An evanescent-mode tunable dual-band filter with independently-controlled center frequencies

This paper presents the design of a tunable dual-band bandpass filter based on evanescent-mode cavity resonators with two capacitive loadings which result in two independently tunable resonant frequencies. Small filter size is achieved since the two modes share the same physical volume of a single cavity. In addition, the internal and external couplings of the filter can be controlled independently at the two passbands to create flexible frequency responses. An example of the proposed filter design is prototyped in a substrate-integrated fashion having two tunable passbands, a lower tuning band of 1.156-1.741 GHz with 3-dB bandwidth of 76-156MHz and insertion loss of 3.137-1.109 dB, and an upper tuning band of 2.242-3.648 GHz with 3-dB bandwidth of 125-553MHz and insertion loss of 7.551-1.299 dB.