Design and Development of Dual Polarized Conjugate Matched Feed for Satellite Communications

Abstract

Conjugate matched feed supresses secondary cross-pol of offset reflector by utilizing higher order mode (TE₂₁) along with fundamental mode (TE₁₁) in a circular feed itself. In this paper, physically realizable stable co-axial structure of TE₂₁ mode coupler and co-axial horn were designed and tested for dual polarization applications. The procedure for designing of co-axial horn for maintaining phase difference between the modes is also discussed. The secondary pattern of the matched feed with offset reflector having F/D of 0.7 and 45° offset angle for dual linear polarization was analyzed using physical optics (PO) in GRASP (Ticra tool). The observation revealed 7 dB improvement in the secondary cross-polar performance for both polarizations using matched feed as compared to TE₁₁ feed over 7.8% bandwidth. The primary measurement of the feed alone was carried out in an anechoic chamber, and the measured primary pattern was compared with the simulated value. The designed feed could be an alternative of dual reflector antenna used in satellite communications.