Inverted Coaxial Diaphragm Loaded Circular Waveguide High Frequency Characteristics

As a key component of a traveling-wave-tube(TWT), the slow wave system(SWS) basically determines the performance of TWT.The main difficulty of seeking novel slow-wave structure comes from the contradiction of openness and closeness of system. Weaker dispersion and wider bandwidth require the openness within certain dimensional range; conversely, improving heat dissipation and enhancing the power level require more closeness.The purpose of this dissertation is to achieve a high power and relatively wide bandwidth system on the basis of the traditional disc-loaded waveguide. By loading disc on the inner conductor of coaxial system periodically, a novel slow-wave structure can be constructed, which is named as inverted coaxial structure. This structure, which is a closed structure, has the merits of broad frequency band, easy fabrication and so on. In order to improve the performance, we can make slot on the outer conductor, then an open inverted coaxial high frequency structure is constructed. In this dissertation, both closed-inverted disc-loaded coaxial structure and open-inverted system are investigated; the dispersion equation, the interaction equation and the"hot"dispersion of beam-wave interaction in the structure are derived and numerically calculated. The major achievements are listed as the followings:1. The high frequency characteristic of a inverted-coaxial rectangular-groove–disk loaded circular waveguide structure is analyzed. The fields in this system are obtained by the way of field theory. Considering both fast waves and slow waves, the dispersion equation of this structure is deduced by utilizing the matching conditions at different interfaces. The results of dispersion characteristic by our theory agree well with the simulation results. By numerical calculation, the influence of the depth of groove and the width of disk on the dispersion characteristic and the interaction impedance are studied.2. The linear theory of the beam-wave interaction in an inverted-coaxial disc-loaded circular groove structure is studied. Using self-consistent theory, "hot" dispersion equation of the small signal gain are obtained. The influence of beam voltage, current and electron beam radius on the gain and bandwidth is researched, and the influence of the depth and width of disk on small signal gain are also considered.3. The dispersion equation and coupling impedance expressions of an inverted coaxial arbitrarily-shaped-groove disc-loaded slow-wave structure are achieved and the influence of different disc shape on high frequency characteristic of this structure is analyzed.4. An open inverted coaxial disc-loaded circular waveguide structure is also investigated primarily. The field expressions of gap area, center area and disc-loaded area are derived and the dispersion of this structure is achieved by utilizing the field matching conditions at the interfaces. Meanwhile, the linear theory of beam-wave interaction in this structure is investigated and the "hot" dispersion equation of the structure is achieved.