US2828443A - Electron discharge devices - Google Patents

Description

E. c. DENCH ELECTRON DISCHARGE DEVICES Filed July 28, 1951 2 Sheets-Sheet 1 m a F at, /I

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197' OIPMF) United States Patent Patented=- Ma @1958 This invention relates to electron discharge "devices, --and:rnore particularly to electronidischarge;devices of .the magnetron type.

Magnetron oscillators have beenideveloped to a degree of .e'flijciencyaand reliability 'as sources ofh gh frequency of microwave energy. In the microwaverregion, magnetron osc'illators areof outstanding importance,

'sincelhey .are more eflicient than any ofJthe. other known "types of'..hi'gh fre quency oscillationgenerators. "The field of application.'of magnetron oscillators has, however,

:been restricted, (due; to the. difliculty" heretofore encountered in linearly modulating the amplitude output. ofthe *magnetron. "WhileLit 'iswell'knownl that magnetron oscillators may be pulse modulated by pulsing the plate voltage applied' to i the magnetron, such modulation is restricted to' applications where 'Lit is desired that "the output be -ei'ther' zero *or' some maximum "value asf'for example; in 'pulse echo' 'radariapplications. 'Atte'mpts'fto produce modulationofithe output of thecmagnetronms- -cillatorto-obtain values between zero and maximum outputby variation bf'the anode voltage '.have been Lunsatisfactory; sincethe rmagnetron oscillator output does "not varylinearly with varia'tion ofthe anode voltage.

"Moreover;at-values'of the anode voltage where less than mairimum' power 'outpntis producedflhe magnetron oscillator is *likely -to operate "in "an entirely :Idi'fferent mode, producing a difierent outputpowerand adiiferent output frequency at a substantially reduced efficiency.

This invention-discloses a structure, whereby'thefouta put amplitude of a magnetron oscillator may beva'ried inn-substantially linear'manner with respect to a'modulationinput signal.

Briefly, this invention comprises a grid structure insulated from bo'ththe 'anode'and the cathode of --a mag- -netron and positioned "outside the main electron -stream but-in close proximity thereto'and adjacentthe' portions ofthe anode-members which are closest-to "the cathode.

While the grid structure maybe of any "desired type and shape, itiis-desirable that the surface thereof be contoured to act upon the *mairrelectronstream along "a considerable-portion thereof.

-By warying the potential 1 applied to the grid "structure :with respect toathe anodestructure,- the amplitudeoutput i-ofrtheoscillations=generated bythe device may be varied.

The grid structure draws little or no eurrent,and,there- :fore, the modulating power required to produce a high 'degree of mo'dulation of the "output is relatively-small.

5111 addition, 'the :grid =strueture unay "be designed-fie :haue:arel-atively low-capacitance with'respecttothennode rand :cathode, "and, t therefore, the upper "limit of the range :of -irnodulation frequencies which may be effectively applied :to the grid structure is relatively 'high, being, for example, row the: order-of several-megacycles.

This :invention furthendiscloses a plurality o'f specific rembodiments -which have been dound to be particularly useful. iIn a *firs't :embodiment, the 1 magnetron aoseillator comprises a plurality of anode members linsulatedly supportedt-imspaced relationwith respect tma cathode. 'A

. lumped constant transmission -line connects r adjacent-of -the-.anode. members together. ..Such--a device has -been i fOUHd-iO-b6-US6fLlI for .generating oscillations .-at fre- 5 quencies on the order ofna few hundredmegacycles. lhe 7. grid structure. comprises. an.auxiliary:electrodemadeup of a. pair of adjacent anodecmembers which is. connected together. and insulated with. respect to .the remainderaof .theandde members. 'Themain .anode structure comprismg all ano'deamembers. other than-the:aforesaidapainof anode members "constitutes a' nonreentrant slow -wave energy transmission structure. The. grid structurep con- 'trol electrode ispositioned entirely withinlithe. gap:formed b'etween'the ends of this -nonreentrant structure. I

' This inventionfurther discloses anotherembodimentof a magnetronos'c'fllator adapted-to operate: in-the. microwave region. This device. comprises a cavity magnetron fro'm-whichith'ree 6f the-andde smernbers have beenre- Lmove'd soas'to form a nonreentrantslow wave energy zoftrans'mission fst'ructure; AA grid structureahas .ben-substituted fforfithel removed anode members, said. structure "having. a curvd'inner. surface spaced. from the cathode by a distance substantially equal tolthe Idistance between .the cathode and thevanoderrne'rnber tips. This .gridstruc- :ture ispos'i'tionedientirely within theqgapIformed between the ends of'the nonreentrant structure.

