Performance of a high T c superconducting ultralow-loss microwave stripline filter

Abstract

We report the successful fabrication of a five‐pole interdigital stripline filter made of the 93 K superconductor Y₁Ba₂Cu₃O_y coated on a silver substrate, with a center frequency of 8.5 GHz and an extremely high rejection ratio of 80 dB. The lowest insertion loss measured was 0.1 dB at 12 K, with a return loss better than 16 dB, representing significant improvements over a similar Cu filter, and comparable to low T_c filters. The insertion loss appears to be limited by extrinsic factors such as tuning mismatch and joint losses, and not by the superconducting material losses.