Fig. 1. （a） The perspective for the 3D model of the multi-corrugated waveguide SWS，（b） the top view with dimensional parameters of MCW SWS

Fig. 2. Dispersion and coupling impedance characteristics with the variation of geometric size (a) the pillar length l, (b) the waveguide width w, (c) the period of MCW p

Fig. 3. The dispersion curve and coupling impedance of the MCW with dimensions in Table I. note： the beam line of 12.9 kV is superimposed

Fig. 4. the 3D model and the assembly sketch of the MCW SWSs

Fig. 5. Fabricated MCW SWS with input-output coupler

Fig. 6. the photograph of the vector network analyzer and the tested result

Fig. 7. comparison between simulation and measured S-parameters of the fabricated MCW SWSs

Fig. 8. Model of the three-beam MCW circuit in CST PARTICLE STUDIO

Fig. 9. the variation of input and output signal with time in the frequency of 34 GHz

Fig. 10. Frequency spectrum of the output signal

Fig. 11. Energy distribution of electron beam along the transmission direction（z）

Fig. 12. the output power and gain versus frequency for the MCW TWT

Fig. 13. the electronic efficiency of the MCW TWT in the 29~39 GHz frequency band