De¢.1o,19.46. - ‘ 'G_L, USSELMAN 2,412,372 MAGNETRON Filed Oct. 26, 1943 -DC . , sv- mvENToR g ATTORNEY ' , ' Patented Dec. 10, 1946' 2,412,372 UNITED "STATES PATENT orifice = ` y _ 2,412,312 MAGNETRON 'y _ George L. Usselxnan, Port Jefferson, N. Y., assign ‘or to Radio Corporation of America, a corpora tion- of Delaware Application october 26, 1943, serial No. 507,697 16 Claims. (Cl. 179-1715) 1 2. This invention relates generally .to ultra high frequency magnetron oscillation generators, and particularly to magnetrons of the type having an `upon which the electrons impinge are designated anode so constructed that it forms a circuit reso nant to the frequencyA at which the device is in tended to operate. s L. The cathode is K and extends linearly along the central axis of the magnetron or central chamber. Split disc-like rings GI and G2 are shown around each` end of the cathode K and 1o cated at each end ofthe magnetron central chamber. The envelope of the magnetron, which is evacuated, is not shown in order to simplify For the purpose of generating ultra high fre quency oscillations modulated in amplitude, it is the drawing. , ' known to employ a magnetron having an anode An important feature of the magnetron of the provided on its inner surface with a plurality of 10 substantially cylindrical grooves or cavities dis invention lies in the novel construction of the grooves‘or cavities by reason of which the lip posed parallel to and symmetrical with the cath circle or inner walls of the central chamber tapers ode. The grooves or cavities form tubes having outwardly in going from lthe top to the bottom, inductances dependent upon the dimensions thereof, and the portions of the anode between 15 and the diameters vof the grooves grow larger -the grooves form capacitances with each other from end e to end e’, as shown. The order of the change in dimensions may be reversed with and with the cathode, the capacitances valso be out añecting the principles of the invention. ing dependent upon the dimensions of these por A ñeld magnet with poles N and S (north and' tions and the spacing thereof relative to each other and to the cathode. The anode of this 20 south) produces a magnetic iield parallel to the type of magnetron can be said to be composed of cathode to influence the movement of the elec- ‘» a plurality of inwardlyv projecting anode por trons emanating from the cathode. If_ desired, _this magnet may be replaced by a iield coil sur tions. These anode portions may comprise an rounding the anode and producing an intense even number and be substantially or effectively spaced from one another by one-half wavelength 25 but constant magnetic field which has flux lines running parallel4 through the envelope in a di- f at the operating frequency of oscillations. Ref erence is herein made to Hansell United' States `rection parallel to the cathode. The disc-like rings GI and G2 may be referred Patent #2,217,745, granted October 15, 1940, and to as grids or control electrodes and are shown to Samuel United States Patent #2,063,342, De cember 8, 1936, for this known type of mag 30 connected to opposite ends of the secondary wind netron. ing S of an audio frequency transformer T to whose primary Winding P is applied the audio The present invention, broadly stated, is a modulating signal in the form of speech or Aoscil modification of the foregoing type of magnetron lations. The ring grids are by-passed to" the" which makes it possible to obtain frequency modulated oscillations in a novel and eflicient 35 anode A by condensers B. The midpoint ofthe manner. ' A more detailed description of the invention follows in'conjunction with a drawing wherein: Figure 1 shows substantially a half sectional view, partly in perspective, of a magnetron in ac cordance with the present invention, in a circuit for producing frequency modulated oscillations; secondary winding S is connected to a source of negative bias potential. The anode A is grounded at GRD, while high negative direct current po tential and 10W voltage heater current are sup plied to the cathode K through leads J and H, respectively. It will thus be seen that the anode ' A is at a high direct current positive potential ’ relative to the cathode K. An output or pick-` I up loop D is located in one of the grooves or Figure 2 shows a plan view of the magnetron of Figure 1 with the pole face removed to show 45 cavities for abstracting ultra high frequency oscillations. This loop connects to a suitable the configuration of the anode groves more com and pletely. output circuit such as a transmission line or an The magnetron of the invention isshown as having an anode A provided with eight grooves tenna by means of leads F. ' ~ The