High-Q LaAlO/sub 3/ dielectric resonator shielded by YBCO-films
We have investigated a dielectric resonator consisting of a single crystalline LaAlO/sub 3/-cylinder shielded by a cylindrically shaped copper cavity with endplates made from epitaxial films of YBa/sub 2/Cu/sub 3/O/sub 7/ or niobium. For YBa/sub 2/Cu/sub 3/O/sub 7/ films unloaded quality factors Q/sub 0/ of 4.5/spl middot/10/sup 5/ at 10 K and 1.3/spl middot/10/sup 5/ at 77 K were achieved at 11.6 GHz using a compact shielding cavity with a diameter of 15 mm and a height of 3.8 mm. The loss contributions of the dielectric resonator, the normal conducting cylinder wall, and the superconducting endplates, with one of them being separated by a small distance h from the dielectric cylinder, were calculated by modeling the electromagnetic fields of the TE/sub 0/spl nu//spl mu//-modes. The dielectric loss tangent of the LaAlO/sub 3/-cylinders was found to be 10/sup -6/ at 4.3 K and f=11.6 GHz and to increase slightly with temperature. Moreover, the calculations indicate the tunability of the resonance frequency by changing h over a range of 1 GHz without significant degradation of Q/sub 0/. These resonators are considered to be useful devices for stable oscillators and narrowband filters.<<ETX>>