US2585794A - Magnetron - Google Patents

Description

Feb.12,1952 J.KURSHAN Em. 2,585,794

MAGNETRON Filed Oct.v 25. 1947 u 2 SHEETS-SHEET 2 film r l i :Snnentors TERDME KURSHAN {6MM-Vanaf. if 3 LLI'J'YD 1:. SMITH Patented Feb. 12, 1952 VIKMAGNETRON Jerome Kurshan, Princeton, .N...J., and vLloyd-P.

Smith, Ithaca, N. Y., assignors to Radio CorporationofAmerica, a corporation of.Delaware 'Application .October.25, 1947, SerialNo." 782,192

l 17.Claims. .'Ihis invention :relates to magnetrons fand particularly concerns vmagnetrons 'especially 'suited ffor frequency-modulation.

fWith the usual form l;of`-rnagnetron,l the `variation tof the potential difference between the anode and cathode at modulation.frequencies-to produce frequency-'modulation of the outputalso Yproduces undesirable 4and excessive amplitude modulation. YIn.=ana1ysis :of'lthe operating; characteristics of a magnetromgitzhasbeen found that :forfconstantranode current, :the 'power output delpendsuponthe intensity .fof the'unidirectional or -directcurrent electricfi'eld ator 'near the anode and that ithe frequency "of .the .oscillations 'generated depends upon :thezmanner in which fthe .intensity `of the lunidirectional or directfcurrent Y"e'lectricrleld varies Iwith the-.distance between Ythe vanodeand cathode.

vIn accordance lwith-aprimary*object of :the invention, the direct lcurrent-lrleldLintensity Anear the anode is maintainedcsubstantially'constant While Ythe vdirect current electricvfield distribution between theanodes-andacathode isvariedrat ymodulation frequencies, thus tcLobtain frequencymodulation of the/magnetron output zat a `'substantially v,constant power level. vMore -zspecically, the relationfbetween the pow-er output fof .fa lmagnetron and frequency*l of lthe'oscillations :gen-- erate'd" by it 'arecon'trolled' by "a pair-'of iieldfelec- 'trodes, preferably `in fthefformf-offimperforatecylinders coaxial with .the cathode, `-Whose'fringe rfields;extendinto' the spacebetweenfthe electrodes and whose'direct current :potential .differs 'from that of the anode by a substantially xedamount, affording the desired frequency-output -characvteristic.

'lIJhe yLinvention .further I:resides fin .th'e methods -ff J operation/andi theifeatures A of "construction, fcombnation :fand'iarrangement 'hereinafter ldisy'closed Y f Eorl.a :more 'detailed understanding ofthe .tin- #Mentionv tand for :illustration of :an :embodiment lthereof, reierenceiisvfmfade to -sthe'iaccompanyin'g drawings, inzwhich:

: filig. 1, partly :in isection,lzis .a xfrcnt elevational AAviewrofl-amagnetromtube Fig. 2 is a plan View in section taken :vonzline 2-2 of'Fg. 1;

Fig. 3 is. aside elevational VViewv in section 'taken Yalong line.3-3 of Fig. l;

.F.ig.4v 4 is-an vexploded View of rtheelectrode-as- .sembly shown inFigs. rL-.S and .Eig isaschematic circuit diagram .Voir-.a fre- .quencyfmodulated .oscillator Yutilizing the tube .of the precedingfiigures.

Referring to the drawings, `an elongated,. indirectly-heated cathodelll is disposed axially of `a cylindrical cathode space dened bytwo groups of anode segments vI I, I2 disposed in a circular array. As Will hereinafter appear, all of the segments of both groups have-the same directcurrent potential, and aref-.all of thesame instantaneous modulating-frequency potential. Atgany .particular instant, however, -the segments II.are.of one polarity and the intervening segments `I2 are of vopposite polarity .sofaras .the high-frequency oscillations generated -by the tube-.are concerned. Y Y

Inthe particular form of'magnetron shown,

which utilizes a Ytuned circut--externally of the tube envelope, the anode segments-I I` extend .from the rear lace of a metal plate AI3 at the Y.tips of lteeth or radial bars `III `iormed `byopeningsl through the 1plate and -`equally angular-ly vspa-ced about the axisv ofthe lsegment array. Similarly, the Vanode segments I2 extend from the Yfront face of a metal plate I6 at theltips of teeth I-'I formed by circular openings or slots .leorsthe like. The openingslof plate I.3,are so `angu- Vlarlystaggered with respectvto the'openings I8 inplate It that when the-plates are intheirassembled position, the two groups of segments I I-I Zinterleave to forma cylindrical segmented -anode surface. l

