Subsurface Communications with Special Reference to Antenna Structure

Abstract

Attempts have been made in this paper to present some discussions on specific antenna structures suitable for subsurface communication. A brief outline of the salient features regarding subsurface propagation is also given. The first section covers, in brief, the different modes of subsurface propagation, choice of a suitable operating frequency range, antenna depth, etc. Next the important observations made by different investigators have been summarized (a detailed bibliography has been given at the end of the paper). The results of the investigations carried out by the authors at IIT, Kharagpur, on buried antennas have been discussed in the following sections. The transmission line theory is applied in obtaining the input impedance of the linear buried antenna. An expression for the propagation constant along this transmission line is obtained. The expressions for the far-zone electric fields along the interface of earth to air due to a subsurface linear antenna and a subsurface helical antenna are also presented. Plots showing the variation of the input impedance and radiation efficiency of the linear antenna with frequency have been given. The polar plots in the last section exhibit the variations of electric field strength due to a submerged helical antenna and compares the same with the field strength of a linear one.