Present and projected performance of high-temperature superconducting filters

Because of the difficulties of growing high-temperature superconductor (HTS) films on both sides of a substrate, it is convenient to use normal-conducting ground planes to fabricate HTS microstrip filters. The insertion losses in a filter have been estimated from calculation of the effect of normal-conducting ground plane on the losses of an HTS microstrip line. It is shown that, even with a gold ground plane, the performance of current filters could be limited by mismatch losses rather than conductor losses, and that above Ka-band the benefits of using an HTS ground plane are only marginal.<>