Coherent radiation in serial arrays of Josephson junctions

We measured IV-characteristics of a planar array of about 362 shunted intrinsic Josephson junctions in microbridges made from the Tl₂Ba₂CaCu₂O₈ layers which were grown epitaxially on 20° misaligned LaAlO₃ substrates. The IV-characteristics contained resonant particularities (jumps of voltages) with a main period of 17 mV. We showed that the origin of particularities was the interaction of Josephson generation with the internal resonant mode of the system. We modeled this interaction considering the radiation of junctions into the transmission line and found that strong synchronization of junctions appeared in the vicinity of the first particularity. The estimate of the ac power emitted into free space was 0.05-0.1 microwatt, whereas the power of 0.3-0.5 mW was emitted inside the resonant system.