Study On High-power Microwave Transmission And Mode Conversion

High Power Microwave(HPM) system are consisting of the high-power microwave sources, mode conversion, transmission system, and radiation system. Microwave transmission and mode conversion system was studied in this thesis, it plays an important role on the way the microwave output, the operating mode, and the size of the structure, it also determines whether the whole HPM system can work effectively. The transmission system include transitions and mode converters which matches the source and the radiation system. Transition is mainly used for matching microwave transmission structure, and mode converter is to used to match operating modes. They can realize this function by adjusting the transmission structure of those devices. A detailed discussion has been made on cylindrical waveguide structure based mode converter and Transition, including three structures, they are the mode converter of waveguide structure with the axis is bending, the transition with the radius tapered structure, as well as radiation system of the corrugated waveguide structure. In this thesis, converters and transitions with different structures has been designed by numerical analysis. This work was Supported by the gyrotron pre-study project, an axis para-curve bend waveguide mode converters has been designed and is under test.The main work of the thesis are as follows:1. The theoretical analysis of the mode coupling for the over-mode circular waveguide with axis bend, radius tapered waveguide and corrugated waveguide was undertaken, according to coupled-wave theory. Thus, the coupled wave transmission line equation and the corresponding coupling coefficient expression was obtained.2. According to the waveguide coupling theory, a program for calculating the waveguide structure parameter has been designed. the result computed by the program has been compared to the experiment result and the simulation result, it shows a good accordance between these results. Since the program is fast in computation, the optimal geometric parameters can be quickly obtained, which provides a great convenient for the design of similar mode converter and transition.3. Over-mode bend circular waveguide mode converter with different structure profile(arc sine, exponential, Gaussian, cubic, perturbation, parabola) were studied, these converters are used to handle TM01-TE11, TE01-TM11 and TE01-TE11 mode convert. Mode converters and transitions with parallel or vertical input and output waveguides has also been studied. In addition,a TE01-TM11 mode converter with para-curve structure has been manufactured.4. Transition with tapered radius and different profile were studied. When an adjustable fit function has been used to design the structure profile, the size of the transition can be made much shorter, thus this kind of transition has a good prospect.5. A TE11-HE11 mode converter with corrugated straight waveguide structure was studied, the output Gaussian mode from the mode converter is better than the output mode from the smooth gradient waveguide.