Patent GB-704378-A (GB)
Title: Improvements in or relating to discharge tubes for generating, amplifying, or modulating millimetre waves
IPC: H01J19/80
Filed: 1951-12-21
Abstract: 704,378. Travelling-wave tubes; magnetrons. PHILIPS ELECTRICAL INDUSTRIES, Ltd. Dec. 21, 1951 [Dec. 29, 1950], No. 29951/51. Class 39(1) [Also in Group XL(b)] A tube for amplifying, generating or modulating millimetre waves, i.e. whose wavelength is in the range of a few tenths of a millimetre and a centimetre, and in which the resonant system comprises a plurality of parallel coplanar wires #/2 long which oscillate with antinodes at their centres and nodes at their ends and so that adjacent wires oscillate in antiphase, and which interact with an electron beam flowing normal to the axes of the elements but parallel to the plane in which they lie, is characterized in that the wires are of tungsten or molybdenum and are strung transversely on a conductive frame whose longitudinal axis is parallel to the electron paths. In one form, Fig. 1, cathode 1 and beam forming plates 2 produce a flat electron beam which is focused magnetically. Thick and thin tungsten or molybdenum wires 5, 6, are strung alternately on molybdenum frame 4 and goldsoldered thereto. After soldering the frame is stretched parallel to the wires to make them taut. The thick wires 5 are connected by two strips 7 to make their effective length slightly less than #/2 that of the thin wires being slightly greater than #/2 so as to ensure that adjacent wires oscillate in phase opposition. The beam velocity is such that it traverses the distance between two adjacent wires in a half period, and it may be necessary to progressively decrease the wire spacing towards the collector 3 to maintain synchronism as the beam loses energy. Loops 9, 8 supply and remove energy for amplifier operation, or if the device is a self excited oscillator loop 9 is removed. In a modification, Fig. 3a (not shown) the frame is inserted in a waveguide which has separate input and output guides transverse thereto. Another modification, Fig 3b (not shown) operates as a linear magnetron with crossed electric and magnetic fields. In this case the frame and, plate-like electrode at cathode potential which has a recess at one end to accommodate a filament cathode may or may not be enclosed in a waveguide. In another form, Figs. 5, 6, which shows a detailed construction, seven frames 18, six of which carry the spaced wires, are piled up and heated, the gold solder securing the wires to the frames partly melting and securing the whole assembly together as a unit which is inserted within a rectangular sectioned casing 16 with four intervening conductive strips 29. The apertures in the frames have bevelled edges so that the thick wires are of smaller effective length than the thin ones, Fig. 6. One end of frames 18 is widened to take a flat cathode 22 held by mica plates 21 and stay rods 23. A grid 25 is carried on stay rods 24, and the grid and cathode leads pass through openings 26 in the casing 16. The casing 16 functions as a rectangular sectioned waveguide the internal cross-sectional dimensions of which are #/2 and #/2 to # respectively. The mean depth of each side of each frame 18, measured parallel to the wires is #/4 The end parts 30 of frames 18 are #/4 long in the direction of wave propagation so as to provide impedance transformers to an external waveguide (not shown) coupled to the open flanged end 17. The external guide has a choke joint at the coupling end to prevent escape of energy, Fig. 4 (not shown). The grid 25 is slightly negative to the cathode and the frames 18 are highly positive so a number of flat beams are formed, which are focused by. a magnetic field. The tube shown is an oscillator but may be used as an amplifier by the provision of an input coupling loop or aperture in the guide wall near the cathode; in this case the provision of damping means may be necessary to prevent self oscillation. The tube operates at about 8 mms. but may be scaled down to operate at 0.5 to 1 mm. The frames can be piled up to a total thickness of #/2 to # and their length may be up to 3#/2 to 2#.