Development of Adjustable Mode-Converter in High-Power Microwave Transmission System

本文介绍了一种在实验室中现场可灵活调节的新型模式转换器，用于大尺寸波导系统中高功率微波的模式控制技术。本研究取得的新成果如下：1.本文提出了一种利用红外摄像机图像在计算机上进行数字处理，快速测量宽范围微波功率分布，并达到实际应用要求精度的方法。该方法用于以下模态分析.发展了一种基于测量波导平切端辐射微波功率分布的模式分析技术.本文提出了一种改进的模式分析方法，它采用一个弯曲的反射面天线来分离不同的模式。该方法结合红外摄像成像技术快速完成模态分析.基于模式匹配法建立了数值计算方法，系统地分析了模式转换器的模式转换特性，并将其充分用于模式转换器的优化设计。理论结果用2和3中所述的模态分析技术进行了实验检验。理论分析结果与实验结果吻合较好，表明理论分析的正确性，对研制新型大功率可调模式变换器具有指导意义.通过对结构参数的迭代修改，可调模式变换器成功地工作在200kW的高功率水平。最大功率，这是有限的电弧在转换管，增加了通过减少捕获模式的数量，并通过圆形的阶梯式结的管具有不同的半径的角落。实验测试表明，非圆化阶跃变换器的理论分析结果可以推广到改进型变换器的实际应用中。

Technology of mode-control of high-powe microwaves in an oversize waveguide system is deveolped in terms of a new type of mode converter which is flexibly adjustable on site in a laboratory. New features obtained in this research program are as follows :1. Amethod is developed for a quick measurement of the distribution of a wide range of microwave power with an accuracy required in practical usage by employing IR camera images which are numerically processed on a computer. This method is utilized in the following mode analyses.2. Development is made in a mode analysis technique based on a measured distribution of microwave power radicated from the flat-cut end of the waveguide.3. An improved technique of mode analysis is invented which employs a curved reflector antenna to separate different modes spatially. This method completes the mode analyses quickly when comined with the IR camera image technique.4. Numerical scheme is developed on the basis of mode-matching method for systematic analysis of the mode-conversion characteristics of the converter, and is fully employed for optimization of the mode converter. The theoretical results are tested experimentally with the mode-analysis technique as described in 2 and 3. A good agreement indicates the validity of the theoretical analysis as a guide in develping a new type of adjustable mode converter to be used at high power.5. The adjustable mode converter is successfully operated at high power level of 200kW after iterative modification of the geometrical parameters. The maximum power, which is limited by arcing in the converter tube, is increased by decreasing the number of trapped modes and by rounding the corner of the stepwise junction of tubes with different radii. The experimental tests demonstrate that the results of the theoretical analyses for unrounded step converter can be extended for practical application to the modified converter.