The admittance of a parallel-plate waveguide aperture illuminating a metal sheet

The admittance of a parallel-plate waveguide aperture having an infinite flange and illuminating a metal sheet is determined by two separate methods: 1) wedge diffraction theory; 2) an integral transform solution. Numerical computations obtained by either method are in excellent agreement and are verified experimentally. A Smith chart is employed to show that, for a given aperture width, the admittance locus coalesces about the half-space value as the metal sheet recedes to infinity. A strong interaction between the aperture and the metal sheet occurs for distances in the vicinity of integral multiples of one half-wavelength. The interaction becomes much more localized with respect to distance as the distance to the sheet is increased; however, the admittance is always infinite at these distances.