| The high power microwave exist a broad market in defense and industrial areas with the characteristics of high power and high energy. The high power microwave system includes high power supply, the first stage power amplifier, microwave source, transmission link and antenna. The gyrotron is one of the new high power microwave source. With the characteristics of high peak power and high gain, the gyrotron has been widely used in radar, electronic warfare and other aspects. The mode converter is an important part of the microwave system, whose function is to improve the energy transmission efficiency of transfer mode by changing the microwave mode. So the mode conversion plays a significant role in microwave engineering applications.Based on the wide application background of the high power microwave, this article has done a depth theoretical analysis and simulation research on the mode converter of the gyrotron. Analyzed and discussed the full mode conversion link by the intermediary mode of TE11. TE0n-TE01, TE01-TE11 and TE11-HE11 mode converters have been designed. The main work of this paper concludes the following parts:1 Make an overview on history, value and research status of the high power microwave technology, gyrotron devices and the mode converter.2 By using the standing wave expansion method, derived the coupled wave equations of bending waveguide and gradient radius waveguide from Maxwell’s equations. Give the coupling coefficient expression of these two types of waveguide. Studied the mode coupled problem in the bend axis waveguide and gradient radius waveguide. Discussed coupled wave equations numerical optimization methods under different circumstances.3 Based on the coupled wave equations of gradient radius waveguide, made a design program to have numerical analysis and optimization on the Ku-band TE03-TE02, TE02-TE01 mode converter of gyrotron. Then simulated the optimal design structure of the converter in CST, compared the results between numerical analysis and simulation to verify the reliability of program and the performance of designed mode converter.4 Analysis and design the Ku-band TE01-TE11 mode converter with bending axis structure. Based on the mode coupling theory, the computer program which is to optimize the converter structure has been written by the phase rematch method. Two different geometric period converters have been designed. The optimized results of these two different converter structures are given. Then these converters are simulated by HFSS. According to the simulation results verify the reliability of the numerical optimization procedure. Discuss the effects on conversion efficiency and bandwidth by different periodic structures.5 Design the Ku-band TE11-HE11 smooth walled mode converter with the gradient radius structure. This smooth converter is better than the traditional converter with circumferential slot structure. It can avoid the microwave breakdown under the high-power and high-frequency circumstances. The designed converter contour is consisted of the parabolic curve combined with the sine curve. The TE11-HE11 mode converter is designed by numerical optimization program. The optimized structure parameters of the converter are given in this paper. Then the designed converter is simulated by HFSS and CST. The simulation results can verify the reliability of the program by comparison with the numerical simulation results. Another TE11-HE11 converter is designed by using a sine curve combination with a parabolic curve as the structure contour. The effects on the converter properties are discussed by comparing these two different types structure, the results show that different types of curve functions have a significant impact on the converter performance. |
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