Single-Element-Controlled Tunable Waveguide Diplexer With Quasi-Contiguous Channels

This article proposes the first single-element-controlled tunable waveguide diplexer (SC-TWD) with quasi-contiguous channels. The systematic design methodology for the proposed SC-TWD, including the practical synthesis theory and implementation method, is presented and demonstrated by a prescribed design. In detail, the synthesis method can be used to extract the element variable coupling matrix (EVCM) according to the given design specifications. Based on the extracted EVCM, we develop waveguide realization techniques for both resonator tuning and coupling control. With the synthesis and realization techniques, the SC-TWD can be implemented. The demonstrative SC-TWD consists of two cascaded-quartet (CQ) channels with synchronously tunable quasi-elliptic passbands and a fixed H-plane T junction as the signal combing configuration. As the control element is adjusted (driven by a stepper motor), the response of the diplexer maintains stable with a nearly constant 90-MHz channel gap, and only the frequency of the diplexer is tuned from 18.94/19.8 to 19.66/20.51 GHz [with total 700-MHz frequency tuning range (FTR)]. The tunable diplexer is fabricated, and it is assembled with an automatic driving mechanism. Good experiment results are measured and verify the proposed design methodology.