A multimode feed for compact offset parabolic reflector antenna system

In this paper the design of a multimode corrugated feed at centre frequency of 7.25 GHz is presented, which reduces very high level of cross polarization in an offset parabolic reflector antenna system. The higher order modes TE 21 and TM 11 are generated in proper phase and magnitude in addition to the dominant, TE 11 mode, which are passed through the corrugated structure to generate HE 11 and HE 21 modes. The feed was then used as a source to illuminate aperture of offset parabolic reflector antenna having offset angle of 90 deg and very small F/D of 0.4.The secondary patterns were simulated using method of physical optic. Significant reduction in cross polarization is obtained compared to illumination of offset reflector by conventional corrugated feed.