The effect of ground plane size on the input admittance of a rectangular waveguide-fed aperture

Abstract

An experimental investigation was undertaken to determine how large a ground plane is necessary to insure best possible experimental agreement with calculated values of admittance and susceptance for a rectangular waveguide-fed aperture. One method of calculating the aperture admittance is briefly outlined. The experimental work is outlined and the results presented in graphical and tabular form. It was found that a minimum flange of 2 wavelengths in the directions perpendicular to the broad dimension of the waveguide is required to insure agreement of the conductance to within 2$ and the susceptance to within 5$ of the calculated values. It was found that in the direction perpendicular to the narrow dimension of the waveguide, a flange of total width of 0.9x was still large enough to insure this same agreement, even though the aperture width was slightly over 0.8x. The experiment also showed that type of conductor is not a critical factor.