Summary: The electromagnetic eigenfrequencies in a perfectly conducting spheroidal cavity are determined analytically. The analytical determination is possible in the case of small values of , , where is the interfocal distance of the spheroidal cavity and the length of its rotation axis. In this case exact, closed-form expressions are obtained for the expansion coefficients and in the resulting relation
Analogous expressions are obtained with the use of the parameter (for ), where is the length of the other axis of the spheroidal cavity. The electromagnetic field is expressed in terms of spheroidal eigenvectors. Numerical results are given for the lower-order modes.