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A Compact Varactor-Tuned Dual-Passband Filter Using Stepped Impedance Resonators

Abstract A compact dual-passband varactor-tuned filter using stepped impedance resonators (SIRs) is proposed in this paper. The SIRs with varactors centrally attached are coupled with an input/output transmission line. The structure is realized by dividing the input line from a normal coupling structure into two lines of a dual-finger structure. When the bias voltage is loaded, extra blocking capacitance is needless, which is good for eliminating parasitic and reducing insertion loss. The center frequency of the upper passband can be tuned from 1.18GHz to 1.64GHz by changing the value of the bias voltage across the varactor, and meanwhile the center frequency of the lower passband is fixed at 900 MHz. The measured results show that the proposed filter can provide flexible selectivity and good stopband characteristic. The measured performances are in good agreement with the simulated ones.