Design and Method of a Slow-Wave Structure based on Symmetric Grating for Traveling Wave Tube

Excellent performance of high-frequency structures is critical to the development of millimeter wave and terahertz traveling wave tubes (TWTs). The plane symmetric grating structure (SGS) has the advantages of large transverse dimension, simple structure and easy to manufacture with one-dimensional processing. The TM₁₁ mode in SGS has characteristics of high coupling impedance and strong resonance, but its bandwidth is narrow, which limits its application in sheet beam traveling wave tube. It is found that the bandwidth of SGS can be effectively expanded by loading the coupled waveguide (operating in TE₁₀ mode) in parallel with the symmetric grating in this paper. The attempt to expand the bandwidth of SGS has been done in the Ka-band. The results show that the relative bandwidth of SGS can be widened from 0.03% to 8.3%. Besides, a G-band TWT is designed, and the cross-sectional area of its slow wave structure is more than twice that of the traditional high frequency structure. The PIC simulation results demonstrate that the maximum power is 169 W at 219 GHz, corresponding to a gain of 27.2 dB, and the -3dB bandwidth is 10.5 GHz.