A Large-Frequency-Ratio Multichannel Bandpass Filter Based on Structure-Shared Mode-Composite Air-Filled Cavity Resonators

A novel structure-shared mode-composite (SSMC) air-filled cavity resonator is presented. It is found that by adding a series of periodic metallic pins with a lattice arrangement into a rectangular waveguide (RW) cavity, the cavity can be equivalent to several individual subcavities in the stopband of the periodic pin structures and equivalent to a loaded RW cavity with a miniaturized size at frequencies lower than the stopband. By this means, the SSMC cavity can simultaneously support two TE101-like modes at different frequencies, which is hard to fulfill in conventional cavity resonators. The frequency ratio of the two modes can be controlled flexibly by properly designing the arrangement of the loaded pin units. A dual-band bandpass cavity filter with a large frequency ratio of 4.7 is then designed with the use of three SSMC cavities. The filter has three 27-GHz channels and one 5.8-GHz channel, whose compact geometries are shared with each other successfully. Benefitting from the low-loss characteristics of the air-filled cavity resonators, promising insertion losses are obtained as well. The proposed SSMC cavity resonator and the filter provide a new means to realize the large-frequency-ratio multichannel components.