satellite systems hrs become h i t e d by the avWk bandwidth One Abrrract-In the past few years, the aprcity of c o m m u a i a h method of o v a c o m i n g this limit.tion is to rewe the bandwidth by employmgsp~y~htedmtennrbe;rmrmd/~ortbogolrrlpol * .. Thir papa surveys the required a a t e n n r k d m o A o g y . The xuuttipkbcrm sp.cecnft mtenru pzobkm is a d -, and the current dm@ statas is sumrmri zed. The eyth temmd rntennr f a 8 d d p o h i z e d system is discused rlarg with pohrivtion measurement kclmiqua P W , circuits for compensating the depohription realthg from prec@%.tion on the proprgrtion path are presented.
Abstruct-The hyperboloidal lens antenna with an electric dipole feed located at its focal point radiates no cross-polarized fields. The cross-polarization levels generated by the lateral displacement of the dipole feed are compnted, as well as the beam deviation factor, coma lobe level, gain degradation, and radiation pattern. Results are presented as a fnnction of lens parameters.
r e u t e l COMSAT L a b o r a t o r i e s Clarksburg, Maryland I n t r o d u c t i o n The communication capaeity of a b a n d w i d t h l i m i t e d s a te l l i t e communications system can be increased by reu s i n g t h e allocated bandwidth on each beam of a m u l t i p l ebeam s p a c e c r a f t a n t e n n a . B a n d w i d t h r e u s e r e q u i r e s be maintained a t a t o l e r a b l e l e v e l . The antenna design t h a t t h e i n t e r f e r e n c e r e s u l t i n g from beam c o u p l i n g t o a c c o m p l i s h t h i s o b j e c t i v e may u s e combinations of p o l a r i z a t i o n o r t h o g o n a l i t y and beam shaping. Beam I s o l a t i o n F o r E beams t r a n s m i t t e d f r o m the s a t e l l i t e and occupyi n g the same frequency bands, the beam i s o l a t i o n as-~ measured a t a n e a r t h s t a t i o n i s t h e r a t i o o f w a n t e d -t ounwanted r e c e i v e d s i g n a l p o w e r s , Pw/Pu: I f the d e s i r e d beam i s t h e i-th beam, t h e n t h e i s o l a t l o n c a n b e g i v e n a s ( a s s u m i n g i n c o h e r e n t i n t e r f e r i n g s i g n a l s ) r . where g i i s t h e f i e l d p r o d u c e d by t h e i-th beam. ri i s of the i-th beam and the r e c e i v e a n t e n n a [l]. A t y p it h e p o l a r i z a t i o n mismatch (Ozlrlll) b e t w e e n t h e f i e l d cal o b j e c t i v e i s t h a t the i s o l a t i o n d u e t o the spacec r a f t a n t e n n a b e w i t h i n the 30-35-dB range. Earth Coverage Antennas -P o l a r i z a t i o n O r t h o g o n a l i t y The coordinate system i s shown i n F i g u r e 1. P r i n c i p a l and cross-polarized components of the f a r -f i e l d p a t t e r n are d e f i n e d a s ET and ET, r e s p e c t i v e l y . The d e s i g n of an antenna w i t h no " c r o s s p o l a r i z a t i o n " d o e s n o t a s s u r e that t h e f a r f i e l d s of two such orthogonal antennas w i l l b e i s o l a t e d a t a l l beam a n q l e s . A s an example, a p a t t e r n given approximately by sin; has no E 7 comd i p o l e o r i e n t e d a l o n g ' t h e z -a x i s a n d -h a v i n g a f a r -f i e l d p o n e n t a n d h e n c e n o " c r o s s p o l a r i z a t i o n " . F o r ' a s e c o n d , o r t h o g o n a l d i p o l e , s i t u a t e d a l o n g the z -a x i s of F i g u r e 1, i t c a n b e o b s e r v e d f r o m t h e s t e r e o g r a p h i c p r o j e c t i o n [ 2 ] o f t h e p o l a r i z a t i o n o f e a c h d i p o l e ( F i g u r e 2 ) t h a t 287
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