"Other'i.arid"ifufther objects and advantages of thisain- 'v'ention 'vl ilPbecorne' apparent aslt-h'e deseription'thereof jprogresses, *reference "being 'h'ad to the accompanying "drawings;wherein: p

Fig. l illu's't'r'ates 1a., Partially, broken away, Ltransverse, cross-sectional view :of. a fir'st embodiment of "this inven- "tion;

'Fig. 2""illustrates a longitudinal, (cross-sectionalwiew *of'the'deviceillustrated. in Fig. Iftaken along. line zz -"of Fig. 1;

"Fig.3 illustrates a partiallybroken away, transverse, cross-sectional view er laf'further embodiment of this. in- 'vention; and I Fig." "4' illustrates "diagrammatically a modulation lsystern-1n which -the devices illustrated 'in Fi'gs. 1, T2 or 1' 3 'may be used.

Referi'ing'now to'FigsSIand 2; there is shov'vn amagnetromanodestructure comprising an anode cylinder 10 "whoseen'ds '-are'closed "by upper' and lowe1' end,;pla'tes il and 12, C respectively. Lower endplate I'Z -has an aperture i-'3 thereininto "which' is sealed a-meta'llic cylinder 1 4. "The lower end of cylinder 1'4 is .s'eale'd'by a .gla'ss'bea'd 15. Read 15"was s'ealed'to c'ylinder'1'4"followingevacuationand processing of the "device. Upper end plate 11 contains an aperture 16 therein through :which ei(tends a cathode support cylinder 17, "the 'inner end 'o'f *whichis connected to "a cathode structure "'18. Cathode structure"18 comprises a substantiallycoiitinuous "cathode 5 cylinder I9 coated 'withelectron emissive material. The ends-of cylinder "19 .are'clo'sedby' end" shie1ds 20 comprising disks of slightly "larger. diameter than the cylinder l9. Disks 20, cylinder 19 and cylinder '10 are -Jallpositioned"coaxially,thepcrtions of disks zfl which 'overhangcylin'der 1'9 aetingto preventsubs'taiitial inove :me'nt-T'of eleetr'ons -ernit-ted' from the coating "on Tc linder 19iin a directi'on paralll'to the axisf theredf. 7 port :cylinder 17 :is somewhat snialler i'n 'diamterttian the aperture .T16 in e1fd plate 11, 'andyaccordi'ngly, is spaced 5 :from en'd llplate 1 1 at it "passes therethrough.

A :support cylinder 21 ofinsulating material, such as glass, surrounds support cylinder-"17 coaxial ther''v'vith, orre'ien'duo'f cylinder zl being sealed into addc'e's'sfin end iplate 1:1 surrounding aperture I'6.' "The Oihrblid or :cyliiader-FZI wliih is outside theeVacUated "space defined By rayIinHer I'Oand entlplates 11 and 1 2 is sealedto a 3 metal cup 22 which, in turn, is attached to support cylinder 17. The end of cylinder 17 which extends out beyond cup 22 is attached to a glass sealing cylinder 23 which, in turn, is sealed to a metallic cup 24. Cup 24, in turn, is attached to an electrode structure 25 connected to a rod 26 which extends through support cylinder 17 spaced therefrom into the interior of the cathode structure 18 where it is connected to one end of a heater coil, not shown. The other end of the heater coil is connected to cathode cylinder 19 such that, by application of a heater voltage supply between electrode 25 and cup 22 by means of a heater voltage supply 27, a heater current will flow in the heater coil, thereby heating cathode cylinder 19 and causing the coating thereon to emit electrons.

Surrounding cathode structure 18 and spaced therefrom is a plurality of anode members 28. Anode members 28 are rods of conductive material whose axes are positioned parallel to the axis of anode cylinder and cathode structure 18. Rods 28 extend out through apertures in upper end plate 11 and are insulated therefrom by means of ceramic beads 29 which seal rods 28 into the apertures in plate 11 and rigidly support them with respect thereto. Inductors 30 and capacitors 31 are connected to the external ends of rods 28 to form a lumped constant transmission line having a low frequency pass characteristic.

