US2942143A

US2942143A - Travelling wave tube amplifier

Info

Publication number: US2942143A
Application number: US696118A
Authority: US
Inventors: Epsztein Bernard
Original assignee: CSF Compagnie Generale de Telegraphie sans Fil SA
Current assignee: Thales SA
Priority date: 1956-12-04
Filing date: 1957-11-13
Publication date: 1960-06-21
Anticipated expiration: 1977-06-21
Also published as: GB828497A; DE1108335B; FR1162425A

Description

June 2l, 1'960 B. EPszTElN TRAVELLING WAVE TUBE AMPLIFIER 2 Sheets-Sheet 1 Filed Nov. 13, 1957 June 21, 1960 B. EPszTElN TRAVELLING wAvE: TUBE AMPLIFIER 2 Sheets-Sheet 2 Filed Nov. 15, 1957 United States Patent l rRAvELLiNG WAVE TUBE AMPLIFIER Bernard Epszten, Paris, France, assigner to Compagnie Generale de Telegraphie Sans Fil, Paris, France Filed Nov. 13, 1957, Ser. No. 696,118

Claims priority, application France Dec. 4,1956

Claims. (Cl. S15-3.5)

The present invention relates to forward travelling wave amplifiers of cylindrical structure. More particularly, the present invention relates to the details of delay lines utilized lin forward wave amplifier tubes.

Helix-type delay lines are already known in the prior art. Moreover, it is known that the travelling wave tubes of the prior artvwhich utilize such helix-type delay lines have a relatively large gain and a relatively large bandpass. However, the use of such lines in high-powered tubes poses serious problems, particularly as to cooling of the delay lines and manner of support or securing thereof which are `rather difficult to resolve. In fact, a helix-type delay line is constituted by a spirally wound wire of relatively large length; it is, therefore, particularly diicult to cool the spirally wound wire of the helix-type delay line and tomaintain the same in place since the helix, Le., the spiral turns thereof, are deformed under the action of heat. These inconveniences found in connection with helix-type delay lines of the prior art may be reduced, for example, by fixing or securing the helix at several points thereof, distributed over the entire length thereof, by means of metallic rods or the like brazed to an external metallic tube which is coaxial with respect to the helix. However, as a result of such rod-like securing means, the width of the band-pass of the tube is considerably reduced.

On the other hand, delay line circuits are also already known in the prior art which are constituted by a circular guide provided with and loaded by metallic disks, each including in the center thereof an orifice or aperture for the passage of the electron beam. Such a disk-type delay line circuit is relatively sturdy, and does not offer the inconveniences and disadvantages of the helix-type delay line insofar as .cooling and securing or fastening of the line is concerned; however, tubes which are equipped with delay lines including metallic disks possess a reduced gain and a relatively small band-pass.

It has already been proposed to solve these difficulties by providing a delay line in the form of a series of ringlike or annular members of which each is connected with a metallic cylinder or guide, surrounding coaxially the line, by means of n radial rods or spokes forming supports therefor, with the angular displacement between the supports of each pair of successive annular members being equal to The United States Patent 2,768,322 to Fletcher is representative of this prior art type delay line.

While this last-described type of line possesses advantages insofar as sturdiness and band-pass are concerned in comparison with the aforementioned helix-type delay lines or the dislotype delay lines, this last-described delay line possesses' an inverse dispersion characteristic of the fundamental space wave so that forward wave amplifiers which utilize such type of delay line function or operate by the interaction with a space harmonic of which the dispersion is forward, and not with the fundamental space wave.

However, tubes utilizing and operating by the interaction with a space harmonic other than the fundamental, with all other things remaining equal, have a smaller coupling resistance and a narrower band-pass than tubes operating or functioning by interaction with the fundamental.

Accordingly, the present invention has for its object the provision of a delay line for a forward wave ampliiier which obviates the disadvantages noted hereinabove in connection with the prior art devices.

Another object of the present invention is the provision of a delay line for a forward wave amplifier which is essentially non-dispersive, which corresponds to a forward dispersion of the fundamental space harmonic thereof, and which is simultaneously rigid, sturdy and easy -to build.