The plates I3, I-6 are-positioned vWithin the tube envelope by headers I9, .20 of micaor equivalent insulating material, having elongated positioning ,slots through which pass the upper andlower ends of the spaced plates. The plates I3, IB are held in their Vproper spaced position at utheir lowerends by a framework comprising-bars 2|,

22 respectively Welded to the plates I3, I6 :and .-joined` at theirends .bycross bars 23 of glass, or

equivalent.insulatingr material. At .their upper ends, the'plates I3, It are held in .proper spaced position'vby alframework comprisingbars 21d-"25 respectively attached to the plates and joined together by insulating cross .bars Z6. The anode assembly is held to the upper header I9 by'terminal clips 21-28 respectively mechanicallyxand electrically connected to the anode plates I'3-'I6 above the-header and having clamping tips 29-30 which extend through openings I3l of the header vand-.arebent to engage its undersurface.

The terminals 21-28 are respectively Aconnected to `rleads :32, ,.33 which .extend through the .tube envelope for connection to an external .tuned circuit, :suchas .aparallel line, .concentric lineY or .the likepresonant at the frequencyo'f oscillations .generated bythe-magnetron tube. Y

`disposed internally of the cathode.

The pairs of metal rods 34, 35, held to the lower header 20 by clamping clips 3B, support the cathode I9 and the leads for the heater which is These rods also extend through the header 29 to support the lower frame formed by the bar members 2I, 22 and 23. Two pairs of bars 3-9, 40 extend from the insulating cross bars 26 of the upper frame with their lower ends respectively attached, as by welding, to condenser plates 43, 44, which are insulated from the -outer faces of the plates I3, I6 by thin sheets 45, 46 of mica or similar insulating material. A pair of bars 41, 48 are attach-ed as by Welding at their upper ends to the condenser plates 43, 44 and respectively attached at their lower ends to a pair oi iield electrodes 49 and 50. Each of the field electrodes 49, 50 is in the form of an imperforate cylinder of thin sheet metal l held in position close to the anode segments Il,

I2 and concentric with the cathode I 0 by its ycorresponding support 41 or 48. The eld electrodes 49, 59 are positioned closer to the anode segments II, I2 than to the cathode I0, as illustrated `in Fig. l. The field electrodes 49, 59 extend a substantial distance into the anode-cathode space from the opposite ends thereof and terminate substantially short of one another to leave a substantial intermediate portion of the cathode area directly exposed to the anode segments.

Suitable means, such as the magnets'designated N and S in Figs. 3 and 5, are used to provide a constant magnetic field parallel to the axis of the cathode I -to cause the electrons traveling from the cathode to the anode to follow curved paths in the usual magnetron fashion.

Referring to Fig. 5, the anode leads 32, 33 are connected to the open end of a resonant parallel line formed by bars I, 52 along which a snorting bar 53 is slidable for tuning apurposes. The shorting bar is connected by conductor 54 to the positive terminal of a suitable source 55 of constant high direct current voltage whose negative terminal is connected by conductor 56 to ythe cathodepIU of Vthe magnetron. The heater leads 51 are connected to a suitable source S of heating current not shown.

In accordance with the present invention, the field electrodes 49, 50 provide means for maintaining the direct current eld intensity at the anode substantially constant while the direct current electric field distribution between the anode andthe cathode is varied at modulation freqpencies. For the moment assuming absence of the field electrodes 49, 50, the oscillations gerierated by the magnetron may be frequency-modulated by superimposing a modulating signal voltage upon the anode-cathode direct current voltage provided by the source 55; more specifically, the secondary 58 of a modulating transformer 59 may be included in the conductor 55 between the source 55 and the cathode ID of the tube, and the primary 60 of the transformer connected to a suitable source of modulating signal voltage at audio, video or other frequencies substantially lower` than the frequency of oscillation of the magnetron.l The resulting frequencymodulation is, however, accompanied by excessive variation of the output at the modulation 1 frequencies.

`extend into the unobstructed space between the anode and cathode surfaces. The application of ythe modulating voltage causes the direct current j electric field distribution ybetween the anode and cathode to vary with consequent corresponding variation of the frequency of the oscillations generated by the magnetron but because the direct current electric field is maintained substantially constant in the vicinity o f the anode, the frequency modulation is not, as in prior magnetrons, accompanied by substantial amplitudemodulation.

As the exact held-electrode potential which affords minimum amplitude-modulation cannot be precisely predicted, there is pro-vided, in shunt to the direct current voltage source 55, a voltage divider 6I whose adjustable contact 62 is connected by lead 63 to the eld electrodes 49, 50. It

is thus a simple matter, in any particular system,A

to adjust the positive potential of the field-electrodes until the desired frequency modulationoutput characteristic is obtained.

