With the development of high-power microwave technology, the demand for high-power microwave system has moved towards miniaturization and compactness. Realizing high-efficiency and high-power operation under low magnetic field is an important trend for miniaturization and compactness.

In order to improve the power and efficiency of high-power microwave source under low guiding magnetic field (< 0.4 T), a high-efficiency coaxial dual-mode relativistic Cherenkov oscillator (RCO) under a low guiding magnetic field is proposed.

Traditional over-mode RCO is mostly limited to single mode operation, which greatly restricts the further improvement of efficiency. The proposed RCO adopts the dual-mode working mechanism, works in both coaxial quasi-TEM mode and TM₀₁ mode. The dual-mode working mechanism allows the electron beam to interact with multiple modes, thereby improving power capacity and efficiency simultaneously. In particle-in-cell simulation, when the guiding magnetic field is only 0.35 T, the RCO achieves a microwave output of 3 GW with a beam-wave conversion efficiency of 40%. At the same time, aiming at the RF breakdown phenomenon in the experiment, the power capacity is improved by increasing the number of slow wave structure periods, which is verified by both simulation and experiment.

In the experiment, under a magnetic field of 0.37 T, the output power is 2.85 GW with a pulse width of 57 ns and a conversion efficiency of 34%.

Both simulation and experimental results show that the proposed RCO can work stably with high efficiency and high power under the low magnetic field, and the results obtained under the low magnetic field provide strong support for the development of miniaturization of high-power microwave systems.