Analysis of multi-beam folded waveguide traveling-wave tube for terahertz radiation

Abstract

A new proposal, multi-beam (MB) and power combining (PC) folded waveguide (FW) circuit, which can enhance the interaction efficiency and output power of terahertz (THz) traveling wave tubes, is presented in the paper. Operating with multiple electron beams and PC means that a larger beam current and higher combining power can be obtained. Firstly, equivalent circuit model of MB-FW is used to analyze its cold characteristics. Secondly, small signal model of MB-FW is also applied to evaluate its Pierce gain. Lastly, CST code is implemented to simulate high frequency, transmission, and interaction characteristics of MB-PC-FW. The results show this circuit can produce output power of over 15 W with six electron beams in 3 dB bandwidth range of 129–146 GHz when input power, each beam voltage, and current are set to 20 mW, 15.55 kV, and 12 mA, respectively. The output power, gain, and efficiency are 25 W, 31.02 dB, and 2.23% at 0.14 THz, respectively. Whereas, the single-beam folded waveguide circuit can only produce output power of 0.8 W in 3 dB bandwidth range of 135–147 GHz, and the output power, gain and efficiency are only 1.6 W, 22.03 dB, and 0.85% at 0.14 THz, respectively. The output power is raised tens of times and the interaction efficiency is raised several times in 3 dB bandwidth, and the 3 dB bandwidth is wider. In 3 dB bandwidth, the combining efficiency is not below 90%.