Surface resistance of superconducting films by a microstrip ring resonator technique

A ring microstrip resonator technique has been set up to measure the surface impedance of superconducting films in the range 1-20 GHz as a function of temperature and both DC and RF field amplitude. The method has been tested on Nb films and extended to both metallic compounds of interest for thin-film-coated accelerating cavity applications (NbTiN) and high T/sub c/ oxide superconducting films of potential interest for microwave circuit applications such as high-quality YBCO and BSCCO compounds, including, in the latter compound, samples obtained by liquid phase epitaxy. The results confirm that losses at the grain boundaries or twinning planes play an important role in determining the residual term and the high magnetic field degradation of the surface resistance in both metallic and high-T/sub c/ superconducting films.<>