This is accomplished in the following manner. Adjacent anode members are connected together through inductors, and are connected to a common ground plane for high frequencies, namely, upper end plate 11, through capacitors. The inductors 30 are mounted on support rings 32 and 33 which are supported with respect to end plate 11 by means of rods 34. A magnetic field is maintained in the space between cathode 18 and anode members 28 by means of a coil 35 surrounding anode cylinder 10 and through which may be passed a magnetizing current. One pair of adjacent anode members, designated by 36, is connected directly together and is insulated from the remainder of the anode members, since none of the inductors 30 and capacitors 31 is connected to the members 36. The main anode structure comprising all anode members other than members 36 constitutes a nonreentrant slow wave energy transmission structure. Members 36 form an auxiliary electrode which is connected to one terminal of a modulation source 37, the other terminal of which is connected to the anode cylinder 10. An anode voltage supply 38 is provided, one side of which is connected to cup 22, and the other side of which is connected through a high impedance 39 to one of the anode members 28. Impedance 39 prevents loading of the transmission line by the power supply 38 at the operating frequency of the device.

The specific details of the inductors, capacitors and anode members are more clearly set forth in copending application, Serial No. 81,804, filed March 16, 1949, by William C. Brown and Edward C. Dench, entitled Magnetron Amplifier, now Patent No. 2,673,306, issued March 23, 1954, to William C. Brown. In addition, the aforesaid copending application describes the method whereby the anode members 28, inductors 30 and capacitors 31 form a network which will interact with electrons from the cathode in the presence of crossed electrostatic and electromagnetic fields to produce oscillations whose frequency is determined by the cutofi frequency of the anode structure. This frequency is commonly called 7r mode of operation of the device. An output for the device is provided by merely connecting a wire to one of. the anode members, as at 40.

Referring now to Fig. 3, there is shown a further embodiment of this invention wherein the anode structure is of the cavity resonator type adapted to operate at microwave frequencies. The anode structure comprises an anode cylinder 41. Extending radially inwardly from the inner surface of cylinder 41 is a plurality of anode members 42 comprising substantially planar conductors. Adjacent pairs of anode members 42, together with the space therebetween, define cavity resonators. Alternate anode members 42 are connected together at points adjacent their inner ends on their upper and lower sides by conductive strapping 43 in order to eliminate spurious modes of oscillation of the device.

Positioned inside the space defined by the inner ends of the anode members 42 is a cathode structure 44 comprising a cathode cylinder coated with electron-emissive material. Cathode 44 is substantially similar to cathode 18 described in connection with Figs. 1 and 2. Cathode 44 is supported with respect to an end plate 45 closing one end of cylinder 41 in substantially the same manner that cathode 18 is supported with respect to end plate 11 in Figs. 1 and 2.

An output coupling device 46 is provided comprising a conductive rod 47, one end of which is connected to the conductive strapping 43, and the other end of which extends out through an aperture 48 in cylinder 41. A conductive cylinder 49 is threadedly sealed into aperture 48 and extends outwardly from cylinder 41 surrounding conductive rod 47 but spaced therefrom. A glass seal 50 is provided between conductive rod 47 and outer conductor 49 to maintain a vacuum within the device.

At a point in the anode structure substantially opposite to the output coupling device 46, three of the anode members 42, together with the conductive strapping 43 associated therewith, have been eliminated. An auxiliary electrode or grid 51 has been substituted for the three anode members, said auxiliary electrode or grid comprising a conductive member 52 positioned adjacent the inner ends of the anode members 42. The anode structure comprises anode cylinder 41, anode members 42, and conductive strapping 43. This anode structure constitutes a nonre-entrant slow-wave energy transmission structure. The inner surface of member 52 which faces the cathode 44 is curved to conform to the contour of the average electron path which runs circularly about the cathode in the space between the anode members 42 and the cathode. Member 52 is supported by means of a rod 53 which extends outwardly through anode cylinder 41 and is sealed by means of a glass seal 54 to an outer conductive cylinder 55 surrounding rod 53 and sealed to cylinder 41. The grid 51 is positioned entirely within the gap formed between the ends of the nonreentrant slow wave energy transmission structure. It is V to be clearly understood that, while the device shown in Figs. 1 and 2 is of the unstrapped anode structure type while the device shown in Fig. 3 is of the strapped anode structure type, either a strapped anode or unstrapped anode design could be used for both the species of Figs. 1 and 2 and the species of Fig. 3.

Referring now to Fig. 4, there is shown diagrammatically a modulation system in which the devices of Figs. 1 and 2 or 3 may be used. There is shown a magnetron device 56 comprising an anode structure 57, cathode structure 58 and auxiliary electrode or grid structure 59 which may be of the type illustrated in Figs. 1 and 2 or of the type illustrated in Fig. 3.

