Mode spectrum analysis for microwave components formed by nonstandard waveguides




Yu, Seng Yong

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Microwave telecommunication 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 and, therefore, computationally efficient and accurate numerical methods are indispensable. The objective of this work is to develop a framework for the computer-aided analysis and design of microwave components containing cross sections with arbitrarily positioned ridges. A new formulation to obtain the eigenmode spectra of irregular waveguides is presented. The method uses modified modes of regular waveguide housings as expansion terms and leads to a classical eigenvalue problem. A constraint function is introduced to satisfy the boundary conditions for TM modes; TE modes are obtained straightforwardly. This procedure is then combined with a mode-matching code in order to analyze and optimize waveguide structures involving resonating components. The general approach is applied to multiple ridged waveguide structures in rectangular and circular waveguide technologies. Convergence is demonstrated, and applicability of the developed algorithm is tested through the design of waveguide filters, transformers, polarizers and polarization-rotating components. Two new configurations of circular T-septum and key-shaped below-cutoff filters are introduced. Whenever possible, the designs are validated by independent means. Excellent agreement is obtained between the approach presented in this thesis and other full-wave field solvers.



Microwave, Waveguides, Telecommunication systems, Technologies