US3258640A - Travelling wave tubes having multiple slow wave structures - Google Patents

Travelling wave tubes having multiple slow wave structures Download PDF

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US3258640A
US3258640A US3258640DA US3258640A US 3258640 A US3258640 A US 3258640A US 3258640D A US3258640D A US 3258640DA US 3258640 A US3258640 A US 3258640A
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slow wave
helix
helices
structures
electron beam
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J23/00—Details of transit-time tubes of the types covered by group H01J25/00
    • H01J23/36—Coupling devices having distributed capacitance and inductance, structurally associated with the tube, for introducing or removing wave energy
    • H01J23/40—Coupling devices having distributed capacitance and inductance, structurally associated with the tube, for introducing or removing wave energy to or from the interaction circuit
    • H01J23/42—Coupling devices having distributed capacitance and inductance, structurally associated with the tube, for introducing or removing wave energy to or from the interaction circuit the interaction circuit being a helix or a helix-derived slow-wave structure
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J23/00—Details of transit-time tubes of the types covered by group H01J25/00
    • H01J23/16—Circuit elements, having distributed capacitance and inductance, structurally associated with the tube and interacting with the discharge
    • H01J23/24—Slow-wave structures, e.g. delay systems
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J25/00—Transit-time tubes, e.g. klystrons, travelling-wave tubes, magnetrons
    • H01J25/34—Travelling-wave tubes; Tubes in which a travelling wave is simulated at spaced gaps
    • H01J25/36—Tubes in which an electron stream interacts with a wave travelling along a delay line or equivalent sequence of impedance elements, and without magnet system producing an H-field crossing the E-field
    • H01J25/38—Tubes in which an electron stream interacts with a wave travelling along a delay line or equivalent sequence of impedance elements, and without magnet system producing an H-field crossing the E-field the forward travelling wave being utilised

