Design of a Tunable Dual‐Band Bandstop Filter Based on Dual‐Mode Resonators

ABSTRACT A tunable dual‐band bandstop filter based on dual‐mode resonators was proposed in this letter. The dual‐mode resonator was constituted on an asymmetric stub‐loaded resonator which can ensure that both the odd‐mode and even‐mode maintain strong coupling with the main transmission line. Additionally, the asymmetric structure can increase the coupling between the transmission line and resonators without adjusting the distance between them. Through adjusting the tunable capacitors loaded on the dual‐band resonators, the independent tuning of the center frequency for both the odd‐mode and even‐mode stopbands can be achieved, and good rejection level can also be maintained. A third order tunable dual‐band bandstop filter was designed and fabricated. The simulated results were agreement well with the measured ones.