Compact but powerful and efficient magnetrons are in service for various high-power microwave applications owing to their additional superiority of low-cost mass production. However, the magnetron's inherent instability in frequency and phase over a relatively wide spectrum limits the versatile availability of the magnetron for possible advanced applications, including a long-distance wireless power transfer system (WPTS) that employs the magnetron as a unit source of a phased array system. The authors present a methodology suppressing a long-term instability of the S-band commercial magnetron harnessed by the phase-locking-loop (PLL) injection controlling and fixing the phase and frequency of the magnetron to the extent of the precision for a WPTS. The long-term drift of the phase exactly replicating the anode voltage fluctuations is successfully suppressed by the implementation of a DC power supply to compensate the cooling effects of the heater, which contributes to extreme stabilization of the phase (peak to peak 0.2 • ) for high-power (1kW). And eligibility for the unit source of a phase-arrayed WPTS is proven by varying the output power while maintaining the phase at a constant.INDEX TERMS Magnetrons, noise, phase-locking-loop (PLL), series parallel resonant converter (SPRC), cooling effect.

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