Line Wave Tube Slow-wave Structure Of The Theoretical And Experimental Research

Traveling wave tubes (TWT) are very important microwave amplifiers, which are widely used in many electronic equipments, such as radars, communications, radio and electronic warfare. Dispersion and interaction impedance of the slow-wave structures are two cold-test parameters which determine the working voltage, frequency band, efficiency and gain of TWT. Because of the disadvantages such as low automatism, timeworn, the foreign measurement equipments can not meet the demands of measurement on-line.In this thesis, the theoretical and experimental researches of slow-wave structures in TWT (SWS) are analyzed. The main results are as follows:1. Basic methods for measuring dispersion and interaction impedance of SWS are analyzed in order to choose the best test method. The resonant and nonresonant perturbation theories are deduced in detail. The formers often used in computer simulation, however, the latter in experiments because it is not easy to make up a resonant helical SWS. Similarly, because it is difficult to find a slender and strong dielectric rod, slim metal wires are used as perturbers in the measurements of interaction impedance.2.After the selection of measurement methods, the author design a measurement system which contains three departments: Movement department,Data collection department and Center control department. The Movement department comprises servo motor, servo amplifier and motion control card; The Data collection department contains Vector Network Analyzer and GPIB card; The software of Center control department is based on Visual Basic.3. The system has practically measured one helical SWS sample. Through the comparison with the results simulated by HFSS and TWTCAD, validate its good measure consistency.4. This paper uses high frequency simulation software (HFSS) to study the effects of the helical TWT attenuator on the propagation characteristics of the electromagnetic wave. Modeling of the attenuator, we have taken the material conductivity and thickness into the consideration, which is better to approximate the real model than usually surface resistivity method. The study presents the effects of the surface resistivity, conductivity and thickness of the attenuator on the attenuation and phase constants of an electromagnetic wave in the helical slow-wave structure. A comparative study between two models, namely, the equivalent uniform dielectric layer and the separate rods, reveals the limitation of the equivalent uniform dielectric layer method. The research results bring direct guidance to the design of the helical TWT attenuator.The measurement system has passed the project acceptance and applied patent.