A combined mode-matching and coupled-integral-equations technique for the design of narrow-band H-plane waveguide diplexers

This paper focuses on a new concept in diplexer design, namely a combination of the standard mode-matching technique (MMT) with the coupled-integral-equations technique (CIET), the latter being used only for the synthesis and analysis of the individual channel filters. Several major advantages are associated with this approach. First, for a full-cycle analysis of a diplexer configuration, the combined method reduces the CPU time significantly compared to ordinary MMT. Secondly, the number of basis functions in the CIET can be reduced during optimization without a shift in frequency as matrix sizes do not depend on the number of modes. In standard MMT algorithms, a reduced number of modes is usually associated with a (sometimes remarkable) shift towards lower frequencies. Thirdly, the CIET-at almost no additional computational cost-allows the extraction of the generalized scattering matrix so that the results are easily interfaced with mode-matching calculations of other components.