Effect of Random Circuit Fabrication Errors on Small-Signal Gain and Phase in Traveling-Wave Tubes

Motivated by current interest in submillimeter and terahertz (THz) slow-wave vacuum electronic amplifiers, which employ miniature, difficult-to-manufacture slow-wave circuits, we evaluate the effects of small random fabrication errors on the small-signal characteristics of a traveling wave tube. The classical 1-D small-signal theory of Pierce, generalized to allow axially varying circuit characteristics, is applied. Random, axially varying perturbations are introduced in the circuit phase velocity mismatch , the gain parameter , and the cold-tube circuit loss , in Pierce notation. Results from a first-order perturbation analysis of the small-signal equations, which are confirmed by numerical analysis, show that the standard deviations in the output phase and in the small-signal gain are linearly proportional to the standard deviations of the individual perturbations in , , and . Our study confirms that the effects of perturbations in the circuit phase velocity dominate the effects of perturbations in and .