ABSTRACT
Suspended s l o t l i n e is a s lo t l i n e suspended in th e H -plane o f a r e c t a n g u la r w aveguide housing. This t h e s is p r e s e n ts a r ig o r o u s a n a ly s is o f t h i s l i n e and i t s v a r ia n t s f o r c u t- o ff fre q u e n c y , p r o p a g a tio n c o n s ta n t, b a n d w id th , power h a n d lin g c a p a b i l i t y , c h a r a c t e r is t ic im pedance and lo s s e s . The s tr u c tu r e s a n a ly s e d are: sym m etric suspended s l o t l i n e , suspended s lo t l i n e w ith a r b i t r a r y lo c a te d s l o t , s in g l e f i n suspended s l o t l i n e , s in g le f i n b i l a t e r a l s lo t l i n e and a n t ip o d a l suspended s l o t l i n e s . A s lo t l i n e re s o n a to r was a ls o a n a ly s e d f o r the re s o n a n t fre q u e n c y and e n d - e ffe c t. A ll the r e s u lt s p e r t a in to the s lo t l i n e in X-band w aveguide ho u sing .
S ym m etric suspended s lo t lin e was f i r s t a n a ly s e d u s in g in t e g r a l e q u a tio n a p p ro a ch and f i n c u rre n t as unknown. The a n a ly s is was c a r r ie d o u t i n s p e c t r a l dom ain u s in g method o f moments. The G re e n ’ s f u n c t io n s were o b ta in e d u s in g s p e c tr a l domain im m ittan c e ap p ro a ch . C u t- o ff fre q u e n c y and p r o p a g a tio n c o n s ta n t f o r odd as w e ll as even modes o f the s t r u c t u r e were d e te rm in e d . The s tr u c t u r e was a ls o fo u n d to s u p p o rt LSM-mode w hich is the fundam ental mode o f a p a r t i a l l y f i l l e d r e c t a n g u la r w aveguide. The n u m e rical s o l u t io n was fo u n d to e x h ib it r e l a t i v e convergence b e h av io u r.
The f i n c u r r e n t approach is observed to be i n e f f i c i e n t s in c e i t r e q u ir e s more number o f b a s is f u n c t io n s f o r an a c c u r a te s o l u t io n . T h e re fo re , th e s t r u c t u r e was l a t e r a n a ly s e d u s in g s l o t f i e l d as unknown in th e i n t e g r a l e q u a tio n approach. S e p a ra te b a s is f u n c t io n s were used f o r th e odd and even modes. The b a s is f u n c t io n s used f o r th e odd-mode a re same as t h a t used f o r the a n a ly s is o f f i n l in e s . For th e even-mode, b a s is f u n c t i o n s in power s e r ie s e x pansio n were used.
The c u t - o f f fre q u e n c y was o b ta in e d by s u b s t i t u t i n g th e p r o p a g a tio n c o n s ta n t /3=0 in the d e te rm in a n t o f th e c o e f f i c i e n t m a tr ix and f i n d i n g i t s z e ro . The com puter programme was s ta n d a r d is e d by c o m p u tin g the c u t - o f f fre q u e n c y and p r o p a g a tio n c o n s ta n t o f f i n l i n e . Then the r e s u l t s f o r suspended s lo t l i n e were computed and compared w ith those a v a i l a b l e i n th e p u b lis h e d l i t e r a t u r e . The agreem ent was e x c e lle n t in a l l th e c a s e s . The c u t - o f f c h a r a c t e r i s t ic s and p r o p a g a t io n c o n s ta n t fo r
Copyright
IIT Kharagpur
a suspended s l o t l i n e w ith a r b i t r a r y lo c a te d s lo t is a ls o p re s e n te d . The measurement o f p ro p a g a tio n c o n s ta n t was c a r r ie d out f o r an a r b i t r a r y lo c a te d s l o t . The agreement between the measured and computed v a lu e s is found to be f a i r l y good. E x c it a t io n o f suspended s lo t l i n e by w aveguide and suspended m ic r o s t r ip a re a ls o d isc u ss e d .
E l e c t r i c f i e l d d i s t r i b u t i o n f o r the odd, even and I.SM modes was computed and p l o t t e d . Even /odd e l e c t r i c f i e l d d i s t r i b u t i o n s were found to be s i m i l a r to the even /odd f i e l d d i s t r i b u t i o n s fo r co up le d m ic r o s t r ip s . F ie ld d i s t r i b u t i o n fo r the even-mode f o r d i f f e r e n t s lo t w id th s show t h a t the amount of power c o up le d from the lower h a l f to the upper h a l f o f the s l o t l in e in c re a se s w ith in cre a se in s lo t w id th . T his w i l l be u s e f u l f o r the d e s ig n o f d i r e c t i o n a l c o u p le rs and power d iv id e r s .
C h a r a c t e r is t ic impedance based on pow er-voltage Z (P ,V ) and v o lta g e - c u r r e n t Z (V, I ) d e f i n i t i o n s was computed fo r th e odd-mode. The r a t i o Z (P ,V )/Z (V, I ) reaches 4/rt as the w id th o f the s lo t approaches
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the f u l l w id th o f th e waveguide. The c o n d u c to r and d i e l e c t r i c lo s s e s f o r the odd and th e even modes were c a lc u la t e d . The v a r i a t i o n o f even-mode c o n d u c to r lo s s is s im ila r to t h a t o f a r e c ta n g u la r w aveguide p r o p a g a tin g the TE^-mode. But the m agnitu d e o f the lo s s is more due to th e p re sen ce o f the f i n s . The maximum s l o t e l e c t r i c f i e l d o f a s in g le f i n suspended s l o t l i n e f o r u n it power flo w was computed and compared w ith t h a t o f f i n l i n e . I t was found t h a t th e s lo t f i e l d in suspended s l o t l i n e i s low er compared to the f i n l i n e r e s u lt in g in la r g e r power h a n d lin g c a p a b i l i t y .
A n a ly s is o f th e v a r ia n t s o f the suspended s lo t l i n e showed th a t a n t ip o d a l b i l a t e r a l s lo t l in e can be d e s ig n e d to have a c u t - o f f fre q u e n c y o f a b o u t 850MHz w ith an X-band w aveguide h o u s in g . T h is w i l l r e s u l t in m i n i a t u r i s a t i o n o f c i r c u i t s . The short-end e f f e c t is abo u t 11.5% in s l o t l i n e re s o n a to r compared to about 8% in f i n l i n e r e s o n a to r .
M e t a l l i s a t i o n p la n e in suspended s l o t l i n e is c o m p a tib le w ith suspended s t r i p and c o p la n a r w aveguides. T h e re fo re , i t s h o u ld be e a s ie r to in t e g r a t e suspended s lo t l i n e w it h the se l in e s and d ev e lo p u s e fu l d o u b le - la y e r com ponents.
