Study On A Novel Support Rod Helix TWT At Ka-band

In this thesis,based on the research project of broadband high-efficiency millimeter wave Traveling-Wave Tubes(TWT),a helical traveling wave tube works at the Ka band(26.5~40GHz)is designed.According to the perspective of expanding the bandwidth,a novel fan-shaped metal-dielectric support rod helix slow wave structure is selected.The slow-wave structure has been studied by theory and simulation for its high-frequency characteristics,energy transmission devices,and beam-wave interaction characteristics.Some results have been obtained.The main work of the thesis is as follows:1.The fan-shaped metal-dielectric support rod helix slow wave structure with weak dispersion characteristics is selected as the research object,and the dimensions of slow wave structure is optimized after observing the high frequency characteristics of the helix slow wave structure.A suitable slow wave structure for working at the Ka band is obtained,Comparing with several common support rod structures,this structure has weaker dispersion and wider bandwidth.2.A coaxial input-output coupling structure that can be connected to a standard coaxial connector has been designed for a fan-shaped metal-medium clamped helical slow-wave circuit.By optimizing the design,the VSWR is less than 1.55 in the 25-40 GHz operating band.Broadband transmission can be achieved.3.The interaction simulation of the fan-shaped metal-dielectric support rod helix TWT is carried out.On the basis of simple uniform pitch design,the helix pitch and magnetic field step technology is used to overcome the defocus of electron beam,and the output power and electronic efficiency of the TWT is further improved in the working frequency band.The final design results show that when the working voltage is9 kV and the working current is 210 m A,the gain of the traveling wave tube in the whole frequency band of 24~40GHz is between 37.7dB~48.7dB,the electronic efficiency is between 15.18%~19.42%,and the output power is greater than 286 W.Comparing with the results of original design,these results increase by more than 4.19% on the electron efficiency,the growth rate of output power is more than 4.3%,especially in the range of26~37GHz,the electron efficiency increase by more than 11.8%,the growth rate of output power up to 11.9%.the design results are helpful to design improved fan-shapedmetal-dielectric support rod applied for high efficiency broadband millimeter wave helix TWT.4.Besides stepping design,we need to design a multistage depressed collector for this helix traveling wave tube to improve the electronic efficiency of the slow wave system.In the 3D electromagnetic simulation software CST,the four depressed collector is designed,we can find no electronic overflow or regurgitation occurred from the simulation of electron trajectories,and according to the relevant information to calculate the collection efficiency reached 80.6%,it shows that the collector design is reasonable.5.The high-frequency structure and energy transmission device of a Ka(29-31GHz)/Q(43.5-45.5GHz)dual-band fan-shaped metal-dielectric support rod helix are processed,and the transmission characteristics is tested.Test results show that,the VSWR is less than 2.5 over the Ka-band,;the VSWR is less than 1.5 over the Q-band,.