Design of quasi-independently reconfigurable dual-band BPF

Abstract

In the paper, a dual-band microstrip bandpass filter (BPF) featuring high selectivity and quasi-independently reconfigurable frequencies is proposed. The proposed BPF is realized using two sets of asymmetric quarter-wavelength short stub-loaded resonators. The source-load coupling is achieved by adopting a parallel-coupled three-line structure, which can generate multiple transmission zeros (TZs) and enhance the selectivity of each passband greatly. By adjusting the electrical length ratio of the resonators, the center frequencies of the two passbands can be controlled quasi-independently. Ultimately, four varactor diodes of SMV1430 are employed to realize the dual-band reconfigurability. The tuning ranges of the two passbands of the proposed BPF are 430 MHz and 900 MHz, respectively, with insertion loss consistently below 5 dB across the entire tuning range. To validate the design methodology, a prototype of the filter was fabricated and tested, demonstrating good correlation between measured and simulated results.