The input admittance of a prolate-spheroidal monopole antenna fed by a magnetic frill

A realistic model is presented for the prolate-spheroidal monopole antenna fed through an image plane by a coaxial line. In the model, a magnetic current frill replaces the coaxial aperture in the image plane, and this current is approximated using the electric field for the transverse electromagnetic mode in the coaxial line. An analytical expression is derived for the input admittance of the antenna in the form of an infinite series involving special functions, and an efficient method for summing this series is presented. This method applies for spheroids that have height-to-width ratios covering a large range. An experimental model for the antenna is described, and admittances measured using this model are compared with the theoretical results. The two are found to be in very good agreement.