US2821659A - Magnetron - Google Patents

Description

Jan-l 1958 J. FEINSTEIN 2,821,659

MAGNETRON Filed Nov. 18, 1954 INVENTOR J. FE/NSTE/N OLMDF A ATTORNEY United States Patent MAGNETRON Joseph Feinstein, Morristown, N. 1., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application November 18, 1954, Serial No. 469,644

18 Claims. (Cl. 315-3957) This invention relates to electron discharge devices and more particularly to multicavity magnetrons.

When oscillations start to build up in a resonant circuit comprising a ring of cavity resonators, such as in a multicavity magnetron, competition exists between the various possible modes of oscillation. Generally it is desired to have oscillation occur in what is referred to as the rr-mode. However, under various conditions the build-up of oscillation in a different mode may be preferred by the circuit; this build-up of oscillation in other than the desired 1r-m0d6 of oscillation is referred to as moding. The usual approach to the moding problem has been two-fold: mode frequency separation and selective mode loading. The frequencies of the modes of the magnetron resonator system near that of the 1r-mode would ordinarily be closely grouped were not steps taken to separate them. Priorly mode separation has generally been accomplished by two methods. The first, and more common, has been to increase the coupling by conductive connections between the resonators and particularly by employing straps; this is generally referred to as strapping. This increases the frequency separation by increasing the coupling between resonators. The second method has been to use cavities tuned alternately to different frequencies; this latter method has been employed in what is generally referred to as the rising-sun anode structure. This method increases the frequency separa tion by detuning the adjacent resonators relative to one another.

Further to prevent moding, selective loading of the degenerate or unwanted mode most likely to oscillate in place of the 1r-mode has also been employed. This mode is generally the one closest in frequency to the 1r-mode. Selective loading may be obtained by changes in the internal anode structure of the magnetron or by elements located external to the magnetron and particularly in the output wave guide connected to the magnetron.

These prior methods have not generally proven satisfactory at higher frequencies. Strapping is limited in the number of resonators that may be employed. Further the two approaches of frequency separation and mode loading are not independent of each other, the selective loading in fact tending to hinder the mode separation. At high frequencies this has been found to raise serious problems in prior structures.

It is a general object of this invention to provide improved anode structures for multicavity magnetrons.

Further objects of this invention include improving the frequency separation of the mode of oscillations of a magnetron, enabling improved operation of magnetrons at high frequencies, and preventing moding in magnetrons when operated at high frequencies.

As mentioned above, the mode separation in a magnetron can be varied as the coupling between adjacent resonant cavities is varied. In accordance with one aspect of this invention, optimum coupling between adjacent resonators is attained not by conductive connections,

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such as straps, but by a capacitive coupling adjacent the inductive regions of the resonators.

In one specific illustrative embodiment of this invention a magnetron comprises a plurality of hollow anode segments mounted circumferentially around the central or cathode cavity. Advantageously the anode segments may be formed as hollow vanes as by the forming or bending of a metal strip. At the base of each vane are a pair of capacitance members extending inwardly toward each other and defining a small capacitive gap. The vanes may advantageously be supported from an outer anode rim by T-shaped members which provide the end closure for the resonator slots defined between adjacent anode segments. Two adjacent T-shaped members also define a capacitive gap, of slightly larger dimensions, directly adjacent, and electrically in parallel with the first gap. The two T-shaped members thus also enclose a hollow portion.

For the 1r-mode of oscillation, there is no potential across these capacitive gaps and therefore no 1r-Il'l0d6 energy is stored in these gaps. For other modes of oscillation, however, a potential difierence does exist across the gaps and energy of these modes is stored; the optimum condition for mode separation is that one half of the energy of the unwanted modes is stored in the capacitance gaps, the other half being stored in the capacitance of the resonators itself.

In order to utilize the potential difference between these two points defining the capacitance gap at the base of each anode vane, it is necessary that this coupling capacitance not be shorted by the anode vane or segment itself. Accordingly, each anode segment is made hollow to serve as a choke and prevent the continuous conducting path of the anode segment providing an electrical short across the gap. As the area of the anode vane is limited, the choke defined by the hollow vane also is limited; accordingly, it is advisable to have the gap across the base of the anode vane small to have a high capacitance so that the choke section may be also quite small. The inductances of these choke sections should be sufficiently great that they have a negligible shunting effect on the capacitance gaps at the frequencies of the magnetron. Thus the high capacitance, low impedance gap is advantageously employed with the small choke section possible in the anode vane.

