The Numerical Simulation Of The Cold Characteristics Of The Rectangular Gate Slow Wave Structure, Applied To The Vacuum Tube

Vacuum electron tubes are a kind of electron devices, which have been widely used in radar system, electronic countermeasure and satellite communication with its high power and high frequency. A traveling-wave tube is a kind of vacuum electron tubes. A slow-wave structure is an important component of traveling-wave tubes, where electromagnetic wave interacts with electron beams. The growth of the communications industry has imposed a demand for high frequency and micro-scale. Recent development in micro-fabrication has provided new opportunities for fabricating micro-vacuum electron devices, especially with rectangular waveguide-grating slow-wave structure.With the development of software technology and the improvement of computer performance, computer simulation technology has been widely applied in the research of microwave tubes. Assisted by some essential experiments, the Computer Aided Design technology brings some benefits in research and development process, which result in major savings in development time and cost.The method combining theory analysis and computer simulation was used in the thesis. The dispersion and coupling impedance of rectangular waveguide-grating slow-wave structure and the power loss of folded waveguide (FWG) slow-wave structure were studied. The chief jobs were:Based on the theory of improved SMA (single mode approximation), the mechanism of rectangular waveguide grating slow-wave structure was presented in this thesis. The cold characteristics such as dispersion and coupling impedance were analyzed and the interrelated theoretical equations were deduced. Dispersion and coupling impedance theoretical equations of FWG were summarized and the approximate theoretical equations of power loss of FWG were summarized in the thesis.Using electromagnetic simulation codes MAFIA and MWS, simulation of characteristics of the rectangular waveguide-grating slow-wave structure were carried out. Characteristics of one period of rectangular waveguide-grating slow-wave structure were analyzed using periodic boundary conditions, including field distribution and the relation between one period phase shift and resonance frequency. The dispersion curve was draw in MATLAB. It was founded in the curve that phase velocity in the rectangular waveguide-grating slow-wave structure could not be reduced and the slow-wave ratio was above 0.5.The method of calculating coupling impedance of bi-planar rectangular waveguide-grating slow-wave structure was analyzed in the thesis and the coupling impedance curve was draw in MATLAB. It was founded in the curve that the coupling impedance of bi-planar rectangular waveguide-grating was 0-40Ω between the frequency of 112-124 GHz. Effects on cold characteristics when changing grating height, period length, grating gap and up-down vane gap were analyzed. Effects on cold characteristics when the offset of up-down vane along axial direction is half a period length were also analyzed. The results showed that the system pass band became narrow and impedance increased when increasing grating height and period length; Effects on cold characteristics were very small when changing grating gap and keeping period length invariant; The system pass band became wide and impedance decreases when increasing the up-down vane gap. Cold characteristics kept almost invariable when the offset of up-down vane along axial direction was half a period length.The power loss characteristics of FWG were analyzed approximately. The power loss values of different frequencies around central frequency of FWG were calculated. The results agreed with theoretical analysis. Effects of the values of waveguide narrow side and the metal materials from which FWG is made on power loss were analyzed. The results showed that the attenuation constant decreased when increasing the metal's conductivity; the attenuation constant decreased when increasing the value of waveguide narrow side.The analysis methods can be applied to the study of other types of slow-wave structures, which is a good preparation for further simulation. The numerical simulation results can be very useful in microwave tube's theoretical analysis, especially in millimeter and THz range and can be used as a guide to the design and development of practical devices.