Compact dual-band balanced bandpass filter based on circular SIW cavity

Abstract A compact dual-band balanced bandpass filter with high frequency selectivity and adjustable passband based on the perturbed circular substrate integrated waveguide cavity is firstly proposed in this paper. Two pairs of metallic vias are located at 45°direction of cavities to separate a pair of degenerate modes (TM 110 modes) to achieve the differential-mode (DM) dual-band response. Moreover, the perturbation vias can also be used to control the center frequency of the second DM passband while the first one still stays unaffected. The introduction of source-load coupling makes the filter exhibit excellent selectivity. And four controllable transmission zeros appear near two DM passbands. Finally, good common-mode suppression has been got owing to the proposed balanced structure. The measured results are in accordance with the simulated ones well.