Surface resistance measurement of modified QMG superconducting bulks

We investigated the microwave properties of high-temperature superconductor (HTS) bulks for high-power microwave applications. The HTS bulk samples of Dy–Ba–Cu–O and Gd–Ba–Cu–O, were prepared using the modified quench and melt growth (QMG) process. The relationship among the bulk surface mirror polishing process, oxygen annealing process, and surface resistance (Rs) was also investigated. The Rs of the HTS bulks was measured using the dielectric resonator method at 21.8 GHz for the TE011 mode. The measurement temperature was varied from 20 to 95 K. We found that the annealing after surface mirror polishing was more effective to obtain low Rs than polishing after annealing. Although the Rs value of the optimized Dy–Ba–Cu–O bulk sample at 20 K was twofold larger than that of the high-quality YBa2Cu3O7−δ thin film fabricated by THEVA GmbH, the Rs value was even low enough to be used for microwave devices. These results indicate that Dy–Ba–Cu–O bulk superconductors are feasible for applications to high-power transmit filters for mobile communication systems.