However, in accordance with another aspect of the invention, additional energy of the unwanted mode fields is stored in the capacitance gap defined between the ends of adjacent T-shaped sections supporting the anode vanes. As noted above, these second gaps are directly adjacent and in parallel with the primary gaps at the base of the anode vanes. A second choke section is also provided for these gaps; this choke section is advantageously defined by the hollow portion bounded by two adjacent T-shaped members and the outer supporting rim. In this case there is no limitation necessarily imposed on the area of this choke section, as the diameter of the outer rim and the length of the T-shaped members may be increased as desired. It is thus possible to have these secondary gaps of low capacitance values for the storage of the field energy of the unwanted modes.

As only the unwanted mode energy is stored in these gaps, loading of the unwanted modes can readily be attained, in accordance with another specific embodiment of this invention, by introducing a lossy dielectric into these gaps. This can be a material, such as barium titanate, which can introduce loss to reduce the Q of the unwanted modes. The insertion of a lossy dielectric material possessing a loss factor tangent 9 in these capacitors has a first order effect of reducing the Q of the unwanted modes to 1/ tan 6. There is actually also a second order 3 effect tending to reduce the mode separation, but this remains negligible until loss factors of the order umty are reached.

It -is a feature-of this invention that an anodeyfor employment in a magnetroncompriseaplurality of-hollow anode segmentshavingcapacitance memoers at the base of the anode extending across the hollow portion and defining a capacitance gap.

It is a further feature of this-invention that the anode segments be supported by conductive members defining a second capacitance gap directly-adjacent and parallel to each of the firstgaps, the conductive members also defining a hollow choke portion communicating with the second gap.

It is another feature of certain embodiments of this invention that-a lossy dielectric material be inserted into the capacitance gaps thus defined in the anode structure. I

It is a still further feature of "this invention thata magnetron comprise hollow anode segments having capacitance gaps across the base thereof for the storage of energy of the unwanted modes of oscillation, the hollow portions serving as choke sections to prevent the shorting of the capacitance gaps by the anode segments themselves.

A complete understanding of this invention and of the various features thereof may be gained from consideration or" the following detaileddescription and the accompanying drawing, in which:

Fig. 1 is a sectional view of a'magnetron illustrative of one specific embodiment of this invention;

Fig. 2 is aplan view of the anode and cathode structures of the embodiment of Fig. 1 taken along the line 22 thereof; and

Fig. 3 is a partial plarrview of an anode structure in accordance with another specific illustrative embodiment of this invention.

Referring now to the drawing, the specific illustrative embodiment of this invention depicted in Fig. 1 comprises an anode structure :10, best seen in Fig. 2, mounted by a circular rim member 11 between the two pole pieces 12 and 13. A cathode sleeve 15 extends through the central aperture of: the anode it) and has coated thereon an electron emissive coating between apair of magnetic collars 17. A heater element 19 extends within the cathode sleeve 15 and is connected to a pair of leads 20. One lead :20 is connected to an inner cylindrical terminal conductor '21 and the other to an outer cylindrical terminal conductor 22, the two terminals and 22 being insulated K The output resonator 32 of the anode structure is 'conected, through a dumbbell or basically H-shaped transformer section 33, as is known in the art, to an output Wave guide section 35' through which the energy of the magnetron is transmitted to external circuitry. The output wave guide section 35 serves as an impedance transformer between the output of the magnetron and the external circuitry and has hermetically sealedthereto a window 36 transparent to the passage of microwave energy.

Heat radiating vanes 38 are advantageously supported 'by a metallic bodymember 39 in which is also located the dum beil shaped wave guide output section 33. An xhatisttubul'ation 49 is secured toa side aperture in the pole piece 13-to enable the exhausting of the magnetron.

