Study On W-Band Traveling-Wave Tube Based Upon Sine Waveguide Slow-Wave Structure

As a broadband high-power millimeter wave source,the W-band traveling-wave tube(TWT)has broad application prospects in the fields of radar,electromagnetic countermeasures,satellite communications,etc.How to develop such devices is a key subject for the development of vacuum electronics.When the operating frequency is increased,the size of the high-frequency structure becomes smaller and the loss increases;Moreover,the increase of the current density of the circular electron beam will bring great difficulties to the bunching of the electron beam,making it difficult to increase the current of the beam-wave interaction,which will result in a decrease in the output power of the device.This not only requires exploring new millimeter-wave terahertz low-loss slowwave structures(SWSs),but also needs to open up new ways to increase the operating current of the device.In recent years,due to the advantages of large current,low current density and small space charge force of the sheet electron beam(SEB),the SEB TWT has become a research hotspot in the field of high-power devices at home and abroad.At the same time,our research group also proposed a sine waveguide(SWG)SWS,which has the characteristics of low transmission loss,low reflection,easy processing,and natural SEB tunnel.Based on this,this dissertation has carried out the research of SWG SWS SEB device.From theoretical analysis,simulation design and experiment,respectively,a new type of SWG—flat-roofed SWG SWS SEB TWT has conducted in-depth research.The main work and innovations of this dissertation are as follows:1.The theory of the flat-roofed SWG and the experimental verification of its low loss characteristics are carried out.The field matching method is used to obtain the dispersion equation and interaction impedance expression of the flat-roofed SWG.The calculation results show that,compared with the conventional SWG,the flat-roofed SWG has higher interaction impedance while maintaining good transmission characteristics;The precision machining method of flat-roofed SWG is proposed.The SWS with surface roughness of 100-110 nm is processed by nano-CNC technology,and its transmission characteristics are experimentally studied.The test results show that: in the operating frequency band,the unit loss is 0.36 d B/cm,and the unit loss of the folded waveguide is twice than that of the flat-roofed SWG under the same size.2.The research of W-band SEB broadband TWT is carried out.First,a highfrequency transmission system of flat-roofed SWG TWT is designed,including SWS,ridge waveguide input and output coupling structure,bragg structure and pillbox window.The simulation calculation shows that the voltage standing wave ratio(VSWR)of the high frequency system is less than 1.5,in the frequency range of 90-100 GHz.Then a SWB electronic optical system is designed,the working voltage of the SEB electron gun is 19 k V,the current is 200 m A,and the beam-waist size is 0.8mm×0.2mm.The PCM magnetic focusing system is designed,and the transmission distance of the SEB exceeds10 cm.Finally,the beam-wave interaction is carried out,and the output power is greater than 55 W in the frequency range of 90-100 GHz.3.The experimental research of W-band flat-roofed SWG TWT is studied.Experimental research on various components of W-band flat-roofed SWG TWT highfrequency system,SEB electron gun and magnetic focusing system;The transmission factor of the SEB electronic optical system is tested;and the hot test experiment of the TWT is carried out.The test results show that: in the frequency range of 90-100 GHz,the VSWR of pillbox window is less than 1.3,and the VSWR of whole high-frequency system is less than 1.8.Under the bunching of the PCM magnetic focusing system,the electron transmission factor reaches 87.15%,and the transmission distance exceeds 10 cm.In the frequency range of 90-100 GHz,the output power of W-band flat-roofed SWG TWT is more than 30 W,the gain is greater than 16 d B,and the 3d B bandwidth is larger than10 GHz.The maximum output power is 54.5W at 96 GHz,and the gain is 18.5d B.4.The design scheme of a two-stage flat-roofed SWG TWT is proposed.The twostage flat-roofed SWG and phase-velocity tapered technology are used to obtain the highfrequency interaction scheme of W-band broadband high-power TWT.With the operating voltage of 19 k V and current of 200 m A,the output power is more than 140 W,and gain more than 31.5d B in the frequency range of 90-100 GHz.The maximum output power is276 W,and the gain is 34.4d B at 94 GHz.5.The SWS of dual-beam flat-roofed SWG is proposed.This structure has two SEB tunnels,which can double the input current of the TWT without increasing the current density,while still maintaining broadband and low loss characteristics.Beam-wave interaction simulation results show that: in the frequency range of 89-100 GHz,the output power is greater than 500 W,and the gain exceeds 37 d B.There is a maximum output power of 756.6W and a gain of 38.73 d B at 93 GHz.The proposal of the dual-beam flatroofed SWG brings a new idea for further improving the output power and gain of the TWT.