A Novel Tunable Dual-Band Filter to Achieve a Wide Tuning Range Using One Tuning Element

This paper introduces a new configuration for tunable dual-band filters that can cover a wide tuning range while using just one tuning element. The resonator setup consists of two lambda/4 resonators, operating in adjacent frequency bands. These two resonators are connected to conducting rod mounted inside a cavity that is shaped to allow tuning the resonant frequencies of the two resonators as the rod rotates around its axis. The longer resonator covers the lower band of the tuning range, while the shorter one covers the higher band. Importantly, the tunability of these resonators is entirely independent. This means that when one of these resonators is coupled with the input probe, the other one is decoupled, and vice versa. A two-pole tunable filter has been designed with a tuning range from 2 to 3.5 GHz to verify the concept.