FEM with guiding magnetic field based on simultaneous fundamental and high-harmonic oscillations

A novel scheme of a FEM-oscillator with a guiding magnetic field is based on the excitation of two (traveling and near-cutoff) modes at the same frequency but at different bunch-harmonics. The use of the near-cutoff mode provides a selective feedback in a simple microwave system. High electronic efficiency is achieved due to coupling of the traveling wave with the electron beam at the fundamental bunch-harmonic.