US2765425A

US2765425A - Magnetron

Info

Publication number: US2765425A
Application number: US651317A
Authority: US
Inventors: Millman Sidney
Original assignee: Individual
Current assignee: Individual
Priority date: 1946-03-01
Filing date: 1946-03-01
Publication date: 1956-10-02
Anticipated expiration: 1973-10-02
Also published as: GB674035A

Description

MAGNETRON 2 Sheets-Sheet l Filed March l, 1946 ff/wf A mwmvfW/f/Jejm. r.. l Fam., l L -1 i w\. ,Q

United States Patent O 'i MAGNETRON Sidney Millman, Brooklyn, N. Y., assignor to the United ates of America as represented by the Secretary of Application March 1, 1946, Serial No. 651,317

41 Claims. (Cl. S15-39.65)

This invention relates to ultra-high frequency generators of magnetron type in which ultra-high frequency oscillations are generated by a number of resonators set into oscillations by high velocity electrons moving along curvilinear or orbital paths, these paths being followed by the electrons because of the joint action of the static and radio frequency electromagnetic fields.

It is an object of this invention to provide an irnproved anode structure for a magnetron, the improvement residing in shaping of the resonant cavities of the anode so as to produce the desired energy conversions and degree of frequency separation between the desired mode of operation and the remaining undesired modes.

An additional object of this invention is to provide an improved anode structure for a magnetron which is inherently capable of converting efliciently the available energy into the pi-mode oscillations and separating this Inode from all other modes solely by imparting two reiterative geometric patterns to two series of cavities of the anode, one of which has a longer resonant wave length than the other, the long wave cavities alternating with the short wave cavities.

Yet another object of this invention is to provide an improved anode structure for a magnetron having adjacent resonant cavities of different size, the ratio of the resonant wave length of the larger cavity to the resonant wave length of the smaller cavity being in the range of 2.5 to 1.3. In this configuration the radio frequency voltage across the openings of the longer resonators is greater than across the openings of the shorter resonators.

Still another object of this invention is to provide an anode structure for a high-frequency magnetron in which the desired conversion of the electron energy into the pimode and resulting optimum frequency separation between the pi-mode and the remaining modes is obtained without any strapping of the metallic vanes of the anode but by using two different geometric configurations for resonant cavities of the anode, one type of cavity alternating with the cavity of the second type around the circumference f the anode, the strapless anode structure making it possible to obtain the desired energy conversion, rnode separation and general tube behavior which is .independent of the anode length, thus enabling one to use longer anodes and longer cathodes than in the strapped tubes and thereby obtaining higher power output.

These and other features of the invention will be more clearly understood from the following detailed description and the accompanying drawings in which:

Figure l is a vertical, section view of the magnetron taken along the axis of the magnetron;

Figure 2 is a cross-sectional View of the magnetron illustrated in Fig. l taken along line 2 2;

Figure 3 is an enlarged sector of the anode of the magnetron illustrated in Figs. l and 2;

Figures 4 through 6 are cross-sectional views of several additional examples of possible anode structures.

