Compact 2-pole and 4-Pole 1.5–0.9 GHz constant absolute bandwidth tunable filters

Compact 2-pole and 4-pole tunable filters have been developed to cover the 0.9–1.5 GHz bandwidth. The proposed filters are based on a mixed coupling to ensure a near constant absolute bandwidth during tuning operation. They are fabricated on a duroid substrate (εr=3.2) and tuned using varactor diodes. The 2-pole and 4-pole filters respectively result in a 60 +/−9 MHz and a 74 +/− 15 MHz 3-dB absolute bandwidth on a wide tuning range (> 40 %).