US2726291A

US2726291A - Traveling wave tube

Info

Publication number: US2726291A
Application number: US396459A
Authority: US
Inventors: Calvin F Quate
Original assignee: Bell Telephone Laboratories Inc
Current assignee: AT&T Corp
Priority date: 1953-12-07
Filing date: 1953-12-07
Publication date: 1955-12-06
Anticipated expiration: 1972-12-06

Description

Dec. 6, 1955 c. F. QUATE TRAVELING WAVE TUBE F'iled Dec. 7

lNVENTOR C. F. QUA TE By J. Mk5

A TTORA/EV United States Patent ice 26291 Patented Dec. 6, 1955 netic energy is being extracted from them. A very advantageous arrangement is provided in conjunction with 2 726 291 these successive circuits for supplying to them radio frequency signals in the proper phases. The arrangement TRAVELING WAVE TUBE 5 is an improvement over that disclosed in a copending Calvin F. Quate, Berkeley Heights, N. 3., assignor to 35 5221 5 3222 3 2:: Z gg gg Kompfner on Bell Telephone Laboratories, Incorporated, New York, p N'Yq a cfimemfion New York A more complete understanding of the lnventlon, to-

gether wlth a better appreciation of 1ts advantages Wlll APPliwfiml Deflembel 1953, Serial PIG-396,459 10 best .be gained from a study of the following detailed description given in connection with the accompanying 8 Claims (CL 179-171) drawing in which the single figure shows in schematic form a traveling wave tube employing successive electron stream signal wave interaction circuits. This invention relates to devices utilizing electron Referring now particularly to the drawing, the figure beams and more particularly to traveling wave tubes. shows an illustrative embodiment of a traveling wave An object of this invention is to improve the efiiciency tube 10 made in accordance with the invention. In this of traveling wave tubes. embodiment electrons are beamed by any convenient Traveling wave tube amplification of wave energy means along an axis enclosed within an evacuated envemakes use of the interaction which results between an lope of suitable dimensions. The electrons can be conelectron stream and the electric field of a traveling or fined to the axis of flow by any convenient means such propagating electromagnetic wave when the electron as a longitudinal magnetic field aligned parallel to the stream is beamed in coupling relation to the wave electric axis. For purposes of simplicity, however, no such means field. When the electron stream is properly synchronized has been shown in the drawing. As the electrons travel with the traveling wave, some of the kinetic energy of along the axis of flow they are acted upon by successive the electrons is transformed into electromagnetic energy. electromagnetic fields maintained around the electron The electrons, as a result of this transformation, are stream by appropriate means. Here these means include slowed down in proportion to the energy extracted from

