| Sheet beam traveling wave tube(TWT) is one of the high-power vacuum electron devices(VEDs) operated in millimeter wave and sub-millimeter wave spectra. A sheet electron beam is preferred over a pencil beam for its merits of high power radiation density and high beam-wave interaction efficiency due to the greater electric current, lower current density and larger interaction area, which can bring about the high output power and a compact structure. During the recent decades, the study and development of the sheet beam TWT make it play a large role in the military and industrial applications, such as radar, satellite communications and electronic countermeasures(EMC). With the rapid advancement of modern microwave techniques, the demand for high operation band and high output power devices becomes more and more active, and it is the aim for the researchers. As the crucial part of the sheet beam TWT for transmitting the microwave, the input/output coupler and output window significantly determine the performance of sheet beam TWTs on account of the transmission, reflection, isolation and bandwidth of them and more because of the low localized heat generated by dissipation power when microwave passes through the output window. Therefore, the requirements of the design of the input and output couplers and output windows operating in sheet beam devices are becoming higher and higher. Input\output coupler and the output window are as an important component of sheet beam TWT, the performance and bandwidth of input/output couplers, and the dissipation power generated by microwave passing through the output window, impact on the work of the tube. So study and design of a low reflection, high isolation and broadband input\output coupler, as well as high power capacity and broadband output window has great significance.In this thesis, various novel input/output couplers with great characteristics of low reflection, high isolation, high transmission in W-band is designed. In limited circumstances, the work is mainly concentrated into the manufacture and test of input and output couplers working in Q-band and Ku-band. What’s more, in order to successfully achieve the ideal transmission performance of sheet beam TWTs, a broadband and multilayer output window with high power output capacity is also proposed. The main work of the thesis is as follows:1. This paper introduce the background and significance of the sheet beam traveling wave tube studies firstly. Then the research status and the development trends of the input and output couplers and output windows both domestically and abroad is expounded. For the design, theories of the design of couplers is introduced, such as hole-coupling theory, phase-matching theory, Dolph-Chebyshev curve theory based on field-matching method and the pattern matching of the Blagg gate establish on the method of mode match and cascade matrix theory; The field-matching method of multilayer output windows and the heat conduction theory of thermal analysis is also briefly presented.2. Plenty of novel input and output couplers in W band are designed by electromagnetic simulation software HFSS. Multi-apertures in E plane and H plane are employed to respectively design couplers; Combining Matlab program, a compact coupler with Chebyshev distribution is proposed, performance is improved by inclining the coupling aperture; A L bend of low reflection and high isolation adopting multi-Blagg reflectors and multistage matched steps, and a improved structure is gotten by optimizing the Blagg reflectors; Blagg reflectors and Y branch waveguide are used to design a input coupler with high isolation and ultra-band. Based on the above couplers and limited testing condition, Chebyshev distribution and Y branch waveguide couplers in Q band and L bend waveguide coupler in Ku coupler in Q band is fabricated and measured, the measured results keep a good agreement with simulated results.3. The structure of a multilayer output window with high output power capacity operating at a wide frequency range is designed by adopting the HFSS. Based on the fieldmatching theory, the transmission matrix method is established. And the transmission characteristic of the output window is verified through numerical calculation and simulation. At the same time, the effect of the presence of gaps between the windows on the transmission performance is also analyzed.4. The contents and functions of the software ANSYS Workbench are briefly introduced. And the general processes of thermal analysis of output window via associating the HFSS and ANSYS Workbench are elaborated in detail. At the meantime, vast researches are performed to obtain the effects of temperature distribution, power capacity and the gaps between windows on the maximum output power capacity. |
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