GB779583A - Improvements in or relating to travelling wave tubes - Google Patents

Abstract

779,583. Travelling-wave tubes. TELEFUNKEN GES. June 8, 1954 [June 5, 1953], No. 16706/54. Class 39(1). Wave attenuating means are provided in the space between the helix of a travelling-wave tube and any surrounding tubular metal structure such as a focusing coil or permanent magnet or a metal screen or an electrostatic focusing cylinder or a metal portion of the tube envelope, to reduce or suppress spurious reflected waves generated in the waveguide formed by the said tubular metal structure. In one embodiment, Fig. 1, the helix 3 is supported by three rods of insulating material such as ceramic provided in known manner with a layer 31 of damping material to attenuate reflected waves in the immediate vicinity of the helix. Members 10 and 11 which act in a manner similar to that of a wave rejector are provided on the insulating rods in the space between the helix 3 and the coil or permanent magnet 4. Alternative forms of wave attenuating members comprise annuli threaded on the insulating rods and dimensioned so as to act as resonant windows, or a number of annuli may be fixed on a metal tube at such a distance from each other that the member acts as a rejector, or at such a distance that the member acts as a retarding line comprising a series of resonant circuits, or a metal cylinder may be placed inside the tube envelope surrounding the helix so as to leave insufficient space for transmission of the spurious waves. When the tube envelope comprises a metal portion the wave attenuators may be grooves 16 and 17, Fig. 7, formed in the metal wall 15, or metal tubes 23 and 24, Fig. 8, each connected to the wall 15 by a flange 18. The individual attenuating members may be tuned to different frequencies in order to suppress a wide band of frequencies. Thus, the members 10 and 11 in Fig. 1, the slots 16 and 17 in Fig. 7 or the metal tubes 23 and 24 in Fig. 8 may be of different lengths. The attenuating members may be located outside the tube envelope. For example, members of the form shown in Fig. 8 may be located in the space between the glass tube envelope and the surrounding metal former of a beam focusing coil. Alternatively the focusing coil may be divided into sections 41, 42, 43 &c., Fig. 11, with intermediate spaces to act as impedances in the path of the spurious waves. Short circuit rings 32 may be provided for tuning purposes and to prevent the escape of high frequency energy.