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

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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.