Study On Quasi-optical Excitation And Testing Technology Of High Order Waveguide Mode

As an important high-power millimeter wave source,the cyclotron oscillation tube has a wide range of application needs in industrial heating,radar,directed energy weapons and other fields,and is one of the current hot spots in the research of domestic and foreign electric vacuum devices.The quasi-optical mode converter is the core component of the cyclotron oscillation tube,which converts the high-order waveguide mode involved in the injection-wave interaction into the quasi-Gaussian mode for easy direct transmission and radiation,and at the same time realizes effective injection-wave separation,providing a technical basis for the introduction of the buck collection stage.Therefore,the development of an exciter that can simulate the operating mode of the cyclotron is a necessary prerequisite to complete quantitative testing of the performance of quasi-optical mode converters.However,there are two major technical difficulties in the study of such high-order waveguide mode exciter:firstly,to suppress the parasitic low-order modes and improve the purity of the target modes;secondly,to quantitatively test and evaluate the excited high-order modes.An in-depth theoretical and experimental research has been carried out around the above technical difficulties in the paper,and the main research contents are as follows.First,from the mechanism of parasitic mode generation,the theoretical study of high-order waveguide mode excitation is carried out,and the research ideas and technical means to achieve the suppression of parasitic modes by introducing the coaxial structure to increase the isolation of target modes and peripheral modes,using the combination of half-open resonant cavity mode selection and long-range Bragg resonant coupling are proposed.On this basis,the theoretical optimization and simulation modeling of the W-band left-rotation TE₅₃ mode exciter are completed,and the technical difficulties of quantitative analysis of the output higher-order mode purity,which cannot be given directly in the simulation software,are successfully solved.Its calculation results show that at the operating frequency of 95.75 GHz,the mode conversion efficiency of the left-handed TE₅₃ mode exciter with a circular waveguide right-handed TE₁₁ input and a circular waveguide output is greater than 92%,and the mode purity is better than 96%.Second,the hardware platform of the W-band spatial field amplitude phase test system was designed and built,including the frequency source module,the spread spectrum component,the amplitude phase detection module and the planar scan subsystem at the receiver,taking into account the existing test instruments in the laboratory.The test method to improve the efficiency and accuracy of 2D spatial field test is proposed,which is a low-cost solution for the development of similar millimeter-wave spatial field test platform.Third,in view of the technical difficulties such as the complex two-dimensional field scanning of the output mode of the high-order mode exciter is time-consuming and the accurate working frequency point is difficult to be accurately judged,combined with the characteristics of the spatial field distribution of the high-order mode,the optimized test process combining multi-frequency point one-dimensional preliminary scanning and single-frequency point fast two-dimensional fine scanning is proposed,which greatly improves the efficiency of the exciter test.The method is also used to conduct detailed tests on the designed circular waveguide TE₅₃ mode exciter,which fully verifies the effectiveness of the test method.It lays the experimental foundation for the further research of the subsequent exciter.