattern of the broadband circular
waveguide feed at (a) 10GHz(b) 12GHz (c) 14GHz (d) 16GHz and (e)
18GHz
-62-
(c)
(d)
(e)
Fig 58 continued
-63-
(a)
(b)
(c)
Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-64-
(d)
(e)
Fig 59 continued
-65-
Fig 510 shows the feed performance versus the choke depth When the
choke depth is varied from 535mm to 95mm the E- and H-plane patterns
are strongly affected The optimum value of choke depth is 75mm(035λ0 at
14GHz) which gives equal E- and H-plane radiation patterns and leads to
low back radiation
Fig 511 shows the feed performance versus the choke slot width tch The
choke slot width is varied from 09mm to 21mm Radiation patterns and
reflection coefficients are not sensitive to the choke slot width The final
choke slot width is selected to be 09mm considering the feed diameter
minimization and the manufacturability The overall diameter of the proposed
feed is 369mm which is increased from the 207mm of the waveguide
inside diameter due to the use of four chokes
-66-
(a)
(b)
(c)
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection coefficient
-67-
(a)
(b)
(c)
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and (c)
reflection coefficient
-68-
Next we investigated corrugations placed on the outer wall of the feed
Four corrugations applied to the outer surface of the circular waveguide The
corrugation depth is 465mm(0215λ0 at 14GHz) The primary purpose of
using corrugations is to further reduce the back radiation Increasing the
number of corrugations beyond four has little effect in reducing the back
radiation
Figs 512 and 513 show the effect of corrugations on the E- and H-plane
patterns Fig 514 shows the parametric study of the corrugation depth lcor
The corrugation depth is varied from 40mm and 645mm The optimum
value of the corrugation depth is found to be 465mm
-69-
(a)
(b)
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern at (a) 12GHz and (b) 14GHz
-70-
(a)
(b)
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern at (a) 12GHz and (b) 14GHz
-71-
(a)
(b)
(c)
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection coefficient
-72-
The phase center location is important in placing the feed in a reflector
antenna[8] The phase center variation with frequency should be small Fig
515 shows the effect of chokes and corrugations on the phase center The
curve with circle corresponds to the case without chokes and corrugations
The phase center varies from -326mm and -190mm away from the feeds
aperture plane It means the phase center is located inside the waveguide
The curve with triangles corresponds to the case with chokes The curve with
squares to the case with chokes and corrugations The phase center varies
from 0mm to -302mm
From Fig 515 we can observed that phase center variation reduced by the
corrugation and three cases phase center calculated in φ=450 plane
parameter sweep values are given in Table 52
10 12 14 16 181
0
-1
-2
-3
-4
-5
-6
Pha
se c
ente
r (m
m)
Frequency (GHz)
choke+corrugatuion without choke corrugation with choke
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
-73-
Frequency
(GHz)
Phase center from the aperture plane
(mm)
Without
chokes and
corrugations
With
chokes
With chokes
and
corrugations
1000 -326 062 000
1100 -187 030 -002
1200 -563 -208 -065
1300 -296 -154 -202
1400 -319 -314 -302
1500 -201 -203 -241
1600 -242 -233 -207
1700 -208 -208 -186
1800 -190 -157 -132
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
Based on the foregoing parametric studies optimum dimensions of the
broadband circular waveguide feed are obtained as shown in Table 53
-74-
Table 53 Optimum dimensions of the broadband circular waveguide feed
Parameter Designation Value (mm)
2a Waveguide inside diameter 2070
d Waveguide outside diameter 3690
lcrLength of the circular waveguide section 1430
m Distance between the aperture plane and the first corrugation 950
xDistance from the last corrugation to the end of the cylindrical outer surface
550
ltrLength of the rectangular-to-circularwaveguide transition 4465
lrcLength of the rectangular waveguide section 1430
tch Choke slot width 090
lch Choke depth 750
t Choke metal width 090
lcor Corrugation depth 465
tcor Corrugation metal width 100
s Corrugation slot width 10
lp Probe length 530
sp Probe position from the back short 530
din Probe diameter 127
b Inside height of the rectangular waveguide 857
tw Waveguide wall thickness 500
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-28-
Fig 33 shows the effect of the choke depth The E-plane pattern is more
sensitive to the choke depth than the H-plane pattern The choke depth has a
strong influence on the reflection coefficient when it is 360mm By properly
choosing the choke depth we can equalize the E- and H-plane patterns The
optimum value of the choke depth is 410mm which is 0249λ0 at 1825GHz
The choke slot width tch in the range of 06-12mm has almost no effect
on the H-plane pattern and the reflection coefficient For the E-plane pattern
tch of 12mm has some effect on the E-plane radiation pattern as shown in
Fig 34
Fig 35 shows the feed performance versus the dielectric ring length We
observe in Fig 35 that the dielectric length ld has an optimum value of
1168mm which does no effect on the H-plane pattern and tha the value of
1048mm has some effect on the E-plane pattern and the reflection
coefficient
Fig 36 shows E-plane and H-plane patterns and the reflection coefficient
versus the dielectric thickness With the optimum value of the dielectric
thickness t obtained from the Fig 36 is 155mm The larger values of td has
much stronger effects on the E-plane pattern and the reflection coefficient
The H-plane pattern is not sensitive to the dielectric ring thickness
-29-
(a)
(b)
(c)
Fig 33 Feed performance versus the choke depth (a) E-plane pattern
(b) H-plane pattern and (c) reflection coefficient
-30-
(a)
(b)
(c)
Fig 34 Feed performance versus the choke slot width (a) E-plane pattern
(b) H-plane pattern and (c) reflection coefficient
-31-
(a)
(b)
(c)
Fig 35 Feed performance versus the dielectric ring length (a) E-plane
pattern (b) H-plane pattern and (c) reflection coefficient
-32-
(a)
(b)
(c)
Fig 36 Feed performance versus the dielectric ring thickness (a) E-plane
pattern(b) H-plane pattern and (c) reflection coefficient
-33-
From the above parametric analysis an optimum feed design is obtained
The result is shown in Table 31 Fig 37 shows the 2D gain patterns of
designed feed The antenna has a gain of 903dB 933dB and 956dB at
171GHz 1825GHz and 19GHz respectively
Fig 38 shows E- and H-plane radiation patterns of the designed feed The
feed has E- and H-plane 10-dB beamwidths of 60 and 59 degrees at 17GHz
The feed has a front-to-back ration of 1900dB 2490dB and 2200dB at
171GHz 1825GHz and 19GHz respectively Table 32 summarizes the
performance of the designed narrow-band circular waveguide feed
The designed feed has a greatly improved performance over that of a
simple coax-fed feed described in Section 23
Table 31 Dimensions of the designed narrow-band circular feed
Parameter Designation Value(mm)
a Waveguide inside radius 640
l Feed length 2890
lp Probe length 363
sp Probe position from the back short 616
din Probe diameter 127
dout Diameter of coaxial cables outer conductor 400
t Thickness of choked wall 050
tch Choke slot width 100
lch Choke depth 410
ld Dielectric ring length 1168
td Dielectric ring thickness 155
d1 Waveguide outside diameter 1680
-34-
(a)
(b)
Fig 37 2D gain patterns of the narrow-band circular waveguide feed at
(a) 17GHz (b) 1825GHz and (c) 19GHz
-35-
(c)
Fig 37 continued
-36-
(a)
(b)
(c)
Fig 38 E- and H-plane patterns of the narrow-band circular waveguide feed
at (a) 10GHz (b) 1825GHz and (c) 195GHz
-37-
Frequency(GHz)
Gain(dB)
E-H-plane10-dB beamwidths
(deg)
Front-to-back ratio(dB)
Phase centerlocation
(From feeds aperture plane
toward reflector)
(mm)
1700 903 6059 20 062
1825 933 6060 25 004
1900 956 5759 22 007
Table 32 Performance of the narrow-band circular waveguide feed
The designed narrow-band feed is fabricated and its performance is
measured and compared with the simulation results The designed feed is
fabricated in a numerically-controlled machining center The fabricated antenna
is shown in Fig 39
Fig 39 Photograph of the fabricated feed
-38-
Fig 310 shows a comparison of the measured and simulated reflection
coefficients The measured reflection coefficient is less than -10dB over
171-197GHz The agreement between simulated and measured results are
good
Fig 311 shows the E- and H-plane patterns of the fabricated feed at
187GHz The feed has 90dB gain simulation and measurement results are in
good agreement
The fabricated antennarsquos 10dB beamwidth is 60 degrees in both E and H
planes at 187GHz The front-to-back ratio is 21dB
Fig 310 Reflection coefficient of the fabricated feed
-39-
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Fee
d H
orn
Gain
- d
B
Angle - degree
(a)
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Feed H
orn
Gain
- d
B
Angle - degree
(b)
Fig 311 Gain patterns of the fabricated feed at 187 GHz (a) E-plane and
(b) H-plane
-40-
IV Design of Circular Waveguide Feeds Loaded with a
Dielectric Rod
In this section circular waveguide feeds loaded with a dielectric rod feed
are investigated A comprehensive discussion of the circular waveguide loaded
with a dielectric rod is given by Kumar[7] Inserting a dielectric material
inside the circular waveguide improves the E- and H-plane pattern symmetry
In general dielectric-loaded circular waveguide feeds show good performance
only over a narrow bandwidth
Fig 41 shows the geometry of a circular waveguide loaded with a
dielectric rod The waveguide length is 400mm and the wall thickness is
05mm The dielectric rods diameter is 207mm The dielectric rod is
extended 05 wavelength beyond the waveguide open end The dielectric
constant εr is changed and the feeds performance is observed
Fig 41 Geometry of a circular waveguide loaded with a uniform dielectric
rod
-41-
Fig 42 is the radiation pattern of the feed with εr = 25 and L = 05λ0 at
9GHz E- and H-plane 10-dB beamwidths are 810 and 807 degrees
respectively The front-to-back ratio is 18dB The antenna gain is 71dB
(a)
(b)
Fig 42 Radiation pattern at 9GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 05λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-42-
Fig 43 shows the radiation pattern of the feed with εr = 21 at 10GHz
E- and H-plane 10-dB beamwidths are 70 and 71 degrees respectively The
front-to-back ratio is 19dB The antenna gain is 83dB
(a)
(b)
Fig 43 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 21 and L = 05λ0 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-43-
Fig 44 shows the radiation pattern of the feed with εr = 30 at 8GHz
E- and H-plane 10-dB beamwidths are 83 and 824 degrees respectively The
front-to-back ratio is 17dB The antenna gain is 73dB
(a)
(b)
Fig 44 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 30 and L = 05λ0 at 8GHz (a) 2D radiation pattern
and (b) E- and H-plane patterns
-44-
Fig 45 shows the radiation pattern of the feed with εr = 50 at 18GHz
E- and H-plane 10-dB beamwidths are 56 and 54 degrees respectively The
front-to-back ratio is 27dB The antenna gain is 105dB The feed has a good
pattern symmetry and low back radiation
(a)
(b)
Fig 45 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 50 and L = 05λ0 at 18GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-45-
Fig 46 is the radiation pattern of the feed with εr = 25 and L = 10λ0 at
10GHz E- and H-plane 10-dB beamwidths are 50 and 48 degrees
respectively The front-to-back ratio is 16dB The antenna gain is 105dB
(a)
(b)
Fig 46 Radiation pattern at 10GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 10λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-46-
Fig 47 shows the geometry of a circular waveguide with a tapered
dielectric rod The designed feed has the following dimension L = 1λ0 d =
1λ0 and εr =25 at 10GHz The waveguide length is 40mm and the wall
thickness is 05mm
L
Dielectricd3
Fig 47 Geometry of a circular waveguide loaded with a tapered dielectric
rod
Fig 48 shows the radiatio pattern of the designed feed E- and H-plane
10-dB beamwidths are 575 and 564 degrees respectively The front-to-back
ratio is 377dB The antenna gain is 94dB The designed feed has an
excellent beamwidth symmetry and a very low back radiation
-47-
(a)
(b)
Fig 48 Radiation pattern of a circular waveguide loaded with a tapered
dielectric rod with L = 1λ0 d = 1λ0 and εr =25 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-48-
Fig 49 shows the geometry of a spherical ended dielectric rod feed
diameter of 06λ0 at 10GHz with a dielectric constant of 25 and L= 03λ0
Fig 410 shows the radiation patterns of the designed feed E- and H-plane
10-dB beamwidths are both 63 degrees The front-to-back ratio is 24dB The
antenna gain is 864dB
Fig 49 Geometry of a circular waveguide loaded with a spherical ended
dielectric rod
-49-
(a)
(b)
Fig 410 Radiation pattern of a circular waveguide loaded wht a spherical
ended dielectric rod with d = 06λ0 L = 03λ0 and εr =25 at 10GHz (a) 3D
radiation pattern and (b) E- and H-plane patterns
-50-
V Design of a Broadband Circular Waveguide Feed
In this chapter the design of a broadband circular waveguide feed is
presented At microwave frequencies the feed is often a circular waveguide
with chokes and corrugations around the aperture Chokes and corrugations
equalize E- and H-plane patterns and reduce the back radiation
The proposed feed is designed to operate over 10-18GHz The design starts
with the optimization of the coaxial-to-rectangular waveguide adapter
employed for good mode purity over a broad frequency range Next a
rectangular-to-circular waveguide transition is optimized Finally chokes and
corrugations are designed for improved pattern symmetry and low back
radiation
The proposed feed structure is shown in Fig 51 The feed consist of the
following parts a coaxial-to-rectangular waveguide adapter a rectangular-to-
circular waveguide transition a circular waveguide section four quarter-wave
chokes around the feeds aperture and four corrugations on the feeds outer
surface
The computer simulation shows the above arrangement offers good radiation
patterns over a broad frequency range The broadband operation is obtained
by exciting the TE11 mode in the circular waveguide using the TE10 mode of
the rectangular waveguide which is in turn excited by a coaxial probe
-51-
Chokes
Coaxial-to-waveguide transition
Circular wavguide
Corrugations
Mode transition
(a)
(b)
Fig 51 Structure of the proposed broadband circular waveguide feed
(a) CAD model and (b) cross-sectional view
For the coaxial-to-rectangular waveguide adapter an SMA connector with
the probe diameter of 127 mm is employed The coaxial probe inserted into
the waveguide energizes the feed and excites the dominant TE10 mode in
-52-
the rectangular waveguide The impedance matching is achieved by adjusting
the probe distance sp from the back short and the probe length lp
(a)
(b)
Fig 52 Reflection coefficient of the coaxial-to-rectangular adapter versus
(a) probe length lp and (b) the probe position sp
Fig 52 shows the reflection coefficient versus the various values of probe
lengths lp and probe positions sp The probe length lp is adjusted to obtain
antenna impedance matching and the probe distance sp is adjusted to obtain a
-53-
desired resonant frequency
Next a transition between rectangular and circular waveguide is designed
The transition section converts the TE10 mode in the rectangular waveguide to
TE11 mode in the circular waveguide and vice versa The transition is built
in a form of a taper for easy fabrication[22]
(a)
(b)
Fig 53 Structure of the rectangular-to-circular waveguide transition
(a) 3D view and (b) cross sectional view
The dimensions of the final optimized transition are as follows The length
of the rectangular waveguide section is 143mm The rectangular waveguides
width a and height b are 207mm and 857mm respectively The length of
the circular waveguide section is 143mm The inside diameter of the circular
-54-
waveguide is 207mm(097 wavelength at 14GHz) The length of transition
region ltr is 4465mm(approximately equal to 2λ0 at 14GHz) Fig 54 shows
the field distribution inside the mode converter
(a)
(b)
Fig 54 Field distribution inside the mode converter at
(a) 10GHz (b) 14GHz and (c) 18GHz
-55-
(c)
Fig 54 continued
Finally multiple chokes are investigated Figs 55 56 and 57 show the
feed performance without chokes The reflection coefficient is less than -10dB
over 10-19GHz The antenna has a gain of 921dB to 1189dB over
10-19GHz
Fig 55 Reflection coefficient of the broadband circular waveguide feed
without chokes and corrugations
-56-
(a)
(b)
(c)
Fig 56 E- and H-plane patterns of the broadband circular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-57-
(d)
(e)
Fig 56 continued
-58-
(a)
(b)
Fig 57 2D radiation patterns of the broadband cicular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-59-
(c)
(d)
Fig 57 continued
-60-
(e)
Fig 57 continued
To achieve equal beamwidths in E and H planes over a wide frequency
range chokes and corrugations are employed Table51 summarizes the
performance of a feed without chokes and corrugations
Table 51 Performance of the broadband circular waveguide feed without
chokes and corrugations
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
1000 940 6061 15
1200 972 6159 17
1400 920 5957 21
1600 1070 4751 29
1800 1188 5352 21
-61-
Four quarter-wavelength chokes are introduced in the feed design which
has a slot depth of 75mm and slot width of 09mm The choke slot spacing
is 18mm The choke design is investigated by applying the choke one by
one and the effect on the E- and H-plane patterns are observed as illustrated
in Figs 58 and 59 The use of chokes makes the E-plane pattern narrower
The H-plane pattern is not affected Chokes increase the gain slightly and
reduce back radiation
(a)
(b)
Fig 58 Effect of chokes on the E-plane pattern of the broadband circular
waveguide feed at (a) 10GHz(b) 12GHz (c) 14GHz (d) 16GHz and (e)
18GHz
-62-
(c)
(d)
(e)
Fig 58 continued
-63-
(a)
(b)
(c)
Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-64-
(d)
(e)
Fig 59 continued
-65-
Fig 510 shows the feed performance versus the choke depth When the
choke depth is varied from 535mm to 95mm the E- and H-plane patterns
are strongly affected The optimum value of choke depth is 75mm(035λ0 at
14GHz) which gives equal E- and H-plane radiation patterns and leads to
low back radiation
Fig 511 shows the feed performance versus the choke slot width tch The
choke slot width is varied from 09mm to 21mm Radiation patterns and
reflection coefficients are not sensitive to the choke slot width The final
choke slot width is selected to be 09mm considering the feed diameter
minimization and the manufacturability The overall diameter of the proposed
feed is 369mm which is increased from the 207mm of the waveguide
inside diameter due to the use of four chokes
-66-
(a)
(b)
(c)
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection coefficient
-67-
(a)
(b)
(c)
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and (c)
reflection coefficient
-68-
Next we investigated corrugations placed on the outer wall of the feed
Four corrugations applied to the outer surface of the circular waveguide The
corrugation depth is 465mm(0215λ0 at 14GHz) The primary purpose of
using corrugations is to further reduce the back radiation Increasing the
number of corrugations beyond four has little effect in reducing the back
radiation
Figs 512 and 513 show the effect of corrugations on the E- and H-plane
patterns Fig 514 shows the parametric study of the corrugation depth lcor
The corrugation depth is varied from 40mm and 645mm The optimum
value of the corrugation depth is found to be 465mm
-69-
(a)
(b)
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern at (a) 12GHz and (b) 14GHz
-70-
(a)
(b)
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern at (a) 12GHz and (b) 14GHz
-71-
(a)
(b)
(c)
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection coefficient
-72-
The phase center location is important in placing the feed in a reflector
antenna[8] The phase center variation with frequency should be small Fig
515 shows the effect of chokes and corrugations on the phase center The
curve with circle corresponds to the case without chokes and corrugations
The phase center varies from -326mm and -190mm away from the feeds
aperture plane It means the phase center is located inside the waveguide
The curve with triangles corresponds to the case with chokes The curve with
squares to the case with chokes and corrugations The phase center varies
from 0mm to -302mm
From Fig 515 we can observed that phase center variation reduced by the
corrugation and three cases phase center calculated in φ=450 plane
parameter sweep values are given in Table 52
10 12 14 16 181
0
-1
-2
-3
-4
-5
-6
Pha
se c
ente
r (m
m)
Frequency (GHz)
choke+corrugatuion without choke corrugation with choke
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
-73-
Frequency
(GHz)
Phase center from the aperture plane
(mm)
Without
chokes and
corrugations
With
chokes
With chokes
and
corrugations
1000 -326 062 000
1100 -187 030 -002
1200 -563 -208 -065
1300 -296 -154 -202
1400 -319 -314 -302
1500 -201 -203 -241
1600 -242 -233 -207
1700 -208 -208 -186
1800 -190 -157 -132
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
Based on the foregoing parametric studies optimum dimensions of the
broadband circular waveguide feed are obtained as shown in Table 53
-74-
Table 53 Optimum dimensions of the broadband circular waveguide feed
Parameter Designation Value (mm)
2a Waveguide inside diameter 2070
d Waveguide outside diameter 3690
lcrLength of the circular waveguide section 1430
m Distance between the aperture plane and the first corrugation 950
xDistance from the last corrugation to the end of the cylindrical outer surface
550
ltrLength of the rectangular-to-circularwaveguide transition 4465
lrcLength of the rectangular waveguide section 1430
tch Choke slot width 090
lch Choke depth 750
t Choke metal width 090
lcor Corrugation depth 465
tcor Corrugation metal width 100
s Corrugation slot width 10
lp Probe length 530
sp Probe position from the back short 530
din Probe diameter 127
b Inside height of the rectangular waveguide 857
tw Waveguide wall thickness 500
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-29-
(a)
(b)
(c)
Fig 33 Feed performance versus the choke depth (a) E-plane pattern
(b) H-plane pattern and (c) reflection coefficient
-30-
(a)
(b)
(c)
Fig 34 Feed performance versus the choke slot width (a) E-plane pattern
(b) H-plane pattern and (c) reflection coefficient
-31-
(a)
(b)
(c)
Fig 35 Feed performance versus the dielectric ring length (a) E-plane
pattern (b) H-plane pattern and (c) reflection coefficient
-32-
(a)
(b)
(c)
Fig 36 Feed performance versus the dielectric ring thickness (a) E-plane
pattern(b) H-plane pattern and (c) reflection coefficient
-33-
From the above parametric analysis an optimum feed design is obtained
The result is shown in Table 31 Fig 37 shows the 2D gain patterns of
designed feed The antenna has a gain of 903dB 933dB and 956dB at
171GHz 1825GHz and 19GHz respectively
Fig 38 shows E- and H-plane radiation patterns of the designed feed The
feed has E- and H-plane 10-dB beamwidths of 60 and 59 degrees at 17GHz
The feed has a front-to-back ration of 1900dB 2490dB and 2200dB at
171GHz 1825GHz and 19GHz respectively Table 32 summarizes the
performance of the designed narrow-band circular waveguide feed
The designed feed has a greatly improved performance over that of a
simple coax-fed feed described in Section 23
Table 31 Dimensions of the designed narrow-band circular feed
Parameter Designation Value(mm)
a Waveguide inside radius 640
l Feed length 2890
lp Probe length 363
sp Probe position from the back short 616
din Probe diameter 127
dout Diameter of coaxial cables outer conductor 400
t Thickness of choked wall 050
tch Choke slot width 100
lch Choke depth 410
ld Dielectric ring length 1168
td Dielectric ring thickness 155
d1 Waveguide outside diameter 1680
-34-
(a)
(b)
Fig 37 2D gain patterns of the narrow-band circular waveguide feed at
(a) 17GHz (b) 1825GHz and (c) 19GHz
-35-
(c)
Fig 37 continued
-36-
(a)
(b)
(c)
Fig 38 E- and H-plane patterns of the narrow-band circular waveguide feed
at (a) 10GHz (b) 1825GHz and (c) 195GHz
-37-
Frequency(GHz)
Gain(dB)
E-H-plane10-dB beamwidths
(deg)
Front-to-back ratio(dB)
Phase centerlocation
(From feeds aperture plane
toward reflector)
(mm)
1700 903 6059 20 062
1825 933 6060 25 004
1900 956 5759 22 007
Table 32 Performance of the narrow-band circular waveguide feed
The designed narrow-band feed is fabricated and its performance is
measured and compared with the simulation results The designed feed is
fabricated in a numerically-controlled machining center The fabricated antenna
is shown in Fig 39
Fig 39 Photograph of the fabricated feed
-38-
Fig 310 shows a comparison of the measured and simulated reflection
coefficients The measured reflection coefficient is less than -10dB over
171-197GHz The agreement between simulated and measured results are
good
Fig 311 shows the E- and H-plane patterns of the fabricated feed at
187GHz The feed has 90dB gain simulation and measurement results are in
good agreement
The fabricated antennarsquos 10dB beamwidth is 60 degrees in both E and H
planes at 187GHz The front-to-back ratio is 21dB
Fig 310 Reflection coefficient of the fabricated feed
-39-
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Fee
d H
orn
Gain
- d
B
Angle - degree
(a)
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Feed H
orn
Gain
- d
B
Angle - degree
(b)
Fig 311 Gain patterns of the fabricated feed at 187 GHz (a) E-plane and
(b) H-plane
-40-
IV Design of Circular Waveguide Feeds Loaded with a
Dielectric Rod
In this section circular waveguide feeds loaded with a dielectric rod feed
are investigated A comprehensive discussion of the circular waveguide loaded
with a dielectric rod is given by Kumar[7] Inserting a dielectric material
inside the circular waveguide improves the E- and H-plane pattern symmetry
In general dielectric-loaded circular waveguide feeds show good performance
only over a narrow bandwidth
Fig 41 shows the geometry of a circular waveguide loaded with a
dielectric rod The waveguide length is 400mm and the wall thickness is
05mm The dielectric rods diameter is 207mm The dielectric rod is
extended 05 wavelength beyond the waveguide open end The dielectric
constant εr is changed and the feeds performance is observed
Fig 41 Geometry of a circular waveguide loaded with a uniform dielectric
rod
-41-
Fig 42 is the radiation pattern of the feed with εr = 25 and L = 05λ0 at
9GHz E- and H-plane 10-dB beamwidths are 810 and 807 degrees
respectively The front-to-back ratio is 18dB The antenna gain is 71dB
(a)
(b)
Fig 42 Radiation pattern at 9GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 05λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-42-
Fig 43 shows the radiation pattern of the feed with εr = 21 at 10GHz
E- and H-plane 10-dB beamwidths are 70 and 71 degrees respectively The
front-to-back ratio is 19dB The antenna gain is 83dB
(a)
(b)
Fig 43 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 21 and L = 05λ0 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-43-
Fig 44 shows the radiation pattern of the feed with εr = 30 at 8GHz
E- and H-plane 10-dB beamwidths are 83 and 824 degrees respectively The
front-to-back ratio is 17dB The antenna gain is 73dB
(a)
(b)
Fig 44 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 30 and L = 05λ0 at 8GHz (a) 2D radiation pattern
and (b) E- and H-plane patterns
-44-
Fig 45 shows the radiation pattern of the feed with εr = 50 at 18GHz
E- and H-plane 10-dB beamwidths are 56 and 54 degrees respectively The
front-to-back ratio is 27dB The antenna gain is 105dB The feed has a good
pattern symmetry and low back radiation
(a)
(b)
Fig 45 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 50 and L = 05λ0 at 18GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-45-
Fig 46 is the radiation pattern of the feed with εr = 25 and L = 10λ0 at
10GHz E- and H-plane 10-dB beamwidths are 50 and 48 degrees
respectively The front-to-back ratio is 16dB The antenna gain is 105dB
(a)
(b)
Fig 46 Radiation pattern at 10GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 10λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-46-
Fig 47 shows the geometry of a circular waveguide with a tapered
dielectric rod The designed feed has the following dimension L = 1λ0 d =
1λ0 and εr =25 at 10GHz The waveguide length is 40mm and the wall
thickness is 05mm
L
Dielectricd3
Fig 47 Geometry of a circular waveguide loaded with a tapered dielectric
rod
Fig 48 shows the radiatio pattern of the designed feed E- and H-plane
10-dB beamwidths are 575 and 564 degrees respectively The front-to-back
ratio is 377dB The antenna gain is 94dB The designed feed has an
excellent beamwidth symmetry and a very low back radiation
-47-
(a)
(b)
Fig 48 Radiation pattern of a circular waveguide loaded with a tapered
dielectric rod with L = 1λ0 d = 1λ0 and εr =25 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-48-
Fig 49 shows the geometry of a spherical ended dielectric rod feed
diameter of 06λ0 at 10GHz with a dielectric constant of 25 and L= 03λ0
Fig 410 shows the radiation patterns of the designed feed E- and H-plane
10-dB beamwidths are both 63 degrees The front-to-back ratio is 24dB The
antenna gain is 864dB
Fig 49 Geometry of a circular waveguide loaded with a spherical ended
dielectric rod
-49-
(a)
(b)
Fig 410 Radiation pattern of a circular waveguide loaded wht a spherical
ended dielectric rod with d = 06λ0 L = 03λ0 and εr =25 at 10GHz (a) 3D
radiation pattern and (b) E- and H-plane patterns
-50-
V Design of a Broadband Circular Waveguide Feed
In this chapter the design of a broadband circular waveguide feed is
presented At microwave frequencies the feed is often a circular waveguide
with chokes and corrugations around the aperture Chokes and corrugations
equalize E- and H-plane patterns and reduce the back radiation
The proposed feed is designed to operate over 10-18GHz The design starts
with the optimization of the coaxial-to-rectangular waveguide adapter
employed for good mode purity over a broad frequency range Next a
rectangular-to-circular waveguide transition is optimized Finally chokes and
corrugations are designed for improved pattern symmetry and low back
radiation
The proposed feed structure is shown in Fig 51 The feed consist of the
following parts a coaxial-to-rectangular waveguide adapter a rectangular-to-
circular waveguide transition a circular waveguide section four quarter-wave
chokes around the feeds aperture and four corrugations on the feeds outer
surface
The computer simulation shows the above arrangement offers good radiation
patterns over a broad frequency range The broadband operation is obtained
by exciting the TE11 mode in the circular waveguide using the TE10 mode of
the rectangular waveguide which is in turn excited by a coaxial probe
-51-
Chokes
Coaxial-to-waveguide transition
Circular wavguide
Corrugations
Mode transition
(a)
(b)
Fig 51 Structure of the proposed broadband circular waveguide feed
(a) CAD model and (b) cross-sectional view
For the coaxial-to-rectangular waveguide adapter an SMA connector with
the probe diameter of 127 mm is employed The coaxial probe inserted into
the waveguide energizes the feed and excites the dominant TE10 mode in
-52-
the rectangular waveguide The impedance matching is achieved by adjusting
the probe distance sp from the back short and the probe length lp
(a)
(b)
Fig 52 Reflection coefficient of the coaxial-to-rectangular adapter versus
(a) probe length lp and (b) the probe position sp
Fig 52 shows the reflection coefficient versus the various values of probe
lengths lp and probe positions sp The probe length lp is adjusted to obtain
antenna impedance matching and the probe distance sp is adjusted to obtain a
-53-
desired resonant frequency
Next a transition between rectangular and circular waveguide is designed
The transition section converts the TE10 mode in the rectangular waveguide to
TE11 mode in the circular waveguide and vice versa The transition is built
in a form of a taper for easy fabrication[22]
(a)
(b)
Fig 53 Structure of the rectangular-to-circular waveguide transition
(a) 3D view and (b) cross sectional view
The dimensions of the final optimized transition are as follows The length
of the rectangular waveguide section is 143mm The rectangular waveguides
width a and height b are 207mm and 857mm respectively The length of
the circular waveguide section is 143mm The inside diameter of the circular
-54-
waveguide is 207mm(097 wavelength at 14GHz) The length of transition
region ltr is 4465mm(approximately equal to 2λ0 at 14GHz) Fig 54 shows
the field distribution inside the mode converter
(a)
(b)
Fig 54 Field distribution inside the mode converter at
(a) 10GHz (b) 14GHz and (c) 18GHz
-55-
(c)
Fig 54 continued
Finally multiple chokes are investigated Figs 55 56 and 57 show the
feed performance without chokes The reflection coefficient is less than -10dB
over 10-19GHz The antenna has a gain of 921dB to 1189dB over
10-19GHz
Fig 55 Reflection coefficient of the broadband circular waveguide feed
without chokes and corrugations
-56-
(a)
(b)
(c)
Fig 56 E- and H-plane patterns of the broadband circular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-57-
(d)
(e)
Fig 56 continued
-58-
(a)
(b)
Fig 57 2D radiation patterns of the broadband cicular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-59-
(c)
(d)
Fig 57 continued
-60-
(e)
Fig 57 continued
To achieve equal beamwidths in E and H planes over a wide frequency
range chokes and corrugations are employed Table51 summarizes the
performance of a feed without chokes and corrugations
Table 51 Performance of the broadband circular waveguide feed without
chokes and corrugations
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
1000 940 6061 15
1200 972 6159 17
1400 920 5957 21
1600 1070 4751 29
1800 1188 5352 21
-61-
Four quarter-wavelength chokes are introduced in the feed design which
has a slot depth of 75mm and slot width of 09mm The choke slot spacing
is 18mm The choke design is investigated by applying the choke one by
one and the effect on the E- and H-plane patterns are observed as illustrated
in Figs 58 and 59 The use of chokes makes the E-plane pattern narrower
The H-plane pattern is not affected Chokes increase the gain slightly and
reduce back radiation
(a)
(b)
Fig 58 Effect of chokes on the E-plane pattern of the broadband circular
waveguide feed at (a) 10GHz(b) 12GHz (c) 14GHz (d) 16GHz and (e)
18GHz
-62-
(c)
(d)
(e)
Fig 58 continued
-63-
(a)
(b)
(c)
Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-64-
(d)
(e)
Fig 59 continued
-65-
Fig 510 shows the feed performance versus the choke depth When the
choke depth is varied from 535mm to 95mm the E- and H-plane patterns
are strongly affected The optimum value of choke depth is 75mm(035λ0 at
14GHz) which gives equal E- and H-plane radiation patterns and leads to
low back radiation
Fig 511 shows the feed performance versus the choke slot width tch The
choke slot width is varied from 09mm to 21mm Radiation patterns and
reflection coefficients are not sensitive to the choke slot width The final
choke slot width is selected to be 09mm considering the feed diameter
minimization and the manufacturability The overall diameter of the proposed
feed is 369mm which is increased from the 207mm of the waveguide
inside diameter due to the use of four chokes
-66-
(a)
(b)
(c)
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection coefficient
-67-
(a)
(b)
(c)
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and (c)
reflection coefficient
-68-
Next we investigated corrugations placed on the outer wall of the feed
Four corrugations applied to the outer surface of the circular waveguide The
corrugation depth is 465mm(0215λ0 at 14GHz) The primary purpose of
using corrugations is to further reduce the back radiation Increasing the
number of corrugations beyond four has little effect in reducing the back
radiation
Figs 512 and 513 show the effect of corrugations on the E- and H-plane
patterns Fig 514 shows the parametric study of the corrugation depth lcor
The corrugation depth is varied from 40mm and 645mm The optimum
value of the corrugation depth is found to be 465mm
-69-
(a)
(b)
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern at (a) 12GHz and (b) 14GHz
-70-
(a)
(b)
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern at (a) 12GHz and (b) 14GHz
-71-
(a)
(b)
(c)
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection coefficient
-72-
The phase center location is important in placing the feed in a reflector
antenna[8] The phase center variation with frequency should be small Fig
515 shows the effect of chokes and corrugations on the phase center The
curve with circle corresponds to the case without chokes and corrugations
The phase center varies from -326mm and -190mm away from the feeds
aperture plane It means the phase center is located inside the waveguide
The curve with triangles corresponds to the case with chokes The curve with
squares to the case with chokes and corrugations The phase center varies
from 0mm to -302mm
From Fig 515 we can observed that phase center variation reduced by the
corrugation and three cases phase center calculated in φ=450 plane
parameter sweep values are given in Table 52
10 12 14 16 181
0
-1
-2
-3
-4
-5
-6
Pha
se c
ente
r (m
m)
Frequency (GHz)
choke+corrugatuion without choke corrugation with choke
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
-73-
Frequency
(GHz)
Phase center from the aperture plane
(mm)
Without
chokes and
corrugations
With
chokes
With chokes
and
corrugations
1000 -326 062 000
1100 -187 030 -002
1200 -563 -208 -065
1300 -296 -154 -202
1400 -319 -314 -302
1500 -201 -203 -241
1600 -242 -233 -207
1700 -208 -208 -186
1800 -190 -157 -132
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
Based on the foregoing parametric studies optimum dimensions of the
broadband circular waveguide feed are obtained as shown in Table 53
-74-
Table 53 Optimum dimensions of the broadband circular waveguide feed
Parameter Designation Value (mm)
2a Waveguide inside diameter 2070
d Waveguide outside diameter 3690
lcrLength of the circular waveguide section 1430
m Distance between the aperture plane and the first corrugation 950
xDistance from the last corrugation to the end of the cylindrical outer surface
550
ltrLength of the rectangular-to-circularwaveguide transition 4465
lrcLength of the rectangular waveguide section 1430
tch Choke slot width 090
lch Choke depth 750
t Choke metal width 090
lcor Corrugation depth 465
tcor Corrugation metal width 100
s Corrugation slot width 10
lp Probe length 530
sp Probe position from the back short 530
din Probe diameter 127
b Inside height of the rectangular waveguide 857
tw Waveguide wall thickness 500
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-30-
(a)
(b)
(c)
Fig 34 Feed performance versus the choke slot width (a) E-plane pattern
(b) H-plane pattern and (c) reflection coefficient
-31-
(a)
(b)
(c)
Fig 35 Feed performance versus the dielectric ring length (a) E-plane
pattern (b) H-plane pattern and (c) reflection coefficient
-32-
(a)
(b)
(c)
Fig 36 Feed performance versus the dielectric ring thickness (a) E-plane
pattern(b) H-plane pattern and (c) reflection coefficient
-33-
From the above parametric analysis an optimum feed design is obtained
The result is shown in Table 31 Fig 37 shows the 2D gain patterns of
designed feed The antenna has a gain of 903dB 933dB and 956dB at
171GHz 1825GHz and 19GHz respectively
Fig 38 shows E- and H-plane radiation patterns of the designed feed The
feed has E- and H-plane 10-dB beamwidths of 60 and 59 degrees at 17GHz
The feed has a front-to-back ration of 1900dB 2490dB and 2200dB at
171GHz 1825GHz and 19GHz respectively Table 32 summarizes the
performance of the designed narrow-band circular waveguide feed
The designed feed has a greatly improved performance over that of a
simple coax-fed feed described in Section 23
Table 31 Dimensions of the designed narrow-band circular feed
Parameter Designation Value(mm)
a Waveguide inside radius 640
l Feed length 2890
lp Probe length 363
sp Probe position from the back short 616
din Probe diameter 127
dout Diameter of coaxial cables outer conductor 400
t Thickness of choked wall 050
tch Choke slot width 100
lch Choke depth 410
ld Dielectric ring length 1168
td Dielectric ring thickness 155
d1 Waveguide outside diameter 1680
-34-
(a)
(b)
Fig 37 2D gain patterns of the narrow-band circular waveguide feed at
(a) 17GHz (b) 1825GHz and (c) 19GHz
-35-
(c)
Fig 37 continued
-36-
(a)
(b)
(c)
Fig 38 E- and H-plane patterns of the narrow-band circular waveguide feed
at (a) 10GHz (b) 1825GHz and (c) 195GHz
-37-
Frequency(GHz)
Gain(dB)
E-H-plane10-dB beamwidths
(deg)
Front-to-back ratio(dB)
Phase centerlocation
(From feeds aperture plane
toward reflector)
(mm)
1700 903 6059 20 062
1825 933 6060 25 004
1900 956 5759 22 007
Table 32 Performance of the narrow-band circular waveguide feed
The designed narrow-band feed is fabricated and its performance is
measured and compared with the simulation results The designed feed is
fabricated in a numerically-controlled machining center The fabricated antenna
is shown in Fig 39
Fig 39 Photograph of the fabricated feed
-38-
Fig 310 shows a comparison of the measured and simulated reflection
coefficients The measured reflection coefficient is less than -10dB over
171-197GHz The agreement between simulated and measured results are
good
Fig 311 shows the E- and H-plane patterns of the fabricated feed at
187GHz The feed has 90dB gain simulation and measurement results are in
good agreement
The fabricated antennarsquos 10dB beamwidth is 60 degrees in both E and H
planes at 187GHz The front-to-back ratio is 21dB
Fig 310 Reflection coefficient of the fabricated feed
-39-
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Fee
d H
orn
Gain
- d
B
Angle - degree
(a)
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Feed H
orn
Gain
- d
B
Angle - degree
(b)
Fig 311 Gain patterns of the fabricated feed at 187 GHz (a) E-plane and
(b) H-plane
-40-
IV Design of Circular Waveguide Feeds Loaded with a
Dielectric Rod
In this section circular waveguide feeds loaded with a dielectric rod feed
are investigated A comprehensive discussion of the circular waveguide loaded
with a dielectric rod is given by Kumar[7] Inserting a dielectric material
inside the circular waveguide improves the E- and H-plane pattern symmetry
In general dielectric-loaded circular waveguide feeds show good performance
only over a narrow bandwidth
Fig 41 shows the geometry of a circular waveguide loaded with a
dielectric rod The waveguide length is 400mm and the wall thickness is
05mm The dielectric rods diameter is 207mm The dielectric rod is
extended 05 wavelength beyond the waveguide open end The dielectric
constant εr is changed and the feeds performance is observed
Fig 41 Geometry of a circular waveguide loaded with a uniform dielectric
rod
-41-
Fig 42 is the radiation pattern of the feed with εr = 25 and L = 05λ0 at
9GHz E- and H-plane 10-dB beamwidths are 810 and 807 degrees
respectively The front-to-back ratio is 18dB The antenna gain is 71dB
(a)
(b)
Fig 42 Radiation pattern at 9GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 05λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-42-
Fig 43 shows the radiation pattern of the feed with εr = 21 at 10GHz
E- and H-plane 10-dB beamwidths are 70 and 71 degrees respectively The
front-to-back ratio is 19dB The antenna gain is 83dB
(a)
(b)
Fig 43 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 21 and L = 05λ0 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-43-
Fig 44 shows the radiation pattern of the feed with εr = 30 at 8GHz
E- and H-plane 10-dB beamwidths are 83 and 824 degrees respectively The
front-to-back ratio is 17dB The antenna gain is 73dB
(a)
(b)
Fig 44 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 30 and L = 05λ0 at 8GHz (a) 2D radiation pattern
and (b) E- and H-plane patterns
-44-
Fig 45 shows the radiation pattern of the feed with εr = 50 at 18GHz
E- and H-plane 10-dB beamwidths are 56 and 54 degrees respectively The
front-to-back ratio is 27dB The antenna gain is 105dB The feed has a good
pattern symmetry and low back radiation
(a)
(b)
Fig 45 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 50 and L = 05λ0 at 18GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-45-
Fig 46 is the radiation pattern of the feed with εr = 25 and L = 10λ0 at
10GHz E- and H-plane 10-dB beamwidths are 50 and 48 degrees
respectively The front-to-back ratio is 16dB The antenna gain is 105dB
(a)
(b)
Fig 46 Radiation pattern at 10GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 10λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-46-
Fig 47 shows the geometry of a circular waveguide with a tapered
dielectric rod The designed feed has the following dimension L = 1λ0 d =
1λ0 and εr =25 at 10GHz The waveguide length is 40mm and the wall
thickness is 05mm
L
Dielectricd3
Fig 47 Geometry of a circular waveguide loaded with a tapered dielectric
rod
Fig 48 shows the radiatio pattern of the designed feed E- and H-plane
10-dB beamwidths are 575 and 564 degrees respectively The front-to-back
ratio is 377dB The antenna gain is 94dB The designed feed has an
excellent beamwidth symmetry and a very low back radiation
-47-
(a)
(b)
Fig 48 Radiation pattern of a circular waveguide loaded with a tapered
dielectric rod with L = 1λ0 d = 1λ0 and εr =25 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-48-
Fig 49 shows the geometry of a spherical ended dielectric rod feed
diameter of 06λ0 at 10GHz with a dielectric constant of 25 and L= 03λ0
Fig 410 shows the radiation patterns of the designed feed E- and H-plane
10-dB beamwidths are both 63 degrees The front-to-back ratio is 24dB The
antenna gain is 864dB
Fig 49 Geometry of a circular waveguide loaded with a spherical ended
dielectric rod
-49-
(a)
(b)
Fig 410 Radiation pattern of a circular waveguide loaded wht a spherical
ended dielectric rod with d = 06λ0 L = 03λ0 and εr =25 at 10GHz (a) 3D
radiation pattern and (b) E- and H-plane patterns
-50-
V Design of a Broadband Circular Waveguide Feed
In this chapter the design of a broadband circular waveguide feed is
presented At microwave frequencies the feed is often a circular waveguide
with chokes and corrugations around the aperture Chokes and corrugations
equalize E- and H-plane patterns and reduce the back radiation
The proposed feed is designed to operate over 10-18GHz The design starts
with the optimization of the coaxial-to-rectangular waveguide adapter
employed for good mode purity over a broad frequency range Next a
rectangular-to-circular waveguide transition is optimized Finally chokes and
corrugations are designed for improved pattern symmetry and low back
radiation
The proposed feed structure is shown in Fig 51 The feed consist of the
following parts a coaxial-to-rectangular waveguide adapter a rectangular-to-
circular waveguide transition a circular waveguide section four quarter-wave
chokes around the feeds aperture and four corrugations on the feeds outer
surface
The computer simulation shows the above arrangement offers good radiation
patterns over a broad frequency range The broadband operation is obtained
by exciting the TE11 mode in the circular waveguide using the TE10 mode of
the rectangular waveguide which is in turn excited by a coaxial probe
-51-
Chokes
Coaxial-to-waveguide transition
Circular wavguide
Corrugations
Mode transition
(a)
(b)
Fig 51 Structure of the proposed broadband circular waveguide feed
(a) CAD model and (b) cross-sectional view
For the coaxial-to-rectangular waveguide adapter an SMA connector with
the probe diameter of 127 mm is employed The coaxial probe inserted into
the waveguide energizes the feed and excites the dominant TE10 mode in
-52-
the rectangular waveguide The impedance matching is achieved by adjusting
the probe distance sp from the back short and the probe length lp
(a)
(b)
Fig 52 Reflection coefficient of the coaxial-to-rectangular adapter versus
(a) probe length lp and (b) the probe position sp
Fig 52 shows the reflection coefficient versus the various values of probe
lengths lp and probe positions sp The probe length lp is adjusted to obtain
antenna impedance matching and the probe distance sp is adjusted to obtain a
-53-
desired resonant frequency
Next a transition between rectangular and circular waveguide is designed
The transition section converts the TE10 mode in the rectangular waveguide to
TE11 mode in the circular waveguide and vice versa The transition is built
in a form of a taper for easy fabrication[22]
(a)
(b)
Fig 53 Structure of the rectangular-to-circular waveguide transition
(a) 3D view and (b) cross sectional view
The dimensions of the final optimized transition are as follows The length
of the rectangular waveguide section is 143mm The rectangular waveguides
width a and height b are 207mm and 857mm respectively The length of
the circular waveguide section is 143mm The inside diameter of the circular
-54-
waveguide is 207mm(097 wavelength at 14GHz) The length of transition
region ltr is 4465mm(approximately equal to 2λ0 at 14GHz) Fig 54 shows
the field distribution inside the mode converter
(a)
(b)
Fig 54 Field distribution inside the mode converter at
(a) 10GHz (b) 14GHz and (c) 18GHz
-55-
(c)
Fig 54 continued
Finally multiple chokes are investigated Figs 55 56 and 57 show the
feed performance without chokes The reflection coefficient is less than -10dB
over 10-19GHz The antenna has a gain of 921dB to 1189dB over
10-19GHz
Fig 55 Reflection coefficient of the broadband circular waveguide feed
without chokes and corrugations
-56-
(a)
(b)
(c)
Fig 56 E- and H-plane patterns of the broadband circular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-57-
(d)
(e)
Fig 56 continued
-58-
(a)
(b)
Fig 57 2D radiation patterns of the broadband cicular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-59-
(c)
(d)
Fig 57 continued
-60-
(e)
Fig 57 continued
To achieve equal beamwidths in E and H planes over a wide frequency
range chokes and corrugations are employed Table51 summarizes the
performance of a feed without chokes and corrugations
Table 51 Performance of the broadband circular waveguide feed without
chokes and corrugations
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
1000 940 6061 15
1200 972 6159 17
1400 920 5957 21
1600 1070 4751 29
1800 1188 5352 21
-61-
Four quarter-wavelength chokes are introduced in the feed design which
has a slot depth of 75mm and slot width of 09mm The choke slot spacing
is 18mm The choke design is investigated by applying the choke one by
one and the effect on the E- and H-plane patterns are observed as illustrated
in Figs 58 and 59 The use of chokes makes the E-plane pattern narrower
The H-plane pattern is not affected Chokes increase the gain slightly and
reduce back radiation
(a)
(b)
Fig 58 Effect of chokes on the E-plane pattern of the broadband circular
waveguide feed at (a) 10GHz(b) 12GHz (c) 14GHz (d) 16GHz and (e)
18GHz
-62-
(c)
(d)
(e)
Fig 58 continued
-63-
(a)
(b)
(c)
Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-64-
(d)
(e)
Fig 59 continued
-65-
Fig 510 shows the feed performance versus the choke depth When the
choke depth is varied from 535mm to 95mm the E- and H-plane patterns
are strongly affected The optimum value of choke depth is 75mm(035λ0 at
14GHz) which gives equal E- and H-plane radiation patterns and leads to
low back radiation
Fig 511 shows the feed performance versus the choke slot width tch The
choke slot width is varied from 09mm to 21mm Radiation patterns and
reflection coefficients are not sensitive to the choke slot width The final
choke slot width is selected to be 09mm considering the feed diameter
minimization and the manufacturability The overall diameter of the proposed
feed is 369mm which is increased from the 207mm of the waveguide
inside diameter due to the use of four chokes
-66-
(a)
(b)
(c)
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection coefficient
-67-
(a)
(b)
(c)
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and (c)
reflection coefficient
-68-
Next we investigated corrugations placed on the outer wall of the feed
Four corrugations applied to the outer surface of the circular waveguide The
corrugation depth is 465mm(0215λ0 at 14GHz) The primary purpose of
using corrugations is to further reduce the back radiation Increasing the
number of corrugations beyond four has little effect in reducing the back
radiation
Figs 512 and 513 show the effect of corrugations on the E- and H-plane
patterns Fig 514 shows the parametric study of the corrugation depth lcor
The corrugation depth is varied from 40mm and 645mm The optimum
value of the corrugation depth is found to be 465mm
-69-
(a)
(b)
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern at (a) 12GHz and (b) 14GHz
-70-
(a)
(b)
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern at (a) 12GHz and (b) 14GHz
-71-
(a)
(b)
(c)
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection coefficient
-72-
The phase center location is important in placing the feed in a reflector
antenna[8] The phase center variation with frequency should be small Fig
515 shows the effect of chokes and corrugations on the phase center The
curve with circle corresponds to the case without chokes and corrugations
The phase center varies from -326mm and -190mm away from the feeds
aperture plane It means the phase center is located inside the waveguide
The curve with triangles corresponds to the case with chokes The curve with
squares to the case with chokes and corrugations The phase center varies
from 0mm to -302mm
