The power derived from N identical power amplifiers are combined in any one of N different output ports by controlling the relative phases of the signals propagating along N different transmission lines energized, respectively, by the N amplifiers. In particular, the N output ports are longitudinally distributed along said lines, and are coupled thereto through networks that are responsive to a different mode of excitation, where each mode is a different arrangement of input signal phases. It is an advantage of such a system that all the switching is done in the amplfiiers'' relatively low-power input circuits rather than in the high-power output circuits.