An algorithm for computing the radiation pattern of large segmented reflector antennas

Abstract

Moorestown, NJ f o r m e r l y w i t h t h e J o i n t I n s t i t u t e f o r Advancement o f F l i g h t S c i e n c e Hampton, VA The need f o r v e r y l a r g e a p e r t u r e s f o r r e m o t e s e n s i n g f r o m o r b i t i n g s a t e l l i t e p l a t f o r m s has r e c e n t l y drawn a t t e n t i o n t o t h e l a r g e r e f l e c t o r . F o r a r e f l e c t o r a n t e n n a t o be f e a s i b l e i n t h i s a p p l i c a t i o n , i t w o u l d e i t h e r h a v e t o b e c a r r i e d i n t o space i n a f u r l e d c o n f i g u r a t i o n and deployed upon reaching orbit, or i t would have t o be transported in pieces, or panels, and assembled at a s p a c e p l a t f o r m . I n e i t h e r c a s e , t h e r e f l e c t o r s u r f a c e will d i f f e r from any well defined mathematical surface. This fact, coupled w i t h t h e p r o b a b l e d i s t o r t i o n s w h i c h a n y r e f l e c t o r o f s i g n i f i c a n t size would undergo in the space environment, and t h e tremendous c o n s t r u c t i o n c o s t f o r such a r e f l e c t o r make i m p e r a t i v e t h e a b i l i t y t o a c c u r a t e l y c a l c u l a t e t h e r a d i a t i o n p a t t e r n s o f a n y c a n d i d a t e c o n f i g u r a t i o n . The w o r k r e p o r t e d i n t h i s p a p e r a d d r e s s e s t h e p r o b l e m o f t h e c a l c u l a t i o n o f t h e r a d i a t i o n p a t t e r n s o f a l a r g e r e f l e c t o r made up o f s m a l l e r s e c t i o n s or panels. The approach taken i s t o adapt and e x t e n d a n e x i s t i n g a l g o r i t h m f o r t h e c o m p u t a t i o n o f r a d i a t i o n p a tterms o f smooth r e f l e c t o r s u r f a c e s . The e x i s t i n g a l g o r i t h m u s e s g e o m e t r i c a l o p t i c s t o compute t h e t a n g e n t i a l e l e c t r i c f i e l d o n a p l a n e i n f r o n t o f t h e r e f l e c t o r . The t a n g e n t i a l e l e c t r i c f i e l d i s t h e n i n t e g r a t e d o v e r t h e a p e r t u r e p l a n e t o p r o v i d e t h e s e c o n d a r y p a t t e r n o f t h e r e f l e c t o r . The development o f t h e e x i s t i n g a l g o r i t h m and i t s a p p l i c a t i o n s have been p r e s e n t e d i n t h e l i t e r a t u r e [1,5] and a t e a r l i e r m e e t i n g s [2,3,41 and will n o t be d i s c u s s e d i n t h i s paper. The extension treats each panel as a s e p a r a t e r e f l e c t o r . T h e The w o r k r e p o r t e d i n t h i s summary was s u p p o r t e d b y t h e N a t i o n a l Aeronautics and Space A d m i n i s t r a t i o n t h r o u g h g r a n t number NSG 1588.