No abstract

The p o s s i b i l i t y of using the input admittance method of diagnosing plasmas has been proposed for some time; however, a p r o p e r t h e o r e t i c a l r e l a t i o n s h i p bctwcen t h e p l a m a p r o p e r t i e s m.d the terminal admittance of an antenna was n o t a v a i l a b l e u n t i l two o r t h r e e y e a r s ago ( r e f . 1, 2). An antenna which has been studied in some t h e o r e t i c a l d e t a i l i s shown i n f i g u r e 1. It cons i s t s ol' a rectangular waveguide, opening onto an infinite ground plane, which i s coated with a plasma. The teG1inal admittance of the structure may be computed from the expression ( r e f . 1) where t h e e l e c t r i c f i e l d , x , i s assumed t o b e of t h e same form as t h e domi n a n t m0 mode i n t h e waveguide, and Vo i s the applied voltage on t h e s l o t . A detailea analysis of the boundary value problem reveals that the magnetic f i e l d , 2 , depends upon t h e d i e l e c t r i c c o n s t a n t of the plasma, hence the electron density. The terainal admittance of the structure vas computed by R. C. Rudduck of Ohio State University under grant NASG-445 ( r e f . 1). I n o r d e r t o check t h e computations and the validityof the assumptions incorporated i n t h e t h e o r y , the normalized input admittance, Y.p/Ygl, was measured for the case where a i r i s t h e e x t e r n a l medium. The measurements were performed u t i l i z i n g b o t h a 12" x 12" ground plane and a 1.625'' x 1.625" flange.The a p e r t u r e dimensions were .4" x .9", and measurenents were made over a frequency range of 8.2 t o 12.4 ghz. 106

The design and development of a resonant array of circumferential shunt slots cut into the broad wall of a ring waveguide are presented. This antenna, which is recessed into a metal cylinder and dielectric coated, provides nearly omnidirectional coverage.Calculations using an idealized model consisting of a dielectric-coated Bush-mounted array on a metal cylinder were performed and used as the primary basis for design. The array recess design was experimentally determined and shorn to control the elevation pattern when the recessed array is mounted on a variety of spacecraft shapes. The tolerance problems and the related trapped wave effects encountered in the development of the array are discussed.