Aperture fields and gain of open-ended parallel-plate waveguides

Abstract

The fields at the open end of a parallel-plate waveguide with a <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">TE_{10}</tex> mode incident are calculated. For plate spacings greater than about 0.6 wavelengths, these are well approximated by incident and first-order diffracted fields. Consequently single diffraction at the aperture alone is often adequate for pattern calculations and, although no more complicated, is superior to the Kirchhoff result, even for on-axis calculations. Numerical values for Kirchhoff, geometrical theory of diffraction and exact on-axis gain demonstrate this. In contrast, for TEM incidence, both methods yield the exact on-axis gain. Application of these results to the improvement of gain prediction of horns is discussed.