Study On Traveling Wave Technology Of Multi - Note Terahertz Folded Waveguide

When the operation frequency of traveling wave tube (TWT) rises up to Terahertz (ab. "THz") band, the output power of TWT will fall severity. To improve the output power of THz TWT, the dissertation will perform the study of the power combining, muliple electron beams and higher order mode TWT.The fundamental mode (FM), power combining and multi-beam (MB) THz folded waveguide (FW) TWT has been investigated. Firstly, The high frequency characteristics, transmission characteristics, beam-wave interaction characteristics and power combining characteristics of the THz TWT have been analyzed via the theoretical and numerical methods of TWT. Meanwhile, the change of the phase and magnitude of TWT effecting on the combining efficiency also was discussed. A D-band combining FW TWT is proposed and designed. When the beam current is 12 mA and the beam voltage is 15.75 kV, the saturated output power,3 dB bandwidth and combining efficiency are 8.7 W,12 GHz and not below 90%, respectively, however, the saturated output power of the single beam TWT is only 3.64 W. The maximum phase shift and amplitude ratio are 55°and 0.75, thus, the combining efficiency is up 80%.The fundamental mode, parallel, multiple beams THz FW structure has been given. The equivalent circuit model and the small signal gain theory based on the mode coupling theory have been expressed. Using theoretical calculation and numercial simulation, the cold-test performance, transmission performance and beam-wave interaction performance were calculated. The 0.14 THz fundamental mode parallel three beams FWTWT is accomplished. The results demonstrate the saturated output power and 3 dB bandwidth are 22.5 W and 25 GHz (128 GHz-153 GHz) under 12 mA beam current and 15.75 kV beam voltage. Comparing with the single beam FWTWT, the output power and electronics effeciency are raised more than sixand two times and the 3 dB bandwidth was widen twice. Meanwhile, the power combing charateristics of FM-MB-FW TWT was also studied.The fundamental mode, serial, multiple beams THz FW structure has been proposed. The dispersion, coupling impedance, gain,3 dB bandwidth and electronic efficiency of the structure were analyzed. The project of the 0.14 THz, serial, three-beam FWTWT is achieved. The 57.7 W saturated output power is gained at 0.14 THz when the beam current and voltage are 12 mA and 9.55 kV. Comparison with the parallel, three-beam TWT, the output power and interaction efficiency were enhanced several times. Lastly, the power combining performance of the serial MB-FW THz TWT has also been studied.The higher order mode, muli-beam THz folded waveguide structure was depicted. The mode distribution, high frequency characteristics, transmission characteristics, beam-wave interaction characteristics of the overmode THz TWT have been researched. The results indicate the reasonable design will ensure the overmoded THz TWT can work at TE30 stably. The dielectric load can supress the other modes. The way enlarged the dimensions of SWS and added the beam current and lowered the focusing magnetic field and thermal load. Via multiple electron beams, the current can been increased farther and the output power of overmoded THz TWT was improved.The two- and three- port and series FW structures were fabricated. The experimental platforms of the tested-dimensions and transmission characteristics of FW were set up. The error and surface smoothness and transmission performance of MB-FW structure were evaluated and guided the change of the fabrication process. Between the fabrication and design there was the bias which was attributed to the process error and the error from the connection amony different compenents. It also was meaning to the optimization design of MB-FW. The experiment results depicted the combing efficiency is not below 80% and the S11 is below-15 dB.In summary, these schemes, including power combing, fundamental mode multiple beams and overmoded mulitiple beams, indeed can enhance the current and dimensions of THz TWT and increased the output power, interaction efficiency, gain of THz TWT. They were the blueprints used to fabricating the wideband and large power THz radiation source and will drive the farther development of the super bandwidth, high rate THz commnunication system and remote, high resolution THz radar system.