Definitions

  • FIGS. 1 A first figure.
  • travelling wave tube includes backward wave oscillator or amplifier tubes in which the energy of wave propagation along the slow wave structure is oppositely directed to the electron stream.
  • an electron beam is projected from an electron gun along the axis of a wire helix to an electron collector electrode.
  • the dimensions of the helix are chosen to provide slow wave propagation along the axis of the helix with a phase velocity approximately the same as that of the electrons of the beam. These dimensions, therefore, depend, inter alia, upon the desired frequency of operation of the travelling Wave tube and also upon the accelerating voltage applied to the electrons of the beam.
  • the helix is typically made of wire 0.010" diameter, wound at 30 turns per inch with the helix having a mean diameter of 0.090".
  • Such a helix is conveniently and conventionally supported between three parallel dielectric rods extending between the electron gun and electron collector electrode. If it were desired to operate a travelling wave tube at a comparatively low beam accelerating voltage-say, 100 volts-even at much lower frequencies, the helix would have to be wound of very fine wire at many turns per unit axial length. Difliculties would then arise in supporting the helix and avoiding distortion to its geometry; the conventional three rod support becomes impracticable.
  • a slow wave structure which has an arrangement surrounding the electron beam of a set of slow wave structures whose fields couple to one another and to the electron beam in such a manner as to provide along the electron beam path a means for the propagation of electro-magnetic Waves in a slow mode in which the electric vector is predominantly longitudinal.
  • Each of the structures, of which there are at least three, is of the same class of slow wave structure.
  • the structures may all be helices or they may all be ladder type structures of similar form.
  • the structures are arranged parallel to one another, side-by-side, symmetrically around the electron beam axis and should not overlap in planes transverse to that axis-Le. in the case of helices, for example, the turns of one helix should neither touch nor overlap those of its neighbour.
  • FIG. 1 is a diagrammatic illustration of a travelling wave tube according to the invention employing a set of helices for the slow wave structure;
  • FIG. 2 is a cross section through the plane IIII of FIG. 1;
  • FIGS. 3 and 4 illustrate the general arrangement of the individual helices in embodiments such as that of FIGS. 1 and 2;
  • FIG. 5 illustrates the electric field configuration produced in the arrangement of FIGS. 3 and 4;
  • FIG. 6 illustrates an alternative form of h.f. feed for the slow wave structure
  • FIGS. 7 to 9 relate to ladder type slow wave structures, FIGS. 7 and 9 showing respective arrangements according to the invention of structures derived from the basic ladder structure of FIG. 8.
  • an electron gun 1 having a cathode 2 focusing electrode 3 and anode 4 is mounted within an envelope portion 5, from which projects an elongated envelope portion 6 of smaller diam eter surrounding the electron beam path and the composite slow wave structure and which at its far end carries an electron collector electrode 7.
  • the composite slow wave structure comprises a set of helices each wound upon a dielectric rod 8 the rods being parallel to the electron beam axis and symmetrically arranged about that axis as shown in FIG. 2.
  • the dielectric rods are supported at their ends in a pair of metal sleeves 9.
  • Input and output couplings for the composite slow wave structure are provided by externally contra-wound helical couplers illustrated at 10.
  • FIGS. 3 and 4 The general arrangement of the composite slow wave structure is illustrated in FIGS. 3 and 4.
  • FIG. 3 eight similar helices 11 are shown, each wound upon its own support rod 8.
  • the centres of the rods lie upon a circle whose centre is the electron beam axis and are spaced from one another by a distance d as indicated in FIG. 4.
  • the electron beam indicated in FIG. 3 at 12 passes close to the helices so that the beam electrons interact with the external fields of the helices.
  • a simple transmission line theory shows that irrespective of whether all the helices are wound in the same direction, or, in the case of an even number, alternate ones are contrawound, two modes of slow wave propagation are possible. The faster of these modes has a predominantly longitudinal electric field as illustrated in FIG.
  • the lines of electric force 13 flow from node to node along the length of each helix so that the electric vector is predominantly longitudinal.
  • lines of electric force tend to be directed transversely from on helix to its adjacent neighbour so that any electric field near the axis is predominantly transverse.
  • the mode illustrated in FIG. 5 the in-phase modeis utilised.
  • the propagation constant of the composite slow wave structure may be expressed in terms of the propagation constants of th individual helices, together with terms involving the distance d.
  • For maximum band Width and freedom from unwanted Hartree harmonics we prefer to dimension the individual helices so that ya for each helix is approximately 1.5, being the radial phase constant of propagation and a the radius of the helix.
  • the interaction impedance for the composite structure will be higher than that given by the simple theory, so that a compensating effect is obtained.
  • the six helix structure is more dispersive than a single helix, and this is, in general, true for any member of slow wave structures whether of the helix class or otherwise.
  • the dispersion can be increased when using the helix class by contrawinding alternate helices or adjacent groups of helices, the symmetry of the arrangement still being preserved.
  • the dispersion may also b varied by choice of the spacing of.
  • a six helix structure was used, all helices being wound in the same direction.
  • the helix was wound with 0.002 inch diameter tungsten wire at 250 turns per inch on ceramic rods each of diameter 0.075 inch.
  • the length of each helix was 4 /2 inches with a beam 0.083 inch in diameter carrying a current of 2 ma. with a beam voltage centered on 100 v.
  • the beam diameter was chosen as in conventional single helix travelling wave tubes to occupy about 0.8 of the available spacing.
  • a maximum gain of 20 db was obtained at 760 mc./s. and 118 volts on the beam.
  • the amplifier was voltage-tuned by varying the beam voltage over the range 86-125 volts, the average gain in the frequency range 1020-710 mc./s. being about db.
  • coupling to the slow wave structure is indicated as by means of contra-wound helix couplers 10. If P be the pitch of the individual helices of the slow wave structure and F be the pitch of the outer coupling helix then, approximately where D is the mean diameter of coupling helix and S is the mean distance between coupling helix and inner helix.
  • the power is transferred to the structure by a spatial heating process.
  • the coupling length of the outer helix can be found very approximately from the usual helical coupler theory. This value, however, will be shorter than actually required because the spacing between inner helices tends to reduce the coupling to the outer helix.
  • waveguide coupling is used.
  • the individual helices are closely surrounded by a glass envelope 19, which projects in an analogous manner to the conventional travelling wave tube through a waveguide 20.
  • the ends of the helices terminate flush with the inner wall of the waveguide.
  • a metal drift tube 21, held in between the helices of the slow wave structure and surrounding the electron beam, projects transversely across the waveguide and is joined to a choke sleeve 22, which co-operates with a flange 23, projecting from the waveguide wall to form a conventional waveguide choke for passage of the envelope 19.
  • FIG. 7 illustrates an arrangement of four juxtaposed ladder type slow wave structures, together forming a composite slow wave structure for use in high frequency embodiments of the invention.
  • Each component slow wave structure of FIG. 7 can be regarded as derived from the ladder structure of FIG. 8 which is made up of a pair of side plates 24, between which stretches a transverse grating 25 of parallel resonators, here shown as slots, but which could be bars, inclined to the normal between the side plates 24 so as to produce an assy-mmetry in the electric field distribution and enable it to propagate over a finite band of frequencies.
  • the slotted grating 26 corresponds to the grating 25 of FIG.
  • the adjacent slow wave structure has the grating 28 corresponding to the grating 25, the vanes 27 corresponding to the upper portions of the skirts 24 and the adjacent gratings 26 and 30 corresponding to the lower skirts of the side walls 24.
  • FIG. 9 shows diagrammatically an end view of an arrangement of six slow wave structures of the ladder type assembled together in an analogous manner to the four structures of FIG. 7 and comprises webs 27 and similar gratings 31.
  • the gratings 31 can take other forms than those illustrated in FIG. 8 such for example, as an intersecting structure of conductors forming a mesh such as disclosed in U.S. Patent No. 3,090,886, issued May 21, 1963, and assigned to the same assignee as the instant application.
  • the electron beam is projected along the axis of the composite slow wave structure, as in the case of the multiple helix embodiments.
  • Coupling to input and output feeders may be effected in various ways known to those skilled in the art; one method of coupling would be to mount the composite slow wave structure between input and output waveguides normal to the axis of the electron beam, as in many conventional travelling wave tubes, and to have extensions of the individual grating projecting into the respective waveguides through slots cut in the waveguide walls.
  • a travelling wave tube including an envelope means for projecting an electron beam along a given axis of said envelope and at least three slow wave structures of the same form positioned radially and symmetrically about said beam with the axes of propagation of said structures parallel to said given axis and the electric field having a predominantly longitudinal mode, each said structure being electromagnetically coupled to and spaced apart from the electron beam and the adjacent structure, and signal coupling means around said envelope adjacent and spaced from the ends of said slow wave structure for electromagnetically coupling power into and out of respective said ends.
  • a travelling wave tube according to claim 1 in which the slow wave structures are helices whose pitch circles are spaced apart from one another and from said beams.
  • each slow wave structure is formed by a uni-planar grating of parallel conductors arranged in a mesh formation between a pair of side walls.
  • a travelling wave tube according to claim 2 wherein adjacent said helices are wound alternately in opposite directions.
  • a travelling wave tube including an envelope, an electron gun beam forming structure, a slow wave structure and an electron collector electrode aligned along a given axis of said envelope, in which the slow wave structure is formed by a set of at least three similar helices each Wound upon a dielectric support rod, and signal coupling means around said envelope adjacent and spaced from the ends of said helices for electromagnetically coupling power into and out of respective said ends
  • the travelling wave tube further including means mounting the helices and rods symmetrically surrounding and parallel to the given axis and beam in an electromagnetically coupled spaced relationship with the electron beam and with one another, and the electric field within said tube having a predominantly longitudinal mode.
  • a travelling wave tube in which the ends of each rod are mounted in a metal sleeve and each helix is joined at its respective ends to the adjacent sleeve.
  • said signal coupling means includes a Waveguide feeder and means for coupling the slow wave structure thereto, said coupling means for said waveguide feeder comprising a drift tube having one end inserted between the helices of the slow wave structure and surrounding the electron beam, said drift tube extending transversely through said waveguide feeder, and a choke at the other end slee ve mounted on the far end of the drift tube continuous with the opposite waveguide wall.
  • Apparatus including a travelling Wave tube according to claim 7 wherein said signal coupling means includes a contrawound helix coupler surrounding the travelling wave tube about one end of the slow wave structure.