In this specific embodiment ofthe invention, the anode structure 10. as-seen in Figu2, comprises a. pluralityof hollow anode vanes or= segments 45 ='which may advantageously be each 'formed'of a single strip of a conducting material; each anode vane encompasses a hollow choke section 4'6. 'At'thebase of eachva'ne ts and astending inwardly across the hollow section 46 are a pair of capacitance gap defining members 47; members 47 thus define a plurality of capacitance gaps 48 which serve to couple capacitively adjacent resonator slots 49 defined between adjacent *anode' vanes 45.

The resonator slots-49--are-open adjacent the central cavity of the anode, in which cavity the cathode sleeve 1. S 'is located, and :are-e'ach closed at their other "end'bya T-shaped-support 'member SL Secured to ac'h'-'cross or T-section of members 51 are one side of eachof two adjacent anode vanes 45-and theone capacitance member 47 connected to each side. Between adjacent cross or T-sections of members-5'1thereisthus defined a second capacitance gap 53, which gap is directly adjacent and electrically parallel to the primary gaps 48 defined by members47 secured to the base of the anode vanes 45.

A hollowchokesection 54 is defined between adjacent T-shaped membersfil by the adjacent members'o'l and thesupportingcircular rim member 11. The individual anode vanes 45 are thus each supported bytwo T-shaped members 51 which'in turn are secured to the outer rim member 11.

ln-accordance with anaspect of this invention, mode separation is attained by the capacitive coupling 'between adjacent resonators "49 afforded by the capacitive-gaps 4-8-and 53 and specifically by the storage of field energy of unwanted modes in these gaps. Th hollow sections 46 and 54 define inductance chokes which prevent the capacitance, gaps from being shorted by the conducting paths of tlie anodevanean'd support members, respectively. 'As the hollow section' lfi within the anode vane 45 is limited in area, the capacitance. gap 48 is advantageously of a 'sufficiently small sizeso that the choke section can adequately assure that the conducting path ofthe vaneha's a negligible shunting effect on the capacitance 'ga'p48 associated with'the vane. The hollow sections 54, however, "may'be formed of substantially any desired size by; increasing the diameter of the-outer circular'rim 1'1 'a'nd'the length of the upright portions of'the T-shaped memberssl. Capacitance gaps 53 accordingly may a'dva'ritage'ously'be-larger than the primary cap'acitance'g'aps 48.

The modeseparation'in'the anode-structureof'Fig. 2 is attained'by this capacitive coupling between adjacent resonators 49 and essentially across the base of each anode segment. The inductive'ch'okes formed by the hollow sections 46 within theanodc vanes 45 themselvesprevent shorting'of the'capacitancesthus formed 'bet'we'en'the two parts of the 'anod'ese'gments"45. Andthe'supporting members 51-forthe"anode vanes'provide'both additional coupling capacitance and another choke section to enable storageofmore energy'of the unwanted modes.

As there is now-mode potential betweenadjacent resonators'and thus thereis only'field energy of the unwanted modes storedinthe coupling capacitances defined by gaps 48 and 53, the unwanted'modes ma'y'readily 'be loaded by inserting a lossydielectric into'these gaps. In the specific illustrative "embodiment depicted in Fig. 3, this has been do'ne. Advantageously the lossydielec'tric 56, which'may be'of barium titanate'or other dielectric material having a high lossfactor, is secured directly to the gap definingme'mbersythis may'bc'done 'by plating a thin layer-of silver onto thQSlClQSCftlle dielectric material 56 and silver b'ra'zing the silver plated dielectric material to 'the'sides ofthe gap defining members.

lt is to be understood that the above-described arrangem'ents'are' illustrative of the application of the principles of the invention. Numerous-other arrangementsmay be devised by th'ose'skilledin thea'rt without departing from the-spirit and scope of the invention.

l. A ina'gfietr'oncomprisinga plurality of "anodesegine'nts defining resonant cavities between adjacent segments, said segments having hollow portions therein, and capacitance members at the base of said segments across said hollow portions and defining capacitance gaps for the storage of energy of unwanted modes of oscillation, said hollow portions serving as choke sections to prevent the shorting of said capacitance gaps by the anode segments.