A still further object of the present invention is the provision of a delay line which readily enables a relatively large dissipation of heat to permit use thereof for high-powered tubes.

Still another object of the present invention is the provision of an amplifier having a large useful band-pass, a large gain and a high power.

Thus, the present invention has for its object the provision of a delay line which simultaneously conserves the advantage of sturdiness of the delay line as found in the type of line having annular members as described above, but which, in contradistinction thereto, offers the desired characteristics of forward dispersion of the fundamental space harmonic. By reason of this fact, such delay line is particuiarly useful in connection with forward wave amplifiers which function or operate by interaction with the fundamental space wave, and in such application this type of delay line assures a still larger band-pass than the band-pass of the preceding line, and with a larger gain due to the relatively high coupling resistance.

A still further object of the present invention is the provision `of a forward travelling wave amplifier which utilizes such a delay line.

These and other objects, features and advantages of the present invention will become more obvious from the following description when taken in connectigLwitl-i the accompanying drawing, which shows, for purposes of illustration only, several embodiments in accordance with the present invention, and wherein:

Figure l is an axial longitudinal cross-sectional view through `one embodiment of a forward wave amplifier tube provided with a delay line in accordance with the present invention taken along line I-I of Figure 2;

Figure 2 is a cross-sectional view taken along line II-H of Figure l;

Figure 3 is a cross-sectional view similar to Figure 2 of another embodiment of a tube provided with a delay line in accordance with the present invention;

Figure 4 is a cross-sectional view similar to Figure 2 of still a further embodiment of a tube provided with a delay line in accordance with the present invention, and

Figure 5 is an axial longitudinal cross-sectional view through a different embodiment of an amplifier tube in accordance with the present invention.

The delay line in accordance with the present invention includes, similar to the line mentioned hereinabove, a metallic guide which preferably but not necessarily constitutes the external envelope of the tube, and which includes coaxial metallic ring-like annular members, each secured to the wall of the tube by n radial metallic spokes or rod-like supports, as seen `in cross-sectional views at right angle to the axis of the tube. However, in contradistinction to the aforementioned known type of delay Patented 'June 2l, i960 line, the delay line in accordance with the present invention is characterized by the combination of features that the angular displacement between spokes or rod-like support members of successive ring-like or annular members is zero and that n metallic filler members are disposed along the inner wall of the tube in the sectors delimited by the radial spoke-like support members, which filler members extend over the entire length ofthe tube and form auxiliary base members of which every section in a plane perpendicular to the axis of the tube has the shape of a sector of an annulus.

According to one preferred embodiment in accordance with the present invention, each auxiliary basemember is provided with ridge portions directedperpendicularly to the axis of the tube, each ridge portion being disposed between two successive annular or ring members of the delay line.

Referring now to the drawing, wherein like reference numerals are used throughout the various views to designate like parts, and more particularly to Figures l and 2, reference numeral 1 designates therein a metallic guide member also constituting the metallic cylindrical envelope of a. forward wave amplifier tube, The cyl-indrical envelope 1 is closed at the right end thereof, as viewed in Figure l, by an electron collector element 2 of a propriate conventional construction and at the other end thereof, by an insulating base 3 in which is disposed the electron gun including an annular cathode 4, a heater filament 5, a focusing electrode 6 and an accelerating anode 7. The cathode 4 is so constructed as to emit a `tubular electron beam 8. The cathode 4 is carried at a negative potential with respect to the envelope 1 by means of a conventional power supply or voltage source of any appropriate construction and designated by reference numeral 9.

Coaxial metallic annular or ring-like members 1G are disposed in cross sections of the tube at right angles to the axis thereof. Each annular or ring-like member 10 is secure to the envelope 1 by two metallic spoke-like rod or support members 11 and 12 which are directed along a diameter of the annulus or ring as shown in Figure 2. The spoke-like rod or support members 11 and 12 which support the annular or ring-like members 10 are all parallel with respect to each other. In other words, successive support members 11 and 12 each form an aligned array, respectively, in an axial plane.

