US2870368A - Electron beam tubes - Google Patents

Description

Jan. 20, 1959 c. L.. cUcclA 2,870,368

ELECTRON BEAM TUBES 4 sheets-sht 1 Filed July 14. 1953` INVENTOR.

Jan. 2o, 1959 C. L. CUCCIA 2,870,368

ELECTRON BEAM TUBES Filed July 14, 1953 l '4 SheetS-Sheef 2 #Sw-ffl INI ENTUR.

TTOR NE Y Jan. 20, 1959 C. 1 CUCCIA 2,870,368 l ELEGTRON BEAM TUBES Filed July 14. 1953 4 Sheets-Sheet 3 INVE N TOR.

mmm/awww? vTTORNE Y Jan- 20, 1959 c. l.. c ucclA ELECTRON BEAM TUBES 4 Sheets-Sheet 4 Fiied Ju1y'14, 1953 United States Patent ELncrno'N BEAM TUBES Carmen Louis Cuccia, Princeton, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application July 14, 1953, Serial No. 367,941

17 Claims. (Cl. B15-5.49)

The present invention relates to electron beam tubes and circuits therefor, and particularly to beam tubes of the electron coupler type used for modulating devices.

In an electron coupler tube, as described in C. L. Cuccia, Patent No. 2,542,797, assigned to Radio Corporation of America, an electron beam is projected along a path extending in succession through an input region upon which is impressed a radio frequency electric field transverse to the beam path and an output region to which the beam gives up energy by inducing a second transverse radio frequency field. Each of the two regions includes a pair of opposed field-defining electrodes located on opposite sides of the beam path and coupled to a resonant circuit, which may be either an external circuit or some form of cavity resonator forming part of the tube structure itself. The input and output circuit are adapted to be coupled to a radio frequency source and a useful load, respectively. The beam is subjected to a constant axial magnetic field. The magnetic field strength H is adjusted to a value such that the angular cyclotron frequency la (1)0- m of an electron in said field is equal to w, where e and m are the charge and mass, respectively, of an electron, and o is the angular frequency of the radio frequency field set up in the input region. Under these conditions, as the beam passes through the input region the electrons are caused by the crossed electric and magnetic fields to move in spiral paths of increasing radii about the original beam axis, absorbing energy from the input region and the radio frequency source coupled thereto. Since they have the same angular and axial velocities, all the spirally traveling electrons in the beam lie at any instant on the linear directrix of a cone, and the envelope of the rotating or revolving beam is a cone. Hence, the beam is sometimes termed a cone-directrixf or rotating pencil beam. ln the output region the rotating beam gives up spiral energy to the region and coupled load by inducing radio frequency voltages on the field defining plates and thereby setting up a transverse radio frequency field in that region. As spiral energy is abstracted from the beam the radii of the electron paths are progressively reduced, and hence, the envelope of the beam in the output region is an inverted cone. The electron, coupler tube may be used as a modulator by coupling an unmodulated carrier signal to the input region and modulating the beam current or the transit time by a modulating signal thus producing a modulated carrier signal in the output load, as disclosed in said Cuccia patent. On the other hand, an amplitude modulated signal coupled to the input region will be faithfully reproduced in the output of the device.

`In a copending application of C. L. Cuccia, Serial No. 216,320, led March 19, 1951, now U. S. Patent No; 2,806,172, granted September 10, 1957, assigned to the Radio Corporation of America, several two-region elecltron coupler tubes are disclosed in which a coupling beam is passed through the input and output regions and an auxiliary beam is passed through one of these regions,- for stabilizing or modulating purposes. When the auxiliary beam is passed through the output region the output of the device can be modulated by varying the auxiliary beam current. However, this arrangement has the disadvantage that it requires relatively high values of beam current, as vcompared to the coupling beam current, to produce amplitude modulation in the neighborhood of percent. The principles of auxiliary beam modulation of the electron coupler are also described in a paper by C. L. Cuccia on pages 72-99, inclusive, RCA Review, vol. XIV, March 1953.

