Miniature HTS spiral cavity resonator for mobile telephone bands

Work on a miniaturized cavity resonator operating at around 900 MHz is repo rted. This uses a superconducting spiral resonator to enable its size to be reduced substantially in comparison with conventional cavity realizations: the new cavity fits within a 2 cm cube. The superconducting spiral structu re was made of YBa2Cu3Ox or Tl2Ba2CaCu2Ox on a 1 cm(2) substrate of lanthan um aluminate (LaAlO3). The unloaded e-factors at temperatures below T-c wer e ten and four times greater than with an equivalent copper spiral, for YBC O and TBCCO respectively. The reason for the poor result with TBCCO is pres umed to be due to low film quality. The Q factors showed a relatively small power dependence from -40 dBm to +11 dBm input power. A simulation of the cavity predicted resonance at 860 MHz, compared with 840 MHz measured, and a Q-factor similar to that found with YBCO (approximate to 1000).