The Slow-wave Structure Designed To Improve The Microwave Properties

In slow-wave systems, electromagnetic waves transmitted therein have a phase velocity lower than the light velocity and thus interact with electrons substantially. Besides they have a quite flat dispersion curve and thus can be applied for widely ranging frequencies. Therefore the slow-wave systems are widely used in various kinds of microwave tubes.Slow-wave systems generally employ periodic structures, and the electromagnetic waves transmitted therein are required to satisfy very complicated boundary conditions. The spiral curve structure can be used in slow-wave systems. Theoretically an analytic description for spiral curve slow-wave systems can be achieved after much simplification and approximation. The theoretical result thus obtained, however, is difficult to satisfy the requirements of practical applications due to the much approximation employed as well as the tremendous varieties of the practical structures.The present article works on the simulation of the performances of the spiral curve slow-wave systems utilizing the MWS simulation software of CST Inc, Germany. In this article the influences of various structural parameters on slow-wave characteristics are investigated, slow-wave characteristics under different screening cases are compared, and more applicable results with more varieties as compared to theoretical analyses are obtained, all of which may help the design of spiral curve slow-wave systems.As the research indicates, the structural parameters of the spiral curve slow-wave systems have complicated influence on its fundamental wave dispersion characteristics and coupling impedance. The frequency width of the fundamental wave depends primarily on the inner diameter of the spiral curve, and with the inner diameter fixed, the phase velocity of the fundamental wave can be adjusted by changing the spiral pitch. With different structural parameters, the coupling impedance curve decays with frequency in different rates, and there are optimum values of spiral curve thickness among other parameters for the coupling impedance to be maximum. The dispersion curve in the case of insulator wrapper is flatter than that for PEC wrapper, while the coupling impedance decays more rapidly.