It is known in the art of magnetrons that the geometry of the multicavity anodes is such that thewhirling or roice tating electrons can sustain, under varying operating conditions, a number of modes of oscillation in the anode resonators, one mode of oscillation being followed or replaced by another mode. This is especially true when the geometry of the anode structure is such that there is no wide frequency separation between the sustainable modes. Since only one frequency is desired in the output circuit, .it becomes desirable to separate the selected single frequency mode from the remaining modes by a suiiiciently wide frequency difference so as to exclude the appearance of the undesired frequencies in the output circuit of the magnetron for a wide range of operating conditions. The experimental and theoretical analysis relating to the phenomena taking place in the discharge space and resonant cavities of the magnetron indicates that the most efficient conversion of the electron energy created in the discharge space takes place when there is no competition for the energy between one mode and the remaining modes of oscillation. Thus, from an ideal point of View, it would be desirable to eliminate the competition from all other modes of resonance except one, since this would result in such synchronization and bunching of the moving electrons, and the concomitant creation of the radio frequency electromagnetic fields in the anode region by the induced radio frequency oscillations in the anode resonators, as to produce the most eiiicient conversion of the electron energy into the previously mentioned single, stable mode of resonance. Such ideal conditions are not realizable in practice, and the best eiiiciencies in the practical operation of the magnetrons are obtainable when a single mode is separated from the remaining modes by a suiciently large frequency diiference so that there is no competition between the preferred mode and the remaining modes, and an optimum amount of electron energy present in the discharge space of the magnetron is converted into the preferred mode of oscillation. In the past such separation of the modes has been accomplished by the so-called strapping of the alternate equipotential regions at the tips of anode vanes, this strapping comprising, in the majority of the cases, two metallic rings, each of which connects the respective alternate equipotential regions of the anode vanes to each other. This method of obtaining the mode separation is satisfactory for the magnetrons of relatively low frequency since the physical dimensions of low frequency anodes are such that no insurmountable mechanical difficulties are experienced in introducing the above-mentioned rings into the anode structure, connecting the desired vanes with the proper ring, and leaving sufficiently large clearances between one ring and the alternate vanes not connected to this ring. However, as the dimensions of the anode, or

of individual resonators, are decreased for increasing the frequency obtainable with the oscillators of this type, it becomes increasingly difficult to incorporate the strapping into the anode structure. Although satisfactory mode separations by themselves are obtainable when strapping is used, there are additional limitations, other than mechanical, to this method. For example, the axial length of the anode, that is, the thickness of the anode block, cannot exceed a certain fraction of the generated wave length. lf this rule is not observed, a pi-like mode is introduced for which there is a voltage variation along the length of each vane. This mode gets sufiiciently close in wave length to the desired pi-mode to become a source of mode competition with the desired mode.

The invention discloses a new type of anode for a magnetron in which the more favorable energy conversions and separation of the pi-mode from the remaining modes are obtained by making one half of the resonant cavities in the anode larger than the remaining half of cavities, and by positioning these cavities around the circumference of the anode so that a large cavity is adjacentto a small cavity; thatis, there is an alternating series of large and small cavities. The exact geometric pattern of the cavities may differ from anode to anode, and even with a single anode, so long as the resonant wave length ratio of large cavity to' small cavity is substantially in the range of 2.5 to 1.3. The most widely used anode patterns at present arethe hole-and-slot and the vane, pattern; for a more detailed description of the vane pattern 'reference is made tormy application entitled Magnetron filed on March 1, 1 946, Serial No. 651,318. now Patent No. 2,635,210. Both of these patterns may be readily modified to obtain the above-mentioned resonant wave lengths ratio, and, if so desired, the hole-and-slot pattern may be combined with the vane pattern in a single anode; the resulting patterns are illustrated in Figs. 1 to 6, and particularly in Figs. 3 to 6. They illustrate four -specific patterns by the way of an example; the invention is not restricted to any specific pattern, and other patterns may be used for obtaining the sought results. In Figs. 1 through 3 a modified vanepattern is illustrated in which the radial length of every other lresonant cavity in the anode is longer than the radial .length of the remaining alternate resonant cavities. This results in the anode pattern illustrated in Fig. 2, which has been given the name of Rising Sun anode, or Rising Sun magnetron because of some similarity between this pattern and the Japanese ag. This terminology has been accepted by the art, so that it is now known in the art a's the Rising Sun magnetron.