principles of operation of the magnetro or cavities, although it should be understood that 50 and its circuit will now be described. In gen any other desired number of grooves can be em ployed. The upper end of these cavities are des ignated e, while the lower ends are designated e'. The lips of the cavities which define the bound- ‘ eral, when free electrons are liberated from the cathode K by the action ofy heat, they are pulled toward the anode by its positive potential. Now it is known that when an electron moves perpendic aries of the inwardly protruding anode portions 55 ularly across a magnetic field it will describe a 2,418,878 l v I 3 ~ concentric or curved path in the magnetic field. The curvature. of the path depends upon the vof the magnetron of Figures 1 and 2 are entirely illustrative and not definitive.' It should be strength óf the- magnetic ñeld and the velocity The velocity depends on the potential difference between the cathode and anode. _When certain adjustments of the i‘leld - understood that the theoretical explanation given above is for the purpose of exposition in order r vof the electron. that the inventionmay be better appreciated. While this explanation is believed to be correct, it is notl of necessity complete. nor does the operation of the invention depend upon its ac strength and .anode voltage are made, the elec- . trons will curve into the magnetron inner walls and start feeble oscillations in the cavities. Once oscillations have started, alternate positive and negative potentials appear on the lips L of the cavities. The electrons, in passing these alter curacy or otherwise. w - ì l. An electron discharge device comprising cathode electrode and an anode electrode cooper nately charged cavity lips in their curved orbits, become hunched in groups. . What is claimed is: atively disposed with respect to said cathode, said By proper adjust anode having an electron receiving portion in ments of Áfield strength and anode potential, proximity to said cathode and a grooved portion these bunches of electrons are caused to fall at spaced from said first portion forming an induct reduced velocity on the negatively charged lips ‘ ance which together with the capacitances be of the cavities. 'I'his increases the efllciency of tween said electrodes constitutes an electrical cir the magnetron and causes the oscillations in the cuit, said grooved portion tapering from. one end cavities to grow stronger so thatv comparatively 20 to the other. large amounts of ultra high frequency power may 2. An electron discharge device comprising a be obtained from this type of magnetron. , cathode. and an anode having electron receiving The electrons from the cathode ,K are caused ` surfaces disposed about said cathode. said anode to move toward the anode in either the larger or having also a plurality of longitudinal groovœ the smaller end of the magnetron by the differ 26 in its inner walls disposed remote from, and sym ences of negative bias potentials on ring grids metrical with said cathode, said grooves being -Gi and G2 produced by the applied signals. In ` smaller at one end than at the other. A ’ other words, if ring grid Gi is more' negative than 3. An electron discharge device comprising an grid G2. the electrons will be forced to occupy, or ' anode having arms bounding a cavity and form be repelled to. the smaller dimensioned portions ao ing an inductance, said arms and said cavity of the magnetron, as a result of which the fre tapering from one end to the other. quency of the magnetron oscillations will be in 4. An electron discharge device comprising a creased. Again,'if in the audio signal cycle the cathode and a continuous anode surrounding said grid G2 is biased more negative than grid- GI, cathode, said anode having an even number of then the electrons, willbe forced to occupy the portion of the magnetron chamber having larger regularly spaced portions bent inwardly toward said cathode and terminating in juxtaposed sur dimensions as a consequence of which the fre faces, thereby substantially enclosing a plurality quency of themagnetron will be decreased. This of cavities, said cavities each having an opening followsbecause with proper design, changes in which tapers from one end to a larger opening dimensions of a magnetron changes its operat 40 at the other end, and means for producing a ing frequency. due to changes in the orbital paths magnetic i‘leld with flux lines running parallel to taken by the electrons. Of course, this ordinarily said cathode. ' ' 'f requires changes 4in magnetic field density and 5. A magnetron oscillator comprising an elec cathode-to-anode potential. Howevena certain tron discharge device having an enclosing vessel amount of