From Fig 515 we can observed that phase center variation reduced by the
corrugation and three cases phase center calculated in φ=450 plane
parameter sweep values are given in Table 52
10 12 14 16 181
0
-1
-2
-3
-4
-5
-6
Pha
se c
ente
r (m
m)
Frequency (GHz)
choke+corrugatuion without choke corrugation with choke
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
-73-
Frequency
(GHz)
Phase center from the aperture plane
(mm)
Without
chokes and
corrugations
With
chokes
With chokes
and
corrugations
1000 -326 062 000
1100 -187 030 -002
1200 -563 -208 -065
1300 -296 -154 -202
1400 -319 -314 -302
1500 -201 -203 -241
1600 -242 -233 -207
1700 -208 -208 -186
1800 -190 -157 -132
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
Based on the foregoing parametric studies optimum dimensions of the
broadband circular waveguide feed are obtained as shown in Table 53
-74-
Table 53 Optimum dimensions of the broadband circular waveguide feed
Parameter Designation Value (mm)
2a Waveguide inside diameter 2070
d Waveguide outside diameter 3690
lcrLength of the circular waveguide section 1430
m Distance between the aperture plane and the first corrugation 950
xDistance from the last corrugation to the end of the cylindrical outer surface
550
ltrLength of the rectangular-to-circularwaveguide transition 4465
lrcLength of the rectangular waveguide section 1430
tch Choke slot width 090
lch Choke depth 750
t Choke metal width 090
lcor Corrugation depth 465
tcor Corrugation metal width 100
s Corrugation slot width 10
lp Probe length 530
sp Probe position from the back short 530
din Probe diameter 127
b Inside height of the rectangular waveguide 857
tw Waveguide wall thickness 500
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-31-
(a)
(b)
(c)
Fig 35 Feed performance versus the dielectric ring length (a) E-plane
pattern (b) H-plane pattern and (c) reflection coefficient
-32-
(a)
(b)
(c)
Fig 36 Feed performance versus the dielectric ring thickness (a) E-plane
pattern(b) H-plane pattern and (c) reflection coefficient
-33-
From the above parametric analysis an optimum feed design is obtained
The result is shown in Table 31 Fig 37 shows the 2D gain patterns of
designed feed The antenna has a gain of 903dB 933dB and 956dB at
171GHz 1825GHz and 19GHz respectively
Fig 38 shows E- and H-plane radiation patterns of the designed feed The
feed has E- and H-plane 10-dB beamwidths of 60 and 59 degrees at 17GHz
The feed has a front-to-back ration of 1900dB 2490dB and 2200dB at
171GHz 1825GHz and 19GHz respectively Table 32 summarizes the
performance of the designed narrow-band circular waveguide feed
The designed feed has a greatly improved performance over that of a
simple coax-fed feed described in Section 23
Table 31 Dimensions of the designed narrow-band circular feed
Parameter Designation Value(mm)
a Waveguide inside radius 640
l Feed length 2890
lp Probe length 363
sp Probe position from the back short 616
din Probe diameter 127
dout Diameter of coaxial cables outer conductor 400
t Thickness of choked wall 050
tch Choke slot width 100
lch Choke depth 410
ld Dielectric ring length 1168
td Dielectric ring thickness 155
d1 Waveguide outside diameter 1680
-34-
(a)
(b)
Fig 37 2D gain patterns of the narrow-band circular waveguide feed at
(a) 17GHz (b) 1825GHz and (c) 19GHz
-35-
(c)
Fig 37 continued
-36-
(a)
(b)
(c)
Fig 38 E- and H-plane patterns of the narrow-band circular waveguide feed
at (a) 10GHz (b) 1825GHz and (c) 195GHz
-37-
Frequency(GHz)
Gain(dB)
E-H-plane10-dB beamwidths
(deg)
Front-to-back ratio(dB)
Phase centerlocation
(From feeds aperture plane
toward reflector)
(mm)
1700 903 6059 20 062
1825 933 6060 25 004
1900 956 5759 22 007
Table 32 Performance of the narrow-band circular waveguide feed
The designed narrow-band feed is fabricated and its performance is
measured and compared with the simulation results The designed feed is
fabricated in a numerically-controlled machining center The fabricated antenna
is shown in Fig 39
Fig 39 Photograph of the fabricated feed
-38-
Fig 310 shows a comparison of the measured and simulated reflection
coefficients The measured reflection coefficient is less than -10dB over
171-197GHz The agreement between simulated and measured results are
good
Fig 311 shows the E- and H-plane patterns of the fabricated feed at
187GHz The feed has 90dB gain simulation and measurement results are in
good agreement
The fabricated antennarsquos 10dB beamwidth is 60 degrees in both E and H
planes at 187GHz The front-to-back ratio is 21dB
Fig 310 Reflection coefficient of the fabricated feed
-39-
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Fee
d H
orn
Gain
- d
B
Angle - degree
(a)
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Feed H
orn
Gain
- d
B
Angle - degree
(b)
Fig 311 Gain patterns of the fabricated feed at 187 GHz (a) E-plane and
(b) H-plane
-40-
IV Design of Circular Waveguide Feeds Loaded with a
Dielectric Rod
In this section circular waveguide feeds loaded with a dielectric rod feed
are investigated A comprehensive discussion of the circular waveguide loaded
with a dielectric rod is given by Kumar[7] Inserting a dielectric material
inside the circular waveguide improves the E- and H-plane pattern symmetry
In general dielectric-loaded circular waveguide feeds show good performance
only over a narrow bandwidth
Fig 41 shows the geometry of a circular waveguide loaded with a
dielectric rod The waveguide length is 400mm and the wall thickness is
05mm The dielectric rods diameter is 207mm The dielectric rod is
extended 05 wavelength beyond the waveguide open end The dielectric
constant εr is changed and the feeds performance is observed
Fig 41 Geometry of a circular waveguide loaded with a uniform dielectric
rod
-41-
Fig 42 is the radiation pattern of the feed with εr = 25 and L = 05λ0 at
9GHz E- and H-plane 10-dB beamwidths are 810 and 807 degrees
respectively The front-to-back ratio is 18dB The antenna gain is 71dB
(a)
(b)
Fig 42 Radiation pattern at 9GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 05λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-42-
Fig 43 shows the radiation pattern of the feed with εr = 21 at 10GHz
E- and H-plane 10-dB beamwidths are 70 and 71 degrees respectively The
front-to-back ratio is 19dB The antenna gain is 83dB
(a)
(b)
Fig 43 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 21 and L = 05λ0 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-43-
Fig 44 shows the radiation pattern of the feed with εr = 30 at 8GHz
E- and H-plane 10-dB beamwidths are 83 and 824 degrees respectively The
front-to-back ratio is 17dB The antenna gain is 73dB
(a)
(b)
Fig 44 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 30 and L = 05λ0 at 8GHz (a) 2D radiation pattern
and (b) E- and H-plane patterns
-44-
Fig 45 shows the radiation pattern of the feed with εr = 50 at 18GHz
E- and H-plane 10-dB beamwidths are 56 and 54 degrees respectively The
front-to-back ratio is 27dB The antenna gain is 105dB The feed has a good
pattern symmetry and low back radiation
(a)
(b)
Fig 45 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 50 and L = 05λ0 at 18GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-45-
Fig 46 is the radiation pattern of the feed with εr = 25 and L = 10λ0 at
10GHz E- and H-plane 10-dB beamwidths are 50 and 48 degrees
respectively The front-to-back ratio is 16dB The antenna gain is 105dB
(a)
(b)
Fig 46 Radiation pattern at 10GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 10λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-46-
Fig 47 shows the geometry of a circular waveguide with a tapered
dielectric rod The designed feed has the following dimension L = 1λ0 d =
1λ0 and εr =25 at 10GHz The waveguide length is 40mm and the wall
thickness is 05mm
L
Dielectricd3
Fig 47 Geometry of a circular waveguide loaded with a tapered dielectric
rod
Fig 48 shows the radiatio pattern of the designed feed E- and H-plane
10-dB beamwidths are 575 and 564 degrees respectively The front-to-back
ratio is 377dB The antenna gain is 94dB The designed feed has an
excellent beamwidth symmetry and a very low back radiation
-47-
(a)
(b)
Fig 48 Radiation pattern of a circular waveguide loaded with a tapered
dielectric rod with L = 1λ0 d = 1λ0 and εr =25 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-48-
Fig 49 shows the geometry of a spherical ended dielectric rod feed
diameter of 06λ0 at 10GHz with a dielectric constant of 25 and L= 03λ0
Fig 410 shows the radiation patterns of the designed feed E- and H-plane
10-dB beamwidths are both 63 degrees The front-to-back ratio is 24dB The
antenna gain is 864dB
Fig 49 Geometry of a circular waveguide loaded with a spherical ended
dielectric rod
-49-
(a)
(b)
Fig 410 Radiation pattern of a circular waveguide loaded wht a spherical
ended dielectric rod with d = 06λ0 L = 03λ0 and εr =25 at 10GHz (a) 3D
radiation pattern and (b) E- and H-plane patterns
-50-
V Design of a Broadband Circular Waveguide Feed
In this chapter the design of a broadband circular waveguide feed is
presented At microwave frequencies the feed is often a circular waveguide
with chokes and corrugations around the aperture Chokes and corrugations
equalize E- and H-plane patterns and reduce the back radiation
The proposed feed is designed to operate over 10-18GHz The design starts
with the optimization of the coaxial-to-rectangular waveguide adapter
employed for good mode purity over a broad frequency range Next a
rectangular-to-circular waveguide transition is optimized Finally chokes and
corrugations are designed for improved pattern symmetry and low back
radiation
The proposed feed structure is shown in Fig 51 The feed consist of the
following parts a coaxial-to-rectangular waveguide adapter a rectangular-to-
circular waveguide transition a circular waveguide section four quarter-wave
chokes around the feeds aperture and four corrugations on the feeds outer
surface
The computer simulation shows the above arrangement offers good radiation
patterns over a broad frequency range The broadband operation is obtained
by exciting the TE11 mode in the circular waveguide using the TE10 mode of
the rectangular waveguide which is in turn excited by a coaxial probe
-51-
Chokes
Coaxial-to-waveguide transition
Circular wavguide
Corrugations
Mode transition
(a)
(b)
Fig 51 Structure of the proposed broadband circular waveguide feed
(a) CAD model and (b) cross-sectional view
For the coaxial-to-rectangular waveguide adapter an SMA connector with
the probe diameter of 127 mm is employed The coaxial probe inserted into
the waveguide energizes the feed and excites the dominant TE10 mode in
-52-
the rectangular waveguide The impedance matching is achieved by adjusting
the probe distance sp from the back short and the probe length lp
(a)
(b)
Fig 52 Reflection coefficient of the coaxial-to-rectangular adapter versus
(a) probe length lp and (b) the probe position sp
Fig 52 shows the reflection coefficient versus the various values of probe
lengths lp and probe positions sp The probe length lp is adjusted to obtain
antenna impedance matching and the probe distance sp is adjusted to obtain a
-53-
desired resonant frequency
Next a transition between rectangular and circular waveguide is designed
The transition section converts the TE10 mode in the rectangular waveguide to
TE11 mode in the circular waveguide and vice versa The transition is built
in a form of a taper for easy fabrication[22]
(a)
(b)
Fig 53 Structure of the rectangular-to-circular waveguide transition
(a) 3D view and (b) cross sectional view
The dimensions of the final optimized transition are as follows The length
of the rectangular waveguide section is 143mm The rectangular waveguides
width a and height b are 207mm and 857mm respectively The length of
the circular waveguide section is 143mm The inside diameter of the circular
-54-
waveguide is 207mm(097 wavelength at 14GHz) The length of transition
region ltr is 4465mm(approximately equal to 2λ0 at 14GHz) Fig 54 shows
the field distribution inside the mode converter
(a)
(b)
Fig 54 Field distribution inside the mode converter at
(a) 10GHz (b) 14GHz and (c) 18GHz
-55-
(c)
Fig 54 continued
Finally multiple chokes are investigated Figs 55 56 and 57 show the
feed performance without chokes The reflection coefficient is less than -10dB
over 10-19GHz The antenna has a gain of 921dB to 1189dB over
10-19GHz
Fig 55 Reflection coefficient of the broadband circular waveguide feed
without chokes and corrugations
-56-
(a)
(b)
(c)
Fig 56 E- and H-plane patterns of the broadband circular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-57-
(d)
(e)
Fig 56 continued
-58-
(a)
(b)
Fig 57 2D radiation patterns of the broadband cicular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-59-
(c)
(d)
Fig 57 continued
-60-
(e)
Fig 57 continued
To achieve equal beamwidths in E and H planes over a wide frequency
range chokes and corrugations are employed Table51 summarizes the
performance of a feed without chokes and corrugations
Table 51 Performance of the broadband circular waveguide feed without
chokes and corrugations
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
1000 940 6061 15
1200 972 6159 17
1400 920 5957 21
1600 1070 4751 29
1800 1188 5352 21
-61-
Four quarter-wavelength chokes are introduced in the feed design which
has a slot depth of 75mm and slot width of 09mm The choke slot spacing
is 18mm The choke design is investigated by applying the choke one by
one and the effect on the E- and H-plane patterns are observed as illustrated
in Figs 58 and 59 The use of chokes makes the E-plane pattern narrower
The H-plane pattern is not affected Chokes increase the gain slightly and
reduce back radiation
(a)
(b)
Fig 58 Effect of chokes on the E-plane pattern of the broadband circular
waveguide feed at (a) 10GHz(b) 12GHz (c) 14GHz (d) 16GHz and (e)
18GHz
-62-
(c)
(d)
(e)
Fig 58 continued
-63-
(a)
(b)
(c)
Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-64-
(d)
(e)
Fig 59 continued
-65-
Fig 510 shows the feed performance versus the choke depth When the
choke depth is varied from 535mm to 95mm the E- and H-plane patterns
are strongly affected The optimum value of choke depth is 75mm(035λ0 at
14GHz) which gives equal E- and H-plane radiation patterns and leads to
low back radiation
Fig 511 shows the feed performance versus the choke slot width tch The
choke slot width is varied from 09mm to 21mm Radiation patterns and
reflection coefficients are not sensitive to the choke slot width The final
choke slot width is selected to be 09mm considering the feed diameter
minimization and the manufacturability The overall diameter of the proposed
feed is 369mm which is increased from the 207mm of the waveguide
inside diameter due to the use of four chokes
-66-
(a)
(b)
(c)
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection coefficient
-67-
(a)
(b)
(c)
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and (c)
reflection coefficient
-68-
Next we investigated corrugations placed on the outer wall of the feed
Four corrugations applied to the outer surface of the circular waveguide The
corrugation depth is 465mm(0215λ0 at 14GHz) The primary purpose of
using corrugations is to further reduce the back radiation Increasing the
number of corrugations beyond four has little effect in reducing the back
radiation
Figs 512 and 513 show the effect of corrugations on the E- and H-plane
patterns Fig 514 shows the parametric study of the corrugation depth lcor
The corrugation depth is varied from 40mm and 645mm The optimum
value of the corrugation depth is found to be 465mm
-69-
(a)
(b)
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern at (a) 12GHz and (b) 14GHz
-70-
(a)
(b)
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern at (a) 12GHz and (b) 14GHz
-71-
(a)
(b)
(c)
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection coefficient
-72-
The phase center location is important in placing the feed in a reflector
antenna[8] The phase center variation with frequency should be small Fig
515 shows the effect of chokes and corrugations on the phase center The
curve with circle corresponds to the case without chokes and corrugations
The phase center varies from -326mm and -190mm away from the feeds
aperture plane It means the phase center is located inside the waveguide
The curve with triangles corresponds to the case with chokes The curve with
squares to the case with chokes and corrugations The phase center varies
from 0mm to -302mm
From Fig 515 we can observed that phase center variation reduced by the
corrugation and three cases phase center calculated in φ=450 plane
parameter sweep values are given in Table 52
10 12 14 16 181
0
-1
-2
-3
-4
-5
-6
Pha
se c
ente
r (m
m)
Frequency (GHz)
choke+corrugatuion without choke corrugation with choke
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
-73-
Frequency
(GHz)
Phase center from the aperture plane
(mm)
Without
chokes and
corrugations
With
chokes
With chokes
and
corrugations
1000 -326 062 000
1100 -187 030 -002
1200 -563 -208 -065
1300 -296 -154 -202
1400 -319 -314 -302
1500 -201 -203 -241
1600 -242 -233 -207
1700 -208 -208 -186
1800 -190 -157 -132
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
Based on the foregoing parametric studies optimum dimensions of the
broadband circular waveguide feed are obtained as shown in Table 53
-74-
Table 53 Optimum dimensions of the broadband circular waveguide feed
Parameter Designation Value (mm)
2a Waveguide inside diameter 2070
d Waveguide outside diameter 3690
lcrLength of the circular waveguide section 1430
m Distance between the aperture plane and the first corrugation 950
xDistance from the last corrugation to the end of the cylindrical outer surface
550
ltrLength of the rectangular-to-circularwaveguide transition 4465
lrcLength of the rectangular waveguide section 1430
tch Choke slot width 090
lch Choke depth 750
t Choke metal width 090
lcor Corrugation depth 465
tcor Corrugation metal width 100
s Corrugation slot width 10
lp Probe length 530
sp Probe position from the back short 530
din Probe diameter 127
b Inside height of the rectangular waveguide 857
tw Waveguide wall thickness 500
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-32-
(a)
(b)
(c)
Fig 36 Feed performance versus the dielectric ring thickness (a) E-plane
pattern(b) H-plane pattern and (c) reflection coefficient
-33-
From the above parametric analysis an optimum feed design is obtained
The result is shown in Table 31 Fig 37 shows the 2D gain patterns of
designed feed The antenna has a gain of 903dB 933dB and 956dB at
171GHz 1825GHz and 19GHz respectively
Fig 38 shows E- and H-plane radiation patterns of the designed feed The
feed has E- and H-plane 10-dB beamwidths of 60 and 59 degrees at 17GHz
The feed has a front-to-back ration of 1900dB 2490dB and 2200dB at
171GHz 1825GHz and 19GHz respectively Table 32 summarizes the
performance of the designed narrow-band circular waveguide feed
The designed feed has a greatly improved performance over that of a
simple coax-fed feed described in Section 23
Table 31 Dimensions of the designed narrow-band circular feed
Parameter Designation Value(mm)
a Waveguide inside radius 640
l Feed length 2890
lp Probe length 363
sp Probe position from the back short 616
din Probe diameter 127
dout Diameter of coaxial cables outer conductor 400
t Thickness of choked wall 050
tch Choke slot width 100
lch Choke depth 410
ld Dielectric ring length 1168
td Dielectric ring thickness 155
d1 Waveguide outside diameter 1680
-34-
(a)
(b)
Fig 37 2D gain patterns of the narrow-band circular waveguide feed at
(a) 17GHz (b) 1825GHz and (c) 19GHz
-35-
(c)
Fig 37 continued
-36-
(a)
(b)
(c)
Fig 38 E- and H-plane patterns of the narrow-band circular waveguide feed
at (a) 10GHz (b) 1825GHz and (c) 195GHz
-37-
Frequency(GHz)
Gain(dB)
E-H-plane10-dB beamwidths
(deg)
Front-to-back ratio(dB)
Phase centerlocation
(From feeds aperture plane
toward reflector)
(mm)
1700 903 6059 20 062
1825 933 6060 25 004
1900 956 5759 22 007
Table 32 Performance of the narrow-band circular waveguide feed
The designed narrow-band feed is fabricated and its performance is
measured and compared with the simulation results The designed feed is
fabricated in a numerically-controlled machining center The fabricated antenna
is shown in Fig 39
Fig 39 Photograph of the fabricated feed
-38-
Fig 310 shows a comparison of the measured and simulated reflection
coefficients The measured reflection coefficient is less than -10dB over
171-197GHz The agreement between simulated and measured results are
good
Fig 311 shows the E- and H-plane patterns of the fabricated feed at
187GHz The feed has 90dB gain simulation and measurement results are in
good agreement
The fabricated antennarsquos 10dB beamwidth is 60 degrees in both E and H
planes at 187GHz The front-to-back ratio is 21dB
Fig 310 Reflection coefficient of the fabricated feed
-39-
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Fee
d H
orn
Gain
- d
B
Angle - degree
(a)
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Feed H
orn
Gain
- d
B
Angle - degree
(b)
Fig 311 Gain patterns of the fabricated feed at 187 GHz (a) E-plane and
(b) H-plane
-40-
IV Design of Circular Waveguide Feeds Loaded with a
Dielectric Rod
In this section circular waveguide feeds loaded with a dielectric rod feed
are investigated A comprehensive discussion of the circular waveguide loaded
with a dielectric rod is given by Kumar[7] Inserting a dielectric material
inside the circular waveguide improves the E- and H-plane pattern symmetry
In general dielectric-loaded circular waveguide feeds show good performance
only over a narrow bandwidth
Fig 41 shows the geometry of a circular waveguide loaded with a
dielectric rod The waveguide length is 400mm and the wall thickness is
05mm The dielectric rods diameter is 207mm The dielectric rod is
extended 05 wavelength beyond the waveguide open end The dielectric
constant εr is changed and the feeds performance is observed
Fig 41 Geometry of a circular waveguide loaded with a uniform dielectric
rod
-41-
Fig 42 is the radiation pattern of the feed with εr = 25 and L = 05λ0 at
9GHz E- and H-plane 10-dB beamwidths are 810 and 807 degrees
respectively The front-to-back ratio is 18dB The antenna gain is 71dB
(a)
(b)
Fig 42 Radiation pattern at 9GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 05λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-42-
Fig 43 shows the radiation pattern of the feed with εr = 21 at 10GHz
E- and H-plane 10-dB beamwidths are 70 and 71 degrees respectively The
front-to-back ratio is 19dB The antenna gain is 83dB
(a)
(b)
Fig 43 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 21 and L = 05λ0 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-43-
Fig 44 shows the radiation pattern of the feed with εr = 30 at 8GHz
E- and H-plane 10-dB beamwidths are 83 and 824 degrees respectively The
front-to-back ratio is 17dB The antenna gain is 73dB
(a)
(b)
Fig 44 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 30 and L = 05λ0 at 8GHz (a) 2D radiation pattern
and (b) E- and H-plane patterns
-44-
Fig 45 shows the radiation pattern of the feed with εr = 50 at 18GHz
E- and H-plane 10-dB beamwidths are 56 and 54 degrees respectively The
front-to-back ratio is 27dB The antenna gain is 105dB The feed has a good
pattern symmetry and low back radiation
(a)
(b)
Fig 45 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 50 and L = 05λ0 at 18GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-45-
Fig 46 is the radiation pattern of the feed with εr = 25 and L = 10λ0 at
10GHz E- and H-plane 10-dB beamwidths are 50 and 48 degrees
respectively The front-to-back ratio is 16dB The antenna gain is 105dB
(a)
(b)
Fig 46 Radiation pattern at 10GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 10λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-46-
Fig 47 shows the geometry of a circular waveguide with a tapered
dielectric rod The designed feed has the following dimension L = 1λ0 d =
1λ0 and εr =25 at 10GHz The waveguide length is 40mm and the wall
thickness is 05mm
L
Dielectricd3
Fig 47 Geometry of a circular waveguide loaded with a tapered dielectric
rod
Fig 48 shows the radiatio pattern of the designed feed E- and H-plane
10-dB beamwidths are 575 and 564 degrees respectively The front-to-back
ratio is 377dB The antenna gain is 94dB The designed feed has an
excellent beamwidth symmetry and a very low back radiation
-47-
(a)
(b)
Fig 48 Radiation pattern of a circular waveguide loaded with a tapered
dielectric rod with L = 1λ0 d = 1λ0 and εr =25 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-48-
Fig 49 shows the geometry of a spherical ended dielectric rod feed
diameter of 06λ0 at 10GHz with a dielectric constant of 25 and L= 03λ0
Fig 410 shows the radiation patterns of the designed feed E- and H-plane
10-dB beamwidths are both 63 degrees The front-to-back ratio is 24dB The
antenna gain is 864dB
Fig 49 Geometry of a circular waveguide loaded with a spherical ended
dielectric rod
-49-
(a)
(b)
Fig 410 Radiation pattern of a circular waveguide loaded wht a spherical
ended dielectric rod with d = 06λ0 L = 03λ0 and εr =25 at 10GHz (a) 3D
radiation pattern and (b) E- and H-plane patterns
-50-
V Design of a Broadband Circular Waveguide Feed
In this chapter the design of a broadband circular waveguide feed is
presented At microwave frequencies the feed is often a circular waveguide
with chokes and corrugations around the aperture Chokes and corrugations
equalize E- and H-plane patterns and reduce the back radiation
The proposed feed is designed to operate over 10-18GHz The design starts
with the optimization of the coaxial-to-rectangular waveguide adapter
employed for good mode purity over a broad frequency range Next a
rectangular-to-circular waveguide transition is optimized Finally chokes and
corrugations are designed for improved pattern symmetry and low back
radiation
The proposed feed structure is shown in Fig 51 The feed consist of the
following parts a coaxial-to-rectangular waveguide adapter a rectangular-to-
circular waveguide transition a circular waveguide section four quarter-wave
chokes around the feeds aperture and four corrugations on the feeds outer
surface
The computer simulation shows the above arrangement offers good radiation
patterns over a broad frequency range The broadband operation is obtained
by exciting the TE11 mode in the circular waveguide using the TE10 mode of
the rectangular waveguide which is in turn excited by a coaxial probe
-51-
Chokes
Coaxial-to-waveguide transition
Circular wavguide
Corrugations
Mode transition
(a)
(b)
Fig 51 Structure of the proposed broadband circular waveguide feed
(a) CAD model and (b) cross-sectional view
For the coaxial-to-rectangular waveguide adapter an SMA connector with
the probe diameter of 127 mm is employed The coaxial probe inserted into
the waveguide energizes the feed and excites the dominant TE10 mode in
-52-
the rectangular waveguide The impedance matching is achieved by adjusting
the probe distance sp from the back short and the probe length lp
(a)
(b)
Fig 52 Reflection coefficient of the coaxial-to-rectangular adapter versus
(a) probe length lp and (b) the probe position sp
Fig 52 shows the reflection coefficient versus the various values of probe
lengths lp and probe positions sp The probe length lp is adjusted to obtain
antenna impedance matching and the probe distance sp is adjusted to obtain a
-53-
desired resonant frequency
Next a transition between rectangular and circular waveguide is designed
The transition section converts the TE10 mode in the rectangular waveguide to
TE11 mode in the circular waveguide and vice versa The transition is built
in a form of a taper for easy fabrication[22]
(a)
(b)
Fig 53 Structure of the rectangular-to-circular waveguide transition
(a) 3D view and (b) cross sectional view
The dimensions of the final optimized transition are as follows The length
of the rectangular waveguide section is 143mm The rectangular waveguides
width a and height b are 207mm and 857mm respectively The length of
the circular waveguide section is 143mm The inside diameter of the circular
-54-
waveguide is 207mm(097 wavelength at 14GHz) The length of transition
region ltr is 4465mm(approximately equal to 2λ0 at 14GHz) Fig 54 shows
the field distribution inside the mode converter
(a)
(b)
Fig 54 Field distribution inside the mode converter at
(a) 10GHz (b) 14GHz and (c) 18GHz
-55-
(c)
Fig 54 continued
Finally multiple chokes are investigated Figs 55 56 and 57 show the
feed performance without chokes The reflection coefficient is less than -10dB
over 10-19GHz The antenna has a gain of 921dB to 1189dB over
10-19GHz
Fig 55 Reflection coefficient of the broadband circular waveguide feed
without chokes and corrugations
-56-
(a)
(b)
(c)
Fig 56 E- and H-plane patterns of the broadband circular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-57-
(d)
(e)
Fig 56 continued
-58-
(a)
(b)
Fig 57 2D radiation patterns of the broadband cicular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-59-
(c)
(d)
Fig 57 continued
-60-
(e)
Fig 57 continued
To achieve equal beamwidths in E and H planes over a wide frequency
range chokes and corrugations are employed Table51 summarizes the
performance of a feed without chokes and corrugations
Table 51 Performance of the broadband circular waveguide feed without
chokes and corrugations
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
1000 940 6061 15
1200 972 6159 17
1400 920 5957 21
1600 1070 4751 29
1800 1188 5352 21
-61-
Four quarter-wavelength chokes are introduced in the feed design which
has a slot depth of 75mm and slot width of 09mm The choke slot spacing
is 18mm The choke design is investigated by applying the choke one by
one and the effect on the E- and H-plane patterns are observed as illustrated
in Figs 58 and 59 The use of chokes makes the E-plane pattern narrower
The H-plane pattern is not affected Chokes increase the gain slightly and
reduce back radiation
(a)
(b)
Fig 58 Effect of chokes on the E-plane pattern of the broadband circular
waveguide feed at (a) 10GHz(b) 12GHz (c) 14GHz (d) 16GHz and (e)
18GHz
-62-
(c)
(d)
(e)
Fig 58 continued
-63-
(a)
(b)
(c)
Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-64-
(d)
(e)
Fig 59 continued
-65-
Fig 510 shows the feed performance versus the choke depth When the
choke depth is varied from 535mm to 95mm the E- and H-plane patterns
are strongly affected The optimum value of choke depth is 75mm(035λ0 at
14GHz) which gives equal E- and H-plane radiation patterns and leads to
low back radiation
Fig 511 shows the feed performance versus the choke slot width tch The
choke slot width is varied from 09mm to 21mm Radiation patterns and
reflection coefficients are not sensitive to the choke slot width The final
choke slot width is selected to be 09mm considering the feed diameter
minimization and the manufacturability The overall diameter of the proposed
feed is 369mm which is increased from the 207mm of the waveguide
inside diameter due to the use of four chokes
-66-
(a)
(b)
(c)
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection coefficient
-67-
(a)
(b)
(c)
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and (c)
reflection coefficient
-68-
Next we investigated corrugations placed on the outer wall of the feed
Four corrugations applied to the outer surface of the circular waveguide The
corrugation depth is 465mm(0215λ0 at 14GHz) The primary purpose of
using corrugations is to further reduce the back radiation Increasing the
number of corrugations beyond four has little effect in reducing the back
radiation
Figs 512 and 513 show the effect of corrugations on the E- and H-plane
patterns Fig 514 shows the parametric study of the corrugation depth lcor
The corrugation depth is varied from 40mm and 645mm The optimum
value of the corrugation depth is found to be 465mm
-69-
(a)
(b)
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern at (a) 12GHz and (b) 14GHz
-70-
(a)
(b)
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern at (a) 12GHz and (b) 14GHz
-71-
(a)
(b)
(c)
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection coefficient
-72-
The phase center location is important in placing the feed in a reflector
antenna[8] The phase center variation with frequency should be small Fig
515 shows the effect of chokes and corrugations on the phase center The
curve with circle corresponds to the case without chokes and corrugations
The phase center varies from -326mm and -190mm away from the feeds
aperture plane It means the phase center is located inside the waveguide
The curve with triangles corresponds to the case with chokes The curve with
squares to the case with chokes and corrugations The phase center varies
from 0mm to -302mm
From Fig 515 we can observed that phase center variation reduced by the
corrugation and three cases phase center calculated in φ=450 plane
parameter sweep values are given in Table 52
10 12 14 16 181
0
-1
-2
-3
-4
-5
-6
Pha
se c
ente
r (m
m)
Frequency (GHz)
choke+corrugatuion without choke corrugation with choke
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
-73-
Frequency
(GHz)
Phase center from the aperture plane
(mm)
Without
chokes and
corrugations
With
chokes
With chokes
and
corrugations
1000 -326 062 000
1100 -187 030 -002
1200 -563 -208 -065
1300 -296 -154 -202
1400 -319 -314 -302
1500 -201 -203 -241
1600 -242 -233 -207
1700 -208 -208 -186
1800 -190 -157 -132
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
Based on the foregoing parametric studies optimum dimensions of the
broadband circular waveguide feed are obtained as shown in Table 53
-74-
Table 53 Optimum dimensions of the broadband circular waveguide feed
Parameter Designation Value (mm)
2a Waveguide inside diameter 2070
d Waveguide outside diameter 3690
lcrLength of the circular waveguide section 1430
m Distance between the aperture plane and the first corrugation 950
xDistance from the last corrugation to the end of the cylindrical outer surface
550
ltrLength of the rectangular-to-circularwaveguide transition 4465
lrcLength of the rectangular waveguide section 1430
tch Choke slot width 090
lch Choke depth 750
t Choke metal width 090
lcor Corrugation depth 465
tcor Corrugation metal width 100
s Corrugation slot width 10
lp Probe length 530
sp Probe position from the back short 530
din Probe diameter 127
b Inside height of the rectangular waveguide 857
tw Waveguide wall thickness 500
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-33-
From the above parametric analysis an optimum feed design is obtained
The result is shown in Table 31 Fig 37 shows the 2D gain patterns of
designed feed The antenna has a gain of 903dB 933dB and 956dB at
171GHz 1825GHz and 19GHz respectively
Fig 38 shows E- and H-plane radiation patterns of the designed feed The
feed has E- and H-plane 10-dB beamwidths of 60 and 59 degrees at 17GHz
The feed has a front-to-back ration of 1900dB 2490dB and 2200dB at
171GHz 1825GHz and 19GHz respectively Table 32 summarizes the
performance of the designed narrow-band circular waveguide feed
The designed feed has a greatly improved performance over that of a
simple coax-fed feed described in Section 23
Table 31 Dimensions of the designed narrow-band circular feed
Parameter Designation Value(mm)
a Waveguide inside radius 640
l Feed length 2890
lp Probe length 363
sp Probe position from the back short 616
din Probe diameter 127
dout Diameter of coaxial cables outer conductor 400
t Thickness of choked wall 050
tch Choke slot width 100
lch Choke depth 410
ld Dielectric ring length 1168
td Dielectric ring thickness 155
d1 Waveguide outside diameter 1680
-34-
(a)
(b)
Fig 37 2D gain patterns of the narrow-band circular waveguide feed at
(a) 17GHz (b) 1825GHz and (c) 19GHz
-35-
(c)
Fig 37 continued
-36-
(a)
(b)
(c)
Fig 38 E- and H-plane patterns of the narrow-band circular waveguide feed
at (a) 10GHz (b) 1825GHz and (c) 195GHz
-37-
Frequency(GHz)
Gain(dB)
E-H-plane10-dB beamwidths
(deg)
Front-to-back ratio(dB)
Phase centerlocation
(From feeds aperture plane
toward reflector)
(mm)
1700 903 6059 20 062
1825 933 6060 25 004
1900 956 5759 22 007
Table 32 Performance of the narrow-band circular waveguide feed
The designed narrow-band feed is fabricated and its performance is
measured and compared with the simulation results The designed feed is
fabricated in a numerically-controlled machining center The fabricated antenna
is shown in Fig 39
Fig 39 Photograph of the fabricated feed
-38-
Fig 310 shows a comparison of the measured and simulated reflection
coefficients The measured reflection coefficient is less than -10dB over
171-197GHz The agreement between simulated and measured results are
good
Fig 311 shows the E- and H-plane patterns of the fabricated feed at
187GHz The feed has 90dB gain simulation and measurement results are in
good agreement
The fabricated antennarsquos 10dB beamwidth is 60 degrees in both E and H
planes at 187GHz The front-to-back ratio is 21dB
Fig 310 Reflection coefficient of the fabricated feed
-39-
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Fee
d H
orn
Gain
- d
B
Angle - degree
(a)
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Feed H
orn
Gain
- d
B
Angle - degree
(b)
Fig 311 Gain patterns of the fabricated feed at 187 GHz (a) E-plane and
(b) H-plane
-40-
IV Design of Circular Waveguide Feeds Loaded with a
Dielectric Rod
In this section circular waveguide feeds loaded with a dielectric rod feed
are investigated A comprehensive discussion of the circular waveguide loaded
with a dielectric rod is given by Kumar[7] Inserting a dielectric material
inside the circular waveguide improves the E- and H-plane pattern symmetry
In general dielectric-loaded circular waveguide feeds show good performance
only over a narrow bandwidth
Fig 41 shows the geometry of a circular waveguide loaded with a
dielectric rod The waveguide length is 400mm and the wall thickness is
05mm The dielectric rods diameter is 207mm The dielectric rod is
extended 05 wavelength beyond the waveguide open end The dielectric
constant εr is changed and the feeds performance is observed
Fig 41 Geometry of a circular waveguide loaded with a uniform dielectric
rod
-41-
Fig 42 is the radiation pattern of the feed with εr = 25 and L = 05λ0 at
9GHz E- and H-plane 10-dB beamwidths are 810 and 807 degrees
respectively The front-to-back ratio is 18dB The antenna gain is 71dB
(a)
(b)
Fig 42 Radiation pattern at 9GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 05λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-42-
Fig 43 shows the radiation pattern of the feed with εr = 21 at 10GHz
E- and H-plane 10-dB beamwidths are 70 and 71 degrees respectively The
front-to-back ratio is 19dB The antenna gain is 83dB
(a)
(b)
Fig 43 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 21 and L = 05λ0 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-43-
Fig 44 shows the radiation pattern of the feed with εr = 30 at 8GHz
E- and H-plane 10-dB beamwidths are 83 and 824 degrees respectively The
front-to-back ratio is 17dB The antenna gain is 73dB
(a)
(b)
Fig 44 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 30 and L = 05λ0 at 8GHz (a) 2D radiation pattern
and (b) E- and H-plane patterns
-44-
Fig 45 shows the radiation pattern of the feed with εr = 50 at 18GHz
E- and H-plane 10-dB beamwidths are 56 and 54 degrees respectively The
front-to-back ratio is 27dB The antenna gain is 105dB The feed has a good
pattern symmetry and low back radiation
(a)
(b)
Fig 45 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 50 and L = 05λ0 at 18GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-45-
Fig 46 is the radiation pattern of the feed with εr = 25 and L = 10λ0 at
10GHz E- and H-plane 10-dB beamwidths are 50 and 48 degrees
respectively The front-to-back ratio is 16dB The antenna gain is 105dB
(a)
(b)
Fig 46 Radiation pattern at 10GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 10λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-46-
Fig 47 shows the geometry of a circular waveguide with a tapered
dielectric rod The designed feed has the following dimension L = 1λ0 d =
1λ0 and εr =25 at 10GHz The waveguide length is 40mm and the wall
thickness is 05mm
L
Dielectricd3
Fig 47 Geometry of a circular waveguide loaded with a tapered dielectric
rod
Fig 48 shows the radiatio pattern of the designed feed E- and H-plane
10-dB beamwidths are 575 and 564 degrees respectively The front-to-back
ratio is 377dB The antenna gain is 94dB The designed feed has an
excellent beamwidth symmetry and a very low back radiation
-47-
(a)
(b)
Fig 48 Radiation pattern of a circular waveguide loaded with a tapered
dielectric rod with L = 1λ0 d = 1λ0 and εr =25 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-48-
Fig 49 shows the geometry of a spherical ended dielectric rod feed
diameter of 06λ0 at 10GHz with a dielectric constant of 25 and L= 03λ0
Fig 410 shows the radiation patterns of the designed feed E- and H-plane
10-dB beamwidths are both 63 degrees The front-to-back ratio is 24dB The
antenna gain is 864dB
Fig 49 Geometry of a circular waveguide loaded with a spherical ended
dielectric rod
-49-
(a)
(b)
Fig 410 Radiation pattern of a circular waveguide loaded wht a spherical
ended dielectric rod with d = 06λ0 L = 03λ0 and εr =25 at 10GHz (a) 3D
radiation pattern and (b) E- and H-plane patterns
-50-
V Design of a Broadband Circular Waveguide Feed
In this chapter the design of a broadband circular waveguide feed is
presented At microwave frequencies the feed is often a circular waveguide
with chokes and corrugations around the aperture Chokes and corrugations
equalize E- and H-plane patterns and reduce the back radiation
The proposed feed is designed to operate over 10-18GHz The design starts
with the optimization of the coaxial-to-rectangular waveguide adapter
employed for good mode purity over a broad frequency range Next a
rectangular-to-circular waveguide transition is optimized Finally chokes and
corrugations are designed for improved pattern symmetry and low back
radiation
The proposed feed structure is shown in Fig 51 The feed consist of the
following parts a coaxial-to-rectangular waveguide adapter a rectangular-to-
circular waveguide transition a circular waveguide section four quarter-wave
chokes around the feeds aperture and four corrugations on the feeds outer
surface
The computer simulation shows the above arrangement offers good radiation
patterns over a broad frequency range The broadband operation is obtained
by exciting the TE11 mode in the circular waveguide using the TE10 mode of
the rectangular waveguide which is in turn excited by a coaxial probe
-51-
Chokes
Coaxial-to-waveguide transition
Circular wavguide
Corrugations
Mode transition
(a)
(b)
Fig 51 Structure of the proposed broadband circular waveguide feed
(a) CAD model and (b) cross-sectional view
For the coaxial-to-rectangular waveguide adapter an SMA connector with
the probe diameter of 127 mm is employed The coaxial probe inserted into
the waveguide energizes the feed and excites the dominant TE10 mode in
-52-
the rectangular waveguide The impedance matching is achieved by adjusting
the probe distance sp from the back short and the probe length lp
(a)
(b)
Fig 52 Reflection coefficient of the coaxial-to-rectangular adapter versus
(a) probe length lp and (b) the probe position sp
Fig 52 shows the reflection coefficient versus the various values of probe
lengths lp and probe positions sp The probe length lp is adjusted to obtain
antenna impedance matching and the probe distance sp is adjusted to obtain a
-53-
desired resonant frequency
Next a transition between rectangular and circular waveguide is designed
The transition section converts the TE10 mode in the rectangular waveguide to
TE11 mode in the circular waveguide and vice versa The transition is built
in a form of a taper for easy fabrication[22]
(a)
(b)
Fig 53 Structure of the rectangular-to-circular waveguide transition
(a) 3D view and (b) cross sectional view
The dimensions of the final optimized transition are as follows The length
of the rectangular waveguide section is 143mm The rectangular waveguides
width a and height b are 207mm and 857mm respectively The length of
the circular waveguide section is 143mm The inside diameter of the circular
-54-
waveguide is 207mm(097 wavelength at 14GHz) The length of transition
region ltr is 4465mm(approximately equal to 2λ0 at 14GHz) Fig 54 shows
the field distribution inside the mode converter
(a)
(b)
Fig 54 Field distribution inside the mode converter at
(a) 10GHz (b) 14GHz and (c) 18GHz
-55-
(c)
Fig 54 continued
Finally multiple chokes are investigated Figs 55 56 and 57 show the
feed performance without chokes The reflection coefficient is less than -10dB
over 10-19GHz The antenna has a gain of 921dB to 1189dB over
10-19GHz
Fig 55 Reflection coefficient of the broadband circular waveguide feed
without chokes and corrugations
-56-
(a)
(b)
(c)
Fig 56 E- and H-plane patterns of the broadband circular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-57-
(d)
(e)
Fig 56 continued
-58-
(a)
(b)
Fig 57 2D radiation patterns of the broadband cicular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-59-
(c)
(d)
Fig 57 continued
-60-
(e)
Fig 57 continued
To achieve equal beamwidths in E and H planes over a wide frequency
range chokes and corrugations are employed Table51 summarizes the
performance of a feed without chokes and corrugations
Table 51 Performance of the broadband circular waveguide feed without
chokes and corrugations
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
1000 940 6061 15
1200 972 6159 17
1400 920 5957 21
1600 1070 4751 29
1800 1188 5352 21
-61-
Four quarter-wavelength chokes are introduced in the feed design which
has a slot depth of 75mm and slot width of 09mm The choke slot spacing
is 18mm The choke design is investigated by applying the choke one by
one and the effect on the E- and H-plane patterns are observed as illustrated
in Figs 58 and 59 The use of chokes makes the E-plane pattern narrower
The H-plane pattern is not affected Chokes increase the gain slightly and
reduce back radiation
(a)
(b)
Fig 58 Effect of chokes on the E-plane pattern of the broadband circular
waveguide feed at (a) 10GHz(b) 12GHz (c) 14GHz (d) 16GHz and (e)
18GHz
-62-
(c)
(d)
(e)
Fig 58 continued
-63-
(a)
(b)
(c)
Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-64-
(d)
(e)
Fig 59 continued
-65-
Fig 510 shows the feed performance versus the choke depth When the
choke depth is varied from 535mm to 95mm the E- and H-plane patterns
are strongly affected The optimum value of choke depth is 75mm(035λ0 at
14GHz) which gives equal E- and H-plane radiation patterns and leads to
low back radiation
Fig 511 shows the feed performance versus the choke slot width tch The
choke slot width is varied from 09mm to 21mm Radiation patterns and
reflection coefficients are not sensitive to the choke slot width The final
choke slot width is selected to be 09mm considering the feed diameter
minimization and the manufacturability The overall diameter of the proposed
feed is 369mm which is increased from the 207mm of the waveguide
inside diameter due to the use of four chokes
-66-
(a)
(b)
(c)
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection coefficient
-67-
(a)
(b)
(c)
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and (c)
reflection coefficient
-68-
Next we investigated corrugations placed on the outer wall of the feed
Four corrugations applied to the outer surface of the circular waveguide The
corrugation depth is 465mm(0215λ0 at 14GHz) The primary purpose of
using corrugations is to further reduce the back radiation Increasing the
number of corrugations beyond four has little effect in reducing the back
radiation
Figs 512 and 513 show the effect of corrugations on the E- and H-plane
patterns Fig 514 shows the parametric study of the corrugation depth lcor
The corrugation depth is varied from 40mm and 645mm The optimum
value of the corrugation depth is found to be 465mm
-69-
(a)
(b)
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern at (a) 12GHz and (b) 14GHz
-70-
(a)
(b)
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern at (a) 12GHz and (b) 14GHz
-71-
(a)
(b)
(c)
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection coefficient
-72-
The phase center location is important in placing the feed in a reflector
antenna[8] The phase center variation with frequency should be small Fig
515 shows the effect of chokes and corrugations on the phase center The
curve with circle corresponds to the case without chokes and corrugations
The phase center varies from -326mm and -190mm away from the feeds
aperture plane It means the phase center is located inside the waveguide
The curve with triangles corresponds to the case with chokes The curve with
squares to the case with chokes and corrugations The phase center varies
from 0mm to -302mm
From Fig 515 we can observed that phase center variation reduced by the
corrugation and three cases phase center calculated in φ=450 plane
parameter sweep values are given in Table 52
10 12 14 16 181
0
-1
-2
-3
-4
-5
-6
Pha
se c
ente
r (m
m)
Frequency (GHz)
choke+corrugatuion without choke corrugation with choke
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
-73-
Frequency
(GHz)
Phase center from the aperture plane
(mm)
Without
chokes and
corrugations
With
chokes
With chokes
and
corrugations
1000 -326 062 000
1100 -187 030 -002
1200 -563 -208 -065
1300 -296 -154 -202
1400 -319 -314 -302
1500 -201 -203 -241
1600 -242 -233 -207
1700 -208 -208 -186
1800 -190 -157 -132
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
Based on the foregoing parametric studies optimum dimensions of the
broadband circular waveguide feed are obtained as shown in Table 53
-74-
Table 53 Optimum dimensions of the broadband circular waveguide feed
Parameter Designation Value (mm)
2a Waveguide inside diameter 2070
d Waveguide outside diameter 3690
lcrLength of the circular waveguide section 1430
m Distance between the aperture plane and the first corrugation 950
xDistance from the last corrugation to the end of the cylindrical outer surface
550
ltrLength of the rectangular-to-circularwaveguide transition 4465
lrcLength of the rectangular waveguide section 1430
tch Choke slot width 090
lch Choke depth 750
t Choke metal width 090
lcor Corrugation depth 465
tcor Corrugation metal width 100
s Corrugation slot width 10
lp Probe length 530
sp Probe position from the back short 530
din Probe diameter 127
b Inside height of the rectangular waveguide 857
tw Waveguide wall thickness 500
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-34-
(a)
(b)
Fig 37 2D gain patterns of the narrow-band circular waveguide feed at
(a) 17GHz (b) 1825GHz and (c) 19GHz
-35-
(c)
Fig 37 continued
-36-
(a)
(b)
(c)
Fig 38 E- and H-plane patterns of the narrow-band circular waveguide feed
at (a) 10GHz (b) 1825GHz and (c) 195GHz
-37-
Frequency(GHz)
Gain(dB)
E-H-plane10-dB beamwidths
(deg)
Front-to-back ratio(dB)
Phase centerlocation
(From feeds aperture plane
toward reflector)
(mm)
1700 903 6059 20 062
1825 933 6060 25 004
1900 956 5759 22 007
Table 32 Performance of the narrow-band circular waveguide feed
The designed narrow-band feed is fabricated and its performance is
measured and compared with the simulation results The designed feed is
fabricated in a numerically-controlled machining center The fabricated antenna
is shown in Fig 39
Fig 39 Photograph of the fabricated feed
-38-
Fig 310 shows a comparison of the measured and simulated reflection
coefficients The measured reflection coefficient is less than -10dB over
171-197GHz The agreement between simulated and measured results are
good
Fig 311 shows the E- and H-plane patterns of the fabricated feed at
187GHz The feed has 90dB gain simulation and measurement results are in
good agreement
The fabricated antennarsquos 10dB beamwidth is 60 degrees in both E and H
planes at 187GHz The front-to-back ratio is 21dB
Fig 310 Reflection coefficient of the fabricated feed
-39-
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Fee
d H
orn
Gain
- d
B
Angle - degree
(a)
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Feed H
orn
Gain
- d
B
Angle - degree
(b)
Fig 311 Gain patterns of the fabricated feed at 187 GHz (a) E-plane and
(b) H-plane
-40-
IV Design of Circular Waveguide Feeds Loaded with a
Dielectric Rod
In this section circular waveguide feeds loaded with a dielectric rod feed
are investigated A comprehensive discussion of the circular waveguide loaded
with a dielectric rod is given by Kumar[7] Inserting a dielectric material
inside the circular waveguide improves the E- and H-plane pattern symmetry
In general dielectric-loaded circular waveguide feeds show good performance
only over a narrow bandwidth
Fig 41 shows the geometry of a circular waveguide loaded with a
dielectric rod The waveguide length is 400mm and the wall thickness is
05mm The dielectric rods diameter is 207mm The dielectric rod is
extended 05 wavelength beyond the waveguide open end The dielectric
constant εr is changed and the feeds performance is observed
Fig 41 Geometry of a circular waveguide loaded with a uniform dielectric
rod
-41-
Fig 42 is the radiation pattern of the feed with εr = 25 and L = 05λ0 at
9GHz E- and H-plane 10-dB beamwidths are 810 and 807 degrees
respectively The front-to-back ratio is 18dB The antenna gain is 71dB
(a)
(b)
Fig 42 Radiation pattern at 9GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 05λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-42-
Fig 43 shows the radiation pattern of the feed with εr = 21 at 10GHz
E- and H-plane 10-dB beamwidths are 70 and 71 degrees respectively The
front-to-back ratio is 19dB The antenna gain is 83dB
(a)
(b)
Fig 43 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 21 and L = 05λ0 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-43-
Fig 44 shows the radiation pattern of the feed with εr = 30 at 8GHz
E- and H-plane 10-dB beamwidths are 83 and 824 degrees respectively The
front-to-back ratio is 17dB The antenna gain is 73dB
