Compact dual-band balanced bandpass filter using CRLH resonator with intrinsic common-mode suppression and multiple transmission zeros

Abstract

In this paper, a newly composite right-/left-handed (CRLH) resonator is presented and applied to constitute a compact dual-band balanced bandpass filter (BPF). The proposed CRLH resonator contains two spiral coupled line segments. By imposing the differential-mode (DM) and common-mode (CM) excitation, the DM and CM equivalent circuits of the presented resonator and their lumped-element circuit models are built for investigating the resonant property. The CRLH resonator has two DM resonances and are adopted to design two DM passbands. Also, the CM resonances are all far away from DM resonances, achieved intrinsic desirable CM rejection within DM frequency range without any auxiliary elements. Attributing to the mixed electric and magnetic coupling between two coupled resonators and the introduced source-loaded coupling, multiple transmission zeros are obtained and therefore enhance the selectivity and attenuation in stopband. Finally, a well-designed dual-band balanced BPF is fabricated. Verification of the presented structure and design method’s validity is evidenced by the measured results, which are in agreement with the simulations.