Exploring further potentials of over-moded primary feeds for parabolic reflector antennas

The application of over-moded circular waveguide feeds was further studied in offset reflector antennas for both virtual array formation with displaced phase centre locations and low cross polarized antennas. A dual-mode circular waveguide feed was analytically modeled. The modes included the TE11 and TE21 type modes. The distinct feature of the proposed model was in its capability to represent more asymmetrical properties by selecting different tapering numbers of the fundamental TE11 mode. This added extra degrees of freedom to effectively shape the primary feed patterns to eventually displace the phase centre location of the reflector antenna or provide more asymmetric feed patterns to better compensate the inherent cross polarization of the offset reflector antennas. Some examples for both applications were presented. For the virtual array antenna, multiple phase centre antenna was achieved within a single aperture. This significantly reduces the cost and volume of the traditional multi-aperture antennas. As for the low cross-talk applications, the results were also promising as the reduced cross polarizations were below -50 dB even for reflectors with large offset angles.