| Terahertz wave plays an important role in the electromagnetic wave spectrum.The long wave part of terahertz wave is adjacent to millimeter and sub-millimeter wave,while the short wave part of terahertz wave is adjacent to infrared ray.Compared with microwave and millimeter wave,the atmospheric attenuation of terahertz wave is much higher.As a result,high power terahertz radiation sources or power amplifiers are necessary to ensure the effective range and the signal quality of electronic devices using terahertz wave.As one of the solutions to overcome the high atmospheric attenuation in terahertz frequency band,vacuum electronic devices have substantial advantages at high power in terahertz frequency band.For this reason,vacuum electronic devices have great potential on the applications in many terahertz electronic systems such as high data rate wireless communication,high resolution imaging and high accuracy detection.Among the variety of vacuum electronic devices,traveling wave tubes have the capability of broad bandwidth and high gain,so this type of vacuum electronic device has been widely studied worldwide.In this paper,terahertzs traveling wave tubes such as 220 GHz traveling wave tubes and 340 GHz traveling wave tubes has been studied.The space charge field based on Green’s function is theoretically investigated,and the one dimentional nonlinear beam-wave interaction model and code based on the electron disc model with finite thickness are established.The slow wave structure characteristics of the novel non circular bend folded wave guide slow wave structure are investigated.The novel edge aligned staggered double vane slow wave structure is presented and its slow wave structure charactersictics are also investigated.A 220 GHz traveling wave tube and a 340 GHz traveling wave tube are designed and demonstrated respectively.Firstly,for the charactersitcis of high space charge density in terahertz traveling wave tubes,the Green’s function in particle static coordinate system is solved.The expression of the space charge field in laboratory coordinate system and the space charge field of the electron disc model with finite thickness are also derived.The infinite thin disc model in the classic one dimensional large signal theory is replaced by the electron disc model with finite thickness,a new one dimenosional beam-wave interaction code are established.For the design scheme of a 220 GHz traveling wave tube,the result of the one dimenosional beam-wave interaction code and the three dimensional particle simulation are compared.The validity of the one dimenosional beam-wave interaction code has been demonstrated.Secondly,for the band edge instability of the classic folded wave guide slow wave structure,the solution of employing the novel non circular bend folded wave guide slow wave structure in 220 GHz traveling wave tubes are proposed.The influence of the non circular bend on the cold characteristics of the fundamental mode in non circular bend folded wave guide slow wave structure such as dispersion,interaction impedance on the electron beam tunnel center and attenuation are analyzed.The influence of the non circular bend on the band edge characteristics of the non circular bend folded wave guide slow wave structure such as cut off frequency,electric field profile and interaction impedance on the electron beam tunnel center are also analyzed.The non circular bend folded wave guide slow wave structure in a 220 GHz traveling wave tube is designed using the influence of the the non circular bend on the non circular bend folded wave guide slow wave structure.The beam-wave interaction of non circular bend folded wave guide slow wave structure in the 220 GHz traveling wave tube is investigated using the one dimensional nonlinear beam-wave interaction code and particle simulation.The prototype of 220 GHz traveling wave tube is demonstrated,achieving 20 W of continuous wave output power,32 d B of gain and 7.6 GHz of bandwidth.The band edge instability of the classic folded wave guide slow wave structure is solved.Finally,for 340 GHz traveling wave tubes,the electromagnetic field profile and the cold characteristics of the fundamental mode and higher mode in the novel edge aligned staggered double vane slow wave structure such as dispersion,interaction impedance on the electron beam tunnel center and attenuation are investigated.The specific interaction impedance profile on the cross section of the edge aligned staggered double vane slow wave structure is found.The higher mode of this slow wave structure is unable to cause band edge oscillation at high voltage.The influence of the tolerance of fabrication and assembling on the band edge characteristics of the edge aligned staggered double vane slow wave structure in 340 GHz traveling wave tubes and the possibility of band edge oscillation are analyzed.The edge aligned staggered double vane slow wave structure in a 340 GHz traveling wave tube is designed.The beam-wave interaction of edge aligned staggered double vane slow wave structure in the 340 GHz traveling wave tube is investigated using the one dimensional nonlinear beam-wave interaction code and particle simulation.The prototype of 340 GHz traveling wave tube is demonstrated,achieving 1 W of continuous wave output power,18 d B of gain and 25 GHz of bandwidth. |
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