(a)
(b)
Fig 44 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 30 and L = 05λ0 at 8GHz (a) 2D radiation pattern
and (b) E- and H-plane patterns
-44-
Fig 45 shows the radiation pattern of the feed with εr = 50 at 18GHz
E- and H-plane 10-dB beamwidths are 56 and 54 degrees respectively The
front-to-back ratio is 27dB The antenna gain is 105dB The feed has a good
pattern symmetry and low back radiation
(a)
(b)
Fig 45 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 50 and L = 05λ0 at 18GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-45-
Fig 46 is the radiation pattern of the feed with εr = 25 and L = 10λ0 at
10GHz E- and H-plane 10-dB beamwidths are 50 and 48 degrees
respectively The front-to-back ratio is 16dB The antenna gain is 105dB
(a)
(b)
Fig 46 Radiation pattern at 10GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 10λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-46-
Fig 47 shows the geometry of a circular waveguide with a tapered
dielectric rod The designed feed has the following dimension L = 1λ0 d =
1λ0 and εr =25 at 10GHz The waveguide length is 40mm and the wall
thickness is 05mm
L
Dielectricd3
Fig 47 Geometry of a circular waveguide loaded with a tapered dielectric
rod
Fig 48 shows the radiatio pattern of the designed feed E- and H-plane
10-dB beamwidths are 575 and 564 degrees respectively The front-to-back
ratio is 377dB The antenna gain is 94dB The designed feed has an
excellent beamwidth symmetry and a very low back radiation
-47-
(a)
(b)
Fig 48 Radiation pattern of a circular waveguide loaded with a tapered
dielectric rod with L = 1λ0 d = 1λ0 and εr =25 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-48-
Fig 49 shows the geometry of a spherical ended dielectric rod feed
diameter of 06λ0 at 10GHz with a dielectric constant of 25 and L= 03λ0
Fig 410 shows the radiation patterns of the designed feed E- and H-plane
10-dB beamwidths are both 63 degrees The front-to-back ratio is 24dB The
antenna gain is 864dB
Fig 49 Geometry of a circular waveguide loaded with a spherical ended
dielectric rod
-49-
(a)
(b)
Fig 410 Radiation pattern of a circular waveguide loaded wht a spherical
ended dielectric rod with d = 06λ0 L = 03λ0 and εr =25 at 10GHz (a) 3D
radiation pattern and (b) E- and H-plane patterns
-50-
V Design of a Broadband Circular Waveguide Feed
In this chapter the design of a broadband circular waveguide feed is
presented At microwave frequencies the feed is often a circular waveguide
with chokes and corrugations around the aperture Chokes and corrugations
equalize E- and H-plane patterns and reduce the back radiation
The proposed feed is designed to operate over 10-18GHz The design starts
with the optimization of the coaxial-to-rectangular waveguide adapter
employed for good mode purity over a broad frequency range Next a
rectangular-to-circular waveguide transition is optimized Finally chokes and
corrugations are designed for improved pattern symmetry and low back
radiation
The proposed feed structure is shown in Fig 51 The feed consist of the
following parts a coaxial-to-rectangular waveguide adapter a rectangular-to-
circular waveguide transition a circular waveguide section four quarter-wave
chokes around the feeds aperture and four corrugations on the feeds outer
surface
The computer simulation shows the above arrangement offers good radiation
patterns over a broad frequency range The broadband operation is obtained
by exciting the TE11 mode in the circular waveguide using the TE10 mode of
the rectangular waveguide which is in turn excited by a coaxial probe
-51-
Chokes
Coaxial-to-waveguide transition
Circular wavguide
Corrugations
Mode transition
(a)
(b)
Fig 51 Structure of the proposed broadband circular waveguide feed
(a) CAD model and (b) cross-sectional view
For the coaxial-to-rectangular waveguide adapter an SMA connector with
the probe diameter of 127 mm is employed The coaxial probe inserted into
the waveguide energizes the feed and excites the dominant TE10 mode in
-52-
the rectangular waveguide The impedance matching is achieved by adjusting
the probe distance sp from the back short and the probe length lp
(a)
(b)
Fig 52 Reflection coefficient of the coaxial-to-rectangular adapter versus
(a) probe length lp and (b) the probe position sp
Fig 52 shows the reflection coefficient versus the various values of probe
lengths lp and probe positions sp The probe length lp is adjusted to obtain
antenna impedance matching and the probe distance sp is adjusted to obtain a
-53-
desired resonant frequency
Next a transition between rectangular and circular waveguide is designed
The transition section converts the TE10 mode in the rectangular waveguide to
TE11 mode in the circular waveguide and vice versa The transition is built
in a form of a taper for easy fabrication[22]
(a)
(b)
Fig 53 Structure of the rectangular-to-circular waveguide transition
(a) 3D view and (b) cross sectional view
The dimensions of the final optimized transition are as follows The length
of the rectangular waveguide section is 143mm The rectangular waveguides
width a and height b are 207mm and 857mm respectively The length of
the circular waveguide section is 143mm The inside diameter of the circular
-54-
waveguide is 207mm(097 wavelength at 14GHz) The length of transition
region ltr is 4465mm(approximately equal to 2λ0 at 14GHz) Fig 54 shows
the field distribution inside the mode converter
(a)
(b)
Fig 54 Field distribution inside the mode converter at
(a) 10GHz (b) 14GHz and (c) 18GHz
-55-
(c)
Fig 54 continued
Finally multiple chokes are investigated Figs 55 56 and 57 show the
feed performance without chokes The reflection coefficient is less than -10dB
over 10-19GHz The antenna has a gain of 921dB to 1189dB over
10-19GHz
Fig 55 Reflection coefficient of the broadband circular waveguide feed
without chokes and corrugations
-56-
(a)
(b)
(c)
Fig 56 E- and H-plane patterns of the broadband circular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-57-
(d)
(e)
Fig 56 continued
-58-
(a)
(b)
Fig 57 2D radiation patterns of the broadband cicular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-59-
(c)
(d)
Fig 57 continued
-60-
(e)
Fig 57 continued
To achieve equal beamwidths in E and H planes over a wide frequency
range chokes and corrugations are employed Table51 summarizes the
performance of a feed without chokes and corrugations
Table 51 Performance of the broadband circular waveguide feed without
chokes and corrugations
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
1000 940 6061 15
1200 972 6159 17
1400 920 5957 21
1600 1070 4751 29
1800 1188 5352 21
-61-
Four quarter-wavelength chokes are introduced in the feed design which
has a slot depth of 75mm and slot width of 09mm The choke slot spacing
is 18mm The choke design is investigated by applying the choke one by
one and the effect on the E- and H-plane patterns are observed as illustrated
in Figs 58 and 59 The use of chokes makes the E-plane pattern narrower
The H-plane pattern is not affected Chokes increase the gain slightly and
reduce back radiation
(a)
(b)
Fig 58 Effect of chokes on the E-plane pattern of the broadband circular
waveguide feed at (a) 10GHz(b) 12GHz (c) 14GHz (d) 16GHz and (e)
18GHz
-62-
(c)
(d)
(e)
Fig 58 continued
-63-
(a)
(b)
(c)
Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-64-
(d)
(e)
Fig 59 continued
-65-
Fig 510 shows the feed performance versus the choke depth When the
choke depth is varied from 535mm to 95mm the E- and H-plane patterns
are strongly affected The optimum value of choke depth is 75mm(035λ0 at
14GHz) which gives equal E- and H-plane radiation patterns and leads to
low back radiation
Fig 511 shows the feed performance versus the choke slot width tch The
choke slot width is varied from 09mm to 21mm Radiation patterns and
reflection coefficients are not sensitive to the choke slot width The final
choke slot width is selected to be 09mm considering the feed diameter
minimization and the manufacturability The overall diameter of the proposed
feed is 369mm which is increased from the 207mm of the waveguide
inside diameter due to the use of four chokes
-66-
(a)
(b)
(c)
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection coefficient
-67-
(a)
(b)
(c)
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and (c)
reflection coefficient
-68-
Next we investigated corrugations placed on the outer wall of the feed
Four corrugations applied to the outer surface of the circular waveguide The
corrugation depth is 465mm(0215λ0 at 14GHz) The primary purpose of
using corrugations is to further reduce the back radiation Increasing the
number of corrugations beyond four has little effect in reducing the back
radiation
Figs 512 and 513 show the effect of corrugations on the E- and H-plane
patterns Fig 514 shows the parametric study of the corrugation depth lcor
The corrugation depth is varied from 40mm and 645mm The optimum
value of the corrugation depth is found to be 465mm
-69-
(a)
(b)
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern at (a) 12GHz and (b) 14GHz
-70-
(a)
(b)
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern at (a) 12GHz and (b) 14GHz
-71-
(a)
(b)
(c)
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection coefficient
-72-
The phase center location is important in placing the feed in a reflector
antenna[8] The phase center variation with frequency should be small Fig
515 shows the effect of chokes and corrugations on the phase center The
curve with circle corresponds to the case without chokes and corrugations
The phase center varies from -326mm and -190mm away from the feeds
aperture plane It means the phase center is located inside the waveguide
The curve with triangles corresponds to the case with chokes The curve with
squares to the case with chokes and corrugations The phase center varies
from 0mm to -302mm
From Fig 515 we can observed that phase center variation reduced by the
corrugation and three cases phase center calculated in φ=450 plane
parameter sweep values are given in Table 52
10 12 14 16 181
0
-1
-2
-3
-4
-5
-6
Pha
se c
ente
r (m
m)
Frequency (GHz)
choke+corrugatuion without choke corrugation with choke
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
-73-
Frequency
(GHz)
Phase center from the aperture plane
(mm)
Without
chokes and
corrugations
With
chokes
With chokes
and
corrugations
1000 -326 062 000
1100 -187 030 -002
1200 -563 -208 -065
1300 -296 -154 -202
1400 -319 -314 -302
1500 -201 -203 -241
1600 -242 -233 -207
1700 -208 -208 -186
1800 -190 -157 -132
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
Based on the foregoing parametric studies optimum dimensions of the
broadband circular waveguide feed are obtained as shown in Table 53
-74-
Table 53 Optimum dimensions of the broadband circular waveguide feed
Parameter Designation Value (mm)
2a Waveguide inside diameter 2070
d Waveguide outside diameter 3690
lcrLength of the circular waveguide section 1430
m Distance between the aperture plane and the first corrugation 950
xDistance from the last corrugation to the end of the cylindrical outer surface
550
ltrLength of the rectangular-to-circularwaveguide transition 4465
lrcLength of the rectangular waveguide section 1430
tch Choke slot width 090
lch Choke depth 750
t Choke metal width 090
lcor Corrugation depth 465
tcor Corrugation metal width 100
s Corrugation slot width 10
lp Probe length 530
sp Probe position from the back short 530
din Probe diameter 127
b Inside height of the rectangular waveguide 857
tw Waveguide wall thickness 500
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-35-
(c)
Fig 37 continued
-36-
(a)
(b)
(c)
Fig 38 E- and H-plane patterns of the narrow-band circular waveguide feed
at (a) 10GHz (b) 1825GHz and (c) 195GHz
-37-
Frequency(GHz)
Gain(dB)
E-H-plane10-dB beamwidths
(deg)
Front-to-back ratio(dB)
Phase centerlocation
(From feeds aperture plane
toward reflector)
(mm)
1700 903 6059 20 062
1825 933 6060 25 004
1900 956 5759 22 007
Table 32 Performance of the narrow-band circular waveguide feed
The designed narrow-band feed is fabricated and its performance is
measured and compared with the simulation results The designed feed is
fabricated in a numerically-controlled machining center The fabricated antenna
is shown in Fig 39
Fig 39 Photograph of the fabricated feed
-38-
Fig 310 shows a comparison of the measured and simulated reflection
coefficients The measured reflection coefficient is less than -10dB over
171-197GHz The agreement between simulated and measured results are
good
Fig 311 shows the E- and H-plane patterns of the fabricated feed at
187GHz The feed has 90dB gain simulation and measurement results are in
good agreement
The fabricated antennarsquos 10dB beamwidth is 60 degrees in both E and H
planes at 187GHz The front-to-back ratio is 21dB
Fig 310 Reflection coefficient of the fabricated feed
-39-
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Fee
d H
orn
Gain
- d
B
Angle - degree
(a)
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Feed H
orn
Gain
- d
B
Angle - degree
(b)
Fig 311 Gain patterns of the fabricated feed at 187 GHz (a) E-plane and
(b) H-plane
-40-
IV Design of Circular Waveguide Feeds Loaded with a
Dielectric Rod
In this section circular waveguide feeds loaded with a dielectric rod feed
are investigated A comprehensive discussion of the circular waveguide loaded
with a dielectric rod is given by Kumar[7] Inserting a dielectric material
inside the circular waveguide improves the E- and H-plane pattern symmetry
In general dielectric-loaded circular waveguide feeds show good performance
only over a narrow bandwidth
Fig 41 shows the geometry of a circular waveguide loaded with a
dielectric rod The waveguide length is 400mm and the wall thickness is
05mm The dielectric rods diameter is 207mm The dielectric rod is
extended 05 wavelength beyond the waveguide open end The dielectric
constant εr is changed and the feeds performance is observed
Fig 41 Geometry of a circular waveguide loaded with a uniform dielectric
rod
-41-
Fig 42 is the radiation pattern of the feed with εr = 25 and L = 05λ0 at
9GHz E- and H-plane 10-dB beamwidths are 810 and 807 degrees
respectively The front-to-back ratio is 18dB The antenna gain is 71dB
(a)
(b)
Fig 42 Radiation pattern at 9GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 05λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-42-
Fig 43 shows the radiation pattern of the feed with εr = 21 at 10GHz
E- and H-plane 10-dB beamwidths are 70 and 71 degrees respectively The
front-to-back ratio is 19dB The antenna gain is 83dB
(a)
(b)
Fig 43 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 21 and L = 05λ0 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-43-
Fig 44 shows the radiation pattern of the feed with εr = 30 at 8GHz
E- and H-plane 10-dB beamwidths are 83 and 824 degrees respectively The
front-to-back ratio is 17dB The antenna gain is 73dB
(a)
(b)
Fig 44 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 30 and L = 05λ0 at 8GHz (a) 2D radiation pattern
and (b) E- and H-plane patterns
-44-
Fig 45 shows the radiation pattern of the feed with εr = 50 at 18GHz
E- and H-plane 10-dB beamwidths are 56 and 54 degrees respectively The
front-to-back ratio is 27dB The antenna gain is 105dB The feed has a good
pattern symmetry and low back radiation
(a)
(b)
Fig 45 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 50 and L = 05λ0 at 18GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-45-
Fig 46 is the radiation pattern of the feed with εr = 25 and L = 10λ0 at
10GHz E- and H-plane 10-dB beamwidths are 50 and 48 degrees
respectively The front-to-back ratio is 16dB The antenna gain is 105dB
(a)
(b)
Fig 46 Radiation pattern at 10GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 10λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-46-
Fig 47 shows the geometry of a circular waveguide with a tapered
dielectric rod The designed feed has the following dimension L = 1λ0 d =
1λ0 and εr =25 at 10GHz The waveguide length is 40mm and the wall
thickness is 05mm
L
Dielectricd3
Fig 47 Geometry of a circular waveguide loaded with a tapered dielectric
rod
Fig 48 shows the radiatio pattern of the designed feed E- and H-plane
10-dB beamwidths are 575 and 564 degrees respectively The front-to-back
ratio is 377dB The antenna gain is 94dB The designed feed has an
excellent beamwidth symmetry and a very low back radiation
-47-
(a)
(b)
Fig 48 Radiation pattern of a circular waveguide loaded with a tapered
dielectric rod with L = 1λ0 d = 1λ0 and εr =25 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-48-
Fig 49 shows the geometry of a spherical ended dielectric rod feed
diameter of 06λ0 at 10GHz with a dielectric constant of 25 and L= 03λ0
Fig 410 shows the radiation patterns of the designed feed E- and H-plane
10-dB beamwidths are both 63 degrees The front-to-back ratio is 24dB The
antenna gain is 864dB
Fig 49 Geometry of a circular waveguide loaded with a spherical ended
dielectric rod
-49-
(a)
(b)
Fig 410 Radiation pattern of a circular waveguide loaded wht a spherical
ended dielectric rod with d = 06λ0 L = 03λ0 and εr =25 at 10GHz (a) 3D
radiation pattern and (b) E- and H-plane patterns
-50-
V Design of a Broadband Circular Waveguide Feed
In this chapter the design of a broadband circular waveguide feed is
presented At microwave frequencies the feed is often a circular waveguide
with chokes and corrugations around the aperture Chokes and corrugations
equalize E- and H-plane patterns and reduce the back radiation
The proposed feed is designed to operate over 10-18GHz The design starts
with the optimization of the coaxial-to-rectangular waveguide adapter
employed for good mode purity over a broad frequency range Next a
rectangular-to-circular waveguide transition is optimized Finally chokes and
corrugations are designed for improved pattern symmetry and low back
radiation
The proposed feed structure is shown in Fig 51 The feed consist of the
following parts a coaxial-to-rectangular waveguide adapter a rectangular-to-
circular waveguide transition a circular waveguide section four quarter-wave
chokes around the feeds aperture and four corrugations on the feeds outer
surface
The computer simulation shows the above arrangement offers good radiation
patterns over a broad frequency range The broadband operation is obtained
by exciting the TE11 mode in the circular waveguide using the TE10 mode of
the rectangular waveguide which is in turn excited by a coaxial probe
-51-
Chokes
Coaxial-to-waveguide transition
Circular wavguide
Corrugations
Mode transition
(a)
(b)
Fig 51 Structure of the proposed broadband circular waveguide feed
(a) CAD model and (b) cross-sectional view
For the coaxial-to-rectangular waveguide adapter an SMA connector with
the probe diameter of 127 mm is employed The coaxial probe inserted into
the waveguide energizes the feed and excites the dominant TE10 mode in
-52-
the rectangular waveguide The impedance matching is achieved by adjusting
the probe distance sp from the back short and the probe length lp
(a)
(b)
Fig 52 Reflection coefficient of the coaxial-to-rectangular adapter versus
(a) probe length lp and (b) the probe position sp
Fig 52 shows the reflection coefficient versus the various values of probe
lengths lp and probe positions sp The probe length lp is adjusted to obtain
antenna impedance matching and the probe distance sp is adjusted to obtain a
-53-
desired resonant frequency
Next a transition between rectangular and circular waveguide is designed
The transition section converts the TE10 mode in the rectangular waveguide to
TE11 mode in the circular waveguide and vice versa The transition is built
in a form of a taper for easy fabrication[22]
(a)
(b)
Fig 53 Structure of the rectangular-to-circular waveguide transition
(a) 3D view and (b) cross sectional view
The dimensions of the final optimized transition are as follows The length
of the rectangular waveguide section is 143mm The rectangular waveguides
width a and height b are 207mm and 857mm respectively The length of
the circular waveguide section is 143mm The inside diameter of the circular
-54-
waveguide is 207mm(097 wavelength at 14GHz) The length of transition
region ltr is 4465mm(approximately equal to 2λ0 at 14GHz) Fig 54 shows
the field distribution inside the mode converter
(a)
(b)
Fig 54 Field distribution inside the mode converter at
(a) 10GHz (b) 14GHz and (c) 18GHz
-55-
(c)
Fig 54 continued
Finally multiple chokes are investigated Figs 55 56 and 57 show the
feed performance without chokes The reflection coefficient is less than -10dB
over 10-19GHz The antenna has a gain of 921dB to 1189dB over
10-19GHz
Fig 55 Reflection coefficient of the broadband circular waveguide feed
without chokes and corrugations
-56-
(a)
(b)
(c)
Fig 56 E- and H-plane patterns of the broadband circular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-57-
(d)
(e)
Fig 56 continued
-58-
(a)
(b)
Fig 57 2D radiation patterns of the broadband cicular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-59-
(c)
(d)
Fig 57 continued
-60-
(e)
Fig 57 continued
To achieve equal beamwidths in E and H planes over a wide frequency
range chokes and corrugations are employed Table51 summarizes the
performance of a feed without chokes and corrugations
Table 51 Performance of the broadband circular waveguide feed without
chokes and corrugations
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
1000 940 6061 15
1200 972 6159 17
1400 920 5957 21
1600 1070 4751 29
1800 1188 5352 21
-61-
Four quarter-wavelength chokes are introduced in the feed design which
has a slot depth of 75mm and slot width of 09mm The choke slot spacing
is 18mm The choke design is investigated by applying the choke one by
one and the effect on the E- and H-plane patterns are observed as illustrated
in Figs 58 and 59 The use of chokes makes the E-plane pattern narrower
The H-plane pattern is not affected Chokes increase the gain slightly and
reduce back radiation
(a)
(b)
Fig 58 Effect of chokes on the E-plane pattern of the broadband circular
waveguide feed at (a) 10GHz(b) 12GHz (c) 14GHz (d) 16GHz and (e)
18GHz
-62-
(c)
(d)
(e)
Fig 58 continued
-63-
(a)
(b)
(c)
Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-64-
(d)
(e)
Fig 59 continued
-65-
Fig 510 shows the feed performance versus the choke depth When the
choke depth is varied from 535mm to 95mm the E- and H-plane patterns
are strongly affected The optimum value of choke depth is 75mm(035λ0 at
14GHz) which gives equal E- and H-plane radiation patterns and leads to
low back radiation
Fig 511 shows the feed performance versus the choke slot width tch The
choke slot width is varied from 09mm to 21mm Radiation patterns and
reflection coefficients are not sensitive to the choke slot width The final
choke slot width is selected to be 09mm considering the feed diameter
minimization and the manufacturability The overall diameter of the proposed
feed is 369mm which is increased from the 207mm of the waveguide
inside diameter due to the use of four chokes
-66-
(a)
(b)
(c)
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection coefficient
-67-
(a)
(b)
(c)
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and (c)
reflection coefficient
-68-
Next we investigated corrugations placed on the outer wall of the feed
Four corrugations applied to the outer surface of the circular waveguide The
corrugation depth is 465mm(0215λ0 at 14GHz) The primary purpose of
using corrugations is to further reduce the back radiation Increasing the
number of corrugations beyond four has little effect in reducing the back
radiation
Figs 512 and 513 show the effect of corrugations on the E- and H-plane
patterns Fig 514 shows the parametric study of the corrugation depth lcor
The corrugation depth is varied from 40mm and 645mm The optimum
value of the corrugation depth is found to be 465mm
-69-
(a)
(b)
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern at (a) 12GHz and (b) 14GHz
-70-
(a)
(b)
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern at (a) 12GHz and (b) 14GHz
-71-
(a)
(b)
(c)
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection coefficient
-72-
The phase center location is important in placing the feed in a reflector
antenna[8] The phase center variation with frequency should be small Fig
515 shows the effect of chokes and corrugations on the phase center The
curve with circle corresponds to the case without chokes and corrugations
The phase center varies from -326mm and -190mm away from the feeds
aperture plane It means the phase center is located inside the waveguide
The curve with triangles corresponds to the case with chokes The curve with
squares to the case with chokes and corrugations The phase center varies
from 0mm to -302mm
From Fig 515 we can observed that phase center variation reduced by the
corrugation and three cases phase center calculated in φ=450 plane
parameter sweep values are given in Table 52
10 12 14 16 181
0
-1
-2
-3
-4
-5
-6
Pha
se c
ente
r (m
m)
Frequency (GHz)
choke+corrugatuion without choke corrugation with choke
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
-73-
Frequency
(GHz)
Phase center from the aperture plane
(mm)
Without
chokes and
corrugations
With
chokes
With chokes
and
corrugations
1000 -326 062 000
1100 -187 030 -002
1200 -563 -208 -065
1300 -296 -154 -202
1400 -319 -314 -302
1500 -201 -203 -241
1600 -242 -233 -207
1700 -208 -208 -186
1800 -190 -157 -132
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
Based on the foregoing parametric studies optimum dimensions of the
broadband circular waveguide feed are obtained as shown in Table 53
-74-
Table 53 Optimum dimensions of the broadband circular waveguide feed
Parameter Designation Value (mm)
2a Waveguide inside diameter 2070
d Waveguide outside diameter 3690
lcrLength of the circular waveguide section 1430
m Distance between the aperture plane and the first corrugation 950
xDistance from the last corrugation to the end of the cylindrical outer surface
550
ltrLength of the rectangular-to-circularwaveguide transition 4465
lrcLength of the rectangular waveguide section 1430
tch Choke slot width 090
lch Choke depth 750
t Choke metal width 090
lcor Corrugation depth 465
tcor Corrugation metal width 100
s Corrugation slot width 10
lp Probe length 530
sp Probe position from the back short 530
din Probe diameter 127
b Inside height of the rectangular waveguide 857
tw Waveguide wall thickness 500
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-36-
(a)
(b)
(c)
Fig 38 E- and H-plane patterns of the narrow-band circular waveguide feed
at (a) 10GHz (b) 1825GHz and (c) 195GHz
-37-
Frequency(GHz)
Gain(dB)
E-H-plane10-dB beamwidths
(deg)
Front-to-back ratio(dB)
Phase centerlocation
(From feeds aperture plane
toward reflector)
(mm)
1700 903 6059 20 062
1825 933 6060 25 004
1900 956 5759 22 007
Table 32 Performance of the narrow-band circular waveguide feed
The designed narrow-band feed is fabricated and its performance is
measured and compared with the simulation results The designed feed is
fabricated in a numerically-controlled machining center The fabricated antenna
is shown in Fig 39
Fig 39 Photograph of the fabricated feed
-38-
Fig 310 shows a comparison of the measured and simulated reflection
coefficients The measured reflection coefficient is less than -10dB over
171-197GHz The agreement between simulated and measured results are
good
Fig 311 shows the E- and H-plane patterns of the fabricated feed at
187GHz The feed has 90dB gain simulation and measurement results are in
good agreement
The fabricated antennarsquos 10dB beamwidth is 60 degrees in both E and H
planes at 187GHz The front-to-back ratio is 21dB
Fig 310 Reflection coefficient of the fabricated feed
-39-
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Fee
d H
orn
Gain
- d
B
Angle - degree
(a)
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Feed H
orn
Gain
- d
B
Angle - degree
(b)
Fig 311 Gain patterns of the fabricated feed at 187 GHz (a) E-plane and
(b) H-plane
-40-
IV Design of Circular Waveguide Feeds Loaded with a
Dielectric Rod
In this section circular waveguide feeds loaded with a dielectric rod feed
are investigated A comprehensive discussion of the circular waveguide loaded
with a dielectric rod is given by Kumar[7] Inserting a dielectric material
inside the circular waveguide improves the E- and H-plane pattern symmetry
In general dielectric-loaded circular waveguide feeds show good performance
only over a narrow bandwidth
Fig 41 shows the geometry of a circular waveguide loaded with a
dielectric rod The waveguide length is 400mm and the wall thickness is
05mm The dielectric rods diameter is 207mm The dielectric rod is
extended 05 wavelength beyond the waveguide open end The dielectric
constant εr is changed and the feeds performance is observed
Fig 41 Geometry of a circular waveguide loaded with a uniform dielectric
rod
-41-
Fig 42 is the radiation pattern of the feed with εr = 25 and L = 05λ0 at
9GHz E- and H-plane 10-dB beamwidths are 810 and 807 degrees
respectively The front-to-back ratio is 18dB The antenna gain is 71dB
(a)
(b)
Fig 42 Radiation pattern at 9GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 05λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-42-
Fig 43 shows the radiation pattern of the feed with εr = 21 at 10GHz
E- and H-plane 10-dB beamwidths are 70 and 71 degrees respectively The
front-to-back ratio is 19dB The antenna gain is 83dB
(a)
(b)
Fig 43 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 21 and L = 05λ0 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-43-
Fig 44 shows the radiation pattern of the feed with εr = 30 at 8GHz
E- and H-plane 10-dB beamwidths are 83 and 824 degrees respectively The
front-to-back ratio is 17dB The antenna gain is 73dB
(a)
(b)
Fig 44 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 30 and L = 05λ0 at 8GHz (a) 2D radiation pattern
and (b) E- and H-plane patterns
-44-
Fig 45 shows the radiation pattern of the feed with εr = 50 at 18GHz
E- and H-plane 10-dB beamwidths are 56 and 54 degrees respectively The
front-to-back ratio is 27dB The antenna gain is 105dB The feed has a good
pattern symmetry and low back radiation
(a)
(b)
Fig 45 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 50 and L = 05λ0 at 18GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-45-
Fig 46 is the radiation pattern of the feed with εr = 25 and L = 10λ0 at
10GHz E- and H-plane 10-dB beamwidths are 50 and 48 degrees
respectively The front-to-back ratio is 16dB The antenna gain is 105dB
(a)
(b)
Fig 46 Radiation pattern at 10GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 10λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-46-
Fig 47 shows the geometry of a circular waveguide with a tapered
dielectric rod The designed feed has the following dimension L = 1λ0 d =
1λ0 and εr =25 at 10GHz The waveguide length is 40mm and the wall
thickness is 05mm
L
Dielectricd3
Fig 47 Geometry of a circular waveguide loaded with a tapered dielectric
rod
Fig 48 shows the radiatio pattern of the designed feed E- and H-plane
10-dB beamwidths are 575 and 564 degrees respectively The front-to-back
ratio is 377dB The antenna gain is 94dB The designed feed has an
excellent beamwidth symmetry and a very low back radiation
-47-
(a)
(b)
Fig 48 Radiation pattern of a circular waveguide loaded with a tapered
dielectric rod with L = 1λ0 d = 1λ0 and εr =25 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-48-
Fig 49 shows the geometry of a spherical ended dielectric rod feed
diameter of 06λ0 at 10GHz with a dielectric constant of 25 and L= 03λ0
Fig 410 shows the radiation patterns of the designed feed E- and H-plane
10-dB beamwidths are both 63 degrees The front-to-back ratio is 24dB The
antenna gain is 864dB
Fig 49 Geometry of a circular waveguide loaded with a spherical ended
dielectric rod
-49-
(a)
(b)
Fig 410 Radiation pattern of a circular waveguide loaded wht a spherical
ended dielectric rod with d = 06λ0 L = 03λ0 and εr =25 at 10GHz (a) 3D
radiation pattern and (b) E- and H-plane patterns
-50-
V Design of a Broadband Circular Waveguide Feed
In this chapter the design of a broadband circular waveguide feed is
presented At microwave frequencies the feed is often a circular waveguide
with chokes and corrugations around the aperture Chokes and corrugations
equalize E- and H-plane patterns and reduce the back radiation
The proposed feed is designed to operate over 10-18GHz The design starts
with the optimization of the coaxial-to-rectangular waveguide adapter
employed for good mode purity over a broad frequency range Next a
rectangular-to-circular waveguide transition is optimized Finally chokes and
corrugations are designed for improved pattern symmetry and low back
radiation
The proposed feed structure is shown in Fig 51 The feed consist of the
following parts a coaxial-to-rectangular waveguide adapter a rectangular-to-
circular waveguide transition a circular waveguide section four quarter-wave
chokes around the feeds aperture and four corrugations on the feeds outer
surface
The computer simulation shows the above arrangement offers good radiation
patterns over a broad frequency range The broadband operation is obtained
by exciting the TE11 mode in the circular waveguide using the TE10 mode of
the rectangular waveguide which is in turn excited by a coaxial probe
-51-
Chokes
Coaxial-to-waveguide transition
Circular wavguide
Corrugations
Mode transition
(a)
(b)
Fig 51 Structure of the proposed broadband circular waveguide feed
(a) CAD model and (b) cross-sectional view
For the coaxial-to-rectangular waveguide adapter an SMA connector with
the probe diameter of 127 mm is employed The coaxial probe inserted into
the waveguide energizes the feed and excites the dominant TE10 mode in
-52-
the rectangular waveguide The impedance matching is achieved by adjusting
the probe distance sp from the back short and the probe length lp
(a)
(b)
Fig 52 Reflection coefficient of the coaxial-to-rectangular adapter versus
(a) probe length lp and (b) the probe position sp
Fig 52 shows the reflection coefficient versus the various values of probe
lengths lp and probe positions sp The probe length lp is adjusted to obtain
antenna impedance matching and the probe distance sp is adjusted to obtain a
-53-
desired resonant frequency
Next a transition between rectangular and circular waveguide is designed
The transition section converts the TE10 mode in the rectangular waveguide to
TE11 mode in the circular waveguide and vice versa The transition is built
in a form of a taper for easy fabrication[22]
(a)
(b)
Fig 53 Structure of the rectangular-to-circular waveguide transition
(a) 3D view and (b) cross sectional view
The dimensions of the final optimized transition are as follows The length
of the rectangular waveguide section is 143mm The rectangular waveguides
width a and height b are 207mm and 857mm respectively The length of
the circular waveguide section is 143mm The inside diameter of the circular
-54-
waveguide is 207mm(097 wavelength at 14GHz) The length of transition
region ltr is 4465mm(approximately equal to 2λ0 at 14GHz) Fig 54 shows
the field distribution inside the mode converter
(a)
(b)
Fig 54 Field distribution inside the mode converter at
(a) 10GHz (b) 14GHz and (c) 18GHz
-55-
(c)
Fig 54 continued
Finally multiple chokes are investigated Figs 55 56 and 57 show the
feed performance without chokes The reflection coefficient is less than -10dB
over 10-19GHz The antenna has a gain of 921dB to 1189dB over
10-19GHz
Fig 55 Reflection coefficient of the broadband circular waveguide feed
without chokes and corrugations
-56-
(a)
(b)
(c)
Fig 56 E- and H-plane patterns of the broadband circular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-57-
(d)
(e)
Fig 56 continued
-58-
(a)
(b)
Fig 57 2D radiation patterns of the broadband cicular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-59-
(c)
(d)
Fig 57 continued
-60-
(e)
Fig 57 continued
To achieve equal beamwidths in E and H planes over a wide frequency
range chokes and corrugations are employed Table51 summarizes the
performance of a feed without chokes and corrugations
Table 51 Performance of the broadband circular waveguide feed without
chokes and corrugations
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
1000 940 6061 15
1200 972 6159 17
1400 920 5957 21
1600 1070 4751 29
1800 1188 5352 21
-61-
Four quarter-wavelength chokes are introduced in the feed design which
has a slot depth of 75mm and slot width of 09mm The choke slot spacing
is 18mm The choke design is investigated by applying the choke one by
one and the effect on the E- and H-plane patterns are observed as illustrated
in Figs 58 and 59 The use of chokes makes the E-plane pattern narrower
The H-plane pattern is not affected Chokes increase the gain slightly and
reduce back radiation
(a)
(b)
Fig 58 Effect of chokes on the E-plane pattern of the broadband circular
waveguide feed at (a) 10GHz(b) 12GHz (c) 14GHz (d) 16GHz and (e)
18GHz
-62-
(c)
(d)
(e)
Fig 58 continued
-63-
(a)
(b)
(c)
Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-64-
(d)
(e)
Fig 59 continued
-65-
Fig 510 shows the feed performance versus the choke depth When the
choke depth is varied from 535mm to 95mm the E- and H-plane patterns
are strongly affected The optimum value of choke depth is 75mm(035λ0 at
14GHz) which gives equal E- and H-plane radiation patterns and leads to
low back radiation
Fig 511 shows the feed performance versus the choke slot width tch The
choke slot width is varied from 09mm to 21mm Radiation patterns and
reflection coefficients are not sensitive to the choke slot width The final
choke slot width is selected to be 09mm considering the feed diameter
minimization and the manufacturability The overall diameter of the proposed
feed is 369mm which is increased from the 207mm of the waveguide
inside diameter due to the use of four chokes
-66-
(a)
(b)
(c)
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection coefficient
-67-
(a)
(b)
(c)
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and (c)
reflection coefficient
-68-
Next we investigated corrugations placed on the outer wall of the feed
Four corrugations applied to the outer surface of the circular waveguide The
corrugation depth is 465mm(0215λ0 at 14GHz) The primary purpose of
using corrugations is to further reduce the back radiation Increasing the
number of corrugations beyond four has little effect in reducing the back
radiation
Figs 512 and 513 show the effect of corrugations on the E- and H-plane
patterns Fig 514 shows the parametric study of the corrugation depth lcor
The corrugation depth is varied from 40mm and 645mm The optimum
value of the corrugation depth is found to be 465mm
-69-
(a)
(b)
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern at (a) 12GHz and (b) 14GHz
-70-
(a)
(b)
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern at (a) 12GHz and (b) 14GHz
-71-
(a)
(b)
(c)
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection coefficient
-72-
The phase center location is important in placing the feed in a reflector
antenna[8] The phase center variation with frequency should be small Fig
515 shows the effect of chokes and corrugations on the phase center The
curve with circle corresponds to the case without chokes and corrugations
The phase center varies from -326mm and -190mm away from the feeds
aperture plane It means the phase center is located inside the waveguide
The curve with triangles corresponds to the case with chokes The curve with
squares to the case with chokes and corrugations The phase center varies
from 0mm to -302mm
From Fig 515 we can observed that phase center variation reduced by the
corrugation and three cases phase center calculated in φ=450 plane
parameter sweep values are given in Table 52
10 12 14 16 181
0
-1
-2
-3
-4
-5
-6
Pha
se c
ente
r (m
m)
Frequency (GHz)
choke+corrugatuion without choke corrugation with choke
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
-73-
Frequency
(GHz)
Phase center from the aperture plane
(mm)
Without
chokes and
corrugations
With
chokes
With chokes
and
corrugations
1000 -326 062 000
1100 -187 030 -002
1200 -563 -208 -065
1300 -296 -154 -202
1400 -319 -314 -302
1500 -201 -203 -241
1600 -242 -233 -207
1700 -208 -208 -186
1800 -190 -157 -132
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
Based on the foregoing parametric studies optimum dimensions of the
broadband circular waveguide feed are obtained as shown in Table 53
-74-
Table 53 Optimum dimensions of the broadband circular waveguide feed
Parameter Designation Value (mm)
2a Waveguide inside diameter 2070
d Waveguide outside diameter 3690
lcrLength of the circular waveguide section 1430
m Distance between the aperture plane and the first corrugation 950
xDistance from the last corrugation to the end of the cylindrical outer surface
550
ltrLength of the rectangular-to-circularwaveguide transition 4465
lrcLength of the rectangular waveguide section 1430
tch Choke slot width 090
lch Choke depth 750
t Choke metal width 090
lcor Corrugation depth 465
tcor Corrugation metal width 100
s Corrugation slot width 10
lp Probe length 530
sp Probe position from the back short 530
din Probe diameter 127
b Inside height of the rectangular waveguide 857
tw Waveguide wall thickness 500
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-37-
Frequency(GHz)
Gain(dB)
E-H-plane10-dB beamwidths
(deg)
Front-to-back ratio(dB)
Phase centerlocation
(From feeds aperture plane
toward reflector)
(mm)
1700 903 6059 20 062
1825 933 6060 25 004
1900 956 5759 22 007
Table 32 Performance of the narrow-band circular waveguide feed
The designed narrow-band feed is fabricated and its performance is
measured and compared with the simulation results The designed feed is
fabricated in a numerically-controlled machining center The fabricated antenna
is shown in Fig 39
Fig 39 Photograph of the fabricated feed
-38-
Fig 310 shows a comparison of the measured and simulated reflection
coefficients The measured reflection coefficient is less than -10dB over
171-197GHz The agreement between simulated and measured results are
good
Fig 311 shows the E- and H-plane patterns of the fabricated feed at
187GHz The feed has 90dB gain simulation and measurement results are in
good agreement
The fabricated antennarsquos 10dB beamwidth is 60 degrees in both E and H
planes at 187GHz The front-to-back ratio is 21dB
Fig 310 Reflection coefficient of the fabricated feed
-39-
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Fee
d H
orn
Gain
- d
B
Angle - degree
(a)
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Feed H
orn
Gain
- d
B
Angle - degree
(b)
Fig 311 Gain patterns of the fabricated feed at 187 GHz (a) E-plane and
(b) H-plane
-40-
IV Design of Circular Waveguide Feeds Loaded with a
Dielectric Rod
In this section circular waveguide feeds loaded with a dielectric rod feed
are investigated A comprehensive discussion of the circular waveguide loaded
with a dielectric rod is given by Kumar[7] Inserting a dielectric material
inside the circular waveguide improves the E- and H-plane pattern symmetry
In general dielectric-loaded circular waveguide feeds show good performance
only over a narrow bandwidth
Fig 41 shows the geometry of a circular waveguide loaded with a
dielectric rod The waveguide length is 400mm and the wall thickness is
05mm The dielectric rods diameter is 207mm The dielectric rod is
extended 05 wavelength beyond the waveguide open end The dielectric
constant εr is changed and the feeds performance is observed
Fig 41 Geometry of a circular waveguide loaded with a uniform dielectric
rod
-41-
Fig 42 is the radiation pattern of the feed with εr = 25 and L = 05λ0 at
9GHz E- and H-plane 10-dB beamwidths are 810 and 807 degrees
respectively The front-to-back ratio is 18dB The antenna gain is 71dB
(a)
(b)
Fig 42 Radiation pattern at 9GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 05λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-42-
Fig 43 shows the radiation pattern of the feed with εr = 21 at 10GHz
E- and H-plane 10-dB beamwidths are 70 and 71 degrees respectively The
front-to-back ratio is 19dB The antenna gain is 83dB
(a)
(b)
Fig 43 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 21 and L = 05λ0 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-43-
Fig 44 shows the radiation pattern of the feed with εr = 30 at 8GHz
E- and H-plane 10-dB beamwidths are 83 and 824 degrees respectively The
front-to-back ratio is 17dB The antenna gain is 73dB
(a)
(b)
Fig 44 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 30 and L = 05λ0 at 8GHz (a) 2D radiation pattern
and (b) E- and H-plane patterns
-44-
Fig 45 shows the radiation pattern of the feed with εr = 50 at 18GHz
E- and H-plane 10-dB beamwidths are 56 and 54 degrees respectively The
front-to-back ratio is 27dB The antenna gain is 105dB The feed has a good
pattern symmetry and low back radiation
(a)
(b)
Fig 45 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 50 and L = 05λ0 at 18GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-45-
Fig 46 is the radiation pattern of the feed with εr = 25 and L = 10λ0 at
10GHz E- and H-plane 10-dB beamwidths are 50 and 48 degrees
respectively The front-to-back ratio is 16dB The antenna gain is 105dB
(a)
(b)
Fig 46 Radiation pattern at 10GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 10λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-46-
Fig 47 shows the geometry of a circular waveguide with a tapered
dielectric rod The designed feed has the following dimension L = 1λ0 d =
1λ0 and εr =25 at 10GHz The waveguide length is 40mm and the wall
thickness is 05mm
L
Dielectricd3
Fig 47 Geometry of a circular waveguide loaded with a tapered dielectric
rod
Fig 48 shows the radiatio pattern of the designed feed E- and H-plane
10-dB beamwidths are 575 and 564 degrees respectively The front-to-back
ratio is 377dB The antenna gain is 94dB The designed feed has an
excellent beamwidth symmetry and a very low back radiation
-47-
(a)
(b)
Fig 48 Radiation pattern of a circular waveguide loaded with a tapered
dielectric rod with L = 1λ0 d = 1λ0 and εr =25 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-48-
Fig 49 shows the geometry of a spherical ended dielectric rod feed
diameter of 06λ0 at 10GHz with a dielectric constant of 25 and L= 03λ0
Fig 410 shows the radiation patterns of the designed feed E- and H-plane
10-dB beamwidths are both 63 degrees The front-to-back ratio is 24dB The
antenna gain is 864dB
Fig 49 Geometry of a circular waveguide loaded with a spherical ended
dielectric rod
-49-
(a)
(b)
Fig 410 Radiation pattern of a circular waveguide loaded wht a spherical
ended dielectric rod with d = 06λ0 L = 03λ0 and εr =25 at 10GHz (a) 3D
radiation pattern and (b) E- and H-plane patterns
-50-
V Design of a Broadband Circular Waveguide Feed
In this chapter the design of a broadband circular waveguide feed is
presented At microwave frequencies the feed is often a circular waveguide
with chokes and corrugations around the aperture Chokes and corrugations
equalize E- and H-plane patterns and reduce the back radiation
The proposed feed is designed to operate over 10-18GHz The design starts
with the optimization of the coaxial-to-rectangular waveguide adapter
employed for good mode purity over a broad frequency range Next a
rectangular-to-circular waveguide transition is optimized Finally chokes and
corrugations are designed for improved pattern symmetry and low back
radiation
The proposed feed structure is shown in Fig 51 The feed consist of the
following parts a coaxial-to-rectangular waveguide adapter a rectangular-to-
circular waveguide transition a circular waveguide section four quarter-wave
chokes around the feeds aperture and four corrugations on the feeds outer
surface
The computer simulation shows the above arrangement offers good radiation
patterns over a broad frequency range The broadband operation is obtained
by exciting the TE11 mode in the circular waveguide using the TE10 mode of
the rectangular waveguide which is in turn excited by a coaxial probe
-51-
Chokes
Coaxial-to-waveguide transition
Circular wavguide
Corrugations
Mode transition
(a)
(b)
Fig 51 Structure of the proposed broadband circular waveguide feed
(a) CAD model and (b) cross-sectional view
For the coaxial-to-rectangular waveguide adapter an SMA connector with
the probe diameter of 127 mm is employed The coaxial probe inserted into
the waveguide energizes the feed and excites the dominant TE10 mode in
-52-
the rectangular waveguide The impedance matching is achieved by adjusting
the probe distance sp from the back short and the probe length lp
(a)
(b)
Fig 52 Reflection coefficient of the coaxial-to-rectangular adapter versus
(a) probe length lp and (b) the probe position sp
Fig 52 shows the reflection coefficient versus the various values of probe
lengths lp and probe positions sp The probe length lp is adjusted to obtain
antenna impedance matching and the probe distance sp is adjusted to obtain a
-53-
desired resonant frequency
Next a transition between rectangular and circular waveguide is designed
The transition section converts the TE10 mode in the rectangular waveguide to
TE11 mode in the circular waveguide and vice versa The transition is built
in a form of a taper for easy fabrication[22]
(a)
(b)
Fig 53 Structure of the rectangular-to-circular waveguide transition
(a) 3D view and (b) cross sectional view
The dimensions of the final optimized transition are as follows The length
of the rectangular waveguide section is 143mm The rectangular waveguides
width a and height b are 207mm and 857mm respectively The length of
the circular waveguide section is 143mm The inside diameter of the circular
-54-
waveguide is 207mm(097 wavelength at 14GHz) The length of transition
region ltr is 4465mm(approximately equal to 2λ0 at 14GHz) Fig 54 shows
the field distribution inside the mode converter
(a)
(b)
Fig 54 Field distribution inside the mode converter at
(a) 10GHz (b) 14GHz and (c) 18GHz
-55-
(c)
Fig 54 continued
Finally multiple chokes are investigated Figs 55 56 and 57 show the
feed performance without chokes The reflection coefficient is less than -10dB
over 10-19GHz The antenna has a gain of 921dB to 1189dB over
10-19GHz
Fig 55 Reflection coefficient of the broadband circular waveguide feed
without chokes and corrugations
-56-
(a)
(b)
(c)
Fig 56 E- and H-plane patterns of the broadband circular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-57-
(d)
(e)
Fig 56 continued
-58-
(a)
(b)
Fig 57 2D radiation patterns of the broadband cicular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-59-
(c)
(d)
Fig 57 continued
-60-
(e)
Fig 57 continued
To achieve equal beamwidths in E and H planes over a wide frequency
range chokes and corrugations are employed Table51 summarizes the
performance of a feed without chokes and corrugations
Table 51 Performance of the broadband circular waveguide feed without
chokes and corrugations
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
1000 940 6061 15
1200 972 6159 17
1400 920 5957 21
1600 1070 4751 29
1800 1188 5352 21
-61-
Four quarter-wavelength chokes are introduced in the feed design which
has a slot depth of 75mm and slot width of 09mm The choke slot spacing
is 18mm The choke design is investigated by applying the choke one by
one and the effect on the E- and H-plane patterns are observed as illustrated
in Figs 58 and 59 The use of chokes makes the E-plane pattern narrower
The H-plane pattern is not affected Chokes increase the gain slightly and
reduce back radiation
(a)
(b)
Fig 58 Effect of chokes on the E-plane pattern of the broadband circular
waveguide feed at (a) 10GHz(b) 12GHz (c) 14GHz (d) 16GHz and (e)
18GHz
-62-
(c)
(d)
(e)
Fig 58 continued
-63-
(a)
(b)
(c)
Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-64-
(d)
(e)
Fig 59 continued
-65-
Fig 510 shows the feed performance versus the choke depth When the
choke depth is varied from 535mm to 95mm the E- and H-plane patterns
are strongly affected The optimum value of choke depth is 75mm(035λ0 at
14GHz) which gives equal E- and H-plane radiation patterns and leads to
low back radiation
Fig 511 shows the feed performance versus the choke slot width tch The
choke slot width is varied from 09mm to 21mm Radiation patterns and
reflection coefficients are not sensitive to the choke slot width The final
choke slot width is selected to be 09mm considering the feed diameter
minimization and the manufacturability The overall diameter of the proposed
feed is 369mm which is increased from the 207mm of the waveguide
inside diameter due to the use of four chokes
-66-
(a)
(b)
(c)
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection coefficient
-67-
(a)
(b)
(c)
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and (c)
reflection coefficient
-68-
Next we investigated corrugations placed on the outer wall of the feed
Four corrugations applied to the outer surface of the circular waveguide The
corrugation depth is 465mm(0215λ0 at 14GHz) The primary purpose of
using corrugations is to further reduce the back radiation Increasing the
number of corrugations beyond four has little effect in reducing the back
radiation
Figs 512 and 513 show the effect of corrugations on the E- and H-plane
patterns Fig 514 shows the parametric study of the corrugation depth lcor
The corrugation depth is varied from 40mm and 645mm The optimum
value of the corrugation depth is found to be 465mm
-69-
(a)
(b)
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern at (a) 12GHz and (b) 14GHz
-70-
(a)
(b)
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern at (a) 12GHz and (b) 14GHz
-71-
(a)
(b)
(c)
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection coefficient
-72-
The phase center location is important in placing the feed in a reflector
antenna[8] The phase center variation with frequency should be small Fig
515 shows the effect of chokes and corrugations on the phase center The
curve with circle corresponds to the case without chokes and corrugations
