Radiation from an infinite, GAP excited dipole immersed in a radically inhomogeneous plasma layer

Abstract

length, gap excited, thick, cylindrical dipole is studied for aThe far field electromagnetic radiation from an infinite variety of concentric coatings. This antenna configuation is representative of that employed for reentry vehicles where the entire vehicle approximates a large cylindrical antenna fed at the center across a small gap. The plasma layer is modeled as infinite in length, isotropic, cold. and inhomogeneous in only the radial direction, The radiation characteristics Of this antenna have previously been investigated only for homogeneous layers . 1 , 2 , 3The antenna radiation field is formulated as a boundary value problem by direct application of Maxwell's equations for the electric and magnetic fields. Solutions are obtained by a method of steepest descent integration for the antenna in One, two, and ten concentric homogeneous layers, permitting approximais shown in Figure 1. The electric and magnetic fields in each tion of a single homogeneous layer. The geometry of the problem layer are readily formulated in Bessel functions of zero and first order. The tangential fields are matched at each inter-The equatlons are numerically solved using the value of face, resulting in 2p + 1 simultaneous equations to be solved. integration variable at the saddle point, resulting in very fast computation times. layers, radiation patterns are computed for an antenna with a TO illustrate the effects of representative reentry plasma value. The plasma layers are those given by Swift&, withcircumference of one free space wavelength, a commonly selected variable electron density to obtain parametric results. The quantity computed is E P V where E is the transverse electric field, P is the distange fo the fied point, and V is the source voltage. The radiation patterns for invisid and bsundary layer flows at high altitude are shown in Figures 2 and 3 , The 234