Study On Several Issues Of A 6-18ghz Wide-band Helix Traveling-wave Tube

With the continuous development of theory and technology,helix traveing-wave tube(TWT)has been widely used in electronic countermeasure,radar and communication due to its excellent performances such as wide bandwidth,high power and high efficiency.Based on the design of 6~18GHz wideband helix TWT,this thesis concentrates on improving electronic efficiency,suppressing the second harmonic and pulling helix current down.On the strength of the initial model of a 6~18GHz metal fan-shaped fins loaded with T-shaped medium support rods helix TWT,some key dimension parameters of slow-wave structure are optimized in this paper to acquire low voltage and wide working frequency band.According to the optimized slow-wave structure,the beamwave interaction of this TWT is simulated.It also explores the methods of improving electronic efficiency and output power,suppressing the second harmonic and pulling helix current down.After that,a suitable,excellent design scheme of wideband helix TWT is abtained.The main contents and research methods of this paper are as follows:1.Based on the initial model of a 6~18GHz metal fan-shaped fins loaded with Tshaped medium support rods helix TWT,the high frequency characteristics of the slowwave structure is calculated by HFSS.The effects of changes in some key parameters of the slow-wave structure are analysed,such as the thickniss,width and inside radius of helix,the inside radius and central angle of the loaded metal fins,the inside radius of tube and the pitch of helix.At last,a well-behaved slow-wave structure is acquired by choosing proper dimension parameters.2.The beam-wave interaction of the TWT is simulated by using large signal simulation software ORION.Under three methods including uniform pitch with uniform magnetic,the negative-positive-negative pitches with uniform magnetic and the negativepositive-negative pitches with multiple magnetic jumpings styles,the output power,electronic efficiency,the second harmonic ratio and helix current of TWT are analysed.At last,a desired simulation result is obtained: with the working voltage 3150 V and the beam current 115 mA,this TWT adopts negative-positive-negative pitches with multiple magnetic jumpings style.Within the frequency band 6~18GHz,the gain is 30.58~51.23 dB,the output power is 61~79W,the electronic efficiency is 17.02%~22%,the second harmonic ratio in 6GHz is-6.01 dB,the helix current in hole band is 0mA.Compared with the uniform pitch with uniform magnetic,within the working frequency band,the maximum gain has a decline around 10 dB,the maximum increase of output power and electronic efficiency is over 30 W and 8% respectively,the second harmonic ratio has a decline with 2.98 dB and the maximun decrease of helix current is beyond 40.25 mA.3.The ORION software was used to preliminarily design and optimize the electron gun,and the optimized current results were substituted into the interaction program for joint simulation.At the same time,according to the above theoretical design,the tube is fabricated to accomplish hot-test.The experimental result shows that when the operating voltage is 3010 V and the current is 110 mA,the output power in the working frequency band is greater than 46 W,the electronic efficiency is beyond 13.9%,the second harmonic ratio is less than-3.8dB and the helix current is under 7.5mA.