US3099766A - High capacity travelling wave tube for amplifying ultra high frequencies - Google Patents

Description

HIGH CAPACITY TRAVELLING WAVE TUBE FOR July 30, 1963 'w. VEITH ETAL 3,099,766

AMPLIFYING ULTRA HIGH FREQUENCIES- Filed Oct. 30, 1961 10 'III II 1 r (1,1

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3,699,766 Patented July 30, 1963 fire 3,tl99,766 HIGH CAPACHY TRAVELLENG WAVE TUBE FGR AMPLIFYENG ULTRA HIGH FREQUENCIES Werner Veith and Paul Meyerer, Munich, Germany, as-

Signors to Siemens & Halslre Aktiengesellschaft, Berlin and Munich, a corporation of Germany Filed Oct. 30, 1961, Ser. No. 148,656 Claims priority, application Germany Nov. 2, 1964) 9 Claims. (Cl. 315-35) This invention is concerned with a high capacity travelling wave tube, especially for the amplification of ultra high frequencies, employing purely electrostatic focusing of the electron beam, wherein the electron beam which is guided about the tube axis along a spiral path interacts with an electromagnetic Wave which is propagated along this spiral path.

There is already known a travelling wave tube wherein the electrons are propagated upon helical paths along a helical delay line surrounding a preferably cylindrical cathode. The corresponding tube is constructed in the manner of a magnetic field tube. Accordingly, for guiding or focusing the electron beam, there is required a magnetic field cooperating with additional electric fields.

There is also known a travelling wave tube with purely electrostatic focusing in which the electron beam is upon an orbital path guided through the radial field of a cylinder condenser, one electrode of which is constructed as a delay line, so that an electromagnetic wave can azimuthally spread upon such electrode. The delay effected by this line is in accordance with the supposition customary for travelling wave tubes so selected that the phase angle velocity of the electromagnetic Wave is approximately equal to the angular velocity of the electrons. The orbital path of the electron beam is stabilized by the equilibrium obtaining between the force, acting due to the electrostatic field of the cylinder condenser, and the centrifugal force of the electrons. The considerable advantage of this known travelling wave tube resides in that no magnetic field is required for the guidance of the electron beam. However, the power of this tube is relatively low due to the limited length of the orbital path.

The object of the invention is to provide a high capacity travelling wave tube with purely electrostatic focusing.

It might be feasible to realize this object by modifying the above indicated known travelling Wave tube with purely electrostatic focusing in accordance with the previously indicated magnetic field tube. Accordingly, the electron beam would in such tube run upon a spiral path between an inner conductor and a delay line surrounding the inner conductor along the spiral path of the electron beam, whereby the inner conductor would have to be connected with a high positive voltage.

However, it was found that such a tube would have a number of drawbacks: Maximum coupling between the electron beam and the delay line would be from the outset impossible since an electron beam running along a spiral path has the greatest density interiorly, that is, upon the side facing away from the delay line; moreover, the electrons move increasingly away from the delay line due to yielding energy to the high frequency field of the line, thereby further reducing the coupling between the electron beam and the delay line. The coupling between the electron beam and the delay line would also be aifected by the fact that the delay line Would not have a closed or continuous surface, such as the outer electrode of a cylinder condenser, but would be formed, due to the periodic structure, by individual rods or webs. To the electron beam would be imparted an angular path, instead of a circular path, so that the electrons would be in the region of the interaction areas lying between the rods or webs, farther away from the delay line than they would 2 be in the case of an ideal cylinder condenser. In order to obtain a satisfactory coupling, it would be necessary to guide the electron beam so close along the delay line that the release of secondary electrons would be unavoidable. The released secondary electrons would impact the positively biased inner electrode with high velocity, thereby causing an impermissible heating of the tube.

It is, therefore, for the solution of the problems underlying the objects of the present invention, in connection with a high capacity or high power travelling wave tube, especially for amplifying highest frequencies, with purely electrostatic focusing of the electron beam, wherein the electron beam, which is guided about the tube axis upon a spiral path interacts with an electromagnetic wave propagated along this path, in accordance with the invention proposed, to guide the electron beam within a spirally wound hollow delay line or wave guide structure with periodic openings of at least the wall parts thereof facing the tube axis, in the space between a metallic element (outer electrode) arranged within and electrically separated from the delay line structure and the wall parts thereof lying toward the tube axis (inner electrode) which are connected with a direct positive potential.

