Hybrid mode feed horns for reflector antennas operating at 20/30GHz

Geen, David Charles (2005) Hybrid mode feed horns for reflector antennas operating at 20/30GHz. Doctoral thesis, Northumbria University.

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Abstract

This thesis presents the findings of an investigation into hybrid mode feed horns for use in the next generation of reflector antennas for satellite communications at Ka- band. Within the thesis, general field theory is developed and subsequently applied to specific horn-types in an effort to understand and explore the limits of the bandwidth over which they can offer suitable radiation characteristics. Studies into the use of both corrugated and dielectric-loaded horns identify a shortfall in their performance, particularly in the context as feeds for elliptical reflector antennas at Ka-band, as a consequence of the sizeable frequency separation between the Transmit and Receive functions. The need to operate at two widely separated bands, with little concern for the performance at all frequencies in between, affords the opportunity to take advantage of two exclusive mechanisms to independently optimise the performance at two sub- bands, corresponding to the Transmit and Receive functions. The 'dual-band' concept is explored by extending the field theory developed earlier in the thesis, this being applied to a corrugated structure with secondary mechanism that takes effect once the performance as a consequence of the corrugations themselves begins to degrade. The theory is tested by way of a practical investigation comparing the measured performance of different horn types, including a novel horn borne out of the dual- band concept described above. This led to the need to develop, construct and evaluate a suitable anechoic chamber, the work associated with this also being included in the thesis as an appendix. The results are reviewed in the context of the Ka-band application against both RF and practical design goals with the conclusion that the novel dual-band horn offers superior performance with respect to the state-of-the-art.

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