2. An anode for employment in magnetrons comprising a plurality of anode segments defining resonant cavities between adjacent segments, said segments having hollow portions therein, capacitance members at the base of said segments across said hollow portions and defining capacitance gaps, and means supporting said anode segments.

3. An anode in accordance with claim 2 wherein said supporting means comprises conductive means defining second capacitance gaps positioned adjacent said firstmentioned gaps, said conductive means having hollow portions communicating with said second capacitance gaps.

4. An anode in accordance with claim 3 wherein said second capacitance gaps are longer than said first-mentioned capacitance gaps.

5. An anode for employment in magnetrons comprising a plurality of anode segments defining resonant cavities between adjacent segments, said segments having hollow portions therein, capacitance members at the base of said members extending inwardly across said hollow portions and defining capacitance gaps, means supporting said anode segments, and lossy dielectric elements positioned in said gaps.

6. A magnetron comprising a cathode, a plurality of anode segments encompassing said cathode, said anode segments defining resonant cavities between adjacent segments and said segments having hollow portions therein, capacitance members at the base of said segments and extending inwardly across said hollow portions, the capacitance members of each segment defining a capacitance gap for storage of energy of unwanted modes of oscillation of the magnetron and the impedances of said gaps and said hollow portions being such that said gaps are not appreciably shunted by said anode segments, and means supporting said anode segments.

7. A magnetron in accordance with claim 6 comprising lossy dielectric elements positioned in said gaps to load the unwanted modes of oscillation of the magnetron.

8. A magnetron in accordance with claim 6 wherein said supporting means comprises conductive means defining second capacitance gaps positioned adjacent said firstmentioned gaps, said conductive means having hollow portions communicating with said second gaps and the impedances of said second gaps and said second-mentioned hollow portions being such that said second gaps are not appreciably shunted by said conductive means.

9. A magnetron in accordance with claim 8 comprising lossy dielectric elements positioned in said gaps to load the unwanted modes of oscillation of the magnetron.

10. A magnetron comprising a cathode, a plurality of anode segments encompassing said cathode and defining resonant cavities between adjacent anode segments, means including portions of said segments defining a capacitance gap between each two adjacent resonant cavities, and means supporting said anode segments, said supporting means including conductive means defining a second gap between adjacent resonant cavities.

11. A magnetron comprising a cathode, a plurality of anode segments encompassing said cathode and defining resonant cavities between adjacent anode segments, means including portions of said segments defining a capacitance gap between each two adjacent resonant cavities, means supporting said anode segments, and lossy dielectric elements positioned in said gaps.

12. A conductive circuit element comprising a plurality of hollow conductive members, means mounting said conductive members circumferentially, adjacent ones of said conductive members defining resonant cavities, and a pair of conductive elements mounted on each of said hollow conductive members external of said resonant cavities and extending inwardly across the hollow thereof, said conductive members defining capacitance gaps between adjacent ones of said resonant cavities.

13. A conductive circuit element in accordance with claim 12 comprising lossy dielectric elements positioned in said gaps.

14. A conductive circuit element in accordance with claim 12 wherein said mounting means comprises means defining second capacitance gaps and having apertures therein communicating with said second gaps.

15. A conductive circuit element in accordance with claim 14 comprising lossy dielectric elements positioned in said priorly mentioned and said second gaps.

16. A conductive circuit element in accordance with claim 14 wherein said second gaps are larger than said priorly mentioned gaps and said apertures are larger than the 'hollow defined by said conductive members.

17. A conductive circuit element comprising a plurality of thin vane segments, means mounting said segments circumferentially, adjacent ones of said segments defining resonant cavities therebetween, and a pair of conductive members mounted on each of said vanes at the base thereof and extending inwardly of each segment, each pair of conductive members defining a capacitance gap across the base of each segment.

18. A conductive circuit element in accordance with claim 17 wherein said mounting means comprises means defining a second capacitance gap adjacent each of said priorly mentioned gaps and communicating therewith and having an aperture therein adjacent each of said second gaps and communicating therewith.

References Cited in the file of this patent UNITED STATES PATENTS 2,480,126 Frankel "um-"n-.." Aug. 30, 1949

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