Although the magnetron specifically illustrated ls of the type using an external tuned circuit, it shall be understood the invention is applicable to the types of magnetron utilizing resonant cavities opening into the anode-cathode space, for example, the magnetrons may be generally of the construction disclosed'in -application Serial No. 758,692. It shall further be understood that although the magnetron disclosed herein is one utilizing eight anode segments, the field electrodes may be disposed within the anode-cathode space of a magnetron having a larger or smaller number of anode segments. In all cases, it` is desirable that the field electrodes be held at constant high-frequency potential by bypassing them to the outside of the anode plates I3, I6 or equivalent anode block. Although the field electrodes were included primarily to minimize undesired amplitude-modulation, they inherently provide a means of altering the frequency-modulation characteristics of a multi-segment magnetron and may be utilized to improve the frequency-modulation characteristic even at sacrifice of constancy of output.

What is claimed is:

1. A magnetron comprising anode structure defining a cylindrical anode surface of constant diameter, a cathode within said anode structure and extending axially of said anode surface, and a hollow cylindrical imperforate eld electrode positionedcloser to said anode surface than to said cathode and encircling a substantialpart of said cathode within said anode surface and insulated from said anode structure and said cathode, a substantial part of the length of ysaid cathode being directly exposed to said anode structure.

2. A magnetron comprising anode structure defining a cylindrical anode surfaceVa cathode extending axially of said anode surface, and'cylindrical eld electrodes positioned closer t'o said anode surface than to lsaid cathode and encircling opposite end regions of said cathode within said anode surface and insulated from the anode structure and said cathode; a substantial interte f1 mediate por-tion fof fthe-cathode V'area fzbeing fdif'rectly exposed tofsaidfanode'estructure.

3.'f=A-1magnetron comprising fanode structure fdeiiriingfaf lc'fliriblrical anod'efsurface, a cathode, eX-tending vaxially of saifdf-anoide` surf ace, a field electrode 'interposedbetween :a part of said cath- --ode and vsaid anode surface l'for controlling the 4i'direct :fcurrent'iie'ld at said'anode surface, and fabypass Acondenser. internally connectedbetween "said 'iildfflectrodefandf said anode structure.

4. A magnetron fcomprising segmented f-anode -"st'I-'vucturedefining a cylin'z'irical"anode surface, a 'cathode Y'extendingaxially of said surface, la vpair "of cylindrical lfeld electrodes respectively encircling oppositei ends 'olfsaid' cathode 4and' insulated therefrom, and"bypass condensers respectively connected iinternallyof the magnetron between said field electrodes and the outer surface of.

said cathode in a'direction transverse tothe elecl ,tron path therebetween.a 'field electrode hav- 'ing a -portion 'thereof vinterposed between .substantial por-tions of said anode and said-.cathode, a substantial portion of 'the length of said cathode being 1 directly exposed to said anode,

andffabypass condenser connected between-said :eld electrode and saidfianode.

'7. A magnetron comprising an anode, a cathode spaced from said anode, means adjacent said anode for providing a constant magnetic field within and transverse to the path of electrons between said cathode and said anode, and field electrodes having portions thereof positioned closer to said anode than to said cathode and interposed between the end portions of said cathode and substantial portions of said anode, the intermediate portion of said cathode between said end portions being directly exposed to said anode.

8. A magnetron comprising an anode, a cathode spaced from said anode, means adjacent said anode for providing a constant magnetic eld within and transverse to the path of electrons between said cathode and said anode, and imperforate field electrodes having kportions thereof positioned closer to said anode than to said cathode and interposed between the end portions of said cathode and substantial portions of said anode, the intermediate portion of said cathode between said end portions being directly exposed to said anode.

9. A magnetron comprising an anode structure dening a cylindrical cathode space of constant diameter, an elongated cathode extending coaxially within said space, means adjacent said anode structure for providing a constant magnetic field within said space parallel to said cathode, and a hollow cylindrical field electrode having a portion thereof positioned closer to said anode than to said cathode and interposed coaxially between substantial portions of said cathode and said anode structure.

