GB780050A - Travelling wave tubes - Google Patents

Abstract

780,050. Impedance matching. STANDARD TELEPHONES & CABLES, Ltd. April 29, 1955 [May 3, 1954], No. 12511/55. Class 40(8). [Also in Groups XXXVI and XL (a)] The helix of a travelling-wave tube is coupled to input and output coaxial line feeders by a transmission line section of intermediate impedance comprising a ground plane conductor in the form of a disc 3, Fig. 1, or strip 23, Fig. 3, a ceramic disc 17, and a radial conducting strip (line conductor) 16, the conductor 3 or 23 being connected to the outer conductor of the feeder line and conductor 16 to the inner conductor of the feeder line and to the helix, the ceramic discs 17 being sealed across a tubular ceramic envelope 4. The line 3, 16, 17 has a length of n#/4 (nodd) and strip 16 has a tapered section 18. The line section carries a TEM mode. Strip 16 is bonded to dielectric 17 and the thickness of the dielectric 17 is a small fraction of #/4. A strip 18 of tapered width is attached to strip 16 and provides a smooth impedance transition to travelling-wave tube helix 8 to which it is connected at its free end. The inner conductor of the coaxial feeder 12 is connected to the line section by bridging member 20, the line section being shorted at this end by flange 21. If member 17 is of ceramic, members 16, 17 and 3, 17 are joined by any suitable ceramic-metal sealing technique such as the tungsten oxide or the Mo-Fe method, and members 16, 17 are sealed to ceramic envelope 4 by means of a glaze. The output coupling arrangement is similar. Plates 3, 6 -form polepieces of permanent magnet or coil 5 and the helix 8 is carried by dielectric rods or tube 9 of glass or quartz held at their ends in the central apertures of plates 3, 6. In a modifcation, Fig. 3, the device has an all-ceramic envelope 27, the line section having metal strip 23 bonded to dielectric sheet 24 and strip 25 being connected to helix 8a by tapered strip 18 as before. The ceramic envelope is sealed to line section 23, 24, 25 by glaze. The inner conductor 19a of the coaxial feeder is soldered or welded to strip 25, and a similar joint could be used in Fig. 1. The gun end of the device of Fig. 1 comprises ceramic base-plate 30 sealed to glass or ceramic stem 33 by glaze. The ceramic plate 30 has conductive strips 31, Fig. 4, applied by a ceramic-metal sealing technique, the strips 31 having terminal posts 32 for the gun leads. There may be three or more strips 31 and the ceramic disc 30 can be ridged between the strips to increase the D.C. breakdown potential. The external leads to strips 31 are spring fingers 35, Fig. 1, or are soldered to tags 34. Specifications 703,601 and 721,806, [Group XL (c)], are referred to.