MICROWAVE PROPERTIES OF YBCO THIN-FILMS IN THE WEAKLY COUPLED GRAIN MODEL

Microwave properties of highly oriented thin YBCO films deposited on Y SZ and LaAlO3 substrates were investigated at 3 GHz and 4.3 GHz using microstrip resonator technique. The microwave characteristics of the f ilms 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 p roperties and could be considered at least as samples with ''strong'' weak links. Unloaded e-factor of microstrip resonators prepared from s uch films and Cu ground plane reached 3000 at 77 K.