Propagation and radiation characteristics of rectangular corrugated waveguides

Dewey, Richard James (1978) Propagation and radiation characteristics of rectangular corrugated waveguides. University of Southampton, Doctoral Thesis.

Abstract

The thesis is concerned with the propagation and radiation characteristics of rectangular metal waveguides with transverse corrugations on one, two or all four walls. A rigorous field analysis is performed for a rectangular structure with finite thickness corrugations on one wall or the equivAlent problem of symmetrical corrugations on two opposing walls. The resulting determinantal expressions specify the complete mode spectrum and are manipulated into a form which reveals the orthogonal nature of HE and EH modes supported by the structure. This also simplifies numerical evaluation of the characteristic equation by allowing mode sets to be defined by sub-determinants rather than the full determinantal expression. Theoretical predictions for the HEm slow wave dispersion characteristic are confirmed by experimental measurements.An abrupt plain/corrugated waveguide junction arrangement is considered for the structure with transverse corrugations on one broad wall and variational expressions developed for the junction admittance ratio. This considerably reduces the amount of empirical adjustment needed to achieve optimum input VSWR to the HEip slow wave.Differential phase shift between the lowest order orthogonal modes in a rectangular waveguide with symmetrical corrugations on two opposing walls is examined. A mathematical model is established which shows close correspondence between predicted and measured values and is useful for the design of circular polarisers and differential phase shift equalisers. A field analysis is carried out for the rectangular structure with corrugations on all four walls. It is found that the expressions can tot be simplified in the way that had been possible for the simpler structures. The resulting expressions comprise a pair of simultaneous deteiminantal relations which must be solved iteratively for the transverse propagation constants. The equations are examined in the context of a separability relation and found to vindicate the assertion that a separable modal solution can not be formulated for the fully corrugated structure. However this in no way. implies that propagation of power in the structure is impaired, simply that the boundary configuration poses a more difficult problem. A mathematical model is developed to specify the vector radiation properties of the small flare angle rectangular horn corrugated on two opposing walls. The ability of this modal to approximate the fully corrugated rectangular horn is investigated.

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