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Dual‐band bandpass filters using coupled fork‐shaped resonators with controllable fractional bandwidths

This article presents a novel dual‐band bandpass filter with controllable fractional bandwidths for the upper passband.Two open‐circuited stubs are attached to the center of a stepped impedance resonator to form a fork‐shaped resonator. As one port of this resonator is on the ground plane for an odd‐mode equivalent circuit, the variations of resonant frequencies are analyzed just for an even‐mode excitation. From the analyses, three tentative resonant frequencies are decided, and then the dimensions of the resonators are optimized. For coupled resonators, by optimizing the overlapped lengths of outside‐ and center‐open stubs, the desired center frequencies of the dual passbands and the tunable characteristics of the upper passband are obtained, respectively. The measured results of the proposed dual‐band filters on three stages are confirmed with the simulated results. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:722–725, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26653