High Q coaxial waveguide devices are found in superior performance filters for wireless applications, they are used with cavity perturbation techniques to measure complex permittivity, they underpin the operation of scanning microwave microscopes and are of ongoing importance in the design of space division multiple access beamforming antennas. The coaxial 'T' junction transition formed between the feed and the coaxial waveguide airspace is a key junction in all of these waveguide coaxial systems. The study of this transition was the starting point for this research. In previous literature, a Green's theorem has been used to characterise a coaxial 'T' junction. In this thesis the model has been extended to include higher order propagating modes, evanescent modes, partial and full height probes, and any general form of coaxial termination. The final model is capable of analysing the S-parameters of multiport coaxial devices, and the energy distribution of the modes within the coaxial airspace. Several different coaxial systems were constructed and experimentally investigated including a coaxial resonator, a non-standard coaxial waveguide unknown load, and a beamforming antenna. In all cases the dyadic Green's function model was demonstrated to model accurately the performance of the multi-mode coaxial system. The major advantage of this approach is its inherent closed form nature lending itself to a computationally efficient means of formulating Sparameters, synthesising field patterns within the waveguide airspace and for shaping beam forming antenna radiation patterns. The model has successfully been applied to the design and experimental validation of the algorithm for several overmoded coaxial applications including: coaxial load characterisation, overmoded characteristic impedance formulations, overmoded resonant cavity and SDMA beamforming antenna design. Further applications to material measurement, direction of arrival estimations and mutual compensation matrices for antenna beamformers are under review. In essence, a powerful generic tool for the design and prediction of the electromagnetic characteristics of single and multiple probe overmoded coaxial devices has arisen from this investigation.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:601114 |
| Date | January 2006 |
| Creators | Davis, John G. |
| Publisher | University of Manchester |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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