Tunable dual-band bandpass filter for multi-standard applications

A new tunable dual-mode dual bandpass filter (DBPF) is presented based on coupled-line resonators structure. The center frequency and bandwidth can be individually tuned in each band with varactors, which are loaded at the end and middle of the coupled resonators. Varactor diodes can adjust the lower band from GPS to GSM standards (from 1.57 to 1.85 GHz), and the higher band for GSM, UMTS, WiFi and WiMAX applications (from 1.85 to 2.5 GHz). The LC equivalent model of the proposed filter is presented to analyze the resonator at odd- and even-mode frequencies to prove the favorable role of each varactor in tuning the center frequency and bandwidth. To validate the simulation results, the proposed filter is fabricated and measured. Measurement results are in good agreement with LC equivalent model and simulation results. (C) 2019 Published by Elsevier GmbH.