A Fourth Order Waveguide Bandpass Filter with Compact Size on Transversal Coupling Topology

A fourth order waveguide bandpass filter (BPF) with 60 MHz bandwidth and center frequency at 3 GHz is presented in this letter. Compared to the conventional waveguide BPFs, the proposed filter is composed of cavities to be arrayed in a stacked manner, instead of the ladder manner. As a result, the whole filter only occupies a half or fourth size of its conventional counterparts, at the expense of increasing its insertion loss from 0.09 to 0.19 dB. Due to the transversal coupling topology, each cavity constituting the filter could be independently realized as a first-order sub-filter, simplifying the synthesis process. Besides, a pair of transmission zero (TZ) is generated at the two sides of passband so as to improve the selectivity of filter. The measured results reasonably support the validity of the proposed filter.