The input admittance of thin prolate spheroidal dipole antennas with finite gap widths

The effect of the ultraspherical gap field distribution on the admittance of solid circular cylindrical dipole antennas has rigorously been analysed in Do-Nhat (1987) and Do-Nhat and MacPhie (1989). In the present paper the authors extend the analysis to the problem of thin prolate spheroidal dipole antennas with the consideration of 3 types of gap fields: Dirac´s function gap field distribution, uniform gap field distribution, and ultraspherical gap field distribution. The numerical results for the input admittance of thin prolate spheroidal antennas, as well as their current distributions are compared for the above mentioned gap excitations. Furthermore, for the given ultraspherical gap field distribution, the difference of the input admittance between very thin solid circular cylindrical dipoles, and very thin spheroidal dipoles is shown. This is possible since the prolate spheroidal functions of the second kind (Do-Nhat and MacPhie, 1994) have been developed for spheroids whose parameter /spl xi/ may approach 1. Also the asymptotic expansion of a particular term (introduced by Infeld (1947)) of the slowly convergent spheroidal susceptance is obtained (Do-Nhat and MacPhie, 1994) to facilitate the computation of the spheroidal susceptance with high accuracy.<>