frequency variation can be obtained 45 containing an electrode having arms bounding a by causing the electrons to oscillate in various cavity and forming an inductance, said arms regions of the magnetron having different . terminating. in juxtaposed substantially parallel dimensions but with fixed magnetic field and lines, said cavity having an opening which tapers \ fixed electric potentials. Because of the fact that from one end to an opening of different dimen the Q of a circuit becomes lower as the operat 60 sions at the other end. ing frequency becomes higher, it is possible to 6. An oscillation generator comprising an elec obtain more frequency deviation at these high tron discharge device having a cathode and a frequencies than that usually obtained at the lower frequencies. In other words, a high fre anode consisting of an even number of regularly quency circuit can be frequency modulated over a wider band when compared to that obtained spaced portions bent inwardly toward said cath ode and terminating in juxtaposed surfaces to in low frequency oscillators, although the per lcentage of frequency variation might be the same in both cases. The ileld strength and electric potentials serve as limiting factors controlling `the amount of frequency deviation obtainable from the magnetron of this invention. ‘l The ring grids GI and G2 -are shown split in one place in order to eliminate the possibility of magnetic effect on them. Grids GI and G2 are by-passed with condensers B to prevent the radio frequency from aifecting the modulating circuits. Insulation and mounting means are not shown since they do not- ail'ect the principle of opera continuous anode surrounding said cathode, said ` thereby form an even number of similarly ar ranged cavities, said cavities each having an opening which is smaller at one end 4than at its other end, means for subjecting the electrons emanating from said cathode to a magnetic ñeld in a direction running substantially parallel to said cathod'e, and means for modulating the oscillations produced. 7. An electron discharge device comprising a cathode and a continuous anode surrounding said cathode, said anode having arms bounding a cavity and forming an inductance, said arms and said cavity tapering from one end to the other. tion which the invention describes. 'I'he cooling 70 and a pair of control electrodes at >opposite ends fins usually fastened to the anode are omitted ` of said cathode and located between said cathode here for simplicity. Only such parts of the mag and the adjacent surfaces of said anode. netron considered necessary for the description 8. An electron discharge device comprising a ‘ ' of the invention are shown. cathode and a continuous anode surrounding said It should be understood that the dimensions 75 cathode, said anode having an even number of 2,412,372 5 regularly spaced portions bent inwardly toward and located at opposite- ends of >said, chamber, said cathode and terminating in juxtaposed sur said control electrodes substantially surround- , faces to thereby substantially -enclosing a plural ing said cathode in said planes, means for pro ducing a magnetic ñeld having flux lines running parallel to said cathode, and means coupled vto both of said control electrodes for modulating the oscillations produced by said electron discharge ity of cavities, said anode spaced portions sur rounding a central chamber along whose axis the cathode is located, said chamber tapering from one end to the other, and a pair of disc-like con trol electrodes at opposite ends of said chamber device, said last means including an audio fre quency transformer having a primary winding 9. An electron discharge device comprising-a l0 coupled to a source of modulating potentials'and substantially surrounding said cathode. cathode and a continuous anodesurrounding said cathode, said anode having an even number of a secondary winding each of whose terminals is y connected to a different control electrode. regularly spaced portions bent inwardly toward 13. A frequency modulation system comprising said cathode thereby enclosing a central cham ber along whose axis the cathode is> located, ad an electron discharge device oscillator having jacent anode spaced portions also formingv grooves with one another winch form induct ances, said central chamber and saidl grooves tapering in the same direction from one end to 15 within an evacuated envelopeal cathodeand a continuous lanode surrounding said cathode, said anode havinga number of regularly spaced por tions bent inwardly toward'said cathode thereby enclosing Aa central chamber along whose axis the other, a pair of disc-like control electrodes 20 the cathode is located, adjacent anode spaced