Patent GB-767191-A (GB)
Title: Improvements in or relating to travelling wave tubes
Inventor: ROBINSON NORMAN WRIGHT
IPC: H01J23/26
Filed: 1953-11-17
Abstract: 767,191. Travelling wave tubes. MULLARD RADIO VALVE CO., Ltd. Nov. 17, 1953, No. 31864/53. Class 39(1). [Also in Group XL(b)] A travelling wave tube comprises a conductive plate 1, Fig. 1, supporting a conductive helix insulatedly, the helix having a helical continuation at at least one end bent at an angle thereto and terminating in a straight portion, the distance between the straight portion and the plate varying progressively to provide a desired impedance termination. The angle may be 85- 95 degrees, preferably 90 degrees. The gun can therefore be brought up close to the end of the conductive helix. In one form metal plate 1, Fig. 1, has semi-circular channels 2, 3, 4 for holding the helix and its continuations, and a larger channel 5 for supporting the gun. Curved lugs 6, 7 are provided for securing the assembly to the tube envelope (not shown). An insulating helix is seated in channels 2, 3, 4 and carries the conductive helix which is of uniform pitch throughout. In manufacture the conductive helix and the insulating helix are wound on straight mandrels and the insulating (glass) helix is heated and bent so that its two parts make an angle of 90 degrees. The conductive helix is then inserted into the insulating helix by a gentle twisting movement. At the end of channel 4 the helix is led over the last turn of insulating helix 12 and terminates in a straight portion 14, Fig. 7, which gradually approaches plate 1 by means of glass spacing beads 15 of graduated size to form a tapered transmission line, conductor 14 being soldered at its free end to the inner conductor of a coaxial line (not shown) and plate 1 being connected to the outer conductor. The other end of the helix is similarly terminated but extends through an aperture 17 in the plate and along the underside thereof to prevent interaction between the straight conductors 14, 16. The gun and insulating helix are held in position by a metal cover plate, Figs. 3, 4 (not shown) with channels in registry with those in plate 1, which is soldered to plate 1. The beads 15 may be substituted by powdered quartz fuzed to plate 1. The connections to the gun, collector and getter are brought out at one end, and to the helix at the other end, of the tube. The input is connected to conductor 14 which provides a more gradual impedance transition than conductor 16. The helical continuations of the main helix may comprise transition portions of gradually increasing pitch as described in Specification 767,190. The insulating helix may contact the conductive helix at about one point in each turn of the conductive helix. The insulating and conductive helices may be wound in the same or in opposite senses. The straight portion 14, Fig. 7, may be a wire or strip and instead of being carried on graduated beads may be tapered so that its centre line varies in distance from the plate, or may be associated with a tapered trough in the plate. The collector may be supported via an insulator from the plate. A numerical example is given. Specification 691,399 is also referred to.