Traveling-wave tube gain fluctuations with frequency

Periodic traveling-wave tube gain fluctuations with frequency are described in terms of fundamental tube parameters and readily measurable quantities using the simplified one-wave theory of Pierce. An analysis of the feedback existing in a traveling-wave amplifier due to mismatches in the discontinuity regions is presented. Thus, the form, periodicity, and magnitude of these fluctuations and their dependence upon the beam voltage are quantitatively determined. The microwave structure is analyzed from a network point of view and the circuit parameters are defined with mismatches in the lumped center attenuator and at the ends of the slow-wave transmission line. The gain fluctuations are related to the cold circuit parameters and standing wave measurements. Pertinent experimental data, indicating the correlation of gain fluctuations to vswr variations, are included, in addition to an elementary discussion of the distortion effects possible due to such periodic gain variations in a traveling-wave tube.