Author: Uma Balaji

Publisher:

Published: 1997

Total Pages:

ISBN-13:

RF/microwave terrestrial point-to-point and satellite communication systems employ a large number of waveguide components operating at microwave and millimeter wave frequencies. Accurate design of these components for optimum performance of the overall system is critical. To achieve this, computationally efficient and accurate numerical methods are indispensable tools in the design and optimization of components and subsystems. Among the large variety of potentially suitable numerical methods, the mode matching method in conjunction with the generalized scattering matrix technique has been found to be one of the most reliable and straightforward techniques to design waveguide components. In the past the method has been mainly applied to eigenvalue and scattering problems in rectangular waveguides. In this thesis, the mode matching method is extended to ridge waveguide problems in circular waveguides and thus closes a gap in the literature that has existed for a long time. The thesis begins with a study of the basic principles of the mode matching method as it is known from rectangular waveguides. These principles are then applied to the analysis of the rectangular ridged and coaxial waveguide, followed by an eigenvalue analysis of ridged circular waveguide. Rather than rectangular ridges, ridges of uniform angular thickness (conically shaped) are used in the circular waveguide to avoid a mixed coordinate system which would render the mode matching method computationally very inefficient. On the other hand, conically shaped ridges are as easy to fabricate as rectangular ridges and are not detrimental to the electrical performance of the component. The thesis then continues to treat the discontinuity problem at the interface between the empty circular waveguide and ridged circular waveguide. To verify the computed scattering parameters, measurements were performed and good agreement was found. By cascading several discontinuities transformers and evanescent mode filters were designed. A fifth order filter was designed and fabricated and also here good agreement between measured and computed data was found. The final chapter in the thesis analyses the coupling between orthogonal modes in the presence of an asymmetric discontinuity. Determining the coupling factor between orthogonal modes is an integral part of the design of polarizers and dual mode filters and for conically shaped ridges, has not been published in the open literature yet. To realize various coupling coefficients, a single or double ridges must be placed at an arbitrary angle to the exciting wave. The mode matching method is extended to include also this case and various convergence tests have been performed to validate the algorithm . As a final example, the algorithm has been applied to design a circular polarizer with two ridges. Although only two-port problems are treated in this thesis, the basic framework for the mode matching method in circular waveguide has been established and can now be extended to three-port problems. This will be the subject of future work to analyze and design power dividers and orthomode transducers.