An experimental study of plasma sheath effects on antennas

Abstract

A pl asma s imulation techn iqu e has been d eve loped which ca n be used to s t udy the effec ts of homoge neou s or inh omoge neo us plasma s hea th on the radia ti on pa tt ern de te ri ora ti on a nd input im · peda nce of microwave antennas. A tan k has been des igned and cons tru cted for us e in the s imulation tec hn iq1le whi ch ca n re produ ce by mea ns of real di e lectri c mate ri als the dielectric co ns tant e nco unt· e red in plasma cove red a nte nn a re earc h.Th e radia ti on patte rn s and the input im pedances of an a nnular s lot and a thin and long rec tang ular s lot have been s uccessfull y measured in th e prese nce of a s imul ated loss less, homoge neo us, and iso· tropic plasma laye r of varie d thi c kn ess . Co mpariso n with the ava il ab le theore ti ca l d a ta indi cates a ge nerally good agreeme nt, alth ough so me differe nces e xist. In the case of th e radiation patterns th ese differences are attributed to the finit e di s tan ce be twee n t he radi ator and the rece ivin g a nt e nna on one hand a nd th e inh e re nt inaccu racy of th e saddle point method of int egrati on in ce rt a in reg ions on th e ot he r ha nd.

An antenna system using a plasma column having a central conductor and excited by a waveguide

“…Pattern distortion due to a plasma sheath surrounding an antenna and in particular the emergence of enhanced radiation peaks is theoretically [Harris, 1968;Tamir and Oliner, 1962;Hasserjian, 1965] and experimentally [lacanco and Meltz, 1964;Tyras et al, 1965;Harem and Tyras, 1966;Swift et al, 1969] a well-understood phenomenon. These peaks in the radiation pattern are attributed to the excitation of leaky waves on plasma surfaces.…”