The principal object of the present :invention is to provide electron coupler tubes capable of producing high depths of modulation with modulating beam currents of the order of the coupling beam currents.

A distinguishing feature of the invention is the use of an electron coupler tube having three interaction regions, instead of two as in previous coupler tubes. In the embodiments illustrated, three cavity resonators are arranged in line, end-to-end. One end cavity is an input cavity With coupling means for connection to an input radio frequency generator to establish a transverse electric field in the cavity. An electron gun at the end of the tube projects a coupling beam through the input cavity and at least the middle cavity. ln some embodiments, the other end cavity is the output cavity while in one the output is taken from the middle cavity. In each embodiment a modulating beam is projected through one or two of the cavities other than the input cavity for amplitude modulating the output power of the tube.

In the accompanying drawing:

Fig. l is a longitudinal sectional View, partly schematic, of one embodiment of an electron coupler tube incorporating the present invention;

Figs. 2 and 3 are transverse sectional. views taken on lines 2 2 and 3 3, respectively of Fig. l;

Figs. 4, 5 and 6 are sketches referred to in the explanation of the operation of the tube of Figs. 1-3.

Fig. 7 is a view similar to Fig. l of a second embodiment of the invention;

Figs. 8, 9 and 10 are sketches relating to the operation of the tube of Fig. 7;

Fig. 11 is a view similar to Fig. 1 of a third embodiment;

Figs. 12, 13 and 14 are sketches relating to the operation of the tube of Fig. 11;

Fig. 15 is a view similar to Fig. 1 of a fourth embodiment; and

Figs. 16, 17 and 18 are sketches relating to the operation of the tube of Fig. 15.

Referring first to Figs. 1-3, there is shown an electron beam tube having an elongated metal envelope 1. The interior of the envelope 1 is divided by three transverse metal partitions 3, 5 and 7 into three cavities 9, 11 and 13, and an electron gun compartment 11S. Three pairs of opposed pole faces 17, 19 and 21 are mounted in the three cavities 9, 11 and 13 by extensions 23, 25 and 27, respectively, to provide a transverse electric field region between the opposed pole faces in each cavity. Each pair of pole faces together with the surrounding wall of the envelope and the adjacent partitions form a coaxial line cavity resonator of the type shown in Figs. 5 and l5 to 18 of Cuccia Patent No. 2,542,797. The pole faces may be in the form of flat plates, as shown, or may be accurate in cross-section transverse to the longitudinal central axis Z-Z as shown in said patent. Cavity 9, the one nearest the gun compartment l5, is provided with means, which may be a coupling loop 29 and coaxial transmission line 31, adapted to be coupled to an external radiofrequency source, for exciting an electromagnetic yradio frequency electric field between the pole faces in that cavity, which serves as the input cavity of the tube. The output cavity which is -the third cavity 13 in the embodiment of Figs. 1 6, is provided with means, vsuch as coupling loop 33 and transmission line 3S, for extracting radio frequency energy therefrom. The second -cavity 11, which has no radio frequency inpu't or output means, serves as a part of the electronic modulating means of the present invention, in a manner to be described. Each pair of pole faces, 17-2L constitutes .an electrode structure adapted to be energized .to 'establish a radio frequency electric tiel-d extending Ybetween the pole faces which serve as field-defining electrodes.

The three partitions 3, 5 and 7 are provided with apertures 37, 39 and 41, respectively, at one yside of the central axis and aligned with ar rst electron gun G1 mounted by suitable means in the compartment i5. The gun G1 comprises a cathode 43, a control grid 4S and an accelerating electrode which, as shown, is the apertured partition 3. The cathode 43 and grid 4S are provided with leads 47 and 49, sealed through the envelope in insulated relation, for connection to direct current 4voltage sources. As shown the cathode 43 is maintained .at a low negative potential relative to the cavity lstructure and ground by a battery 51, and the grid 45' is given a suitable bias potential by a battery 53.

