Design of dielectric-covered resonant slots in a rectangular waveguide

A summary is given of the effects of a dielectric cover upon the resonant frequency, the resonant conductance of a longitudinal shunt slot, and the power coupled out of a waveguide by a pair of near circularly polarized crossed slots. Typical data curves are presented which illustrate these changes due to variations in the dielectric constant and thickness of the cover. A simple modification of Stevenson´s free-space theory for resonant slots radiating into a homogeneous dielectric half-space is used in conjunction with the plane-wave reflection coefficient to predict bounds on the conductance and power variations for dielectric thicknesses greater than about one-quarter wavelength. The accuracy of this simple theory in predicting measurements on dielectric-covered slots is similar to the accuracy of Stevenson´s free-space theory within about 9 percent for the shunt slots and about 15 percent for the cross slots.