High-power microwave sources have been developed intensively during recent years for applications in high-power radars and communications, high-energy charged particle accelerators, thermonuclear plasma heating, and electronic defense warfare. A novel approach is described to generate large numbers of high-power microwave sources which not only operate at the same frequencies but also have their phases under control. One immediate application is by combining this large number of sources coherently to produce much higher power levels which a single device could not possibly reach. Using magnetron arrays to produce such unique microwave sources is feasible and has been demonstrated by computer particle simulations. However, this concept can very well be applied to other microwave devices.