The advantage of the travelling wave tube according to the invention resides in that the high frequency energy is despite the absence of a magnetic field, similarly as in a magnetron, not derived from the kinetic energy of the electrons but from the potential energy of the electrostatic field. An electron moving in the space between the outer electrode and the inner electrode would be subjected to braking forces upon giving off kinetic energy for conversion into high frequency energy. Since the electron loses thereby centrifugal force, it will reach a path nearer to the inner electrode, which extends upon a potential plane of a higher potential than that of the original path. The electron accordingly retains the same angular velocity, so that the synchronism is preserved which exists between the electrons of the electron beam and an elec tromagnetic wave propagated along the delay line. The electrons thereby move ever closer to the inner electrode, whereby the coupling between the electron beam and the high frequency field of the delay line is further improved.

In order to avoid, in a travelling wave tube according to the invention, undue disturbance of the high frequency properties of the delay line, it is advantageous to construct the outer electrode so that it comes in the region of the webs between which extends the high frequency field, closer to the inner electrode than in the range of the interaction areas between the webs. Such construction of the outer electrode also has the advantage that the electron beam is guided particularly close to the inner electrode in the regions of the interaction areas.

The efficiency of a travelling wave tube according to the invention can be increased, based upon an interaction mechanism which is similar to that of a magnetron, by constructing the collector for the electron beam of electrically mutually separated parts, and by connecting to the individual parts a direct potential of such magnitude that the respective impact energy of the electrons becomes as low as possible. The par-ts of the collector which are subjected to the impact of electrons extending along a lower potential plane are for this purpose placed on a direct po tential which is correspondingly lower than that connected to the parts which are subjected to the impact of electrons extending along higher potential planes.

Further features and details of the invention shall now be explained with reference to the schematic figures shown in the accompanying drawing in which parts not absolutely necessary for an understanding of the invention have been omitted. Corresponding parts are identically referenced in the various figures.

FIG. 1 represents a cross-sectional view of a cylinder condenser;

FIG. 2 shows the amplifier part of a travelling wave tube formed by such a cylinder condenser, wherein the inner electrode is formed by webs of a delay line structure;

FIG. 3 indicates a structure having a polygonal outer electrode;

FIG. 4 shows an outer electrode of another configuration;

FIG. 5 illustrates a portion of an example of an embodiment of a travelling .wave tube according to the invention; and

FIG. 6 shows in sectional view the collector end of a travelling wave tube according to the invention, having a particularly advantageous collector for the electron beam.

Referring now to FIG. 1, showing in cross-sectional representation a cylinder condenser, numeral 1 indicates the outer electrode and numeral 2 the inner electrode. The amplifier part of a travelling wave tube according to the invention forms approximately such a cylinder condenser, whereby the inner electrode 2 is however formed by parts of a delay line structure represented as webs or rods 3 (-FIG. 2) between which extends the high frequency field of the line. The remaining parts of the de.ay line structure, which are to be enveloped by the outer electrode 1, have been omitted from the drawing. To the rods 3 is, as compared with the outer electrode 1, connected a high direct potential, resulting in an electrostatic field indicated in FIG. 3 by the arrows 4. Within the space between the outer electrode l and the rods 3 is guided an electron beam upon the path 5, such beam being guided in stable manner due to the fact that the force acting as a result of the electrostatic field is in equilibrium with the outwardly directed centrifugal force of the electrons. The path '5 is not circular as in the case of an ideal cylinder condenser, but angular. The angular form has, as compared with the circular form, the advantage that the electrons come closer to the interaction paths lying bet-ween the rods 3 than they come to the rods. The coupling between the electron beam and the high frequency field, which is already relatively good owing to the greater density interiorly of the electron beam, is thereby improved.

The angular path of the electrons can be emphasized by appropriate configuration of the outer electrode, such that the outer electrode comes in the region of the rods or webs 3 closer to the inner electrode than in the regions of the interaction areas extending between the rods 3. Such configuration also avoids detrimentally affecting the delay line by the outer electrode. A suitable embodiment of a polygonal outer electrode is shown in FIG. 3 and another embodiment thereof is shown in FIG. 4.

