Design of Helix Pitch Profile for Broadband Traveling-Wave Tubes

To improve the performance of a broadband traveling-wave tube (TWT), a helix pitch profile incorporating a section with reduced phase velocity followed by a positive phase-velocity taper is used. A simple technique to design a pitch profile of this kind is elaborated upon and later applied to an existing 6-18-GHz uniform pitch mini-TWT to improve its interaction efficiency. By using the newly designed helix, a TWT is developed, which shows increases in electronic efficiency and output power up to 8.75% points and 2.6 dB (75 W), respectively. Further application of this method to another uniform pitch baseline tube results in similar improvements.