| As one of the important role in electron vacuum devices family,gyrotron traveling wave tube(gyro-TWT)has properties of high output power and broad bandwidth and has been widely applying in millimeter radar,millimeter communication,electronic warfare,and so on.However,when gyro-TWT works with low order modes such as TE11 or TE01 at W or even higher frequency band,its size of high frequency circuits would be small.This comes with design complications,including limited power capacity,higher possibility of electronic interception as well as higher manufacturing accuracy requirement.Using the high order mode as the operating mode can effectly solve this problem.So the reseach of high order Gyro-TWT has important meaning.Based on high order gyro-TWT reseach,this paper has made some work in two aspects,firstly doing some reseach on the high frequency interaction circuits and input/output structure of the gyro-TWT which works with TE12 mode and secondly doing some research on the low/high order modes excited devices which are constantly used in gyro-TWT.The mian reseach and results are shown as follows.The high frequency circuits of the TE12 mode gyro-TWT is designed and researched in chapter 2.Firstly,the oscillating current of the operating TE12 mode and the TE41 mode which dispersion curve nearly coincides with the one of TE12 mode based on the small signal theory.The calculating results showns that when the magnetic field set as 0.988 times the size of the tangent magnetic field,the oscillating current of the TE12 and TE41 modes would above 10 A.Thus,the absolute instability can be avoided when the working current is set as 10 A.Based on the small signal theory the lossless oscillating length and the loss size when the oscillating length reach 20 cm of the modes which would occur backward wave oscillation,as their dispersion curves intersect electron cyclotron dispersion curve at negative half axis of kz.Then,the loss of the material to each modes has been simulated and analyzed based on the results calculated by the small signal theory,and high frequency circuits with lossy material distributed loaded has been confirmed,which can stably work.Lastly,the influence of the changed length of lossless waveguide or size of voltage or size of magnetic field,and so on,to the output of the circuits has been analyzed.The input and output structure of the TE12 mode gyro-TWT has been researched in chapter 3.The input converter with single Y-branch structure and Bragg reflecting waveguide has been designed.Two kinds of Bragg reflecting waveguide have been designed.The Bragg reflecting waveguide solves the problem of size too small of the traditional cutoff waveguide in the high frequency band.A mode converter with rectangular Bragg reflecting waveguide has been fabricated and tested.To improve the conversion efficiency of the converter,a converter with double twist Y-branches structure has been designed.The simulation results show that the conversion of TE12 mode has improved from-1dB to-0.5dB.The middle layer of the output window is sapphire with thickness of 1mm,and the match layers are quartz with thickness of 0.46 mm.The simulation and theory calculation results show the bandwidth of window satisfys the design requirement,the results of the heat analysis show the output window can work effectively,and lastly a single layer sapphire window is fabricated and tested.The mode excited devices used in gyro-TWT have been researched in chapter 4.Firstly,a new TE0n/TE2n/TE1n' mode excited structure has been proposed,the design idea is rectangular TE10 mode ? rectangular TEn'0 mode ? circular TE0n/TE2n/TE1n' mode.And its characteristics are being able to excite both low order and high order modes,compact size,easily being fabricated,high conversion efficiency,and relatively broad bandwidth.Based on our proposed structure,a low order TE01 mode excited device,TE01 and TE21 mode excited devies(with same topology),and a TE13 mode excited device have been designed,fabricated and tested.Simultaneously,a TE12 mode excited device has been designed to use in the TE12 mode gyro-TWT.At last,a TE13 input mode converter has been designed and tested.Compare to TE12 mode input converter,the compting modes in the TE13 mode converter more difficult to suppress.To overcome it,a method of using grooves on the sides of the waveguide has been proposed.It can damage the electrnic field of the competing modes and suppress the forming of them.And the conversion efficiency of the designed mode can be improved.Research of high order mode gyro-TWT can avoid the problem of limited power capacity,manufacturing dificulty,and so on,because of small size when adopting a lower order mode.The study of low/high order mode excited device has important meaning to cold and hot test of gyro-TWT. |
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