Realization of a Highly Miniaturized Wideband Bandpass Filter at the UHF Band

A niobium-based low temperature superconducting 7-pole bandpass filter with a wide bandwidth at the UHF band is designed and tested. The filter has a relative bandwidth of 80% and is extremely miniaturized with a total dimension of less than 3 mm × 1 mm. The filter topology is that of the bandpass transformed lowpass prototype filter with alternating shunt and series resonators. The filter has a wide spurious free stopband up to 4 GHz. The measured results are in very good agreement with theoretical design predictions.