GB1082048A - High frequency electron discharge devices - Google Patents

Abstract

1,082,048. Transit-time tubes; impedance matching. VARIAN ASSOCIATES. Feb. 9, 1965 [Feb. 21, 1964], No. 5642/65. Headings H1D and H1W. A waveguide window, forming a vacuum seal for e.g. a travelling-wave tube, comprises a dielectric block 14 arranged in a rectangular or round waveguide 13 between two E-plane discontinuities 15, 16. The nature of the discontinuities is prescribed partly by the output impedance of the tube and the impedance of the load, which may be a standard waveguide. The dielectric constant of the chosen material for the block, e.g. fused quartz, alumina, beryllia. single-crystal sapphire, is used to determine its axial length which is made to approximate an electrical length of n# g /2 where # g is the guide wavelength at the centre frequency of the pass-band. The aspect ratio of the block and hence the dimensions of guide section B are then chosen to give the maximum band-width consistent with mode-free operation, using known techniques. The best position of the window with respect to the position of one of the discontinuities (the position of the other meanwhile remaining arbitrary) is then determined experimentally using VSWR measurements to plot the admittance function of the window on a Smith chart. The desired shape of the plot is one which can be moved to circle the origin by the addition of the other E-plane discontinuity on the other side of the window. Details of the procedure are described and illustrated in the Specification. The discontinuities are not necessarily on the same broad face of the waveguide and each discontinuity may be distributed between opposite faces. An inductive iris 18 may be added.