GB760033A - Improvements in or relating to travelling wave tubes - Google Patents

Abstract

760,033. Travelling-wave tubes. WESTERN ELECTRIC CO., Inc. Dec. 29, 1953 [Dec. 30, 1952], No. 36055/53. Class 39(1). [Also in Group XL(b)] A travelling-wave tube comprises a hollow wave guide surrounding a cylindrical ridge apertured to form an array of slot resonators individually transverse to the direction of wave propagation but the array extending in the direction of wave propagation, the ridge being in contact with one wall of the guide, the longitudinal spacing of the slots being equal to a small fraction of the free space wavelength of operation. In one form, Fig. 1, a hollow tube 12 with ¢ slot resonators 13 is brazed to one wall of a rectangular waveguide 11, the the beam passes through tube 12. Tube 12 may be replaced by a wire helix. The guide ends are curved so as to decrease the height of tube 12 above the guide wall, for impedance matching. The curved ends of the guide have openings for the insertion of tube 12 during assembly and for the passage of the beam, and have sealed windows to maintain the vacuum. A magnetic focussing field is produced by pole pieces forming parts of the tube wall, Fig. 3 (not shown). The device may use a conventional mode, or preferably a spatial harmonic mode, of positive or negative phase velocity, and may function as an amplifier or oscillator. In another embodiment, Fig. 2 (not shown) a wire helix contacts an inner guide wall via a sheet of dielectric such as mica. The helix can be replaced by a number of discrete wire loops. These circuits may be used in a backward wave oscillator, Fig. 3 (not shown) in which case the collector end of the guide-helix is terminated by a wedge of lorry material to minimize reflections, and the end adjacent the gun is curved and taken out through the tube wall at 90 degrees. Frequency modulation is achieved by suitable modulation of the beam velocity. The wave guides need not be of rectangular cross section. The devices may work at millimetre wavelengths. The design is discussed mathematically, and a numerical example is given.