Patent GB-804437-A (GB)
Title: Improvements in and relating to travelling-wave electron discharge devices
IPC: H01J23/083
Filed: 1955-05-12
Abstract: 804,437. Travelling wave tubes. VARIAN ASSOCIATES. May 12, 1955 [June 17, 1954.] No. 13803/55. Class 39(1). A backward wave oscillator tube, Fig. 1, comprises a cathode 2 indirectly heated by a filament 3 energized from a source 4. The electrons are focussed by an electrode 21 and accelerated by an anode 5 to pass through a bifilar helix consisting of two helices 11 and 12 supported in a tubular member 13 of glass or ceramic which is supported by insulating washers 14 from the glass or ceramic envelope 15 which is sealed at one end to the anode 5 by a tubular member 16 and closed at the other end by a collector structure 17 which is maintained at a higher potential than the anode 5 by a battery 19, but may alternatively be at the same potential or at a lower potential than the anode. The ends 11<SP>1</SP> and 12<SP>1</SP> of the helices 11 and 12 are led through the envelope .15 and connected to tapping points on the battery 19. The opposite ends of the helices are extended as a parallel wire transmission live and connected to spaced rings 22 and 23 which are carried by the inner wall of the envelope 15 and are capacitively coupled to flanges 24 and 25 provided at the opposite sides of an output waveguide 26. The electron beam is focused by the electric field of the helices so that no magnetic focusing coil is necessary. A coating 30 of resistance material is provided on the end of the tubular member 13 to eliminate standing waves and the production of forward travelling waves. Tuning is effected by varying the accelerating voltage by adjusting the contact 27. In an alternative arrangement, Fig. 5 (not shown), instead of employing the resistance material 30 on the member 13, the ends 11<SP>1</SP> and 12<SP>1</SP> of the helices before being led through the envelope are extended in the form of a parallel wire transmission line on an insulating strip which is coated with resistance material. The tube has a metal envelope and the waveguide 26 is led through the envelope and terminates in a cylindrical surface separated by an insulating cylinder from the rings 22 and 23. In a further arrangement, Fig. 9 (not shown), having an insulating envelope, the rings 22 and 23 are capacitively coupled through the envelope to a surrounding circular waveguide from which the output is taken by a coaxial line or a further waveguide. A magnetic focusing coil is supplied so the helices in this case may be at the same D.C. potential. In another arrangement, Fig. 11 (not shown), also employing magnetic focusing the ends of the helices are connected directly to the sides of an output waveguide which extends along the tube and through the metal envelope and is sealed by a window. The other ends of the helices are wound around the end of the tubular member 13 and are coated with resistance material. In the tube shown in Fig. 10 a cathode 37 produces an annular beam of electrons which pass within the bifilar helix 11, 12. The terminal 12<SP>11</SP> of helix 12 is connected through ring 23 to a choke coil 38 wrapped around an insulating sleeve 39 mounted on the insulating tube 13 and connected through a terminal 40 to a tapping point on a battery 19<SP>1</SP>, similarly, terminal 11<SP>1</SP> of helix 11 is connected through a ring 42 to a choke coil 43 which is connected through a terminal 40<SP>1</SP> to another tapping point on battery 19<SP>1</SP>. The tube may be operated as a backward wave amplifier, or by providing a matching load on waveguide 44 may be operated as a backward wave oscillator.