Frequency-tunable bandstop-bandpass dual-function microwave filter

This letter presents a frequency-tunable, dual-function, microwave filter with both bandpass and bandstop functionalities. The filter uses a single switch to change the functionality minimizing the insertion loss, and it can replace a traditional filter bank structure that contains two filters and two switches. Frequency-tunable substrate-integrated waveguide (SIW) resonators are adopted in this filter design. Measured results show that both bandpass and bandstop responses can be tuned from 3.0 GHz to 3.6 GHz. The measured minimum insertion loss at the center frequency is 1.1 dB for the bandpass mode and the attenuation at the center frequency is greater than 40 dB over the entire frequency tuning range.