The phase center varies from -326mm and -190mm away from the feeds
aperture plane It means the phase center is located inside the waveguide
The curve with triangles corresponds to the case with chokes The curve with
squares to the case with chokes and corrugations The phase center varies
from 0mm to -302mm
From Fig 515 we can observed that phase center variation reduced by the
corrugation and three cases phase center calculated in φ=450 plane
parameter sweep values are given in Table 52
10 12 14 16 181
0
-1
-2
-3
-4
-5
-6
Pha
se c
ente
r (m
m)
Frequency (GHz)
choke+corrugatuion without choke corrugation with choke
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
-73-
Frequency
(GHz)
Phase center from the aperture plane
(mm)
Without
chokes and
corrugations
With
chokes
With chokes
and
corrugations
1000 -326 062 000
1100 -187 030 -002
1200 -563 -208 -065
1300 -296 -154 -202
1400 -319 -314 -302
1500 -201 -203 -241
1600 -242 -233 -207
1700 -208 -208 -186
1800 -190 -157 -132
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
Based on the foregoing parametric studies optimum dimensions of the
broadband circular waveguide feed are obtained as shown in Table 53
-74-
Table 53 Optimum dimensions of the broadband circular waveguide feed
Parameter Designation Value (mm)
2a Waveguide inside diameter 2070
d Waveguide outside diameter 3690
lcrLength of the circular waveguide section 1430
m Distance between the aperture plane and the first corrugation 950
xDistance from the last corrugation to the end of the cylindrical outer surface
550
ltrLength of the rectangular-to-circularwaveguide transition 4465
lrcLength of the rectangular waveguide section 1430
tch Choke slot width 090
lch Choke depth 750
t Choke metal width 090
lcor Corrugation depth 465
tcor Corrugation metal width 100
s Corrugation slot width 10
lp Probe length 530
sp Probe position from the back short 530
din Probe diameter 127
b Inside height of the rectangular waveguide 857
tw Waveguide wall thickness 500
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-38-
Fig 310 shows a comparison of the measured and simulated reflection
coefficients The measured reflection coefficient is less than -10dB over
171-197GHz The agreement between simulated and measured results are
good
Fig 311 shows the E- and H-plane patterns of the fabricated feed at
187GHz The feed has 90dB gain simulation and measurement results are in
good agreement
The fabricated antennarsquos 10dB beamwidth is 60 degrees in both E and H
planes at 187GHz The front-to-back ratio is 21dB
Fig 310 Reflection coefficient of the fabricated feed
-39-
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Fee
d H
orn
Gain
- d
B
Angle - degree
(a)
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Feed H
orn
Gain
- d
B
Angle - degree
(b)
Fig 311 Gain patterns of the fabricated feed at 187 GHz (a) E-plane and
(b) H-plane
-40-
IV Design of Circular Waveguide Feeds Loaded with a
Dielectric Rod
In this section circular waveguide feeds loaded with a dielectric rod feed
are investigated A comprehensive discussion of the circular waveguide loaded
with a dielectric rod is given by Kumar[7] Inserting a dielectric material
inside the circular waveguide improves the E- and H-plane pattern symmetry
In general dielectric-loaded circular waveguide feeds show good performance
only over a narrow bandwidth
Fig 41 shows the geometry of a circular waveguide loaded with a
dielectric rod The waveguide length is 400mm and the wall thickness is
05mm The dielectric rods diameter is 207mm The dielectric rod is
extended 05 wavelength beyond the waveguide open end The dielectric
constant εr is changed and the feeds performance is observed
Fig 41 Geometry of a circular waveguide loaded with a uniform dielectric
rod
-41-
Fig 42 is the radiation pattern of the feed with εr = 25 and L = 05λ0 at
9GHz E- and H-plane 10-dB beamwidths are 810 and 807 degrees
respectively The front-to-back ratio is 18dB The antenna gain is 71dB
(a)
(b)
Fig 42 Radiation pattern at 9GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 05λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-42-
Fig 43 shows the radiation pattern of the feed with εr = 21 at 10GHz
E- and H-plane 10-dB beamwidths are 70 and 71 degrees respectively The
front-to-back ratio is 19dB The antenna gain is 83dB
(a)
(b)
Fig 43 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 21 and L = 05λ0 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-43-
Fig 44 shows the radiation pattern of the feed with εr = 30 at 8GHz
E- and H-plane 10-dB beamwidths are 83 and 824 degrees respectively The
front-to-back ratio is 17dB The antenna gain is 73dB
(a)
(b)
Fig 44 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 30 and L = 05λ0 at 8GHz (a) 2D radiation pattern
and (b) E- and H-plane patterns
-44-
Fig 45 shows the radiation pattern of the feed with εr = 50 at 18GHz
E- and H-plane 10-dB beamwidths are 56 and 54 degrees respectively The
front-to-back ratio is 27dB The antenna gain is 105dB The feed has a good
pattern symmetry and low back radiation
(a)
(b)
Fig 45 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 50 and L = 05λ0 at 18GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-45-
Fig 46 is the radiation pattern of the feed with εr = 25 and L = 10λ0 at
10GHz E- and H-plane 10-dB beamwidths are 50 and 48 degrees
respectively The front-to-back ratio is 16dB The antenna gain is 105dB
(a)
(b)
Fig 46 Radiation pattern at 10GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 10λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-46-
Fig 47 shows the geometry of a circular waveguide with a tapered
dielectric rod The designed feed has the following dimension L = 1λ0 d =
1λ0 and εr =25 at 10GHz The waveguide length is 40mm and the wall
thickness is 05mm
L
Dielectricd3
Fig 47 Geometry of a circular waveguide loaded with a tapered dielectric
rod
Fig 48 shows the radiatio pattern of the designed feed E- and H-plane
10-dB beamwidths are 575 and 564 degrees respectively The front-to-back
ratio is 377dB The antenna gain is 94dB The designed feed has an
excellent beamwidth symmetry and a very low back radiation
-47-
(a)
(b)
Fig 48 Radiation pattern of a circular waveguide loaded with a tapered
dielectric rod with L = 1λ0 d = 1λ0 and εr =25 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-48-
Fig 49 shows the geometry of a spherical ended dielectric rod feed
diameter of 06λ0 at 10GHz with a dielectric constant of 25 and L= 03λ0
Fig 410 shows the radiation patterns of the designed feed E- and H-plane
10-dB beamwidths are both 63 degrees The front-to-back ratio is 24dB The
antenna gain is 864dB
Fig 49 Geometry of a circular waveguide loaded with a spherical ended
dielectric rod
-49-
(a)
(b)
Fig 410 Radiation pattern of a circular waveguide loaded wht a spherical
ended dielectric rod with d = 06λ0 L = 03λ0 and εr =25 at 10GHz (a) 3D
radiation pattern and (b) E- and H-plane patterns
-50-
V Design of a Broadband Circular Waveguide Feed
In this chapter the design of a broadband circular waveguide feed is
presented At microwave frequencies the feed is often a circular waveguide
with chokes and corrugations around the aperture Chokes and corrugations
equalize E- and H-plane patterns and reduce the back radiation
The proposed feed is designed to operate over 10-18GHz The design starts
with the optimization of the coaxial-to-rectangular waveguide adapter
employed for good mode purity over a broad frequency range Next a
rectangular-to-circular waveguide transition is optimized Finally chokes and
corrugations are designed for improved pattern symmetry and low back
radiation
The proposed feed structure is shown in Fig 51 The feed consist of the
following parts a coaxial-to-rectangular waveguide adapter a rectangular-to-
circular waveguide transition a circular waveguide section four quarter-wave
chokes around the feeds aperture and four corrugations on the feeds outer
surface
The computer simulation shows the above arrangement offers good radiation
patterns over a broad frequency range The broadband operation is obtained
by exciting the TE11 mode in the circular waveguide using the TE10 mode of
the rectangular waveguide which is in turn excited by a coaxial probe
-51-
Chokes
Coaxial-to-waveguide transition
Circular wavguide
Corrugations
Mode transition
(a)
(b)
Fig 51 Structure of the proposed broadband circular waveguide feed
(a) CAD model and (b) cross-sectional view
For the coaxial-to-rectangular waveguide adapter an SMA connector with
the probe diameter of 127 mm is employed The coaxial probe inserted into
the waveguide energizes the feed and excites the dominant TE10 mode in
-52-
the rectangular waveguide The impedance matching is achieved by adjusting
the probe distance sp from the back short and the probe length lp
(a)
(b)
Fig 52 Reflection coefficient of the coaxial-to-rectangular adapter versus
(a) probe length lp and (b) the probe position sp
Fig 52 shows the reflection coefficient versus the various values of probe
lengths lp and probe positions sp The probe length lp is adjusted to obtain
antenna impedance matching and the probe distance sp is adjusted to obtain a
-53-
desired resonant frequency
Next a transition between rectangular and circular waveguide is designed
The transition section converts the TE10 mode in the rectangular waveguide to
TE11 mode in the circular waveguide and vice versa The transition is built
in a form of a taper for easy fabrication[22]
(a)
(b)
Fig 53 Structure of the rectangular-to-circular waveguide transition
(a) 3D view and (b) cross sectional view
The dimensions of the final optimized transition are as follows The length
of the rectangular waveguide section is 143mm The rectangular waveguides
width a and height b are 207mm and 857mm respectively The length of
the circular waveguide section is 143mm The inside diameter of the circular
-54-
waveguide is 207mm(097 wavelength at 14GHz) The length of transition
region ltr is 4465mm(approximately equal to 2λ0 at 14GHz) Fig 54 shows
the field distribution inside the mode converter
(a)
(b)
Fig 54 Field distribution inside the mode converter at
(a) 10GHz (b) 14GHz and (c) 18GHz
-55-
(c)
Fig 54 continued
Finally multiple chokes are investigated Figs 55 56 and 57 show the
feed performance without chokes The reflection coefficient is less than -10dB
over 10-19GHz The antenna has a gain of 921dB to 1189dB over
10-19GHz
Fig 55 Reflection coefficient of the broadband circular waveguide feed
without chokes and corrugations
-56-
(a)
(b)
(c)
Fig 56 E- and H-plane patterns of the broadband circular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-57-
(d)
(e)
Fig 56 continued
-58-
(a)
(b)
Fig 57 2D radiation patterns of the broadband cicular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-59-
(c)
(d)
Fig 57 continued
-60-
(e)
Fig 57 continued
To achieve equal beamwidths in E and H planes over a wide frequency
range chokes and corrugations are employed Table51 summarizes the
performance of a feed without chokes and corrugations
Table 51 Performance of the broadband circular waveguide feed without
chokes and corrugations
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
1000 940 6061 15
1200 972 6159 17
1400 920 5957 21
1600 1070 4751 29
1800 1188 5352 21
-61-
Four quarter-wavelength chokes are introduced in the feed design which
has a slot depth of 75mm and slot width of 09mm The choke slot spacing
is 18mm The choke design is investigated by applying the choke one by
one and the effect on the E- and H-plane patterns are observed as illustrated
in Figs 58 and 59 The use of chokes makes the E-plane pattern narrower
The H-plane pattern is not affected Chokes increase the gain slightly and
reduce back radiation
(a)
(b)
Fig 58 Effect of chokes on the E-plane pattern of the broadband circular
waveguide feed at (a) 10GHz(b) 12GHz (c) 14GHz (d) 16GHz and (e)
18GHz
-62-
(c)
(d)
(e)
Fig 58 continued
-63-
(a)
(b)
(c)
Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-64-
(d)
(e)
Fig 59 continued
-65-
Fig 510 shows the feed performance versus the choke depth When the
choke depth is varied from 535mm to 95mm the E- and H-plane patterns
are strongly affected The optimum value of choke depth is 75mm(035λ0 at
14GHz) which gives equal E- and H-plane radiation patterns and leads to
low back radiation
Fig 511 shows the feed performance versus the choke slot width tch The
choke slot width is varied from 09mm to 21mm Radiation patterns and
reflection coefficients are not sensitive to the choke slot width The final
choke slot width is selected to be 09mm considering the feed diameter
minimization and the manufacturability The overall diameter of the proposed
feed is 369mm which is increased from the 207mm of the waveguide
inside diameter due to the use of four chokes
-66-
(a)
(b)
(c)
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection coefficient
-67-
(a)
(b)
(c)
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and (c)
reflection coefficient
-68-
Next we investigated corrugations placed on the outer wall of the feed
Four corrugations applied to the outer surface of the circular waveguide The
corrugation depth is 465mm(0215λ0 at 14GHz) The primary purpose of
using corrugations is to further reduce the back radiation Increasing the
number of corrugations beyond four has little effect in reducing the back
radiation
Figs 512 and 513 show the effect of corrugations on the E- and H-plane
patterns Fig 514 shows the parametric study of the corrugation depth lcor
The corrugation depth is varied from 40mm and 645mm The optimum
value of the corrugation depth is found to be 465mm
-69-
(a)
(b)
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern at (a) 12GHz and (b) 14GHz
-70-
(a)
(b)
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern at (a) 12GHz and (b) 14GHz
-71-
(a)
(b)
(c)
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection coefficient
-72-
The phase center location is important in placing the feed in a reflector
antenna[8] The phase center variation with frequency should be small Fig
515 shows the effect of chokes and corrugations on the phase center The
curve with circle corresponds to the case without chokes and corrugations
The phase center varies from -326mm and -190mm away from the feeds
aperture plane It means the phase center is located inside the waveguide
The curve with triangles corresponds to the case with chokes The curve with
squares to the case with chokes and corrugations The phase center varies
from 0mm to -302mm
From Fig 515 we can observed that phase center variation reduced by the
corrugation and three cases phase center calculated in φ=450 plane
parameter sweep values are given in Table 52
10 12 14 16 181
0
-1
-2
-3
-4
-5
-6
Pha
se c
ente
r (m
m)
Frequency (GHz)
choke+corrugatuion without choke corrugation with choke
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
-73-
Frequency
(GHz)
Phase center from the aperture plane
(mm)
Without
chokes and
corrugations
With
chokes
With chokes
and
corrugations
1000 -326 062 000
1100 -187 030 -002
1200 -563 -208 -065
1300 -296 -154 -202
1400 -319 -314 -302
1500 -201 -203 -241
1600 -242 -233 -207
1700 -208 -208 -186
1800 -190 -157 -132
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
Based on the foregoing parametric studies optimum dimensions of the
broadband circular waveguide feed are obtained as shown in Table 53
-74-
Table 53 Optimum dimensions of the broadband circular waveguide feed
Parameter Designation Value (mm)
2a Waveguide inside diameter 2070
d Waveguide outside diameter 3690
lcrLength of the circular waveguide section 1430
m Distance between the aperture plane and the first corrugation 950
xDistance from the last corrugation to the end of the cylindrical outer surface
550
ltrLength of the rectangular-to-circularwaveguide transition 4465
lrcLength of the rectangular waveguide section 1430
tch Choke slot width 090
lch Choke depth 750
t Choke metal width 090
lcor Corrugation depth 465
tcor Corrugation metal width 100
s Corrugation slot width 10
lp Probe length 530
sp Probe position from the back short 530
din Probe diameter 127
b Inside height of the rectangular waveguide 857
tw Waveguide wall thickness 500
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-39-
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Fee
d H
orn
Gain
- d
B
Angle - degree
(a)
-180 -135 -90 -45 0 45 90 135 180-20
-15
-10
-5
0
5
10
Simulation Measurement
Feed H
orn
Gain
- d
B
Angle - degree
(b)
Fig 311 Gain patterns of the fabricated feed at 187 GHz (a) E-plane and
(b) H-plane
-40-
IV Design of Circular Waveguide Feeds Loaded with a
Dielectric Rod
In this section circular waveguide feeds loaded with a dielectric rod feed
are investigated A comprehensive discussion of the circular waveguide loaded
with a dielectric rod is given by Kumar[7] Inserting a dielectric material
inside the circular waveguide improves the E- and H-plane pattern symmetry
In general dielectric-loaded circular waveguide feeds show good performance
only over a narrow bandwidth
Fig 41 shows the geometry of a circular waveguide loaded with a
dielectric rod The waveguide length is 400mm and the wall thickness is
05mm The dielectric rods diameter is 207mm The dielectric rod is
extended 05 wavelength beyond the waveguide open end The dielectric
constant εr is changed and the feeds performance is observed
Fig 41 Geometry of a circular waveguide loaded with a uniform dielectric
rod
-41-
Fig 42 is the radiation pattern of the feed with εr = 25 and L = 05λ0 at
9GHz E- and H-plane 10-dB beamwidths are 810 and 807 degrees
respectively The front-to-back ratio is 18dB The antenna gain is 71dB
(a)
(b)
Fig 42 Radiation pattern at 9GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 05λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-42-
Fig 43 shows the radiation pattern of the feed with εr = 21 at 10GHz
E- and H-plane 10-dB beamwidths are 70 and 71 degrees respectively The
front-to-back ratio is 19dB The antenna gain is 83dB
(a)
(b)
Fig 43 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 21 and L = 05λ0 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-43-
Fig 44 shows the radiation pattern of the feed with εr = 30 at 8GHz
E- and H-plane 10-dB beamwidths are 83 and 824 degrees respectively The
front-to-back ratio is 17dB The antenna gain is 73dB
(a)
(b)
Fig 44 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 30 and L = 05λ0 at 8GHz (a) 2D radiation pattern
and (b) E- and H-plane patterns
-44-
Fig 45 shows the radiation pattern of the feed with εr = 50 at 18GHz
E- and H-plane 10-dB beamwidths are 56 and 54 degrees respectively The
front-to-back ratio is 27dB The antenna gain is 105dB The feed has a good
pattern symmetry and low back radiation
(a)
(b)
Fig 45 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 50 and L = 05λ0 at 18GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-45-
Fig 46 is the radiation pattern of the feed with εr = 25 and L = 10λ0 at
10GHz E- and H-plane 10-dB beamwidths are 50 and 48 degrees
respectively The front-to-back ratio is 16dB The antenna gain is 105dB
(a)
(b)
Fig 46 Radiation pattern at 10GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 10λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-46-
Fig 47 shows the geometry of a circular waveguide with a tapered
dielectric rod The designed feed has the following dimension L = 1λ0 d =
1λ0 and εr =25 at 10GHz The waveguide length is 40mm and the wall
thickness is 05mm
L
Dielectricd3
Fig 47 Geometry of a circular waveguide loaded with a tapered dielectric
rod
Fig 48 shows the radiatio pattern of the designed feed E- and H-plane
10-dB beamwidths are 575 and 564 degrees respectively The front-to-back
ratio is 377dB The antenna gain is 94dB The designed feed has an
excellent beamwidth symmetry and a very low back radiation
-47-
(a)
(b)
Fig 48 Radiation pattern of a circular waveguide loaded with a tapered
dielectric rod with L = 1λ0 d = 1λ0 and εr =25 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-48-
Fig 49 shows the geometry of a spherical ended dielectric rod feed
diameter of 06λ0 at 10GHz with a dielectric constant of 25 and L= 03λ0
Fig 410 shows the radiation patterns of the designed feed E- and H-plane
10-dB beamwidths are both 63 degrees The front-to-back ratio is 24dB The
antenna gain is 864dB
Fig 49 Geometry of a circular waveguide loaded with a spherical ended
dielectric rod
-49-
(a)
(b)
Fig 410 Radiation pattern of a circular waveguide loaded wht a spherical
ended dielectric rod with d = 06λ0 L = 03λ0 and εr =25 at 10GHz (a) 3D
radiation pattern and (b) E- and H-plane patterns
-50-
V Design of a Broadband Circular Waveguide Feed
In this chapter the design of a broadband circular waveguide feed is
presented At microwave frequencies the feed is often a circular waveguide
with chokes and corrugations around the aperture Chokes and corrugations
equalize E- and H-plane patterns and reduce the back radiation
The proposed feed is designed to operate over 10-18GHz The design starts
with the optimization of the coaxial-to-rectangular waveguide adapter
employed for good mode purity over a broad frequency range Next a
rectangular-to-circular waveguide transition is optimized Finally chokes and
corrugations are designed for improved pattern symmetry and low back
radiation
The proposed feed structure is shown in Fig 51 The feed consist of the
following parts a coaxial-to-rectangular waveguide adapter a rectangular-to-
circular waveguide transition a circular waveguide section four quarter-wave
chokes around the feeds aperture and four corrugations on the feeds outer
surface
The computer simulation shows the above arrangement offers good radiation
patterns over a broad frequency range The broadband operation is obtained
by exciting the TE11 mode in the circular waveguide using the TE10 mode of
the rectangular waveguide which is in turn excited by a coaxial probe
-51-
Chokes
Coaxial-to-waveguide transition
Circular wavguide
Corrugations
Mode transition
(a)
(b)
Fig 51 Structure of the proposed broadband circular waveguide feed
(a) CAD model and (b) cross-sectional view
For the coaxial-to-rectangular waveguide adapter an SMA connector with
the probe diameter of 127 mm is employed The coaxial probe inserted into
the waveguide energizes the feed and excites the dominant TE10 mode in
-52-
the rectangular waveguide The impedance matching is achieved by adjusting
the probe distance sp from the back short and the probe length lp
(a)
(b)
Fig 52 Reflection coefficient of the coaxial-to-rectangular adapter versus
(a) probe length lp and (b) the probe position sp
Fig 52 shows the reflection coefficient versus the various values of probe
lengths lp and probe positions sp The probe length lp is adjusted to obtain
antenna impedance matching and the probe distance sp is adjusted to obtain a
-53-
desired resonant frequency
Next a transition between rectangular and circular waveguide is designed
The transition section converts the TE10 mode in the rectangular waveguide to
TE11 mode in the circular waveguide and vice versa The transition is built
in a form of a taper for easy fabrication[22]
(a)
(b)
Fig 53 Structure of the rectangular-to-circular waveguide transition
(a) 3D view and (b) cross sectional view
The dimensions of the final optimized transition are as follows The length
of the rectangular waveguide section is 143mm The rectangular waveguides
width a and height b are 207mm and 857mm respectively The length of
the circular waveguide section is 143mm The inside diameter of the circular
-54-
waveguide is 207mm(097 wavelength at 14GHz) The length of transition
region ltr is 4465mm(approximately equal to 2λ0 at 14GHz) Fig 54 shows
the field distribution inside the mode converter
(a)
(b)
Fig 54 Field distribution inside the mode converter at
(a) 10GHz (b) 14GHz and (c) 18GHz
-55-
(c)
Fig 54 continued
Finally multiple chokes are investigated Figs 55 56 and 57 show the
feed performance without chokes The reflection coefficient is less than -10dB
over 10-19GHz The antenna has a gain of 921dB to 1189dB over
10-19GHz
Fig 55 Reflection coefficient of the broadband circular waveguide feed
without chokes and corrugations
-56-
(a)
(b)
(c)
Fig 56 E- and H-plane patterns of the broadband circular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-57-
(d)
(e)
Fig 56 continued
-58-
(a)
(b)
Fig 57 2D radiation patterns of the broadband cicular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-59-
(c)
(d)
Fig 57 continued
-60-
(e)
Fig 57 continued
To achieve equal beamwidths in E and H planes over a wide frequency
range chokes and corrugations are employed Table51 summarizes the
performance of a feed without chokes and corrugations
Table 51 Performance of the broadband circular waveguide feed without
chokes and corrugations
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
1000 940 6061 15
1200 972 6159 17
1400 920 5957 21
1600 1070 4751 29
1800 1188 5352 21
-61-
Four quarter-wavelength chokes are introduced in the feed design which
has a slot depth of 75mm and slot width of 09mm The choke slot spacing
is 18mm The choke design is investigated by applying the choke one by
one and the effect on the E- and H-plane patterns are observed as illustrated
in Figs 58 and 59 The use of chokes makes the E-plane pattern narrower
The H-plane pattern is not affected Chokes increase the gain slightly and
reduce back radiation
(a)
(b)
Fig 58 Effect of chokes on the E-plane pattern of the broadband circular
waveguide feed at (a) 10GHz(b) 12GHz (c) 14GHz (d) 16GHz and (e)
18GHz
-62-
(c)
(d)
(e)
Fig 58 continued
-63-
(a)
(b)
(c)
Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-64-
(d)
(e)
Fig 59 continued
-65-
Fig 510 shows the feed performance versus the choke depth When the
choke depth is varied from 535mm to 95mm the E- and H-plane patterns
are strongly affected The optimum value of choke depth is 75mm(035λ0 at
14GHz) which gives equal E- and H-plane radiation patterns and leads to
low back radiation
Fig 511 shows the feed performance versus the choke slot width tch The
choke slot width is varied from 09mm to 21mm Radiation patterns and
reflection coefficients are not sensitive to the choke slot width The final
choke slot width is selected to be 09mm considering the feed diameter
minimization and the manufacturability The overall diameter of the proposed
feed is 369mm which is increased from the 207mm of the waveguide
inside diameter due to the use of four chokes
-66-
(a)
(b)
(c)
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection coefficient
-67-
(a)
(b)
(c)
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and (c)
reflection coefficient
-68-
Next we investigated corrugations placed on the outer wall of the feed
Four corrugations applied to the outer surface of the circular waveguide The
corrugation depth is 465mm(0215λ0 at 14GHz) The primary purpose of
using corrugations is to further reduce the back radiation Increasing the
number of corrugations beyond four has little effect in reducing the back
radiation
Figs 512 and 513 show the effect of corrugations on the E- and H-plane
patterns Fig 514 shows the parametric study of the corrugation depth lcor
The corrugation depth is varied from 40mm and 645mm The optimum
value of the corrugation depth is found to be 465mm
-69-
(a)
(b)
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern at (a) 12GHz and (b) 14GHz
-70-
(a)
(b)
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern at (a) 12GHz and (b) 14GHz
-71-
(a)
(b)
(c)
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection coefficient
-72-
The phase center location is important in placing the feed in a reflector
antenna[8] The phase center variation with frequency should be small Fig
515 shows the effect of chokes and corrugations on the phase center The
curve with circle corresponds to the case without chokes and corrugations
The phase center varies from -326mm and -190mm away from the feeds
aperture plane It means the phase center is located inside the waveguide
The curve with triangles corresponds to the case with chokes The curve with
squares to the case with chokes and corrugations The phase center varies
from 0mm to -302mm
From Fig 515 we can observed that phase center variation reduced by the
corrugation and three cases phase center calculated in φ=450 plane
parameter sweep values are given in Table 52
10 12 14 16 181
0
-1
-2
-3
-4
-5
-6
Pha
se c
ente
r (m
m)
Frequency (GHz)
choke+corrugatuion without choke corrugation with choke
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
-73-
Frequency
(GHz)
Phase center from the aperture plane
(mm)
Without
chokes and
corrugations
With
chokes
With chokes
and
corrugations
1000 -326 062 000
1100 -187 030 -002
1200 -563 -208 -065
1300 -296 -154 -202
1400 -319 -314 -302
1500 -201 -203 -241
1600 -242 -233 -207
1700 -208 -208 -186
1800 -190 -157 -132
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
Based on the foregoing parametric studies optimum dimensions of the
broadband circular waveguide feed are obtained as shown in Table 53
-74-
Table 53 Optimum dimensions of the broadband circular waveguide feed
Parameter Designation Value (mm)
2a Waveguide inside diameter 2070
d Waveguide outside diameter 3690
lcrLength of the circular waveguide section 1430
m Distance between the aperture plane and the first corrugation 950
xDistance from the last corrugation to the end of the cylindrical outer surface
550
ltrLength of the rectangular-to-circularwaveguide transition 4465
lrcLength of the rectangular waveguide section 1430
tch Choke slot width 090
lch Choke depth 750
t Choke metal width 090
lcor Corrugation depth 465
tcor Corrugation metal width 100
s Corrugation slot width 10
lp Probe length 530
sp Probe position from the back short 530
din Probe diameter 127
b Inside height of the rectangular waveguide 857
tw Waveguide wall thickness 500
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-40-
IV Design of Circular Waveguide Feeds Loaded with a
Dielectric Rod
In this section circular waveguide feeds loaded with a dielectric rod feed
are investigated A comprehensive discussion of the circular waveguide loaded
with a dielectric rod is given by Kumar[7] Inserting a dielectric material
inside the circular waveguide improves the E- and H-plane pattern symmetry
In general dielectric-loaded circular waveguide feeds show good performance
only over a narrow bandwidth
Fig 41 shows the geometry of a circular waveguide loaded with a
dielectric rod The waveguide length is 400mm and the wall thickness is
05mm The dielectric rods diameter is 207mm The dielectric rod is
extended 05 wavelength beyond the waveguide open end The dielectric
constant εr is changed and the feeds performance is observed
Fig 41 Geometry of a circular waveguide loaded with a uniform dielectric
rod
-41-
Fig 42 is the radiation pattern of the feed with εr = 25 and L = 05λ0 at
9GHz E- and H-plane 10-dB beamwidths are 810 and 807 degrees
respectively The front-to-back ratio is 18dB The antenna gain is 71dB
(a)
(b)
Fig 42 Radiation pattern at 9GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 05λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-42-
Fig 43 shows the radiation pattern of the feed with εr = 21 at 10GHz
E- and H-plane 10-dB beamwidths are 70 and 71 degrees respectively The
front-to-back ratio is 19dB The antenna gain is 83dB
(a)
(b)
Fig 43 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 21 and L = 05λ0 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-43-
Fig 44 shows the radiation pattern of the feed with εr = 30 at 8GHz
E- and H-plane 10-dB beamwidths are 83 and 824 degrees respectively The
front-to-back ratio is 17dB The antenna gain is 73dB
(a)
(b)
Fig 44 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 30 and L = 05λ0 at 8GHz (a) 2D radiation pattern
and (b) E- and H-plane patterns
-44-
Fig 45 shows the radiation pattern of the feed with εr = 50 at 18GHz
E- and H-plane 10-dB beamwidths are 56 and 54 degrees respectively The
front-to-back ratio is 27dB The antenna gain is 105dB The feed has a good
pattern symmetry and low back radiation
(a)
(b)
Fig 45 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 50 and L = 05λ0 at 18GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-45-
Fig 46 is the radiation pattern of the feed with εr = 25 and L = 10λ0 at
10GHz E- and H-plane 10-dB beamwidths are 50 and 48 degrees
respectively The front-to-back ratio is 16dB The antenna gain is 105dB
(a)
(b)
Fig 46 Radiation pattern at 10GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 10λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-46-
Fig 47 shows the geometry of a circular waveguide with a tapered
dielectric rod The designed feed has the following dimension L = 1λ0 d =
1λ0 and εr =25 at 10GHz The waveguide length is 40mm and the wall
thickness is 05mm
L
Dielectricd3
Fig 47 Geometry of a circular waveguide loaded with a tapered dielectric
rod
Fig 48 shows the radiatio pattern of the designed feed E- and H-plane
10-dB beamwidths are 575 and 564 degrees respectively The front-to-back
ratio is 377dB The antenna gain is 94dB The designed feed has an
excellent beamwidth symmetry and a very low back radiation
-47-
(a)
(b)
Fig 48 Radiation pattern of a circular waveguide loaded with a tapered
dielectric rod with L = 1λ0 d = 1λ0 and εr =25 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-48-
Fig 49 shows the geometry of a spherical ended dielectric rod feed
diameter of 06λ0 at 10GHz with a dielectric constant of 25 and L= 03λ0
Fig 410 shows the radiation patterns of the designed feed E- and H-plane
10-dB beamwidths are both 63 degrees The front-to-back ratio is 24dB The
antenna gain is 864dB
Fig 49 Geometry of a circular waveguide loaded with a spherical ended
dielectric rod
-49-
(a)
(b)
Fig 410 Radiation pattern of a circular waveguide loaded wht a spherical
ended dielectric rod with d = 06λ0 L = 03λ0 and εr =25 at 10GHz (a) 3D
radiation pattern and (b) E- and H-plane patterns
-50-
V Design of a Broadband Circular Waveguide Feed
In this chapter the design of a broadband circular waveguide feed is
presented At microwave frequencies the feed is often a circular waveguide
with chokes and corrugations around the aperture Chokes and corrugations
equalize E- and H-plane patterns and reduce the back radiation
The proposed feed is designed to operate over 10-18GHz The design starts
with the optimization of the coaxial-to-rectangular waveguide adapter
employed for good mode purity over a broad frequency range Next a
rectangular-to-circular waveguide transition is optimized Finally chokes and
corrugations are designed for improved pattern symmetry and low back
radiation
The proposed feed structure is shown in Fig 51 The feed consist of the
following parts a coaxial-to-rectangular waveguide adapter a rectangular-to-
circular waveguide transition a circular waveguide section four quarter-wave
chokes around the feeds aperture and four corrugations on the feeds outer
surface
The computer simulation shows the above arrangement offers good radiation
patterns over a broad frequency range The broadband operation is obtained
by exciting the TE11 mode in the circular waveguide using the TE10 mode of
the rectangular waveguide which is in turn excited by a coaxial probe
-51-
Chokes
Coaxial-to-waveguide transition
Circular wavguide
Corrugations
Mode transition
(a)
(b)
Fig 51 Structure of the proposed broadband circular waveguide feed
(a) CAD model and (b) cross-sectional view
For the coaxial-to-rectangular waveguide adapter an SMA connector with
the probe diameter of 127 mm is employed The coaxial probe inserted into
the waveguide energizes the feed and excites the dominant TE10 mode in
-52-
the rectangular waveguide The impedance matching is achieved by adjusting
the probe distance sp from the back short and the probe length lp
(a)
(b)
Fig 52 Reflection coefficient of the coaxial-to-rectangular adapter versus
(a) probe length lp and (b) the probe position sp
Fig 52 shows the reflection coefficient versus the various values of probe
lengths lp and probe positions sp The probe length lp is adjusted to obtain
antenna impedance matching and the probe distance sp is adjusted to obtain a
-53-
desired resonant frequency
Next a transition between rectangular and circular waveguide is designed
The transition section converts the TE10 mode in the rectangular waveguide to
TE11 mode in the circular waveguide and vice versa The transition is built
in a form of a taper for easy fabrication[22]
(a)
(b)
Fig 53 Structure of the rectangular-to-circular waveguide transition
(a) 3D view and (b) cross sectional view
The dimensions of the final optimized transition are as follows The length
of the rectangular waveguide section is 143mm The rectangular waveguides
width a and height b are 207mm and 857mm respectively The length of
the circular waveguide section is 143mm The inside diameter of the circular
-54-
waveguide is 207mm(097 wavelength at 14GHz) The length of transition
region ltr is 4465mm(approximately equal to 2λ0 at 14GHz) Fig 54 shows
the field distribution inside the mode converter
(a)
(b)
Fig 54 Field distribution inside the mode converter at
(a) 10GHz (b) 14GHz and (c) 18GHz
-55-
(c)
Fig 54 continued
Finally multiple chokes are investigated Figs 55 56 and 57 show the
feed performance without chokes The reflection coefficient is less than -10dB
over 10-19GHz The antenna has a gain of 921dB to 1189dB over
10-19GHz
Fig 55 Reflection coefficient of the broadband circular waveguide feed
without chokes and corrugations
-56-
(a)
(b)
(c)
Fig 56 E- and H-plane patterns of the broadband circular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-57-
(d)
(e)
Fig 56 continued
-58-
(a)
(b)
Fig 57 2D radiation patterns of the broadband cicular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-59-
(c)
(d)
Fig 57 continued
-60-
(e)
Fig 57 continued
To achieve equal beamwidths in E and H planes over a wide frequency
range chokes and corrugations are employed Table51 summarizes the
performance of a feed without chokes and corrugations
Table 51 Performance of the broadband circular waveguide feed without
chokes and corrugations
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
1000 940 6061 15
1200 972 6159 17
1400 920 5957 21
1600 1070 4751 29
1800 1188 5352 21
-61-
Four quarter-wavelength chokes are introduced in the feed design which
has a slot depth of 75mm and slot width of 09mm The choke slot spacing
is 18mm The choke design is investigated by applying the choke one by
one and the effect on the E- and H-plane patterns are observed as illustrated
in Figs 58 and 59 The use of chokes makes the E-plane pattern narrower
The H-plane pattern is not affected Chokes increase the gain slightly and
reduce back radiation
(a)
(b)
Fig 58 Effect of chokes on the E-plane pattern of the broadband circular
waveguide feed at (a) 10GHz(b) 12GHz (c) 14GHz (d) 16GHz and (e)
18GHz
-62-
(c)
(d)
(e)
Fig 58 continued
-63-
(a)
(b)
(c)
Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-64-
(d)
(e)
Fig 59 continued
-65-
Fig 510 shows the feed performance versus the choke depth When the
choke depth is varied from 535mm to 95mm the E- and H-plane patterns
are strongly affected The optimum value of choke depth is 75mm(035λ0 at
14GHz) which gives equal E- and H-plane radiation patterns and leads to
low back radiation
Fig 511 shows the feed performance versus the choke slot width tch The
choke slot width is varied from 09mm to 21mm Radiation patterns and
reflection coefficients are not sensitive to the choke slot width The final
choke slot width is selected to be 09mm considering the feed diameter
minimization and the manufacturability The overall diameter of the proposed
feed is 369mm which is increased from the 207mm of the waveguide
inside diameter due to the use of four chokes
-66-
(a)
(b)
(c)
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection coefficient
-67-
(a)
(b)
(c)
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and (c)
reflection coefficient
-68-
Next we investigated corrugations placed on the outer wall of the feed
Four corrugations applied to the outer surface of the circular waveguide The
corrugation depth is 465mm(0215λ0 at 14GHz) The primary purpose of
using corrugations is to further reduce the back radiation Increasing the
number of corrugations beyond four has little effect in reducing the back
radiation
Figs 512 and 513 show the effect of corrugations on the E- and H-plane
patterns Fig 514 shows the parametric study of the corrugation depth lcor
The corrugation depth is varied from 40mm and 645mm The optimum
value of the corrugation depth is found to be 465mm
-69-
(a)
(b)
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern at (a) 12GHz and (b) 14GHz
-70-
(a)
(b)
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern at (a) 12GHz and (b) 14GHz
-71-
(a)
(b)
(c)
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection coefficient
-72-
The phase center location is important in placing the feed in a reflector
antenna[8] The phase center variation with frequency should be small Fig
515 shows the effect of chokes and corrugations on the phase center The
curve with circle corresponds to the case without chokes and corrugations
The phase center varies from -326mm and -190mm away from the feeds
aperture plane It means the phase center is located inside the waveguide
The curve with triangles corresponds to the case with chokes The curve with
squares to the case with chokes and corrugations The phase center varies
from 0mm to -302mm
From Fig 515 we can observed that phase center variation reduced by the
corrugation and three cases phase center calculated in φ=450 plane
parameter sweep values are given in Table 52
10 12 14 16 181
0
-1
-2
-3
-4
-5
-6
Pha
se c
ente
r (m
m)
Frequency (GHz)
choke+corrugatuion without choke corrugation with choke
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
-73-
Frequency
(GHz)
Phase center from the aperture plane
(mm)
Without
chokes and
corrugations
With
chokes
With chokes
and
corrugations
1000 -326 062 000
1100 -187 030 -002
1200 -563 -208 -065
1300 -296 -154 -202
1400 -319 -314 -302
1500 -201 -203 -241
1600 -242 -233 -207
1700 -208 -208 -186
1800 -190 -157 -132
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
Based on the foregoing parametric studies optimum dimensions of the
broadband circular waveguide feed are obtained as shown in Table 53
-74-
Table 53 Optimum dimensions of the broadband circular waveguide feed
Parameter Designation Value (mm)
2a Waveguide inside diameter 2070
d Waveguide outside diameter 3690
lcrLength of the circular waveguide section 1430
m Distance between the aperture plane and the first corrugation 950
xDistance from the last corrugation to the end of the cylindrical outer surface
550
ltrLength of the rectangular-to-circularwaveguide transition 4465
lrcLength of the rectangular waveguide section 1430
tch Choke slot width 090
lch Choke depth 750
t Choke metal width 090
lcor Corrugation depth 465
tcor Corrugation metal width 100
s Corrugation slot width 10
lp Probe length 530
sp Probe position from the back short 530
din Probe diameter 127
b Inside height of the rectangular waveguide 857
tw Waveguide wall thickness 500
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-41-
Fig 42 is the radiation pattern of the feed with εr = 25 and L = 05λ0 at
9GHz E- and H-plane 10-dB beamwidths are 810 and 807 degrees
respectively The front-to-back ratio is 18dB The antenna gain is 71dB
(a)
(b)
Fig 42 Radiation pattern at 9GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 05λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-42-
Fig 43 shows the radiation pattern of the feed with εr = 21 at 10GHz
E- and H-plane 10-dB beamwidths are 70 and 71 degrees respectively The
front-to-back ratio is 19dB The antenna gain is 83dB
(a)
(b)
Fig 43 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 21 and L = 05λ0 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-43-
Fig 44 shows the radiation pattern of the feed with εr = 30 at 8GHz
E- and H-plane 10-dB beamwidths are 83 and 824 degrees respectively The
front-to-back ratio is 17dB The antenna gain is 73dB
(a)
(b)
Fig 44 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 30 and L = 05λ0 at 8GHz (a) 2D radiation pattern
and (b) E- and H-plane patterns
-44-
Fig 45 shows the radiation pattern of the feed with εr = 50 at 18GHz
E- and H-plane 10-dB beamwidths are 56 and 54 degrees respectively The
front-to-back ratio is 27dB The antenna gain is 105dB The feed has a good
pattern symmetry and low back radiation
(a)
(b)
Fig 45 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 50 and L = 05λ0 at 18GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-45-
Fig 46 is the radiation pattern of the feed with εr = 25 and L = 10λ0 at
10GHz E- and H-plane 10-dB beamwidths are 50 and 48 degrees
respectively The front-to-back ratio is 16dB The antenna gain is 105dB
(a)
(b)
Fig 46 Radiation pattern at 10GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 10λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-46-
Fig 47 shows the geometry of a circular waveguide with a tapered
dielectric rod The designed feed has the following dimension L = 1λ0 d =
1λ0 and εr =25 at 10GHz The waveguide length is 40mm and the wall
thickness is 05mm
L
Dielectricd3
Fig 47 Geometry of a circular waveguide loaded with a tapered dielectric
rod
Fig 48 shows the radiatio pattern of the designed feed E- and H-plane
10-dB beamwidths are 575 and 564 degrees respectively The front-to-back
ratio is 377dB The antenna gain is 94dB The designed feed has an
excellent beamwidth symmetry and a very low back radiation
-47-
(a)
(b)
Fig 48 Radiation pattern of a circular waveguide loaded with a tapered
dielectric rod with L = 1λ0 d = 1λ0 and εr =25 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-48-
Fig 49 shows the geometry of a spherical ended dielectric rod feed
diameter of 06λ0 at 10GHz with a dielectric constant of 25 and L= 03λ0
Fig 410 shows the radiation patterns of the designed feed E- and H-plane
10-dB beamwidths are both 63 degrees The front-to-back ratio is 24dB The
antenna gain is 864dB
Fig 49 Geometry of a circular waveguide loaded with a spherical ended
dielectric rod
-49-
(a)
(b)
Fig 410 Radiation pattern of a circular waveguide loaded wht a spherical
ended dielectric rod with d = 06λ0 L = 03λ0 and εr =25 at 10GHz (a) 3D
radiation pattern and (b) E- and H-plane patterns
-50-
V Design of a Broadband Circular Waveguide Feed
In this chapter the design of a broadband circular waveguide feed is
presented At microwave frequencies the feed is often a circular waveguide
with chokes and corrugations around the aperture Chokes and corrugations
equalize E- and H-plane patterns and reduce the back radiation
The proposed feed is designed to operate over 10-18GHz The design starts
with the optimization of the coaxial-to-rectangular waveguide adapter
employed for good mode purity over a broad frequency range Next a
rectangular-to-circular waveguide transition is optimized Finally chokes and
corrugations are designed for improved pattern symmetry and low back
radiation
The proposed feed structure is shown in Fig 51 The feed consist of the
following parts a coaxial-to-rectangular waveguide adapter a rectangular-to-
circular waveguide transition a circular waveguide section four quarter-wave
chokes around the feeds aperture and four corrugations on the feeds outer
surface
The computer simulation shows the above arrangement offers good radiation
patterns over a broad frequency range The broadband operation is obtained
by exciting the TE11 mode in the circular waveguide using the TE10 mode of
the rectangular waveguide which is in turn excited by a coaxial probe
-51-
Chokes
Coaxial-to-waveguide transition
Circular wavguide
Corrugations
Mode transition
(a)
(b)
Fig 51 Structure of the proposed broadband circular waveguide feed
(a) CAD model and (b) cross-sectional view
For the coaxial-to-rectangular waveguide adapter an SMA connector with
the probe diameter of 127 mm is employed The coaxial probe inserted into
the waveguide energizes the feed and excites the dominant TE10 mode in
-52-
the rectangular waveguide The impedance matching is achieved by adjusting
the probe distance sp from the back short and the probe length lp
(a)
(b)
Fig 52 Reflection coefficient of the coaxial-to-rectangular adapter versus
(a) probe length lp and (b) the probe position sp
Fig 52 shows the reflection coefficient versus the various values of probe
lengths lp and probe positions sp The probe length lp is adjusted to obtain
antenna impedance matching and the probe distance sp is adjusted to obtain a
-53-
desired resonant frequency
Next a transition between rectangular and circular waveguide is designed
The transition section converts the TE10 mode in the rectangular waveguide to
TE11 mode in the circular waveguide and vice versa The transition is built
in a form of a taper for easy fabrication[22]
(a)
(b)
Fig 53 Structure of the rectangular-to-circular waveguide transition
(a) 3D view and (b) cross sectional view
The dimensions of the final optimized transition are as follows The length
of the rectangular waveguide section is 143mm The rectangular waveguides
width a and height b are 207mm and 857mm respectively The length of
the circular waveguide section is 143mm The inside diameter of the circular
-54-
waveguide is 207mm(097 wavelength at 14GHz) The length of transition
region ltr is 4465mm(approximately equal to 2λ0 at 14GHz) Fig 54 shows
the field distribution inside the mode converter
(a)
(b)
Fig 54 Field distribution inside the mode converter at
(a) 10GHz (b) 14GHz and (c) 18GHz
-55-
(c)
Fig 54 continued
Finally multiple chokes are investigated Figs 55 56 and 57 show the
feed performance without chokes The reflection coefficient is less than -10dB
over 10-19GHz The antenna has a gain of 921dB to 1189dB over
10-19GHz
Fig 55 Reflection coefficient of the broadband circular waveguide feed
without chokes and corrugations
-56-
(a)
(b)
(c)
Fig 56 E- and H-plane patterns of the broadband circular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-57-
(d)
(e)
Fig 56 continued
-58-
(a)
(b)
Fig 57 2D radiation patterns of the broadband cicular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-59-
(c)
(d)
Fig 57 continued
-60-
(e)
Fig 57 continued
To achieve equal beamwidths in E and H planes over a wide frequency
range chokes and corrugations are employed Table51 summarizes the
performance of a feed without chokes and corrugations
Table 51 Performance of the broadband circular waveguide feed without
chokes and corrugations
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
1000 940 6061 15
1200 972 6159 17
1400 920 5957 21
1600 1070 4751 29
1800 1188 5352 21
-61-
Four quarter-wavelength chokes are introduced in the feed design which
has a slot depth of 75mm and slot width of 09mm The choke slot spacing
is 18mm The choke design is investigated by applying the choke one by
one and the effect on the E- and H-plane patterns are observed as illustrated
in Figs 58 and 59 The use of chokes makes the E-plane pattern narrower
The H-plane pattern is not affected Chokes increase the gain slightly and
reduce back radiation
(a)
(b)
Fig 58 Effect of chokes on the E-plane pattern of the broadband circular
waveguide feed at (a) 10GHz(b) 12GHz (c) 14GHz (d) 16GHz and (e)
18GHz
-62-
(c)
(d)
(e)
Fig 58 continued
-63-
(a)
(b)
(c)
Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-64-
(d)
(e)
Fig 59 continued
-65-
Fig 510 shows the feed performance versus the choke depth When the
choke depth is varied from 535mm to 95mm the E- and H-plane patterns
are strongly affected The optimum value of choke depth is 75mm(035λ0 at
14GHz) which gives equal E- and H-plane radiation patterns and leads to
low back radiation
Fig 511 shows the feed performance versus the choke slot width tch The
choke slot width is varied from 09mm to 21mm Radiation patterns and
reflection coefficients are not sensitive to the choke slot width The final
choke slot width is selected to be 09mm considering the feed diameter
minimization and the manufacturability The overall diameter of the proposed
feed is 369mm which is increased from the 207mm of the waveguide
inside diameter due to the use of four chokes
-66-
(a)
(b)
(c)
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection coefficient
-67-
(a)
(b)
(c)
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and (c)
reflection coefficient
-68-
Next we investigated corrugations placed on the outer wall of the feed
Four corrugations applied to the outer surface of the circular waveguide The
corrugation depth is 465mm(0215λ0 at 14GHz) The primary purpose of
using corrugations is to further reduce the back radiation Increasing the
number of corrugations beyond four has little effect in reducing the back
radiation
Figs 512 and 513 show the effect of corrugations on the E- and H-plane
patterns Fig 514 shows the parametric study of the corrugation depth lcor
The corrugation depth is varied from 40mm and 645mm The optimum
value of the corrugation depth is found to be 465mm
-69-
(a)
(b)
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern at (a) 12GHz and (b) 14GHz
-70-
(a)
(b)
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern at (a) 12GHz and (b) 14GHz
-71-
(a)
(b)
(c)
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection coefficient
-72-
The phase center location is important in placing the feed in a reflector
antenna[8] The phase center variation with frequency should be small Fig
515 shows the effect of chokes and corrugations on the phase center The
curve with circle corresponds to the case without chokes and corrugations
The phase center varies from -326mm and -190mm away from the feeds
aperture plane It means the phase center is located inside the waveguide
The curve with triangles corresponds to the case with chokes The curve with
squares to the case with chokes and corrugations The phase center varies
from 0mm to -302mm
From Fig 515 we can observed that phase center variation reduced by the
corrugation and three cases phase center calculated in φ=450 plane
