Resonances in Waveguide Antennas with Dielectric Plugs

The radiation from a parallel-plate waveguide with infinitesimally thin walls is one of the relatively few electromagnetic boundary value problems for which the Wiener-Hopf integral equation technique may be applied to obtain a closed form solution. 1 Unfortunately, this elegant mathematical technique quickly loses its usefulness even when rather minor modifications of the physical system are introduced, such as, for example, by allowing the waveguide to have finite wall thickness or loading the waveguide with a dielectric material. The somewhat simpler problem of determining the radiation admittance of a waveguide terminated in an infinite conducting plane has been treated by several workers using the variational technique. 2 - 3 The field of the incident wave is used to approximate the true aperture field in these calculations. The results thus obtained appear adequate for engineering purposes. The implication is t h a t the radiation admittance of an empty waveguide is rather insensitive to the approxima2305