Compact varactor-tuned dual-mode filter with center frequency and bandwidth control

This article presents a novel compact tunable bandpass filter (BPF) with center frequency and bandwidth control based on open-circuited stub-loaded half-wavelength resonator (SLR). Analyses of frequency and bandwidth tunable of the proposed resonators and external quality factor implemented by tunable J inverter to gain a stable filtering performance are discussed. Both theory and experiment are provided to validate the proposed filter. From the experimental results, it is found that the proposed filter can keep a constant bandwidth over the frequency tuning range with an insertion loss of less than 0.9 dB and increase the 1-dB bandwidth from 120 MHz to 430 MHz when center frequency locates at 1.3 GHz with an insertion loss of 0.5-1.7 dB. Simulation and measurements are in excellent agreement. (c) 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:803-806, 2016