Modified radiation pattern and gain formulae for small-aperture horn antennas

Modified radiation pattern and gain expressions are presented for small aperture horn antennas. The E-plane pattern is identical to that provided by the classical Stratton-Chu formula, while the H-plane pattern is a modification of the Stratton-Chu formula accounting for fringe currents radiating from the edge of the aperture. An empirical approach is taken to determine the coefficient applied to the radiating currents. Comparison with measurements indicates that it is possible to predict the half-power beamwidths within a degree and gain to within a fraction of a dB.