Multimode interference generation in the horn-reflector antenna system during multipath fading

A model for the generation of multimode interference in the horn-reflector antenna system is described. This interference arises due to the off-axis arrival of a signal-bearing ray during multipath fading, the excitation of a higher-order mode in the waveguide system, and the creation of an echo by the reflection and reconversion of this higher-order mode to the dominant mode. The results of calculations based on this model are qualitatively and quantitatively in agreement with the measurements made by P. Balaban (1989). The model predicts that the effects will be worse for vertical polarization and with tilted horn-reflector antennas. The multimoding generated will be worse at 6 GHz than at 4 GHz because of the increasing sharpness of the antenna patterns with increasing frequency. The discussion is limited to 6 GHz, although similar properties will be exhibited above 4.08 GHz where the TE₂₁° mode can propagate in WC-281 waveguide