Gain of a E-plane sectoral horn--A failure of the Kirchhoff theory and a new proposal

Accurate absolute gain measurements on a typical 10-cm band
E
-plane sectoral horn are described which demonstrate the conventional gain expression underestimates by 20 percent or more. More refined Kirchhoff expressions give little improvement. A new gain formula, incorporating the exact on-axis
TE_{10}
mode field of an open-ended parallel-plate waveguide and yielding much closer agreement with experiment, is proposed.