Compact microstrip stepped impedance dual-band bandpass filter with high selectivity

A compact tri-section stepped impedance dual-band bandpass filter is presented. The tri-section stepped impedance resonator (SIR) is adopted to result in two tunable passbands. It offers further reduced overall size than conventional two-section SIR. The locations of the two passbands can be adjusted by changing the ratio of impedance. The measured results exhibit a good dual-band filtering performance with return losses higher than -17dB. Two transmission zeros ensure a high out-of-band rejection. With the new structure, the filter has not only high selectivity but also compact size.