A Dual Polarized Horn With a Scanning Beam

7/27/2019 A Dual Polarized Horn With a Scanning Beam

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A DUAL POLARISED HORN WITH A SCANNING BEAMZvi Frank

El bi t Computers Ltd.Nes-Ziona

I s r a e lp resen t be ing designed

E a L B e a nVert. LEFT

CENTER

SummaryThe proposed antenna i s a sp e c i a l t y p e o fMulti-Beam Antenna (MBA). Such an te nna s ar e of

course we l l known in the l i t e r a t u r e . The uniquef e a t u r e o f t h i s p a r t i c u l a r a nt en na is that beamscanning i s ach ieved with in the c onfines o f a s in g lehorn.h igh g a in a re c l e a r l y e v id e n t i n t h i s d e s ig n .

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The additional advantages of compactness and

The antenna described i s a compact quad-ridgedhorn. Each ridge i n th e horn i s f e d se p a ra t e ly a tfour orthogonal input s t o a square waveguide.

By means o f an R.F . network consisting of anumber of 180 degrees Hybrids and delay lines, thebeam of th e horn can be switched i n azimuth over110 degree s, The nominal gain of th e horn i s morethan 8 dBi. The aper ture si ze i s about 0 . 6 ~ 0 6wave-leng ths a t the low end of the band. The length ofthe an tenna i s le ss than th r ee qu a r te r o f a wave-leng th a t th e low end. The antenna i s extremelyrugged and i s designed t o ope ra te under seve reenvironmental conditions.

Desc r ip t ion of AntennaA ske tch of the quad-ridged i s shown in

Fig. 1. A squa re waveguide wit h four orthogonalinputs provides a launcher f o r th e compact horn. Thehorn i s mounted diagonally as shown schematically inFig. 2 . This i s neces sary t o provide two phasec e n te r s i n t h e h o r i z on ta l p l a n e r e q u i re d fo rs tee r ing the beam.with the switching arrangement are shown in F i g . 2 .

The summation matrix together

From the ve ct or diagram o f Fig. 3 it i s o bse rv e dth a t t he ou tpu t por ts o f th e 180 degrees hybrids " A "and "B" y ie ld v e r t i c a l a nd h o r i z o n ta l p o la r i sa t io n s .

I t i s a l s o c l e a r t h a t e a ch p a i r o f v e r t i c a l andh o r i z o n ta l p o la r i sa t io n s a re o ut o f phase.summation of th ese outputs v ia a second set o f 180'hybrids p rov ides ve r t ica l and hor izon ta lp o la r i sa t io n s a t o utp ut " X" and "Y" r e sp e c t iv e ly .

Direc t

Switching o f th e beam i n azimuth i s a t t a in e d b ymeans o f the four t ra ns fe r switches and su i ta b led e l a y l i n e s .

Ea ch p o la r i sa t io n c an be s t e e re d t o t h e l e f t o rr ig h t by sw i t c h in g in a su i t a b l e d e l a y l i n e .arrangement in F i g . 2 i s fo r a th re e beam antenna.However more beams a re p os si bl e with a more complexfeed ma tr ix .

The

An a l t e rn a t i v e a r ra ng e me n t fo r t h i s h orn a sshown i n F i g . 4 y i e l d s a s t e e r a b l e c i r c u l a r l ypo la r ised horn .

The present design operates over an octavebandwidth. An antenna with a wider bandwith i s a t

SWITCHI 2 3 4 3

I o n0 0 0

FIG. ISKETCH OF QUAD-FED HORN

F I G . 2CONFIGURATION NO. 1

DLOCK DIAGIW or FEED H ~ T R I X

kI OR '.lo

Hor. LEFTR l G l l T

2 .2 .8155


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VECTOR DIAGRAM FOR FEED MATRIX

+ +A = 1 t 2 - HORIZONTAL POLARISATIO N (RIGHT)B = 1 - 2 1 VERTICAL POLARISATI ON (DOWN)C = 3 t 4 - HORIZONTAL POLARISATION (LEFT)+ ++ +

+ +D - 3 - 4 f VERTICAL POLARISATI ON (UP)A - C = --C HORIZONTAL POLARISATION (RIGHT)B - D = 1 VERTICAL POLARISATION (DOWN)+ +

F I G . N O . 3

: 'odal An\n,ilysi~A a-dal analysis has been made or, t h i s h o rn ,

However, the results ofthe mathematical de ta i l s o f which w i l l not bep r e s en t e d i n t h i s p a p e r .t h e a n a l y s i s s how t h a t t h e v e r t i c a l and h o r i z o n t a lp o l a r i s a t i o n s a r e g e ne r at e d b y TE and Th! mo6esrespec t ive ly . The consequence of th i s ana lys i sp r e d i c t s a wide beamwidth f o r t h e h o r i z o n t a lpo l a r i sa t i on and a narrow bean: fo r the ve r t i ca lp o l a r i s a t i o n .v e r i f i e d t h i s a n a l y s i s.

