Superconducting NbTi and Pb(Cu) bandpass filters

Superconducting Nb0.45>Ti0.55and Pb electroplated on Cu bandpass microwave filters have been constructed to investigate their low loss properties at 4.7 K. An interdigital stripline filter configuration was selected as the optimum structure for future applications. The filter was designed to operate at 8.45 GHz with an equal ripple bandwidth of 0.15 GHz. The insertion loss and the noise temperature contribution were measured at 4.7 K. In addition, the insertion loss was studied as a function of out-of-band power (up to 1 watt) and temperature (4.7 K to Tc). Results on an OFHC Cu filter are included for comparison.