Novel Dual-Band Filter Incorporating Defected SIR and Microstrip SIR

This letter presents a novel approach to design dual-band bandpass filter by using defected stepped impedance resonator (DSIR) and microstrip stepped impedance resonator (MSIR). A pair of MSIRs on the upper plane forms a cross coupled filtering passage, and a pair of DSIRs at the lower plane constructs a linear phase filtering passage. Both of them are fed by a common T-shaped microstrip feed line with source-load coupling. Then they are directly combined to construct a compact dual-band filter with two passbands centering at 2.35 GHz and 3.15 GHz, respectively. The measurement results agree well with the full-wave electromagnetic designed responses.