Analysis of the noise spectra of a drifting multi-velocity beam

The minimum noise factor of beam-type microwave amplifiers is determined by the manner in which noise waves propagate in the low velocity region adjacent to the cathode. This multivelocity region has been analysed hitherto by means of machine integrations of the Boltzmann transport equation. In contrast, the present paper presents an analytical solution which provides closed-form expressions for the noise pow3 (r spectra (S, π, Φ) along the beam. In particular, a final steady state, that exists far downstream and in which the noise waves are washed out, is described.