Modification of superconducting bandpass filter structures using different image impedances

A new bandpass filter design is presented which uses arbitrary image impedance of the superconducting thin film coupled lines. In order to investigate the performance of different superconducting bandpass filters with different image impedances, we have selected and designed 4-pole Chebyshev 50 (Omega) and 75 (Omega) coupled line superconducting bandpass filters which have the same passband of 11.7 approximately 12.4 GHz. The measured result of the 75 (Omega) coupled line superconducting bandpass filter agrees with the result of the 50 (Omega) coupled line superconducting bandpass filter. The technique used in this paper to change the filter structure is particularly attractive because of its application to improve the power-handling ability of superconducting passive device and its possibility to reduce the size of superconducting thin film microwave device which has the limitation of superconducting thin film size.