Sept. 24, 1946.
2,408,235
Filed Dec. 31, 1941
Patented Sept. 24, 1946 2,408,235
UNITED STATES PATENT OFFICE
Percy L. Spencer, West Newton, Mass., assignor to Raytheon Manufacturing Company, Newton, Mass., a corporation of Delaware
Application December 31, 1941, Serial No. 425,071
10 Claims. (Cl. 250—27.5)
This invention relates to a magnetron, and more particularly to one which has a plurality of possible oscillating modes, each determined primarily by the geometry of the internal structure of the magnetron. A device of this kind is in-tended to oscillate in a predetermined principal mode so as to generate a predetermined frequency. Heretofore the existence of additional modes of oscillation have introduced serious difficulties. Such additional modes have caused spurious oscillations to be generated, thus consuming energy which reduced the efficiency and effectiveness of the device.
An object of this invention is substantially to eliminate the undesired character of the additional or spurious modes of oscillation by utilizing them to reinforce the principal or normal oscillator mode of a magnetron.
Another object is to provide means for tuning one mode of oscillation independent of another so as to bring both modes into synchronism.
A further object is to increase the efficiency and effectiveness of a magnetron of the foregoing type.
The foregoing and other objects of this invention will be best understood from the following description of an exemplification thereof, reference being had to the accompanying drawings, wherein:
Fig. 1 is a transverse section of a magnetron embodying my invention, taken along line 1-1 of Fig. 3;
Fig. 2 is a transverse cross-section of the tube shown in Fig. 1, taken along line 2—2 of Fig. 3;
Fig. 3 is a longitudinal cross-section taken along line 3—3 of Fig. 2; and
Fig. 4 is a diagram of the anode arm inter-connections existing in the tube of Figs. 1-3.
The magnetron illustrated in the drawings comprises an envelope I which is preferably made of a block of conductive material, such as copper. This block forms the anode of the magnetron. The block has hollow end sections which are covered by caps 2 and 3, likewise of conductive material such as copper. Between the hollow end sections of the block 1 is located a central bridging portion 4. The portion 4 is provided with a central bore 5 within which is supported substantially at the center thereof a cathode 6 which may be of the indirectly-heated oxide-coated thermionic type. The cathode is supported by a pair of cathode lead-in conductors 7 and 8 sealed through glass seals 9 and I0 mounted at the outer ends of pipes 11 and 12 hermetically fastened within the walls of the block I adjacent the upper and lower hollow end sections. A plurality of slots 13 extend radially from the central bore 5, and each of said slots terminates in a circular opening 14 extending through the bridging portion 4. In this way the anode structure is provided with a plurality of wedge-shaped arms 15 to 22, inclusive, the faces of which cooperate as anode sections with the cathode 6.
When such a magnetron is placed between suitable magnetic poles 23 and 24 to create a longitudinal magnetic field and the device is energized, oscillations are set up. These oscillations may be led out from the tube by means of a coupling loop 25 extending into one of the cylindrical openings 14 and having one end thereof fastened to the inner wall of said opening. The other end of the coupling loop 25 is connected to a lead wire 26 which passes through a glass seal 27 mounted at the outer end of a pipe 28 likewise hermetically fastened through the wall of the envelope 1. An additional conducting pipe, not shown, may be electrically connected to the pipe 28, and forms with the wire 26 a concentric line through which the high frequency oscillations generated by the magnetron may be conducted to a suitable utilization circuit.
A capacity exists between the cathode 6 and the face of each of the anode sections 15-22. Also capacitances exist between the side walls of each of the slots 13. The inner walls of the openings 14 constitute inductances. The anode, therefore, is so designed and spaced relative to the cathode that the inductances and the capacitances de-scribed constitute circuits which are tuned, and thus are resonant at a predetermined frequency at which the device is to be operated. The device is intended to operate so that each bore 14 and its adjacent arms form a circuit tuned to the frequency at which each of the other bores 14 and its adjacent arms oscillate.
