Study On The Short-millimeter-wave Folded Waveguide Traveling Wave Tube

The short millimeter wave has enormous potential for high data rate communications, advanced electronic materials spectroscopy, space research, medicine, biology, surveillance, and remote sensing. Nowadays high-power radiation sources in short millimeter wave frequency range are attractive in above applications. Traveling wave tube is one of the most widely used in short millimeter wave frequency range equipment of vacuum electronic devices, due to its characteristics such as high output power, high electronic efficiency and high gain. Folded waveguide has solid structure and good thermal stability(full-metal) which make it has many advantages including low fabricating cost, high mechanical strength, high power capability and wide frequency bandwidth in the short millimeter wave frequency range. In addition, the input and output circuit transitions of folded waveguide TWTs are simple to be designed, microfabricated folded waveguide TWT is an appropriate device which can be used in short millimeter wave range.Therefore, this paper studies on the short-millimeter-wave folded waveguide traveling wave tube. The main work of this paper are listed as follows:1. A 140-GHz folded waveguide traveling wave tube(TWT) with a big circular electron beam tunnel is designed in this paper. By using computer software, we analyzed the high-frequency characteristics of slow-wave structure. After then the TWT’s transmission system, including pill-box window, impedance hyperbolic transformer and sever absorber are designed. Periodic permanent magnet focusing system is also shown in this paper. Finally, the beam-wave reaction are calculated by particle-in-cell computer code. From the results, we can get up to 85 W output power and 25 dB gain at the center frequency.2. An experimental test for the 140-GHz folded waveguide TWT we designed is carried out. The VSWR of pill-box window we designed is less than 1.1 at the center frequency, and the VSWR of the whole TWT is 1.8. More than 20 dB gain of the TWT is measured at the range of 137-144 GHz and a 25 dB saturated gain is obseverd at 140 GHz.3. A 220-GHz folded-waveguide TWT is present then.We design the high-frequency structure, pill-box window, impedance hyperbolic transformer, sever absorber, electron gun and periodic permanent magnet system of the TWT.Caculated by 3-D particle-in-cell code,the output power of TWT is up to 61.74 W and the gain is 26.9dB at the center frequency.4. An investigation of angular log-periodic folded waveguide is carried out to find a novel slow-wave structure to reduce the voltage of TWT. The high-frequency characteristics of this structure are calculated by using a new method.This research provides a new way to reduce the voltage of TWT.