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US3258640D 1960-03-24 Travelling wave tubes having multiple slow wave structures Expired - Lifetime US3258640A (en)

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GB10408/60A GB934794A (en) 1960-03-24 1960-03-24 Improvements in or relating to travelling wave tubes

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US3258640A true US3258640A (en) 1966-06-28

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US (1) US3258640A (enrdf_load_stackoverflow)
BE (1) BE601683A (enrdf_load_stackoverflow)
GB (1) GB934794A (enrdf_load_stackoverflow)
NL (1) NL262776A (enrdf_load_stackoverflow)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4232249A (en) * 1978-09-28 1980-11-04 Bell Telephone Laboratories, Incorporated Beam-switched traveling wave tube

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2679019A (en) * 1947-12-02 1954-05-18 Rca Corp High-frequency electron discharge device
US2789247A (en) * 1948-07-23 1957-04-16 Philips Corp Traveling wave tube
US2801361A (en) * 1948-12-10 1957-07-30 Bell Telephone Labor Inc High frequency amplifier
US2831142A (en) * 1951-10-03 1958-04-15 Kazan Benjamin Slow-wave structures

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2679019A (en) * 1947-12-02 1954-05-18 Rca Corp High-frequency electron discharge device
US2789247A (en) * 1948-07-23 1957-04-16 Philips Corp Traveling wave tube
US2801361A (en) * 1948-12-10 1957-07-30 Bell Telephone Labor Inc High frequency amplifier
US2831142A (en) * 1951-10-03 1958-04-15 Kazan Benjamin Slow-wave structures

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4232249A (en) * 1978-09-28 1980-11-04 Bell Telephone Laboratories, Incorporated Beam-switched traveling wave tube

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BE601683A (fr) 1961-09-25
NL262776A (enrdf_load_stackoverflow)
GB934794A (en) 1963-08-21

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