Insulated dipole antenna in a dissipative dense medium

Abstract

The driving-point impedance of a linear antenna is determined if the current distribution along the antenna is known. This current satisfies an integral equation which may be obtained approximately by the moment method. An antenna insulated from the surrounding lossy medium may be approximately analyzed by using the equivalent lossy transmission line concept. When the magnitude of the dielectric constant of the lossy medium is either very large or very small compared with that of the insulation layer, approximate solutions are obtained in the literature(4,7). Using this method, a dipole antenna usable in the underground in the frequency range from 20MHz to 80MHz is designed and fabricated. This dipole antenna is fed by a coaxial cable through one half section of the dipole like the sleeve monopole antenna. The input impedance of this antenna is calculated by assuming the sources, one at the center of the dipole and the other at the one end of the dipole where feeding cable and antenna are discontinuous. The measured input impedance is compared with the above calculation and such a design method is shown to provide good results.