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We have investigated experimentally a novel type of self-synchronizing two-dimensional Josephson junction array based on special symmetry breaking network architectures. The measurements confirm the theoretical prediction that in such "selector Josephson networks" the Josephson oscillators mutually synchronize into a coherent in-phase state and that such arrays are capable of emitting maximum coherent microwave power in the entire theoretically expected frequency range. The DC biased oscillator array operates coherently even without a reinjection of the generated microwave by an external load or by a resonator cavity. The selector network possesses a much higher tolerance against imperfections, perturbations and load parameter variations than conventional regular two-dimensional or one-dimensional arrays. The experimental sample has been fabricated in an industrial process using Nb-technology, in effect providing relatively large spreads in the array junction parameters. The measured frequency range goes from 85 GHz up to 380 GHz with a maximum microwave power of 0.16 /spl mu/W matched to a coupled load for an array with only 100 active Nb-AlO/sub x/-Nb junctions.