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The design and development of a tri-mode conjugate matched feed, to suppress the unwanted high cross-polarisation and beam squinting in an offset parabolic reflector antenna, are presented. In a smooth-walled cylindrical waveguide, TE11, TM11 and TE21 modes are combined in proper amplitude and phase to configure a tri-mode conjugate matched feed. The performance of the proposed tri-mode horn was evaluated, and its simulated far-field radiation pattern is found to be in close agreement with the measured radiation pattern. This horn was then used as a primary feed device to illuminate the linearly polarised offset parabolic reflector antenna, and significant reduction in the cross-polarisation has been achieved in the secondary radiation pattern. Similarly, by illuminating the offset reflector with a circularly polarised matched feed, a squint-free radiation pattern has been achieved.
Date of Publication: November 2010