Research On Several Crucial Issues In High-Power Traveling-Wave Devices

Traveling wave device is a kind of linear beam vacuum electronic device(VED)which utilizes the interaction between the electron beam and traveling wave and generates energy exchange.They are widely used in various military and civilian fields because of their high power,high efficiency,and good stability.They are the two most widely used microwave sources in electronic systems.With the rapid development of radar technology,electronic countermeasures,and satellite communication,precision tracking,high-resolution imaging technology,high-speed communication and large data capacity transmission technology have been widely used,which puts forward higher requirements for the development of high-power traveling wave devices.During the development of high-power traveling wave devices,there are some key technical problems,such as backward-wave oscillation(BWO),high-power broadband energy transmission technology,and so on.Besides,with the rapid development of solid-state devices,it is urgent to develop new traveling wave devices with high power and high efficiency,to give the traditional electric vacuum devices new vitality and maintain their advantages in the competition with solid-state devices.Because of this,the theoretical analysis,simulation design,and experimental methods are used in this dissertation to study key issues such as BWO,high-power broadband energy transmission technology,and the design of new high-power traveling wave devices.The following innovative work has been specifically carried out:1.The theory of BWO and its suppression method are studied.Based on Peirce's classical small-signal theory,the characteristic equation and the backward-wave gain of backward-wave tube are solved.Taking a helix traveling-wave tube(TWT)as an example,the threshold length of BWO is calculated numerically.Besides,the expression of small-signal gain of backward-wave with phase velocity gradient is derived,and the suppression law of the BWO by different gradual or jump circuits is analyzed,which provides a theoretical basis and design ideas for the suppression technology of BWO in high-power broadband traveling wave amplifier.2.Two kinds of high-power broadband energy transmission devices with excellent performance are designed and tested.One is a tapered coaxial window.Compared with the traditional coaxial window,the novel tapered coaxial window has higher power capacity,smaller dielectric loss,and better reliability,and greatly reduces the risk of voltage breakdown and ignition.The experimental test shows that the voltage standing wave ratio(VSWR)of the tapered coaxial window loaded with the interaction circuit is less than 1.72 in the frequency range of 8-18 GHz.The other is the double-ridge waveguide window.The windows such as the double-ridge waveguide circular window and the single-sided/double-sided welded double-ridge waveguide square window are designed respectively,and the conversion structure of in-line and feed-back coaxial-double ridged waveguide is designed.The experimental results show that the VSWR of the double-ridge waveguide window loaded with the output section interaction circuit is less than 1.91 in the frequency range of 8-18 GHz.The results show that the double-ridge waveguide window not only has small reflection,large power capacity,and wideband but also has the advantages of simple structure,easy processing,high mechanical strength,and high reliability.3.A high-power broadband technology scheme of helix traveling-wave tube is proposed.The slow-wave circuit with double-graded radius and pitch is adopted,and the output section adopts pitch gradual change and step-by-step jump to suppress the BWO under high-power and high-current operation.The slow-wave circuit scheme is designed reasonably by large signal software,and the whole tube scheme and working parameters are obtained.On this basis,the beam-wave interaction is studied by using CST Particle Studio.The simulation results show that the output power is more than 6.21 k W,the gain is more than 41.7 d B,and the electronic efficiency is more than 21.5% in the frequency range of 8-18 GHz,which represents the higher power level in this frequency band in domestic research reports.4.The experimental verification of the high-power broadband technology of X/Ku band helix TWT is carried out.Based on the previous research,the high-power energy transmission device and the interaction circuit are fabricated and assembled,the welding process of double-ridge waveguide energy transmission device is explored,the cold measurement tuning fixture and other components are designed,and the double-graded radius and pitch slow-wave circuit is processed and assembled,and the cold and hot test experiments are carried out.The cold test results show that the VSWR of input and output are less than 1.68 and 1.83 respectively in the frequency range of 8-18 GHz.Finally,the hot test results show that the output power is more than 5.06 k W and the gain is more than 34.1 d B under the condition of a 6% working ratio.The “power hole” was not detected in the hot experiment,and the feasibility of the design scheme of high-power broadband technology and BWO suppression in the previous article is verified by experiments.This hot experimental power represents the higher power level in this frequency band in domestic research reports,and it is also in the advanced ranks in international research reports.5.A new type of high power and miniaturized backward wave oscillator is proposed.Based on the widespread concern of metamaterials(MTMs)in the field of VEDs in recent years,a novel MTM slow-wave structure(SWS)is proposed.The equivalent constitutive parameters are extracted by the S-parameter method,which proves its “double negative characteristics” and miniaturization.A cascaded MTM backward wave oscillator is designed based on the design idea of a drift tube in extended interaction klystron(EIK).Through the beam-wave interaction simulation,the output power is more than 4.36 MW,and the maximum electronic efficiency is 41.22% in the frequency range of 4.834-4.869 GHz.The results show that the new type of high-power MTM backward wave oscillator not only has high power and high efficiency but also has the advantages of miniaturization,simple structure,easy processing,all-metal structure,and natural electron beam channel.The new type of high-power metamaterial backward wave oscillator provides a new research direction for traditional electric vacuum devices and is a potential high-power traveling wave device.