Compact dual-band bandpass filter using stub-loaded stepped impedance resonators with mixed electric and magnetic couplings

A compact dual-band bandpass filter (BPF) using two stub-loaded stepped impedance resonators (SLSIRs) is presented. The first and the second resonant modes of the SLSIR can be independently controlled by the length of the open stub and the impedance ratio of the SIR, respectively. Mixed electric and magnetic coupling between two SLSIRs of the dual-band BPF are utilized to produce multiple transmission zeros in the filter response. A dual-band BPF operating at 1.27 and 2.45 GHz is designed and fabricated, and it demonstrates high passband selectivity and large isolation between the two passbands. The measured minimum insertion losses are 0.90 and 0.92 dB, and the passband return losses are better than 13 and 18.5 dB, respectively.