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3632 IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 60, NO. 8, AUGUST 2012

SIW-Based Array Antennas With Sequential Feedingfor X-Band Satellite Communication

Eun-Young Jung, Jae W. Lee, Member, IEEE, Taek K. Lee, Member, IEEE, and Woo-Kyung Lee, Member, IEEE

AbstractNovel phased array antennas suitable for X-bandsatellite communication are introduced and investigated forright-handed circular polarization (RHCP) in a multi-layeredfabrication. The primary function of the proposed antennas is totransmit high quality data obtained from satellites and the ground

station systems with the lowest amount of loss. For accuratedata transmission, the important parameters regarding antennaspecifications and electrical performance are the antenna gain andthe high-purity polarization. Hence, this paper describes novelprocedures for gain enhancements of the array antennas working

at X-band (from 8.0 to 8.5 GHz) with an RHCP characteristic,including a single element, 2 2 array, and 2 4 array withfour-way and eight-way power dividers, respectively. Taking into

consideration the long-distance communication between a satelliteand ground station, a substrate-integrated waveguide structurehas been proposed, in particular because it is known to have low

radiation loss and a low weight comparable to that of a microstrip,as well as low material loss similar to that of a metal-surroundedwaveguide.

Index TermsArray antenna, right-handed circular polariza-tion (RHCP), sequential feeding, substrate-integrated waveguide(SIW).

I. INTRODUCTION

AS INTEREST in satellite communication systems has

increased in modern satellite-related industries, it has

become more difficult to obtain cutting-edge technology

for payload and ground systems from other countries. Most

X-band satellite antennas are usually employed to undertake

the data transmission of high resolution captured and detected

images from a satellite to a ground station. In this paper, with

consideration given to the light weight, easy integration, and

low radiation loss requirements that are inherent in long-dis-

tance communication, a novel substrate-integrated waveguide

(SIW)-based array antenna as a preferred choice over the con-

ventional microstrip line has been proposed and analyzed with

several configurations. In particular, this proposed SIW-based

structure as a replacement for a microstrip line has been appliedfor many passive and active devices by researchers [1][4].

Manuscript received March 01, 2011; revised January 26, 2012; acceptedFebruary 15, 2012. Date of publication May 22, 2012; date of current ver-sion July 31, 2012. This work was supported in by the National Space Lab-oratory (NSL) Program through the Korea Science and Engineering Founda-tion funded by the Ministry of Education, Science and Technology under GrantS10801000159-08A0100-15910.

The authors are with the School of Electronics, Telecommunica-tion, and Computer Engineering, Korea Aerospace University, Goyang,Gyeonggi-do 412-791, Korea (e-mail: [email protected]; [email protected];[email protected]; [email protected]).

Color versions of one or more of the figures in this paper are available onlineat http://ieeexplore.ieee.org.

Digital Object Identifier 10.1109/TAP.2012.2201075

Fig. 1. Electricalcharacteristics of an SIW-basedsingle antenna. (a) Reflectioncoefficients. (b) RHCP gain and axial ratio.

As a candidate for possessing the necessary high power trans-

mission and low loss characteristics, SIW structures using via

arrays to replace the side walls show similar characteristics as

metallic rectangular waveguide encompassed by metals [5],

[6]. In order to properly verify the low radiation loss from an

SIW-based transmission line, the crosstalk problem between

two transmission lines has been treated with comparison data

in [6]. In order to increase the transmission efficiency between

satellite and ground system and enhance the antenna gain, the

design procedure, simulation, and measured data of SIW-based

2 2 and 2 4 array antennas have been introduced with a

single element operating at X-band from 8 to 8.5 GHz as shown

in Fig. 1. The electrical performances depicted in Fig. 1 show

the reflection coefficient, right-handed circular polarization

(RHCP) gain, and axial ratio bandwidths of a single antenna.

