RF properties of low and high temperature superconducting films

In this paper we report on r.f. measurements performed on Nb3Sn and YBa2Cu3O7-d (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 ZS is studied at different temperatures (4 K < T < Tc) and frequencies in the range 1 - 10 GHz. For Nb3Sn films a set of consistent data is reported in describing the non linear behavior observed. The nature of the breakdown field is investigated considering the effects of a d.c. field externally applied. For YBCO films, different 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 underline similarities and differences between Low Temperature (LTS) and High Temperature Superconductors (HTS).