helices

11, 12, 13, 14, 15, and 16 placed around electron them. As the average velocity of the electrons decreases, stream 17 at points successively along its path from elechowever, they fall more and more out of synchronism tron gun 18 to collector anode 19. Each of these helices with the traveling Wave until finally no useful exchange is maintained at potentials successively higher than the of energy is possible. To compensate for the nonunipotential of cathode or gun 18. That is, helix 11 is formity in the average velocity of the electrons, it has maintained at a potential higher than that of electron gun been suggested that in a conventional helical traveling 18, but lower than the potential of helix 12, and each sucwave tube the pitch of the propagating helix be made to ceeding helix along the length of the tube from gun 18 vary from greater to smaller down the length of the electo collector 19 is maintained at a higher electrical potentron stream. In this manner the axial velocity of the tial than its preceding helix closer to the gun 18. In traveling wave can be slowed down in proportion to the this embodiment these potentials are supplied by sources slowing down of the electrons. This arrangement un- 20, 21, 22, 23, and 24 connected to helices 11 through fortunately suffers from the disadvantages that the pitch 16 as shown. While the voltages provided by these taper for efiicient operation is a function of, among other sources may be equal to each other it should be underpararneters, steady state beam current. Accordingly, for stood that they may be adjusted separately to any desired a given physical helix structure of this type, there is value when it is convenient to do so. Surrounding. each only one value of beam current and one value of radio of helices 11 through 16 is a respective one of helices frequency power level within a very narrow range, which 25 through 36. By means of these outer helices radio can be used efficiently. Other beam currents and other frequency signals can be impressed in turn upon the inner power levels require difierent helix tapers. As a result, helices and the electron stream. A radio frequency input the versatility or flexibility of operation of this kind of signal circuit consisting of hollow wave guide 31 is contubev is undesirably limited. The present invention seeks nected at appropriate points along it to each of helices to provide a traveling wave tube which approaches, al- 25 through 30 by means of probes 32 through .37. The though it does not achieve, 100 per cent efiiciency, and spacings along the guide between successive probes are which is not limited to operation with a single-valued made so that the phases of the voltages applied to helices beam current and single radio frequency power level. As 25 through 30 have the proper relationship to each other will appear, one of the advantages of the invention is and to the phase of the signal propagating along the electhat the tendency of the electrons to fall out of synchrotron stream. The amount of the voltage applied to a nism with the traveling wave field can easily be compenhelix can conveniently be varied by adjusting the depth sated for electrically rather than in the mechanical way of penetration into the guide 31 of the probe connected suggested previously and outlined above. to the helix. In this manner the efiiciency of operation In accordance with the present invention, in one speof tube 10 can be maximized by avoiding overbunching cific embodiment thereof, a number of slow wave circuits of the electron stream. The output ends of helices 25 such as wire wound helices are positioned in succession through 30 are connected in a way similar to the input along and surrounding the path of an electron stream. connections by means of probes 38 through 43 inserted in As the electrons pass through each successive circuit they hollow wave guide 44. give up energy to the radio frequency field in this region The lengths of helices 25 through 30 and their respecand as a result their average velocity is decreased. Each tive inner helices 11 through 16 should each be substancircuit is maintained at a higher direct potential than tially one-half the beat wavelength, that is, the wavethat of the preceding circuit so that the electrons when length of the standing Wave which would appear on a passing from the electrostatic field of one circuit to that uniform transmission line made up of concentric helices of the next are accelerated by an amount corresponding such as 11 and 25. The pitches of the two helices comto the potential difierence between; the two circuits. Thus prising the inner and outer helices of each pair should the average velocity of the electrons can bev maintained within certain limits even though a large amount of kibe approximately the same in magnitude but in opposite sense. Under these conditions, wave energy applied to the left or upstream end of an outer helix such as helix 25 will be almost entirely transferred onto the inner helix such as helix 11 before it reaches the end of the outer helix. Thus, both the input and output ends of the outer helices will be located at voltage antinodes and the ends of the inner helices will be located at voltage nodes. Throughout the specification the term upstream is used to denote a point or location closer to the electron gun than the point or location with which it is being compared. Conversely, the term downstream denotes a point or location closer to the collector than the point with which it is being compared. The beat wavelength is most easily determined by measurement although it can be determined in the way disclosed in copending application of R. Kompfner, Serial No. 355,028, filed May 14, 1953.

For eflicient operation of tube 10, the depth of probe 45 into guide 31 should be varied until the proper bunching voltage is applied to electron stream 17 via bunching cavity 46. Sources 20 through 24 may also be adjusted individually to insure that the electrons are in proper synchronism with the electric fields traveling down the various helices. The pitch of these helices, of course, determines the velocity at which these fields travel which should be approximately equal to the velocity of the electron stream.

As the electrons travel along the path of stream 17, which is congruent with the common axis of the successive helices, they first come to the region surrounded by any suitable electron stream bunching means such as the cavity 46 which is shown or a short helix similar to helix 11 in which some of the electrons are retarded and others are accelerated in accordance with the variations in intensity of the signal wave propagating along the helix. By this action the electrons are bunched into groups which proceed down the tube, being timed by means of adjustable delay 47 and the gap between buncher 46 and helix 11, to reach the region surrounded by helix 11 at the proper instant to be retarded by the signal wave propagating along the helix. The tube circuit parameters are arranged so that while within this region the electrons are decelerated by an amount corresponding to the voltage supplied by battery 20. The number of times the electrons are accelerated and decelerated in this way as they travel to the anode 19 determines the total amount of energy which can be extracted from them and consequently the amount of wave amplification obtainable.

The degree of bunching of the electron stream produced by buncher 46 is a factor determining the efiiciency of tube 10. As the bunching becomes more perfect the elficiency increases and this effect makes tube useful as a high level expander, that is, an amplifier whose gain increases as the signal level increases.

