Fully Reconfigurable Coaxial Resonator Filter with Dual Tuning Option

This paper presents a coaxial bandpass filter tunable in center frequency and bandwidth. Different tuning states are achieved by using movable posts in the resonator cavities. This technique changes the field strength coupling through the iris, which influences the bandwidth of a bandpass filter. Different insertion depths of two movable posts in each resonator allow for bandwidth variation at a constant center frequency. A variation of the gap between the dual-post changes the center frequency between 1.9 GHz to 2.9 GHz, resulting in a center frequency tunability of $\tau_{f0}=34\%$ and a bandwidth tunability between $\tau_{min}=50\%$ and $\tau_{\it max}=80\%$.