Patent GB-724083-A (GB)
Title: Improvements in or relating to space discharge devices employing resonators
IPC: H01J23/24
Filed: 1951-03-16
Abstract: 724,083. Velocity modulated tubes. WESTERN ELECTRIC CO., Inc. March. 16, 1951 [March 18, 1950], No. 6362/51. Class 39 (1). A high frequency electron discharge device comprises a succession of resonators of small electron obstructing area arranged along and within a hollow waveguide so as to interact directly with an electron beam projected past the resonators from a source at or near one end of the guide. A small electron obstructing area is defined as 0-33 1/3 per cent. for resonators in the form of wires, strips or apertures in a conducting sheet, or 10-50 per cent. for multiple series of elements or wire grids. The device may function as a filter type structure supporting travelling waves or as a multi-resonator klystron. In one form, Fig. 1B, the array of wires 16 is arranged within an evacuated portion of a rectangular metal guide 11 defined by glass windows 12, 14 sealed to the guide wall by flanges 13, 15. Input and output guides are attached at the open ends. The wires 16 are a little less than #/ 4  long, are secured at one end only to the guide wall, and their length at the input and output ends is progressively reduced as shown to give proper impedance terminations. The device has indirectly heated cathode 17, accelerating grid 23 and collector 28 the leads to which pass through insulating bushings in the guide walls. A longitudinal magnetic focusing field may be provided by a solenoid or electromagnet (not shown). For filter operation adjacent wires are spaced by about nine tenths of half an electronic wavelength or less, i.e. so the device operates not too near cut-off where the attenuation would be large. For multi-resonator klystron operation the spacing is half an electronic wavelength (cut-off) or slightly larger, e.g. one and two tenths times this value. An electronic wavelength is defined as the free space wavelength of the wave times the ratio electron velocity: velocity of light. If the resonator elements are more than normally lossy the multiresonator operation obtains over a wider frequency range. The wires 16 may be of circular or strip form with the broad faces transverse to the electron stream. In another form, Figs. 2A, 2B (not shown) the #/ 4  resonators are formed by a slotted metal sheet, and the ends of the guide are bent at right angles to its main portion, the electron stream being projected into the guide from a side tube comprising a glass bulb and short intermediate metal tube. The fins between the slots are edge on to the electron stream and are tapered at the input and output ends to provide an impedance match. The bends in the guide are provided with 45 degree corners. The operation is similar to that of Fig. 1B i.e. the length of each fin in the direction of electron flow being less than half an electronic wavelength for travelling wave operation, and greater than half an electronic wavelength for multiresonator klystron operation. The slots between the fins can be up to half an electronic wavelength wide, but are preferably # to “ of an electronic wavelength wide. In a modification, Fig. 3 (not shown) the slots and fins each extend along the electron path for more than half of an electronic wavelength and 'spatial harmonic operation' is utilized as described in Specifications 652,219 and 714,832. The guide is bent only at the input end and is sealed at either end by a glass or ceramic window sealed to a metal plate sealed by a flange member to the guide walls. The cathode chamber is metallic except for a glass seal for the leads and the connecting tube to the guide extends into the chamber and forms the accelerating electrode, and the beam is made initially convergent by an annular focusing electrode surrounding the cathode. In another form, Fig. 4A, which will operate only as a multiresonator klystron, the resonant wires 64 are secured at both ends to the wall of a rectangular or circular guide 65; they are slightly less than #/2 long and are spaced apart by about half an electronic wavelength. The input and output couplings are by way of glass or ceramic lenses 68, 72 to focus the microwaves, conical members 70, 73 and metal sheets 69 formed with one or more dumbbell shaped resonant slots. The cathode 67 is directly heated. Lenses 68, 72 may be on opposite sides of envelope 65; the lenses may be replaced by guides or horn antennae. In a modification, Fig. 5 (not shown) the input and output are by way of coaxial lines to and from drum shaped cavity resonators at either end of the array of wires. In another form, Fig. 6A also operable only as a multiresonator kylstron, a thin metal sheet 91 is formed with an array of dumbbell shaped resonant apertures and extends along a rectangular guide 92. The distances between opposite aperture edges lie between a quarter and a half of an electronic wavelength. The electron beam is of sheet form and passes on both sides of the metal sheet 91. The input and output coupling is by way of parts 104, 105; 108, 109 on opposite sides of sheet 91, and baffles 106, 107 have central apertures of such dimensions as to block the wave when the beam is turned off. In further forms, Figs. 7, 8 (not shown) an array of #/ 2  parallel slanting wires or two such arrays slanting in opposite directions are used as resonators. The slanting of the wires increases the coupling between them so travelling wave operation is possible. In another form, Fig. 9A the resonators each comprise two. mesh grids 122 and an intervening wall portion, the grids consisting of a few coarse wires or many fine wires; either travelling wave or multiresonator kylstron operation can be utilized.. Input and output guides 125, 127 are coupled to the grids via glass or ceramic windows 126, 128 rather less than #/ 4  from the closed ends of the guides. The first grid 122 serves also as an accelerating grid. In the forms utilizing travelling wave operation loss may be introduced by plating the wires or slotted sheets with iron, or by depositing carbon or inserting ceramic material between the resonators. For a certain minimum distance from the input along the resonators, for which a formula is given, no loss material is provided, and the attenuation may be distributed uniformly over the remainder of the resonators or lumped at a point beyond the minimum distance.