Rigorous CAD of multiport coupled rectangular waveguide components

Based on the simple mode-matching key-building block of the single double-plane step discontinuity, a general modal admittance formulation is presented for the rigorous CAD of longitudinal multi-channel or -aperture coupled rectangular waveguide structures of arbitrary size and location. The theory involves an arbitrary number of rectangular coupling structures, different size and finite thickness of the coupling elements, as well as immediate higher-order mode interaction of all discontinuities. The efficiency of the design method is demonstrated at two new filter examples: a metal insert Ku-band bandstop filter (12-18 GHz, WR-62) with an E-plane bypass waveguide structure, and a low-cost lowloss Ku-band four-aperture iris coupled bandpass filter. The theory is verified by comparison with measured results.