In a single structure shown in Fig. 1(a), to overcome problems

0018-926X/$31.00 2012 IEEE

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JUNG et al.: SIW-BASED ARRAY ANTENNAS WITH SEQUENTIAL FEEDING FOR X-BAND SATELLITE COMMUNICATION 3633

such as feeding loss, undesirable radiation, and reduced effi-

ciency caused by using a hybrid coupled and series microstrip

feeding structure, novel SIW-based and cavity-backed ring-slot

antenna unified with a SIW and coaxial feeding network having

low-loss and broadband impedance matching characteristics

has been proposed for RHCP generation. In order to improve

the narrow bandwidth in terms of axial ratio and enhance the

CP-gain, SIW-based 2 2 and 2 4 array antennas with a

sequential feeding scheme having a phase delay characteristic

and low radiation loss have been designed and investigated for

the application of X-band satellite communication antennas. In

Section II, the design of the 2 2 array antenna and four-way

power divider embedded into substrate are discussed. Also in

Section III, the detailed design procedure of the 2 4 array

antenna and eight-way power divider are dealt with, and the

electrical characteristics are discussed. Finally, in Section IV,

the effects of a sequential feeding scheme on the axial ratio

and a simple operating principle of the proposed phased array

are summarized, and this is followed by a brief conclusion in

Section V.

II. SIW-BASED 2 2 ARRAY ANTENNA

A. Four-Way Power Divider in the Bottom Layer

In order to design the 2 2 array antenna using a single

element shown in Fig. 1, it was necessary to design a power

divider providing equal amplitude at each output port in the

2 2 array. For radiation efficiency and easy fabrication in

multi-layers, the SIW-based four-way equal power divider was

designed and measured as a replacement for the microstrip

structures [7][10]. Fig. 2 depicts the configuration and elec-

trical performances of the four-way power divider embedded

into substrate. In general, the operating frequency of the pro-

posed four-way power divider is dependent on the separated

distance parameter, fd, between the central feeding point

and the extended guiding via. Hence, the center frequency,

8.25 GHz within 88.5 GHz, results in the determination of

optimum parameter value, fd equal to 8.2 mm.

As estimated from the data shown in Fig. 2(b), it is guaran-

teed that the simulated bandwidth of the reflection coefficients

amounts to 2.5 GHz ranging from 7.0 to 9.5 GHz, covering all

the required impedance bandwidth from 8.0 to 8.5 GHz.

B. 2 2 Array Antenna in the Top Layer

By increasing the number of single antennas shown in Fig. 1and incorporating the array antenna with the four-way power

divider shown in Fig. 2 in a double layer, a novel SIW-based

2 2 array antenna has been designed as shown in Fig. 3, and

the parameter values have been optimized for the best electrical

performances.

While four radiating elements and 90 phase-delay lines with

a progressive phase shift for sequential feeding are aligned in

the top layer, the SIW-embedded four-way power divider and

additional phase-delay lines occupy the bottom layer. For an

equal ground effect between the grounds of the two layers and

signal transitions between the two layers, ground vias and the

RF signal via transition for signal transmission without loss, as

shown in Fig. 3, are employed, respectively. The overall res-

onant frequency of the 2 2 array antenna shown in Fig. 3(a)

Fig. 2. SIW-based four-way equal power divider. (a) Structure of four-waypower divider. (b) Characteristic of -parameter.

is determined by controlling the radius R1 of the circular patch

with the cavity under the patch antenna as follows [11]:

(1)

(2)

(3)

where CF and K11 refer to the correction factor and thefirst root

of the first-kind differentiated Bessel function of TM11 mode,

respectively. The constant, , and parameter, , are the speed

of light and the radius of the circular patch, respectively.

As mentioned previously, oneof the requirements of the2 2

array antenna for satellite communication is the generation of

the RHCP characteristic. This RHCP/left-handed circular polar-

ization (LHCP) generation is usually dependent on the location

of theshorting via inside the circular patch and therotation angle

of the shorting via [12], [13]. As important parameters for

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Fig. 3. Structure of SIW-based 2 2 array antenna. (a) Radiating antennas inthe top layer. (b) Power divider in the bottom layer.

impedance matching, the parameters, gr and gw, can be modeled

as asymmetrical inductive diaphragms changing the inductance

and leading to the satisfaction of the matching condition at the

input port [14]. The final optimized parameter values are sum-

marized in Table I for the best performances.