Such an outer electrode can be produced in particularly simple manner by drilling holes in an originally circular structure at points lying opposite the interaction areas. In FIGS. 3 and 4, the bars 3 are angularly formed in the direction of the outer electrode so as to obtain in the regions of the bars a stronger concentration of the electrostatic field.

FIG. 5 shows a partial view of m embodiment of a travelling wave tube according to the invention. The hollow delay line or wave guide structure 6, the inner wall of which is broken in meandering manner, is wound spirally. The tongue or finger-like wall parts 7 remaining between the meandering open portions correspond to the rods or bars 3 in FIGS. 2 to 4. interiorly of the structure 6 is disposed 21 Likewise spirally wound metal member 8 which is electrically separated from the structure 6. The metal member 8 may be held by means of a member 9 which is sealed by fusing in the outer wall of the structure '6 and which shall also serve as a terminal. The metal member 8 is placed on cathode potential referred to a voltage of 0 volt or less, and the structure '6 disposed opposite thereto is placed on a high direct voltage. The electron beam 10 is thereby in stable manner guided upon l its path between the metal structure 8 and the webs 7.

Decisive for the interaction mechanism of the tube is only the periodic structure of the delay line as such, and it should therefore suffice to arrange a delay line with periodic structure only upon the inside of the electron beam 163'. However, it was found that such a delay line cannot be advantageously dimensioned. Accordingly, in a travelling wave tube according to the invention, the main mass of the delay line structure is always disposed on the outside. The outer wall of the delay has structure 6 therefore can advantageously form the outer wall of the tube.

The arrangement of the main mass of the delay line on the outside necessarily results in loading of the outer electrode, such loading in turn resulting in a shifting of the conduction character toward longer waves. Accordingly, the geometrical dimensions of the delay line structure can thereby be held smaller than in the case of a line without loading, whereby the geometrical dimensioning of the tube is further facilitated.

The advantage of the construction of the outer electrode 8 in the manner illustrated in FIG. 5, namely, with radially inwardly directed band- like extensions 11 and 12 respectively at the upper and the lower margin thereof, resides in that it prevents an intertwined how of the electron beam longitudinally of the tube. The band- like extensions 11 and 12 accordingly function in the manner of auxiliary focusing electrodes.

A delay line according to FIG. 5 is in simple manner constructed from a hollow cylindrical copper block. Such block is machined so that there remains interiorly of the wall a fiat band-shaped spindle corresponding to the horizontal parts of the delay line structure 6. Into the free ledge of the spindle are milled an odd number of grooves which are symmetrically distributed over the circumference thereof. Into these grooves are soldered webs at the center thereof, after inserting the outer elctrode into the line. The length of the webs exceeds the pitch of the spindle, so that the ends of the webs interlace interdigitally in the direction of the spindle.

A delay line structure according to FIG. 5 has a rearwardly running fundamental wave. For amplifier operation, the tube must therefore be dimensioned so that the electron beam is in synchronism with the first forwardly running partial wave. This results in the advantage that the dispersion of the forwardly running first partial wave is in the illustrated delay line structure very slight.

FIG. 6 shows a sectional view of the collector end of a travelling wave tube provided with a particularly advantageous collector. Owing to the interaction with the high frequency field of the delay line, the electrons of the electron beam move at the end of the tube along paths of different radii. The electrons with the greatest energy loss follow the smallest radius, therefore moving closely interiorly at the inner wall of the delay line structure 6.

The electrons with the least energy loss move outside at the outer electrode ll. The collector is therefore subdivided into three annular metal members 13, 14, 15. These metal members are electrically mutually separated and connected to different potentials. The rnetal member 13 with the smallest diameter receives the highest positive direct potential and the metal member 15 with the greatest diameter receives the lowest positive direct potential. This arrangement makes it possible to keep the respective impact energy of the electrons low.

The invention is not inherently limited to the illustrated and described embodiments. It is in particular possible to use in place of the delay line according to FIG. 5 another suitable periodic structure.