parameter sweep values are given in Table 52
10 12 14 16 181
0
-1
-2
-3
-4
-5
-6
Pha
se c
ente
r (m
m)
Frequency (GHz)
choke+corrugatuion without choke corrugation with choke
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
-73-
Frequency
(GHz)
Phase center from the aperture plane
(mm)
Without
chokes and
corrugations
With
chokes
With chokes
and
corrugations
1000 -326 062 000
1100 -187 030 -002
1200 -563 -208 -065
1300 -296 -154 -202
1400 -319 -314 -302
1500 -201 -203 -241
1600 -242 -233 -207
1700 -208 -208 -186
1800 -190 -157 -132
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
Based on the foregoing parametric studies optimum dimensions of the
broadband circular waveguide feed are obtained as shown in Table 53
-74-
Table 53 Optimum dimensions of the broadband circular waveguide feed
Parameter Designation Value (mm)
2a Waveguide inside diameter 2070
d Waveguide outside diameter 3690
lcrLength of the circular waveguide section 1430
m Distance between the aperture plane and the first corrugation 950
xDistance from the last corrugation to the end of the cylindrical outer surface
550
ltrLength of the rectangular-to-circularwaveguide transition 4465
lrcLength of the rectangular waveguide section 1430
tch Choke slot width 090
lch Choke depth 750
t Choke metal width 090
lcor Corrugation depth 465
tcor Corrugation metal width 100
s Corrugation slot width 10
lp Probe length 530
sp Probe position from the back short 530
din Probe diameter 127
b Inside height of the rectangular waveguide 857
tw Waveguide wall thickness 500
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-42-
Fig 43 shows the radiation pattern of the feed with εr = 21 at 10GHz
E- and H-plane 10-dB beamwidths are 70 and 71 degrees respectively The
front-to-back ratio is 19dB The antenna gain is 83dB
(a)
(b)
Fig 43 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 21 and L = 05λ0 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-43-
Fig 44 shows the radiation pattern of the feed with εr = 30 at 8GHz
E- and H-plane 10-dB beamwidths are 83 and 824 degrees respectively The
front-to-back ratio is 17dB The antenna gain is 73dB
(a)
(b)
Fig 44 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 30 and L = 05λ0 at 8GHz (a) 2D radiation pattern
and (b) E- and H-plane patterns
-44-
Fig 45 shows the radiation pattern of the feed with εr = 50 at 18GHz
E- and H-plane 10-dB beamwidths are 56 and 54 degrees respectively The
front-to-back ratio is 27dB The antenna gain is 105dB The feed has a good
pattern symmetry and low back radiation
(a)
(b)
Fig 45 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 50 and L = 05λ0 at 18GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-45-
Fig 46 is the radiation pattern of the feed with εr = 25 and L = 10λ0 at
10GHz E- and H-plane 10-dB beamwidths are 50 and 48 degrees
respectively The front-to-back ratio is 16dB The antenna gain is 105dB
(a)
(b)
Fig 46 Radiation pattern at 10GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 10λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-46-
Fig 47 shows the geometry of a circular waveguide with a tapered
dielectric rod The designed feed has the following dimension L = 1λ0 d =
1λ0 and εr =25 at 10GHz The waveguide length is 40mm and the wall
thickness is 05mm
L
Dielectricd3
Fig 47 Geometry of a circular waveguide loaded with a tapered dielectric
rod
Fig 48 shows the radiatio pattern of the designed feed E- and H-plane
10-dB beamwidths are 575 and 564 degrees respectively The front-to-back
ratio is 377dB The antenna gain is 94dB The designed feed has an
excellent beamwidth symmetry and a very low back radiation
-47-
(a)
(b)
Fig 48 Radiation pattern of a circular waveguide loaded with a tapered
dielectric rod with L = 1λ0 d = 1λ0 and εr =25 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-48-
Fig 49 shows the geometry of a spherical ended dielectric rod feed
diameter of 06λ0 at 10GHz with a dielectric constant of 25 and L= 03λ0
Fig 410 shows the radiation patterns of the designed feed E- and H-plane
10-dB beamwidths are both 63 degrees The front-to-back ratio is 24dB The
antenna gain is 864dB
Fig 49 Geometry of a circular waveguide loaded with a spherical ended
dielectric rod
-49-
(a)
(b)
Fig 410 Radiation pattern of a circular waveguide loaded wht a spherical
ended dielectric rod with d = 06λ0 L = 03λ0 and εr =25 at 10GHz (a) 3D
radiation pattern and (b) E- and H-plane patterns
-50-
V Design of a Broadband Circular Waveguide Feed
In this chapter the design of a broadband circular waveguide feed is
presented At microwave frequencies the feed is often a circular waveguide
with chokes and corrugations around the aperture Chokes and corrugations
equalize E- and H-plane patterns and reduce the back radiation
The proposed feed is designed to operate over 10-18GHz The design starts
with the optimization of the coaxial-to-rectangular waveguide adapter
employed for good mode purity over a broad frequency range Next a
rectangular-to-circular waveguide transition is optimized Finally chokes and
corrugations are designed for improved pattern symmetry and low back
radiation
The proposed feed structure is shown in Fig 51 The feed consist of the
following parts a coaxial-to-rectangular waveguide adapter a rectangular-to-
circular waveguide transition a circular waveguide section four quarter-wave
chokes around the feeds aperture and four corrugations on the feeds outer
surface
The computer simulation shows the above arrangement offers good radiation
patterns over a broad frequency range The broadband operation is obtained
by exciting the TE11 mode in the circular waveguide using the TE10 mode of
the rectangular waveguide which is in turn excited by a coaxial probe
-51-
Chokes
Coaxial-to-waveguide transition
Circular wavguide
Corrugations
Mode transition
(a)
(b)
Fig 51 Structure of the proposed broadband circular waveguide feed
(a) CAD model and (b) cross-sectional view
For the coaxial-to-rectangular waveguide adapter an SMA connector with
the probe diameter of 127 mm is employed The coaxial probe inserted into
the waveguide energizes the feed and excites the dominant TE10 mode in
-52-
the rectangular waveguide The impedance matching is achieved by adjusting
the probe distance sp from the back short and the probe length lp
(a)
(b)
Fig 52 Reflection coefficient of the coaxial-to-rectangular adapter versus
(a) probe length lp and (b) the probe position sp
Fig 52 shows the reflection coefficient versus the various values of probe
lengths lp and probe positions sp The probe length lp is adjusted to obtain
antenna impedance matching and the probe distance sp is adjusted to obtain a
-53-
desired resonant frequency
Next a transition between rectangular and circular waveguide is designed
The transition section converts the TE10 mode in the rectangular waveguide to
TE11 mode in the circular waveguide and vice versa The transition is built
in a form of a taper for easy fabrication[22]
(a)
(b)
Fig 53 Structure of the rectangular-to-circular waveguide transition
(a) 3D view and (b) cross sectional view
The dimensions of the final optimized transition are as follows The length
of the rectangular waveguide section is 143mm The rectangular waveguides
width a and height b are 207mm and 857mm respectively The length of
the circular waveguide section is 143mm The inside diameter of the circular
-54-
waveguide is 207mm(097 wavelength at 14GHz) The length of transition
region ltr is 4465mm(approximately equal to 2λ0 at 14GHz) Fig 54 shows
the field distribution inside the mode converter
(a)
(b)
Fig 54 Field distribution inside the mode converter at
(a) 10GHz (b) 14GHz and (c) 18GHz
-55-
(c)
Fig 54 continued
Finally multiple chokes are investigated Figs 55 56 and 57 show the
feed performance without chokes The reflection coefficient is less than -10dB
over 10-19GHz The antenna has a gain of 921dB to 1189dB over
10-19GHz
Fig 55 Reflection coefficient of the broadband circular waveguide feed
without chokes and corrugations
-56-
(a)
(b)
(c)
Fig 56 E- and H-plane patterns of the broadband circular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-57-
(d)
(e)
Fig 56 continued
-58-
(a)
(b)
Fig 57 2D radiation patterns of the broadband cicular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-59-
(c)
(d)
Fig 57 continued
-60-
(e)
Fig 57 continued
To achieve equal beamwidths in E and H planes over a wide frequency
range chokes and corrugations are employed Table51 summarizes the
performance of a feed without chokes and corrugations
Table 51 Performance of the broadband circular waveguide feed without
chokes and corrugations
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
1000 940 6061 15
1200 972 6159 17
1400 920 5957 21
1600 1070 4751 29
1800 1188 5352 21
-61-
Four quarter-wavelength chokes are introduced in the feed design which
has a slot depth of 75mm and slot width of 09mm The choke slot spacing
is 18mm The choke design is investigated by applying the choke one by
one and the effect on the E- and H-plane patterns are observed as illustrated
in Figs 58 and 59 The use of chokes makes the E-plane pattern narrower
The H-plane pattern is not affected Chokes increase the gain slightly and
reduce back radiation
(a)
(b)
Fig 58 Effect of chokes on the E-plane pattern of the broadband circular
waveguide feed at (a) 10GHz(b) 12GHz (c) 14GHz (d) 16GHz and (e)
18GHz
-62-
(c)
(d)
(e)
Fig 58 continued
-63-
(a)
(b)
(c)
Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-64-
(d)
(e)
Fig 59 continued
-65-
Fig 510 shows the feed performance versus the choke depth When the
choke depth is varied from 535mm to 95mm the E- and H-plane patterns
are strongly affected The optimum value of choke depth is 75mm(035λ0 at
14GHz) which gives equal E- and H-plane radiation patterns and leads to
low back radiation
Fig 511 shows the feed performance versus the choke slot width tch The
choke slot width is varied from 09mm to 21mm Radiation patterns and
reflection coefficients are not sensitive to the choke slot width The final
choke slot width is selected to be 09mm considering the feed diameter
minimization and the manufacturability The overall diameter of the proposed
feed is 369mm which is increased from the 207mm of the waveguide
inside diameter due to the use of four chokes
-66-
(a)
(b)
(c)
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection coefficient
-67-
(a)
(b)
(c)
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and (c)
reflection coefficient
-68-
Next we investigated corrugations placed on the outer wall of the feed
Four corrugations applied to the outer surface of the circular waveguide The
corrugation depth is 465mm(0215λ0 at 14GHz) The primary purpose of
using corrugations is to further reduce the back radiation Increasing the
number of corrugations beyond four has little effect in reducing the back
radiation
Figs 512 and 513 show the effect of corrugations on the E- and H-plane
patterns Fig 514 shows the parametric study of the corrugation depth lcor
The corrugation depth is varied from 40mm and 645mm The optimum
value of the corrugation depth is found to be 465mm
-69-
(a)
(b)
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern at (a) 12GHz and (b) 14GHz
-70-
(a)
(b)
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern at (a) 12GHz and (b) 14GHz
-71-
(a)
(b)
(c)
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection coefficient
-72-
The phase center location is important in placing the feed in a reflector
antenna[8] The phase center variation with frequency should be small Fig
515 shows the effect of chokes and corrugations on the phase center The
curve with circle corresponds to the case without chokes and corrugations
The phase center varies from -326mm and -190mm away from the feeds
aperture plane It means the phase center is located inside the waveguide
The curve with triangles corresponds to the case with chokes The curve with
squares to the case with chokes and corrugations The phase center varies
from 0mm to -302mm
From Fig 515 we can observed that phase center variation reduced by the
corrugation and three cases phase center calculated in φ=450 plane
parameter sweep values are given in Table 52
10 12 14 16 181
0
-1
-2
-3
-4
-5
-6
Pha
se c
ente
r (m
m)
Frequency (GHz)
choke+corrugatuion without choke corrugation with choke
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
-73-
Frequency
(GHz)
Phase center from the aperture plane
(mm)
Without
chokes and
corrugations
With
chokes
With chokes
and
corrugations
1000 -326 062 000
1100 -187 030 -002
1200 -563 -208 -065
1300 -296 -154 -202
1400 -319 -314 -302
1500 -201 -203 -241
1600 -242 -233 -207
1700 -208 -208 -186
1800 -190 -157 -132
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
Based on the foregoing parametric studies optimum dimensions of the
broadband circular waveguide feed are obtained as shown in Table 53
-74-
Table 53 Optimum dimensions of the broadband circular waveguide feed
Parameter Designation Value (mm)
2a Waveguide inside diameter 2070
d Waveguide outside diameter 3690
lcrLength of the circular waveguide section 1430
m Distance between the aperture plane and the first corrugation 950
xDistance from the last corrugation to the end of the cylindrical outer surface
550
ltrLength of the rectangular-to-circularwaveguide transition 4465
lrcLength of the rectangular waveguide section 1430
tch Choke slot width 090
lch Choke depth 750
t Choke metal width 090
lcor Corrugation depth 465
tcor Corrugation metal width 100
s Corrugation slot width 10
lp Probe length 530
sp Probe position from the back short 530
din Probe diameter 127
b Inside height of the rectangular waveguide 857
tw Waveguide wall thickness 500
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-43-
Fig 44 shows the radiation pattern of the feed with εr = 30 at 8GHz
E- and H-plane 10-dB beamwidths are 83 and 824 degrees respectively The
front-to-back ratio is 17dB The antenna gain is 73dB
(a)
(b)
Fig 44 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 30 and L = 05λ0 at 8GHz (a) 2D radiation pattern
and (b) E- and H-plane patterns
-44-
Fig 45 shows the radiation pattern of the feed with εr = 50 at 18GHz
E- and H-plane 10-dB beamwidths are 56 and 54 degrees respectively The
front-to-back ratio is 27dB The antenna gain is 105dB The feed has a good
pattern symmetry and low back radiation
(a)
(b)
Fig 45 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 50 and L = 05λ0 at 18GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-45-
Fig 46 is the radiation pattern of the feed with εr = 25 and L = 10λ0 at
10GHz E- and H-plane 10-dB beamwidths are 50 and 48 degrees
respectively The front-to-back ratio is 16dB The antenna gain is 105dB
(a)
(b)
Fig 46 Radiation pattern at 10GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 10λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-46-
Fig 47 shows the geometry of a circular waveguide with a tapered
dielectric rod The designed feed has the following dimension L = 1λ0 d =
1λ0 and εr =25 at 10GHz The waveguide length is 40mm and the wall
thickness is 05mm
L
Dielectricd3
Fig 47 Geometry of a circular waveguide loaded with a tapered dielectric
rod
Fig 48 shows the radiatio pattern of the designed feed E- and H-plane
10-dB beamwidths are 575 and 564 degrees respectively The front-to-back
ratio is 377dB The antenna gain is 94dB The designed feed has an
excellent beamwidth symmetry and a very low back radiation
-47-
(a)
(b)
Fig 48 Radiation pattern of a circular waveguide loaded with a tapered
dielectric rod with L = 1λ0 d = 1λ0 and εr =25 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-48-
Fig 49 shows the geometry of a spherical ended dielectric rod feed
diameter of 06λ0 at 10GHz with a dielectric constant of 25 and L= 03λ0
Fig 410 shows the radiation patterns of the designed feed E- and H-plane
10-dB beamwidths are both 63 degrees The front-to-back ratio is 24dB The
antenna gain is 864dB
Fig 49 Geometry of a circular waveguide loaded with a spherical ended
dielectric rod
-49-
(a)
(b)
Fig 410 Radiation pattern of a circular waveguide loaded wht a spherical
ended dielectric rod with d = 06λ0 L = 03λ0 and εr =25 at 10GHz (a) 3D
radiation pattern and (b) E- and H-plane patterns
-50-
V Design of a Broadband Circular Waveguide Feed
In this chapter the design of a broadband circular waveguide feed is
presented At microwave frequencies the feed is often a circular waveguide
with chokes and corrugations around the aperture Chokes and corrugations
equalize E- and H-plane patterns and reduce the back radiation
The proposed feed is designed to operate over 10-18GHz The design starts
with the optimization of the coaxial-to-rectangular waveguide adapter
employed for good mode purity over a broad frequency range Next a
rectangular-to-circular waveguide transition is optimized Finally chokes and
corrugations are designed for improved pattern symmetry and low back
radiation
The proposed feed structure is shown in Fig 51 The feed consist of the
following parts a coaxial-to-rectangular waveguide adapter a rectangular-to-
circular waveguide transition a circular waveguide section four quarter-wave
chokes around the feeds aperture and four corrugations on the feeds outer
surface
The computer simulation shows the above arrangement offers good radiation
patterns over a broad frequency range The broadband operation is obtained
by exciting the TE11 mode in the circular waveguide using the TE10 mode of
the rectangular waveguide which is in turn excited by a coaxial probe
-51-
Chokes
Coaxial-to-waveguide transition
Circular wavguide
Corrugations
Mode transition
(a)
(b)
Fig 51 Structure of the proposed broadband circular waveguide feed
(a) CAD model and (b) cross-sectional view
For the coaxial-to-rectangular waveguide adapter an SMA connector with
the probe diameter of 127 mm is employed The coaxial probe inserted into
the waveguide energizes the feed and excites the dominant TE10 mode in
-52-
the rectangular waveguide The impedance matching is achieved by adjusting
the probe distance sp from the back short and the probe length lp
(a)
(b)
Fig 52 Reflection coefficient of the coaxial-to-rectangular adapter versus
(a) probe length lp and (b) the probe position sp
Fig 52 shows the reflection coefficient versus the various values of probe
lengths lp and probe positions sp The probe length lp is adjusted to obtain
antenna impedance matching and the probe distance sp is adjusted to obtain a
-53-
desired resonant frequency
Next a transition between rectangular and circular waveguide is designed
The transition section converts the TE10 mode in the rectangular waveguide to
TE11 mode in the circular waveguide and vice versa The transition is built
in a form of a taper for easy fabrication[22]
(a)
(b)
Fig 53 Structure of the rectangular-to-circular waveguide transition
(a) 3D view and (b) cross sectional view
The dimensions of the final optimized transition are as follows The length
of the rectangular waveguide section is 143mm The rectangular waveguides
width a and height b are 207mm and 857mm respectively The length of
the circular waveguide section is 143mm The inside diameter of the circular
-54-
waveguide is 207mm(097 wavelength at 14GHz) The length of transition
region ltr is 4465mm(approximately equal to 2λ0 at 14GHz) Fig 54 shows
the field distribution inside the mode converter
(a)
(b)
Fig 54 Field distribution inside the mode converter at
(a) 10GHz (b) 14GHz and (c) 18GHz
-55-
(c)
Fig 54 continued
Finally multiple chokes are investigated Figs 55 56 and 57 show the
feed performance without chokes The reflection coefficient is less than -10dB
over 10-19GHz The antenna has a gain of 921dB to 1189dB over
10-19GHz
Fig 55 Reflection coefficient of the broadband circular waveguide feed
without chokes and corrugations
-56-
(a)
(b)
(c)
Fig 56 E- and H-plane patterns of the broadband circular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-57-
(d)
(e)
Fig 56 continued
-58-
(a)
(b)
Fig 57 2D radiation patterns of the broadband cicular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-59-
(c)
(d)
Fig 57 continued
-60-
(e)
Fig 57 continued
To achieve equal beamwidths in E and H planes over a wide frequency
range chokes and corrugations are employed Table51 summarizes the
performance of a feed without chokes and corrugations
Table 51 Performance of the broadband circular waveguide feed without
chokes and corrugations
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
1000 940 6061 15
1200 972 6159 17
1400 920 5957 21
1600 1070 4751 29
1800 1188 5352 21
-61-
Four quarter-wavelength chokes are introduced in the feed design which
has a slot depth of 75mm and slot width of 09mm The choke slot spacing
is 18mm The choke design is investigated by applying the choke one by
one and the effect on the E- and H-plane patterns are observed as illustrated
in Figs 58 and 59 The use of chokes makes the E-plane pattern narrower
The H-plane pattern is not affected Chokes increase the gain slightly and
reduce back radiation
(a)
(b)
Fig 58 Effect of chokes on the E-plane pattern of the broadband circular
waveguide feed at (a) 10GHz(b) 12GHz (c) 14GHz (d) 16GHz and (e)
18GHz
-62-
(c)
(d)
(e)
Fig 58 continued
-63-
(a)
(b)
(c)
Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-64-
(d)
(e)
Fig 59 continued
-65-
Fig 510 shows the feed performance versus the choke depth When the
choke depth is varied from 535mm to 95mm the E- and H-plane patterns
are strongly affected The optimum value of choke depth is 75mm(035λ0 at
14GHz) which gives equal E- and H-plane radiation patterns and leads to
low back radiation
Fig 511 shows the feed performance versus the choke slot width tch The
choke slot width is varied from 09mm to 21mm Radiation patterns and
reflection coefficients are not sensitive to the choke slot width The final
choke slot width is selected to be 09mm considering the feed diameter
minimization and the manufacturability The overall diameter of the proposed
feed is 369mm which is increased from the 207mm of the waveguide
inside diameter due to the use of four chokes
-66-
(a)
(b)
(c)
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection coefficient
-67-
(a)
(b)
(c)
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and (c)
reflection coefficient
-68-
Next we investigated corrugations placed on the outer wall of the feed
Four corrugations applied to the outer surface of the circular waveguide The
corrugation depth is 465mm(0215λ0 at 14GHz) The primary purpose of
using corrugations is to further reduce the back radiation Increasing the
number of corrugations beyond four has little effect in reducing the back
radiation
Figs 512 and 513 show the effect of corrugations on the E- and H-plane
patterns Fig 514 shows the parametric study of the corrugation depth lcor
The corrugation depth is varied from 40mm and 645mm The optimum
value of the corrugation depth is found to be 465mm
-69-
(a)
(b)
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern at (a) 12GHz and (b) 14GHz
-70-
(a)
(b)
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern at (a) 12GHz and (b) 14GHz
-71-
(a)
(b)
(c)
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection coefficient
-72-
The phase center location is important in placing the feed in a reflector
antenna[8] The phase center variation with frequency should be small Fig
515 shows the effect of chokes and corrugations on the phase center The
curve with circle corresponds to the case without chokes and corrugations
The phase center varies from -326mm and -190mm away from the feeds
aperture plane It means the phase center is located inside the waveguide
The curve with triangles corresponds to the case with chokes The curve with
squares to the case with chokes and corrugations The phase center varies
from 0mm to -302mm
From Fig 515 we can observed that phase center variation reduced by the
corrugation and three cases phase center calculated in φ=450 plane
parameter sweep values are given in Table 52
10 12 14 16 181
0
-1
-2
-3
-4
-5
-6
Pha
se c
ente
r (m
m)
Frequency (GHz)
choke+corrugatuion without choke corrugation with choke
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
-73-
Frequency
(GHz)
Phase center from the aperture plane
(mm)
Without
chokes and
corrugations
With
chokes
With chokes
and
corrugations
1000 -326 062 000
1100 -187 030 -002
1200 -563 -208 -065
1300 -296 -154 -202
1400 -319 -314 -302
1500 -201 -203 -241
1600 -242 -233 -207
1700 -208 -208 -186
1800 -190 -157 -132
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
Based on the foregoing parametric studies optimum dimensions of the
broadband circular waveguide feed are obtained as shown in Table 53
-74-
Table 53 Optimum dimensions of the broadband circular waveguide feed
Parameter Designation Value (mm)
2a Waveguide inside diameter 2070
d Waveguide outside diameter 3690
lcrLength of the circular waveguide section 1430
m Distance between the aperture plane and the first corrugation 950
xDistance from the last corrugation to the end of the cylindrical outer surface
550
ltrLength of the rectangular-to-circularwaveguide transition 4465
lrcLength of the rectangular waveguide section 1430
tch Choke slot width 090
lch Choke depth 750
t Choke metal width 090
lcor Corrugation depth 465
tcor Corrugation metal width 100
s Corrugation slot width 10
lp Probe length 530
sp Probe position from the back short 530
din Probe diameter 127
b Inside height of the rectangular waveguide 857
tw Waveguide wall thickness 500
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-44-
Fig 45 shows the radiation pattern of the feed with εr = 50 at 18GHz
E- and H-plane 10-dB beamwidths are 56 and 54 degrees respectively The
front-to-back ratio is 27dB The antenna gain is 105dB The feed has a good
pattern symmetry and low back radiation
(a)
(b)
Fig 45 Radiation pattern of the circular waveguide loaded with a uniform
dielectric rod with εr = 50 and L = 05λ0 at 18GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-45-
Fig 46 is the radiation pattern of the feed with εr = 25 and L = 10λ0 at
10GHz E- and H-plane 10-dB beamwidths are 50 and 48 degrees
respectively The front-to-back ratio is 16dB The antenna gain is 105dB
(a)
(b)
Fig 46 Radiation pattern at 10GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 10λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-46-
Fig 47 shows the geometry of a circular waveguide with a tapered
dielectric rod The designed feed has the following dimension L = 1λ0 d =
1λ0 and εr =25 at 10GHz The waveguide length is 40mm and the wall
thickness is 05mm
L
Dielectricd3
Fig 47 Geometry of a circular waveguide loaded with a tapered dielectric
rod
Fig 48 shows the radiatio pattern of the designed feed E- and H-plane
10-dB beamwidths are 575 and 564 degrees respectively The front-to-back
ratio is 377dB The antenna gain is 94dB The designed feed has an
excellent beamwidth symmetry and a very low back radiation
-47-
(a)
(b)
Fig 48 Radiation pattern of a circular waveguide loaded with a tapered
dielectric rod with L = 1λ0 d = 1λ0 and εr =25 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-48-
Fig 49 shows the geometry of a spherical ended dielectric rod feed
diameter of 06λ0 at 10GHz with a dielectric constant of 25 and L= 03λ0
Fig 410 shows the radiation patterns of the designed feed E- and H-plane
10-dB beamwidths are both 63 degrees The front-to-back ratio is 24dB The
antenna gain is 864dB
Fig 49 Geometry of a circular waveguide loaded with a spherical ended
dielectric rod
-49-
(a)
(b)
Fig 410 Radiation pattern of a circular waveguide loaded wht a spherical
ended dielectric rod with d = 06λ0 L = 03λ0 and εr =25 at 10GHz (a) 3D
radiation pattern and (b) E- and H-plane patterns
-50-
V Design of a Broadband Circular Waveguide Feed
In this chapter the design of a broadband circular waveguide feed is
presented At microwave frequencies the feed is often a circular waveguide
with chokes and corrugations around the aperture Chokes and corrugations
equalize E- and H-plane patterns and reduce the back radiation
The proposed feed is designed to operate over 10-18GHz The design starts
with the optimization of the coaxial-to-rectangular waveguide adapter
employed for good mode purity over a broad frequency range Next a
rectangular-to-circular waveguide transition is optimized Finally chokes and
corrugations are designed for improved pattern symmetry and low back
radiation
The proposed feed structure is shown in Fig 51 The feed consist of the
following parts a coaxial-to-rectangular waveguide adapter a rectangular-to-
circular waveguide transition a circular waveguide section four quarter-wave
chokes around the feeds aperture and four corrugations on the feeds outer
surface
The computer simulation shows the above arrangement offers good radiation
patterns over a broad frequency range The broadband operation is obtained
by exciting the TE11 mode in the circular waveguide using the TE10 mode of
the rectangular waveguide which is in turn excited by a coaxial probe
-51-
Chokes
Coaxial-to-waveguide transition
Circular wavguide
Corrugations
Mode transition
(a)
(b)
Fig 51 Structure of the proposed broadband circular waveguide feed
(a) CAD model and (b) cross-sectional view
For the coaxial-to-rectangular waveguide adapter an SMA connector with
the probe diameter of 127 mm is employed The coaxial probe inserted into
the waveguide energizes the feed and excites the dominant TE10 mode in
-52-
the rectangular waveguide The impedance matching is achieved by adjusting
the probe distance sp from the back short and the probe length lp
(a)
(b)
Fig 52 Reflection coefficient of the coaxial-to-rectangular adapter versus
(a) probe length lp and (b) the probe position sp
Fig 52 shows the reflection coefficient versus the various values of probe
lengths lp and probe positions sp The probe length lp is adjusted to obtain
antenna impedance matching and the probe distance sp is adjusted to obtain a
-53-
desired resonant frequency
Next a transition between rectangular and circular waveguide is designed
The transition section converts the TE10 mode in the rectangular waveguide to
TE11 mode in the circular waveguide and vice versa The transition is built
in a form of a taper for easy fabrication[22]
(a)
(b)
Fig 53 Structure of the rectangular-to-circular waveguide transition
(a) 3D view and (b) cross sectional view
The dimensions of the final optimized transition are as follows The length
of the rectangular waveguide section is 143mm The rectangular waveguides
width a and height b are 207mm and 857mm respectively The length of
the circular waveguide section is 143mm The inside diameter of the circular
-54-
waveguide is 207mm(097 wavelength at 14GHz) The length of transition
region ltr is 4465mm(approximately equal to 2λ0 at 14GHz) Fig 54 shows
the field distribution inside the mode converter
(a)
(b)
Fig 54 Field distribution inside the mode converter at
(a) 10GHz (b) 14GHz and (c) 18GHz
-55-
(c)
Fig 54 continued
Finally multiple chokes are investigated Figs 55 56 and 57 show the
feed performance without chokes The reflection coefficient is less than -10dB
over 10-19GHz The antenna has a gain of 921dB to 1189dB over
10-19GHz
Fig 55 Reflection coefficient of the broadband circular waveguide feed
without chokes and corrugations
-56-
(a)
(b)
(c)
Fig 56 E- and H-plane patterns of the broadband circular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-57-
(d)
(e)
Fig 56 continued
-58-
(a)
(b)
Fig 57 2D radiation patterns of the broadband cicular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-59-
(c)
(d)
Fig 57 continued
-60-
(e)
Fig 57 continued
To achieve equal beamwidths in E and H planes over a wide frequency
range chokes and corrugations are employed Table51 summarizes the
performance of a feed without chokes and corrugations
Table 51 Performance of the broadband circular waveguide feed without
chokes and corrugations
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
1000 940 6061 15
1200 972 6159 17
1400 920 5957 21
1600 1070 4751 29
1800 1188 5352 21
-61-
Four quarter-wavelength chokes are introduced in the feed design which
has a slot depth of 75mm and slot width of 09mm The choke slot spacing
is 18mm The choke design is investigated by applying the choke one by
one and the effect on the E- and H-plane patterns are observed as illustrated
in Figs 58 and 59 The use of chokes makes the E-plane pattern narrower
The H-plane pattern is not affected Chokes increase the gain slightly and
reduce back radiation
(a)
(b)
Fig 58 Effect of chokes on the E-plane pattern of the broadband circular
waveguide feed at (a) 10GHz(b) 12GHz (c) 14GHz (d) 16GHz and (e)
18GHz
-62-
(c)
(d)
(e)
Fig 58 continued
-63-
(a)
(b)
(c)
Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-64-
(d)
(e)
Fig 59 continued
-65-
Fig 510 shows the feed performance versus the choke depth When the
choke depth is varied from 535mm to 95mm the E- and H-plane patterns
are strongly affected The optimum value of choke depth is 75mm(035λ0 at
14GHz) which gives equal E- and H-plane radiation patterns and leads to
low back radiation
Fig 511 shows the feed performance versus the choke slot width tch The
choke slot width is varied from 09mm to 21mm Radiation patterns and
reflection coefficients are not sensitive to the choke slot width The final
choke slot width is selected to be 09mm considering the feed diameter
minimization and the manufacturability The overall diameter of the proposed
feed is 369mm which is increased from the 207mm of the waveguide
inside diameter due to the use of four chokes
-66-
(a)
(b)
(c)
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection coefficient
-67-
(a)
(b)
(c)
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and (c)
reflection coefficient
-68-
Next we investigated corrugations placed on the outer wall of the feed
Four corrugations applied to the outer surface of the circular waveguide The
corrugation depth is 465mm(0215λ0 at 14GHz) The primary purpose of
using corrugations is to further reduce the back radiation Increasing the
number of corrugations beyond four has little effect in reducing the back
radiation
Figs 512 and 513 show the effect of corrugations on the E- and H-plane
patterns Fig 514 shows the parametric study of the corrugation depth lcor
The corrugation depth is varied from 40mm and 645mm The optimum
value of the corrugation depth is found to be 465mm
-69-
(a)
(b)
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern at (a) 12GHz and (b) 14GHz
-70-
(a)
(b)
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern at (a) 12GHz and (b) 14GHz
-71-
(a)
(b)
(c)
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection coefficient
-72-
The phase center location is important in placing the feed in a reflector
antenna[8] The phase center variation with frequency should be small Fig
515 shows the effect of chokes and corrugations on the phase center The
curve with circle corresponds to the case without chokes and corrugations
The phase center varies from -326mm and -190mm away from the feeds
aperture plane It means the phase center is located inside the waveguide
The curve with triangles corresponds to the case with chokes The curve with
squares to the case with chokes and corrugations The phase center varies
from 0mm to -302mm
From Fig 515 we can observed that phase center variation reduced by the
corrugation and three cases phase center calculated in φ=450 plane
parameter sweep values are given in Table 52
10 12 14 16 181
0
-1
-2
-3
-4
-5
-6
Pha
se c
ente
r (m
m)
Frequency (GHz)
choke+corrugatuion without choke corrugation with choke
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
-73-
Frequency
(GHz)
Phase center from the aperture plane
(mm)
Without
chokes and
corrugations
With
chokes
With chokes
and
corrugations
1000 -326 062 000
1100 -187 030 -002
1200 -563 -208 -065
1300 -296 -154 -202
1400 -319 -314 -302
1500 -201 -203 -241
1600 -242 -233 -207
1700 -208 -208 -186
1800 -190 -157 -132
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
Based on the foregoing parametric studies optimum dimensions of the
broadband circular waveguide feed are obtained as shown in Table 53
-74-
Table 53 Optimum dimensions of the broadband circular waveguide feed
Parameter Designation Value (mm)
2a Waveguide inside diameter 2070
d Waveguide outside diameter 3690
lcrLength of the circular waveguide section 1430
m Distance between the aperture plane and the first corrugation 950
xDistance from the last corrugation to the end of the cylindrical outer surface
550
ltrLength of the rectangular-to-circularwaveguide transition 4465
lrcLength of the rectangular waveguide section 1430
tch Choke slot width 090
lch Choke depth 750
t Choke metal width 090
lcor Corrugation depth 465
tcor Corrugation metal width 100
s Corrugation slot width 10
lp Probe length 530
sp Probe position from the back short 530
din Probe diameter 127
b Inside height of the rectangular waveguide 857
tw Waveguide wall thickness 500
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-45-
Fig 46 is the radiation pattern of the feed with εr = 25 and L = 10λ0 at
10GHz E- and H-plane 10-dB beamwidths are 50 and 48 degrees
respectively The front-to-back ratio is 16dB The antenna gain is 105dB
(a)
(b)
Fig 46 Radiation pattern at 10GHz of the circular waveguide loaded with a
uniform dielectric rod with εr = 25 and L = 10λ0 (a) 2D radiation pattern
and (b) E- and H-plane patterns
-46-
Fig 47 shows the geometry of a circular waveguide with a tapered
dielectric rod The designed feed has the following dimension L = 1λ0 d =
1λ0 and εr =25 at 10GHz The waveguide length is 40mm and the wall
thickness is 05mm
L
Dielectricd3
Fig 47 Geometry of a circular waveguide loaded with a tapered dielectric
rod
Fig 48 shows the radiatio pattern of the designed feed E- and H-plane
10-dB beamwidths are 575 and 564 degrees respectively The front-to-back
ratio is 377dB The antenna gain is 94dB The designed feed has an
excellent beamwidth symmetry and a very low back radiation
-47-
(a)
(b)
Fig 48 Radiation pattern of a circular waveguide loaded with a tapered
dielectric rod with L = 1λ0 d = 1λ0 and εr =25 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-48-
Fig 49 shows the geometry of a spherical ended dielectric rod feed
diameter of 06λ0 at 10GHz with a dielectric constant of 25 and L= 03λ0
Fig 410 shows the radiation patterns of the designed feed E- and H-plane
10-dB beamwidths are both 63 degrees The front-to-back ratio is 24dB The
antenna gain is 864dB
Fig 49 Geometry of a circular waveguide loaded with a spherical ended
dielectric rod
-49-
(a)
(b)
Fig 410 Radiation pattern of a circular waveguide loaded wht a spherical
ended dielectric rod with d = 06λ0 L = 03λ0 and εr =25 at 10GHz (a) 3D
radiation pattern and (b) E- and H-plane patterns
-50-
V Design of a Broadband Circular Waveguide Feed
In this chapter the design of a broadband circular waveguide feed is
presented At microwave frequencies the feed is often a circular waveguide
with chokes and corrugations around the aperture Chokes and corrugations
equalize E- and H-plane patterns and reduce the back radiation
The proposed feed is designed to operate over 10-18GHz The design starts
with the optimization of the coaxial-to-rectangular waveguide adapter
employed for good mode purity over a broad frequency range Next a
rectangular-to-circular waveguide transition is optimized Finally chokes and
corrugations are designed for improved pattern symmetry and low back
radiation
The proposed feed structure is shown in Fig 51 The feed consist of the
following parts a coaxial-to-rectangular waveguide adapter a rectangular-to-
circular waveguide transition a circular waveguide section four quarter-wave
chokes around the feeds aperture and four corrugations on the feeds outer
surface
The computer simulation shows the above arrangement offers good radiation
patterns over a broad frequency range The broadband operation is obtained
by exciting the TE11 mode in the circular waveguide using the TE10 mode of
the rectangular waveguide which is in turn excited by a coaxial probe
-51-
Chokes
Coaxial-to-waveguide transition
Circular wavguide
Corrugations
Mode transition
(a)
(b)
Fig 51 Structure of the proposed broadband circular waveguide feed
(a) CAD model and (b) cross-sectional view
For the coaxial-to-rectangular waveguide adapter an SMA connector with
the probe diameter of 127 mm is employed The coaxial probe inserted into
the waveguide energizes the feed and excites the dominant TE10 mode in
-52-
the rectangular waveguide The impedance matching is achieved by adjusting
the probe distance sp from the back short and the probe length lp
(a)
(b)
Fig 52 Reflection coefficient of the coaxial-to-rectangular adapter versus
(a) probe length lp and (b) the probe position sp
Fig 52 shows the reflection coefficient versus the various values of probe
lengths lp and probe positions sp The probe length lp is adjusted to obtain
antenna impedance matching and the probe distance sp is adjusted to obtain a
-53-
desired resonant frequency
Next a transition between rectangular and circular waveguide is designed
The transition section converts the TE10 mode in the rectangular waveguide to
TE11 mode in the circular waveguide and vice versa The transition is built
in a form of a taper for easy fabrication[22]
(a)
(b)
Fig 53 Structure of the rectangular-to-circular waveguide transition
(a) 3D view and (b) cross sectional view
The dimensions of the final optimized transition are as follows The length
of the rectangular waveguide section is 143mm The rectangular waveguides
width a and height b are 207mm and 857mm respectively The length of
the circular waveguide section is 143mm The inside diameter of the circular
-54-
waveguide is 207mm(097 wavelength at 14GHz) The length of transition
region ltr is 4465mm(approximately equal to 2λ0 at 14GHz) Fig 54 shows
the field distribution inside the mode converter
(a)
(b)
Fig 54 Field distribution inside the mode converter at
(a) 10GHz (b) 14GHz and (c) 18GHz
-55-
(c)
Fig 54 continued
Finally multiple chokes are investigated Figs 55 56 and 57 show the
feed performance without chokes The reflection coefficient is less than -10dB
over 10-19GHz The antenna has a gain of 921dB to 1189dB over
10-19GHz
Fig 55 Reflection coefficient of the broadband circular waveguide feed
without chokes and corrugations
-56-
(a)
(b)
(c)
Fig 56 E- and H-plane patterns of the broadband circular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-57-
(d)
(e)
Fig 56 continued
-58-
(a)
(b)
Fig 57 2D radiation patterns of the broadband cicular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-59-
(c)
(d)
Fig 57 continued
-60-
(e)
Fig 57 continued
To achieve equal beamwidths in E and H planes over a wide frequency
range chokes and corrugations are employed Table51 summarizes the
performance of a feed without chokes and corrugations
Table 51 Performance of the broadband circular waveguide feed without
chokes and corrugations
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
1000 940 6061 15
1200 972 6159 17
1400 920 5957 21
1600 1070 4751 29
1800 1188 5352 21
-61-
Four quarter-wavelength chokes are introduced in the feed design which
has a slot depth of 75mm and slot width of 09mm The choke slot spacing
is 18mm The choke design is investigated by applying the choke one by
one and the effect on the E- and H-plane patterns are observed as illustrated
in Figs 58 and 59 The use of chokes makes the E-plane pattern narrower
The H-plane pattern is not affected Chokes increase the gain slightly and
reduce back radiation
(a)
(b)
Fig 58 Effect of chokes on the E-plane pattern of the broadband circular
waveguide feed at (a) 10GHz(b) 12GHz (c) 14GHz (d) 16GHz and (e)
18GHz
-62-
(c)
(d)
(e)
Fig 58 continued
-63-
(a)
(b)
(c)
Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-64-
(d)
(e)
Fig 59 continued
-65-
Fig 510 shows the feed performance versus the choke depth When the
choke depth is varied from 535mm to 95mm the E- and H-plane patterns
are strongly affected The optimum value of choke depth is 75mm(035λ0 at
14GHz) which gives equal E- and H-plane radiation patterns and leads to
low back radiation
Fig 511 shows the feed performance versus the choke slot width tch The
choke slot width is varied from 09mm to 21mm Radiation patterns and
reflection coefficients are not sensitive to the choke slot width The final
choke slot width is selected to be 09mm considering the feed diameter
minimization and the manufacturability The overall diameter of the proposed
feed is 369mm which is increased from the 207mm of the waveguide
inside diameter due to the use of four chokes
-66-
(a)
(b)
(c)
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection coefficient
-67-
(a)
(b)
(c)
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and (c)
reflection coefficient
-68-
Next we investigated corrugations placed on the outer wall of the feed
Four corrugations applied to the outer surface of the circular waveguide The
corrugation depth is 465mm(0215λ0 at 14GHz) The primary purpose of
using corrugations is to further reduce the back radiation Increasing the
number of corrugations beyond four has little effect in reducing the back
radiation
Figs 512 and 513 show the effect of corrugations on the E- and H-plane
patterns Fig 514 shows the parametric study of the corrugation depth lcor
The corrugation depth is varied from 40mm and 645mm The optimum
value of the corrugation depth is found to be 465mm
-69-
(a)
(b)
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern at (a) 12GHz and (b) 14GHz
-70-
(a)
(b)
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern at (a) 12GHz and (b) 14GHz
-71-
(a)
(b)
(c)
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection coefficient
-72-
The phase center location is important in placing the feed in a reflector
antenna[8] The phase center variation with frequency should be small Fig
515 shows the effect of chokes and corrugations on the phase center The
curve with circle corresponds to the case without chokes and corrugations
The phase center varies from -326mm and -190mm away from the feeds
aperture plane It means the phase center is located inside the waveguide
The curve with triangles corresponds to the case with chokes The curve with
squares to the case with chokes and corrugations The phase center varies
from 0mm to -302mm
From Fig 515 we can observed that phase center variation reduced by the
corrugation and three cases phase center calculated in φ=450 plane
parameter sweep values are given in Table 52
10 12 14 16 181
0
-1
-2
-3
-4
-5
-6
Pha
se c
ente
r (m
m)
Frequency (GHz)
choke+corrugatuion without choke corrugation with choke
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
-73-
Frequency
(GHz)
Phase center from the aperture plane
(mm)
Without
chokes and
corrugations
With
chokes
With chokes
and
corrugations
1000 -326 062 000
1100 -187 030 -002
1200 -563 -208 -065
1300 -296 -154 -202
1400 -319 -314 -302
1500 -201 -203 -241
1600 -242 -233 -207
1700 -208 -208 -186
1800 -190 -157 -132
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
Based on the foregoing parametric studies optimum dimensions of the
broadband circular waveguide feed are obtained as shown in Table 53
-74-
Table 53 Optimum dimensions of the broadband circular waveguide feed
Parameter Designation Value (mm)
2a Waveguide inside diameter 2070
d Waveguide outside diameter 3690
lcrLength of the circular waveguide section 1430
m Distance between the aperture plane and the first corrugation 950
xDistance from the last corrugation to the end of the cylindrical outer surface
550
ltrLength of the rectangular-to-circularwaveguide transition 4465
lrcLength of the rectangular waveguide section 1430
tch Choke slot width 090
lch Choke depth 750
t Choke metal width 090
lcor Corrugation depth 465
tcor Corrugation metal width 100
s Corrugation slot width 10
lp Probe length 530
sp Probe position from the back short 530
din Probe diameter 127
b Inside height of the rectangular waveguide 857
tw Waveguide wall thickness 500
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-46-
Fig 47 shows the geometry of a circular waveguide with a tapered
dielectric rod The designed feed has the following dimension L = 1λ0 d =
1λ0 and εr =25 at 10GHz The waveguide length is 40mm and the wall
thickness is 05mm
L
Dielectricd3
Fig 47 Geometry of a circular waveguide loaded with a tapered dielectric
rod
Fig 48 shows the radiatio pattern of the designed feed E- and H-plane
10-dB beamwidths are 575 and 564 degrees respectively The front-to-back
ratio is 377dB The antenna gain is 94dB The designed feed has an
excellent beamwidth symmetry and a very low back radiation
-47-
(a)
(b)
Fig 48 Radiation pattern of a circular waveguide loaded with a tapered
dielectric rod with L = 1λ0 d = 1λ0 and εr =25 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-48-
Fig 49 shows the geometry of a spherical ended dielectric rod feed
diameter of 06λ0 at 10GHz with a dielectric constant of 25 and L= 03λ0
Fig 410 shows the radiation patterns of the designed feed E- and H-plane
10-dB beamwidths are both 63 degrees The front-to-back ratio is 24dB The
antenna gain is 864dB
Fig 49 Geometry of a circular waveguide loaded with a spherical ended
dielectric rod
-49-
(a)
(b)
Fig 410 Radiation pattern of a circular waveguide loaded wht a spherical
ended dielectric rod with d = 06λ0 L = 03λ0 and εr =25 at 10GHz (a) 3D
radiation pattern and (b) E- and H-plane patterns
-50-
V Design of a Broadband Circular Waveguide Feed
In this chapter the design of a broadband circular waveguide feed is
presented At microwave frequencies the feed is often a circular waveguide
with chokes and corrugations around the aperture Chokes and corrugations
equalize E- and H-plane patterns and reduce the back radiation
The proposed feed is designed to operate over 10-18GHz The design starts
with the optimization of the coaxial-to-rectangular waveguide adapter
employed for good mode purity over a broad frequency range Next a
rectangular-to-circular waveguide transition is optimized Finally chokes and
corrugations are designed for improved pattern symmetry and low back
radiation
The proposed feed structure is shown in Fig 51 The feed consist of the
following parts a coaxial-to-rectangular waveguide adapter a rectangular-to-
circular waveguide transition a circular waveguide section four quarter-wave
chokes around the feeds aperture and four corrugations on the feeds outer
surface
The computer simulation shows the above arrangement offers good radiation
patterns over a broad frequency range The broadband operation is obtained
by exciting the TE11 mode in the circular waveguide using the TE10 mode of
the rectangular waveguide which is in turn excited by a coaxial probe
-51-
Chokes
Coaxial-to-waveguide transition
Circular wavguide
Corrugations
Mode transition
(a)
(b)
Fig 51 Structure of the proposed broadband circular waveguide feed
(a) CAD model and (b) cross-sectional view
For the coaxial-to-rectangular waveguide adapter an SMA connector with
the probe diameter of 127 mm is employed The coaxial probe inserted into
the waveguide energizes the feed and excites the dominant TE10 mode in
-52-
the rectangular waveguide The impedance matching is achieved by adjusting
the probe distance sp from the back short and the probe length lp
(a)
(b)
Fig 52 Reflection coefficient of the coaxial-to-rectangular adapter versus
(a) probe length lp and (b) the probe position sp
Fig 52 shows the reflection coefficient versus the various values of probe
lengths lp and probe positions sp The probe length lp is adjusted to obtain
antenna impedance matching and the probe distance sp is adjusted to obtain a
-53-
desired resonant frequency
Next a transition between rectangular and circular waveguide is designed
The transition section converts the TE10 mode in the rectangular waveguide to
TE11 mode in the circular waveguide and vice versa The transition is built
in a form of a taper for easy fabrication[22]
(a)
(b)
Fig 53 Structure of the rectangular-to-circular waveguide transition
(a) 3D view and (b) cross sectional view
The dimensions of the final optimized transition are as follows The length
of the rectangular waveguide section is 143mm The rectangular waveguides
width a and height b are 207mm and 857mm respectively The length of
the circular waveguide section is 143mm The inside diameter of the circular
-54-
waveguide is 207mm(097 wavelength at 14GHz) The length of transition
region ltr is 4465mm(approximately equal to 2λ0 at 14GHz) Fig 54 shows
the field distribution inside the mode converter
(a)
(b)
Fig 54 Field distribution inside the mode converter at
(a) 10GHz (b) 14GHz and (c) 18GHz
-55-
(c)
Fig 54 continued
Finally multiple chokes are investigated Figs 55 56 and 57 show the
feed performance without chokes The reflection coefficient is less than -10dB
over 10-19GHz The antenna has a gain of 921dB to 1189dB over
10-19GHz
Fig 55 Reflection coefficient of the broadband circular waveguide feed
without chokes and corrugations
-56-
(a)
(b)
(c)
Fig 56 E- and H-plane patterns of the broadband circular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-57-
(d)
(e)
Fig 56 continued
-58-
(a)
(b)
Fig 57 2D radiation patterns of the broadband cicular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-59-
(c)
(d)
Fig 57 continued
-60-
(e)
Fig 57 continued
To achieve equal beamwidths in E and H planes over a wide frequency
range chokes and corrugations are employed Table51 summarizes the
performance of a feed without chokes and corrugations
Table 51 Performance of the broadband circular waveguide feed without
chokes and corrugations
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
1000 940 6061 15
1200 972 6159 17
1400 920 5957 21
1600 1070 4751 29
1800 1188 5352 21
-61-
Four quarter-wavelength chokes are introduced in the feed design which
has a slot depth of 75mm and slot width of 09mm The choke slot spacing
is 18mm The choke design is investigated by applying the choke one by
one and the effect on the E- and H-plane patterns are observed as illustrated
in Figs 58 and 59 The use of chokes makes the E-plane pattern narrower
