High-Efficiency Sheet-Beam Extended Interaction Oscillator Operating in the Hard Self-Excitation Regime

The realization of compact and high-power extended interaction oscillators (EIOs) in the millimeter-waveband has attracted much attention. Although phase-velocity tapering (PVT) is known to improve EIO efficiency by enhancing beam–wave interaction, this study reveals that an increase in start-oscillation currents is a limiting factor. To address this, a combined strategy integrating PVT with hard self-excitation (HSE) is investigated. The optimal HSE state is predicted through a 1-D program and achieved by a dynamic voltage source in simulation. Particle-in-cell (PIC) results show the PVT-HSE EIO operating in the Ka-band achieves 32.3 kW output power and 30.5% efficiency at 42.3 kV, representing a 14% efficiency improvement over a comparable PVT-only design. This work validates a simulation pathway with PVT-HSE EIOs, showing the potential for achieving high-efficiency and high-power millimeter-wave sources.