Designing minimum gain variation traveling-wave tubes with a time-shared computer

A computer program for small-signal gain was written to aid in the design of a TWT helix that would miminize gain variation. The program utilizes most of the classic derivations for the solution of gain equation, but also is able to obtain the exact solution for the TWT quartic equation and, in addition, can be run fast enough for use on a time-shared computer. A theoretically optimum helix was designed by synthesizing curves of phase velocity versus frequency for flat gain over wide bandwidths. Use was made of controlled dispersion to achieve theoretically flat gain. The derived phase-velocity curves are compared with various types of existing helices. The four rod-supported, helices with wrap wire are shown to have phase-velocity variations that compare favorably to the theoretical curves and have less gain variation than other mounting schemes.