The H-plane pattern is not affected Chokes increase the gain slightly and
reduce back radiation
(a)
(b)
Fig 58 Effect of chokes on the E-plane pattern of the broadband circular
waveguide feed at (a) 10GHz(b) 12GHz (c) 14GHz (d) 16GHz and (e)
18GHz
-62-
(c)
(d)
(e)
Fig 58 continued
-63-
(a)
(b)
(c)
Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-64-
(d)
(e)
Fig 59 continued
-65-
Fig 510 shows the feed performance versus the choke depth When the
choke depth is varied from 535mm to 95mm the E- and H-plane patterns
are strongly affected The optimum value of choke depth is 75mm(035λ0 at
14GHz) which gives equal E- and H-plane radiation patterns and leads to
low back radiation
Fig 511 shows the feed performance versus the choke slot width tch The
choke slot width is varied from 09mm to 21mm Radiation patterns and
reflection coefficients are not sensitive to the choke slot width The final
choke slot width is selected to be 09mm considering the feed diameter
minimization and the manufacturability The overall diameter of the proposed
feed is 369mm which is increased from the 207mm of the waveguide
inside diameter due to the use of four chokes
-66-
(a)
(b)
(c)
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection coefficient
-67-
(a)
(b)
(c)
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and (c)
reflection coefficient
-68-
Next we investigated corrugations placed on the outer wall of the feed
Four corrugations applied to the outer surface of the circular waveguide The
corrugation depth is 465mm(0215λ0 at 14GHz) The primary purpose of
using corrugations is to further reduce the back radiation Increasing the
number of corrugations beyond four has little effect in reducing the back
radiation
Figs 512 and 513 show the effect of corrugations on the E- and H-plane
patterns Fig 514 shows the parametric study of the corrugation depth lcor
The corrugation depth is varied from 40mm and 645mm The optimum
value of the corrugation depth is found to be 465mm
-69-
(a)
(b)
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern at (a) 12GHz and (b) 14GHz
-70-
(a)
(b)
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern at (a) 12GHz and (b) 14GHz
-71-
(a)
(b)
(c)
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection coefficient
-72-
The phase center location is important in placing the feed in a reflector
antenna[8] The phase center variation with frequency should be small Fig
515 shows the effect of chokes and corrugations on the phase center The
curve with circle corresponds to the case without chokes and corrugations
The phase center varies from -326mm and -190mm away from the feeds
aperture plane It means the phase center is located inside the waveguide
The curve with triangles corresponds to the case with chokes The curve with
squares to the case with chokes and corrugations The phase center varies
from 0mm to -302mm
From Fig 515 we can observed that phase center variation reduced by the
corrugation and three cases phase center calculated in φ=450 plane
parameter sweep values are given in Table 52
10 12 14 16 181
0
-1
-2
-3
-4
-5
-6
Pha
se c
ente
r (m
m)
Frequency (GHz)
choke+corrugatuion without choke corrugation with choke
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
-73-
Frequency
(GHz)
Phase center from the aperture plane
(mm)
Without
chokes and
corrugations
With
chokes
With chokes
and
corrugations
1000 -326 062 000
1100 -187 030 -002
1200 -563 -208 -065
1300 -296 -154 -202
1400 -319 -314 -302
1500 -201 -203 -241
1600 -242 -233 -207
1700 -208 -208 -186
1800 -190 -157 -132
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
Based on the foregoing parametric studies optimum dimensions of the
broadband circular waveguide feed are obtained as shown in Table 53
-74-
Table 53 Optimum dimensions of the broadband circular waveguide feed
Parameter Designation Value (mm)
2a Waveguide inside diameter 2070
d Waveguide outside diameter 3690
lcrLength of the circular waveguide section 1430
m Distance between the aperture plane and the first corrugation 950
xDistance from the last corrugation to the end of the cylindrical outer surface
550
ltrLength of the rectangular-to-circularwaveguide transition 4465
lrcLength of the rectangular waveguide section 1430
tch Choke slot width 090
lch Choke depth 750
t Choke metal width 090
lcor Corrugation depth 465
tcor Corrugation metal width 100
s Corrugation slot width 10
lp Probe length 530
sp Probe position from the back short 530
din Probe diameter 127
b Inside height of the rectangular waveguide 857
tw Waveguide wall thickness 500
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-47-
(a)
(b)
Fig 48 Radiation pattern of a circular waveguide loaded with a tapered
dielectric rod with L = 1λ0 d = 1λ0 and εr =25 at 10GHz (a) 2D radiation
pattern and (b) E- and H-plane patterns
-48-
Fig 49 shows the geometry of a spherical ended dielectric rod feed
diameter of 06λ0 at 10GHz with a dielectric constant of 25 and L= 03λ0
Fig 410 shows the radiation patterns of the designed feed E- and H-plane
10-dB beamwidths are both 63 degrees The front-to-back ratio is 24dB The
antenna gain is 864dB
Fig 49 Geometry of a circular waveguide loaded with a spherical ended
dielectric rod
-49-
(a)
(b)
Fig 410 Radiation pattern of a circular waveguide loaded wht a spherical
ended dielectric rod with d = 06λ0 L = 03λ0 and εr =25 at 10GHz (a) 3D
radiation pattern and (b) E- and H-plane patterns
-50-
V Design of a Broadband Circular Waveguide Feed
In this chapter the design of a broadband circular waveguide feed is
presented At microwave frequencies the feed is often a circular waveguide
with chokes and corrugations around the aperture Chokes and corrugations
equalize E- and H-plane patterns and reduce the back radiation
The proposed feed is designed to operate over 10-18GHz The design starts
with the optimization of the coaxial-to-rectangular waveguide adapter
employed for good mode purity over a broad frequency range Next a
rectangular-to-circular waveguide transition is optimized Finally chokes and
corrugations are designed for improved pattern symmetry and low back
radiation
The proposed feed structure is shown in Fig 51 The feed consist of the
following parts a coaxial-to-rectangular waveguide adapter a rectangular-to-
circular waveguide transition a circular waveguide section four quarter-wave
chokes around the feeds aperture and four corrugations on the feeds outer
surface
The computer simulation shows the above arrangement offers good radiation
patterns over a broad frequency range The broadband operation is obtained
by exciting the TE11 mode in the circular waveguide using the TE10 mode of
the rectangular waveguide which is in turn excited by a coaxial probe
-51-
Chokes
Coaxial-to-waveguide transition
Circular wavguide
Corrugations
Mode transition
(a)
(b)
Fig 51 Structure of the proposed broadband circular waveguide feed
(a) CAD model and (b) cross-sectional view
For the coaxial-to-rectangular waveguide adapter an SMA connector with
the probe diameter of 127 mm is employed The coaxial probe inserted into
the waveguide energizes the feed and excites the dominant TE10 mode in
-52-
the rectangular waveguide The impedance matching is achieved by adjusting
the probe distance sp from the back short and the probe length lp
(a)
(b)
Fig 52 Reflection coefficient of the coaxial-to-rectangular adapter versus
(a) probe length lp and (b) the probe position sp
Fig 52 shows the reflection coefficient versus the various values of probe
lengths lp and probe positions sp The probe length lp is adjusted to obtain
antenna impedance matching and the probe distance sp is adjusted to obtain a
-53-
desired resonant frequency
Next a transition between rectangular and circular waveguide is designed
The transition section converts the TE10 mode in the rectangular waveguide to
TE11 mode in the circular waveguide and vice versa The transition is built
in a form of a taper for easy fabrication[22]
(a)
(b)
Fig 53 Structure of the rectangular-to-circular waveguide transition
(a) 3D view and (b) cross sectional view
The dimensions of the final optimized transition are as follows The length
of the rectangular waveguide section is 143mm The rectangular waveguides
width a and height b are 207mm and 857mm respectively The length of
the circular waveguide section is 143mm The inside diameter of the circular
-54-
waveguide is 207mm(097 wavelength at 14GHz) The length of transition
region ltr is 4465mm(approximately equal to 2λ0 at 14GHz) Fig 54 shows
the field distribution inside the mode converter
(a)
(b)
Fig 54 Field distribution inside the mode converter at
(a) 10GHz (b) 14GHz and (c) 18GHz
-55-
(c)
Fig 54 continued
Finally multiple chokes are investigated Figs 55 56 and 57 show the
feed performance without chokes The reflection coefficient is less than -10dB
over 10-19GHz The antenna has a gain of 921dB to 1189dB over
10-19GHz
Fig 55 Reflection coefficient of the broadband circular waveguide feed
without chokes and corrugations
-56-
(a)
(b)
(c)
Fig 56 E- and H-plane patterns of the broadband circular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-57-
(d)
(e)
Fig 56 continued
-58-
(a)
(b)
Fig 57 2D radiation patterns of the broadband cicular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-59-
(c)
(d)
Fig 57 continued
-60-
(e)
Fig 57 continued
To achieve equal beamwidths in E and H planes over a wide frequency
range chokes and corrugations are employed Table51 summarizes the
performance of a feed without chokes and corrugations
Table 51 Performance of the broadband circular waveguide feed without
chokes and corrugations
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
1000 940 6061 15
1200 972 6159 17
1400 920 5957 21
1600 1070 4751 29
1800 1188 5352 21
-61-
Four quarter-wavelength chokes are introduced in the feed design which
has a slot depth of 75mm and slot width of 09mm The choke slot spacing
is 18mm The choke design is investigated by applying the choke one by
one and the effect on the E- and H-plane patterns are observed as illustrated
in Figs 58 and 59 The use of chokes makes the E-plane pattern narrower
The H-plane pattern is not affected Chokes increase the gain slightly and
reduce back radiation
(a)
(b)
Fig 58 Effect of chokes on the E-plane pattern of the broadband circular
waveguide feed at (a) 10GHz(b) 12GHz (c) 14GHz (d) 16GHz and (e)
18GHz
-62-
(c)
(d)
(e)
Fig 58 continued
-63-
(a)
(b)
(c)
Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-64-
(d)
(e)
Fig 59 continued
-65-
Fig 510 shows the feed performance versus the choke depth When the
choke depth is varied from 535mm to 95mm the E- and H-plane patterns
are strongly affected The optimum value of choke depth is 75mm(035λ0 at
14GHz) which gives equal E- and H-plane radiation patterns and leads to
low back radiation
Fig 511 shows the feed performance versus the choke slot width tch The
choke slot width is varied from 09mm to 21mm Radiation patterns and
reflection coefficients are not sensitive to the choke slot width The final
choke slot width is selected to be 09mm considering the feed diameter
minimization and the manufacturability The overall diameter of the proposed
feed is 369mm which is increased from the 207mm of the waveguide
inside diameter due to the use of four chokes
-66-
(a)
(b)
(c)
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection coefficient
-67-
(a)
(b)
(c)
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and (c)
reflection coefficient
-68-
Next we investigated corrugations placed on the outer wall of the feed
Four corrugations applied to the outer surface of the circular waveguide The
corrugation depth is 465mm(0215λ0 at 14GHz) The primary purpose of
using corrugations is to further reduce the back radiation Increasing the
number of corrugations beyond four has little effect in reducing the back
radiation
Figs 512 and 513 show the effect of corrugations on the E- and H-plane
patterns Fig 514 shows the parametric study of the corrugation depth lcor
The corrugation depth is varied from 40mm and 645mm The optimum
value of the corrugation depth is found to be 465mm
-69-
(a)
(b)
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern at (a) 12GHz and (b) 14GHz
-70-
(a)
(b)
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern at (a) 12GHz and (b) 14GHz
-71-
(a)
(b)
(c)
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection coefficient
-72-
The phase center location is important in placing the feed in a reflector
antenna[8] The phase center variation with frequency should be small Fig
515 shows the effect of chokes and corrugations on the phase center The
curve with circle corresponds to the case without chokes and corrugations
The phase center varies from -326mm and -190mm away from the feeds
aperture plane It means the phase center is located inside the waveguide
The curve with triangles corresponds to the case with chokes The curve with
squares to the case with chokes and corrugations The phase center varies
from 0mm to -302mm
From Fig 515 we can observed that phase center variation reduced by the
corrugation and three cases phase center calculated in φ=450 plane
parameter sweep values are given in Table 52
10 12 14 16 181
0
-1
-2
-3
-4
-5
-6
Pha
se c
ente
r (m
m)
Frequency (GHz)
choke+corrugatuion without choke corrugation with choke
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
-73-
Frequency
(GHz)
Phase center from the aperture plane
(mm)
Without
chokes and
corrugations
With
chokes
With chokes
and
corrugations
1000 -326 062 000
1100 -187 030 -002
1200 -563 -208 -065
1300 -296 -154 -202
1400 -319 -314 -302
1500 -201 -203 -241
1600 -242 -233 -207
1700 -208 -208 -186
1800 -190 -157 -132
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
Based on the foregoing parametric studies optimum dimensions of the
broadband circular waveguide feed are obtained as shown in Table 53
-74-
Table 53 Optimum dimensions of the broadband circular waveguide feed
Parameter Designation Value (mm)
2a Waveguide inside diameter 2070
d Waveguide outside diameter 3690
lcrLength of the circular waveguide section 1430
m Distance between the aperture plane and the first corrugation 950
xDistance from the last corrugation to the end of the cylindrical outer surface
550
ltrLength of the rectangular-to-circularwaveguide transition 4465
lrcLength of the rectangular waveguide section 1430
tch Choke slot width 090
lch Choke depth 750
t Choke metal width 090
lcor Corrugation depth 465
tcor Corrugation metal width 100
s Corrugation slot width 10
lp Probe length 530
sp Probe position from the back short 530
din Probe diameter 127
b Inside height of the rectangular waveguide 857
tw Waveguide wall thickness 500
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-48-
Fig 49 shows the geometry of a spherical ended dielectric rod feed
diameter of 06λ0 at 10GHz with a dielectric constant of 25 and L= 03λ0
Fig 410 shows the radiation patterns of the designed feed E- and H-plane
10-dB beamwidths are both 63 degrees The front-to-back ratio is 24dB The
antenna gain is 864dB
Fig 49 Geometry of a circular waveguide loaded with a spherical ended
dielectric rod
-49-
(a)
(b)
Fig 410 Radiation pattern of a circular waveguide loaded wht a spherical
ended dielectric rod with d = 06λ0 L = 03λ0 and εr =25 at 10GHz (a) 3D
radiation pattern and (b) E- and H-plane patterns
-50-
V Design of a Broadband Circular Waveguide Feed
In this chapter the design of a broadband circular waveguide feed is
presented At microwave frequencies the feed is often a circular waveguide
with chokes and corrugations around the aperture Chokes and corrugations
equalize E- and H-plane patterns and reduce the back radiation
The proposed feed is designed to operate over 10-18GHz The design starts
with the optimization of the coaxial-to-rectangular waveguide adapter
employed for good mode purity over a broad frequency range Next a
rectangular-to-circular waveguide transition is optimized Finally chokes and
corrugations are designed for improved pattern symmetry and low back
radiation
The proposed feed structure is shown in Fig 51 The feed consist of the
following parts a coaxial-to-rectangular waveguide adapter a rectangular-to-
circular waveguide transition a circular waveguide section four quarter-wave
chokes around the feeds aperture and four corrugations on the feeds outer
surface
The computer simulation shows the above arrangement offers good radiation
patterns over a broad frequency range The broadband operation is obtained
by exciting the TE11 mode in the circular waveguide using the TE10 mode of
the rectangular waveguide which is in turn excited by a coaxial probe
-51-
Chokes
Coaxial-to-waveguide transition
Circular wavguide
Corrugations
Mode transition
(a)
(b)
Fig 51 Structure of the proposed broadband circular waveguide feed
(a) CAD model and (b) cross-sectional view
For the coaxial-to-rectangular waveguide adapter an SMA connector with
the probe diameter of 127 mm is employed The coaxial probe inserted into
the waveguide energizes the feed and excites the dominant TE10 mode in
-52-
the rectangular waveguide The impedance matching is achieved by adjusting
the probe distance sp from the back short and the probe length lp
(a)
(b)
Fig 52 Reflection coefficient of the coaxial-to-rectangular adapter versus
(a) probe length lp and (b) the probe position sp
Fig 52 shows the reflection coefficient versus the various values of probe
lengths lp and probe positions sp The probe length lp is adjusted to obtain
antenna impedance matching and the probe distance sp is adjusted to obtain a
-53-
desired resonant frequency
Next a transition between rectangular and circular waveguide is designed
The transition section converts the TE10 mode in the rectangular waveguide to
TE11 mode in the circular waveguide and vice versa The transition is built
in a form of a taper for easy fabrication[22]
(a)
(b)
Fig 53 Structure of the rectangular-to-circular waveguide transition
(a) 3D view and (b) cross sectional view
The dimensions of the final optimized transition are as follows The length
of the rectangular waveguide section is 143mm The rectangular waveguides
width a and height b are 207mm and 857mm respectively The length of
the circular waveguide section is 143mm The inside diameter of the circular
-54-
waveguide is 207mm(097 wavelength at 14GHz) The length of transition
region ltr is 4465mm(approximately equal to 2λ0 at 14GHz) Fig 54 shows
the field distribution inside the mode converter
(a)
(b)
Fig 54 Field distribution inside the mode converter at
(a) 10GHz (b) 14GHz and (c) 18GHz
-55-
(c)
Fig 54 continued
Finally multiple chokes are investigated Figs 55 56 and 57 show the
feed performance without chokes The reflection coefficient is less than -10dB
over 10-19GHz The antenna has a gain of 921dB to 1189dB over
10-19GHz
Fig 55 Reflection coefficient of the broadband circular waveguide feed
without chokes and corrugations
-56-
(a)
(b)
(c)
Fig 56 E- and H-plane patterns of the broadband circular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-57-
(d)
(e)
Fig 56 continued
-58-
(a)
(b)
Fig 57 2D radiation patterns of the broadband cicular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-59-
(c)
(d)
Fig 57 continued
-60-
(e)
Fig 57 continued
To achieve equal beamwidths in E and H planes over a wide frequency
range chokes and corrugations are employed Table51 summarizes the
performance of a feed without chokes and corrugations
Table 51 Performance of the broadband circular waveguide feed without
chokes and corrugations
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
1000 940 6061 15
1200 972 6159 17
1400 920 5957 21
1600 1070 4751 29
1800 1188 5352 21
-61-
Four quarter-wavelength chokes are introduced in the feed design which
has a slot depth of 75mm and slot width of 09mm The choke slot spacing
is 18mm The choke design is investigated by applying the choke one by
one and the effect on the E- and H-plane patterns are observed as illustrated
in Figs 58 and 59 The use of chokes makes the E-plane pattern narrower
The H-plane pattern is not affected Chokes increase the gain slightly and
reduce back radiation
(a)
(b)
Fig 58 Effect of chokes on the E-plane pattern of the broadband circular
waveguide feed at (a) 10GHz(b) 12GHz (c) 14GHz (d) 16GHz and (e)
18GHz
-62-
(c)
(d)
(e)
Fig 58 continued
-63-
(a)
(b)
(c)
Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-64-
(d)
(e)
Fig 59 continued
-65-
Fig 510 shows the feed performance versus the choke depth When the
choke depth is varied from 535mm to 95mm the E- and H-plane patterns
are strongly affected The optimum value of choke depth is 75mm(035λ0 at
14GHz) which gives equal E- and H-plane radiation patterns and leads to
low back radiation
Fig 511 shows the feed performance versus the choke slot width tch The
choke slot width is varied from 09mm to 21mm Radiation patterns and
reflection coefficients are not sensitive to the choke slot width The final
choke slot width is selected to be 09mm considering the feed diameter
minimization and the manufacturability The overall diameter of the proposed
feed is 369mm which is increased from the 207mm of the waveguide
inside diameter due to the use of four chokes
-66-
(a)
(b)
(c)
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection coefficient
-67-
(a)
(b)
(c)
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and (c)
reflection coefficient
-68-
Next we investigated corrugations placed on the outer wall of the feed
Four corrugations applied to the outer surface of the circular waveguide The
corrugation depth is 465mm(0215λ0 at 14GHz) The primary purpose of
using corrugations is to further reduce the back radiation Increasing the
number of corrugations beyond four has little effect in reducing the back
radiation
Figs 512 and 513 show the effect of corrugations on the E- and H-plane
patterns Fig 514 shows the parametric study of the corrugation depth lcor
The corrugation depth is varied from 40mm and 645mm The optimum
value of the corrugation depth is found to be 465mm
-69-
(a)
(b)
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern at (a) 12GHz and (b) 14GHz
-70-
(a)
(b)
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern at (a) 12GHz and (b) 14GHz
-71-
(a)
(b)
(c)
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection coefficient
-72-
The phase center location is important in placing the feed in a reflector
antenna[8] The phase center variation with frequency should be small Fig
515 shows the effect of chokes and corrugations on the phase center The
curve with circle corresponds to the case without chokes and corrugations
The phase center varies from -326mm and -190mm away from the feeds
aperture plane It means the phase center is located inside the waveguide
The curve with triangles corresponds to the case with chokes The curve with
squares to the case with chokes and corrugations The phase center varies
from 0mm to -302mm
From Fig 515 we can observed that phase center variation reduced by the
corrugation and three cases phase center calculated in φ=450 plane
parameter sweep values are given in Table 52
10 12 14 16 181
0
-1
-2
-3
-4
-5
-6
Pha
se c
ente
r (m
m)
Frequency (GHz)
choke+corrugatuion without choke corrugation with choke
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
-73-
Frequency
(GHz)
Phase center from the aperture plane
(mm)
Without
chokes and
corrugations
With
chokes
With chokes
and
corrugations
1000 -326 062 000
1100 -187 030 -002
1200 -563 -208 -065
1300 -296 -154 -202
1400 -319 -314 -302
1500 -201 -203 -241
1600 -242 -233 -207
1700 -208 -208 -186
1800 -190 -157 -132
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
Based on the foregoing parametric studies optimum dimensions of the
broadband circular waveguide feed are obtained as shown in Table 53
-74-
Table 53 Optimum dimensions of the broadband circular waveguide feed
Parameter Designation Value (mm)
2a Waveguide inside diameter 2070
d Waveguide outside diameter 3690
lcrLength of the circular waveguide section 1430
m Distance between the aperture plane and the first corrugation 950
xDistance from the last corrugation to the end of the cylindrical outer surface
550
ltrLength of the rectangular-to-circularwaveguide transition 4465
lrcLength of the rectangular waveguide section 1430
tch Choke slot width 090
lch Choke depth 750
t Choke metal width 090
lcor Corrugation depth 465
tcor Corrugation metal width 100
s Corrugation slot width 10
lp Probe length 530
sp Probe position from the back short 530
din Probe diameter 127
b Inside height of the rectangular waveguide 857
tw Waveguide wall thickness 500
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-49-
(a)
(b)
Fig 410 Radiation pattern of a circular waveguide loaded wht a spherical
ended dielectric rod with d = 06λ0 L = 03λ0 and εr =25 at 10GHz (a) 3D
radiation pattern and (b) E- and H-plane patterns
-50-
V Design of a Broadband Circular Waveguide Feed
In this chapter the design of a broadband circular waveguide feed is
presented At microwave frequencies the feed is often a circular waveguide
with chokes and corrugations around the aperture Chokes and corrugations
equalize E- and H-plane patterns and reduce the back radiation
The proposed feed is designed to operate over 10-18GHz The design starts
with the optimization of the coaxial-to-rectangular waveguide adapter
employed for good mode purity over a broad frequency range Next a
rectangular-to-circular waveguide transition is optimized Finally chokes and
corrugations are designed for improved pattern symmetry and low back
radiation
The proposed feed structure is shown in Fig 51 The feed consist of the
following parts a coaxial-to-rectangular waveguide adapter a rectangular-to-
circular waveguide transition a circular waveguide section four quarter-wave
chokes around the feeds aperture and four corrugations on the feeds outer
surface
The computer simulation shows the above arrangement offers good radiation
patterns over a broad frequency range The broadband operation is obtained
by exciting the TE11 mode in the circular waveguide using the TE10 mode of
the rectangular waveguide which is in turn excited by a coaxial probe
-51-
Chokes
Coaxial-to-waveguide transition
Circular wavguide
Corrugations
Mode transition
(a)
(b)
Fig 51 Structure of the proposed broadband circular waveguide feed
(a) CAD model and (b) cross-sectional view
For the coaxial-to-rectangular waveguide adapter an SMA connector with
the probe diameter of 127 mm is employed The coaxial probe inserted into
the waveguide energizes the feed and excites the dominant TE10 mode in
-52-
the rectangular waveguide The impedance matching is achieved by adjusting
the probe distance sp from the back short and the probe length lp
(a)
(b)
Fig 52 Reflection coefficient of the coaxial-to-rectangular adapter versus
(a) probe length lp and (b) the probe position sp
Fig 52 shows the reflection coefficient versus the various values of probe
lengths lp and probe positions sp The probe length lp is adjusted to obtain
antenna impedance matching and the probe distance sp is adjusted to obtain a
-53-
desired resonant frequency
Next a transition between rectangular and circular waveguide is designed
The transition section converts the TE10 mode in the rectangular waveguide to
TE11 mode in the circular waveguide and vice versa The transition is built
in a form of a taper for easy fabrication[22]
(a)
(b)
Fig 53 Structure of the rectangular-to-circular waveguide transition
(a) 3D view and (b) cross sectional view
The dimensions of the final optimized transition are as follows The length
of the rectangular waveguide section is 143mm The rectangular waveguides
width a and height b are 207mm and 857mm respectively The length of
the circular waveguide section is 143mm The inside diameter of the circular
-54-
waveguide is 207mm(097 wavelength at 14GHz) The length of transition
region ltr is 4465mm(approximately equal to 2λ0 at 14GHz) Fig 54 shows
the field distribution inside the mode converter
(a)
(b)
Fig 54 Field distribution inside the mode converter at
(a) 10GHz (b) 14GHz and (c) 18GHz
-55-
(c)
Fig 54 continued
Finally multiple chokes are investigated Figs 55 56 and 57 show the
feed performance without chokes The reflection coefficient is less than -10dB
over 10-19GHz The antenna has a gain of 921dB to 1189dB over
10-19GHz
Fig 55 Reflection coefficient of the broadband circular waveguide feed
without chokes and corrugations
-56-
(a)
(b)
(c)
Fig 56 E- and H-plane patterns of the broadband circular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-57-
(d)
(e)
Fig 56 continued
-58-
(a)
(b)
Fig 57 2D radiation patterns of the broadband cicular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-59-
(c)
(d)
Fig 57 continued
-60-
(e)
Fig 57 continued
To achieve equal beamwidths in E and H planes over a wide frequency
range chokes and corrugations are employed Table51 summarizes the
performance of a feed without chokes and corrugations
Table 51 Performance of the broadband circular waveguide feed without
chokes and corrugations
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
1000 940 6061 15
1200 972 6159 17
1400 920 5957 21
1600 1070 4751 29
1800 1188 5352 21
-61-
Four quarter-wavelength chokes are introduced in the feed design which
has a slot depth of 75mm and slot width of 09mm The choke slot spacing
is 18mm The choke design is investigated by applying the choke one by
one and the effect on the E- and H-plane patterns are observed as illustrated
in Figs 58 and 59 The use of chokes makes the E-plane pattern narrower
The H-plane pattern is not affected Chokes increase the gain slightly and
reduce back radiation
(a)
(b)
Fig 58 Effect of chokes on the E-plane pattern of the broadband circular
waveguide feed at (a) 10GHz(b) 12GHz (c) 14GHz (d) 16GHz and (e)
18GHz
-62-
(c)
(d)
(e)
Fig 58 continued
-63-
(a)
(b)
(c)
Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-64-
(d)
(e)
Fig 59 continued
-65-
Fig 510 shows the feed performance versus the choke depth When the
choke depth is varied from 535mm to 95mm the E- and H-plane patterns
are strongly affected The optimum value of choke depth is 75mm(035λ0 at
14GHz) which gives equal E- and H-plane radiation patterns and leads to
low back radiation
Fig 511 shows the feed performance versus the choke slot width tch The
choke slot width is varied from 09mm to 21mm Radiation patterns and
reflection coefficients are not sensitive to the choke slot width The final
choke slot width is selected to be 09mm considering the feed diameter
minimization and the manufacturability The overall diameter of the proposed
feed is 369mm which is increased from the 207mm of the waveguide
inside diameter due to the use of four chokes
-66-
(a)
(b)
(c)
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection coefficient
-67-
(a)
(b)
(c)
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and (c)
reflection coefficient
-68-
Next we investigated corrugations placed on the outer wall of the feed
Four corrugations applied to the outer surface of the circular waveguide The
corrugation depth is 465mm(0215λ0 at 14GHz) The primary purpose of
using corrugations is to further reduce the back radiation Increasing the
number of corrugations beyond four has little effect in reducing the back
radiation
Figs 512 and 513 show the effect of corrugations on the E- and H-plane
patterns Fig 514 shows the parametric study of the corrugation depth lcor
The corrugation depth is varied from 40mm and 645mm The optimum
value of the corrugation depth is found to be 465mm
-69-
(a)
(b)
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern at (a) 12GHz and (b) 14GHz
-70-
(a)
(b)
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern at (a) 12GHz and (b) 14GHz
-71-
(a)
(b)
(c)
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection coefficient
-72-
The phase center location is important in placing the feed in a reflector
antenna[8] The phase center variation with frequency should be small Fig
515 shows the effect of chokes and corrugations on the phase center The
curve with circle corresponds to the case without chokes and corrugations
The phase center varies from -326mm and -190mm away from the feeds
aperture plane It means the phase center is located inside the waveguide
The curve with triangles corresponds to the case with chokes The curve with
squares to the case with chokes and corrugations The phase center varies
from 0mm to -302mm
From Fig 515 we can observed that phase center variation reduced by the
corrugation and three cases phase center calculated in φ=450 plane
parameter sweep values are given in Table 52
10 12 14 16 181
0
-1
-2
-3
-4
-5
-6
Pha
se c
ente
r (m
m)
Frequency (GHz)
choke+corrugatuion without choke corrugation with choke
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
-73-
Frequency
(GHz)
Phase center from the aperture plane
(mm)
Without
chokes and
corrugations
With
chokes
With chokes
and
corrugations
1000 -326 062 000
1100 -187 030 -002
1200 -563 -208 -065
1300 -296 -154 -202
1400 -319 -314 -302
1500 -201 -203 -241
1600 -242 -233 -207
1700 -208 -208 -186
1800 -190 -157 -132
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
Based on the foregoing parametric studies optimum dimensions of the
broadband circular waveguide feed are obtained as shown in Table 53
-74-
Table 53 Optimum dimensions of the broadband circular waveguide feed
Parameter Designation Value (mm)
2a Waveguide inside diameter 2070
d Waveguide outside diameter 3690
lcrLength of the circular waveguide section 1430
m Distance between the aperture plane and the first corrugation 950
xDistance from the last corrugation to the end of the cylindrical outer surface
550
ltrLength of the rectangular-to-circularwaveguide transition 4465
lrcLength of the rectangular waveguide section 1430
tch Choke slot width 090
lch Choke depth 750
t Choke metal width 090
lcor Corrugation depth 465
tcor Corrugation metal width 100
s Corrugation slot width 10
lp Probe length 530
sp Probe position from the back short 530
din Probe diameter 127
b Inside height of the rectangular waveguide 857
tw Waveguide wall thickness 500
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-50-
V Design of a Broadband Circular Waveguide Feed
In this chapter the design of a broadband circular waveguide feed is
presented At microwave frequencies the feed is often a circular waveguide
with chokes and corrugations around the aperture Chokes and corrugations
equalize E- and H-plane patterns and reduce the back radiation
The proposed feed is designed to operate over 10-18GHz The design starts
with the optimization of the coaxial-to-rectangular waveguide adapter
employed for good mode purity over a broad frequency range Next a
rectangular-to-circular waveguide transition is optimized Finally chokes and
corrugations are designed for improved pattern symmetry and low back
radiation
The proposed feed structure is shown in Fig 51 The feed consist of the
following parts a coaxial-to-rectangular waveguide adapter a rectangular-to-
circular waveguide transition a circular waveguide section four quarter-wave
chokes around the feeds aperture and four corrugations on the feeds outer
surface
The computer simulation shows the above arrangement offers good radiation
patterns over a broad frequency range The broadband operation is obtained
by exciting the TE11 mode in the circular waveguide using the TE10 mode of
the rectangular waveguide which is in turn excited by a coaxial probe
-51-
Chokes
Coaxial-to-waveguide transition
Circular wavguide
Corrugations
Mode transition
(a)
(b)
Fig 51 Structure of the proposed broadband circular waveguide feed
(a) CAD model and (b) cross-sectional view
For the coaxial-to-rectangular waveguide adapter an SMA connector with
the probe diameter of 127 mm is employed The coaxial probe inserted into
the waveguide energizes the feed and excites the dominant TE10 mode in
-52-
the rectangular waveguide The impedance matching is achieved by adjusting
the probe distance sp from the back short and the probe length lp
(a)
(b)
Fig 52 Reflection coefficient of the coaxial-to-rectangular adapter versus
(a) probe length lp and (b) the probe position sp
Fig 52 shows the reflection coefficient versus the various values of probe
lengths lp and probe positions sp The probe length lp is adjusted to obtain
antenna impedance matching and the probe distance sp is adjusted to obtain a
-53-
desired resonant frequency
Next a transition between rectangular and circular waveguide is designed
The transition section converts the TE10 mode in the rectangular waveguide to
TE11 mode in the circular waveguide and vice versa The transition is built
in a form of a taper for easy fabrication[22]
(a)
(b)
Fig 53 Structure of the rectangular-to-circular waveguide transition
(a) 3D view and (b) cross sectional view
The dimensions of the final optimized transition are as follows The length
of the rectangular waveguide section is 143mm The rectangular waveguides
width a and height b are 207mm and 857mm respectively The length of
the circular waveguide section is 143mm The inside diameter of the circular
-54-
waveguide is 207mm(097 wavelength at 14GHz) The length of transition
region ltr is 4465mm(approximately equal to 2λ0 at 14GHz) Fig 54 shows
the field distribution inside the mode converter
(a)
(b)
Fig 54 Field distribution inside the mode converter at
(a) 10GHz (b) 14GHz and (c) 18GHz
-55-
(c)
Fig 54 continued
Finally multiple chokes are investigated Figs 55 56 and 57 show the
feed performance without chokes The reflection coefficient is less than -10dB
over 10-19GHz The antenna has a gain of 921dB to 1189dB over
10-19GHz
Fig 55 Reflection coefficient of the broadband circular waveguide feed
without chokes and corrugations
-56-
(a)
(b)
(c)
Fig 56 E- and H-plane patterns of the broadband circular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-57-
(d)
(e)
Fig 56 continued
-58-
(a)
(b)
Fig 57 2D radiation patterns of the broadband cicular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-59-
(c)
(d)
Fig 57 continued
-60-
(e)
Fig 57 continued
To achieve equal beamwidths in E and H planes over a wide frequency
range chokes and corrugations are employed Table51 summarizes the
performance of a feed without chokes and corrugations
Table 51 Performance of the broadband circular waveguide feed without
chokes and corrugations
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
1000 940 6061 15
1200 972 6159 17
1400 920 5957 21
1600 1070 4751 29
1800 1188 5352 21
-61-
Four quarter-wavelength chokes are introduced in the feed design which
has a slot depth of 75mm and slot width of 09mm The choke slot spacing
is 18mm The choke design is investigated by applying the choke one by
one and the effect on the E- and H-plane patterns are observed as illustrated
in Figs 58 and 59 The use of chokes makes the E-plane pattern narrower
The H-plane pattern is not affected Chokes increase the gain slightly and
reduce back radiation
(a)
(b)
Fig 58 Effect of chokes on the E-plane pattern of the broadband circular
waveguide feed at (a) 10GHz(b) 12GHz (c) 14GHz (d) 16GHz and (e)
18GHz
-62-
(c)
(d)
(e)
Fig 58 continued
-63-
(a)
(b)
(c)
Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-64-
(d)
(e)
Fig 59 continued
-65-
Fig 510 shows the feed performance versus the choke depth When the
choke depth is varied from 535mm to 95mm the E- and H-plane patterns
are strongly affected The optimum value of choke depth is 75mm(035λ0 at
14GHz) which gives equal E- and H-plane radiation patterns and leads to
low back radiation
Fig 511 shows the feed performance versus the choke slot width tch The
choke slot width is varied from 09mm to 21mm Radiation patterns and
reflection coefficients are not sensitive to the choke slot width The final
choke slot width is selected to be 09mm considering the feed diameter
minimization and the manufacturability The overall diameter of the proposed
feed is 369mm which is increased from the 207mm of the waveguide
inside diameter due to the use of four chokes
-66-
(a)
(b)
(c)
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection coefficient
-67-
(a)
(b)
(c)
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and (c)
reflection coefficient
-68-
Next we investigated corrugations placed on the outer wall of the feed
Four corrugations applied to the outer surface of the circular waveguide The
corrugation depth is 465mm(0215λ0 at 14GHz) The primary purpose of
using corrugations is to further reduce the back radiation Increasing the
number of corrugations beyond four has little effect in reducing the back
radiation
Figs 512 and 513 show the effect of corrugations on the E- and H-plane
patterns Fig 514 shows the parametric study of the corrugation depth lcor
The corrugation depth is varied from 40mm and 645mm The optimum
value of the corrugation depth is found to be 465mm
-69-
(a)
(b)
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern at (a) 12GHz and (b) 14GHz
-70-
(a)
(b)
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern at (a) 12GHz and (b) 14GHz
-71-
(a)
(b)
(c)
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection coefficient
-72-
The phase center location is important in placing the feed in a reflector
antenna[8] The phase center variation with frequency should be small Fig
515 shows the effect of chokes and corrugations on the phase center The
curve with circle corresponds to the case without chokes and corrugations
The phase center varies from -326mm and -190mm away from the feeds
aperture plane It means the phase center is located inside the waveguide
The curve with triangles corresponds to the case with chokes The curve with
squares to the case with chokes and corrugations The phase center varies
from 0mm to -302mm
From Fig 515 we can observed that phase center variation reduced by the
corrugation and three cases phase center calculated in φ=450 plane
parameter sweep values are given in Table 52
10 12 14 16 181
0
-1
-2
-3
-4
-5
-6
Pha
se c
ente
r (m
m)
Frequency (GHz)
choke+corrugatuion without choke corrugation with choke
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
-73-
Frequency
(GHz)
Phase center from the aperture plane
(mm)
Without
chokes and
corrugations
With
chokes
With chokes
and
corrugations
1000 -326 062 000
1100 -187 030 -002
1200 -563 -208 -065
1300 -296 -154 -202
1400 -319 -314 -302
1500 -201 -203 -241
1600 -242 -233 -207
1700 -208 -208 -186
1800 -190 -157 -132
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
Based on the foregoing parametric studies optimum dimensions of the
broadband circular waveguide feed are obtained as shown in Table 53
-74-
Table 53 Optimum dimensions of the broadband circular waveguide feed
Parameter Designation Value (mm)
2a Waveguide inside diameter 2070
d Waveguide outside diameter 3690
lcrLength of the circular waveguide section 1430
m Distance between the aperture plane and the first corrugation 950
xDistance from the last corrugation to the end of the cylindrical outer surface
550
ltrLength of the rectangular-to-circularwaveguide transition 4465
lrcLength of the rectangular waveguide section 1430
tch Choke slot width 090
lch Choke depth 750
t Choke metal width 090
lcor Corrugation depth 465
tcor Corrugation metal width 100
s Corrugation slot width 10
lp Probe length 530
sp Probe position from the back short 530
din Probe diameter 127
b Inside height of the rectangular waveguide 857
tw Waveguide wall thickness 500
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-51-
Chokes
Coaxial-to-waveguide transition
Circular wavguide
Corrugations
Mode transition
(a)
(b)
Fig 51 Structure of the proposed broadband circular waveguide feed
(a) CAD model and (b) cross-sectional view
For the coaxial-to-rectangular waveguide adapter an SMA connector with
the probe diameter of 127 mm is employed The coaxial probe inserted into
the waveguide energizes the feed and excites the dominant TE10 mode in
-52-
the rectangular waveguide The impedance matching is achieved by adjusting
the probe distance sp from the back short and the probe length lp
(a)
(b)
Fig 52 Reflection coefficient of the coaxial-to-rectangular adapter versus
(a) probe length lp and (b) the probe position sp
Fig 52 shows the reflection coefficient versus the various values of probe
lengths lp and probe positions sp The probe length lp is adjusted to obtain
antenna impedance matching and the probe distance sp is adjusted to obtain a
-53-
desired resonant frequency
Next a transition between rectangular and circular waveguide is designed
The transition section converts the TE10 mode in the rectangular waveguide to
TE11 mode in the circular waveguide and vice versa The transition is built
in a form of a taper for easy fabrication[22]
(a)
(b)
Fig 53 Structure of the rectangular-to-circular waveguide transition
(a) 3D view and (b) cross sectional view
The dimensions of the final optimized transition are as follows The length
of the rectangular waveguide section is 143mm The rectangular waveguides
width a and height b are 207mm and 857mm respectively The length of
the circular waveguide section is 143mm The inside diameter of the circular
-54-
waveguide is 207mm(097 wavelength at 14GHz) The length of transition
region ltr is 4465mm(approximately equal to 2λ0 at 14GHz) Fig 54 shows
the field distribution inside the mode converter
(a)
(b)
Fig 54 Field distribution inside the mode converter at
(a) 10GHz (b) 14GHz and (c) 18GHz
-55-
(c)
Fig 54 continued
Finally multiple chokes are investigated Figs 55 56 and 57 show the
feed performance without chokes The reflection coefficient is less than -10dB
over 10-19GHz The antenna has a gain of 921dB to 1189dB over
10-19GHz
Fig 55 Reflection coefficient of the broadband circular waveguide feed
without chokes and corrugations
-56-
(a)
(b)
(c)
Fig 56 E- and H-plane patterns of the broadband circular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-57-
(d)
(e)
Fig 56 continued
-58-
(a)
(b)
Fig 57 2D radiation patterns of the broadband cicular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-59-
(c)
(d)
Fig 57 continued
-60-
(e)
Fig 57 continued
To achieve equal beamwidths in E and H planes over a wide frequency
range chokes and corrugations are employed Table51 summarizes the
performance of a feed without chokes and corrugations
Table 51 Performance of the broadband circular waveguide feed without
chokes and corrugations
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
1000 940 6061 15
1200 972 6159 17
1400 920 5957 21
1600 1070 4751 29
1800 1188 5352 21
-61-
Four quarter-wavelength chokes are introduced in the feed design which
has a slot depth of 75mm and slot width of 09mm The choke slot spacing
is 18mm The choke design is investigated by applying the choke one by
one and the effect on the E- and H-plane patterns are observed as illustrated
in Figs 58 and 59 The use of chokes makes the E-plane pattern narrower
The H-plane pattern is not affected Chokes increase the gain slightly and
reduce back radiation
(a)
(b)
Fig 58 Effect of chokes on the E-plane pattern of the broadband circular
waveguide feed at (a) 10GHz(b) 12GHz (c) 14GHz (d) 16GHz and (e)
18GHz
-62-
(c)
(d)
(e)
Fig 58 continued
-63-
(a)
(b)
(c)
Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-64-
(d)
(e)
Fig 59 continued
-65-
Fig 510 shows the feed performance versus the choke depth When the
choke depth is varied from 535mm to 95mm the E- and H-plane patterns
are strongly affected The optimum value of choke depth is 75mm(035λ0 at
14GHz) which gives equal E- and H-plane radiation patterns and leads to
low back radiation
Fig 511 shows the feed performance versus the choke slot width tch The
choke slot width is varied from 09mm to 21mm Radiation patterns and
reflection coefficients are not sensitive to the choke slot width The final
choke slot width is selected to be 09mm considering the feed diameter
minimization and the manufacturability The overall diameter of the proposed
feed is 369mm which is increased from the 207mm of the waveguide
inside diameter due to the use of four chokes
-66-
(a)
(b)
(c)
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection coefficient
-67-
(a)
(b)
(c)
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and (c)
reflection coefficient
-68-
Next we investigated corrugations placed on the outer wall of the feed
Four corrugations applied to the outer surface of the circular waveguide The
corrugation depth is 465mm(0215λ0 at 14GHz) The primary purpose of
using corrugations is to further reduce the back radiation Increasing the
number of corrugations beyond four has little effect in reducing the back
radiation
Figs 512 and 513 show the effect of corrugations on the E- and H-plane
patterns Fig 514 shows the parametric study of the corrugation depth lcor
The corrugation depth is varied from 40mm and 645mm The optimum
value of the corrugation depth is found to be 465mm
-69-
(a)
(b)
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern at (a) 12GHz and (b) 14GHz
-70-
(a)
(b)
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern at (a) 12GHz and (b) 14GHz
-71-
(a)
(b)
(c)
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection coefficient
-72-
The phase center location is important in placing the feed in a reflector
antenna[8] The phase center variation with frequency should be small Fig
515 shows the effect of chokes and corrugations on the phase center The
curve with circle corresponds to the case without chokes and corrugations
The phase center varies from -326mm and -190mm away from the feeds
aperture plane It means the phase center is located inside the waveguide
The curve with triangles corresponds to the case with chokes The curve with
squares to the case with chokes and corrugations The phase center varies
from 0mm to -302mm
From Fig 515 we can observed that phase center variation reduced by the
corrugation and three cases phase center calculated in φ=450 plane
parameter sweep values are given in Table 52
10 12 14 16 181
0
-1
-2
-3
-4
-5
-6
Pha
se c
ente
r (m
m)
Frequency (GHz)
choke+corrugatuion without choke corrugation with choke
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
-73-
Frequency
(GHz)
Phase center from the aperture plane
(mm)
Without
chokes and
corrugations
With
chokes
With chokes
and
corrugations
1000 -326 062 000
1100 -187 030 -002
1200 -563 -208 -065
1300 -296 -154 -202
1400 -319 -314 -302
1500 -201 -203 -241
1600 -242 -233 -207
1700 -208 -208 -186
1800 -190 -157 -132
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
Based on the foregoing parametric studies optimum dimensions of the
broadband circular waveguide feed are obtained as shown in Table 53
-74-
Table 53 Optimum dimensions of the broadband circular waveguide feed
Parameter Designation Value (mm)
2a Waveguide inside diameter 2070
d Waveguide outside diameter 3690
lcrLength of the circular waveguide section 1430
m Distance between the aperture plane and the first corrugation 950
xDistance from the last corrugation to the end of the cylindrical outer surface
550
ltrLength of the rectangular-to-circularwaveguide transition 4465
lrcLength of the rectangular waveguide section 1430
tch Choke slot width 090
lch Choke depth 750
t Choke metal width 090
lcor Corrugation depth 465
tcor Corrugation metal width 100
s Corrugation slot width 10
lp Probe length 530
sp Probe position from the back short 530
din Probe diameter 127
b Inside height of the rectangular waveguide 857
tw Waveguide wall thickness 500
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-52-
the rectangular waveguide The impedance matching is achieved by adjusting
the probe distance sp from the back short and the probe length lp
(a)
(b)
Fig 52 Reflection coefficient of the coaxial-to-rectangular adapter versus
(a) probe length lp and (b) the probe position sp
Fig 52 shows the reflection coefficient versus the various values of probe
lengths lp and probe positions sp The probe length lp is adjusted to obtain
antenna impedance matching and the probe distance sp is adjusted to obtain a
-53-
desired resonant frequency
Next a transition between rectangular and circular waveguide is designed
The transition section converts the TE10 mode in the rectangular waveguide to
TE11 mode in the circular waveguide and vice versa The transition is built
in a form of a taper for easy fabrication[22]
(a)
(b)
Fig 53 Structure of the rectangular-to-circular waveguide transition
(a) 3D view and (b) cross sectional view
The dimensions of the final optimized transition are as follows The length
of the rectangular waveguide section is 143mm The rectangular waveguides
width a and height b are 207mm and 857mm respectively The length of
the circular waveguide section is 143mm The inside diameter of the circular
-54-
waveguide is 207mm(097 wavelength at 14GHz) The length of transition
region ltr is 4465mm(approximately equal to 2λ0 at 14GHz) Fig 54 shows
the field distribution inside the mode converter
(a)
(b)
Fig 54 Field distribution inside the mode converter at
(a) 10GHz (b) 14GHz and (c) 18GHz
-55-
(c)
Fig 54 continued
Finally multiple chokes are investigated Figs 55 56 and 57 show the
feed performance without chokes The reflection coefficient is less than -10dB
over 10-19GHz The antenna has a gain of 921dB to 1189dB over
10-19GHz
Fig 55 Reflection coefficient of the broadband circular waveguide feed
without chokes and corrugations
-56-
(a)
(b)
(c)
Fig 56 E- and H-plane patterns of the broadband circular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-57-
(d)
(e)
Fig 56 continued
-58-
(a)
(b)
Fig 57 2D radiation patterns of the broadband cicular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-59-
(c)
(d)
Fig 57 continued
-60-
(e)
Fig 57 continued
To achieve equal beamwidths in E and H planes over a wide frequency
range chokes and corrugations are employed Table51 summarizes the
performance of a feed without chokes and corrugations
Table 51 Performance of the broadband circular waveguide feed without
chokes and corrugations
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
1000 940 6061 15
1200 972 6159 17
1400 920 5957 21
1600 1070 4751 29
1800 1188 5352 21
-61-
