Design and Theoretical Analysis of Multibeam Folded Waveguide Traveling-Wave Tube for Subterahertz Radiation

A new proposal—multibeam (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 this paper. Operating with multiple electron beams and PC means that a larger beam current and higher combining power can be obtained. First, equivalent circuit model of MB-FW is used to analyze its cold-test characteristics. Second, small signal model of MB-FW is also applied to evaluate its Pierce gain. Last, the computer simulation technology (CST) code is implemented to simulate high frequency, transmission, and interaction characteristics of MB-PC-FW. The results show this circuit can produce saturated output power of over 66 W with three electron beams in 3-dB bandwidth range of 139–144 GHz. Meanwhile the saturated output power, gain, and efficiency are 95.5 W, 36.79 dB, and 13.8% at 0.14 THz, respectively, whereas the single-beam FW circuit can only produce the saturated output power of 2.63 W in 3-dB bandwidth range of 140–143 GHz. The saturated output power, gain, and efficiency are only 2.7 W, 24.31 dB, and 1.41% at 0.14 THz, respectively.