Electrical and Computer Engineering ETDs

Publication Date



A perfectly conducting prolate spheroidal antenna immersed in a conducting medium is analyzed. It is assumed that the dimensions of the spheroid are small compared to a skin depth in the medium. A gain factor for the antenna as a receiver is computed as a function of the spheroid's axis ratio. The prolate spheroid is assumed to be excited by a circular filament of magnetic current located in the plane of the spheroid's minor axes to approximate excitation by a magnetic toroid. Expressions for the antenna's input admittance and effective length are derived. Some experimental results verifying the derivation of the input conductance are also included. When excited by a toroidal winding, the antenna is represented by an equivalent circuit of a transformer with an N- turn primary and a one-turn secondary feeding a load impedance. Some practical examples of the toroid-prolate spheroid antennas are considered and indicate that if the N turn toroid inductance is large an ideal transformer equivalent circuit applies. When the equivalent transformer is ideal, the real part of the antenna's input impedance is approximated by N2 times the secondary resistance. The antenna is shown to have a Q of .5 or less for VLF and relatively constant effective length, indicating practical operation over a broad range of frequencies. It is also shown that the effect on the antenna's input admittance of an imperfectly conducting prolate spheroid (σ 107 mhos/meter) is negligible for frequencies of interest.


United States Navy

Document Type




Degree Name

Electrical Engineering

Level of Degree


Department Name

Electrical and Computer Engineering

First Committee Member (Chair)

Richard H. Williams

Second Committee Member

Ahmed Erteza

Third Committee Member

Ruben David Kelly