Mode Control Analysis and Large-Signal Design of a High-Power Terahertz Extended Interaction Oscillator

A high-power 200-GHz extended interaction oscillator (EIO) is designed by large-signal analysis. Analyzing different resonant modes, we calculated the mode called, here, as ${L}_{{1}} $ to be the most efficient one for our structure. From eigenmode analysis, it was predicted that the resonator-slow wave structure (SWS) coupling region has a considerable effect on resonant RF mode due to a ${L}_{{1}} \rightarrow {L}_{-{1}} $ mode transformation, where ${L}_{-{1}} $ is a parasitic low-output power resonant mode of the resonator. Using the eigenmode outcomes in addition to large-signal results, we found the optimum dimensions for the coupling region. The designed oscillator was then simulated by Particle-in-Cell (PIC) solver, leading to approximately the same results as those predicted by the mentioned procedure. The observed mode competition of different modes of the oscillator is analyzed and then removed by inserting a lossy layer at a proper location. By properly introducing a stub mode tuner near the output coupler, we could selectively excite the ${L}_{{1}} $ mode and maximize the RF output power to values even higher than those observed in the absence of mode tuner. Stable RF powers up to 2 kW are predicted to be obtainable by the sheet electron beams with beam densities lower than the state of the art.