Helices 11 through 16 provide a desirable way of impressing radio frequency signal voltages on electron stream 17 because they can be connected, without additional radio frequency insulating elements, directly to batteries 20 through 24. If desired, however, these helices can be replaced by appropriate accelerating grids.

The foregoing explanation is intended in illustration and not in limitation of the principles of the invention. Various changes or modifications in the embodiment illustrated may occur to those skilled in the art and these changes may be made without departing from the spirit or scope of the invention as set forth. In particular, instead of helical wave propagating circuits such as those shown, various other wave propagating circuits may be used. Moreover, the number of circuits to be used is not limited to the six shown but may be greater or smaller depending upon the tube efiiciency required. In general, the larger this number, the greater the efliciency.

What is claimed is:

1. In an electronic device, means for forming and projecting an electron stream, means for bunching said .4 stream in accordance with a signal, a plurality of means located along said stream in field coupling relation thereto for causing interaction between said stream and a single electromagnetic wave signal, means for maintaining the average velocities of the electron stream at successive points along it approximately equal to each other, extended input wave guiding means to which said bunching means and said plurality of means located along said stream are connected respectively at successive points of proper phase relation along the wave guiding means, and an extended output wave guiding means to which said plurality of means located along said stream are connected respectively at successive points of proper phase relation therealong.

2. The combination of elements of claim 1 in which said input and output wave guiding means are conductively bounded wave guides.

3. The combination of elements of claim 1 in which each of said plurality of means located along said stream is a pair of concentric coupled helices surrounding the electron stream.

4. The combination of elements of claim 1 in which said means for maintaining the average velocities of the electron stream are a plurality of direct current voltage sources.

5. The combination of elements of claim 1 in which said plurality of means located along said stream include 4 parallel connected helices of equal pitches.

6. In a device which utilizes the interaction between an electron beam and an electromagnetic wave to amplify the wave, means for forming an electron beam and for projecting said beam along a predetermined path, means for bunching the electrons of said beam in accordance with a signal, a plurality of separate interaction circuits arranged in spaced succession along the beam paths for propagating electromagnetic wave energy in coupling proximity with said electron beam, said succession extending along the beam path a distance of several wavelengths and characterized in that each of the interaction circuits has substantially the same phase velocity propagating characteristics, means for maintaining the average velocity of the electron beam substantially the same at the upstream end of each of the successive interaction circuits along the beam path, an extended input wave guiding means to which said bunching means and said plurality of interaction circuits are connected respectively at successive points of proper phase relation along the Wave guiding means, and an extended output wave guiding means to which said plurality of interaction circuits located along said beam path are connected respectively at successive points of proper phase relation therealong.

7. In a device which utilizes the interaction between an electron beam and an electromagnetic wave to amplify the wave, means for forming an electron beam and for projecting said beam along a predetermined path, means for bunching the electrons of said beam in accordance with a signal, a plurality of separate interaction circuits arranged in spaced succession along the beam paths for propagating electromagnetic wave energy in coupling proximity with said electron beam, said succession extending along the beam path a distance of several wavelengths and characterized in that each of its interaction circuits has substantially the same phase velocity propagating characteristics, means for maintaining each interaction circuit of the succesion at a higher D.-C. potential than the adjacent interaction circuit which is upstream thereof, an extended input wave guiding means to which said bunching means and said plurality of interaction circuits are connected respectively at successive points of proper phase relation along the wave guiding means, and an extended output wave guiding means to which said plurality of interaction circuits located along said beam path are connected respectively at successive points of proper phase relation therealong.

8. In a device which utilizes the interaction between an I electron beam and an electromagnetic wave to amplify the wave, means for forming an electron beam and for projecting said beam along a predetermined path, means located along said path for bunching said electron beam in accordance with a signal, a plurality of pairs of helices spaced downstream from said bunching means and arranged in spaced succession over a distance of several operating wavelengths along the beam path for propagating electromagnetic wave energy in coupling relation with said beam, the two helices of each pair having unequal radii and being positioned coaxially and substantially coextensively along a portion of the electron beam for forming a concentric pair having inner and outer helices, the pitch of the inner and outer helices of each of the concentric pairs being equal and of op posite sense, means for maintaining one helix of each References Cited in the file of this patent UNITED STATES PATENTS 2,489,082 De Forest Nov. 22, 1949 2,584,308 Tiley Feb. 4, 1952 2,588,832 Hansell Mar. 11, 1952