Radiation fields from travelling wave antennas in polar terrain

Abstract

A travelling wave antenna is located below the surface of homogeneous polar terrain. The physical properties of the medium, which are the relative dielectric constant and the loss factor, influence the phase velocity and attenuation constant of the travelling wave antenna current. Another influence is Debye relaxation phenomena in ice, where phase velocity and attenuation constant depend on frequency and temperature of the ice. These parameters are included in the formulation of the space and ground wave expressions for the travelling wave antenna. Both horizontally and vertically polarized waves are formulated. Elimination of backfire radiation is described with the necessary terminating impedance modifications. Results are presented as antenna patterns for the preceding variations. Frequency variations appear at 30 and 300 kHz frequencies where the antennas are one wavelength long. Polarization variations are seen with patterns along and perpendicular to the antenna axis. Influence of the loss factor on a travelling wave antenna is illustrated by comparing the radiation pattern with a similar antenna in a lossless medium. Backfire radiation elimination is seen when a matched terminating impedance is replaced by a modified terminating impedance.