Changes may be made within the scope and spirit of the appended claims which define what is believed to be new and desired to have protected by Letters Patent.

We claim:

1. A high capacity travelling wave tube, especially for amplifying ultra high frequencies, with purely electrostatic focusing of the electron beam, wherein the electron beam which is guided about the tube axis upon a helical path, enters into reciprocal action with an electromagnetic wave propagated along such path, said wave spreading with azimuthal delay upon a helically extending hollow delay line structure provided with periodic breaks formed at least in the wall parts thereof facing the tube axis, in the space between a metallic structure, forming an outer electrode, the latter and the delay line extending helically in mutually parallel relation about the tube axis with the outer electrode electrically separated from the delay line structure and wall parts of the delay line structure, forming an inner electrode, said delay line forming a part of a hollow cylindrical metal structure which, jointly with the delay line structure, surrounds the outer electrode.

2. A travelling wave tube according to claim 1, wherein said outer electrode is constructed so that parts thereof come closer to the inner electrode in the area of webs disposed between said periodic breaks than they come at the areas of said breaks.

3. A travelling wave tube according to claim 2 wherein said outer electrode is cross-sectionally polygonal.

4. A travelling wave tube according to claim 2, wherein said outer electrode has circular recesses formed therein at the areas of said breaks.

5. A travelling wave tube according to claim 2, wherein said webs are angularly shaped at the parts thereof which face said outer electrode.

6. A travelling wave tube according to claim 1, wherein said outer electrode is at its respective upper and lower margin provided with a radially inwardly directed extension for limiting the electrode beam longitudinally of the tube aXis'.

7. A travelling wave tube according to claim 6, wherein said delay line structure comprises a generally rectangular shaped wave guide, the wall of said Wave guide facing the tube axis being broken meander-like, said outer conductor being held in said wave guide in insulated relation with respect to the delay line structure.

8. A travelling wave tube according to claim 1, having a collector for the electron beam comprising a plurality of annular electrically separated metallic members of different diameter, the respective members of smaller diameter being placed on a higher positive direct potential than the respective neighboring metal member of smaller diameter.

9. A travelling wave tube according to claim 8, wherein said collector comprises three successively stage-like positioned annular metal members.

References Cited in the file of this patent UNITED STATES PATENTS 2,325,865 Litton Aug. 3, 1943 2,730,678 Dohler et al Jan. 10, 1956 2,844,797 Dench July 22, 1958 2,900,558 Watkins Aug. 18, =-9

3,058,025 Hogg Oct. 9, 1962 FOREIGN PATENTS 1,006,335 France Jan. 23, 1952

Claims (1)

1. A HIGH CAPACITY TRAVELLING WAVE TUBE, ESPECIALLY FOR AMPLIFYING ULTRA HIGH FREQUENCIES, WITH PURELY ELECTROSTATIC FOCUSING OF THE ELECTRON BEAM, WHEREIN THE ELECTRON BEAM WHICH IS GUIDED ABOUT THE TUBE AXIS UPON A HELICAL PATH, ENTERS INTO RECIPROCAL ACTION WITH AN ELECTROMAGNETIC WAVE PROPAGATED ALONG SUCH PATH, SAID WAVE SPREADING WITH AZIMUTHAL DELAY UPON A HELICALLY EXTENDING HOLLOW DELAY LINE STRUCTURE PROVIDED WITH PERIODIC BREAKS FORMED AT LEAST IN THE WALL PARTS THEREOF FACING THE TUBE AXIS, IN THE SPACE BETWEEN A METALLIC STRUCTURE, FORMING AN OUTER ELECTRODE, THE LATTER AND THE DELAY LINE EXTENDING HELICALLY IN MUTUALLY PARALLEL RELATION ABOUT THE TUBE AXIS WITH THE OUTER ELECTRODE ELECTRICALLY SEPARATED FROM THE DELAY LINE STRUCTURE AND WALL PARTS OF THE DELAY LINE STRUCTURE, FORMING AN INNER ELECTRODE, SAID DELAY LINE FORMING A PART OF A HOLLOW CYLINDRICAL METAL STRUCTURE WHICH, JOINTLY WITH THE DELAY LINE STRUCTURE, SURROUNDS THE OUTER ELECTRODE.

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