Broadband Cavity Filter Using Coaxial Resonator

This paper presents a metal cavity broadband bandpass filter, which incorporates two pairs of short-circuited metal cylinders within a cylindrical resonant cavity. Three independent resonant modes are excited in the resonant cavity to form a passband. The first two resonant modes are coaxial modes introduced by the added short-circuited metal cylinders, while the third resonant mode is a probe mode introduced by enhancing source-load coupling. The filter has a center frequency of 2.595 GHz and an absolute bandwidth of 610 MHz. A normalized coupling matrix of the filter was extracted using a comprehensive technical analysis method. The theoretical results derived from the coupling matrix were compared with HFSS full-wave simulation results, showing good agreement and confirming the design's validity.