GB673731A - Improvements relating to electron discharge devices of the velocity modulation type - Google Patents

Abstract

673,731. Velocitymodulated tubes. STANDARD TELEPHONES & CABLES, Ltd. June 16, 1945, No. 15380/45. Class 39 (i). A velocity-modulated tube comprises a tubular resonator 4, Fig. 1, closed at one end of its longitudinal axis, a pair of conducting plates 6 forming a field-free drift space, a long narrow cathode 10, control electrode 11 and accelerator electrode 12 for projecting a beam of electrons through slots 9 of the resonator and perpendicular to its longitudinal axis to excite an electro-magnetic field within the resonator with the lines of electric force parallel to the electron beam, and a closed conducting loop 18, Fig. 4, located in the resonator 50, as to inhibit the generation of a mode of oscillation in which the lines of electric force are directed from the plates 6 to the walls of the resonator. The conducting loop 18 comprises a wire 18<SP>1</SP> connected at one end to a conductor 5 near the point to which the plates 6 are fixed and at the other end to a wall of the resonator 4 near its closed end so as to link a substantial number of magnetic lines of force of the undesired mode of oscillation. The electron beam after passing between the plates 6 passes through the slot 8 to the collector electrode 14. The electrode 14 may be omitted and, the envelope. 1 made of copper to collect the electrons. A screen electrode 13 catches electrons projected backwards from the cathode. The resonator 4 is mounted on a metal disc 2 sealed through the glass envelope 1 and having a hole through which extends the energy abstracting antenna 20 of a conducting loop 19 fixed to the wall of the resonator 4 and perpendicular to the loop 18 so as to link the magnetic lines of force of the desired mode of oscillation. The conductor 5 can be omitted if other means are provided for supporting the plates 6 and for completing the conducting loop 18. The wire 181 may be connected directly across the resonator at a point near the plates 6 so as to be parallel to the electric lines of force of the undesired mode of oscillation. The conducting loop should either have sufficient resistance to be substantially unresonant or should be adjusted to resonate at the frequency of the undesired oscillations. The electron beam may be focused by magnetic means. In the con-. struction shown in Fig. 5 short fins are attached to the walls of the resonator 4 in order to prevent the escape of high-frequency waves through the slots 8 and 9. Mechanical tuning is obtained by coupling the resonator to an adjustable resonator or wave-guide. The device may be coupled to a wave-guide or resonator by inserting the portion 3 of the envelope through a hole in the wall of the resonator or guide, the disc 2 being placed in contact with the outside of the wall. The loop 19 and antenna 20 can be omitted if the cross-section of the resonator 4 above the plates 6 is changed by a suitable taper to a form having re-entrant portions 24, Fig. 6, the disc 2 having an aperture of the same shape and size. Dimensions and electrical characteristics are given. Specifications 537,490 and 597,511 are referred to.