Aside from the obvious mechanical advantage of the Rising Sun magnetron at short wave lengths over the strapped magnetrons, since it does not require any strapping, there are electrical advantages typical of this type of structure, which are as follows:

l. Higher circuit eliiciencies; this advantage becomes increasingly important as the wave length decreases;

2. The mode separation and general tube behavior is independent of the anode length which leads to the possibility of using considerably longer anodes and longer cathodes than in Vthe strapped tubes with the resulting increase in the available power, and

3. Although the problem of mode separation in the Rising Sun anode is, in some respects, similar to that in the Vstrapped tubes, becoming more ditiic'ult with increase in the number of resonators, and with increase in the anode diameter, the present indications are that anodes with greater number of resonators, and therefore of larger cathode and anode diameters, are possible with this structure than with the strapped anodes; thus again appreciably increasing the probability of building magnetrons of shorter wave lengths and higher output power.

Proceeding now with a more detailed description of the Rising Sun anode, an enlarged sector of this type of anode is illustrated in Fig. 3, and the entire anode illustrated at 17 in Figs. 1 and 2. Examination of Figs. 2 and 3 reveals the fact that the anode is composed of small and large resonating cavities alternating with each other around the circumference of the anode, all large cavitieshaving the same pattern and size, which is also true of all small cavities. In the illustrated example of this type of anode, the cross-sections of all cavities are sectors centered on the outer surface of the cathode cylinder 21, so that the side-walls of the cavities are centered on the sarne surface, as illustrated in Fig. 3. The arcs subtending these small and large sectors are centered on the axis of the magnetron. This illustrated geometry need not be followed, if 4so desired, in constructing the Rising Sun anode. Thus the centers of these sectors may be centered on the cathode surface or on a `cylindrical locus whose diameter is smaller or larger than the diameter of the cathode cylinder 21; the diameter of this locus does not represent a critical dimension in the geometry ofthe anode. The

thicknesses

306, 308, v310, etc., of the vanes are preferably all' equal andthe mouth openings 311', 313, '315, etc., are also'pr'eferably equal "to each other. The ratio of thickness, t, of the vane, separating :the two cavities, to the width of the mouth opening, w, is of the order of the optimum values being more nearly in the range of 1.2 to 1.5. This ratio is less critical in the Rising Sun structures than in the vane type structures where the tolerances for this ratio are more critical for any particular size and wave length anode. The ratio of the radius R1 of the cathode cylinder 21 to the radius Rz of the anode is for an eighteen vane magnetron. The ratio of the radial length 303, which is designated by R3, to the radial length 304 of the smaller cavity, which is designated by R4, is of the order of for an eighteen vane magnetron, with the optimum value close to 1.8. This ratio is applicable only to the anodes having the Rising Sun configuration illustrated in Figs. 2 and 3, and it will be different for the resonators having diiieren't shape. In the case under consideration a cavity depth ratio la) R4 for 1.8 corresponds to an approximate value of 1.7 for the ratio of the resonant wavelengths of the same cavities. This approximation changes slightly with a change of the anode diameter. For a larger number of resonators in the anode of the magnetron, the useful range for the *R3/R4l ratio becomes narrower. For instance, with an 18-resonator anode, the above ratio may produce good magnetrons in the range from 1.6 to 2. This does not mean necessarily that one cannot use either lower or higher ratio than the above-mentioned limits, but if the indicated limits are not complied with the efficiency of the magnetron may be lower or the operating range for the Vmagnetron may be compressed due to mode competition. If the number of resonating cavities is increased to 26 it becomes necessary to maintain this ratio close to the 1.8 value, if one is to expect reliable operation. Thus the lesser is `the number of cavities used in the anode structure, the wider is the above mentioned tolerance. The reason for such a variation in the tolerance for the R3/R4 ratio with the number of the resonators in the anode is as follows: if the ratio is made too small, which is equivalent to making of adjacent cavities too nearly alike, there is not enough mode separation. The result is that an anode with small R3/R4 ratio is subject to the same mode-separation difficulties experienced in the operation of the unstrapped vane type magnetrons. Thus the object of having suiciently large R3/R4 ratio is to separate the pi-mode from the other modes. If this ratio is made `too low the next mode on the short wave length side gets too close to the pi-mode. On the higher side, if the Rs/R4 ratio is ymade too high, two electrical ditiiculties'come into play. The first difiiculty is that the radio frequency voltage-across the mouth of the large resonator becomes too high as compared with the radio frequency voltage vacross the mouth of the small resonator, which lowers the operating efficiency; and second, the anode suffers from too much mode separation, and more particularly, the Wave length associated with large resonator becomes too long with the concomitant mode competition.

