Linear antennas in plasma media

Abstract

Abstract : The problems of a gap-excited finite-sized linear antenna, with and without a vacuum sheath, operated in a uniform cold and in a uniform warm lossy plasma medium, have been considered by applying integral equation and boundary value problem techniques. The dependence of the input admittance, the current distribution, and the radiation pattern, upon the collision frequency, the electron temperature, the length of the antenna, the length-to-radius ratio for the antenna, the ratio of the plasma frequency to the operating frequency, and the thickness of a vacuum sheath have been investigated. An integral equation formulation relating the electric field intensity to the current on the antenna, and several boundary value problem formulations concerned with prolate spheroidal antennas, with and without confocal prolate spheroidal vacuum sheaths, have been considered. Admittance curves are given from which the input admittance of a finite linear antenna can be estimated for a wide range of operating conditions and antenna structures. Conductance and susceptance maxima, dependent upon the vacuum sheath thickness, have been observed when using the cold plasma model, for omega < omega sub p. When using the warm plasma model in conjunction with the boundary condition that the normal component of the fluid velocity is zero at the antenna surface or the vacuum sheath surface, the radiation resistance of the antenna, is increased significantly, for the parameters considered. (Author)