Four quarter-wavelength chokes are introduced in the feed design which
has a slot depth of 75mm and slot width of 09mm The choke slot spacing
is 18mm The choke design is investigated by applying the choke one by
one and the effect on the E- and H-plane patterns are observed as illustrated
in Figs 58 and 59 The use of chokes makes the E-plane pattern narrower
The H-plane pattern is not affected Chokes increase the gain slightly and
reduce back radiation
(a)
(b)
Fig 58 Effect of chokes on the E-plane pattern of the broadband circular
waveguide feed at (a) 10GHz(b) 12GHz (c) 14GHz (d) 16GHz and (e)
18GHz
-62-
(c)
(d)
(e)
Fig 58 continued
-63-
(a)
(b)
(c)
Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-64-
(d)
(e)
Fig 59 continued
-65-
Fig 510 shows the feed performance versus the choke depth When the
choke depth is varied from 535mm to 95mm the E- and H-plane patterns
are strongly affected The optimum value of choke depth is 75mm(035λ0 at
14GHz) which gives equal E- and H-plane radiation patterns and leads to
low back radiation
Fig 511 shows the feed performance versus the choke slot width tch The
choke slot width is varied from 09mm to 21mm Radiation patterns and
reflection coefficients are not sensitive to the choke slot width The final
choke slot width is selected to be 09mm considering the feed diameter
minimization and the manufacturability The overall diameter of the proposed
feed is 369mm which is increased from the 207mm of the waveguide
inside diameter due to the use of four chokes
-66-
(a)
(b)
(c)
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection coefficient
-67-
(a)
(b)
(c)
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and (c)
reflection coefficient
-68-
Next we investigated corrugations placed on the outer wall of the feed
Four corrugations applied to the outer surface of the circular waveguide The
corrugation depth is 465mm(0215λ0 at 14GHz) The primary purpose of
using corrugations is to further reduce the back radiation Increasing the
number of corrugations beyond four has little effect in reducing the back
radiation
Figs 512 and 513 show the effect of corrugations on the E- and H-plane
patterns Fig 514 shows the parametric study of the corrugation depth lcor
The corrugation depth is varied from 40mm and 645mm The optimum
value of the corrugation depth is found to be 465mm
-69-
(a)
(b)
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern at (a) 12GHz and (b) 14GHz
-70-
(a)
(b)
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern at (a) 12GHz and (b) 14GHz
-71-
(a)
(b)
(c)
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection coefficient
-72-
The phase center location is important in placing the feed in a reflector
antenna[8] The phase center variation with frequency should be small Fig
515 shows the effect of chokes and corrugations on the phase center The
curve with circle corresponds to the case without chokes and corrugations
The phase center varies from -326mm and -190mm away from the feeds
aperture plane It means the phase center is located inside the waveguide
The curve with triangles corresponds to the case with chokes The curve with
squares to the case with chokes and corrugations The phase center varies
from 0mm to -302mm
From Fig 515 we can observed that phase center variation reduced by the
corrugation and three cases phase center calculated in φ=450 plane
parameter sweep values are given in Table 52
10 12 14 16 181
0
-1
-2
-3
-4
-5
-6
Pha
se c
ente
r (m
m)
Frequency (GHz)
choke+corrugatuion without choke corrugation with choke
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
-73-
Frequency
(GHz)
Phase center from the aperture plane
(mm)
Without
chokes and
corrugations
With
chokes
With chokes
and
corrugations
1000 -326 062 000
1100 -187 030 -002
1200 -563 -208 -065
1300 -296 -154 -202
1400 -319 -314 -302
1500 -201 -203 -241
1600 -242 -233 -207
1700 -208 -208 -186
1800 -190 -157 -132
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
Based on the foregoing parametric studies optimum dimensions of the
broadband circular waveguide feed are obtained as shown in Table 53
-74-
Table 53 Optimum dimensions of the broadband circular waveguide feed
Parameter Designation Value (mm)
2a Waveguide inside diameter 2070
d Waveguide outside diameter 3690
lcrLength of the circular waveguide section 1430
m Distance between the aperture plane and the first corrugation 950
xDistance from the last corrugation to the end of the cylindrical outer surface
550
ltrLength of the rectangular-to-circularwaveguide transition 4465
lrcLength of the rectangular waveguide section 1430
tch Choke slot width 090
lch Choke depth 750
t Choke metal width 090
lcor Corrugation depth 465
tcor Corrugation metal width 100
s Corrugation slot width 10
lp Probe length 530
sp Probe position from the back short 530
din Probe diameter 127
b Inside height of the rectangular waveguide 857
tw Waveguide wall thickness 500
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-53-
desired resonant frequency
Next a transition between rectangular and circular waveguide is designed
The transition section converts the TE10 mode in the rectangular waveguide to
TE11 mode in the circular waveguide and vice versa The transition is built
in a form of a taper for easy fabrication[22]
(a)
(b)
Fig 53 Structure of the rectangular-to-circular waveguide transition
(a) 3D view and (b) cross sectional view
The dimensions of the final optimized transition are as follows The length
of the rectangular waveguide section is 143mm The rectangular waveguides
width a and height b are 207mm and 857mm respectively The length of
the circular waveguide section is 143mm The inside diameter of the circular
-54-
waveguide is 207mm(097 wavelength at 14GHz) The length of transition
region ltr is 4465mm(approximately equal to 2λ0 at 14GHz) Fig 54 shows
the field distribution inside the mode converter
(a)
(b)
Fig 54 Field distribution inside the mode converter at
(a) 10GHz (b) 14GHz and (c) 18GHz
-55-
(c)
Fig 54 continued
Finally multiple chokes are investigated Figs 55 56 and 57 show the
feed performance without chokes The reflection coefficient is less than -10dB
over 10-19GHz The antenna has a gain of 921dB to 1189dB over
10-19GHz
Fig 55 Reflection coefficient of the broadband circular waveguide feed
without chokes and corrugations
-56-
(a)
(b)
(c)
Fig 56 E- and H-plane patterns of the broadband circular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-57-
(d)
(e)
Fig 56 continued
-58-
(a)
(b)
Fig 57 2D radiation patterns of the broadband cicular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-59-
(c)
(d)
Fig 57 continued
-60-
(e)
Fig 57 continued
To achieve equal beamwidths in E and H planes over a wide frequency
range chokes and corrugations are employed Table51 summarizes the
performance of a feed without chokes and corrugations
Table 51 Performance of the broadband circular waveguide feed without
chokes and corrugations
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
1000 940 6061 15
1200 972 6159 17
1400 920 5957 21
1600 1070 4751 29
1800 1188 5352 21
-61-
Four quarter-wavelength chokes are introduced in the feed design which
has a slot depth of 75mm and slot width of 09mm The choke slot spacing
is 18mm The choke design is investigated by applying the choke one by
one and the effect on the E- and H-plane patterns are observed as illustrated
in Figs 58 and 59 The use of chokes makes the E-plane pattern narrower
The H-plane pattern is not affected Chokes increase the gain slightly and
reduce back radiation
(a)
(b)
Fig 58 Effect of chokes on the E-plane pattern of the broadband circular
waveguide feed at (a) 10GHz(b) 12GHz (c) 14GHz (d) 16GHz and (e)
18GHz
-62-
(c)
(d)
(e)
Fig 58 continued
-63-
(a)
(b)
(c)
Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-64-
(d)
(e)
Fig 59 continued
-65-
Fig 510 shows the feed performance versus the choke depth When the
choke depth is varied from 535mm to 95mm the E- and H-plane patterns
are strongly affected The optimum value of choke depth is 75mm(035λ0 at
14GHz) which gives equal E- and H-plane radiation patterns and leads to
low back radiation
Fig 511 shows the feed performance versus the choke slot width tch The
choke slot width is varied from 09mm to 21mm Radiation patterns and
reflection coefficients are not sensitive to the choke slot width The final
choke slot width is selected to be 09mm considering the feed diameter
minimization and the manufacturability The overall diameter of the proposed
feed is 369mm which is increased from the 207mm of the waveguide
inside diameter due to the use of four chokes
-66-
(a)
(b)
(c)
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection coefficient
-67-
(a)
(b)
(c)
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and (c)
reflection coefficient
-68-
Next we investigated corrugations placed on the outer wall of the feed
Four corrugations applied to the outer surface of the circular waveguide The
corrugation depth is 465mm(0215λ0 at 14GHz) The primary purpose of
using corrugations is to further reduce the back radiation Increasing the
number of corrugations beyond four has little effect in reducing the back
radiation
Figs 512 and 513 show the effect of corrugations on the E- and H-plane
patterns Fig 514 shows the parametric study of the corrugation depth lcor
The corrugation depth is varied from 40mm and 645mm The optimum
value of the corrugation depth is found to be 465mm
-69-
(a)
(b)
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern at (a) 12GHz and (b) 14GHz
-70-
(a)
(b)
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern at (a) 12GHz and (b) 14GHz
-71-
(a)
(b)
(c)
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection coefficient
-72-
The phase center location is important in placing the feed in a reflector
antenna[8] The phase center variation with frequency should be small Fig
515 shows the effect of chokes and corrugations on the phase center The
curve with circle corresponds to the case without chokes and corrugations
The phase center varies from -326mm and -190mm away from the feeds
aperture plane It means the phase center is located inside the waveguide
The curve with triangles corresponds to the case with chokes The curve with
squares to the case with chokes and corrugations The phase center varies
from 0mm to -302mm
From Fig 515 we can observed that phase center variation reduced by the
corrugation and three cases phase center calculated in φ=450 plane
parameter sweep values are given in Table 52
10 12 14 16 181
0
-1
-2
-3
-4
-5
-6
Pha
se c
ente
r (m
m)
Frequency (GHz)
choke+corrugatuion without choke corrugation with choke
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
-73-
Frequency
(GHz)
Phase center from the aperture plane
(mm)
Without
chokes and
corrugations
With
chokes
With chokes
and
corrugations
1000 -326 062 000
1100 -187 030 -002
1200 -563 -208 -065
1300 -296 -154 -202
1400 -319 -314 -302
1500 -201 -203 -241
1600 -242 -233 -207
1700 -208 -208 -186
1800 -190 -157 -132
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
Based on the foregoing parametric studies optimum dimensions of the
broadband circular waveguide feed are obtained as shown in Table 53
-74-
Table 53 Optimum dimensions of the broadband circular waveguide feed
Parameter Designation Value (mm)
2a Waveguide inside diameter 2070
d Waveguide outside diameter 3690
lcrLength of the circular waveguide section 1430
m Distance between the aperture plane and the first corrugation 950
xDistance from the last corrugation to the end of the cylindrical outer surface
550
ltrLength of the rectangular-to-circularwaveguide transition 4465
lrcLength of the rectangular waveguide section 1430
tch Choke slot width 090
lch Choke depth 750
t Choke metal width 090
lcor Corrugation depth 465
tcor Corrugation metal width 100
s Corrugation slot width 10
lp Probe length 530
sp Probe position from the back short 530
din Probe diameter 127
b Inside height of the rectangular waveguide 857
tw Waveguide wall thickness 500
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-54-
waveguide is 207mm(097 wavelength at 14GHz) The length of transition
region ltr is 4465mm(approximately equal to 2λ0 at 14GHz) Fig 54 shows
the field distribution inside the mode converter
(a)
(b)
Fig 54 Field distribution inside the mode converter at
(a) 10GHz (b) 14GHz and (c) 18GHz
-55-
(c)
Fig 54 continued
Finally multiple chokes are investigated Figs 55 56 and 57 show the
feed performance without chokes The reflection coefficient is less than -10dB
over 10-19GHz The antenna has a gain of 921dB to 1189dB over
10-19GHz
Fig 55 Reflection coefficient of the broadband circular waveguide feed
without chokes and corrugations
-56-
(a)
(b)
(c)
Fig 56 E- and H-plane patterns of the broadband circular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-57-
(d)
(e)
Fig 56 continued
-58-
(a)
(b)
Fig 57 2D radiation patterns of the broadband cicular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-59-
(c)
(d)
Fig 57 continued
-60-
(e)
Fig 57 continued
To achieve equal beamwidths in E and H planes over a wide frequency
range chokes and corrugations are employed Table51 summarizes the
performance of a feed without chokes and corrugations
Table 51 Performance of the broadband circular waveguide feed without
chokes and corrugations
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
1000 940 6061 15
1200 972 6159 17
1400 920 5957 21
1600 1070 4751 29
1800 1188 5352 21
-61-
Four quarter-wavelength chokes are introduced in the feed design which
has a slot depth of 75mm and slot width of 09mm The choke slot spacing
is 18mm The choke design is investigated by applying the choke one by
one and the effect on the E- and H-plane patterns are observed as illustrated
in Figs 58 and 59 The use of chokes makes the E-plane pattern narrower
The H-plane pattern is not affected Chokes increase the gain slightly and
reduce back radiation
(a)
(b)
Fig 58 Effect of chokes on the E-plane pattern of the broadband circular
waveguide feed at (a) 10GHz(b) 12GHz (c) 14GHz (d) 16GHz and (e)
18GHz
-62-
(c)
(d)
(e)
Fig 58 continued
-63-
(a)
(b)
(c)
Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-64-
(d)
(e)
Fig 59 continued
-65-
Fig 510 shows the feed performance versus the choke depth When the
choke depth is varied from 535mm to 95mm the E- and H-plane patterns
are strongly affected The optimum value of choke depth is 75mm(035λ0 at
14GHz) which gives equal E- and H-plane radiation patterns and leads to
low back radiation
Fig 511 shows the feed performance versus the choke slot width tch The
choke slot width is varied from 09mm to 21mm Radiation patterns and
reflection coefficients are not sensitive to the choke slot width The final
choke slot width is selected to be 09mm considering the feed diameter
minimization and the manufacturability The overall diameter of the proposed
feed is 369mm which is increased from the 207mm of the waveguide
inside diameter due to the use of four chokes
-66-
(a)
(b)
(c)
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection coefficient
-67-
(a)
(b)
(c)
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and (c)
reflection coefficient
-68-
Next we investigated corrugations placed on the outer wall of the feed
Four corrugations applied to the outer surface of the circular waveguide The
corrugation depth is 465mm(0215λ0 at 14GHz) The primary purpose of
using corrugations is to further reduce the back radiation Increasing the
number of corrugations beyond four has little effect in reducing the back
radiation
Figs 512 and 513 show the effect of corrugations on the E- and H-plane
patterns Fig 514 shows the parametric study of the corrugation depth lcor
The corrugation depth is varied from 40mm and 645mm The optimum
value of the corrugation depth is found to be 465mm
-69-
(a)
(b)
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern at (a) 12GHz and (b) 14GHz
-70-
(a)
(b)
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern at (a) 12GHz and (b) 14GHz
-71-
(a)
(b)
(c)
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection coefficient
-72-
The phase center location is important in placing the feed in a reflector
antenna[8] The phase center variation with frequency should be small Fig
515 shows the effect of chokes and corrugations on the phase center The
curve with circle corresponds to the case without chokes and corrugations
The phase center varies from -326mm and -190mm away from the feeds
aperture plane It means the phase center is located inside the waveguide
The curve with triangles corresponds to the case with chokes The curve with
squares to the case with chokes and corrugations The phase center varies
from 0mm to -302mm
From Fig 515 we can observed that phase center variation reduced by the
corrugation and three cases phase center calculated in φ=450 plane
parameter sweep values are given in Table 52
10 12 14 16 181
0
-1
-2
-3
-4
-5
-6
Pha
se c
ente
r (m
m)
Frequency (GHz)
choke+corrugatuion without choke corrugation with choke
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
-73-
Frequency
(GHz)
Phase center from the aperture plane
(mm)
Without
chokes and
corrugations
With
chokes
With chokes
and
corrugations
1000 -326 062 000
1100 -187 030 -002
1200 -563 -208 -065
1300 -296 -154 -202
1400 -319 -314 -302
1500 -201 -203 -241
1600 -242 -233 -207
1700 -208 -208 -186
1800 -190 -157 -132
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
Based on the foregoing parametric studies optimum dimensions of the
broadband circular waveguide feed are obtained as shown in Table 53
-74-
Table 53 Optimum dimensions of the broadband circular waveguide feed
Parameter Designation Value (mm)
2a Waveguide inside diameter 2070
d Waveguide outside diameter 3690
lcrLength of the circular waveguide section 1430
m Distance between the aperture plane and the first corrugation 950
xDistance from the last corrugation to the end of the cylindrical outer surface
550
ltrLength of the rectangular-to-circularwaveguide transition 4465
lrcLength of the rectangular waveguide section 1430
tch Choke slot width 090
lch Choke depth 750
t Choke metal width 090
lcor Corrugation depth 465
tcor Corrugation metal width 100
s Corrugation slot width 10
lp Probe length 530
sp Probe position from the back short 530
din Probe diameter 127
b Inside height of the rectangular waveguide 857
tw Waveguide wall thickness 500
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-55-
(c)
Fig 54 continued
Finally multiple chokes are investigated Figs 55 56 and 57 show the
feed performance without chokes The reflection coefficient is less than -10dB
over 10-19GHz The antenna has a gain of 921dB to 1189dB over
10-19GHz
Fig 55 Reflection coefficient of the broadband circular waveguide feed
without chokes and corrugations
-56-
(a)
(b)
(c)
Fig 56 E- and H-plane patterns of the broadband circular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-57-
(d)
(e)
Fig 56 continued
-58-
(a)
(b)
Fig 57 2D radiation patterns of the broadband cicular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-59-
(c)
(d)
Fig 57 continued
-60-
(e)
Fig 57 continued
To achieve equal beamwidths in E and H planes over a wide frequency
range chokes and corrugations are employed Table51 summarizes the
performance of a feed without chokes and corrugations
Table 51 Performance of the broadband circular waveguide feed without
chokes and corrugations
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
1000 940 6061 15
1200 972 6159 17
1400 920 5957 21
1600 1070 4751 29
1800 1188 5352 21
-61-
Four quarter-wavelength chokes are introduced in the feed design which
has a slot depth of 75mm and slot width of 09mm The choke slot spacing
is 18mm The choke design is investigated by applying the choke one by
one and the effect on the E- and H-plane patterns are observed as illustrated
in Figs 58 and 59 The use of chokes makes the E-plane pattern narrower
The H-plane pattern is not affected Chokes increase the gain slightly and
reduce back radiation
(a)
(b)
Fig 58 Effect of chokes on the E-plane pattern of the broadband circular
waveguide feed at (a) 10GHz(b) 12GHz (c) 14GHz (d) 16GHz and (e)
18GHz
-62-
(c)
(d)
(e)
Fig 58 continued
-63-
(a)
(b)
(c)
Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-64-
(d)
(e)
Fig 59 continued
-65-
Fig 510 shows the feed performance versus the choke depth When the
choke depth is varied from 535mm to 95mm the E- and H-plane patterns
are strongly affected The optimum value of choke depth is 75mm(035λ0 at
14GHz) which gives equal E- and H-plane radiation patterns and leads to
low back radiation
Fig 511 shows the feed performance versus the choke slot width tch The
choke slot width is varied from 09mm to 21mm Radiation patterns and
reflection coefficients are not sensitive to the choke slot width The final
choke slot width is selected to be 09mm considering the feed diameter
minimization and the manufacturability The overall diameter of the proposed
feed is 369mm which is increased from the 207mm of the waveguide
inside diameter due to the use of four chokes
-66-
(a)
(b)
(c)
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection coefficient
-67-
(a)
(b)
(c)
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and (c)
reflection coefficient
-68-
Next we investigated corrugations placed on the outer wall of the feed
Four corrugations applied to the outer surface of the circular waveguide The
corrugation depth is 465mm(0215λ0 at 14GHz) The primary purpose of
using corrugations is to further reduce the back radiation Increasing the
number of corrugations beyond four has little effect in reducing the back
radiation
Figs 512 and 513 show the effect of corrugations on the E- and H-plane
patterns Fig 514 shows the parametric study of the corrugation depth lcor
The corrugation depth is varied from 40mm and 645mm The optimum
value of the corrugation depth is found to be 465mm
-69-
(a)
(b)
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern at (a) 12GHz and (b) 14GHz
-70-
(a)
(b)
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern at (a) 12GHz and (b) 14GHz
-71-
(a)
(b)
(c)
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection coefficient
-72-
The phase center location is important in placing the feed in a reflector
antenna[8] The phase center variation with frequency should be small Fig
515 shows the effect of chokes and corrugations on the phase center The
curve with circle corresponds to the case without chokes and corrugations
The phase center varies from -326mm and -190mm away from the feeds
aperture plane It means the phase center is located inside the waveguide
The curve with triangles corresponds to the case with chokes The curve with
squares to the case with chokes and corrugations The phase center varies
from 0mm to -302mm
From Fig 515 we can observed that phase center variation reduced by the
corrugation and three cases phase center calculated in φ=450 plane
parameter sweep values are given in Table 52
10 12 14 16 181
0
-1
-2
-3
-4
-5
-6
Pha
se c
ente
r (m
m)
Frequency (GHz)
choke+corrugatuion without choke corrugation with choke
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
-73-
Frequency
(GHz)
Phase center from the aperture plane
(mm)
Without
chokes and
corrugations
With
chokes
With chokes
and
corrugations
1000 -326 062 000
1100 -187 030 -002
1200 -563 -208 -065
1300 -296 -154 -202
1400 -319 -314 -302
1500 -201 -203 -241
1600 -242 -233 -207
1700 -208 -208 -186
1800 -190 -157 -132
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
Based on the foregoing parametric studies optimum dimensions of the
broadband circular waveguide feed are obtained as shown in Table 53
-74-
Table 53 Optimum dimensions of the broadband circular waveguide feed
Parameter Designation Value (mm)
2a Waveguide inside diameter 2070
d Waveguide outside diameter 3690
lcrLength of the circular waveguide section 1430
m Distance between the aperture plane and the first corrugation 950
xDistance from the last corrugation to the end of the cylindrical outer surface
550
ltrLength of the rectangular-to-circularwaveguide transition 4465
lrcLength of the rectangular waveguide section 1430
tch Choke slot width 090
lch Choke depth 750
t Choke metal width 090
lcor Corrugation depth 465
tcor Corrugation metal width 100
s Corrugation slot width 10
lp Probe length 530
sp Probe position from the back short 530
din Probe diameter 127
b Inside height of the rectangular waveguide 857
tw Waveguide wall thickness 500
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-56-
(a)
(b)
(c)
Fig 56 E- and H-plane patterns of the broadband circular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-57-
(d)
(e)
Fig 56 continued
-58-
(a)
(b)
Fig 57 2D radiation patterns of the broadband cicular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-59-
(c)
(d)
Fig 57 continued
-60-
(e)
Fig 57 continued
To achieve equal beamwidths in E and H planes over a wide frequency
range chokes and corrugations are employed Table51 summarizes the
performance of a feed without chokes and corrugations
Table 51 Performance of the broadband circular waveguide feed without
chokes and corrugations
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
1000 940 6061 15
1200 972 6159 17
1400 920 5957 21
1600 1070 4751 29
1800 1188 5352 21
-61-
Four quarter-wavelength chokes are introduced in the feed design which
has a slot depth of 75mm and slot width of 09mm The choke slot spacing
is 18mm The choke design is investigated by applying the choke one by
one and the effect on the E- and H-plane patterns are observed as illustrated
in Figs 58 and 59 The use of chokes makes the E-plane pattern narrower
The H-plane pattern is not affected Chokes increase the gain slightly and
reduce back radiation
(a)
(b)
Fig 58 Effect of chokes on the E-plane pattern of the broadband circular
waveguide feed at (a) 10GHz(b) 12GHz (c) 14GHz (d) 16GHz and (e)
18GHz
-62-
(c)
(d)
(e)
Fig 58 continued
-63-
(a)
(b)
(c)
Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-64-
(d)
(e)
Fig 59 continued
-65-
Fig 510 shows the feed performance versus the choke depth When the
choke depth is varied from 535mm to 95mm the E- and H-plane patterns
are strongly affected The optimum value of choke depth is 75mm(035λ0 at
14GHz) which gives equal E- and H-plane radiation patterns and leads to
low back radiation
Fig 511 shows the feed performance versus the choke slot width tch The
choke slot width is varied from 09mm to 21mm Radiation patterns and
reflection coefficients are not sensitive to the choke slot width The final
choke slot width is selected to be 09mm considering the feed diameter
minimization and the manufacturability The overall diameter of the proposed
feed is 369mm which is increased from the 207mm of the waveguide
inside diameter due to the use of four chokes
-66-
(a)
(b)
(c)
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection coefficient
-67-
(a)
(b)
(c)
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and (c)
reflection coefficient
-68-
Next we investigated corrugations placed on the outer wall of the feed
Four corrugations applied to the outer surface of the circular waveguide The
corrugation depth is 465mm(0215λ0 at 14GHz) The primary purpose of
using corrugations is to further reduce the back radiation Increasing the
number of corrugations beyond four has little effect in reducing the back
radiation
Figs 512 and 513 show the effect of corrugations on the E- and H-plane
patterns Fig 514 shows the parametric study of the corrugation depth lcor
The corrugation depth is varied from 40mm and 645mm The optimum
value of the corrugation depth is found to be 465mm
-69-
(a)
(b)
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern at (a) 12GHz and (b) 14GHz
-70-
(a)
(b)
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern at (a) 12GHz and (b) 14GHz
-71-
(a)
(b)
(c)
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection coefficient
-72-
The phase center location is important in placing the feed in a reflector
antenna[8] The phase center variation with frequency should be small Fig
515 shows the effect of chokes and corrugations on the phase center The
curve with circle corresponds to the case without chokes and corrugations
The phase center varies from -326mm and -190mm away from the feeds
aperture plane It means the phase center is located inside the waveguide
The curve with triangles corresponds to the case with chokes The curve with
squares to the case with chokes and corrugations The phase center varies
from 0mm to -302mm
From Fig 515 we can observed that phase center variation reduced by the
corrugation and three cases phase center calculated in φ=450 plane
parameter sweep values are given in Table 52
10 12 14 16 181
0
-1
-2
-3
-4
-5
-6
Pha
se c
ente
r (m
m)
Frequency (GHz)
choke+corrugatuion without choke corrugation with choke
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
-73-
Frequency
(GHz)
Phase center from the aperture plane
(mm)
Without
chokes and
corrugations
With
chokes
With chokes
and
corrugations
1000 -326 062 000
1100 -187 030 -002
1200 -563 -208 -065
1300 -296 -154 -202
1400 -319 -314 -302
1500 -201 -203 -241
1600 -242 -233 -207
1700 -208 -208 -186
1800 -190 -157 -132
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
Based on the foregoing parametric studies optimum dimensions of the
broadband circular waveguide feed are obtained as shown in Table 53
-74-
Table 53 Optimum dimensions of the broadband circular waveguide feed
Parameter Designation Value (mm)
2a Waveguide inside diameter 2070
d Waveguide outside diameter 3690
lcrLength of the circular waveguide section 1430
m Distance between the aperture plane and the first corrugation 950
xDistance from the last corrugation to the end of the cylindrical outer surface
550
ltrLength of the rectangular-to-circularwaveguide transition 4465
lrcLength of the rectangular waveguide section 1430
tch Choke slot width 090
lch Choke depth 750
t Choke metal width 090
lcor Corrugation depth 465
tcor Corrugation metal width 100
s Corrugation slot width 10
lp Probe length 530
sp Probe position from the back short 530
din Probe diameter 127
b Inside height of the rectangular waveguide 857
tw Waveguide wall thickness 500
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-57-
(d)
(e)
Fig 56 continued
-58-
(a)
(b)
Fig 57 2D radiation patterns of the broadband cicular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-59-
(c)
(d)
Fig 57 continued
-60-
(e)
Fig 57 continued
To achieve equal beamwidths in E and H planes over a wide frequency
range chokes and corrugations are employed Table51 summarizes the
performance of a feed without chokes and corrugations
Table 51 Performance of the broadband circular waveguide feed without
chokes and corrugations
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
1000 940 6061 15
1200 972 6159 17
1400 920 5957 21
1600 1070 4751 29
1800 1188 5352 21
-61-
Four quarter-wavelength chokes are introduced in the feed design which
has a slot depth of 75mm and slot width of 09mm The choke slot spacing
is 18mm The choke design is investigated by applying the choke one by
one and the effect on the E- and H-plane patterns are observed as illustrated
in Figs 58 and 59 The use of chokes makes the E-plane pattern narrower
The H-plane pattern is not affected Chokes increase the gain slightly and
reduce back radiation
(a)
(b)
Fig 58 Effect of chokes on the E-plane pattern of the broadband circular
waveguide feed at (a) 10GHz(b) 12GHz (c) 14GHz (d) 16GHz and (e)
18GHz
-62-
(c)
(d)
(e)
Fig 58 continued
-63-
(a)
(b)
(c)
Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-64-
(d)
(e)
Fig 59 continued
-65-
Fig 510 shows the feed performance versus the choke depth When the
choke depth is varied from 535mm to 95mm the E- and H-plane patterns
are strongly affected The optimum value of choke depth is 75mm(035λ0 at
14GHz) which gives equal E- and H-plane radiation patterns and leads to
low back radiation
Fig 511 shows the feed performance versus the choke slot width tch The
choke slot width is varied from 09mm to 21mm Radiation patterns and
reflection coefficients are not sensitive to the choke slot width The final
choke slot width is selected to be 09mm considering the feed diameter
minimization and the manufacturability The overall diameter of the proposed
feed is 369mm which is increased from the 207mm of the waveguide
inside diameter due to the use of four chokes
-66-
(a)
(b)
(c)
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection coefficient
-67-
(a)
(b)
(c)
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and (c)
reflection coefficient
-68-
Next we investigated corrugations placed on the outer wall of the feed
Four corrugations applied to the outer surface of the circular waveguide The
corrugation depth is 465mm(0215λ0 at 14GHz) The primary purpose of
using corrugations is to further reduce the back radiation Increasing the
number of corrugations beyond four has little effect in reducing the back
radiation
Figs 512 and 513 show the effect of corrugations on the E- and H-plane
patterns Fig 514 shows the parametric study of the corrugation depth lcor
The corrugation depth is varied from 40mm and 645mm The optimum
value of the corrugation depth is found to be 465mm
-69-
(a)
(b)
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern at (a) 12GHz and (b) 14GHz
-70-
(a)
(b)
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern at (a) 12GHz and (b) 14GHz
-71-
(a)
(b)
(c)
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection coefficient
-72-
The phase center location is important in placing the feed in a reflector
antenna[8] The phase center variation with frequency should be small Fig
515 shows the effect of chokes and corrugations on the phase center The
curve with circle corresponds to the case without chokes and corrugations
The phase center varies from -326mm and -190mm away from the feeds
aperture plane It means the phase center is located inside the waveguide
The curve with triangles corresponds to the case with chokes The curve with
squares to the case with chokes and corrugations The phase center varies
from 0mm to -302mm
From Fig 515 we can observed that phase center variation reduced by the
corrugation and three cases phase center calculated in φ=450 plane
parameter sweep values are given in Table 52
10 12 14 16 181
0
-1
-2
-3
-4
-5
-6
Pha
se c
ente
r (m
m)
Frequency (GHz)
choke+corrugatuion without choke corrugation with choke
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
-73-
Frequency
(GHz)
Phase center from the aperture plane
(mm)
Without
chokes and
corrugations
With
chokes
With chokes
and
corrugations
1000 -326 062 000
1100 -187 030 -002
1200 -563 -208 -065
1300 -296 -154 -202
1400 -319 -314 -302
1500 -201 -203 -241
1600 -242 -233 -207
1700 -208 -208 -186
1800 -190 -157 -132
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
Based on the foregoing parametric studies optimum dimensions of the
broadband circular waveguide feed are obtained as shown in Table 53
-74-
Table 53 Optimum dimensions of the broadband circular waveguide feed
Parameter Designation Value (mm)
2a Waveguide inside diameter 2070
d Waveguide outside diameter 3690
lcrLength of the circular waveguide section 1430
m Distance between the aperture plane and the first corrugation 950
xDistance from the last corrugation to the end of the cylindrical outer surface
550
ltrLength of the rectangular-to-circularwaveguide transition 4465
lrcLength of the rectangular waveguide section 1430
tch Choke slot width 090
lch Choke depth 750
t Choke metal width 090
lcor Corrugation depth 465
tcor Corrugation metal width 100
s Corrugation slot width 10
lp Probe length 530
sp Probe position from the back short 530
din Probe diameter 127
b Inside height of the rectangular waveguide 857
tw Waveguide wall thickness 500
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-58-
(a)
(b)
Fig 57 2D radiation patterns of the broadband cicular waveguide feed
without chokes and corrugations at (a) 10GHz (b) 12GHz
(c) 14GHz (d) 16GHz and (e) 18GHz
-59-
(c)
(d)
Fig 57 continued
-60-
(e)
Fig 57 continued
To achieve equal beamwidths in E and H planes over a wide frequency
range chokes and corrugations are employed Table51 summarizes the
performance of a feed without chokes and corrugations
Table 51 Performance of the broadband circular waveguide feed without
chokes and corrugations
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
1000 940 6061 15
1200 972 6159 17
1400 920 5957 21
1600 1070 4751 29
1800 1188 5352 21
-61-
Four quarter-wavelength chokes are introduced in the feed design which
has a slot depth of 75mm and slot width of 09mm The choke slot spacing
is 18mm The choke design is investigated by applying the choke one by
one and the effect on the E- and H-plane patterns are observed as illustrated
in Figs 58 and 59 The use of chokes makes the E-plane pattern narrower
The H-plane pattern is not affected Chokes increase the gain slightly and
reduce back radiation
(a)
(b)
Fig 58 Effect of chokes on the E-plane pattern of the broadband circular
waveguide feed at (a) 10GHz(b) 12GHz (c) 14GHz (d) 16GHz and (e)
18GHz
-62-
(c)
(d)
(e)
Fig 58 continued
-63-
(a)
(b)
(c)
Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-64-
(d)
(e)
Fig 59 continued
-65-
Fig 510 shows the feed performance versus the choke depth When the
choke depth is varied from 535mm to 95mm the E- and H-plane patterns
are strongly affected The optimum value of choke depth is 75mm(035λ0 at
14GHz) which gives equal E- and H-plane radiation patterns and leads to
low back radiation
Fig 511 shows the feed performance versus the choke slot width tch The
choke slot width is varied from 09mm to 21mm Radiation patterns and
reflection coefficients are not sensitive to the choke slot width The final
choke slot width is selected to be 09mm considering the feed diameter
minimization and the manufacturability The overall diameter of the proposed
feed is 369mm which is increased from the 207mm of the waveguide
inside diameter due to the use of four chokes
-66-
(a)
(b)
(c)
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection coefficient
-67-
(a)
(b)
(c)
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and (c)
reflection coefficient
-68-
Next we investigated corrugations placed on the outer wall of the feed
Four corrugations applied to the outer surface of the circular waveguide The
corrugation depth is 465mm(0215λ0 at 14GHz) The primary purpose of
using corrugations is to further reduce the back radiation Increasing the
number of corrugations beyond four has little effect in reducing the back
radiation
Figs 512 and 513 show the effect of corrugations on the E- and H-plane
patterns Fig 514 shows the parametric study of the corrugation depth lcor
The corrugation depth is varied from 40mm and 645mm The optimum
value of the corrugation depth is found to be 465mm
-69-
(a)
(b)
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern at (a) 12GHz and (b) 14GHz
-70-
(a)
(b)
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern at (a) 12GHz and (b) 14GHz
-71-
(a)
(b)
(c)
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection coefficient
-72-
The phase center location is important in placing the feed in a reflector
antenna[8] The phase center variation with frequency should be small Fig
515 shows the effect of chokes and corrugations on the phase center The
curve with circle corresponds to the case without chokes and corrugations
The phase center varies from -326mm and -190mm away from the feeds
aperture plane It means the phase center is located inside the waveguide
The curve with triangles corresponds to the case with chokes The curve with
squares to the case with chokes and corrugations The phase center varies
from 0mm to -302mm
From Fig 515 we can observed that phase center variation reduced by the
corrugation and three cases phase center calculated in φ=450 plane
parameter sweep values are given in Table 52
10 12 14 16 181
0
-1
-2
-3
-4
-5
-6
Pha
se c
ente
r (m
m)
Frequency (GHz)
choke+corrugatuion without choke corrugation with choke
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
-73-
Frequency
(GHz)
Phase center from the aperture plane
(mm)
Without
chokes and
corrugations
With
chokes
With chokes
and
corrugations
1000 -326 062 000
1100 -187 030 -002
1200 -563 -208 -065
1300 -296 -154 -202
1400 -319 -314 -302
1500 -201 -203 -241
1600 -242 -233 -207
1700 -208 -208 -186
1800 -190 -157 -132
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
Based on the foregoing parametric studies optimum dimensions of the
broadband circular waveguide feed are obtained as shown in Table 53
-74-
Table 53 Optimum dimensions of the broadband circular waveguide feed
Parameter Designation Value (mm)
2a Waveguide inside diameter 2070
d Waveguide outside diameter 3690
lcrLength of the circular waveguide section 1430
m Distance between the aperture plane and the first corrugation 950
xDistance from the last corrugation to the end of the cylindrical outer surface
550
ltrLength of the rectangular-to-circularwaveguide transition 4465
lrcLength of the rectangular waveguide section 1430
tch Choke slot width 090
lch Choke depth 750
t Choke metal width 090
lcor Corrugation depth 465
tcor Corrugation metal width 100
s Corrugation slot width 10
lp Probe length 530
sp Probe position from the back short 530
din Probe diameter 127
b Inside height of the rectangular waveguide 857
tw Waveguide wall thickness 500
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-59-
(c)
(d)
Fig 57 continued
-60-
(e)
Fig 57 continued
To achieve equal beamwidths in E and H planes over a wide frequency
range chokes and corrugations are employed Table51 summarizes the
performance of a feed without chokes and corrugations
Table 51 Performance of the broadband circular waveguide feed without
chokes and corrugations
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
1000 940 6061 15
1200 972 6159 17
1400 920 5957 21
1600 1070 4751 29
1800 1188 5352 21
-61-
Four quarter-wavelength chokes are introduced in the feed design which
has a slot depth of 75mm and slot width of 09mm The choke slot spacing
is 18mm The choke design is investigated by applying the choke one by
one and the effect on the E- and H-plane patterns are observed as illustrated
in Figs 58 and 59 The use of chokes makes the E-plane pattern narrower
The H-plane pattern is not affected Chokes increase the gain slightly and
reduce back radiation
(a)
(b)
Fig 58 Effect of chokes on the E-plane pattern of the broadband circular
waveguide feed at (a) 10GHz(b) 12GHz (c) 14GHz (d) 16GHz and (e)
18GHz
-62-
(c)
(d)
(e)
Fig 58 continued
-63-
(a)
(b)
(c)
Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-64-
(d)
(e)
Fig 59 continued
-65-
Fig 510 shows the feed performance versus the choke depth When the
choke depth is varied from 535mm to 95mm the E- and H-plane patterns
are strongly affected The optimum value of choke depth is 75mm(035λ0 at
14GHz) which gives equal E- and H-plane radiation patterns and leads to
low back radiation
Fig 511 shows the feed performance versus the choke slot width tch The
choke slot width is varied from 09mm to 21mm Radiation patterns and
reflection coefficients are not sensitive to the choke slot width The final
choke slot width is selected to be 09mm considering the feed diameter
minimization and the manufacturability The overall diameter of the proposed
feed is 369mm which is increased from the 207mm of the waveguide
inside diameter due to the use of four chokes
-66-
(a)
(b)
(c)
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection coefficient
-67-
(a)
(b)
(c)
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and (c)
reflection coefficient
-68-
Next we investigated corrugations placed on the outer wall of the feed
Four corrugations applied to the outer surface of the circular waveguide The
corrugation depth is 465mm(0215λ0 at 14GHz) The primary purpose of
using corrugations is to further reduce the back radiation Increasing the
number of corrugations beyond four has little effect in reducing the back
radiation
Figs 512 and 513 show the effect of corrugations on the E- and H-plane
patterns Fig 514 shows the parametric study of the corrugation depth lcor
The corrugation depth is varied from 40mm and 645mm The optimum
value of the corrugation depth is found to be 465mm
-69-
(a)
(b)
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern at (a) 12GHz and (b) 14GHz
-70-
(a)
(b)
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern at (a) 12GHz and (b) 14GHz
-71-
(a)
(b)
(c)
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection coefficient
-72-
The phase center location is important in placing the feed in a reflector
antenna[8] The phase center variation with frequency should be small Fig
515 shows the effect of chokes and corrugations on the phase center The
curve with circle corresponds to the case without chokes and corrugations
The phase center varies from -326mm and -190mm away from the feeds
aperture plane It means the phase center is located inside the waveguide
The curve with triangles corresponds to the case with chokes The curve with
squares to the case with chokes and corrugations The phase center varies
from 0mm to -302mm
From Fig 515 we can observed that phase center variation reduced by the
corrugation and three cases phase center calculated in φ=450 plane
parameter sweep values are given in Table 52
10 12 14 16 181
0
-1
-2
-3
-4
-5
-6
Pha
se c
ente
r (m
m)
Frequency (GHz)
choke+corrugatuion without choke corrugation with choke
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
-73-
Frequency
(GHz)
Phase center from the aperture plane
(mm)
Without
chokes and
corrugations
With
chokes
With chokes
and
corrugations
1000 -326 062 000
1100 -187 030 -002
1200 -563 -208 -065
1300 -296 -154 -202
1400 -319 -314 -302
1500 -201 -203 -241
1600 -242 -233 -207
1700 -208 -208 -186
1800 -190 -157 -132
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
Based on the foregoing parametric studies optimum dimensions of the
broadband circular waveguide feed are obtained as shown in Table 53
-74-
Table 53 Optimum dimensions of the broadband circular waveguide feed
Parameter Designation Value (mm)
2a Waveguide inside diameter 2070
d Waveguide outside diameter 3690
lcrLength of the circular waveguide section 1430
m Distance between the aperture plane and the first corrugation 950
xDistance from the last corrugation to the end of the cylindrical outer surface
550
ltrLength of the rectangular-to-circularwaveguide transition 4465
lrcLength of the rectangular waveguide section 1430
tch Choke slot width 090
lch Choke depth 750
t Choke metal width 090
lcor Corrugation depth 465
tcor Corrugation metal width 100
s Corrugation slot width 10
lp Probe length 530
sp Probe position from the back short 530
din Probe diameter 127
b Inside height of the rectangular waveguide 857
tw Waveguide wall thickness 500
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-60-
(e)
Fig 57 continued
To achieve equal beamwidths in E and H planes over a wide frequency
range chokes and corrugations are employed Table51 summarizes the
performance of a feed without chokes and corrugations
Table 51 Performance of the broadband circular waveguide feed without
chokes and corrugations
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
1000 940 6061 15
1200 972 6159 17
1400 920 5957 21
1600 1070 4751 29
1800 1188 5352 21
-61-
Four quarter-wavelength chokes are introduced in the feed design which
has a slot depth of 75mm and slot width of 09mm The choke slot spacing
is 18mm The choke design is investigated by applying the choke one by
one and the effect on the E- and H-plane patterns are observed as illustrated
in Figs 58 and 59 The use of chokes makes the E-plane pattern narrower
The H-plane pattern is not affected Chokes increase the gain slightly and
reduce back radiation
(a)
(b)
Fig 58 Effect of chokes on the E-plane pattern of the broadband circular
waveguide feed at (a) 10GHz(b) 12GHz (c) 14GHz (d) 16GHz and (e)
18GHz
-62-
(c)
(d)
(e)
Fig 58 continued
-63-
(a)
(b)
(c)
Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-64-
(d)
(e)
Fig 59 continued
-65-
Fig 510 shows the feed performance versus the choke depth When the
choke depth is varied from 535mm to 95mm the E- and H-plane patterns
are strongly affected The optimum value of choke depth is 75mm(035λ0 at
14GHz) which gives equal E- and H-plane radiation patterns and leads to
low back radiation
Fig 511 shows the feed performance versus the choke slot width tch The
choke slot width is varied from 09mm to 21mm Radiation patterns and
reflection coefficients are not sensitive to the choke slot width The final
choke slot width is selected to be 09mm considering the feed diameter
minimization and the manufacturability The overall diameter of the proposed
feed is 369mm which is increased from the 207mm of the waveguide
inside diameter due to the use of four chokes
-66-
(a)
(b)
(c)
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection coefficient
-67-
(a)
(b)
(c)
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and (c)
reflection coefficient
-68-
Next we investigated corrugations placed on the outer wall of the feed
Four corrugations applied to the outer surface of the circular waveguide The
corrugation depth is 465mm(0215λ0 at 14GHz) The primary purpose of
using corrugations is to further reduce the back radiation Increasing the
number of corrugations beyond four has little effect in reducing the back
radiation
Figs 512 and 513 show the effect of corrugations on the E- and H-plane
patterns Fig 514 shows the parametric study of the corrugation depth lcor
The corrugation depth is varied from 40mm and 645mm The optimum
value of the corrugation depth is found to be 465mm
-69-
(a)
(b)
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern at (a) 12GHz and (b) 14GHz
-70-
(a)
(b)
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern at (a) 12GHz and (b) 14GHz
-71-
(a)
(b)
(c)
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection coefficient
-72-
The phase center location is important in placing the feed in a reflector
antenna[8] The phase center variation with frequency should be small Fig
515 shows the effect of chokes and corrugations on the phase center The
curve with circle corresponds to the case without chokes and corrugations
The phase center varies from -326mm and -190mm away from the feeds
aperture plane It means the phase center is located inside the waveguide
The curve with triangles corresponds to the case with chokes The curve with
squares to the case with chokes and corrugations The phase center varies
from 0mm to -302mm
From Fig 515 we can observed that phase center variation reduced by the
corrugation and three cases phase center calculated in φ=450 plane
parameter sweep values are given in Table 52
10 12 14 16 181
0
-1
-2
-3
-4
-5
-6
Pha
se c
ente
r (m
m)
Frequency (GHz)
choke+corrugatuion without choke corrugation with choke
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
-73-
Frequency
(GHz)
Phase center from the aperture plane
(mm)
Without
chokes and
corrugations
With
chokes
With chokes
and
corrugations
1000 -326 062 000
1100 -187 030 -002
1200 -563 -208 -065
1300 -296 -154 -202
1400 -319 -314 -302
1500 -201 -203 -241
1600 -242 -233 -207
1700 -208 -208 -186
1800 -190 -157 -132
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
Based on the foregoing parametric studies optimum dimensions of the
broadband circular waveguide feed are obtained as shown in Table 53
-74-
Table 53 Optimum dimensions of the broadband circular waveguide feed
Parameter Designation Value (mm)
2a Waveguide inside diameter 2070
d Waveguide outside diameter 3690
lcrLength of the circular waveguide section 1430
m Distance between the aperture plane and the first corrugation 950
xDistance from the last corrugation to the end of the cylindrical outer surface
550
ltrLength of the rectangular-to-circularwaveguide transition 4465
lrcLength of the rectangular waveguide section 1430
tch Choke slot width 090
lch Choke depth 750
t Choke metal width 090
lcor Corrugation depth 465
tcor Corrugation metal width 100
s Corrugation slot width 10
lp Probe length 530
sp Probe position from the back short 530
din Probe diameter 127
b Inside height of the rectangular waveguide 857
tw Waveguide wall thickness 500
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-61-
Four quarter-wavelength chokes are introduced in the feed design which
has a slot depth of 75mm and slot width of 09mm The choke slot spacing
is 18mm The choke design is investigated by applying the choke one by
one and the effect on the E- and H-plane patterns are observed as illustrated
in Figs 58 and 59 The use of chokes makes the E-plane pattern narrower
The H-plane pattern is not affected Chokes increase the gain slightly and
reduce back radiation
(a)
(b)
Fig 58 Effect of chokes on the E-plane pattern of the broadband circular
waveguide feed at (a) 10GHz(b) 12GHz (c) 14GHz (d) 16GHz and (e)
18GHz
-62-
(c)
(d)
(e)
Fig 58 continued
-63-
(a)
(b)
(c)
Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-64-
(d)
(e)
Fig 59 continued
-65-
Fig 510 shows the feed performance versus the choke depth When the
choke depth is varied from 535mm to 95mm the E- and H-plane patterns
are strongly affected The optimum value of choke depth is 75mm(035λ0 at
14GHz) which gives equal E- and H-plane radiation patterns and leads to
low back radiation
Fig 511 shows the feed performance versus the choke slot width tch The
choke slot width is varied from 09mm to 21mm Radiation patterns and
reflection coefficients are not sensitive to the choke slot width The final
choke slot width is selected to be 09mm considering the feed diameter
minimization and the manufacturability The overall diameter of the proposed
feed is 369mm which is increased from the 207mm of the waveguide
inside diameter due to the use of four chokes
-66-
(a)
(b)
(c)
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection coefficient
-67-
(a)
(b)
(c)
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and (c)
reflection coefficient
-68-
Next we investigated corrugations placed on the outer wall of the feed
