High-power, high efficiency wideband TWTs

High-power brazed-helix TWTs are used the world over in telecommunications applications. Recent developments, especially concerning the RF windows for output into standard rectangular waveguide, have allowed the bandwidth of these tube types to be extended to the limits of the waveguide passband itself. Moreover, modifications of the slow-wave structure have improved the interaction efficiency and bandwidth of these TWTs. For example, more than 2 kW CW have been measured between 6.5 and 10.25 GHz with only 1.2 dB output power variation across the band. Still higher power levels will involve new technological solutions, now under study at Thomson-CSF, in particular an internal liquid cooling of the slow-wave structure and a multl-stage depressed collector for even higher efficiency. In the near future, the realization of TWTs delivering even higher CW power levels with even larger bandwidth seem possible.