The gun G1 is arranged as described to project a coupling electron beam through the cavities 9, 11 and 13, for transferring electrical energy from the input cavity 49v to the output cavity 13. An axial magnetic eld of constant field strength H=wo 1) where m 'and e are the electronic mass and charge, respectively, and wo is the angular frequency of the input radio frequency source used to excite the tube, is established along the axis of the tube, parallel to the beam path, ,by suitable means such as magnets havingy pole pieces P and P.

A second electron gun G2 is mounted by suitable means in one end of the second or middle cavity 11, on the opposite side of the central axis from the coupling beam, to project a modulating electron beam through that cavity only, between the pole faces 19. Gun G2 comprises a cathode 5S, a control grid 57 and an accelerating electrode 59 in the form of an apertured plate. Cathode 55 and grid 57 are provided with insulated leads 6l and 63 through the envelope wall for connection to ldirect current and modulation voltage sources. As shown, the cathode 55 is maintained at a low negative potential relative to the cavity structure by a battery 65 The grid and cathode are connected by a grid-biasing battery 67 and a modulator 69 in series, so that the beam current of the modulating beam can be varied between zero and any desired value by varying the grid potential.

The operation of the embodiment of the invention shown in Figs. 1 3 as a modulator will nov be described. When the electrodes of theV coupling beam gun G1 are energized and no energy is introduced into cavity 9, the electrons in the coupling beam travel in substantially straight lines through the three cavities and are collected on the end wall of the cavity 13, as shown by the dashed line in Fig. l. When a source of radio frequency Y energy of frequency w0=He/m is coupled to input cavity 9, the electrons inthe coupling beam are deflected b v the transverse electric and axial magnetic fields and caused to execute spiral paths of constantly increasing radii around the initial beam axis, and thereby form a revolving :cone-directrix beam in the electric field region of the input cavity 9, as described above in connection with Ylili:basicelectronfcouplerfof Cuccia "Patent No. 2,542,797.

The conical envelope of this beam is Shown ,at 7.1 .in

Figs. 4-6. In the space between the first and second regions, where there is no transverse electric field, the

electrons traverse helical paths of constant radii, as shown by the cylindrical envelope 73 in Figs. 4-6. Thus the Y coupling beam enters the second cavity 11 with the spiral l energy obtained from cavity 9, represented by the radius of the envelope 73. n

When the modulating beam is 'biased olf, the second cavity 11 is completely unloaded and the coupling beam K in passing through that cavity will experience a .phase reversal, as indicated by the double-conical envelope 75, with a convergence or cross-over point 77 half way across the pole faces 19. VThe reason for this is that each electron as it enters the region between the pole faces 19 induces smaller and smaller increments of voltage across these pole faces, 180 out of lphase with the voltage applied to input polefaces 17 of cavity A9, 4until-all of its spiral Ienergy has ybeen absorbe-d, at the .cross-over point. Beyond `the cross-:over point each electron rekabsorbs yenergy from the pole faces 19, in phase with the @voltage thereon, until the radius of spiral is theV same as that of envelope 73 to satisfy the condition that there be no net interchange of energy between the beam and the unloaded cavity 11. and third regions, the coupling beam has a cylindrical envelope 79, likeenvelope 73 between the first and second regions. Hence, under the conditions assumed the beam lenters the third ror loutput region with the same amount of spiral energy that it absorbed from the input region `but of opposite -phase. :of the `output load, expressed as the transformed resistance presented across the pole faces 21, has the value defined by:

where V is the beam accelerating voltage in volts, I0 is i the electron beam current in amperes, L is the length of the pole faces 21 and d is the-distance between them, both in centimeters, the beam will converge in the output region as shown at 81 so that the radius of revolution of "the electrons is zero as they leave the region between the -pole faces 21. Equation 2 corresponds to Equation 15 of Cuccia Patent No. 2,542,797. lf the resistance R of the output load were infinite the beam would have a phase-reversal with a cross-over point in the middle of the output region, as in the second region. Therefore, Fig. l4 shows the condition, with zero modulating beam current, of transfer of energy from the input source to the outputload, that is, maximum'power output from the device.

