TBCCO-microstrip filters based on dual-mode ring resonators

Superconducting n-pole filter realizations using lambda-dual-mode ring resonators are described. Results are presented for 2-pole filters and a 4-pole elliptic function filter having bandwidths smaller than 1% at a centre frequency of 4 GHz. Double-sided Tl2Ba2Ca2Cu3Ox-films with very low surface resistance (R-s < 150 mu Omega at 10 GHz and 77 K) on 2 " LaAlO3-substrates were used to fabricate the microstrip filters. The microwave performance of the 2- and 4-pole filters exhibits return loss more than 26 dB and 10 dB, respectively and low insertion loss (<0.5 dB) at 77 K. Furthermore there is a good agreement between the measured passband shape achieved with tuning elements and the computer simulation.