Dual-band bandpass filters with multiple transmission zeros using /4 stepped-impedance resonators

Two novel dual-band microstrip bandpass filters (BPFs) with multiple transmission zeros are proposed in this article. The dual-band BPFs with second-order bandpass responses are due to two /4 stepped-impedance resonators (SIRs). Two passbands (center frequency ratio f(s)/f(0) is 2.36) are realized based on the asymmetric SIRs. The transmission zeros near the passbands can be adjusted conveniently using the stopband transmission characteristic of the open/shorted coupled lines. Two planar microstrip dual-band BPFs (epsilon(r) = 2.65, h = 0.5 mm) with four and six transmission zeros are designed and fabricated. High selectivity and good in-band performances can be achieved in the proposed filters.