Efficiency Enhancement of a Klystron-Like Relativistic Backward Wave Oscillator With Waveguide Reflection and Bunching Promotion

A klystron-like relativistic backward-wave oscillator (KL-RBWO) with transverse electron beam confinement and waveguide reflection, which works well under a magnetic-field strength below that of the cyclotron resonance, is proposed. For this device operating with a low magnetic field, effective suppression of the transverse velocity of electron beams is introduced by a local electric field near the tube head, to promote modulation uniformity of electron beams. Part of the reflected microwave from the output waveguide provides feedback enhancement to the extractor, which strengthens the local standing-wave field. Owing to a stronger electric field that can interact with the electron beam in the extractor and a higher growth of fundamental harmonic current, the efficiency of the KL-RBWO is increased to 40% when guided by a magnetic field of 0.32 T, compared with that of 30% using conventional structures.