Tunable bandstop filter with a 17-to-1 upper passband

Tunable bandstop filters with wide upper passbands are important in systems that operate over a wide frequency range in the presence of dynamic interference. This paper shows a tunable bandstop filter with a 17-to-1 ratio between its upper passband cutoff frequency and its lowest notch center frequency. The wide upper passband results from the combination of highly-loaded resonators and a new external coupling structure that is well-matched to the filter's port impedance over a wide frequency range. The filter described in this paper can attenuate a UHF signal while allowing for low-loss transmission or reception of signals at X-band frequencies.