PHASE-LOCKING OF HTS JOSEPHSON-JUNCTIONS CLOSED INTO A SUPERCONDUCTING LOOP

We investigated the mutual interaction of four high-T-c Josephson junc tions which were closed into a superconducting loop. Phase locking of all four junctions was demonstrated in the temperature range from 4.2K to 48K. Locking intervals of 18% of the critical current were obtaine d up to voltages corresponding to a frequency of 180GHz, according to the second Josephson relation. By comparing our data with numerical si mulations, we could show that the junctions were locked in the in-phas e state and that the circuit can act as a source of coherent radiation which can deliver power to a load.