Full-wave design of canonical waveguide filters by optimization

Full-wave design of canonical waveguide filters by optimization is presented. For full-wave modeling, the filter structure is decomposed into the cascade connection of waveguide step and/or bifurcation discontinuities, and waveguide T-junction discontinuities. Generalized scattering matrices of each discontinuity are obtained using the mode-matching method, from which the filter response can be obtained using the cascading procedure. For optimization design, an error function to be minimized is constructed according to the design specification. Polynomial curve fitting is used to characterize each discontinuity to speed up the optimization process. Full-wave approximate synthesis of input/output and inter-cavity coupling iris dimensions is also described. Design examples of four- and six-cavity canonical waveguide filters are presented to demonstrate the feasibility of the design approach. An experimental four-cavity filter is machined and tested. Measured results are in good agreement with computed results.