Phase locking of HTS Josephson junctions closed into a superconducting loop

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