Full-wave analysis of the high frequency characteristics of the sine waveguide slow-wave structure

Xia Lei,Qing Zhou,Luqi Zhang,Yanyu Wei,Yubin Gong,Xuebing Jiang,Chong Ding,Wenxiang Wang,Yuanyuan Wang,Qian Li,Gangxiong Wu

doi:10.1063/1.4997329

Abstract

A theoretical model for calculation of the high frequency characteristics of the sine waveguide slow-wave structure (SWS) is proposed. The formulas of dispersion and interaction impedances of the hybrid modes are obtained by combining the Helmholtz equation with the appropriate boundary conditions. Using the full wave analysis method, it is proved that the periodic structures with a half-period shift followed leads to a pairwise closing of passbands characteristic of adjacent mode. The sine waveguide SWS for 0.22THz traveling wave tube (TWT) is chosen as an illustrative example to verify the validity of the theoretical model, and the calculation results of the dispersion curve and interaction impedance curve are consistent with the HFSS simulation results. In addition, the influences of dimensions of sine waveguide on the high frequency characteristics of +1st spatial harmonic wave are investigated by numerical calculation. The study indicates that the appropriate SWS parameters are helpful for improving the bandwidth and increasing output power of TWT.

Highlights

traveling wave tube (TWT) is attractive for many applications due to its high power capacity and wide bandwidth
In order to overcome these challenges, the sine waveguide (SWG) slow-wave structure (SWS) was proposed, which combines the advantages of folded waveguide and staggered double vane structure.[8]
The three-dimensional view of a SWG SWS is shown in Fig.[1] (a) and schematic illustration of the SWG in the YZ plane is shown in Fig.[1] (b)

Summary

INTRODUCTION

TWT is attractive for many applications due to its high power capacity and wide bandwidth. A proper theoretical model can accurately evaluate the SWSs performance and save calculation time. It should be noted that the SMA model is not so accurate for describing the high frequency characteristics of sine waveguide SWSs.[10,11] Xie et al.[12] proposed a theoretical model in which the profile of the sine groove is approximately replaced by a series of rectangular steps. This method brings in extra calculation burden.

MODEL AND FIELD DISTRIBUTION

Dispersion relation

Interaction impedance

Validation of model

Parameter analysis