Multi-Band Bandpass Filters with Multiple Levels of Transfer-Function Reconfigurability
This paper reports on the RF design of multi-band bandpass filters (BPFs) along with a simple tuning method to obtain multiple levels of transfer-function reconfigurability. The proposed multi-band BPF concept is based on multi-resonant cells that are incorporated within the two transversal paths of a doublet. It is shown that by solely reconfiguring the resonant frequencies of its constituent resonators, multiple quasi-elliptic-type passbands can be created and controlled in terms of: i) center frequency, ii) bandwidth, and iii) number through their intrinsic RF switching and/or merging. In addition, the proposed filter concept allows for the realization of i) an all-reject state and ii) a single-band BPF state with >5.1:1 BW tuning. The theoretical design principles of the multi-band BPF approach are presented by means of coupling routing diagrams and synthesized examples. For proof-of-concept demonstration purposes, a tri-band BPF microstrip prototype was designed, manufactured, and measured.