Noise in One-Dimensional Electron Beams

Abstract

A generalized theory of noise in one-dimensional electron beams is developed with the aid of the theory of four-terminal networks. No specific assumptions are made as to the input noise velocity and current modulations and their correlation at the potential minimum. The ensuing theory is simpler and more general than the corresponding theories used in the past. Transformations are discussed of the standing wave of the mean-square noise current in drift regions by means of ``lossless beam transducers.'' It is shown that such transformations can be reduced to the formalism of conventional impedance transformations. Expressions are derived for the minimum obtainable noise figures of a velocity-jump amplifier, a klystron, and a traveling-wave tube. It is proved that these expressions present an ultimate limit for the noise figures of the respective tubes with regard to transformations by beam transducers with and without loss.