“Semi-metallic rods” structure for controlling the phase velocity dispersion in helix TWT

Telecommunication transmissions require high power linear amplifiers operating in C, X and Ku bands due to the necessity to manage a large amount of information. Helix TWT is the device adequate for this application since it can provide wide bandwidth and high power level at high frequencies. One of the major difficulties in the design of a wide band TWT relies in the phase velocity dispersion of the helix circuit because the gain across the band is strictly depending on it. For this reason the control of the helix dispersion characteristics has represented and still represents one of the more important techniques in broad band helix TWT design. To this purpose an anisotropic loading structure, consisting of "semi-metallic rods", has been designed and cold tested. The results are presented in this paper.