Review of high power traveling wave tube amplifiers

The authors review work performed on high-power traveling wave tube amplifiers. The tubes operated in the X-band at 8.76 GHz with both a single stage and severed amplifier configuration. The single stage amplifiers provide useful gain (i.e. no oscillation) in the current range from 800 to 1700 A. The output is monochromatic until the output power reaches 70 MW, at which point a sideband structure develops in the frequency spectrum. Above 1.7 kA, the tube goes into oscillation from positive feedback. To eliminate the oscillations, the amplifier was severed. The severed amplifier achieved a total overall power output of about 400 MW, as verified by calorimetry. The power at the carrier frequency was 210 MW, giving an amplifier efficiency of 24%. Theoretical work has been performed to investigate the amplifier performance, including the sidebands. Most of the effects seen here can be attributed to finite length effects.>