A tri-band bandpass filter using stub-loaded SIRS with controllable bandwidths

In this article, we present a tri-band bandpass filter (BPF) based on a stub-loaded stepped-impedance resonator (SIR). The proposed resonator has the compact size based on a short-circuited SIR as well as the controllability of three resonant frequencies by adjusting impedance ratios. Bandwidths for the first and second passbands can be independently controlled using two coupling paths between resonators, while the third bandwidth can be designed by adjusting dimensions of an open-stub loaded to the resonator. Two-pole tri-band BPF is designed and tested at center frequencies of 1.575, 2.4, and 3.5 GHz with fractional bandwidths of 10%, 6%, and 4%, respectively. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:2907–2910, 2014

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