In addition, thereto, two

auxiliary base members

13 and 14, constituted by two metallic filler members, are secured to the inner wall of the envelope 1 facing the free portions of the annular or ring-like members 1G, i.e., in the spaces external of members 1b intermediate support members 11 and 12 thereof. The

base members

13 and 14 extend over the entire length of the extent of the annular or ringelike members 1t). The cross sections of the

members

13 and 14, in planes perpendicular toA the axis of the tube, have the form of sectors of annuli. The assembly of the annular or ring-like members 10 and of the

base members

13 and 14 form, together with the envelope 1, the delay line of the tube. The delay line is coupled with the input circuit and output circuit of the tube by

coaxial lines

15 and 16, respectively, which may be so constructed in any suitable manner as to provide a proper impedance match for a given band-pass or band-width with which the tube is designed to operate.

In the type of delay line in accordance with the present invention `and as described hereinabove, the high-frequency electric field perpendicular to each annular or ring-like member 10 is maximum along the free portions of the annulus or ring Whereas the high-frequency currents which circulate in each annular member are maximum in the support members 11 and 12 thereof. The electric fields of successive annular or ring-like members 10 are coupled with each other as well as the magnetic fields thereof produced by the circulating currents. Adjacent annular members 10, therefore, have both an electric and magnetic coupling with one another. However, if the delay line did not include any

auxiliary base members

13 and 14, the voltages induced by these couplings would mutually oppose one another and the net resultant coupling would, between the annular or ringlike members 10, be very Weak. lt is known that under these conditions the delay line would have a very narrow band-pass. A Y Y The presence of the

auxilitary base members

13 and 14 facing the external free portions of the annular or ringlike members 10, that is, in the neighborhood of these portions where the electric field is maximum, reduces the electric coupling between successive annular members 10, and a portion of the electric lines of force are deviated toward the respective base member instead of directly linking :the annularor ring-like members l@ with each other. Consequently, the magnetic coupling between annular or ring-like members 10 is preponderant andthe annular or ring-like members 10 are thereby strongly coupled with one another. As a result thereof, the delay line possesses a weak dispersion and a large band-pass.V Furthermore, calculations and experiments` both have conrrned that the upper cut-off frequency of the band-pass is very high, `and therefore, the dangers of parasitic oscillations by interaction with a backward space harmonic are very slight. Moreover, the coupling impedance between the electron beam and the high-tref quency Wave is very high, with the electron beam passing at a very close distance from the line and being in interaction with the fundamental wave in the delay line.

The delay line in accordance with the present invention is both sturdy and easy to manufacture. It possesses a high thermal dissipation, due to the presence of the support members in contact with the metallic envelope of the tube; Any thermal expansion is of little significance, for the delay line elements are so constructed as to be resistant againstany torsional deformation. Furthermore, it is possible with a construction in accordance with the present invention to utilize securing support members which are more rigid than the annular or ring-like members 10. Moreover, it is also possible to utilize, in connection therewith, annular or ring-like membersl as Well as spoke-'like rod or support members which are of hollow circular cross section to enable the circulation therethrough of any conventional cooling Huid, such as water or the like.

The delay lines according to Figures 3 and 4 differ from `that of Figures l and 2 only by the number of metallic rod or support members for the annular or ringlike members thereof and by the number of the auxiliary base members.

In the embodiment according to Figure 3, each annular,

or ring-like member 10 is securedto the metallic envelope 1 by a single radial metallic rod or support member 17, the angular displacement between successive or adjacent support members 17 being again zero, i.e., again forming an aligned array in an axial plane. An aux-V iliary electrode or base member 18'of sector-like cross sec` tion is disposed along the inner wall of the envelope 1 fac-4 ing the free portions of the annular member-s 10, and more particularly on the side thereof opposite the support members 17, Le., in the region where the electric field is again maximum. K

ln the embodiment according to Figure 4, each annular or ring-like member 1i) of the delay line is secured to the envelope 1 by three radial metallic rod or support members 19, 20 and Z1 subtending an angle of 120 between cach other, the angular displacement between respective successive or adjacent support members being again zero, ie., corresponding successive support members 19, 2li and Z1 each form an aligned array in an axial plane. Three

auxiliary base members

22, 23 and 24 of sectorlike cross section are disposed along the inner wall of the envelope 1 facing the free portions of the annular members 10, yopposite the

rods

19, 20 and 21.

