However, the previous investigations on FWG-TWTs reveal that their electron efficiency are relatively low, which are mainly limited by the beam-wave interaction impedance [8-13].
In the future, in order to increase the electron efficiency of the interaction, it is feasible to search other novel slow-wave structures which are related to SFWG-SWS.
And the beam-wave interaction simulations are performed to predict the operating characteristics such as saturated output power, gain and electron efficiency.
Figure 15(b) gives the saturated electron efficiency versus the frequency, from which we can see that the saturated electron efficiency is greater than 15.
And also, the electron efficiency can be further improved by means of phase velocity tapers , which will be an important research subject for the sheet-beam coupled-cavity TWT.