UBC Theses and Dissertations
Properties of surface waveguides with discontinuities and perturbations in cross-section Brooke, Gary H.
The first part of this thesis is concerned with theoretical and experimental investigations of step discontinuities on a planar surface waveguide. An approximate theoretical solution to the unbounded discontinuity problem is obtained by bounding the open structure with perfect conductors, since there is a direct relationship between the mode spectra of the two configurations. Mode-matching is used to solve the bounded case. The method is "tested" on four discontinuity configurations considered by other workers. Good agreement with the previous results is obtained in all cases except one for which the original results are shown to be inaccurate. The experimental investigation is carried out on a dielectric coated conductor surface waveguide, supporting the first TM mode, at a frequency of 30 GHz. Standing wave measurements are obtained using a X/2 dipole oriented along the longitudinal component of electric field. The parameters of interest are the magnitude and the phase of the reflection coefficient. The experimental results confirm those obtained theoretically. The theoretical and experimental techniques are later applied in an investigation of a cascaded step discontinuity configuration. The theoretical approach involves the use of wave transmission matrices. Experimental results for the magnitude of the reflection coefficient are found to be in reasonable agreement with theory. The second part of this work describes a theoretical and experimental study of dielectric waveguides, of circular cross-sections, perturbed by axial slots. In particular, the normalized propagation coefficient of the dominant modes with each polarization is determined analytically using a standard perturbation technique and experimentally using an open resonant cavity. The perturbation results give quite a good indication of the trends observed experimentally. It is found that there is an optimum size of the perturbation which gives the maximum separation between the normalized propagation coefficients of the two polarizations.
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