Noise in traveling–wave tubes

A number of experimental traveling-wave tubes have been built for operation in the 3.2 centimeter wavelength region, and series of noise measurements have been made on these tubes. The periodic dependence of noise figure on the separation between the electron gun and the circuit entrance of the traveling-wave tube has been investigated and various characteristics of these curves have been discussed. A modified noise theory has been suggested; comparisons between it and the experimental results show fair agreement. Noise figure reduction by the use of a triode gun has been investigated for two of the experimental tubes, and a method of analysis that should lead to theoretical justification is suggested.