Dual-Polarised Mode Generator for Cross-Polar Ccmpensation in Offset Parabolic Reflector Antennas

It has been recently shown that the depolarisation and beam-squinting effects exhibited by offset parabolic reflector antennas can be suppressed by means of techniques based upon focal-plane field matching and the use of higher-order wave-guide modes. In the past prototype examples of such `matched-feed' devices have been limited to operation with a single hand of polarisation. The limitation has largely been imposed by the performance of the mode generating section of the matched-feed device. This paper describes the salient features of the design and evaluation of a compact dual-polarised mode-generator which provides a means of achieving simultaneous suppression of the cross-polar radiation for two orthogonal linear polarisations. Experimental data, obtained with a K-band prototype device, validate the overall performance of the mode generator when used within a matchedfeed' device to illuminate an accurately profiled offset parabolic reflector.