Compact Multichannel Filters and Multiplexers Based on Dual-Coaxial Resonators

In this brief, compact multi-channel bandpass filters and diplexers are proposed based on dual-coaxial resonators. One coaxial resonator is embedded into the other to form a dual-mode resonator without increasing the size, where the resonant section of one resonator acts as the shielding cavity of the other one. In this way, the two modes of the dual-coaxial resonator are ideally isolated and can be controlled independently. By properly designing the feeding and coupling structures between resonators, the two modes in one dual-coaxial resonator can be excited and coupled to construct different filter channels without influencing each other. Accordingly, multi-channel filters are realized. For verification, a dual-channel and a triple-channel filters are presented. Moreover, the filter channels in a dual-channel filter can be applied to design the diplexer, resulting in a compact size. Experimental results are presented with good in-band responses and high isolation.