Radiation emission from triangular arrays of Josephson junctions

High frequency properties of underdamped Josephson junction arrays consisti ng of parallel biased triangular cells having a Josephson contact in each b ranch are studied. At the applied magnetic field corresponding to half a fl ux quantum in every cell, the junctions transverse to the bias current ("ho rizontal" junctions) oscillate in phase. The radiation emitted by these jun ctions is measured using a double-side band superheterodyne receiver in the 80-120 GHz range, It is found that the radiation has a spectral linewidth of about 80 MHz, which is close to that expected from the RSCJ model for th e de biased "vertical" junctions. Our experimental data confirm that both t he frequency and the linewidth of the horizontal junction oscillations are controlled by the rotating vertical junctions. In the double row array, whe n the two rows are simultaneously driven at the same voltage state, we obse rve a weak radiation peak, which can be explained in terms of a "mixed-mode " dynamics. Numerical simulations that predict this mechanism are in good a ccord with experiment.