Relativistic magnetrons (RMs) are promising high-power microwave (HPM) sources due to their high efficiency, low operating magnetic field, and compact configuration. Miniaturization and lightweight design are critical for expanding their applications. However, the structural dimensions of traditional microwave sources, particularly those operating in low-frequency bands, are constrained by the correlation between wavelength and radial size. As a result, the radial size of their slow-wave structures often needs to be of the same magnitude as the working wavelength, which seriously limits their miniaturization and compact design.

To address this issue, a C-band RM with all-cavity extraction based on metamaterials (MTMs) is proposed in this paper. This design aims to overcome the traditional design limitations, enabling an effective reduction in the device's radial size and weight.

Particle-in-cell (PIC) simulations are conducted using CST Studio Suite to verify the performance of the MTM-based RM. For comparison, a traditional RM with identical key operating parameters such as voltage, magnetic field, internal anode radius, and frequency is simulated to validate the impact of MTMs on reducing the anode outer radius. In addition, preliminary designs of the permanent magnets for both structures are carried out using magnetic field simulation software.

Simulation results show that under an input voltage of 675 kV and a magnetic field of 0.29 T, the designed MTM-based RM generates a TEM-mode output with a power of 1.42 GW at a frequency of 4.3 GHz, corresponding to an efficiency of 52.6%. Compared with that of the traditional RM, when the operating performance metrics are nearly the same, the external anode radius is reduced by 5.5 mm, representing a 12% reduction in size, and the weight of the permanent magnet is reduced by 22.8%.

These results demonstrate that the integration of MTMs effectively reduces the radial size of the C-band RM and the weight of the corresponding permanent magnet, which highlights the significant potential of MTMs in miniaturizing low-frequency HPM sources and provides a viable pathway for the development of lightweight, compact, and practical HPM systems.