The vabove-mentioned physical dimensions of the Rising Sun type magnetron may also be expressed more generally andmore succinctly, especially inthe light-of the resonance phenomena :taking v'place ,in 'the anode, in

terms ofthe ratio of the resonant wave lengths of the large and small resonant cavities the most useful range of this ratio being of the order of 2.5 to 1.3. The pi-mode frequency has a wave-length that is intermediate AL and XS, being the average of these two wavelengths. Also, the height of the anode may have a physical axial length greater than a half wavelength at the pi-mode frequency of the magnetron, thus enabling the magnetron to generate large amounts of power. The lengths of the resonant cavities may also be expressed in terms of the pi-mode frequency, the large cavities being longer than a quarter wavelength and the small cavities being shorter than a quarter wavelength, at said frequency. The size of the cavities may be also considered in terms of the admittances looking into the resonant cavities, the admittance looking into the large resonant cavity being positive, while the admittance looking into the smaller cavities being negative. In other words, the large cavity has an inductive impedance while the small cavity has a capacitive impedance. The actual shape of the resonant cavities therefore may be altered in any desired manner so long as, in the process of designing the cavities, one preserves the values of the admittances looking into the mouths of the two types of cavities, respectively, so that the wave length of the pi-mode and the resonant wave lengths ratio for the two cavity shapes remain constant. This is illustrated in Figs. 4 through 6. Fig. 4 illustrates a well known hole-and-slot pattern for the resonant cavities, which has been modified in accordance with the above teachings. The ratio of the resonant wave length of large cavities 400 to the resonant wave length of small cavities 402 is, as before, of the order of 2.5 to 1.3, and the admittances looking into the

cavities

400 and 300, and 402, and 302, respectively, must remain constant if the anodes illustrated in Figs. 4 and 3 are to sustain pi-mode resonances having equal frequencies. In the hole-and-slot pattern of Fig. 4, generally a=b and a=b c (4) where a and b are the two widths across the mouths of the large and small cavities, respectively, and c is width of the resonators pole-pieces facing an anode.

As in the case of Fig. 3 these dimensions are less critical with the disclosed unstrapped pi-mode magnetron than with the strapped vane type structures.

Fig. 5 discloses combining of the two cavity patterns disclosed in Figs. 3 and 4, in one anode, the hole-and-slot pattern having been arbitrarily assigned for large cavities 500, while the Rising Sun or sector pattern has been selected for the rsmall cavities. The electrical parameter rules enunciated for the Rising Sun anode are also applicable to this pattern.

In Fig. 6, the disclosed pattern may be considered as a modication of the pattern disclosed in Fig. 3. In Fig. 3 the peripheral wall portions of small and

large cavities

600 and 602 respectively are semi-cylindrical surfaces.

While the invention has been disclosed in connection with four specic patterns applied to an 18-cavity anode, as stated before, the teachings of the invention are applicable to the anodes having any other patterns, or a combination of patterns, and to the anodes with larger or smaller number of resonators. g

Referring now to Figs. 1 and 2, they disclose two sectional views of a complete Rising Sun magnetron including a wave guide output circuit. The magnetron is mounted between permanent magnets and 1.1, the faces of the magnets engaging soft iron pole-pieces 12 and 13 which are silver-soldered at corners 14 and 15 to a copper magnetron shell 16. The anode-cathode structure `of the magnetron is mounted between the pole-pieces in spaced relationship with respect to the pole-pieces. A Rising Sun anode 17 is held xedly by shell 16, the shell being sufficiently high to provide two end spaces above and below the cathode-anode assembly. The cathode structure illustrated in the iigures is of the radial type, two tungsten conductors 18 and 20, being used for supporting the cathode cylinder 21 in central position with respect to the anode. The cathode is of usual indirect heater type; a coil 22 being inserted in the hollow portion of the cathode cylinder 21. A concentric line is used for connecting the heater to a source of heater potential 23. This line consists of the previously mentioned central tungsten conductor 20, an insulating sleeve 24 surrounding conductor 20, and an outer cylindrical conductor 25 mounted directly over the insulating sleeve 24. The latter is connected to a conductor 26 imbedded in a glass seal 27 of the cathode assembly.

