US2828445A - Coupling cavities of a magnetron without use of straps - Google Patents

Description

March 25, 1958 E. C. OKRESS COUPLING CAVITIES OF A MAGNETRON WITHOUT USE OF STRAPS FileQ. Aug. 20. 1954 Fig. 3

. INVENTOR Ernest C. Okr ess BY ATTORNEY United States Patent COUPLING CAVITIES OF A MAGNETRON WITHOUT USE OF Ernest -C. Okresg, Elmira, N. ,Y., assignor to Westinghouse Electric Corporation, East .Pittshurgh, 122., .a ..c0rp.oration oiPennsy-lvania Application August'20, 1954, Serial No. 451,224

11 Claims. (Cl. 315-.39;77)

A- magnetron comprising a meresymmetric system of.

identical cavity resonators arranged-incirou'lar larray about a cylindrical cathode can have nodes of electrical oscillation, where N is "the :number of cavities. Of these modes, that one in which alternate resonator segments are of opposite polarity, known as the 71' -mode,- is ordinarily desired 'for operation, and it has been wide practice in-the art to provide {straps which interconnectalternate segments with each other to :provide adequate mode separation and give the 1r mode superior stability over other possible oscillation modes. However, the stabilization of the 1r mode thus attained proves insuificient with certain types of loading-and to increase stabilization, discontinuities (breaks) atpoints in the strapping at such angles to the cavity to which 'the power offtake (transducer) is attachedas-wiill increase the coupling to the transducer of competingosc'illation modes has been resorted to.

Several serious disadvantages have, however, been found to result from use of straps, the most serious being a tendency toelectrical breakdown between the straps and the resonator segments which they by-pass at separation-distances which are limited in magnitude by'desig'n factors. High electric gradient, bombardment by electrons emitted by the cathode and sublimation of electronernissive material deposits on the straps and anode from the cathode surface all contribute to such breakdown tendencies.

In accordance with my present invention lteliminate strapping entirely and interconnect cavities o'fflike phase by what are essentially waveguides at the periphery .of the cylindrical anode structure.

One object of my invention is accordingly to provide an improved method of stabilizing the 1r mode of oscillation in magnetrons.

Another object is to provide a novel type of magnetron in which the 1r mode of oscillation is highly stabilized.

.Another object is to. provide a novel type of magnetron stabilized for the 1r mode of oscillation which is capable of operating with higher voltage gradients than stabilized magnetrons of the prior art.

Another object is to provide a magnetron of novel structure in which there is a wide frequency separation between the 1r mode .of oscillation and competing modes.

Another object is to provide a novel method of destroying the symmetry of doublet fields of modes competing with the 1r mode of oscillationin a magnetron.-

of the p ages. 19 or z w.;.-- ene a k pea as 2,328,445 Patented. Mar. 25,1958

Still another ohjectlistoprovide a novel method of altering the characteristic admittance of the resonant system in a cavity-type magnetron.

.Qther. objects tot-my invention will become evident .uponreading fhe'following description and referring; .to .theilrawings .in which: s

Fig, 1 is a view partlylin .section of a twelve cavity magnetron .emhodyingtheprinciples .of,my invention;

Fig. ,2Qis .a..section;-.along thev lines 11-11 of Fig.1; and

.Fig, 3 ,adetail section showing :a modified diorin of .my jnvent'ion a'nd. .taken along. a. similar .plane to .that of Fig. l.

.Re'ferring inL-detailto Fig. 1, .a magnetron. embodying myfiinvenfion .may comprise a:..conventional cylindrical cathode. 1,, flie per ipheral .ativesurface .of which. is indicated by a dotted circle, coaxial with .an ,annularvanode .2 twelve equally spaced cylindrical .cavitvresonators ',3 ,to :14 of similar dimensions. Each resonator .is connected in usual fashion with the annular inter-action space .15 surrounding cathode .1 .by; cavity interaction slot 16 Ihavingwallscompr'is'ing parallel planes equally spaced .florn. that .axial plane .of the cathode whichineludes ,flie .Of.'IhB" cylindrical cavity. Near. the

periphery .ofetheanod'e are, at each endeface, annular rectangulangrooves 17 and :18-wh'ich-iare the principal ,-I have previously referred to as constitutinguny present invention.

Each odd .(or .even) numbered, cavity resonator .isv connected .to thegroove 17 by .a passage 19 which imavhave arectangiilar section; and each. even, .(or odd) numbered cavityeresonator is connected to the-groove 1'8. byia similar passage.21..

