GB683479A - Improvements in travelling-wave tube - Google Patents

Abstract

683,479. Travelling-wave tubes. SYLVANIA ELECTRIC PRODUCTS, Inc. Nov. 11, 1949 [Nov. 13. 1948], 28983/49. Class 39(i) [Also in Group XL(b)] In a travelling wave amplifier with an input probe, output probe and a helix therebetween metal discs sealed through the envelope are used to provide electrical connection to the probes and mechanical support for the helix. In a modification there may be two or more helices. In one form, Fig. 1, the helix 20 is connected to discs 28, 34 via probes 16, 18 and short circuited matching coaxial stubs 38, 44 and is held accurately straight and axial by three hard glass rods 22 having low loss which fit into notches in the discs 30, 32. The stub outer conductors 40 fit slidingly into cylindrical flanges of the discs 28, 34 and are formed with shoulders 42<SP>1</SP> to limit their tendency to sliding displacement caused by the tensioned helix 20. Discs 28, 34 limit any longitudinal displacement of rods 22. Outside the envelope the copper discs are spun over reinforcing rings 36 and attached to input and cutput rectangular waveguides 24, 26. A further disc (not shown) sealed through the envelope may be provided for mechanical support of the helix at a point between the input and output guides, but since no external contact is required the spun over portion and ring 36 may be omitted. In forming the disc seals the discs are held in axial alignment by jigs and the sealing procedure is carried out as described in Specification 630,136. The probes and inner conductors of the stubs may alternatively be separate members connected electrically and mechanically to one another. The envelope 10 is of soft glass and a magnetic coil between the input and output probes focuses the beam. Lumped attenuators are provided at one or more points along the helix to suppress reflections. In a modification, Figs. 3, 4 (not shown) the helix is supported by four low loss ceramic rods which in turn are held at their centre portions by a metal shield surrounding the helix and at their ends by the inner and outer stub conductors. The shield is carried at either end by discs corresponding to 30, 32, Fig. 1. Axial displacement of the rods is prevented by eyelets at the shorted ends of the stubs. Prior art arrangements in which the helix is supported by ceramic or quartz rods or glass dimples in the envelope are referred to. The Specification as open to inspection under Sect. 91, states that the stubs have a length of #/4 as compared with prior art open ended <SP>#</SP>/ 2 stubs. In the form of Figs. 3 and 4, (not shown) the internal tube parts may be constructed to allow for differential thermal expansion. This subject-matter does not appear in the Specification as accepted.