Jumpers

28 and 29 are used between the tungsten rod 20 and the outer conductor 25 on one side and the cathode cylinder 21 and the heater coil 22 on fthe other side, the jumpers thus completing the heater circuit. The advantages of such concentric line for supplying the necessary heater current resides in the fact that the electromagnetic elds produced in the cathode conductors by the heater current are neutralized and therefore there is no interaction between the magnetic field produced by the permanent magnets and the electromagnetic eld normally produced around heater conductors. Conductor 18 is connected to a source of cathode-anode potential 3i), the positive terminal of this source being grounded at a terminal 31 connected to the outer shell of the magnetron. The glassto-metal seals of the cathode structure are completed by means of a glass envelope 32, a metallic eyelet 33 and a bronze or copper sleeve 34, the latter being soldered to the eyelet and to the shell in the usual manner. A wave guide output circuit 35 is connected to one of the large resonant cavities of the anode through an impedance transformer 36. For a more detailed description of the wave guide output circuit tuned to the pi-mode frequency and illustrated in the figure, reference is made to an application for patent of S. Millman, entitled Wave Guide Output Circuit, filed on March ll, 1946, Serial No. 653,514.

The following are the essential dimensions suitable for a magnetron, the frequency dispersion of which is between 23,744 to 24,224 megacycles, with the anode bloc kept at `70" C:

Number of vanes l18 Anode diameter (2R2, Fig. 3) inches .160 Cathode diameter (2R1) do .096 Small cavity diameter 2(R2-f-R4.) do .-28'8 Large cavity diameter 2(R2-|-R3) do .390 Inner `shell diameter do .'469 Fin thickness do .017 Anode length do 1190 While the invention has fbeen described with reference to several particular embodiments, it will be understood that various modifications of the apparatus shown may be made within the `scope of the following claims.

Iclaim:

l. A magnetron comprising a cylindrical cathode, -a hollow cylindrical anode in coaxial position `wi-th respect to said cathode, said Ianode having a plurality of small and llarge cavities tightly coupled to each other, the sma-ll cavities alternating with the large cavities, the cross-sections of said anode in all planes perpendicular to the axis of said magnetron being identical and said cavities having ysector shapes, the `converging portions of said sectors opening into an intenaction space between said anode and said cathode of said magnetron.

-2. A magnetron las defined in claim l in which the ratio of the radial depth of said large cavities, to the radial depth of said small cavities is substantially in the range of 2.6 to 1.4.

3. A magnetron as defined in claim 1 in which the ratio of the resonant wave length of said large cavities to the resonant wave length of said small cavities is substantially in the range of 2.5 to 1.3.

4. An anode for an ultra-high frequency magnetron, said anode being provided with a plurality of resonant cavities along the circumference of a circle, one half of said cavities having an electrical length longer than M4, and the other half shorter than h4, where )t is the wave length of the pi-mode resonance to which said anode as a whole is tuned by said cavities.

5. An :anode for 1an ultra-high frequency magnetron as defined in claim 4 in which the electrically long cavities alternate with the electrically short cavities laround the circumference of said circle.

r6. A magnetron comprising a cylindrical cathode, a hollow cylindrical anode in coaxial position with respect to said cathode, said anode having a plurality of large hole-and-slot cavities and an equal number of small holeand-slot cavities alternating with said large cavities around the circumference of said anode, all of said cavities opening into the space between `said anode and said cathode, said anode having identical cross-sections in all planes perpendicular to its axis.

