Studies on the classical gain approximations and the aperture-reflection coefficient of rectangular waveguide antennas

The classical approximations for the gain of rectangular waveguide antennas are examined in the light of a previously proposed approximation for the fringe currents at the shorter edges of the waveguide. By using the alternative fringe-current representation, expressions are subsequently presented for estimating the magnitude of the TE₁₀ mode reflection coefficient at the aperture of standard open-ended rectangular waveguides (OEG). The derivation, accomplished by equating total input power to radiated power, assumes negligible resistive loss in the waveguide walls. The reflection coefficient values predicted by the expressions compare favorably with available measured data and with a different analytical technique. A significant application of these expressions would be in predicting the on-axis gain and far-field of the OEG by using Yaghjian´s (1984) formulas