In Table I, parameters and

are essential for the sequential feeding to generate a pro-

gressive phase shift in the top and bottom layers. In the config-

uration depicted in Fig. 3(a) and (b), are

set to be equal to for easy fabrication, and

the difference between the nearest phase-delay lines has been

determined to be equal to 9.56 mm accounting for the

90 phase shift. Contrary to a single antenna, the separated dis-

tance of the nearest radiating slot antenna plays an important

TABLE ISIMULATED DESIGN PARAMETERS AND VALUES OF 2 2 ARRAY ANTENNA

Fig. 4. Simulated and measured reflection coefficients of 2 2 array antenna.

role in determining the number and magnitude of sidelobes and

the mainlobe level, which affects the overall radiation pattern

and total gain. In general, it is well known that the optimized

separated distance between the radiating elements is dependent

on the alignment of the array structure and the main beam di-

rection. In this paper, the minimum separated distance between

radiating elements has been set up to be optimized as by

applying the rule of thumb of [15][17]. The em-

ployed substrate for the fabricated 2 2 array antenna in Fig. 3

is an RT/Duroid 5880 having a relative dielectric constant of 2.2

and a thickness of 1.57 mm. For a perfect ground connection

between the two layers, several ground vias have been adopted.

Under the criterion that the reflection coefficient must be less

than dB, it is observed from Fig. 4 that the measured andsimulated results show wide input impedance bandwidths cov-

ering 1.1 GHz from 7.74 to 8.84 GHz and 1.3 GHz from 7.4 to

8.7 GHz, respectively. As important electrical characteristics,

the RHCP gain and axial ratio of the proposed antenna have

been investigated by using simulations and measurements, as

shown in Fig. 5. There is a discrepancy, which appears as a fre-

quency shift in the data, due to the tolerance error in the manu-

facturing process of the radius of the radiating circular elements.

Fig. 6 delineates simultaneously the RHCP and LHCP gains

in - and -planes at 8.3 and 8.4 GHz of the 2 2 array an-

tenna. It is expected that the cross-polarization level describing

the relative ratio of RHCP (Co-pol.) to LHCP is above 15 dB in

the mainbeam direction of from Fig. 6. This indicates

that the proper position and the optimized rotating angle of

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Fig. 5. RHCP gain and axial ratio result of 2 2 array antenna.

Fig. 6. Measured radiation patterns of 2 2 array antenna. (a) 8.3 GHz (plane, plane). (b) 8.4 GHz ( plane, plane).

shorting via in the radiating elements have been attained and a

reasonable solution has been confirmed.

Fig. 7. -parameter characteristics of eight-way equal power divider.

III. SIW-BASED 2 4 ARRAY ANTENNA

A. Eight-Way Power Divider in the Bottom Layer

As the next step to increase the antenna gain and improve

RHCP purity, a 2 4 array antenna with a novel eight-way

power divider was designed and investigated. The power divider

was installed in the bottom layer fed by the input source in the

overall antenna structure. By selecting the optimum value of the

parameter, fd, to resonate at the operating frequency of 9.3 mm,

the SIW-embedded eight-way power divider satisfying equal di-

vision at all output ports was designed, fabricated, and measured

for comparison. Fig. 7 shows the simulated -parameter char-

acteristics of the eight-way power divider.

B. 2 4 Array Antenna in the Top Layer

With the high data rate required in X-band satellite commu-

nication and the extending 2 2 array antenna taken into con-

sideration, a novel 2 4 array antenna has been proposed to

improve RHCP gain and enhance the CP-purity with an opti-

mized sequential feeding scheme. In a similar configuration to

the 2 2 array antenna described in Section II, the proposed

2 4 array antenna has eight radiating elements in the top layer

[shown in Fig. 8(a)], an eight-way power divider, and phase-

delay lines in the bottom layer [in Fig. 8(b)]. In order to main-

tain the electrical performance, the parameters R1 (slot radius)

and ad (the separate distance) have been newly optimized while

the other parameters are nearly the same as those of the 2 2array antenna.

For sequential feeding which protects the electric field from

being canceled in the opposite elements, the eight elements have

been divided into four groups, namely A, B, C, and D, as shown

in Fig. 9(a) and (b), and each group is fed by a 90 phase-de-

layed line and equal magnitude. However, the feeding signals of

the two elements inside each group are provided by equal phase

and equal amplitude. For example, the total lengths of the delay

lines of the two elements in group A are equal to each other, as

in . At this time, and

are not equal to and , respectively. In a similar way,

the total phase-delay line of one radiating element in group B is

which is equal to the sum of and . The

total difference of the phase-delay line between groups A and B

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Fig. 8. Structure of SIW-based 2 4 array antenna. (a) Top layer. (b) Bottomlayer. (c) Fabricated 2 4 array antenna.

can be calculated as , which

results in the phase difference of 90 . Fig. 8(c) shows the fabri-

cated 2 4 array antenna which measures 141 mm (length) by

109 mm (width). In terms of the reflection coefficients, Fig. 9

depicts a good agreement between the simulated and measured

data covering the required bandwidth from 8 to 8.45 GHz under

the criterion of less than dB. Fig. 10 shows the measured

and simulated data of RHCP gains and axial ratio of the 2 4

array antenna. From Fig. 10, it is seen that the peak gains of

Fig. 9. Simulated and measured reflection coefficients of 2 4 array antenna.