7. A magnetron as defined in claim 6 in which the resonant wave length ratio of any -two adjacent cavities is `a function of `the total number of cavities is substantially in the range of 2.5 to 1.3.

f8. An ultna-high frequency magnetron having a cathode, -a multicavity anode coaxial with and surrounding said cathode, the size of one half of the cavities in said anode being llarger than the size of the remaining half, said larger cavities alternating with the smaller cavities -around the circumference of said anode, said anode having identical cross-sections in lall planes perpendicular to its axis, the yaxial length of said cathode and lanode being greater than M2, where A is a wave length of the pi-mode resonance of said anode, all said -cavities opening into the space between said anode |and said cathode.

9. A multicavity anode for an ultra-high frequency magnet-ron `comprising a plurality of cavity resonators located Ialong Athe circumference of a circle, some of said resonators being tuned to a first frequency, the remaining ones of said resonators being tuned to a second frequency different from said ttirst frequency, said anode having identical cross-sections in all planes parallel to said circle and all resonators having a physical length 'in the direction perpendicular to the plane ofl said circle greater than M2 where A is the operating wavelength.

10. A multicavity anode for an ultra-high frequency magnetron comprising a plurality of cavity resonators located along the circumference of a circle, one-half of said resonators being tuned to a first frequency, the remaining half of said resonators being tuned to a second frequency different from said first frequency, the ratio of the resonant wave length of the resonators tuned to said first frequency to that of the resonators tuned to said second frequency being in the range of 2.5 to 1.3, said resonators tuned to said first frequency `alternating with said resonators tuned to said second frequency along the circumference of said circle, said anode having identical cross-sections in all planes parallel to said circle.

ll. A multicavity anode for an ultra-high frequency magnetron comprising a plurality of cavity resonators located along the circumference of a circle, one-half of said resonators being tuned to a first frequency, the remaining half of said resonators being tuned to -a second frequency different from said first frequency, the resonators tuned to said first frequency having a given geometric configuration and the resonators tuned to said second frequency having the same configuration and different dimensions, said resonators tuned to said first frequency alternating with said resonatorstuned'to said second frequency along the circumference of saidcircle7 said anode having identical cross-sections in all planes kparallel Vto said circle.

12. A multicavity anode for an ultrahigh frequency magnetron comprising a plurality of cavity resonators located along the circumference of a circle, one-half of said resonators being tuned to a first frequency, the remaining half of said resonators being tuned to a second frequency different from said first frequency, the resonators tuned to said first frequency having a given geometric configuration and the resonators tuned to said second frequency having a different geometric configuration, said resonators tuned to said first frequency alternating with said resonators tuned to said second frequency lalong the circumference of said circle, said anode having identical cross-sections in all planes parallel to said circle.

13. An ultra-high frequency magnetron comprising a cylindrical cathode and a cylindrical anode coaxial with said cathode, said anode being provided with a plurality of resonant cavities along the circumference of a circle concentric with said cathode, one-half of said cavities being resonant at va first frequency, the remaining half of said cavities being resonant at a Second frequency different from said first frequency, said cavities tuned to said first frequency alternating with said cavities tuned to said second frequency along the circumference of said circle, said lanode having identical cross-sections in all planes perpendicular lto its axis, said anode being further provided with openings between said cavities and the space between said cathode and said anode.

14. A multicavity anode for an ultra-high frequency magnetron comprising a plurality of cavity resonators located along the circumference of a circle, one-half of said resonators being tuned to a first frequency, 'the remaining half of said resonators being tuned to a second frequency different from said first frequency, said resonators tuned to said first frequency alternating with said resonators tuned to said second frequency along the circumference of said circle7 said lanode having identical cross-sections in all planes parallel to said circle, said cross-sections having the form of a plurality of sectors forming said cavity resonators, said sectors opening into said circle, the sectors tuned to said first frequency having a longer radial length than that of the sectors tuned to said second frequency.

