We report on the results that we have obtained on systems consisting of two arrays of Josephson junctions coupled by means of stripline techniques. One array, formed by a series connection of long junctions is operated on magnetic field-induced singularities of the current–voltage characteristics (Fiske steps) and emits radiation at 250 GHz. The other array detects the emitted radiation and exhibits Shapiro step sum voltages generated by the coherent operation of several hundred junctions.