Four corrugations applied to the outer surface of the circular waveguide The
corrugation depth is 465mm(0215λ0 at 14GHz) The primary purpose of
using corrugations is to further reduce the back radiation Increasing the
number of corrugations beyond four has little effect in reducing the back
radiation
Figs 512 and 513 show the effect of corrugations on the E- and H-plane
patterns Fig 514 shows the parametric study of the corrugation depth lcor
The corrugation depth is varied from 40mm and 645mm The optimum
value of the corrugation depth is found to be 465mm
-69-
(a)
(b)
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern at (a) 12GHz and (b) 14GHz
-70-
(a)
(b)
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern at (a) 12GHz and (b) 14GHz
-71-
(a)
(b)
(c)
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection coefficient
-72-
The phase center location is important in placing the feed in a reflector
antenna[8] The phase center variation with frequency should be small Fig
515 shows the effect of chokes and corrugations on the phase center The
curve with circle corresponds to the case without chokes and corrugations
The phase center varies from -326mm and -190mm away from the feeds
aperture plane It means the phase center is located inside the waveguide
The curve with triangles corresponds to the case with chokes The curve with
squares to the case with chokes and corrugations The phase center varies
from 0mm to -302mm
From Fig 515 we can observed that phase center variation reduced by the
corrugation and three cases phase center calculated in φ=450 plane
parameter sweep values are given in Table 52
10 12 14 16 181
0
-1
-2
-3
-4
-5
-6
Pha
se c
ente
r (m
m)
Frequency (GHz)
choke+corrugatuion without choke corrugation with choke
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
-73-
Frequency
(GHz)
Phase center from the aperture plane
(mm)
Without
chokes and
corrugations
With
chokes
With chokes
and
corrugations
1000 -326 062 000
1100 -187 030 -002
1200 -563 -208 -065
1300 -296 -154 -202
1400 -319 -314 -302
1500 -201 -203 -241
1600 -242 -233 -207
1700 -208 -208 -186
1800 -190 -157 -132
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
Based on the foregoing parametric studies optimum dimensions of the
broadband circular waveguide feed are obtained as shown in Table 53
-74-
Table 53 Optimum dimensions of the broadband circular waveguide feed
Parameter Designation Value (mm)
2a Waveguide inside diameter 2070
d Waveguide outside diameter 3690
lcrLength of the circular waveguide section 1430
m Distance between the aperture plane and the first corrugation 950
xDistance from the last corrugation to the end of the cylindrical outer surface
550
ltrLength of the rectangular-to-circularwaveguide transition 4465
lrcLength of the rectangular waveguide section 1430
tch Choke slot width 090
lch Choke depth 750
t Choke metal width 090
lcor Corrugation depth 465
tcor Corrugation metal width 100
s Corrugation slot width 10
lp Probe length 530
sp Probe position from the back short 530
din Probe diameter 127
b Inside height of the rectangular waveguide 857
tw Waveguide wall thickness 500
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-62-
(c)
(d)
(e)
Fig 58 continued
-63-
(a)
(b)
(c)
Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-64-
(d)
(e)
Fig 59 continued
-65-
Fig 510 shows the feed performance versus the choke depth When the
choke depth is varied from 535mm to 95mm the E- and H-plane patterns
are strongly affected The optimum value of choke depth is 75mm(035λ0 at
14GHz) which gives equal E- and H-plane radiation patterns and leads to
low back radiation
Fig 511 shows the feed performance versus the choke slot width tch The
choke slot width is varied from 09mm to 21mm Radiation patterns and
reflection coefficients are not sensitive to the choke slot width The final
choke slot width is selected to be 09mm considering the feed diameter
minimization and the manufacturability The overall diameter of the proposed
feed is 369mm which is increased from the 207mm of the waveguide
inside diameter due to the use of four chokes
-66-
(a)
(b)
(c)
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection coefficient
-67-
(a)
(b)
(c)
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and (c)
reflection coefficient
-68-
Next we investigated corrugations placed on the outer wall of the feed
Four corrugations applied to the outer surface of the circular waveguide The
corrugation depth is 465mm(0215λ0 at 14GHz) The primary purpose of
using corrugations is to further reduce the back radiation Increasing the
number of corrugations beyond four has little effect in reducing the back
radiation
Figs 512 and 513 show the effect of corrugations on the E- and H-plane
patterns Fig 514 shows the parametric study of the corrugation depth lcor
The corrugation depth is varied from 40mm and 645mm The optimum
value of the corrugation depth is found to be 465mm
-69-
(a)
(b)
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern at (a) 12GHz and (b) 14GHz
-70-
(a)
(b)
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern at (a) 12GHz and (b) 14GHz
-71-
(a)
(b)
(c)
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection coefficient
-72-
The phase center location is important in placing the feed in a reflector
antenna[8] The phase center variation with frequency should be small Fig
515 shows the effect of chokes and corrugations on the phase center The
curve with circle corresponds to the case without chokes and corrugations
The phase center varies from -326mm and -190mm away from the feeds
aperture plane It means the phase center is located inside the waveguide
The curve with triangles corresponds to the case with chokes The curve with
squares to the case with chokes and corrugations The phase center varies
from 0mm to -302mm
From Fig 515 we can observed that phase center variation reduced by the
corrugation and three cases phase center calculated in φ=450 plane
parameter sweep values are given in Table 52
10 12 14 16 181
0
-1
-2
-3
-4
-5
-6
Pha
se c
ente
r (m
m)
Frequency (GHz)
choke+corrugatuion without choke corrugation with choke
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
-73-
Frequency
(GHz)
Phase center from the aperture plane
(mm)
Without
chokes and
corrugations
With
chokes
With chokes
and
corrugations
1000 -326 062 000
1100 -187 030 -002
1200 -563 -208 -065
1300 -296 -154 -202
1400 -319 -314 -302
1500 -201 -203 -241
1600 -242 -233 -207
1700 -208 -208 -186
1800 -190 -157 -132
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
Based on the foregoing parametric studies optimum dimensions of the
broadband circular waveguide feed are obtained as shown in Table 53
-74-
Table 53 Optimum dimensions of the broadband circular waveguide feed
Parameter Designation Value (mm)
2a Waveguide inside diameter 2070
d Waveguide outside diameter 3690
lcrLength of the circular waveguide section 1430
m Distance between the aperture plane and the first corrugation 950
xDistance from the last corrugation to the end of the cylindrical outer surface
550
ltrLength of the rectangular-to-circularwaveguide transition 4465
lrcLength of the rectangular waveguide section 1430
tch Choke slot width 090
lch Choke depth 750
t Choke metal width 090
lcor Corrugation depth 465
tcor Corrugation metal width 100
s Corrugation slot width 10
lp Probe length 530
sp Probe position from the back short 530
din Probe diameter 127
b Inside height of the rectangular waveguide 857
tw Waveguide wall thickness 500
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-63-
(a)
(b)
(c)
Fig 59 Effect of chokes on the H-plane pattern of the broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-64-
(d)
(e)
Fig 59 continued
-65-
Fig 510 shows the feed performance versus the choke depth When the
choke depth is varied from 535mm to 95mm the E- and H-plane patterns
are strongly affected The optimum value of choke depth is 75mm(035λ0 at
14GHz) which gives equal E- and H-plane radiation patterns and leads to
low back radiation
Fig 511 shows the feed performance versus the choke slot width tch The
choke slot width is varied from 09mm to 21mm Radiation patterns and
reflection coefficients are not sensitive to the choke slot width The final
choke slot width is selected to be 09mm considering the feed diameter
minimization and the manufacturability The overall diameter of the proposed
feed is 369mm which is increased from the 207mm of the waveguide
inside diameter due to the use of four chokes
-66-
(a)
(b)
(c)
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection coefficient
-67-
(a)
(b)
(c)
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and (c)
reflection coefficient
-68-
Next we investigated corrugations placed on the outer wall of the feed
Four corrugations applied to the outer surface of the circular waveguide The
corrugation depth is 465mm(0215λ0 at 14GHz) The primary purpose of
using corrugations is to further reduce the back radiation Increasing the
number of corrugations beyond four has little effect in reducing the back
radiation
Figs 512 and 513 show the effect of corrugations on the E- and H-plane
patterns Fig 514 shows the parametric study of the corrugation depth lcor
The corrugation depth is varied from 40mm and 645mm The optimum
value of the corrugation depth is found to be 465mm
-69-
(a)
(b)
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern at (a) 12GHz and (b) 14GHz
-70-
(a)
(b)
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern at (a) 12GHz and (b) 14GHz
-71-
(a)
(b)
(c)
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection coefficient
-72-
The phase center location is important in placing the feed in a reflector
antenna[8] The phase center variation with frequency should be small Fig
515 shows the effect of chokes and corrugations on the phase center The
curve with circle corresponds to the case without chokes and corrugations
The phase center varies from -326mm and -190mm away from the feeds
aperture plane It means the phase center is located inside the waveguide
The curve with triangles corresponds to the case with chokes The curve with
squares to the case with chokes and corrugations The phase center varies
from 0mm to -302mm
From Fig 515 we can observed that phase center variation reduced by the
corrugation and three cases phase center calculated in φ=450 plane
parameter sweep values are given in Table 52
10 12 14 16 181
0
-1
-2
-3
-4
-5
-6
Pha
se c
ente
r (m
m)
Frequency (GHz)
choke+corrugatuion without choke corrugation with choke
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
-73-
Frequency
(GHz)
Phase center from the aperture plane
(mm)
Without
chokes and
corrugations
With
chokes
With chokes
and
corrugations
1000 -326 062 000
1100 -187 030 -002
1200 -563 -208 -065
1300 -296 -154 -202
1400 -319 -314 -302
1500 -201 -203 -241
1600 -242 -233 -207
1700 -208 -208 -186
1800 -190 -157 -132
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
Based on the foregoing parametric studies optimum dimensions of the
broadband circular waveguide feed are obtained as shown in Table 53
-74-
Table 53 Optimum dimensions of the broadband circular waveguide feed
Parameter Designation Value (mm)
2a Waveguide inside diameter 2070
d Waveguide outside diameter 3690
lcrLength of the circular waveguide section 1430
m Distance between the aperture plane and the first corrugation 950
xDistance from the last corrugation to the end of the cylindrical outer surface
550
ltrLength of the rectangular-to-circularwaveguide transition 4465
lrcLength of the rectangular waveguide section 1430
tch Choke slot width 090
lch Choke depth 750
t Choke metal width 090
lcor Corrugation depth 465
tcor Corrugation metal width 100
s Corrugation slot width 10
lp Probe length 530
sp Probe position from the back short 530
din Probe diameter 127
b Inside height of the rectangular waveguide 857
tw Waveguide wall thickness 500
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-64-
(d)
(e)
Fig 59 continued
-65-
Fig 510 shows the feed performance versus the choke depth When the
choke depth is varied from 535mm to 95mm the E- and H-plane patterns
are strongly affected The optimum value of choke depth is 75mm(035λ0 at
14GHz) which gives equal E- and H-plane radiation patterns and leads to
low back radiation
Fig 511 shows the feed performance versus the choke slot width tch The
choke slot width is varied from 09mm to 21mm Radiation patterns and
reflection coefficients are not sensitive to the choke slot width The final
choke slot width is selected to be 09mm considering the feed diameter
minimization and the manufacturability The overall diameter of the proposed
feed is 369mm which is increased from the 207mm of the waveguide
inside diameter due to the use of four chokes
-66-
(a)
(b)
(c)
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection coefficient
-67-
(a)
(b)
(c)
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and (c)
reflection coefficient
-68-
Next we investigated corrugations placed on the outer wall of the feed
Four corrugations applied to the outer surface of the circular waveguide The
corrugation depth is 465mm(0215λ0 at 14GHz) The primary purpose of
using corrugations is to further reduce the back radiation Increasing the
number of corrugations beyond four has little effect in reducing the back
radiation
Figs 512 and 513 show the effect of corrugations on the E- and H-plane
patterns Fig 514 shows the parametric study of the corrugation depth lcor
The corrugation depth is varied from 40mm and 645mm The optimum
value of the corrugation depth is found to be 465mm
-69-
(a)
(b)
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern at (a) 12GHz and (b) 14GHz
-70-
(a)
(b)
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern at (a) 12GHz and (b) 14GHz
-71-
(a)
(b)
(c)
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection coefficient
-72-
The phase center location is important in placing the feed in a reflector
antenna[8] The phase center variation with frequency should be small Fig
515 shows the effect of chokes and corrugations on the phase center The
curve with circle corresponds to the case without chokes and corrugations
The phase center varies from -326mm and -190mm away from the feeds
aperture plane It means the phase center is located inside the waveguide
The curve with triangles corresponds to the case with chokes The curve with
squares to the case with chokes and corrugations The phase center varies
from 0mm to -302mm
From Fig 515 we can observed that phase center variation reduced by the
corrugation and three cases phase center calculated in φ=450 plane
parameter sweep values are given in Table 52
10 12 14 16 181
0
-1
-2
-3
-4
-5
-6
Pha
se c
ente
r (m
m)
Frequency (GHz)
choke+corrugatuion without choke corrugation with choke
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
-73-
Frequency
(GHz)
Phase center from the aperture plane
(mm)
Without
chokes and
corrugations
With
chokes
With chokes
and
corrugations
1000 -326 062 000
1100 -187 030 -002
1200 -563 -208 -065
1300 -296 -154 -202
1400 -319 -314 -302
1500 -201 -203 -241
1600 -242 -233 -207
1700 -208 -208 -186
1800 -190 -157 -132
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
Based on the foregoing parametric studies optimum dimensions of the
broadband circular waveguide feed are obtained as shown in Table 53
-74-
Table 53 Optimum dimensions of the broadband circular waveguide feed
Parameter Designation Value (mm)
2a Waveguide inside diameter 2070
d Waveguide outside diameter 3690
lcrLength of the circular waveguide section 1430
m Distance between the aperture plane and the first corrugation 950
xDistance from the last corrugation to the end of the cylindrical outer surface
550
ltrLength of the rectangular-to-circularwaveguide transition 4465
lrcLength of the rectangular waveguide section 1430
tch Choke slot width 090
lch Choke depth 750
t Choke metal width 090
lcor Corrugation depth 465
tcor Corrugation metal width 100
s Corrugation slot width 10
lp Probe length 530
sp Probe position from the back short 530
din Probe diameter 127
b Inside height of the rectangular waveguide 857
tw Waveguide wall thickness 500
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-65-
Fig 510 shows the feed performance versus the choke depth When the
choke depth is varied from 535mm to 95mm the E- and H-plane patterns
are strongly affected The optimum value of choke depth is 75mm(035λ0 at
14GHz) which gives equal E- and H-plane radiation patterns and leads to
low back radiation
Fig 511 shows the feed performance versus the choke slot width tch The
choke slot width is varied from 09mm to 21mm Radiation patterns and
reflection coefficients are not sensitive to the choke slot width The final
choke slot width is selected to be 09mm considering the feed diameter
minimization and the manufacturability The overall diameter of the proposed
feed is 369mm which is increased from the 207mm of the waveguide
inside diameter due to the use of four chokes
-66-
(a)
(b)
(c)
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection coefficient
-67-
(a)
(b)
(c)
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and (c)
reflection coefficient
-68-
Next we investigated corrugations placed on the outer wall of the feed
Four corrugations applied to the outer surface of the circular waveguide The
corrugation depth is 465mm(0215λ0 at 14GHz) The primary purpose of
using corrugations is to further reduce the back radiation Increasing the
number of corrugations beyond four has little effect in reducing the back
radiation
Figs 512 and 513 show the effect of corrugations on the E- and H-plane
patterns Fig 514 shows the parametric study of the corrugation depth lcor
The corrugation depth is varied from 40mm and 645mm The optimum
value of the corrugation depth is found to be 465mm
-69-
(a)
(b)
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern at (a) 12GHz and (b) 14GHz
-70-
(a)
(b)
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern at (a) 12GHz and (b) 14GHz
-71-
(a)
(b)
(c)
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection coefficient
-72-
The phase center location is important in placing the feed in a reflector
antenna[8] The phase center variation with frequency should be small Fig
515 shows the effect of chokes and corrugations on the phase center The
curve with circle corresponds to the case without chokes and corrugations
The phase center varies from -326mm and -190mm away from the feeds
aperture plane It means the phase center is located inside the waveguide
The curve with triangles corresponds to the case with chokes The curve with
squares to the case with chokes and corrugations The phase center varies
from 0mm to -302mm
From Fig 515 we can observed that phase center variation reduced by the
corrugation and three cases phase center calculated in φ=450 plane
parameter sweep values are given in Table 52
10 12 14 16 181
0
-1
-2
-3
-4
-5
-6
Pha
se c
ente
r (m
m)
Frequency (GHz)
choke+corrugatuion without choke corrugation with choke
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
-73-
Frequency
(GHz)
Phase center from the aperture plane
(mm)
Without
chokes and
corrugations
With
chokes
With chokes
and
corrugations
1000 -326 062 000
1100 -187 030 -002
1200 -563 -208 -065
1300 -296 -154 -202
1400 -319 -314 -302
1500 -201 -203 -241
1600 -242 -233 -207
1700 -208 -208 -186
1800 -190 -157 -132
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
Based on the foregoing parametric studies optimum dimensions of the
broadband circular waveguide feed are obtained as shown in Table 53
-74-
Table 53 Optimum dimensions of the broadband circular waveguide feed
Parameter Designation Value (mm)
2a Waveguide inside diameter 2070
d Waveguide outside diameter 3690
lcrLength of the circular waveguide section 1430
m Distance between the aperture plane and the first corrugation 950
xDistance from the last corrugation to the end of the cylindrical outer surface
550
ltrLength of the rectangular-to-circularwaveguide transition 4465
lrcLength of the rectangular waveguide section 1430
tch Choke slot width 090
lch Choke depth 750
t Choke metal width 090
lcor Corrugation depth 465
tcor Corrugation metal width 100
s Corrugation slot width 10
lp Probe length 530
sp Probe position from the back short 530
din Probe diameter 127
b Inside height of the rectangular waveguide 857
tw Waveguide wall thickness 500
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-66-
(a)
(b)
(c)
Fig 510 Effect of the choke depth in the broadband circular waveguide
feed on (a) E-plane pattern (b) H-plane pattern and (c) reflection coefficient
-67-
(a)
(b)
(c)
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and (c)
reflection coefficient
-68-
Next we investigated corrugations placed on the outer wall of the feed
Four corrugations applied to the outer surface of the circular waveguide The
corrugation depth is 465mm(0215λ0 at 14GHz) The primary purpose of
using corrugations is to further reduce the back radiation Increasing the
number of corrugations beyond four has little effect in reducing the back
radiation
Figs 512 and 513 show the effect of corrugations on the E- and H-plane
patterns Fig 514 shows the parametric study of the corrugation depth lcor
The corrugation depth is varied from 40mm and 645mm The optimum
value of the corrugation depth is found to be 465mm
-69-
(a)
(b)
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern at (a) 12GHz and (b) 14GHz
-70-
(a)
(b)
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern at (a) 12GHz and (b) 14GHz
-71-
(a)
(b)
(c)
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection coefficient
-72-
The phase center location is important in placing the feed in a reflector
antenna[8] The phase center variation with frequency should be small Fig
515 shows the effect of chokes and corrugations on the phase center The
curve with circle corresponds to the case without chokes and corrugations
The phase center varies from -326mm and -190mm away from the feeds
aperture plane It means the phase center is located inside the waveguide
The curve with triangles corresponds to the case with chokes The curve with
squares to the case with chokes and corrugations The phase center varies
from 0mm to -302mm
From Fig 515 we can observed that phase center variation reduced by the
corrugation and three cases phase center calculated in φ=450 plane
parameter sweep values are given in Table 52
10 12 14 16 181
0
-1
-2
-3
-4
-5
-6
Pha
se c
ente
r (m
m)
Frequency (GHz)
choke+corrugatuion without choke corrugation with choke
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
-73-
Frequency
(GHz)
Phase center from the aperture plane
(mm)
Without
chokes and
corrugations
With
chokes
With chokes
and
corrugations
1000 -326 062 000
1100 -187 030 -002
1200 -563 -208 -065
1300 -296 -154 -202
1400 -319 -314 -302
1500 -201 -203 -241
1600 -242 -233 -207
1700 -208 -208 -186
1800 -190 -157 -132
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
Based on the foregoing parametric studies optimum dimensions of the
broadband circular waveguide feed are obtained as shown in Table 53
-74-
Table 53 Optimum dimensions of the broadband circular waveguide feed
Parameter Designation Value (mm)
2a Waveguide inside diameter 2070
d Waveguide outside diameter 3690
lcrLength of the circular waveguide section 1430
m Distance between the aperture plane and the first corrugation 950
xDistance from the last corrugation to the end of the cylindrical outer surface
550
ltrLength of the rectangular-to-circularwaveguide transition 4465
lrcLength of the rectangular waveguide section 1430
tch Choke slot width 090
lch Choke depth 750
t Choke metal width 090
lcor Corrugation depth 465
tcor Corrugation metal width 100
s Corrugation slot width 10
lp Probe length 530
sp Probe position from the back short 530
din Probe diameter 127
b Inside height of the rectangular waveguide 857
tw Waveguide wall thickness 500
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-67-
(a)
(b)
(c)
Fig 511 Effect of the choke slot width of the broadband circular
waveguide feed on (a) E-plane pattern (b) H-plane pattern and (c)
reflection coefficient
-68-
Next we investigated corrugations placed on the outer wall of the feed
Four corrugations applied to the outer surface of the circular waveguide The
corrugation depth is 465mm(0215λ0 at 14GHz) The primary purpose of
using corrugations is to further reduce the back radiation Increasing the
number of corrugations beyond four has little effect in reducing the back
radiation
Figs 512 and 513 show the effect of corrugations on the E- and H-plane
patterns Fig 514 shows the parametric study of the corrugation depth lcor
The corrugation depth is varied from 40mm and 645mm The optimum
value of the corrugation depth is found to be 465mm
-69-
(a)
(b)
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern at (a) 12GHz and (b) 14GHz
-70-
(a)
(b)
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern at (a) 12GHz and (b) 14GHz
-71-
(a)
(b)
(c)
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection coefficient
-72-
The phase center location is important in placing the feed in a reflector
antenna[8] The phase center variation with frequency should be small Fig
515 shows the effect of chokes and corrugations on the phase center The
curve with circle corresponds to the case without chokes and corrugations
The phase center varies from -326mm and -190mm away from the feeds
aperture plane It means the phase center is located inside the waveguide
The curve with triangles corresponds to the case with chokes The curve with
squares to the case with chokes and corrugations The phase center varies
from 0mm to -302mm
From Fig 515 we can observed that phase center variation reduced by the
corrugation and three cases phase center calculated in φ=450 plane
parameter sweep values are given in Table 52
10 12 14 16 181
0
-1
-2
-3
-4
-5
-6
Pha
se c
ente
r (m
m)
Frequency (GHz)
choke+corrugatuion without choke corrugation with choke
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
-73-
Frequency
(GHz)
Phase center from the aperture plane
(mm)
Without
chokes and
corrugations
With
chokes
With chokes
and
corrugations
1000 -326 062 000
1100 -187 030 -002
1200 -563 -208 -065
1300 -296 -154 -202
1400 -319 -314 -302
1500 -201 -203 -241
1600 -242 -233 -207
1700 -208 -208 -186
1800 -190 -157 -132
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
Based on the foregoing parametric studies optimum dimensions of the
broadband circular waveguide feed are obtained as shown in Table 53
-74-
Table 53 Optimum dimensions of the broadband circular waveguide feed
Parameter Designation Value (mm)
2a Waveguide inside diameter 2070
d Waveguide outside diameter 3690
lcrLength of the circular waveguide section 1430
m Distance between the aperture plane and the first corrugation 950
xDistance from the last corrugation to the end of the cylindrical outer surface
550
ltrLength of the rectangular-to-circularwaveguide transition 4465
lrcLength of the rectangular waveguide section 1430
tch Choke slot width 090
lch Choke depth 750
t Choke metal width 090
lcor Corrugation depth 465
tcor Corrugation metal width 100
s Corrugation slot width 10
lp Probe length 530
sp Probe position from the back short 530
din Probe diameter 127
b Inside height of the rectangular waveguide 857
tw Waveguide wall thickness 500
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-68-
Next we investigated corrugations placed on the outer wall of the feed
Four corrugations applied to the outer surface of the circular waveguide The
corrugation depth is 465mm(0215λ0 at 14GHz) The primary purpose of
using corrugations is to further reduce the back radiation Increasing the
number of corrugations beyond four has little effect in reducing the back
radiation
Figs 512 and 513 show the effect of corrugations on the E- and H-plane
patterns Fig 514 shows the parametric study of the corrugation depth lcor
The corrugation depth is varied from 40mm and 645mm The optimum
value of the corrugation depth is found to be 465mm
-69-
(a)
(b)
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern at (a) 12GHz and (b) 14GHz
-70-
(a)
(b)
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern at (a) 12GHz and (b) 14GHz
-71-
(a)
(b)
(c)
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection coefficient
-72-
The phase center location is important in placing the feed in a reflector
antenna[8] The phase center variation with frequency should be small Fig
515 shows the effect of chokes and corrugations on the phase center The
curve with circle corresponds to the case without chokes and corrugations
The phase center varies from -326mm and -190mm away from the feeds
aperture plane It means the phase center is located inside the waveguide
The curve with triangles corresponds to the case with chokes The curve with
squares to the case with chokes and corrugations The phase center varies
from 0mm to -302mm
From Fig 515 we can observed that phase center variation reduced by the
corrugation and three cases phase center calculated in φ=450 plane
parameter sweep values are given in Table 52
10 12 14 16 181
0
-1
-2
-3
-4
-5
-6
Pha
se c
ente
r (m
m)
Frequency (GHz)
choke+corrugatuion without choke corrugation with choke
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
-73-
Frequency
(GHz)
Phase center from the aperture plane
(mm)
Without
chokes and
corrugations
With
chokes
With chokes
and
corrugations
1000 -326 062 000
1100 -187 030 -002
1200 -563 -208 -065
1300 -296 -154 -202
1400 -319 -314 -302
1500 -201 -203 -241
1600 -242 -233 -207
1700 -208 -208 -186
1800 -190 -157 -132
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
Based on the foregoing parametric studies optimum dimensions of the
broadband circular waveguide feed are obtained as shown in Table 53
-74-
Table 53 Optimum dimensions of the broadband circular waveguide feed
Parameter Designation Value (mm)
2a Waveguide inside diameter 2070
d Waveguide outside diameter 3690
lcrLength of the circular waveguide section 1430
m Distance between the aperture plane and the first corrugation 950
xDistance from the last corrugation to the end of the cylindrical outer surface
550
ltrLength of the rectangular-to-circularwaveguide transition 4465
lrcLength of the rectangular waveguide section 1430
tch Choke slot width 090
lch Choke depth 750
t Choke metal width 090
lcor Corrugation depth 465
tcor Corrugation metal width 100
s Corrugation slot width 10
lp Probe length 530
sp Probe position from the back short 530
din Probe diameter 127
b Inside height of the rectangular waveguide 857
tw Waveguide wall thickness 500
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-69-
(a)
(b)
Fig 512 Effect of the number of corrugations of the wideband circular
waveguide feed on the E-plane pattern at (a) 12GHz and (b) 14GHz
-70-
(a)
(b)
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern at (a) 12GHz and (b) 14GHz
-71-
(a)
(b)
(c)
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection coefficient
-72-
The phase center location is important in placing the feed in a reflector
antenna[8] The phase center variation with frequency should be small Fig
515 shows the effect of chokes and corrugations on the phase center The
curve with circle corresponds to the case without chokes and corrugations
The phase center varies from -326mm and -190mm away from the feeds
aperture plane It means the phase center is located inside the waveguide
The curve with triangles corresponds to the case with chokes The curve with
squares to the case with chokes and corrugations The phase center varies
from 0mm to -302mm
From Fig 515 we can observed that phase center variation reduced by the
corrugation and three cases phase center calculated in φ=450 plane
parameter sweep values are given in Table 52
10 12 14 16 181
0
-1
-2
-3
-4
-5
-6
Pha
se c
ente
r (m
m)
Frequency (GHz)
choke+corrugatuion without choke corrugation with choke
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
-73-
Frequency
(GHz)
Phase center from the aperture plane
(mm)
Without
chokes and
corrugations
With
chokes
With chokes
and
corrugations
1000 -326 062 000
1100 -187 030 -002
1200 -563 -208 -065
1300 -296 -154 -202
1400 -319 -314 -302
1500 -201 -203 -241
1600 -242 -233 -207
1700 -208 -208 -186
1800 -190 -157 -132
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
Based on the foregoing parametric studies optimum dimensions of the
broadband circular waveguide feed are obtained as shown in Table 53
-74-
Table 53 Optimum dimensions of the broadband circular waveguide feed
Parameter Designation Value (mm)
2a Waveguide inside diameter 2070
d Waveguide outside diameter 3690
lcrLength of the circular waveguide section 1430
m Distance between the aperture plane and the first corrugation 950
xDistance from the last corrugation to the end of the cylindrical outer surface
550
ltrLength of the rectangular-to-circularwaveguide transition 4465
lrcLength of the rectangular waveguide section 1430
tch Choke slot width 090
lch Choke depth 750
t Choke metal width 090
lcor Corrugation depth 465
tcor Corrugation metal width 100
s Corrugation slot width 10
lp Probe length 530
sp Probe position from the back short 530
din Probe diameter 127
b Inside height of the rectangular waveguide 857
tw Waveguide wall thickness 500
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-70-
(a)
(b)
Fig 513 Effect of the number of corrugations of the broadband circular
waveguide feed on the H-plane pattern at (a) 12GHz and (b) 14GHz
-71-
(a)
(b)
(c)
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection coefficient
-72-
The phase center location is important in placing the feed in a reflector
antenna[8] The phase center variation with frequency should be small Fig
515 shows the effect of chokes and corrugations on the phase center The
curve with circle corresponds to the case without chokes and corrugations
The phase center varies from -326mm and -190mm away from the feeds
aperture plane It means the phase center is located inside the waveguide
The curve with triangles corresponds to the case with chokes The curve with
squares to the case with chokes and corrugations The phase center varies
from 0mm to -302mm
From Fig 515 we can observed that phase center variation reduced by the
corrugation and three cases phase center calculated in φ=450 plane
parameter sweep values are given in Table 52
10 12 14 16 181
0
-1
-2
-3
-4
-5
-6
Pha
se c
ente
r (m
m)
Frequency (GHz)
choke+corrugatuion without choke corrugation with choke
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
-73-
Frequency
(GHz)
Phase center from the aperture plane
(mm)
Without
chokes and
corrugations
With
chokes
With chokes
and
corrugations
1000 -326 062 000
1100 -187 030 -002
1200 -563 -208 -065
1300 -296 -154 -202
1400 -319 -314 -302
1500 -201 -203 -241
1600 -242 -233 -207
1700 -208 -208 -186
1800 -190 -157 -132
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
Based on the foregoing parametric studies optimum dimensions of the
broadband circular waveguide feed are obtained as shown in Table 53
-74-
Table 53 Optimum dimensions of the broadband circular waveguide feed
Parameter Designation Value (mm)
2a Waveguide inside diameter 2070
d Waveguide outside diameter 3690
lcrLength of the circular waveguide section 1430
m Distance between the aperture plane and the first corrugation 950
xDistance from the last corrugation to the end of the cylindrical outer surface
550
ltrLength of the rectangular-to-circularwaveguide transition 4465
lrcLength of the rectangular waveguide section 1430
tch Choke slot width 090
lch Choke depth 750
t Choke metal width 090
lcor Corrugation depth 465
tcor Corrugation metal width 100
s Corrugation slot width 10
lp Probe length 530
sp Probe position from the back short 530
din Probe diameter 127
b Inside height of the rectangular waveguide 857
tw Waveguide wall thickness 500
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-71-
(a)
(b)
(c)
Fig 514 Effect of the corrugation depth of the broadband circular
waveguide feed on (a) E-plane (b) H-plane and (c) reflection coefficient
-72-
The phase center location is important in placing the feed in a reflector
antenna[8] The phase center variation with frequency should be small Fig
515 shows the effect of chokes and corrugations on the phase center The
curve with circle corresponds to the case without chokes and corrugations
The phase center varies from -326mm and -190mm away from the feeds
aperture plane It means the phase center is located inside the waveguide
The curve with triangles corresponds to the case with chokes The curve with
squares to the case with chokes and corrugations The phase center varies
from 0mm to -302mm
From Fig 515 we can observed that phase center variation reduced by the
corrugation and three cases phase center calculated in φ=450 plane
parameter sweep values are given in Table 52
10 12 14 16 181
0
-1
-2
-3
-4
-5
-6
Pha
se c
ente
r (m
m)
Frequency (GHz)
choke+corrugatuion without choke corrugation with choke
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
-73-
Frequency
(GHz)
Phase center from the aperture plane
(mm)
Without
chokes and
corrugations
With
chokes
With chokes
and
corrugations
1000 -326 062 000
1100 -187 030 -002
1200 -563 -208 -065
1300 -296 -154 -202
1400 -319 -314 -302
1500 -201 -203 -241
1600 -242 -233 -207
1700 -208 -208 -186
1800 -190 -157 -132
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
Based on the foregoing parametric studies optimum dimensions of the
broadband circular waveguide feed are obtained as shown in Table 53
-74-
Table 53 Optimum dimensions of the broadband circular waveguide feed
Parameter Designation Value (mm)
2a Waveguide inside diameter 2070
d Waveguide outside diameter 3690
lcrLength of the circular waveguide section 1430
m Distance between the aperture plane and the first corrugation 950
xDistance from the last corrugation to the end of the cylindrical outer surface
550
ltrLength of the rectangular-to-circularwaveguide transition 4465
lrcLength of the rectangular waveguide section 1430
tch Choke slot width 090
lch Choke depth 750
t Choke metal width 090
lcor Corrugation depth 465
tcor Corrugation metal width 100
s Corrugation slot width 10
lp Probe length 530
sp Probe position from the back short 530
din Probe diameter 127
b Inside height of the rectangular waveguide 857
tw Waveguide wall thickness 500
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-72-
The phase center location is important in placing the feed in a reflector
antenna[8] The phase center variation with frequency should be small Fig
515 shows the effect of chokes and corrugations on the phase center The
curve with circle corresponds to the case without chokes and corrugations
The phase center varies from -326mm and -190mm away from the feeds
aperture plane It means the phase center is located inside the waveguide
The curve with triangles corresponds to the case with chokes The curve with
squares to the case with chokes and corrugations The phase center varies
from 0mm to -302mm
From Fig 515 we can observed that phase center variation reduced by the
corrugation and three cases phase center calculated in φ=450 plane
parameter sweep values are given in Table 52
10 12 14 16 181
0
-1
-2
-3
-4
-5
-6
Pha
se c
ente
r (m
m)
Frequency (GHz)
choke+corrugatuion without choke corrugation with choke
Fig 515 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
-73-
Frequency
(GHz)
Phase center from the aperture plane
(mm)
Without
chokes and
corrugations
With
chokes
With chokes
and
corrugations
1000 -326 062 000
1100 -187 030 -002
1200 -563 -208 -065
1300 -296 -154 -202
1400 -319 -314 -302
1500 -201 -203 -241
1600 -242 -233 -207
1700 -208 -208 -186
1800 -190 -157 -132
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
Based on the foregoing parametric studies optimum dimensions of the
broadband circular waveguide feed are obtained as shown in Table 53
-74-
Table 53 Optimum dimensions of the broadband circular waveguide feed
Parameter Designation Value (mm)
2a Waveguide inside diameter 2070
d Waveguide outside diameter 3690
lcrLength of the circular waveguide section 1430
m Distance between the aperture plane and the first corrugation 950
xDistance from the last corrugation to the end of the cylindrical outer surface
550
ltrLength of the rectangular-to-circularwaveguide transition 4465
lrcLength of the rectangular waveguide section 1430
tch Choke slot width 090
lch Choke depth 750
t Choke metal width 090
lcor Corrugation depth 465
tcor Corrugation metal width 100
s Corrugation slot width 10
lp Probe length 530
sp Probe position from the back short 530
din Probe diameter 127
b Inside height of the rectangular waveguide 857
tw Waveguide wall thickness 500
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-73-
Frequency
(GHz)
Phase center from the aperture plane
(mm)
Without
chokes and
corrugations
With
chokes
With chokes
and
corrugations
1000 -326 062 000
1100 -187 030 -002
1200 -563 -208 -065
1300 -296 -154 -202
1400 -319 -314 -302
1500 -201 -203 -241
1600 -242 -233 -207
1700 -208 -208 -186
1800 -190 -157 -132
Table 52 Effect of chokes and corrugations on the phase center of the
broadband circular waveguide feed
Based on the foregoing parametric studies optimum dimensions of the
broadband circular waveguide feed are obtained as shown in Table 53
-74-
Table 53 Optimum dimensions of the broadband circular waveguide feed
Parameter Designation Value (mm)
2a Waveguide inside diameter 2070
d Waveguide outside diameter 3690
lcrLength of the circular waveguide section 1430
m Distance between the aperture plane and the first corrugation 950
xDistance from the last corrugation to the end of the cylindrical outer surface
550
ltrLength of the rectangular-to-circularwaveguide transition 4465
lrcLength of the rectangular waveguide section 1430
tch Choke slot width 090
lch Choke depth 750
t Choke metal width 090
lcor Corrugation depth 465
tcor Corrugation metal width 100
s Corrugation slot width 10
lp Probe length 530
sp Probe position from the back short 530
din Probe diameter 127
b Inside height of the rectangular waveguide 857
tw Waveguide wall thickness 500
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-74-
Table 53 Optimum dimensions of the broadband circular waveguide feed
Parameter Designation Value (mm)
2a Waveguide inside diameter 2070
d Waveguide outside diameter 3690
lcrLength of the circular waveguide section 1430
m Distance between the aperture plane and the first corrugation 950
xDistance from the last corrugation to the end of the cylindrical outer surface
550
ltrLength of the rectangular-to-circularwaveguide transition 4465
lrcLength of the rectangular waveguide section 1430
tch Choke slot width 090
lch Choke depth 750
t Choke metal width 090
lcor Corrugation depth 465
tcor Corrugation metal width 100
s Corrugation slot width 10
lp Probe length 530
sp Probe position from the back short 530
din Probe diameter 127
b Inside height of the rectangular waveguide 857
tw Waveguide wall thickness 500
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-75-
Fig 516 shows the reflection coefficient of the designed feed The
reflection coefficient is less than -10dB over 10-18GHz Figs 517 and 518
show 2D radiation patterns and E- and H-plane patterns The feed has a gain
of 9036dB 1056dB and 119dB at 10GHz 14GHz and 18GHz
respectively The antennas 10-dB beamwidth varies from 63deg and 48deg over
10-18GHz
Fig 516 Reflection coefficient of the designed broadband circular waveguide
feed
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-76-
(a)
(b)
Fig 517 2D radiation patterns of the designed broadband circular waveguide
feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and (e) 18GHz
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-77-
(c)
(d)
Fig 517 continued
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-78-
(e)
Fig 517 continued
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-79-
(a)
(b)
(c)
Fig 518 E- and H-plane patterns of the designed broadband circular
waveguide feed at (a) 10GHz (b) 12GHz (c) 14GHz (d) 16GHz and
(e) 18GHz
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-80-
(d)
(e)
Fig 518 continued
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-81-
Fig 519 shows the phase center variation of the designed feed The phase
center is calculated in φ= 45deg plane At 10GHz the phase center is located
in the aperture plane As the frequency increases the phase center is shifted
gradually into the waveguide from the aperture plane The performances of
the designed feed are summarized in Table 55
10 12 14 16 1800
-05
-10
-15
-20
-25
-30
-35
Pha
se c
ente
r (m
m)
Frequency (GHz)
Fig 519 Phase center variation of the designed broadband circular
waveguide feed
Table 54 Performance of the designed broadband circular waveguide feed
Frequency(GHz)
Gain(dB)
E-H-plane10-dB
beamwidths(deg)
Front-to-back ratio
(dB)
Phase center (mm)
1000 9036 63306300 313 000
1200 1037 53675562 394 -065
1400 1059 51475330 381 -302
1600 1102 49285020 404 -207
1800 1190 42744650 376 -132
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-82-
The designed broadband circular waveguide feed is fabricated The choked
part is separately fabricated using electric discharge machining and assembled
to the remaining part Corrugations and the waveguide body including the
rectangular-to-circular waveguide transition are fabricated using a standard
milling machine The back short is separately fabricated and attached to the
end of the waveguide Fig 520 shows the fabricated feed
Fig 520 Photograph of the fabricated broadband circular waveguide feed
10 11 12 13 14 15 16 17 18 19 20-30
-25
-20
-15
-10
-5
0
S1
1 (
dB
)
Frequency (GHz)
Simulation Measurement
Fig 521 Reflection coefficient of the fabricated broadband circular waveguide
feed
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-83-
Fig 521 shows the reflection coefficient of the fabricated feed The
measured reflection coefficient is less than -95dB over 10-18GHz There are
some differences between the measured and simulated reflection coefficients
which are believed to be due to fabrication tolerances
Figs 522 and 523 show the E- and H-plane patterns of the fabricated
feed at 14GHz Radiation patterns are obtained using a network analyzer and
a manual antenna rotator With a standard gain horn antenna used as a
transmitting antenna the transmission coefficient between the horn and the
feed is measured while the feed is manually rotated Due to limitations in the
pattern measurement setup it can be said that measured patterns are not
highly accurate Measured patterns show 10-dB beamwidths slightly smaller
than the simulated values General shapes of the measured patterns agree
fairly well with the simulation Patterns of the fabricated feed at other
frequencies are not measured but expected to be in good agreement with the
simulation
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-84-
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-d
B
Angle-degree
Measurement Simulation
Fig 522 E-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-180-150-120 -90 -60 -30 0 30 60 90 120 150 180-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Gai
n-dB
Angle-degree
Simulation Measurement
Fig 523 H-plane pattern of the fabricated broadband circular waveguide
feed at 14GHz
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-85-
Conclusion
In this thesis the design of a broadband circular waveguide feed for
parabolic reflector application is investigated Primary requirements for a feed
in a prime-focus reflector antenna are a good pattern symmetry in E and H
planes a low cross polarization a low back radiation and the bandwidth
broad enough to meet the specifications The reduction of the feeds back
radiation is important in the design of low-sidelobe reflector antennas
Before arriving at the final design a preliminary study is carried out on
the performances of common waveguide feeds such as the circular waveguide
open end the square waveguide open end and the circular waveguide open
end loaded with dielectric materials of various shapes The study shows that
with these feeds one can obtain a good feed performance only at a narrow
frequency band
With a view toward developing broadband high-performance feeds for
prime-focus reflector applications two types of the feed are designed The
first one is a compact feed operating at 171-197GHz for use in a reflector
antenna in back-haul applications The feed is basically a coaxial probe-fed
cicular waveguide open end loaded with a dielectric ring and a quarter-wave
choke at the aperture The dielectric ring is utilized to equalize the E- and
H-plane beamwidths while a quarter-wave choke around the aperture
waveguide wall is used to reduce the back radiation
The designed feed has a diameter of 164mm and a length of 289mm The
designed feed is fabricated and its performance is measured The fabricated
feed has a reflection coefficient less than -10dB over 171-197GHz The
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-86-
feed has a good beamwidth symmetry Its 10-dB beamwidth ranges from
57deg to 60deg The front-to-back ratio ranges from 20dB to 25dB
The second feed is designed to have a good performance over 10-18GHz
Based on the structure of the first feed the broadband property is obtained
by feeding the circular waveguide via a rectangular waveguides TE10 mode
The TE10 mode of the rectangular waveguide is converted into the TE11
mode of the circular waveguide by a rectangular-to-circular waveguide
transition The rectangular waveguide is fed by a coaxial probe
Four quarter-wave chokes are formed around the circular waveguides
aperture wall to equalized the E- and H-plane beamwidths over a broad
frequency range and to reduce the back radiation For further reduction of
the back radiation four corrugations are formed on the outer wall of the
circular waveguide
The designed broadband feed has a diameter of 369mm and a length of
7325mm The designed feed has a reflection coefficient less than -10dB over
10-19GHz Its E- and H-plane beamwidths are in good symmetry over
10-18GHz The feeds -10-dB beamwdith ranges from 427deg to 630deg over
10-18GHz while its front-to-back ratio is in the range of 313-404dB
The designed feed is fabricated and its performance is measured The
agreement between the measurement and the simulation is fairly good proving
the validity of the feed design In conclusion this thesis presents a new
broadband circular waveguide feed with an excellent performance over
10-18GHz for use in prime-focus reflector antennas Further areas of the
research may include the application of the designed feed to actual broadband
prime-focus reflector antennas the reduction of the feed diameter and the
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-87-
reduction of the phase center variation
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-88-
REFERENCES
[1] C A Balanis Antenna Theory John Wiley amp Sons 2005
[2] D M Pozar Microwave Engineering 3rd Edition John Wiley amp Sons
2005
[3] A D Olver P J Clarricoats and A A Kishk Microwave Horns and
Feeds IEE Electromagnetic Waves Series 39 IEEE Press 1994
[4] G L James and K L Greene ldquoEffect of wall thickness of radiation
from circular waveguiderdquo Electron Lett vol 14 pp 90-91 Feb 1978
[5] S B Cohn ldquoDesign of simple waveguide to coaxial transitionrdquo Proc
IRE vol 35 issue 9 pp 920-926 Sept1947
[6] K Raghavan A D Olver and P J B Clarricoats ldquoCompact dielectric
feeds for prime focus reflector antennasrdquo Antennas and Propagation
Society International Symposium vol 1 pp350-353 Jun1988
[7] A Kumar ldquoExperimental study of a dielectric rod enclosed by a
waveguide for use as a feedrdquo Electron Lett vol 12 issue 25
pp666-668 Dec1976
[8] L Shafai and A A Kishk ldquoPhase center of small primary feeds and its
effects on the feed performancerdquo Proc Inst Elect Eng Microwaves and
Propag vol 13 pp207-214 1985
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |
-89-
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to supervisor Prof Bierng-
Chearl Ahn for his supervision valuable guidance helpful suggestions and
tolerance I also have to thank committee members of the my thesis Prof
Jae-Hyung Ahn Dr Jae-Hoon Bang for their guidance support and
suggestions I also thank the Applied Electromagnetic Laboratory members for
their help and friendship
I would like to acknowledge the financial support of the BK21
Reasearch-Oriented Consortium of Chungbuk National University
I am most grateful to Ononchimeg Sodnomtseren and Bayanmunkh
Enhbayar who were senior members of Applied Electromagnetic Laboratory
They told me lot of things about the antennas and their designs simulation
software CST Microwave Studio
I would like to thank my family my mother Serjkhuu father Baasantseren
older brothers Gan-Od and Ganbat and older sister Gansuren for supporting
and encouraging me to pursue this degree Without their encouragement I
would not have finished the degree
Finally I thank my friends and Mongolian students in Chungbuk National
University especially my roommate and labmate Tsek and Otgoo They are so
thoughtful always trying to make the difficult parts of lab life run more
smoothly and cheerfully
Odontuya Baasantseren
AEL CBNU Cheongju Korea August 2012
ltstartpagegt15 | |||
yendeg Indtroduction | 1 | ||
yenplusmn Analysis of Circular and Square Waveguide Feeds | 4 | ||
21 Circular Waveguide Radiator | 4 | ||
22 Square Waveguide Radiator | 10 | ||
23 Probe-Fed Circular Waveguide Radiator | 15 | ||
24 Probe-Fed Circular Waveguide Radiator | 20 | ||
yensup2 Design of Compact Circular Waveguide Feeds | 25 | ||
31 Narrow-Band Circular Waveguide Feed | 25 | ||
32 Fabrication and Measurement | 38 | ||
IV Design of Circular Waveguide Feeds Loaded with a Dielectric Rod | 40 | ||
41 Design of dielectric rod feed | 40 | ||
V Design of Broadband Circular Waveguide Feed | 50 | ||
51 Design of Broadband Circular Waveguide Feed | 50 | ||
52 Fabrication and Measurement | 82 | ||
yensup3 Conclusion | 85 | ||
REFERENCES | 88 | ||
ltbodygt |