A theoretical and experimental study of the insulated loop antenna in a dissipative medium

Abstract

The performance of a bare antenna as a radiator in a dissipative medium can be significantly altered by placing a dielectric coating around the antenna. For certain antenna types and specific properties of the dissipative medium, the dielectric insulation has been shown to improve the performance of the antenna. In this paper the thin‐wire circular‐loop antenna centered in an insulating spherical cavity and immersed in an infinite homogeneous isotropic dissipative medium is analyzed. A Fourier series solution for the antenna current distribution is derived. The coefficients of the series are a combination of the coefficients for the loop in an infinite dielectric medium, which were determined previously by Wu [1962], and a second term, which is an infinite sum. The properties of the sum are examined, and expressions for the antenna input admittance, impedance, and electromagnetic field in the dissipative medium are obtained. Numerical results are presented for specific antenna sizes and dissipative media. For the special case of a loop with a uniform current distribution in an electrically small sphere the expression for the input impedance is shown to reduce to a solution previously given by Wait and Spies [1964]. The construction of an experimental model for the antenna is discussed, and antenna input impedances and current distributions measured with the model immersed in various salt‐water solutions are compared with theoretical calculations.