Microwave properties of YBCO thin films in the weakly coupled grain model

Microwave properties of highly oriented thin YBCO films deposited on YSZ and LaAlO3 substrates were investigated at 3 GHz and 4.3 GHz using microstrip resonator technique. The microwave characteristics of the films on YSZ substrates were close to those of a medium containing weak links and were interpreted in the coupled grain model approximation. The YBCO films on LaAlO3 substrates demonstrated very good microwave properties and could be considered at least as samples with ''strong'' weak links. Unloaded e-factor of microstrip resonators prepared from such films and Cu ground plane reached 3000 at 77 K.