volume | PIER Journals

Abstract

This paper presents a varactor-tuned low-pass filter (LPF) with high sharpness-factor and steep stopband suppression at different tunable frequencies using defected ground structure (DGS). By periodic loading four series-parallel capacitive compensation DGS units with high quality factor Q and the varactor diodes in shunt, a central filter is formed. To suppress the spurious passband and improve the rejection of stopband, four extra units in the form of split-ring stepped-impedance DGSs also with high Q factor were introduced and loaded at both ends of the central filter. The prototype of the proposed LPF is designed, fabricated and measured. Simulation and measurement results exhibit a good agreement. The measured results demonstrate a continuous tuning range of 12-13.5 GHz for the cut-off frequency, with an insertion loss in the passband better than 0.8 dB and a sharpness factor less than 1.08 across the entire range. The stopband rejection level is better than 30 dB and can be extended up to 40 GHz.

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Dr. Wei Tang

Dr. Hao-Ran Zhu