Bandpass Filter with Tunable/Switchable In-band Interference Rejection

This paper presents a wideband bandpass filter (BPF) with a tunable and switchable in-band notch. This allows the RF front-end to pass the signal of interest uninterrupted in the absence of an in-band interferer, and reject part of the passband in case a narrowband interferer exists. The BPF is based on a two-path architecture, loaded with resonators on one of the paths to deliver an absorptive notch. The resonators are tuned with varactor diodes, and are deactivated when the diodes are in forward bias. The implemented proof-of-concept hardware operates in the 4.8–7.8 GHz frequency range, with an in-band notch tunable between 5–6.25 GHz, when activated. The transmission lines were implemented as striplines, resulting in a measured insertion loss of 0.6 dB.