Multi-octave traveling-wave tubes

Recent work at RCA has demonstrated that the Traveling-Wave tube can be extended in bandwidth to provide double octave performance with excellent RF parameters. This accomplishment adds significantly to the already unexcelled gain-bandwidth product of the TWT. Obviously, a single Traveling-Wave tube with double octave performance capability can be used in wide band receiver and transmitter chains to replace two (2) standard tubes normally covering the same frequency band. This approach enhances the efficiency of a system, conserves space and power supply requirements. The prerequisites for satisfactory double octave performance -- good gain flatness, control of second harmonic output, and adequate overdrive capability -- must be met to satisfy system needs depending on signal environment. RCA has recently demonstrated double octave performance on a Traveling-Wave tube chain consisting of 10 mW and 5 Watt tubes operating over the 2 to 8.6 GHz band. Both of these tubes use design techniques to obtain so called "anomylous" RF wave dispersion to simultaneously achieve gain flatness and low harmonic output. Harmonic capture is minimized by designing for rising helix synchronous potential as a function of frequency. This technique keeps the bunched beam, containing second harmonic power, in an unfavorable interaction phase which minimizes its effects on the fundamental frequency interaction process. Moreover, excellent gain flatness is obtained with approximately 5 dB gain change across the total bandwidth.