The peripheryuofthe cylindrical anode 2..is enclosed by .a wall of conventional. type whichfhasitsfends, closed in, conventional fashionby end-walls (not shown). The cavity 3 has .an outlet passage through .wall..22 to which is connectedin well-known fashionawaveguidel l which maybe of coaxial .type and which forms agtransducer for power outflow from the magnetron. Coupling-of the transducer may be effected.in,a..well:known;..way 'by a core-rod 25 extending throughpassage .23 and forming a .lo-op26. having itsend connected to the wall of icavityS Flt will be .seen in Figures1 .and. .2 that odd numbered cavity-resonators are .all,connected'-together by .a wave- .guide comprisingthe-groove-17 and .the.passages...'19, whileall evennumbered cavity-resonators are connected together by a. waveguide comprising the groove 18v and passages 21. This can .be shown-to result in altering the inductive couplingwhich exists .between adjacent cavity-resonators .andthis changes the .resonant frequency .of the .system..

.It is possible to increase the insn ranceagainstrany .particular competing mode of. oscillation. interferingjwith the 1r mode by introducing a discontinuity 27 finihe wavetr-ansmission .propertiespf the. grooves-.17 or 18.by'decreasi-ngor increasing. its cross-sectionat a suitable distanceKalong it from thecouplingloop 26;.tov destructively interfere with. sustenance, of. .theconapetmg v.mode .in question. The mutualcoupl-ing between cavities ofiike phase is dependent on the axial1 depth fiend wid-thm ofsthe r s v .7 and 18., and the rad all t t i l -t W dth: :23? 1 of the order of the diameter oi-. the;cavities, and: .w andt m be of the order of the w-idth of the;.interaction slots-lii.

0n the other :handt et ial leng h L p ss seszls l non-resonant low impedance links, and no large electric gradients can develop in them.

It will be noted that the passages 19 or 21 are remote from the cathode 1 where deposits of material sublimed from the cathode and bombardment by electrons from the interaction space are negligible. The electric field in the resonator is likewise a minimum there. Hence little tendency to electric arc-over, such as that mentioned above as found in strapped magnetrons, exists in my arrangement. The structure likewise avoids the use of an asymmetrical resonator system such as those of rising sun type magnetrons and so eliminates the complexities of possible model operation which the duplex cavity-systems of the latter involve.

It may be pointed out that the existence of the transducer at one cavity resonator distorts the 11' mode pattern,

of all magnetrons, but that this distortion will be reduced by my present arrangement of waveguides interconnecting the cavities of like phase. There is also some 'n' mode pattern distortion due to non-uniformity of the resonator slot field along the magnetron axis due to strapping at the ends of the cavities. This distortion is lessened where by present waveguide interconnection system is substituted for prior art strapping.

It is also possible to modify the structure shown in Fig. 1 by substituting ridged waveguides for the simple rectangular channels 17 and 18 to interconnect cavities of like phase. For a given load this system gives an increased stabilization if the ridged waveguide is proportioned to give the desired degree of coupling. Fig. 3 illustrates a ridged waveguide 30 substituted for the channel 17 in Fig. 1. The ridged waveguide is provided with a ridge member 32.

It may be pointed out that the arrangement here disclosed is very much simpler to make and operate than are the coaxial loop strapping systems of the prior art, and is also free of the spurious resonances likely to develop in strap systems because of their higher impedance and liability to resonance in their coupling.

It will also be noted that the coupling passages 19 or 21 need not be positioned exactly in line with the resonator slots 16, but may be ofi-set on one side or the other of that position to attain more complete screening from cathode electrons and sublimation deposits from the cathode.

I claim as my invention:

1. A magnetron comprising a cylindrical cathode and an anode comprising an annulus having an even number of cylindrical cavities with axes substantially parallel to the central axis of said annulus and arranged with their axes at points equally spaced on the circumference of a circle concentric with said annulus, a radial interaction slot connecting each said cavity with the inner surface of said annulus, an annular groove in each end face of each said annulus near the periphery thereof, a first passage from each odd numbered cavity only, said point passages connecting said each odd numbered cavity with one said groove and a second passage for each even numbered cavity only, said second passages connecting said each even numbered cavity with the other said groove.

