Superconducting Coplanar Interdigital Filter With Robust Packaging

A superconducting three-pole Chebyshev band-pass filter is designed, fabricated and tested to be used in microwave set-up in Cryogenic refrigerator. The design is based on the reflected group delay method and it is implemented based on the interdigital configuration in a coplanar waveguide with Niobium (Nb) over Sapphire dielectric. The filter response based on the circuit model (lumped element, J-inverter and coupling matrix synthesis), full wave simulation of its physical realization and s-parameter measurement are compared. With the proper packaging this filter shows only one band-pass from 9.7 GHz to 10.5 GHz over a large span of frequency from 0 GHz to 20 GHz.