We introduced a phase-locking mechanism of millimeter-wave magnetrons coupled through a carefully designed coupling bridge. For such a structure, two Ka-band 22-vane rising-sun magnetron circuits operated in the $\pi $ -mode were phase-locked tightly as a whole through a double-ridged coupler. Moreover, the double-ridged coupler was optimized to suppress mode competition between zero-phase and $\pi $ -phase difference mode, which achieved high-efficiency phase-locking. Total output power of the two identical magnetrons nearly doubled the output power of a free-running magnetron and efficiencies of them were nearly the same. Extension of this phase-locking mechanism to high-power applications appears feasible with more elements in an array of the millimeter-wave magnetrons.

The conventional mutual coupling phase-locking technique uses waveguides to directly connect magnetrons to operate as a whole device. However, this method is not suitable for large-scale phase-locked array applications due to the considerable challenges in achieving the required vacuum level. Thus, the modular magnetron applied to the mutual coupling phase-locking technique was proposed. First, the coupling structure was designed to combine a double-ridged waveguide and a rectangular waveguide for incorporating an RF window. Therefore, a single magnetron could be vacuumed as a modular unit. Subsequently, in simulation, two modular X -band magnetrons connected by a coupling bridge were verified to operate in a phase-locked state with a 0 $^{\circ}$ phase difference, with a phase-locking efficiency of 97.2%. Second, an experimental scheme capable of characterizing directly the phase difference between magnetrons was proposed. In the experiment, multiple sets of time-domain signal data were randomly sampled when the magnetrons were in a stable operating state. The experimental results were essentially consistent with the expected design phase difference of 0 $^{\circ}$ , as the phase difference between the two magnetrons remained consistently between 3 $^{\circ}$ and 5 $^{\circ}$ , with the phase-locking efficiency measured at 91.9%.

We proposed an external coupling structure of millimeter wave magnetron that has the potential to utilize the diffraction output for axial power extraction. For such structure, a 24-vane anode resonator operated in the π mode was tightly coupled to an external coupling structure operated in the 2π mode, through slots in the back walls of alternate cavities of the anode resonator. Moreover, we designed and simulated a Ka-band external coupled magnetron (ECM) in order to demonstrate the effectiveness of the new configuration. Simulation results showed the achievement of maximum microwave power of 108 kW at 35.0 GHz, with 29.6% efficiency.

The scheme of a high-efficiency phase locking based on a novel multiorder cascaded coupling structure is proposed to establish a high-power $2\times 2$ array consisting of four megawatt-level, S-band magnetrons. Every magnetron is designed with only one coupling port to match the cascaded coupling structure, in which a matched, cascaded, standing-wave field is built up to support the phase-locked mode with 0 phase difference between them. To obtain high-efficiency phase locking, the two-order, cascaded, standing-wave field is produced with a small portion of stored energy, which matches with four $\pi $ modes in four magnetrons. Particle-in-cell (PIC) simulation results show that a 0-phase difference between four magnetrons is obtained with every magnetron delivering a peak power of 2.4 MW, which is almost the same as the power of a free-running magnetron. The array can deliver a total power of up to 9.6 MW. The power conversion efficiency of the array is 65.2%, which is almost the same as that of the free-running magnetron. This demonstrates the high-efficiency phase locking. The scheme is promising in developing a large-scale array for higher-power microwave generation.

The first full demonstration of a high-efficiency phase-locking mechanism was accomplished in the millimeter-wave (mm wave) bands. Two modular Ka-band coaxial magnetrons were fabricated and phase-locked. The coaxial magnetron consisted of a conventional structure and a carefully designed coupling port that included an RF window. The coupling ports of two magnetrons were connected by coupling bridges to phase lock the coaxial magnetrons in zero-phase and π-phase difference mode, reaching phase-locking efficiencies of 93.4% and 95.6%, respectively. Two phase-locking modes were both verified by a mode detection system based on a symmetrical E-plane T-junction and a high bandwidth, high sample rate oscilloscope. Signals from the oscilloscope confirmed that phase-locking occurred after 25 ns and was reproducible from pulse to pulse. With higher power and more coaxial magnetrons in arrays, 1 MW may be achievable at Ka-band.

We present the design of a ten-cavity magnetron extracting TE11 mode through compact diffraction output (DO). The effect of the DO length and the depth of the vane on the performance of the ten-cavity magnetron are investigated to design a compact diffraction structure. By adjusting the length of DO and the depth of the tapered cavities to provide a proper Qe, the output power and power conversion efficiency have been improved. Simulation results of the magnetron with compact DO (the length of the DO is about half an operation wavelength) show that the microwave power of 3.0 MW with a high conversion efficiency of 62% at 2.4 GHz is achieved under an applied voltage of 56 kV and a fixed axial magnetic field of 0.24 T. In addition, the length of the anode block is designed longer than the cathode to arrange the permanent magnet, which has been preliminary designed.