Phase velocity taper design algorithms for optimizing broadband power and efficiency in coupled-cavity TWTs

The output circuit section of a traveling-wave tube (TWT) routinely contains an RF phase velocity taper in order to increase RF output power and efficiency. By slowing the phase velocity in approximate synchronism with the decelerating electron beam bunches, the taper increases power transfer from the beam to the RF wave. Recently, a phase velocity taper design algorithm based on the computational optimization technique of simulated annealing was developed and implemented into the NASA multi-dimensional large-signal coupled-cavity TWT computer model. The design algorithm was applied to the Hughes 961HA 59-64 GHz 75-Watt coupled-cavity TWT and the resulting simulated annealing taper provided a very significant increase in the computed RF output power and efficiency at center frequency. This paper describes an improved single frequency simulated annealing algorithm and two new broadband algorithms developed to design phase velocity tapers for optimizing RF efficiency and power over a frequency range.