1-10. IA' fmagnetron 2comprising an anode-.struclture.deningfa:cylindrical-cathodespacefof-Econ- .'stant "diameter, an felongated'z-cathode 'extending fcoaxially .within"saidtspace=means a'djacentfsaid anode-:structure for providing arconstantmagrietic field-.within sa-idsp'ace parallelftorsaidacath- V.1111.' Aimagnetron comprising :an-anode lstructure defining a cylindrical cathode space, an

elongated methoden-extending :fcoaxially rwithin isaid space,irmeans adjacent said :anode structure for j providing a :constant magnetic eld within -said space iparallel :to :said-cathode, and axiallyspaced .i hollow ..cylindrical field Aelectrodes having parts Apositioned closer `to said anode :structure .thantc said 4cathode andnterposedcoaxial- 'lybetween ther end .portions orisaid lcathode @and substantial portions :of 1 said anode structure, ,the Nintermediate portion :of :said cathode :between -saidfendportions being directly exposed' toisaid anodexstructura l2. -A magnetron comprising an .-anodei strucfture dening a cylindrical Acathode space, van

elongated cathode extending coaxially within said space, means Lad-,iacentsaid fanode structure `for 'providing va constantmagnetic eld within said-.space parallel tosaid-cathOde, and axiallyspaced hollow cylindrical imperforate eldelectrodes having `parts positioned .closer to .said

anode structure than to said-cathode andinter- Vposed coaxiallybetween the end portions of said cathode 4and substantial portions of said :anode structure, the intermediate portion of said cath- :ode between .said .end Yportions .being directly exposed kto said anode structure.

13. An electrical system comprising a magnetron having an anode, a cathode spaced from said anode, and a field electrode having a portion thereof interposed between substantial portions of said cathode and said anode, a source of variable direct current voltage connected to said anode and said cathode, and a source of constant direct current voltage connected to said field electrode and said anode, whereby the direct current electric field at said anode and the power output of said magnetron are maintained substantially constant despite variations in the direct current electric field between said anode and said cathode produced by variations of said variable voltage source.

14. An electrical system comprising a magnetron having an anode, a cathode spaced from said anode, and a field electrode having a portion thereof interposed between substantial portions of said cathode and said anode, a source of variable direct current voltage connected to said anode and said cathode, and a source of constant direct current voltage connected to said eld electrode and said anode, whereby the direct current electric iield at said anode and the power output of said magnetron are maintained substantially constant despite variations in the direct current electric field between said anode and said cathode produced by variations of said variable voltage source, and a bypass condenser connected between said field electrode and said anode.

15. An electrical system comprising a magnetron having an anode, a cathode spaced from Y, said anode, and a field electrode having a. p0r- -tionthereof interposed between substantial portions Aof .said cathode and said anode, means providing a constant magnetic field within and transverse to the path of electrons between said cathodeV and said anode, a source of constant voltage and a source of alternating voltage connected in series between said anode and said cathode, and a source of constant voltage connected to said field electrode and said anode to maintain the direct current electric field at said anode and the power output of said magnetron substantially constant despite variations in the direct currentelectric field between said anode and said cathode.

i' 16. An electrical system comprising a magnetron'havng Ian anode, Va cathode spaced from said anode, and a field electrode having a portion thereof interposed between substantial portions of said cathode and said anode,'means pro- Widing a constant magnetic eld within and transverse to the path of electrons between said cathode and said anode, a source of variable direct current voltage connected to said anode and said cathode to modulate the frequency of oscillations generated by said magnetron, and a source of constant direct current voltage connected to said ield electrode and said anode, whereby the direct current electric eld at said anode and the power output of said magnetron are lmaintained substantially constant despite variations in the direct current electric eld between said anode and said cathode produced by variations of said variable voltage source.

17. An`electrical system comprising a magnetron having an anode, a cathode spaced from said anode, and a eld electrode having a portion thereof interposedbetwen substantial portions of said cathode and said anode, means providing a constant magnetic eld within and transverse to the path of electrons between said cathode and said anode, a source of variable directl current voltage connected to said anode and said cathode to modulate the frequency of oscillations generated by said magnetron, and a source of constant direct current voltage connected to said field electrode and said anode, whereby the direct current electric field at said anode and the power output of said magnetron are maintained substantially constant ,despite variations in the direct current electric eld be` tween said anode and said cathode produced by variations of said variable voltage source, and means for adjusting the voltage of said constant voltage source to obtain a desired fref quency modulation-output characteristic.

JEROME VKURSHAN. LLOYD P. SMITH.

, REFERENCES" CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 943,969 DeForest Dec. 21, 1909 1,417,912 Hewitt May 30, 1922 1,976,778 Gossling et a1. Oct. 16, 1934 1,997,053 Gill Apr. 9, 1935 2,000,938 Fay May 14, 1935 2,009,368 Usselman July 23, 1935 2,096,249 Kapteyn Oct. 19, 1937 2,115,521 Fritz et al Apr. 26, 1938 2,147,159 Gutton et al Feb. 14, 1939 2,233,261 Hollmann Feb. 25, 1941 2,238,272 Linder Apr. 15, 1941 2,416,298 Fisk Feb. 25, 1947 FOREIGN PATENTS Number Country Date Y 211,551 Great Britain Feb. 18, 1924

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