Effects of a surrounding conducting medium on antenna analysis

Abstract

Analysis of antennas immersed in conducting media is, in many ways, quite different from the corresponding analysis for antennas in air. The usual simple techniques applied for determining radiation resistance for antennas in the air break down for antennas in conducting media. The normal concepts of antenna gain and antenna pattern break down when the antenna is in a conducting medium. The pattern, for example, becomes highly dependent upon the choice of the origin of the coordinate system. These effects are due to the dissipation of most of the energy in the immediate vicinity of the antenna. Such dissipation is caused by the fields which, for antennas in air, are associated with stored, but not dissipated, energy. The primary purpose of this paper is to illustrate failure of standard antenna analysis techniques when the antennas are in conducting media. Surprisingly, the biconical antenna, whose input impedance requires rather extensive calculations in air, turns out to be extremely simple to analyze in a conducting medium. A discussion of this is presented to show how an analysis can be simplified by the presence of the conducting medium. Comparison of a redefined gain for the biconical, loop, and two forms of straight wire antennas, indicates that there is very little difference between the gains of the different configurations provided the sizes are approximately the same. Although the loop antenna is considered only for dimensions small compared with the wavelength, no such limitation is placed on the other antennas.