Computer-aided design of adaptive antenna matching networks

Abstract

A computer-aided technique has been developed f o r t h e d e s i g n o f m a t c h i n g n e t w o r k s t h a t are a d a p t i v e , i n t h e s e n s e t h a t t h e n e t w o r k c a n b e c o n t r o l l e d by a change i n o n e o r more v o l t a g e s . T h e s e c o n t r o l v o l t a g e s are a u t o m a t i c a l l y v a r i e d w i t h a change i n t h e f r e q u e n c y o f o p e r a t i o n , o v e r w i d e b a n d w i d t h s , i n s u c h a manner t h a t t h e m a t c h between a complex impedance load and source can b e i m p r o v e d o v e r t h a t o b t a i n a b l e w i t h a f i x e d passive network. I n t r o d u c t i o n A computer-aided design technique has been developed at t h e U n i v e r s i t y o f I l l i n o i s f o r matchi n g n e t w o r k s i n t e n d e d f o r use between a load, whose complex impedance v a r i e s w i t h f r e q u e n c y , and a 50 ohm s o u r c e ( l ) ( 2 ) . T h i s t e c h n i q u e c a n b e a p p l i e d t o a c t i v e o r p a s s i v e n e t w o r k s , composed of e i t h e r lumped o r d i s t r i b u t e d e l e m e n t c o m p o n e n t s . The technique i s based upon c h a r a c t e r i z i n g t h e l o a d , t h e e l e m e n t s o f t h e m a t c h i n g n e t w o r k , a n d t h e s o u r c e i n terms o f t h e i r r e s p e c t i v e c a sc a d e d t r a n s f o r m a t i o n m a t r i c e s . A computer program p e r f o m t h e r e q u i r e d m a t r i x m u l t i p l i c a t i o n o n t h e s e c a s c a d e d s e c t i o n s t o o b t a i n a r e s u l t a n t o v e r a l l t r a n s f o r m a t i o n matrix. This transformat i o n m a t r i x i s c o n v e r t e d t o a s c a t t e r i n g m a t r i x t o o b t a i n t h e c o n v e n t i o n a l r e f l e c t i o n c o e f f i c i e n t s a n d t h e t r a n s m i s s i o n c o e f f i c i e n t t h a t c h a r a c t e ri z e s t h e t r a n s f e r of t h e s i g n a l f r o m t h e s o u r c e t o t h e l o a d . The design does not depend,upon developing a c i r c u i t o r m a t h e m a t i c a l model of t h e l o a d . It p r e s u m e s t h a t t h e c o m p l e x r e f l e c t i o n c o e f f i c i e n t of the load would be measured a t an adequate numb e r o f d i s c r e t e f r e q u e n c i e s o v e r t h e d e s i r e d b a n d . The s c a t t e r i n g p a r a m e t e r s o f all v a r i a b l e n e t w o r k elements will a l s o b e a v a i l a b l e , o r w i l l b e measured, a t these frequencies. These measured v a l u e s a r e t h e n u s e d i n t h e d e s i g n , a n d t h e o,vera l l t r a n s f e r c o e f f i c i e n t r e f e r r e d t o a b o v e is obt a i n e d a t e a c h o f t h e s e l e c t e d f r e q u e n c i e s o v e r t h e b a n d w i d t h o f i n t e r e s t . The computer program includes a modified version of Rosenbrock's minimization procedure(3) t o s e l e c t an "optimized" s e t o f e l e m e n t s f o r t h e matching network. The o p t i m i z a t i o n p r o c e d u r e c a n be set up i n t e r m s o f any one o...