Admittance of a Plasma‐Covered Cylindrical Antenna

Abstract

Based on a variational formulation, an expression is derived for the admittance of a circumferential gap in an infinite cylinder covered by a set of coaxial dielectric or plasma layers. The gap is fed by the dominant TEM mode in a narrowly spaced, parallel‐plate, radial waveguide. Numerical computations are presented for a multiple‐layer model of a lossy plasma and for a dielectric layer which supports surface waves. These computations are compared with admittance measurements of a similarly excited metal cylinder surrounded by an annular plasma. The plasma is produced in a long double‐ wall cylindrical vessel by a pulsed d‐c discharge in argon at 0.4 Torr. In the experimef.lt, the radial guide is excited by a small axial probe fed by a conventional coaxial air line. The admittance viewed in the coaxial line is related to the gap admittance by an experimentally determined two‐port network representing the junction region. The measurements are in fair agreement with calculated values based on a three‐layer model of the inhomogeneous plasma and the discharge tube.