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An analysis method based on the coupled-integral-equations technique (CIET) and the mode-matching technique (MMT) is presented for the design of a variety of direct-coupled waveguide filters suitable for applications in the lower gigahertz frequency range. The method is verified by comparison with data obtained through other numerical techniques and measurements. With reference to standard waveguide filters, the issues of filter miniaturization and stopband extension toward higher frequency bands are investigated. For given frequency specifications in the 2-GHz frequency range, examples of rectangular coaxial waveguide filters, ridge waveguide filters, ridge waveguide filters including coupling irises and T-septum waveguide filters are presented. It is demonstrated that the rectangular/square coaxial waveguide filter achieves the highest degree of miniaturization, but that ridge and, especially, T-septum waveguide filter technology is advantageous with respect to stopband performance toward higher frequencies. In particular, a T-septum filter centered at 2.155 GHz is shown to block the entire frequency range up to 7.5 GHz. © 2002 Wiley Periodicals, Inc. Int J RF and Microwave CAE 12: 217–225, 2002.

A new set of edge-conditioned basis functions is used to determine the modal characteristics of a large variety of nonstandard waveguide structures. Since the electromag- netic field includes the proper edge conditions at metallic corners and since the new basis functions are readily Fourier transformed, a considerable reduction in computational effort with respect to standard modal field-matching techniques is observed. Similar to procedures involving other known sets of applicable basis functions, the analysis achieves a higher reliability level, as it completely avoids relative convergence phenomena. The method is demonstrated at the examples of several waveguide structures, such as the L-shape, T-shape, and cross-iris-shape waveguides; the rectangular coaxial waveguide; and the ridged circular waveguide. Results for the cut-off wave numbers of TE and TM modes are shown to be in excellent agreement with those from standard modal field-matching techniques and previously published data. Q 1998 John Wiley & Sons, Inc. Int J RF and Microwave CAE 8: 215)225, 1998.