The Aperture Admittance Waveguide Illuminating a Perfectly Conducting Sheet of a Ground- Plane-mounted

SUMMARY The Fourier transform technique is applied to derive an expression for the aperture admittance of a ground-plane-mounted, transverse electric and magnetic (TEM) mode-excited parallel-plate waveguide illuminating a perfectly conducting sheet. aperture admittance expression, an equivalent circuit is developed. It is shown that there is a 1:l correspondence between elements of the equivalent circuit and higher order modes which exist in the parallel-plate waveguide formed by the ground plane and the reflecting sheet. For the special case where the configuration is treated as a microwave circuit tee junction, the waveguide widths which give the best impedance match are seen to be 0.04 wavelength for the feed guide and 0.03 wavelength for the second guide. Based on the Numerical computations of the reflection coefficient, derived from the aperture admittance, are compared with both the experimental and theoretical results of a similar problem which is solved by application of the geometrical theory of diffraction. General agreement between the two theories except for distances in the vicinity of integral multiples of one half-wavelength is obtained. It is in these regions that strong interactions between the antenna and the reflecting sheet a r e exhibited. It is believed that the differences in agreement in these regions are due to computational inaccuracies associated with the diffraction theory approach, since it is possible to ascertain the accuracy of the results based on the Fourier transform technique by means of the integral test. Finally, for various aperture widths, a Smith chart is employed to show that as the distance between the aperture and the reflecting sheet is increased, the admittance locus tends to coalesce about the admittance value for an infinite half-space.