Signal-interference bandpass filters with dynamic in-band interference suppression

This paper focuses on the design of wide-band bandpass filters (BPFs) with dynamic in-band interference suppression. They are based on a new class of a signal-interference transversal filtering section (TFS) that consists of three signal paths that are effectively combined so that an absorptive notch (AN)-exhibiting theoretically infinite attenuation-is created within the BPF passband. In the devised implementation, the center frequency of the rejection band is reconfigured by altering the resonant frequency of two capacitively-loaded microstrip-line resonators that are incorporated into one of the propagation paths. The proposed design approach allows realizations of filter circuits with approximately 50% smaller size than that of conventional filter cascades shaped by the series connection of a BPF and an AN filter. For proof-of-concept validation purposes, an experimental prototype is built and measured. It demonstrates a tunable AN between 1.8 and 2.5 GHz located within a wide-band passband centered at 2 GHz.