Study On Terahertz Multi-stage Staggered Double Vane Slow-Wave Structure

In recent years, a lot of attentions have been paid to vacuum electronic devices (VEDs) in the higher frequency wavebands, such as millimeter wave and terahertz (THz) wave band. As one type of the VEDs, traveling wave tubes (TWTs) are also studied in some aspects to improve its performance, such as high output power, wide bandwidth, and high beam-wave energy conversion efficiency. The staggered double vane slow-wave structure (SWS) is often used to achieve the above goals. Because of its all metal structure, it can provide large thermal capacity, which means it can sustain high output power. This kind of slow wave circuit has the sheet electron beam tunnel naturally and can be machined simply because of its 2-D configuration. As we all known, the sheet beams can theoretically provide an extremely large current with low emission current density. In addition, they can be more beneficial for generating high output power. Therefore, the sheet beam staggered double vane TWT will be proposed in this paper.We propose a three-stage cascaded SDV TWT, the cold characteristics were theoretically analyzed and relevant calculation method were carried out. Based on that, influence of structural parameters to the dispersion characteristics of the structure was analyzed using quasi-periodic method. Meanwhile, the axial field distribution characteristics of multi-stage slow-wave structure have been analyzed by observing the distribution of the electromagnetic field which build by the high-frequency signals. In addition, a novel coupler formed by height gradually changed grating structure and concentric cylindrical connector was proposed for this structure, and the transmission characteristic of the three-beam structure was analyzed.This paper presents a particle-in-cell simulation of the whole three-stage cascaded staggered double vane slow-wave structure (SWS), it’s operating characteristics were detailed analyzed. The results suggest that>10 W of peak power can be produced between 208 GHz and 238 GHz and a maximum gain of 32.4 dB at 220 GHz, driven by three 20 mA electron beams. The proposed circuit does not require an attenuator and the length of each stage is 27.45 mm. Because of the current density and short circuit length, problems such as fabrication issues, beam interception, electron beam thermal effects and fabrication of tiny concentrated attenuators were improved. Thus, the structure shows application potential as a terahertz radiation source.