Fig. 10. RHCP gain and axial ratio results of 2 4 array antenna.

RHCP in simulation and measured data are 15.2 and 14.6 dBic

at 8.3 and 8.4 GHz, respectively, which represents a 100 MHz

frequency deviation between the two results. However, the de-

viation is small enough to be neglected because of the 1-dB tol-

erance. Meanwhile, it is observed from Fig. 10 that the simu-

lated axial ratio bandwidthcovers 600 MHz from 7.9 to 8.5 GHz

under the criterion of 3 dB, and the measured results reach

550 MHz from 8.1 to 8.65 GHz. The radiation patterns de-

scribed in Fig. 11 show that the beam patterns of the -plane

are sharper than those of the -plane. This phenomenon is due

to the number of array elements in the -plane being longer

than that of the array elements in the -plane.

In Table II, the electrical performances of the proposed three

antennas focused on the SIW-based structure are listed for easy

comparison. As expected, it is seen that the increase of antenna

elements and the employment of sequential feeding result in the

high gain and wide bandwidth with high CP-purity.

IV. EFFECTS OF SEQUENTIAL FEEDING SCHEME

In general, it is well known that the sequential feeding scheme

previously applied in the 2 2 and 2 4 array antenna is useful,

with respect to feeding, for an equal amplitude and a progressive

phase shift between the nearest radiating elements at the output

ports. This feeding scheme leads to an enhancement of axial

ratio bandwidth in the CP-generation of an array antenna and

an improvement of CP-purity [18][20].

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Fig. 11. Measured radiation patterns of 2 4 array antenna. (a) 8.3 GHz (plane, plane). (b) 8.4 GHz ( plane, plane).

TABLE IISUMMARY OF MEASURED ELECTRICAL CHARACTERISTICS OF DESIGNED AND

FABRICATED SIW-BASED ANTENNAS

In this paper, a 90 phase delay line has been employed for

sequential feeding. As a simple principle of high-purity CP-gen-

eration in the proposed SIW-based array antenna, each compo-

nent of the generated electric fields in each radiating element

Fig. 12. Example of the generated E-field direction for 2 2 array antenna.

Fig. 13. Radiation pattern variations of array antenna according to sequentialfeeding. (a) 2 2 array antenna. (b) 2 4 array antenna.

fed from the power divider has considerable importance in the

overalloperationas shown in Fig. 12. If elementsNo. 1, 2, 3, and

4 are fed by an equal amplitude and equal phase reference, the

electric fields at the opposite position will be cancelled out like

the E1s of No. 1 and No. 3 and E1s of No.2 and No. 4. However,

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Fig. 14. Axial ratio variations of array antenna accordingto sequential feeding.(a) 2 2 array antenna. (b) 2 4 array antenna.

this problem can be overcomeby feeding each element with pro-

gressively different phases. Depending on the phase difference

in each element, the electric field E1 generated at No. 1 will be

combined with the electric field E4 generated at No.4 of a 90

phase delayed. From the entire structure shown in Fig. 12, it

is confirmed that all the generated electric fields at an instance

have the same direction by the generation of E1 at No. 1, E4 at

No. 2, E3 at No. 3, and E2 at No. 4. Because of the feeding of

equal phases, field cancellation can be properly avoided.

In order to check the effects of the sequential feeding scheme

on the 2 2 and 2 4 array antenna, the variation of radiation

patterns and axial ratios with/without the phase delay lines have

been simulated and evaluated. In the case with/without phasedelay line, which is shown in Figs. 13(a) and (b), it is observed

that there is a null point due to the field cancellation at the di-

rection of , and a similar phenomenon occurs in both the

2 2 and 2 4 array antennas. In addition, a sequential feeding

scheme affects the axial ratio characteristic as well as the radi-

ation patterns in the array antennas. Hence, Fig. 14 depicts the

axial ratio characteristics before and after a sequential feeding

and phase-delay lines are applied in the case of 2 2 and 2 4

array antennas. It is seen from Fig. 14 that the electrical perfor-

mance with respect to axial ratio without phase delay lines be-

comes about 10 dB worse than those with phase delay lines. The

reason is thought to be the field cancellation generated from the

radiating elements located at the opposite sides when the phase

delay line is not employed.

