Experiments with a 31-cm high-T_c superconducting thin film transmission line

Electrical time-domain measurements and transmission response measurements were made using a 31-cm-long YBaCuO superconducting thin-film microstrip line and a YBaCuO ground plane, each on separate 1-cm LaGaO₃ substrates, with a 125-μm sapphire substrate serving as the dielectric insulator. Degradation of the performance of the line for currents up to the critical current density and for magnetic fields moderately above the lower critical magnetic field H_c1 was evaluated in a variety of simple measurements. The results suggest that current near or exceeding the critical current density, and not magnetic fields exceeding H_c1 , is the major factor degrading the performance of the superconducting microstrip line.