A au,

The delay lines represented in Figures 1 through 4 allV possess a normal dispersion curve, that is, the fundamental space harmonic of the wave propagated in these lines is direct.

A further improvement in accordance with the present invention consists in providing along the surface of each auxiliary base member ridges directed perpendicularly to the axis of the tube, each ridge being disposed between successive annular or ring-like members V of the delay line. Figure 5 shows one embodiment of such improvement. The tube illustrated therein is analogous to that of Figures 1 and 2, but each

base member

13 and 14 is provided with

ridge portions

31 and 32 disposed as shown in Figure 5.

The presence of the

ridge portions

31 and 32 further reduces the electric coupling between successive annular or ring-like members 10. This has as its result, as already indicated hereinabove, a decrease in the dispersion of the delay line and, therefore, an increase in the width of the band-pass of the tube.

It is understood that the present invention is not limited to the embodiments described and shown herein but is susceptible of many changes and modifications within the spirit of the present invention, for example, delay lines having a normal dispersion curve might also include more than three auxiliary base members and more than three support members, the number of the auxiliary base members .and of the support membersbeing equal, and I, therefore, intend to cover all such changes and modifications within the scope of the present invention as encompassed by the appended claims.

`I claim: j i

l. In a forward wave amplifier tube, a delay line co prising a series of separate metallic ring-like members lmutually spaced from each other so .asto for-m individual supporting each of said members within said guide exclusive of the next adjacent member and conductive segment-like members secured to the inside of said guide and extending intermediate said support means over the length of said line.

2. In a forward wave amplier, the combination according to claim l, wherein said support means consists of at least one array of aligned supporting rods.

3. In a forward wave amplifier tube, a `delay line comprising a series of unconnected metal rings mutually spaced along a common axis, a guide member having ya metallic cylindrical surface coaxially surrounding said rings, at least one radial metallic rod supporting each of said rings on said surface, said supporting rod of each `one of said rings being aligned to form an array in an axial plane with supporting rods of adjacent rings, the number of said rods in'said array being equal to the ',for each of said metallic ring-like members for individually number of said rings, and at least one metallic filler member having a form of a cylindrical segment, said segment extending essentially axially over said series of rings in the space between said cylindrical surface of `said guide member and the external surface of said rings,

and being secured to a portion of said cylindrical surface outside the fixation point of said rods on said cylindrical surface.

4. A delay line as claimed in claim 3, wherein each ring is supported by a single rod, said filler member being fixed to a portion of said cylindrical surface opposite the fixation point of said rod on said surface.

5. A delay line as claimed in claim 3, wherein each ring is supported by a plurality of symmetrically distributed rods aligned to form a corresponding number of said arrays, there being provided the same number of said ller members, and each of said members being fixed to a portion of said cylindrical surface between adjacent arrays.

l6. A delay line as claimed in claim 5, wherein each ring is supported by a pair of oppositely directed rods, two filler members being fixed to opposite portions of said surface and having a plane of symmetry at right angles to said rods.

7. A delay line as claimed in claim 5, wherein each ring is supported by three rods mutually shifted by three filler members being clixed to three portions of said sur-face mutually shifted by 120 and having plane of symmetry shifted by `60 with respect to adjacent rods.

8. A delay line as claimed in claim 3, further comprising transverse ridges provided on said. ller members.

9.- A delay line as claimed in claim 8, wherein each transverse ridge is symmetrically positioned between a pair of adjacent rings.

10. A forward wave amplifier tube having a delay line comprising a plurality of unconnected metal rings mutually spaced along a common axis, a metallic envelope having a cylindrical surface essentially coaxially surrounding said rings, at least one essentially radially disposed metallic rod supporting each of said rings on said surface, the supporting rod for each one of said rings being aligned to form an array in an axial plane with supporting rods of adjacent rings, the number of said rods in said `array being equal to the number of said rings, and at least one metallic filler lmember having the shape of a cylindrical segment, said segment extend- Y ing essentially `axially over said series of rings in the space between said cylindrical surface of said guide member and the external surface of said rings, and being secured to a portion of said cylindrical surface outside the xation points of said rods on said cylindrical surface.

References Cited in the file of this patent