V. CONCLUSION

In this paper,a single element and two types of novel array an-

tennas focused on the SIW-based design have been suggested,

designed, and investigated in terms of electrical performances.

In particular, in order to minimize the radiation loss for long-

distance communication, novel SIW-based array antennas have

been employed and sequential feeding has been adopted for anenhancement of RHCP characteristics. As a systematical design

procedure of the SIW-based array antenna, a single element op-

erating at X-band ranging from 8.0 to 8.5 GHz, a 2 2 array an-

tenna with doublelayersincluding a four-way power divider,and

2 4 array antennas with different sequential phase progression

have been designed, fabricated, and measured for verification

between simulation and measured results, and an improvement

in electrical performance has been obtained, particularly with

respect to reflection coefficient bandwidth, antenna gain, and

axial ratio bandwidth. In addition, it is ensured from the data

that the proposed novel structure could be particularly useful

for a small satellite with limitations regarding weight and size.

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Eun-Young Jung received the B.S. and M.S.degrees in electronics, telecommunications, andcomputer engineering from Korea Aerospace Uni-versity, Goyang, Korea, in 2009 and 2011.

Her research interests include UWB antennadesign and array antenna design for satellitecommunication.

Jae W. Lee (S92M98) received the B.S. degreein electronic engineering from Hanyang University,Seoul, Korea, in 1992, and the M.S. and Ph.D. de-grees in electrical engineering (with an emphasis inelectromagnetics) from the Korea Advanced Instituteof Science and Technology (KAIST), Taejon, Korea,1994, and 1998, respectively.

From 1998 to 2004, he was a Senior Member inthe Advanced Radio Technology Department, Radioand Broadcasting Research Laboratory, Electronicsand Telecommunications Research Institute (ETRI),

Taejon, Korea. He later joined the School of Electronics, Telecommunicationsand Computer Engineering, Korea Aerospace University, Goyang, Korea,where he is currently an Associate Professor. From January 2011 to January2012, he was a Visiting Scholar with Clemson University, SC. His researchinterests include high power amplifier design, computational electromagnetics,electromagnetic interference/electromagnetic compatibility analysis on printed

circuit board, and component design in microwave and millimeter-wave.

Taek K. Lee (S83M90) was born in Gyeongbuk,Korea, on January 11, 1958. He received the B.S.degree in electronic engineering from Korea Uni-versity, Seoul, Korea, in 1983, and the M.S. andPh.D. degrees in electrical engineering from theKorea Advanced Institute of Science and Tech-nology (KAIST), Seoul, Korea, in 1985 and 1990,respectively.

From May 1990 to April 1991, he was a Post-doctoral Fellow with The University of Texas atAustin (under a grant from the Korea Science and

Engineering Foundation). From August 1991 to February 1992, he was withKAIST. In March 1992, he joined the faculty of Korea Aerospace University,Goyang, Korea, where he is currently a Professor with the School of Elec-tronics, Telecommunication, and Computer Engineering. From July 2001 toJuly 2002, he was an Associate Visiting Research Professor with the Universityof Illinois at UrbanaChampaign. His research interests include computationalelectromagnetics, antennas, analysis and design of microwave passive circuits,and geophysical scattering.

Woo-Kyung Lee (S94M00) received the B.Sc.and M.Sc. degrees from the Korea Advanced In-stitute of Science and Technology (KAIST), Seoul,

Korea, in 1990 and 1994, and the Ph.D. degree fromthe University College London, United Kingdom, in2000, all in electrical engineering.

From 1999 to 2002, he worked as a ResearchProfessor at SaTReC, KAIST, and was involvedin developing communication and antenna systemsfor small satellite systems. From 2003 to 2004, heworked at Samsung Advanced Institute of Tech-

nology for UWB, antenna, communication system researches. In 2004, hejoined the Electrical Engineering and Avionics Department, Korea AerospaceUniversity, Seoul, Korea, where he currently works as an Associate Professor.His research interests are in the area of communication and radar systemdesign, spaceborne antenna development, image processing, and electroniccounter measure and electronic counter counter measure techniques.

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