RF properties of low and high temperature superconducting films

In this paper we report on r.f. measurements performed on Nb3Sn and YBa2Cu3 O7-delta (YBCO) films grown by sputtering in different configurations. The measurements are performed using a microstrip resonator technique. The r.f. power dependence of the surface impedance Z(s) is studied at different tem peratures (4 K < T < T-c) and frequencies in the range 1-10 GHz. For Nb3Sn films a set of consistent data is reported in describing the non-linear beh avior observed. The nature of the breakdown field is investigated consideri ng the effects of a d.c. field externally applied. For YBCO films, differen t loss mechanisms are observed, depending on the quality of the sample. The data are discussed in the context of different models, in the attempt to u nderline similarities and differences between Low Temperature (LTS) and Hig h Temperature Superconductors (HTS).