Design of an X-band injection phase-controlling overmoded relativistic backward wave oscillator in a low magnetic field

An X-band injection phase-controlling overmoded relativistic backward wave oscillator (RBWO) is presented, which operates at a significantly reduced magnetic field of 0.45 T while achieving 53% power efficiency. The key innovation of this work is the implementation of phase controlling for gigawatt-level microwave in overmoded slow wave structures (SWSs) operating in dual modes, while such SWSs were previously employed only in phase-uncontrolled RBWOs. Theoretical analysis demonstrates that maximum electron beam active power extraction is achieved when both modes operate at an identical frequency. Particle-in-cell simulations validate the design, yielding an output microwave of 1.7 GW at 10 GHz. Under a 500 kW input signal, a phase-controlling bandwidth of ±20 MHz with an accuracy of ±10° is achieved. This work demonstrates the feasibility of high-performance, compact high power microwave sources with substantially reduced magnet requirements.