Background Coherent power combination technology is one of the most effective technical solutions to enhance the radiation power of high-power microwave systems, and has received widespread attention.

Purpose To achieve high-power microwave coherent power combination in Ka-band, a coaxial phase-locked relativistic Cherenkov oscillator is proposed and investigated in this paper.

Methods The device can be divided into two parts: an electron beam pre-modulation zone and a slow-wave energy extraction zone. The electron beam pre-modulation zone is designed for efficient absorption of externally injected microwave power and electron beam pre-modulation. The slow-wave energy extraction zone is responsible for deep modulation of the electron beam and efficient energy conversion. The frequency and phase of the microwave output are steered and regulated by the modulated electron beam.

Results When there is no external injected microwave power, the electron beam pre-modulation zone is inactive, and the device operates in a self-oscillation state, with an output microwave power of 766 MW and a self-oscillation frequency of 29.001 GHz. Under the condition of 5 kW injected microwave power at an injection frequency of 29.000 GHz, the device operates in a phase-locked state, with an output microwave phase jitter better than ±5°, an output power of 801 MW, and an output frequency of 29.000 GHz. Furthermore, the device's injection ratio and phase-locked bandwidth are −52 dB and ±30 MHz, respectively.

Conclusions The design methodology of the Ka band phase-locked relativistic Cherenkov oscillator can be directly extended to other high-frequency bands, establishing a viable technical framework for developing phase-locked HPM sources across millimeter-wave regimes.