EFFICIENCY ENHANCEMENT OF OCTAVE-BANDWIDTH TRAVELING WAVE TUBES BY USE OF MULTISTAGE DEPRESSED COLLECTORS.

Small, three- and five-stage depressed collectors were evaluated in conjunction with a 4. 8- to 9. 6-GHz TWT of 325- to 675-W power output and a beam of 0. 5 microperv. The multistage depressed collector (MDC) performed well even though its design had been optimized for a TWT of identical design but considerably less output power. Despite large, fixed losses (rf losses, interception losses, and harmonic power generated losses), significant efficiency enhancement was demonstrated with both the three- and five-stage depressed collectors. At saturation three-stage collector efficiencies of 77 to 80 percent and five-stage collector efficiencies of 81 to 84 percent were obtained across the frequency band. An overall efficiency of 37. 0 to 44. 3 percent (average of 41. 2 percent) across the frequency band of 4. 8 to 9. 6 GHz was demonstrated with the use of harmonic injection. For operation below saturation, even larger relative improvements in the overall TWT efficiency were demonstrated. Collector performance was relatively insensitive to the degree of regulation of the collector power supply.