US2882440A - Delay lines for travelling wave tubes - Google Patents

Description

April 14, 1959 cs. MOURIER DELAY LINES FOR TRAVELLING WAVE TUBES 3 Sheets-Sheet 1 Filed Nov. '17. 1955 April 14, 1959 G. MOURKER DELAY LINES FOR TRAVELLING WAVE TUBES 5' Sheets-Shet 2 Filegi NOV. 17, 1955 April 14,1959

s MOURIER 2,882,440 I DELAY LINES FOR TRAVELLINGWAVE TUBES Fild Nov. 17, 1955 3 Sheets-Sheet 3 United Sttes Patent DELAY LINES FOR TRAVELLING WAVE TUBES Georges Mourier, Paris, France, assignor to Compa gnie Generale de Telegraphic Sans Fil, a corporation of France Application November 17, 1955, Serial No. 547,491

Claims priority, application France November 29, 1954 9 Claims. (Cl. SIS-3.5)

The present invention relates to a delay line suitable, more particularly, for rectilinear travelling wave tubes, of cylindrical symmetry. Tubes of this type, in which helically shaped delay lines are often used, have a wide frequency band and a high gain per unit of length.

Such delay lines are, however, unsuitable for high power tubes. As is known, the helix of a travelling wave tube generally comprises a long, thin conductor which, in practice, is difficult to mount and cool. Consequently, a tubular metal envelope is used, coaxial with the helix, the latter being secured in said envelope by means of rods spaced along the length of the helix. Such an arrangement considerably reduces the passband of the tube.

The present invention has for its object a new type of delay line for travelling wave tubes which is of sturdier construction and is easier to cool than a helix of similar overall size and performance.

The delay line in accordance with the present invention comprises substantially: a tubular metal member of circular cross-section, and an array of delay elements located in successive cross-sectional planes of said member, each of said elements comprising two rectilinear and colinear portions fixed to the tubular member, and a third portion joining the first two portions, said third portion being in the shape of the arc of a circle coaxial with the tube, the third portions of successive element being located alternately on either side of the aerial plane of symmetry of said member and array.

Preferably, these elements are tubular, the cooling of the tube being ensured by a fluid flowing within said elements.

The invention will be better understood with the aid of the annexed drawings, wherein:

Fig. 1 depicts a longitudinal section and Fig. 2 a transverse cross-section through a plane which includes a delay line element of an amplifying travelling wave tube, without crossed magnetic field, and incorporating a delay line according to the invention;

Fig. 3 is a longitudinal cross-section of an amplifying travelling wave tube, with crossed electric and magnetic fields fitted with a line such as represented in Figures 1 and 2;

Fig. 4 shows the dispersion curve of said line;

Figs. 5 and 6 show a transverse cross-section of two other embodiments of a delay line according to the invention.

The tube of Fig. l, the principle of which is well known, comprises a cylindrical metal envelope 1, one end of which carries a collector electrode 2 and the other end an insulated base 3. The latter supports an emissive cathode 4, a heating filament 5, fed by conductors 6, and a focusing electrode 7 designed to concentrate the electrons in a tubular beam 8, an accelerating anode 9 is connected to envelope 1, said anode having an annular aperture 22 for the passage of the beam. Supply leads 10 are connected to the cathode 4 and the focusing electrode 7. A source of power 11 enables envelope 1 to be brought to a high positive potential with respect to the cathode.

Within tube 1 are arranged in equidistant cross-sectional planes, an array of elements 12, the shape of which will be described hereafter, constituting together with envelope 1 the delay line of the tube. 011 the gun side of the tube, the line is coupled to an input circuit by a coaxial line 13, and on the collector side, to an output circuit, by a coaxial line 14. A winding or coil 15 fed from a direct current source, not shown, establishes an axial magnetic beam focusing field. Envelope 1 is provided with a cooling jacket 16, an inlet 17 and outlet 18 for the circulation of a cooling fluid.

As shown in Fig. 2, each element 12 consists of two substantially rectilinear and colinear portions AB and CD, welded or otherwise fixed to the wall of tube 1 and extending along a portion of the diameter of the tube, and of a semi-circular portion BEC coaxial with the tube structure. The total length ABECD is substantially equal to where A is the minimum wavelength of the operating band of the tube. Located on either side of each element 12 are two further elements which are superposable to said first element by a movement of translation followed by a rotation of about the axis of the system. Elements 12 enclose, about said axis, a cylindrical space through which the beam 8 passes. Elements 12 are tubular defining a hollow interior communicating with space for the coolant bounded by jacket 16, thus efficiently cooling the line. The operation of such a tube is well known and will not be described here.

