Design of Multistate Cavity Diplexers Based on Coaxial Resonators

The design approach for multistate diplexers based on coaxial resonators is presented for the first time in this letter. By partitioning a large cylindrical cavity into multiple sections, a wide range of frequency channels is established, enabling the formation of different states for the diplexer through the selection of specific frequency channels. By introducing cross coupling in the resonators, a transmission zero is achieved within each channel, resulting in sharp out-of-band rejection skirts. The proposed multistate diplexers exhibit improved performance along with compact structures. A third-order four-state diplexer (FSD) is designed and presented, and the same methodology can be applied to create the mth-order and n-state diplexers. To validate this concept, the FSD is fabricated and measured, with the measurement results exhibiting good agreement with the simulation results.