Efficiency Enhancement and Harmonic Reduction of Wideband Helix Traveling-Wave Tubes with Positive Phase Velocity Tapering

Abstract

Using numerical simulations, a wideband (> 1.5 octave) vane loaded helix traveling-wave tube (TWT) was studied, the output section of which is provided with a 'positively' phase velocity tapered helix portion, in which the helix pitch is made to linearly increase with distance towards the output end for reasonably high efficiency values. As compared to a device with a conventional 'negatively' phase velocity tapered helix portion, which gives an efficiency hike only in a narrow band of frequency, the positively tapered device provided a wideband efficiency improvement. Also, over the band, it provided a higher efficiency and a lower second harmonic content than a device with a nontapered portion. Factors such as the beginning position of the taper from the input and the amount of taper were considered in the optimum design for improving efficiency and reducing the second harmonic content of the device.

Design considerations of a 10 GHz helix TWT

“…That can shift the electron bunch to the accelerating phase resulting energy transfer from the wave to the electron beam. A tapered helix can resynchronize the process results an increase in the interaction length to improve the gain of TWT [3,4].…”

Improvements in Performance of Broadband Helix Traveling-Wave Tubes

“…An alternative pitch profile, a positively tapered helix, which was first conceived in the 1960s, can also be used for this purpose [17]. In a recent work, a theoretical study on its usefulness in improving the wideband performance was carried out [18]. The experimental performance of a multioctave band positively tapered helix mini-TWT was first demonstrated by Ghosh et al [19].…”