No abstract

Army m i l l i m e t e r wave radar systems designers i m p o s e e v e r -i n c r e a s i n g r e s t r i c t i o n s o n t u b e volume, weight, and cost while at the same time r e q u i r i n g i m p r o v e d t u b e l i f e and r e l i a b i l i t y . The b u l k i e s t p o r t i o n o f a m i l l i m e t e r wave tube i s comprised o f t h e t h e r m i o n i c e l e c t r o n gun and t h e beam focusing magnet. The t h e r m i o n i c e l e c t r o n gun i s o f t e n t h e s o u r c e o f t u b e f a i l u r e . The magnet accounts f o r a b o u t 30% o f t h e c o s t and 60% o f t h e t u b e volume and weight. An RF a c t i v a t e d , n o n -t h e r m i o n i c , e l e c t r o n gun which employs the principle of secondary electron resonance (mu1 t i p a c t o r ) t o p h a s e -f o c u s e l e c t r o n s i n t o t i g h t , h i g h d e n s i t y e l e c t r o n bunches i s discussed. Since electrons are prebunched w i t h i n t h e gun i t s e l f , l o n g d r i f t l e n g t h s and the attendant need for magnetic focusing are eliminated or minimized, thereby decreasing tube s i z e , w e i g h t , a n d c o s t . R e l i a b t l l t y and l i f e a r e s u b s t a n t i a l l y i n c r e a s e d b y v i r t u e o f t h e f a c t t h a t t h e r m i o n i c e m i s s i o n i s n o t employed. C a p a b i l i t y o f m u l t i p a c t o r guns t o produce s i g n i f i c a n t beam c u r r e n t s has been established by numerous i n v e s t i g a t o r s . The p r a c t i c a b i l i t y and f e a s i b i l i t y o f such guns f o r u s e a t m l l l i m e t e r wavelengths, however, depends not only on their e l e c t r o n c u r r e n t c a p a b i l i t y , b u t a l s o o n t h e i r a b i l i t y t o be d r i v e n by l o w power, compact, RF sources. T e s t v e h i c l e s ( s c a l e d t o 5 GHz) t o demon? s t r a t e r e q u i r e d d r i v e l e v e l s have been b u i l t and e v a l u a t e d a t ET&DL, ERADCOM. Experimental res u l t s show t h a t d r i v e l e v e l s o n t h e o r d e r o f 10 m i l l i w a t t s a r e s u f f i c i e n t , d e m o n s t r a t i n g t h a t s m a l l , l i g h t w e i g h t , s o l i d -s t a t e RF drive sources a r e p r a c t i c a l . T h e o r e t i c a l e v i d e n c e .Is presented showing t h a t t h e l e v e l of d r i v e i s t h e same f o r millimeter frequencies (e.g. 95, 140, 220 GHz) as i t i s f o r t h e 5 GHz s c a l e d t e s t v e h i c l e s .

It is well known that the finite element method leads to large square symmetric matrices which are highly banded. Even if only the half bandwidth is stored it is easy to saturate the computer storage; this is because the half bandwidth contains a large amount of zeros. This paper discusses an alternative approach where a small rectangular section of the full bandwidth is stored, this method leading to a significant reduction in storage requirements.