Enhanced microwave power from triangular arrays of small Josephson junctions

We report on high frequency measurements of underdamped Josephson junction arrays consisting of two rows of parallel biased cells. The rf voltage generated on the junctions transverse to the bias current (horizontal junctions) is detected by a room temperature receiver in the W-band. In order to enhance the emitted power, it has been proposed (S.P.Y.) that the single horizontal junction in each cell be replaced by two (or more) horizontal junctions. This geometry has been proven to have better high frequency performance. Here we present comparative measurements of the output power from two row arrays of different geometries. Among the studied configurations, larger power is obtained from an array with square cells and two horizontal Junctions. In this array, the measured output power is up to about 2 times larger than that in the array with only one horizontal junction, and up to 20 times larger with respect to the array with conventional triangular cells. Experimental data are in good qualitative agreement with numerical simulations.