Compact stepped-impedance resonator bandpass filter with two wide spread passbands

This paper presents the design method for a compact dual-band bandpass filter with a large ratio of center frequencies. Emphasis is placed on circuit synthesis for simultaneously matching the in-band responses at the two designated passbands. In an interdigital configuration, a 0.9/5.8 GHz bandpass filter is designed and fabricated. It is believed that this is the filter has the largest ratio of the center frequencies in comparison with those in open literature. The measured responses show good agreement with the simulation results.