A Method To Determine The Mode Content In Over-mode Rectangular Waveguide Base On Radiation Pattern And Genetic Algorithm

The mode content is an important characteristic of the electromagnetic wave transmitted in waveguides. The size of waveguides determines amounts of modes. Although working on a single mode is a request for a high-power microwave resource, it is hard to realize in research and debugging. On the one hand, the lack of ways to control the cathode ray launch results in a complicated excitation. On the other hand, the system with highly over-mode structure such as the resonance cavity and the output waveguide are used in high-power microwave system in order to improving its power-handing capacity, which means many modes will exist in the high-power microwave system. So the electromagnetic wave propagating in over-mode waveguides has such characteristics as high-power, single short pulse, multimode, mode diversification. Because the over-mode waveguide is an important part of high-power microwave system, it is of great importance to research the electromagnetic wave transmitted and realized in over-mode waveguides to help improving source of high-power microwave system. But those bad characteristics decide the modes are hard to be measured by normal methods, such as using probe, scanning the field pattern, using mode-selective couplers, and etc..This paper proposes a novel technique to solve this problem. The technique determines the mode content in over-mode waveguide from the radiation pattern measurements. A rectangle waveguide is researched by the technique, but the technique also can be applied to other waveguides. The technique is base on measuring radiation pattern to get the information of the mode content, and using the information to determine the mode content by Genetic Algorithm (GA). Measuring radiation pattern can avoid errors by using probe. Calculating complex coefficients of electromagnetic fields mode is an electromagnetic inverse problem. The technique doesn't directly calculate complex coefficients of mode content, but changes the electromagnetic inverse problem to the "positive" problem, and uses the GA to search the complex coefficients. This technique has the advantage of overcoming the problem of ill-posed equations, and doesn't need to measure the...