2. A magnetron comprising a cylindrical cathode and an anode comprising an annulus having an even number of cylindrical cavities with axes substantially parallel to the central axis of said annulus and arranged with their axes at points equally spaced on the circumference of a circle concentric with said annulus, and a radial interaction slot connecting each said cavity with the inner surface and arranged with their axes at points equally spaced on the circumference of a circle concentric with-said annulus,

a radial interaction slot connecting each said cavity with the inner face of said annulus, an annular groove in an end face of said annulus near the periphery thereof, and a passage for every other cavity only, said passages connecting said every other cavity with said groove.

4. An anode for a magnetron comprising an annulus having an even number of cylindrical cavities with axes substantially parallel to the central axis of said annulus and arranged with their axes at points equally spaced on the circumference of a circle concentric with said annulus, a radial interaction slot connecting each said cavity with the inner face of said annulus, an annular groove in each end face of said annulus near the periphery thereof, a first passage for each odd numbered cavity only, said first passages connecting said each odd numbered cavity with one said groove, and a second passage for each odd numbered cavity only, said second passages connecting said each even numbered cavity with the other said groove.

5. An anode for a magnetron comprising an annulus having an even number of cylindrical cavities with axes substantially parallel to the central axis of said annulus and arranged with their axes at points equally spaced on of said annulus, an annular groove in an end face of said annulus near the periphery thereof, a passage for every other cavity only, said passage connecting said every other cavity with said annular groove.

3. An anode for a magnetron comprising an annulus having an even number of cylindrical cavities with axes substantially parallel to the central axis of said annulus the circumference of a circle concentric with said annulus, a radial interaction slot connecting each said cavity with the inner face of said annulus, an annular groove in one end face of said annulus near the periphery thereof, a passage connecting every other cavity with said groove, and a section of altered cross-section at one point in said groove.

6. A11 anode for a magnetron comprising an annulus having an even number of cylindrical cavities with axes substantially parallel to the central axis of said annulus and arranged with their axes at points equally spaced on the circumference of a circle concentric with said annulus, a radial interaction slot connecting each said cavity with the inner face of said annulus, an annular groove in each end face of said annulus near the periphery thereof, a passage connecting each odd numbered cavity with one said groove, a passage connecting each even numbered cavity with the other said groove, and a section of altered cross-section in each said groove.

7. An anode for a magnetron comprising an annulus having an even number of cylindrical cavities with axes substantially parallel to the central axis of said annulus and arranged with their axes at points equally spaced on the circumference of a circle concentric with said annulus, a radial interaction slot connecting each said cavity with the inner face of said annulus, a ridged waveguide encircling the periphery of said annulus at one end face thereof and a passage connecting every other cavity with said ridged waveguide.

8. An anode for a magnetron comprising an annulus having an even number of cylindrical cavities with axes substantially parallel to the central axis of said annulus and arranged with their axes at points equally spaced on the circumference of a circle concentric with said annulus, a radial interaction slot connecting each said cavity with the inner face of said annulus, a ridged waveguide encircling the periphery of said annulus at each end face thereof, a passage connecting each odd numbered cavity m'th one said waveguide, and a passage connecting each even numbered cavity with the other said waveguide.

9. An anode for a magnetron comprising an annulus having an even number of cylindrical cavities with axes substantially parallel to the central axis of said annulus and arranged with their axes at points equally spaced on the circumference of a circle concentric with said annulus, a radial interaction slot connecting each said cavity with the inner face of said annulus, a ridged waveguide encircling the periphery of said annulus at one end face thereof, a passage connecting every other cavity with said ridged waveguide, and a section of altered cross-section at one point in said waveguide.

10. An anode for a magnetron comprising an annulus having an even number of cylindrical cavities with axes substantially parallel to the central axis of said annulus and arranged with their axes at points equally spaced on the circumference of a circle concentric with said annulus, a radial interaction slot connecting each said cavity with the inner face of said annulus, a ridged waveguide encircling the periphery of said annulus at each end face thereof, a passage connecting each odd numbered cavity with one said waveguide, a passage connecting each even numbered cavity with the other said waveguide, and a section of altered cross-section at one point in each said waveguide.

11. A magnetron comprising a central cathode surrounded by an anode, said anode comprising a plurality of segments projecting inwardly toward said cathode, said segments separated by cavity resonators, an annular groove in an end face of said anode near the periphery thereof and a passage for every other cavity resonator only, said passages connecting said every other cavity resonator with said groove.

References Cited in the file of this patent UNITED STATES PATENTS 2,408,234 Spencer Sept. 24, 1946 2,611,110 Powers Sept. 16, 1952

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