Microwave superconducting filters

Four-pole, parallel-coupled microstrip line filters were fabricated using epitaxial YBa/sub 2/Cu/sub 3/O/sub 7/ (YBCO) films deposited by off-axis sputtering on LaAlO/sub 3/ substrates. Filters were made with and without superconducting ground planes. Because it is not yet possible to grow in-situ epitaxial films on both sides of a substrate, two separate substrates were used, one for the filter and one for the ground-plane. The devices were packaged so that the microstrip-to-ground-plane distance was the thickness of one of the substrates (0.43 mm). Passband characteristics, input power, and temperature dependence were measured, as well as the thermal cycling stability.