1.5-GHz band-pass microstrip filters fabricated using EuBaCuO superconducting films

This letter reports the properties of 1.5-GHz band-pass microstrip filters fabricated using EuBacuO superconducting films. Although 3- and 4-pole filters constructed using a superconductor and a silver ground plane exhibited good reproducibility and very low insertion loss of 3∼5 dB at 70 K, in comparison with Cu filters with 16∼27 dB loss at 77 K, the insertion loss was almost constant at temperatures below 70 K. In contrast, the insertion loss in the 4-pole filter with a superconductive ground plane was 1.2 dB at 70 K and 0.6 dB at 28 K. The center frequency and bandwidth at -3 dB were, respectively, 1.45 GHz and 1.4% at temperatures below 70 K.