A varactor-tuned bandpass filter based on lowpass filter and shorted stubs

Abstract

This article presents a tunable bandpass filter (BPF) which is comprised of a chebyshev stepped‐impedance lowpass filter (LPF), three shorted stubs, three varactors, and some blocking capacitors. Detailed design of the LPF, the effects of the shorted stubs, the schematic of the tunable BPF, and the tuning strategies are investigated. By tuning the reversed‐bias voltages of the varactors, which are shunted with the low impedance of the stepped‐impedance LPF, the operating frequency of the filter is changed. After the tunable BPF is designed and simulated, one experiment filter has been fabricated and tested. The measurement results of the experiment filter show that the center frequency of the tunable filter can be reconfigured from 1.09 to 2.44 GHz if the reversed‐bias voltages are altered within 0–30 V. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:879–883, 2014