Simple primary focus feeds for deep reflectors

The radiation characteristics of the coaxial cavity feed antenna are computed numerically. Excellent agreement between the computed and measured radiation patterns is obtained. The numerical method is used to optimise the performance of the antenna as a feed for deep parabolic reflectors (f/D<0.35). The cross-polarisation level is reduced from -16 dB to below -30 dB. The circular waveguide is filled by a dielectric rod to reduce the feed aperture size and consequently increase the radiation patterns beamwidth. The dielectric rod end is shaped to reduce the cross-polarisation level.