15. An anode according to claim 14, wherein said sectors are formed by a plurality of vanes disposed about said circle, said vanes being of equal thickness.

16. An anode according to claim 15, wherein the openings of said sectors into said circle have equal widths.

17. An anode according to claim 16, wherein the thickness of each vane divided by the width of each sector opening has a value lying between 1 and 2.

18. An anode according to claim 1'7, wherein said value lies between 1.2 and 1.5.

19. An anode according to claim 18, wherein the radial length of each long sector divided by the radial length of each shorter sector has a value lying between 1.6 and 2.

20. A multicavity anode for an ultra-high frequency magnetron comprising a plurality of cavity resonators located along the circumference of a circle, one-half of said resonators being tuned to a first frequency, the remaining half of said resonators being tuned to a second frequency different from said first frequency, said resonators tuned to said first frequency lalternating with said resonators tuned to said `second frequency along the circumference of said circle, the resonators having the configuration of a hole-and-slot, the slots of all said resonators opening into said circle and having equal widths, the resonators tuned to said first frequency having different dimensions than the dimensions of those tuned to 'said second frequency, lsaid anode having identical cross-sections in all planes parallel to said circle.

21. An anode according to claim 20, further-.including at least two Vpole pieces disposed about said anode and having a width Vgreater than that of said slots.

22. A multicavity anode for an ultra-high frequency magnetron comprising a plurality of cavity resonators located along the circumference of a circle, one-half of said resonators being tuned to a first frequency, the remaining half of said resonators being tuned to a second frequency different from said first frequency, said resonators tuned to said first frequency alternating with said resonators tuned to said second frequency along the circumference of said circle, the geometrical configuration of the resonators tuned to said first frequency being that of a hole-and-slot, the geometric configuration of the resonators tuned to said second frequency being that of a sector, said anode having identical cross-sections in all planes parallel to said circle.

23. A magnetron according to claim 1, wherein each of said anode cross-sections has the form of a plurality of sectors, the total of said sectors constituting said cavities, the sectors constituting the large cavities having a longer radial length than that of the sectors corresponding to the small cavities.

24. A magnetron according to claim 23, wherein said sectors are formed by a plurality of vanes disposed about the axis of said anode, said vanes being of equal thickness.

25. A magnetron according to claim 24, wherein the openings of said sectors into said interaction space have equal widths.

26. A magnetron according to claim 25, wherein the thickness of each vane divided by the width of each sector opening has a value lying between 1 and 2.

27. A magnetron according to claim 26, wherein said value lies between 1.2 and 1.5.

28. A magnetron according to claim 27, wherein the radial length of each large sector divided by the radial length of each small sector has a value lying between 1.6 and 2.

29. A magnetron according to claim 28, wherein the radius of said cylindrical cathode, as measured from the axis of said cathode to its outer circumference, divided by the radius of said cylindrical anode, as measured from the axis of said cylindrical cathode to the inner circumference of said cylindrical anode, has a value lying between 0.59 and 0.62.

30. A magnetron according to claim 29, wherein all of said sectors converge upon points lying upon the outer circumference of said cylindrical cathode.

31. An ultra-high frequency magnetron comprising an anode disposed about a cathode, said anode being provided with a plurality of cavity resonators, one-half of said resonators being resonant at a rst frequency and the remaining half of said resonators being resonant at a second frequency, the ratio of said irst and second frequencies being dependent upon the total number of cavity resonators and lying in the range of 1.3 to 2.5.

32. A magnetron comprising an anode disposed about a cathode, said anode comprising a resonator structure including at least two cathode resonators therein, one of said cavity resonators having an electrical length longer than a quarter wavelength at the pi-mode frequency of said anode, and the other of said cavity resonators having an electrical length shorter than a quarter wavelength at said pi-mode frequency the ratio of the shorter length to the longer length being of a value to cause said magnetron to oscillate only at said pi-mode frequency.