An anode voltage supply 60 is connected between the anode structure 57 and the cathode structure 58. The auxiliary electrode in grid 59 is connected to one end of the secondary winding 61 of a signal input transformer 62. The other end of secondary winding 61 is connected to the variable tap 63 of a potentiometer 64 which is connected across a battery 65. Battery 65 is connected by a tap 66 substantially at its mid point to cathode 58. The primary winding 67 of transformer 62 is connected to a modulation source which may have a frequency extending from the lower audio range up to a frequency of several megacycles.

By adjusting the tap 63 of potentiometer 64, the bias applied to auxiliary electrode or grid 59 may be made either positive or negative with respect to the cathode 58, dependent upon the average power output which is desired from the magnetron oscillator 56. With modulation voltages applied between the cathode 58 and the auxiliary electrode or grid 59 whose peak amplitudes are on the same order of magnitude as the amplitude of the anode supply voltage, substantially one hundred percent modulation may be achieved by means of this device. If desired, the bias supply may be eliminated and the modulation source connected directly between the anode and the auxiliary electrode or grid, as illustrated in Fig. 1, or between the auxiliary electrode or grid and the cathode.

This completes the description of the particular embodiments of the invention illustrated herein. However, many modifications thereof will be apparent to persons skilled in the art without departing from the spirit and scope of this invention. For example, other forms of anode structures and auxiliary electrode or grid structures may be used, and the positioning of the auxiliary electrode or grid may be varied somewhat from that disclosed herein, depending upon the results desired. Accordingly, it is desired that this invention be not limited by the particular details described herein, except as defined by the appended claims.

What is claimed is:

1. An electron discharge device comprising a nonreentrant slow wave transmission network the ends of which are separated by a gap, a cathode arranged substantially parallel to said network, means for directing a beam of electrons from said cathode adjacent said network in energy-exchanging relation with radio-frequency fields existing along said network, a control electrode positioned entirely within said gap and adjacent the portions of said network which are in proximity with said cathode, and signal input means coupled to said control electrode for modulating the output of said device.

2. An electron discharge device comprising a nonreentrant slow wave transmission network the ends of which are separated by a gap, a source of electrons spaced along a region adjacent a substantial portion of said network, means for directing a beam of electrons from said source adjacent said network in energy-exchanging relation with radio-frequency fields existing along said network, said means for directing including means for producing a magnetic field in the space between said electron source and said network, a grid structure disposed entirely within said gap and adjacent the portions of said network which are in proximity with said source of electrons, and means for supplying a modulation input signal to said grid structure for modulating the output of said device.

3. An electron discharge device comprising a nonreentrant slow wave transmission network the ends of which are separated by a gap, a source of electrons spaced along a region adjacent a substantial portion of said network, means for directing a beam of electrons from said source adjacent said network in energy-exchanging relation with radio-frequency fields existing along said network, said means for directing including means for producing a magnetic field in the space between said electron source and said network, a control electrode positioned entirely within said gap outside the path occupied by the electron beam and disposed adjacent to portions of said network which are in proximity with said source of electrons, and signal input means coupled to said control electrode for modulating the output of said device.

4. An electron discharge device comprising a nonreentrant slow wave transmission network the ends of which are separated by a gap, a source of electrons spaced along a region adjacent a substantial portion of said network, means for directing a beam of electrons from said source adjacent said network in energy-exchanging relation with radio-frequency fields existing along said network, said means for directing including means for producing an electrostatic field between said. electron source and said network and means for producing a magnetic field in the region between said source and said network substantially perpendicular to said electrostatic field, a grid structure disposed entirely in said gap and adjacent to portions of said network which are in proximity with said electron source, and means for applying a modulation input signal to said grid structure for modulating the output of said device.

5. An electron discharge device as recited in claim 4 wherein said network comprises a plurality of members alternate ones of which are interconnected by electrically conductive strapping.

References Cited in the file of this patent UNITED STATES PATENTS 1,775,886 Carpenter Sept. 16, 1930 1,816,682 Langmuir July 28, 1931 2,013,093 Frantz Sept. 3, 1935 2,217,745 Hansell Oct. 15, 1940 2,412,372 Usselman Dec. 10, 1946 2,416,298 Fisk Feb. 25, 1947 2,462,137 Smith Feb. 22, 1949 2,531,972 Doehler et al. Nov. 28, 1950 2,566,087 Lerbs Aug. 28, 1951 2,582,185 Willshaw Jan. 8, 1952 2,673,306 Brown Mar. 23, 1954

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