Microwave radiation from zero field singularities in stacks of two long Josephson junctions

We present experimental results on the radiation emitted from two-stacks of long Josephson junctions with double overlap geometry. Microwave radiation was received from the voltage-locked Zero Field Steps of the c/sup -/ family, corresponding to fluxon-antifluxon pairs oscillating in the stack. It was also received from other current singularities, interpreted as resonances excited by the magnetic field generated by the nonuniform bias currents. In the former case, there is experimental evidence for an appreciable signal, while, theoretically, the net signal produced is expected to be vanishingly small. This event can he explained in terms of a possible delay between the component signals, as the junctions in the stack do not have identical length.