Our measurements on the antenna model

Resul t sV.S.W.R.The VSWR a t p or t "XI' i s shown i n Tic . 5 . TheVSWR a t t he i nput t o the Hybrid Fcrt "Y " i s shown

i n F i g, 6.band. Over most of th e band the \.SW i s b e t t e r t h anThe VS1kR i s b e t t e r t h a n 3 : l over the

L : l .

GainThe swept gai n of t he anten na fo r both vert ic ' land hor izonta l p o la r i s a t i ons i s shwvn in T i p . 7 .The gain i s above 8 dB over most of t h e t , a l ; t A . A t

t h e low end there i s a degrada t ion in Fa i r due t ot h e hi gh VSWR o f the launcher .

FIG. NO . 5 CONFIGURATION NO . 12 o a B / A- - 6 00 0.8C H I B -H 3 001 SWR VSWR AT OUTPUT - XPOLARISATION - V

>

$F Frequency lMHz) 2FF I G . NO . 6 CONFIGURATION NO . 1

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Radia t ion Pa t te rnsH o r i z o n ta l P o la r i sa t io n P a t t e rn sIn the hor izon t a l po la r isa t ion the beamwidths

a re ve ry wide and fo r t h i s reason t he beam switch ingwas no t o f g rea t he lp . Figs. 8 and 9 show typicalp a t t e rn s fo r t h e th re e beam a n te n n as .

A la te r model o f t h i s an tenna has the switchesfo r h o r i z o n ta l p o la r i sa t io n r em ove d.degradation in performance was observed.

No s i g n i f i c a n t

V e r t i c a l P o la r i sa t io nThe patterns 10 and 11 show th e t hr ee beams a tfrequencies low and high ends of the band .

advantage of th e beam switc hing i s v e ry c l e a r h e re .The

Configuration 2 - Circu la r ly Po la r ised HornT h e g a in o f t h e c i r c u la r ly p o la r i se d h o rn i sThe rat he r low gain a t th e lowhown in Fig. 12.end of t he band i s du e t o t h e poor a x i a l r a t i o . T h i s

could be improved with a larger feed adaptor.

CIRNURLI W I S E 0 m ut n i : A -M s - 3.00 d 0 alii Of VLRTICAL w2.0 d0 / REF + .O O d e

2 . 2 . 8157


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3Alternative Feeding ArrangementFeed MatrixA n a l t e rn a t i v e f e e d m a t r ix was designed and i sshown i n Fi g. 13. The new arr ange men t known asConfigura t ion 3 has the advan tage th a t no de lay

l in es a re requ ired . Th is a rrangement i s f a c i l i t a t e dby the fac t t ha t each r idge o f t he gu ide when fedse p a ra t e ly t e n d s to sq u in t o f f C e n te r .

VSWR and GainThe VSWR and gain of Configuration 3 i s

b a s i c a l l y i d e n t i c a l t o C o nf i gu r at i on 1 and hence i snot shown separately.

Rad ia t ion Pa t te rnsT y p ica l r a d i a t i o n p a t t e rn s fo r v e r t i c a l an d

h o r i z o n t a l p a t t e r n s a t t h e e x t r e m i t i e s o f t h e ba ndare shown in F igures 14 t o 17 . These pa t t e rns tendto g ive be t te r az imuth coverage and h igh ga in a ta n g le s up t o f4 5 d e g re e s .t h e r e i s not much di ff er enc e between t he twoc o n f ig u ra t io n s .

ConclusionA quad-fed quad-ridged dual pola ri se d horn hasbeen described.

bandwidth. Arrangement f o r ste e r i ng the beam inazimuth has been described.ly u sefu l when small size, high gain and wideangular coverage i s requ ired .

For wide angular coverage

The horn operates over an octaveThe horn i s p a r t i c u l a r -

AcknowledgmentThe author i s indebte d t o t he Management ofElb i t Compute rs L td. fo r pe rmit t ing h im to pub l ish

t h i s r e p o r t .References

1. The Handbook of Antenna Design. Chapter 6pp. 466 t o 505: Multibeam Antennas. Publishe d byPe te r Pe regr inus L td .2 . Sexon T . (1968) Quadr uply Ridged Horn. Rep.E D L . - M1160. Cont. DAA B07-67-C-0181 pa r . 2 . 1 .3. Johnson and Ja si k. Antenna Enginee ring Handbk.Chap. 40. Second Ed it io n. Publ ish ed by McGraw H i l lBooi

Configuration NoBLOCK D IAGRAMOF FEED MATRIX

2 - 2 . 8158

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A Dual Polarized Horn With a Scanning Beam