THE INPUT ADMITTANCE OF THIN PROLATE SPHEROIDAL DIPOLE ANTENNAS WITH FINITE GAP WIDTHS

The input admittance of a thin prolate spheroidal dipole antenna of major and minor axes a, b and fed by a gap of finite width 2d operating at the wavelength lambda (k = 2 pi/lambda) is expressed as a very slowly convergent sum of symmetric prolate spheroidal angle and radial modal functions whose computation in this paper is facilitated by a novel method for evaluating radial functions of the second kind for small and large order with high accuracy. Then, by using Infeld's method of replacing a sum by an integral, the slowly convergent part of the admittance is evaluated. Three different types of distributions for the gap electric field are considered, and numerical results for the admittance are given as a function of the spheroidal dipole's length (0 less than or equal to 2a less than or equal to lambda) with its thickness (2b greater than or equal to 2 x 10(-5) lambda), as well as the gap ratio d/b, as parameters.