Emission of microwaves from d.c.-biased y-ba-cu-o thin films

We measured microwave emission from d.c. current biased Y-Ba-Cu-O thin films in the temperature range from 300 to 4.2 K. Maximum radiated power (noncoherent) detected at 11.3 GHz within 1 GHz bandwidth was 8 pW at 4.2 K. Radiation level was sensitive to the temperature, d.c. bias current, and applied external magnetic field. We interpret our results in terms of flux motion in the two-dimensional network of Josephson coupled superconducting grains. Some measured emission peaks may suggest that a synchronous radiation of the array of Josephson junctions is present.