Patent GB-654386-A (GB)
Title: Improvements in or relating to high frequency electronic discharge devices
IPC: H03C5/04
Filed: 1947-11-03
Abstract: 654,386. Travelling-wave tubes; magnetrons. WESTERN ELECTRIC CO., Inc. Nov. 3, 1947, No. 29275. Convention date, Nov. 5, 1946. [Class 39 (i)] In a travelling-wave amplifier having input and output means connected by transmission circuit means the transmission circuit for retarding the waves to a velocity substantially lower than that in free space is a block 3, Fig. 2, defining a plurality of cavity resonators 5, 6, 7, or a wire helix 20, Fig. 3, an electron stream is introduced into the field of the travelling-wave in a direction such that the electrons have a component of velocity perpendicular to the direction of travel of the field, and a magnetic field is applied perpendicular to the plane of the paper so that the electrons are bent in the direction of travel of the travelling wave and continuously interact with it to give up energy thereto. In the form of Fig. 2, a flat indirectlyheated cathode with an emissive coating 9 and supported on insulators 14, produces the electrons and a control grid 8 may or may not be provided. A projection 15 collects the electrons finally. The input and output are injected and removed via coaxial lines 1, 2. The resonators need not be arranged in a straight line. The magnetic field is set up by two solenoid coils 11, by an electromagnet 25, 26, Fig. 3, or by a permanent magnet. In operation, electrons which lose energy to the travelling wave move towards the resonator block face and gain energy from the D.C. field between the block and the cathode, so that their velocity in the direction of travel of the wave remains substantially constant. In the form of Fig. 3, the collector 22 is separate from the helix 20 carrying the travelling wave, and a choke coil 23 and byepass capacity formed by insulator 24 prevents leakage of output energy to D.C. source 13 while permitting a positive D.C. potential to be applied to the helix. The helix is of square section and is wound on a cross-shaped ceramic member 21. In a further modification, Fig. 5, the helix 20 serving as a transmission path for the travelling wave is surrounded by a shield 30 which may be of wire mesh, or of perforated material, or of two separate grids one above and one below the helix 20, and may be positive or negative with respect to helix 20. As shown, both the helix 20 and the coil 30 are of rectangular section and are each wound on two insulating strips 34, 35  so that the electrons can pass right through the spaces between the turns of members 20, 30. In operation the electron stream is velocitymodulated in spaces 31, 32, is bunched by drift space action as in the reflex klystron (electrode 33 serving as the reflector electrode), or by elimination of the higher speed electrons which strike electrode 33 while the lower speed electrons are reflected, and the bunched stream returns to spaces 32 and 31 and gives up energy to the travelling wave. Additional bunching of the beam between 31 and 32 on both transits may also be utilized. The electrons are finally collected by the shield 30 or by the helix 20. In further modifications, Figs. 7, 8, 9, 10 (not shown), either the resonator block form or the form using the helix may have only a portion of the flat cathode emissive and a correspondingly short control grid, or may use an electron gun, a separate flat electrode confining the space charge in the interaction region.