`When the modulating beam is turned on, as shown in Fig. 5, that beam will absorb energy from the second point 77 ofthe coupling beam to be shifted toward the exit of the second field region, so that the difference between the spiral lenergy of the coupling beam prior to cross-over and the spiral energy thereof after cross-over is equal to the energy absorbed bythe modulating'beam. Thus, less spiral energy is transferred to the output cavity and load by the coupling beam.

As the modulating beam current `is increased until ,it equals the coupling beam current, the modulating beam will -absorb all vof the rotational or spiral energy of the coupling beam, the latter converging as a cone-directrix beamjin 'the second 'region to zero radius at the A,exit 'thereof, as shown -at v84 in Fig. 6. Where the field geometries for the two beams are not the same this condition will be met Iwhen the resistance presented by the modul-ating beam `will match .that of the ,coupling beam. Hence, no rotational energy is transferred to the output .cavity and load, which is 'the case of zero power output from the In the space between the second When the effective resistance :RY

device. The energy of the modulating beam is dissipated in the partition 7 in the form of heat.

Therefore, it is apparent that, as the modulating beam current is varied between zero and a value equal to that which will cause a resistance match to the coupling beam, the power output of the device is varied from maximum to zero, which represents 100% amplitude modulation of energy transferred from the input source to the output load.

4In each of the electric field regions the slope of the cone directrix is determined by the strength of the electric field within that region, or vice-versa. Hence, where there are two beams in the same region, as in the second region in Figs. 5 and 6, the cones of the two beams will have'the same slope, as shown. One result of this is that the modulating beam will graze the pole face 19 for small beam currents and high electric field strengths, as shown in Fig. 5.

Figs. 7, 11 and l5 show modifications of the modulator tube of Figs. 1-3. The tube elements which are the same as in Fig. 1 have been similarly numbered in these modifications and will not be described in detail again.

In the embodiment of the invention shown in Fig. 7, the coupling beam is projected from gun G1 through the cavities 9, 11 and 13, in succession, as in Fig. 1, the input radio frequency source is coupled into cavity 9, and energy is extracted from cavity 13, as in Fig. l. However, the modulating beam is projected by electron gun G2 in the opposite direction, through the output cavity 13' and the middle cavity 11, instead of the middle cavity only. Gun G1 is mounted by suitable means in a compartment formed by the envelope 1 and an apertured partition 85 which serves as the collector for the coupling beam and as the accelerating electrode of the modulating gun. The aperture 41 in the partition 7 is large enough to pass the modulating beam into the middle cavity 11.

In the operation of the embodiment of Fig. 7, when the modulating beam is off the coupling beam absorbs energy from the first cavity 9, goes through a phase reversal in cavity 11 and gives up maximum power to the third or output cavity 13, exactly as in Fig. 4. When the modulating beam is turned on, as shown in Fig. 9, it will absorb some of the rotational energy from the coupling beam in the output cavity to form a directrix beam 83, thus reducing the power taken by the output load. Upon entering the middle cavity the modulating beam will expand as shown at 87 and load the cavity, thereby causing the cross-over point 77 of the coupling beam to shift toward the output cavity, resulting in reduced power transferred to the output cavity. The modulating beam will also add a component of energy 180 degrees out of phase with the coupling beam in the middle cavity, as a result of the energy it absorbed from the output cavity, which will shift the crossover point still further, thereby further reducing the output power. The modulating beam will braze, as shown in Fig. 9. When the modulating ,beam matches the coupling beam, as shown in Fig. 10, the'modulating beam will absorb all of the rotational energy of the coupling beam in the middle cavity, so that there will be no rotational energy left in the coupling beam for transfer to the output cavity and output load. As a result there will be no energy for the modulating beam to transfer to the middle Vcavity so that both beam paths will be straight in the output cavity 12, as shown at 89 in Fig. 10.

