Research Of 220 GHz T-shape Grating Sheet Beam Traveling-wave Tubes

Terahertz waves are electromagnetic waves with a frequency range between0.1?10 THz,which have great applications in high speed communication,medical imaging,safety inspection,and so on.However,the lack of high power and wide bandwidth terahertz sources has affected the rapid development of terahertz technology.The sheet beam traveling-wave tube(TWT)has the advantages of high power and wide bandwidth,so it is one of the first choices for the development of high performance terahertz sources.Therefore,this paper mainly studies the T-shape grating slow-wave structure(SWS),pill-box window and electron-optical system of 220 GHz sheet beam TWT.The work contents are as follows:1.By using HFSS to analyze the influence of the different T-shape grating SWS parameters on the dispersion characteristics and interaction impedance,the size of the T-shape grating SWS are determined.After comparing with the results of the high frequency characteristics of the rectangular grating SWS,it is found that the interaction impedance of the T-shape grating SWS at 220 GHz is 3.3?,which is about 4.5%higher than the interaction impedance of the rectangular grating SWS.2.A pill-box window that matches the T-shape grating SWS is designed.The simulation results show that S₁₁ is less than-30 d B in the frequency range is209?233 GHz,and the voltage standing wave ratio is less than 1.1.Then,the transmission characteristics of the T-shape grating SWS with pill-box window,H-plane curved waveguides and transition structures(the total length reaches 77.8mm)are analyzed.In the frequency range of 201?224 GHz,S₂₁ is higher than-8 d B,the transmission loss is102.8 d B/m.3.The electron-optical system used in the 220 GHz sheet beam TWT is simulated,the results show that when the beam voltage of the electron gun is 22.8 k V,the beam current is 0.16 A,and the cross section size of the electron beam waist is 0.54 mm×0.06mm.The peak magnetic flux density of the focusing system reaches 0.6 T.When the electron beam channel length is 40mm,the transmission ratio achieves 100%.The collection efficiency of the single-stage depressed collector reaches 90.5%.4.In order to suppress self-oscillation,an attenuator for 220 GHz T-shape grating TWT is designed.The beam-wave interaction of the TWT loaded with the attenuator is simulated,when the input power is 50 m W,the average output power reaches 90W,the gain reaches 32.6 d B,and the electronic efficiency is 2.47%.In order to increase the average output power of the TWT,the SWS is optimized by phase velocity variation.The average output power is increased from 90 W to 112 W,which is increased by 24.4%,the gain is increased from 32.6 d B to 33.5 d B,the electronic efficiency is increased to 3.07%,and the device efficiency is increased to 3.5%.