A new configuration of travelling wave tube (TWT) of mm wave range, consisting of two round helix waveguides with the slot, which are placed coaxially, is studied. The analysis of operational characteristics of amplifier, based on numerical simulation, is carried out.
V. D. Yeremka,
"Coaxial twt of mm wave region", Proc. SPIE 1929, 17th International Conference on Infrared and Millimeter Waves, 192966 (14 December 1992); doi: 10.1117/12.2298339; https://doi.org/10.1117/12.2298339