In the embodiment shown in Fig. 1l all of the structure is the same as in Fig. 7 except for the output loop 33 and line 35, which are coupled to the middle cavity 11, instead of the third cavity 13. In operation, with the modulating beam turned off, as shown in Fig. 12, the tube operates as a simple two-cavity electron coupler. If the output load is matched to the output cavity when the modulating beam is not on, the coupling or input cavity to form a cone-directrix beam and then give up all of its energy in the second or output cavity as shown at 91, thus transferring maximum power from the radio frequency source to the output load. The beam will then pass through the third cavity 13 with only the directcurrent energy due to the beam accelerating voltage.

Whenrthe modulating beam is turned on slightly (with low current) it will pass through the third cavity and into the second or output cavity where it will cause a mismatch between the directrix coupling beam and its effective load. At the instant it is turned on, however, the modulating beam has no rotational energy as it passes through the third cavity, and as it enters the second cavity the initial effect is as if the electron gun 'G2 were located there. The general power transfer eiciency of the coupling beam to the output load, which is dlefned by (1-l-R/R)2 will be reduced, due to the insertion of the modulating beam, resulting in some rotating beam power remaining in the coupling beam as it enters and passes through the third cavity, as shown at 93. This power is absorbed by the modulating beam in the third cavity. The directrix of the modulating beam will be 180 degrees out of phase with the directrix of the coupling beam. When the modulating beam enters the middle cavity its out-of-phase rotational energy will serve to further reduce the amount of power extracted from the coupling beam by the output load. i

As the modulating beam current is increased, more and more rotational energy enters the third cavity to be returned by the modulating beam to the second cavity, 180 degrees out of phase, until, when the beams are matched both beams will form cylinder-directrix beams 9S and no energy will reach the output load.

The embodiment shown in Fig. 15 is essentially a pair of two-cavity electron couplers in series, with the output cavity 11 of the input electron coupler 9-11 acting as the input cavity of the output electron coupler 11-13. The structure is identical with that of Fig. 1 except for the partition 7 which in Fig. l5 has its aperture 39 positioned so that the partition will intercept the coupling beam from gun G1 and allow the modulating beam from gun G2 to enter the third cavity 13.

In operation, with the modulating beam turned oi, as in Fig. 16, the coupling beam absorbs energy froml the input cavity 9 forming a cone-directrix beam 71. Since thereis no load on the middle cavity the coupling beam goes through with a phase-reversal 75 and a crossover point 77 in the middle of the electric eld region, as in Figs. 4 and 8. All of the coupling beam energy is dissipated in the partition 7, and no power is delivered to the output cavity and load. When the modulating beam is turned on, as shown in Fig. 17, the beam absorbs energy from the middle cavity to formi a cone-directrix beam, and the load presented by this beam causes the cross-over point of the coupling beam to move toward the' far end ofthe middle cavity, as in Figs. 5 and 9. The energy absorbed by the modulating beam is equal to the difference between'that represented by the coupling beam before cross-over and that after cross-over. As long as the modulating beam grazes the pole face 19 as shown the modulating beam cannot` reach the output cavity, and hence, no power will be delivered to the load. When the modulating beam current is equal to the coupling beam current, the modulating beam will absorb all of the rotational energy of the coupling beam, which will converge at the end of the pole faces 19, as in Fig. 6. Moreover,

as the modulating beam approaches a match with thev power output vof the tube can b'e switched from izero to full value. The rate at which the power -will go from zero to full value will depend on the cavity design and the 'beam thickness, and the design is chosen to suit various usage requirements.

What is claimed is:

1. An electron beam tube including three electrode structures, each adapted to be energized to establish a radio frequency electric field transverse to a 'predetermined axis of the tube, means for projecting a rst beam of electrons parallel to said axis and through 'the held of at least one but Vnot more than two of said electrode structures, means for projecting a second beam of electrons parallel to said axis and through the elds of at least two of said electrode structures including an electrodeestructureV traversed by `'s'aidfirst beam and 'on'n'ot traversed by said first beam, and means for establishing a ,constant magnetic eld throughall of said structures parallel to said axis.

