Fig. 1. The structure of the DBRRB SWS with T-shaped dielectric rods supporting

Fig. 2. The interaction impedance（a）and normalized phase velocity，（b）vary with L

Fig. 3. The f-phase curve with different L

Fig. 4. The interaction impedance（a）and normalized phase velocity，（b）vary with W/H

Fig. 5. （a）Axial electric field distribution of the SWS in 94GHz，（b）interaction impedance varies with ed

Fig. 6. The dispersion curves of the SWS

Fig. 7. （a）The whole TWT structure，（b）attenuator，（c）three periods gradient structure，（d）three-segment step waveguide

Fig. 8. S-parameters of the step waveguide

Fig. 9. （a）S11 with different S of the TWT，（b）S-parameters with or without attenuator

Fig. 10. The time-domain output signals with（a）and without，（b）input power

Fig. 11. The spectrum of signals

Fig. 12. Electron beam bunching and phase space diagram

Fig. 13. The output power varies with ew and eh

Fig. 14. The input-output power and gain curves

Fig. 15. The output power and gain vary frequency