A Novel Waveguide Quadruplet Combining Dual- and Single-Mode Cavities for the Realization of a Minimum-Length Pseudo-elliptic Filter

This paper presents an original waveguide quadruplet where dual- and single-mode cavities are combined to realize pseudo-elliptic responses while minimizing the longitudinal dimension of the filter. The resulting length of the structure, i.e. the distance between the input and output waveguide flanges, is indeed equal to the one of a lone cavity, which in this case is a dual-mode cavity properly excited at both source and load. Two additional single-mode cavities lying entirely on the transversal plane, i.e. the plane orthogonal to the direction of propagation, are respectively coupled to each of the two modes of the dual-mode cavity. The proposed configuration allows for the realization of pseudo-elliptic responses with two symmetric transmission zeros, as well as asymmetric responses with three transmission zeros. To demonstrate the feasibility of the proposed minimum-length quadruplet, an X-band prototype filter has been designed, manufactured, and successfully measured.