.8 Mm Band High Power Microwave Transition And Output Windows

Circular waveguide tapers are used in gyrotrons to connect waveguide of different diameters. The requirements on such highly overmoded tapers are good match and spurious mode suppression at both waveguide ports.Output window is the core of the gyrotron, which speciality can decide the speciality of the gyrotron greatly. The major subjects of output window design for high power gyrotron are to reduce the reflection and absorption power in order to enhance the gyrotron's stability and protect the output window. In this dissertation the output windows'refection and absorption are analyzed in detail.It is detailedly analyzed to mode coupling characteristics in taper waveguides from the coupled mode theory. Considering weak coupling of modes, the judgement conditions of the main spurious mode excited by the wanted transmission mode in a circular waveguide taper and the destructive conditions of the spurious interference in a finite length of taper waveguide are studied. The reduced formulas for describing the amplitude of the main spurious mode and the formulas of the profile curves of describing taper waveguide are given. The mode coupled characteristics in a Dolph-Chebyshev taper is studied emphatically. The comparable analysis to the performance on preventing mode conversion from the wanted mode to spurious mode for four kinds of taper, which include a kind of similar linear taper waveguide, a kind of upshifted sine profile nonlinear taper and a modified Dolph-Chebyshev taper circular waveguide, is finished by RF calculations.Based on the law of reflect and the law of refract, the study on the connection between thickness and reflectivity of output windows is presented. We design an output window, simulate it with circular waveguide taper.