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Microstrip Antenna Feeds for Offset Reflector Antenna for Cross-polarization Reduction at both Diagonal and Asymmetric Planes

A simple dual-mode (TM11 and TM21) circular microstrip patch antenna as feed for offset reflector antenna (ORA) is proposed in the paper. The concept of conjugate field matching for cross-polar level suppression in radiation pattern of offset reflector is used to achieve a matched feed with appropriate excitation ratio for the two modes. The secondary radiation pattern of the offset reflector has been calculated using geometrical optics technique. Cross-polarization level for both the diagonal and asymmetric plane is studied for the proposed feed excited with both vertical and horizontal polarization separately. The cross-polar level obtained for all the planes were below − 40dB for both kind of linear polarization. Variation in excitation ratio of the modes with variation in F/D ratio has also been investigated.