arranged in different planes and located at oppo site ends of said chamber, said control electrodes ` portions also forming grooves with one another substantiallyv surrounding said cathode in said and said grooves tapering in the same' direction from one end to the other, a pair of control elec planes. l 10. An'electron discharge device comprising a cathode and a continuous anode surrounding said cathode, said anode having an even num ber,of regularly spaced portions bent inwardly toward said cathode thereby enclosing a cen Which- form inductances, said ycentral chamber 25 trodes arranged in different planes and located at opposite ends of said chamber, said control electrodes substantiallysurrounding said cathode in said planes, means for producing a magnetic field having flux lines running parallel to said tral chamber` along whose axis the -cathode is 30 cathode, means for supplying a bias to said con located, adjacent 'anode spaced portions also trol electrodes which is negative relative to said forming grooves with one another which form cathode, and means for changing the relative inductances, said central chamber and said bias of said two control electrodes in accordance grooves tapering in the same direction from one with changesl in modulation potential to thereby end to the other, a pair of control electrodes 35 changethe frequency of the oscillations produced arranged in different planes and located at op by said oscillator, and a load circuit coupled to posite ends of said chamber, said control elec one of said grooves for deriving frequency modu trodes substantially surrounding said cathode in said planes, and means for producing a mag lated oscillations. y 14. »An electron discharge device comprising an netic field with flux lines running parallel to anode having arms bounding a cavity and form said cathode. ingan inductance, said arms and said cavity ta - i 11. An oscillation generator system compris- pering from one end to the other, a cathode for ingk an electron‘discharge device having a cath said device, and a pair of control electrodes at ode and a continuous anode surrounding said opposite ends of said cathode and located be cathode, said anode having a number of. regu 45 tween said cathode and .the adjacent surfaces of larly spaced portions bent inwardly toward said said anode. cathode thereby enclosing a central chamber 15. An electron discharge device comprising an along whose axis the cathode is located, adja anode having arms bounding a cavity and form cent anode spaced portions also forming grooves ing an inductance, said arms and said cavity with one another which form inductances, said 50 tapering from vone end to the other, a cathode central chamber and said grooves tapering in the for said device, and a.y pair of `control electrodes same direction from one end to the other, a at opposite ends of said cathode an-d located be pair of control electrodes arranged in different tween said cathode and the adjacent surfaces , planes and located at opposite ends of said cham-_ of said anode, means for supplying a bias to said ber, said control electrodes `substantially sur 55 control electrodes which is negative relative~to rounding said cathode in said planes, means for said cathode, and a. circuit for changing the bias producing a magnetic field having flux lines run of said pair of control electrodes relative to each ning parallel to said cathode,-and means coupled other in accordance with changes in modula-v to both of said control electrodes for modulating the oscillations produced by said electron dis tion potential. ode thereby enclosing a, central chamber along whose axis the cathode is located, adjacent anode spaced portions also forming grooves with one another which form inductances, said central stituting capacitances with each other and with said cathode, said grooved and other portions forming a tuned circuit, said grooved portions having diñ'erent dimensions at different points _ 16. A magnetron comprising a cathode, an 60 charge device. ~ ` ' anode encompassing said cathode, means for pro 12. An oscillation generator system comprising ducing a magnetic field in the vicinity of and an electron discharge device having 1a cathode parallel to said cathode, said anode having and a continuous anode surrounding said cath grooved portions substantially symmetricallydis ode,rsaid anode having a number of regularly 65 posed with respect to said cathode and constitut spaced portions bent inwardly toward said cath » lng inductances and having other portions- con chamber and said grooves tapering' in the same 70 in their lengths. direction from one end to the other, apair of ` control electrodes arranged in different planes GEORGE L. USSELMAN.