Cascaded Quarter-Circular Mushroom Resonators loaded to Substrate Integrated Waveguide for Semi Selective Bandpass Filter

A bandpass filter with partial sideband selectivity based on two cascaded quarter-circular mushroom resonators (QcMRs) loaded to substrate integrated waveguide (SIW) is presented in this paper. Two cascaded mushroom resonators having shapes of quarter-circular metal patch are placed face to face along their linear edges and loaded into a SIW cavity. The direct electrical coupling between the excited fundamental modes of these two QcMRs controls the maximum power transfer within the resonators loaded into the SIW cavity. A dual-pole passband with a transmission zero (TZ) at a higher sideband is generated after carrying out an EM simulation. The proposed compact filter structure occupies an area of $0.5 \lambda_{0}$ $\times 0.3 \lambda_{0}$ and has its center frequency (CF) at 4 GHz with a 0.75 dB of minimum insertion loss.