33. A magnetron, according to claim 32, further including an output circuit coupled to said resonator structure and tuned to said pi-mode frequency.

34. An anode for an electron tube adapted to operate in the pi-mode frequency, comprising at least two cavity resonators, one of said cavity resonators having an electrical length longer than a quarter wavelength at said pi-mode frequency, the other of said cavity resonators having an electrical length shorter than a quarter wavelength at said pi-mode frequency the ratio of the shorter '-10 length to the longer length being of a value to cause said tube to resonate at said pi-mode frequency.

35. A self-oscillating magnetron device comprising a cathode, an anode structure spaced from said cathode, means to control the oscillating frequency of said magnetron device, said means comprising at least two cavity resonators forming part of said anode structure and having different electrical dimensions, respectively, and output means communicating with said anode structure and tuned to a frequency intermediate the frequencies corresponding, respectively, to the dilferent electrical dimensions of said cavity resonators.

36. An electron discharge device comprising a cathode, an anode structure spaced from said cathode and incorporating two cavity resonators having different electrical dimensions, and output means coupled to one of said cavity resonators and tuned to a frequency intermediate the frequencies corresponding, respectively, to the different electrical dimensions of said cavity resonators.

37. An electron discharge device comprising a cathode, an anode structure spaced from said cathode and incorporating two cavity resonators having different electrical dimensions, and output means communicating with one of said cavity resonators and tuned to a frequency which is the average of the frequencies corresponding, respectively, to the different electrical dimensions of said cavity resonators.

38. An electron discharge device comprising a cathode, an anode structure spaced from said cathode and incorporating two cavity resonators having different electrical dimensions, one of said cavity resonators having electrical dimensions corresponding to a frequency whic is higher than that desired of the output of said device and the other of said cavity resonators having electrical dimensions corresponding to a frequency which is lower than that desired of the output of said device, and output means communicating with one of said cavity resonators and tuned to a frequency intermediate the frequencies corresponding, respectively, to the different electrical dimensions of said cavity resonators.

39. An electron discharge device comprising a cathode, an anode structure spaced from said cathode and incorporating two cavity resonators having different electrical dimensions, one of said cavity resonators having electrical dimensions corresponding to a frequency which is higher than that desired of the output of said device and the other of said cavity resonators having electrical dimensions corresponding to a frequency which is lower than that desired of the output of said device, and output means communicating with one of said cavity resonators and tuned to a frequency which is the average of the frequencies corresponding, respectively, to the different electrical dimensions of said cavity resonators.

40. A multi-resonator magnetron anode member having a central axially extending opening and a plurality of electro-magnetically coupled cavity resonators disposed about and opening into said central opening, each of said resonators having an axial length substantially equal to that of said central opening, and dielectric means in one of said resonators in excess of any dielectric material in another of said resonators to thereby effect an irregularity between said resonators.

4l. A magnetron anode block having a central cylindrical main cavity and a plurality of cavity resonators of equal length in the direction parallel to the axis of the main cavity and disposed about and opening into the main cavity, said anode block comprising a peripheral portion and a plurality of vanes of uniform axial length and thickness extending radially inwardly from said peripheral portion toward said main cavity, the opposite sides of each of said vanes being of different depths in directions perpendicular to the axis of said main cavity and adjacent vanes having sides of the same depth facing one another, the peripheral portion and vanes of said anode block constituting the walls of said cavity reso- 1 1 nators land defining two groups of resonators of different sizes, the resonators of each group being of identical vsize and being alternately disposed with respect to the resonators of the other group, and means for extracting power from one of the cavity resonators of the larger size. 5

References Cited in the le of this patent UNITED STATES PATENTS 2,410,396 Spencer Oct. 29, 1946 10 v12 Linder Feb. 4, 1947 Retherford Dec. 20, 1947 Garner July 26, 1949 Brown Feb. 12, -1952 Rollin Oct. 13, 1953 FOREIGN PATENTS Germany Jan. 8, 1943