Fig. 3 represents an amplifying tube with crossed electrio and magnetic fields, comprising a delay line similar to that of the preceding tube. Said tube comprises substantially the same elements as those of Fig. 1, these elements being designated by like references. The focusing coil 15 has, however, been omitted. Further, a cylindrical electrode 19 extends along the axis of the tube through the insulated base 3; a ring 20 of insulating material serves to insulate said electrode from collector 12.

Source 11 is connected between conductor 19 and en-.

velope 1. Further, a strong electric current is made to flow in said conductor from source 21 connected to both its ends. Two fields are thus generated in the space included between electrodes 1 and 19: a magnetic field produced by the current flowing in electrode'19, the circular lines of force of said field being coaxial with the tube, and an electric field produced by the potential dilference between electrodes 1 and 19, the lines of force of said electric field being radial. The operation of such a tube has been described in the copending application Ser. No. 144,501.

Fig. 4 shows the dispersion curve of the lines depicted in Figures 1 and 3, i.e. the variation of the delay ratio (0 being the velocity of light and v the phase velocity of a wave on the line, the free space wavelength of which is x) as a function of A. It is seen that between the limits A (corresponding substantially to twice the length of an element 12) and A (which, as experience shows differs from A in the order of 20%), the value remains substantially constant at a value close to 3 which is equal-to (,9 being the pitch of the line shown in Figure 1). The pitch of a delay line according to the invention is the distance between two successive delaying elements, located on the same side of the axialplane of symmetry of the member 1. For waves longer than the slope of the curve increases rapidly and the curve attains the value for a wavelength equal to. A The lineiscalled anegative dispersion line. Such lines are particularly suitable for use in amplifier capable of operating in the bandwidth 71 i.e. of a comparatively wide band of about 20% for instance. Both conditions of sturdy construction and adequate cooling have thus been taken care of in this new design, together with a wide passband and a gain comparable to that of a tube incorporating a helix.

Figs. and 6 show two other embodiments difiering from that of Fig. 2 in that portions AB and CD extend along parallel chords in the cross-section of said tube. In Fig. 5, the arc BBC is lessthan a semi-circle whereas in Fig. 6 it is more than a semi-circle. In each of these two embodiments, the total length of each element is still equal to A being the minimum operating wavelength of the tube. In comparison with the embodiment of Fig. 2, the embodiment of Fig. 5 ensures, under similar conditions, a narrower band and a higher gain, while, on the contrary, that of Fig. 6 ensures a wider band and a lower gain.

What is claimed is:

1. In a travelling wave amplifier tube, a delay line comprising a hollow cylindrical tubular member of an electrically conductive material and an array of delaying elements located respectively in cross-sectional planes of said member, each element comprising first and second rectilinear and colinear portions, and a third portion joining said first and second portions, said third portion being inthe shape of an arc of a circle coaxial with said member, the third portion of successive elements being located alternately on either side of the axial plane of symmetry of said member and array.

2. Delay line according to claim 1, in which said delaying elementsare made of metallic tubes having a hollow, interior communicating with the outside of said member.

3. Delay line according to claim 2, further comprising a coolant jacket surrounding said member, means being provided for causing a coolant fluid to flow in the space comprised between said jacket and said member, and in said hollow interior of said delaying elements.

4. Delay line according to claim 1, in which first and second rectilinear portions of each delaying element extend along a diameter of cross-sections of said member, said third portion extending along a semi-circle coaxial with said member.

5. Delay line according to claim 1, in which said are of circle is more than a semi-circle.

6. Delay line according to claim 1, in which said arc of circle is less than a semi-circle.

7. In a travelling wave tube amplifier of the type defining an electron path having an axial direction between an electron-emitting means and a collecting means, a delay line comprising a hollow member of an electrically conductive material disposed about said path and an array of delaying elements located respectively in cross sectional planes of said member, each element comprising first and second essentially rectilinear portions and a third portion joining said first and second portions, said third portion being essentially in the shape of an arc of a circle coaxial with said axis, the third portion of successive elements being located alternately on either side of the axial plane of symmetry of said member and array.

8. In a travelling Wave tube the combination according to claim 7 wherein said tube is of the type having crossed electric and magnetic fields, further comprising means adapted to produce said crossed electric and magnetic fields.

9. In a travelling wave amplifier tube the combination according to claim 8 wherein said means for producing said electric field includes an electrode extending along said axis.

References Cited in the file of this patent UNITED STATES PATENTS 2,678,407 Brown et al. May 11, 1954 2,708,236 Pierce May 10, 1955 2,728,029 Finger Dec. 20, 1955 2,746,036 Walker May 15, 1956 2,800,605 Marchese July 23, 1957 2,802,135 Dodds Aug. 6, 1957 FOREIGN PATENTS 730,687 Great Britain May 25, 1955

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