2. An electron beam' tube as in claim 1, wherein said first .beam is projected through only one of said electrode structures.

3. VAn electron beam Vtube as in cla-im 1, wherein said first beam is projected through two of said electrode structures.

4. An electron beam tube as in claim `3, wherein said second beam is projected through all three electrode structures.

5. An electron beam tube as in claim 3, wherein said second beam is projected through only -two of said electrode structures. v

V6. An electron beam tube as in claim 1, wherein each of said electrode structures comprises a pair of spaced field-defining electrodes parallel to and on opposite sides of said axis.

7. An electron beam tube including three electrode structures, each adapted to be energized to establish a radio-frequency electric held transverse to a predeterminedwaxis of the tube, means for projecting a irst beam of electrons parallel to said axis and through at least one but not more than two of said electrode structures, means for projecting a second beam of electrons parallel to said axis and through at least two of said electrode structures including an electrode structure traversed by said first beam and one not traversed by said first beam, means for establishing a constant magnetic field through all of said electrode structures parallel to said axis, the electrode structure traversed by said second beam only being provided with coupling means adapted to be coupled to a radio-frequency source, and one of the other electrode structures being provided with coupling means adapted to be coupled to an output load.

8. An electron beam tube as in claim 7, further includingr means for varying the beam current of said first beam, to vary the amplitude of the power delivered to. said load.

9. The combination of the electron beam tube of claim 7 with a radio frequency source having an angular frequencyequal to Y where H is the strength of said magnetic held, and e and m are the charge and mass, respectively, of an electron.

10. An electron beam tube includingV rst, second and third electrode structures arranged in va ro'w 'along 'a predetermined axis of the tube, each structure being adapted to be energized to establish a radio frequency electric held vtransverse to said axis, means for projecting a lrst beam of electrons parallel to said axis and through the elds of at least said first and second 'electrode structures in the order named, means for projecting a second beam of electrons parallel to said axis and through at least one vof said second and third electrodek structures only, and means for establishing a constant magnetic eld through nall of saidelectrode structures parallel to said axis.

11. An electron beam tube as in claim i0, wherein said hrst electrode structure is provided with coupling means adaptedl to be coupled to a radiofrequency source, and one of the other electrode structures is provided with coupling means adapted to be coupled to an output load.

12. An electron beam tube as in claim 11, wherein the third electrode structure is the one provided with output coupling means.

13. An electron beam tube as lin claim 12, wherein said first beam is projected through Aall three electrode structures and said second beam is Vprojected through said second electrode structure only.

14. An electron beam tube as in claim l2, wherein said rst beam is projected through all three electrode structures and said second beam is' projected through said third and second electrode structures, in that order.

15. An electron beam tube as in claim 12, wherein said rst beam is projected through said irst and second electrode structures only and said second beamjis projected through said second and third electrode structures only.

16. An electron beam tube as in claim 11, wherein said second electrode structure is the one provided with output coupling means.

17. An electron beam tube including three cavity resonator structures, each adapted to be excited to establish a radio frequency electric field therein transverse to a predetermined axis of the tube, means for projecting a first beam of electrons parallel to -said axis and through at least one but not more than two of said cavity reson'a# tor structures, means for projecting a second beanr of electrons parallel to said axis and through at least ltwo of said cavity resonator structures including a resonator not traversed by said tirst beam, and means for establishing a constant magnetic eld through said cavity -resonator structures parallel to said axis.

References Cited in the tile of this patent UNITED STATES PATENTS 2,233,779 Fritz `Mar. 4,' 1941 2,479,084 Rosenthal Aug. 16, 1949 2,542,797 cuccia Feb. 2o, 195:1 2,565,357 Donal Aug. .21, 1951 2,638,539 Cuccia May 12, 1953 2,687,491 Lee Aug. 24, 1954

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