Research On Interaction Of Folded Wave-guide Traveling Wave Tube

Traveling wave tube(TWT) is one of the popular but important member of the vacuum electron device which is often used in electronic equipment system. Slow wave structure(SWS) is the heart of the traveling wave tube. The performance of the slow wave structure directly determines the technical level of traveling wave tube. Folded waveguide slow wave structure is a novel slow wave structure, which not only with broadband characteristics, but also with large capacity power compared with the traditional spiral structure and coupled cavity structure. Three dimensional particle simulation is the main method for studying of the folded waveguide in current, but this method takes a lot of time and resource. This thesis aims to build a platform where can calculate nonlinear interaction characteristics of the folded waveguide slow wave structure rapidly. We can design folded waveguide TWT in short time.The topic of this thesis is focus of the study of interaction in folded waveguide TWT. In this thesis, the equivalent circuit model, the one-dimensional nonlinear interaction, two-dimensional nonlinear interaction are studied. The main research contents are listed as following.1. This thesis introduced the division of folded waveguide in equivalent model in detail and gave the way to get equivalent circuit component values. With the method of transfer matrix analysis in cascade of transmission line theory, all of the dispersion, coupling impedance, and the value of R/Q of folded waveguide slow wave structure can been calculated. Then a same dimension folded waveguide TWT was calculated by one of the electromagnetic simulation software HFSS, the results of it fit well with the results of equivalent circuit.2. Starting from the Lagrange analysis, the moving equation of electron, the RF field equations, the space charge field equations are obtained, and the one-dimensional nonlinear interaction theory of folded waveguide TWT is established. The simultaneous solution of those equations by using the Runge Kutta method in the Matlab program can get the characteristic of folded waveguide TWT. The program can slightly estimation the nonlinear interaction characteristics of folded waveguide slow wave structure before design.3. In order to improve the calculation precision, the coupled cavity cascade model is applied to the folded waveguide TWT. A software FWGTWT based on two-dimensional nonlinear interaction theory with Matlab was programed. Compared with the one-dimensional code, the calculation results of two-dimensional FWGTWT program are much closer to the actual situation than the one-dimensional results. This is because the one-dimensional linear theory used a lot of approximate relationship, and did not make the influence of the magnetic field into consideration. Then, a comparation with experimental results is made, known that output power is roughly the same, but the gain is higher. Maybe this is caused by the loss of input and output waveguides or windows and so on.