It has been found that in magnetrons of this general type, there has been a tendency for oscillations to be produced, not only in accordance with the above desired mode but also in various undesired spurious modes. One particularly troublesome mode is that in which alternate anode arms form opposite ends of an oscillating circuit extending around the back of a pair of openings 14. As more fully described and claimed in my copending application, Serial No. 421,145, filed December 1, 1941, this spurious oscillating mode can be substantially eliminated by inter-connecting the outer ends of alternate anode arms directly by relatively low impedance paths. In the arrangement as shown herein, such inter-connection is made in somewhat different manner from that shown in my said copending application. As shown in Fig. 1, a conductor 29, preferably of copper, is fastened to and inter-connects the anode arms 21 and 19. Also a similar conductor 30 interconnects anode arms 16 and 13. These two connections are made at one end, for example the upper end of the magnetron structure. At the other end of the structure a conductor 31, preferably of copper, is connected to and interconnects anode arms 15, 17 and 19, while a similar conductor 32 interconnects anode arms 22, 20 and 18. The conductors 31 and 32 overlap at one side of the structure, leaving a gap at the other side of said structure along which the conductor 8 may extend. Similarly at the other end of the structure conductors .29 and 30 leave a gap through which the conductor 7 may extend. In this way these interconnecting conductors may extend beyond the end of the bridging member 4 without interfering with the lead-in conductors 7 and 8, respectively. likewise a gap between the other ends of the conductors 29 and 30, as shown in Fig. 1, forms a gap permitting an arm 34, the purpose of which will be described below, to extend along said gap with-out interference. As will be seen most clearly from Fig. 4, the interconnections described above interconnect alternate -anode arms "directly through 'relatively low impedance conductive paths, thus substantially eliminating the spurious -oscillating mode described-above Therefore the anode' structure' will- oscillate-with each bore 14 -and the adjacent anode arms forming- a` tuned circuit as described above. This mode of oscillation can be termed the "transverse" mode.
On referring to Fig. 4 it will he seen that -a path exists from. the upper end of-anode face 22 to the lower' end along the conductor 32 to the lower end of anode face 20, and thence to the upper end thereof. This circuit contains an appreciable amount of inductance and some capacitance. I have found that under proper conditions, the device can be made to oscillate energetically along such a path. Thus the path traced can be made an oscillating mode which may be termed a "longitudinal" mode of oscillation. Similar oscillating circuits exist respectively between anode faces 21 and 19, 20 and 18, 19 and 17, 18 and 16, and 17 and 15. It will be noted that all of the-above longitudinal oscillating paths are of substantially the' same length' and configuration so that the frequencies of oscillations in this mode are substantially equal. The frequency of these oscillations thus produced determined primarily by the length of the anode faces 15-22. The frequency of these oscillations in the -longitudinal mode can be varied by the dimension of this length without-affecting in any substantial degree' the frequency Of oscillations produced by the transverse mode. I have found that if the thickness of the central-bridging, portion 4 and thus the length of the anode faces are accordingly chosen the frequency of the longitudinal mode can be made equal to the frequency of the transverse mode. When this is done, both modes are strongly energized and reinforce each other. In tubes which I have built in accordance with this invention, I have found that the total length of each longitudinal mode of oscillation is approximately equal to one-half of a wave length of the desired oscillations generated by the magnetron.
It is often difficult to predetermine the dimensions of the structure exactly so as to make the longitudinal and oscillating modes of - exactly the same frequency. ' Therefore it is desirable to pro-vide means for bringing these two modes of oscillation into exact synchronism. For example,- a tuning arrangement as described- and claimed in my ,copending application, Serial No. 420,558, filed November 26, 1941, may be utilized in order to vary the inductance of the transverse oscillating mode for tuning that mode. _This tuning may .be carried out without substantially affecting the frequency of the longitudinal mode. I prefer, however to accomplish this independent tuning by an arrangement as illustrated herein. I have found that a conducting body held adjacent the anode arms 15-22 affects the capacity of the circuit involved in the transverse oscillating mode. Varying the position of this conducting body will vary this capacity while affecting the constants of the longitudinal mode in a very much lesser degree. For the purposes of this device, the effect of this variation on the longitudinal mode maybe considered as substantially zero.
In order to produce this type of tuning, a light flat metal ring 33 is held in juxtaposed position adjacent the anode arms 15-22 at one side of the structure. The ring 33 is split adjacent the lead-in conductor 7 so as to leave a gap permitting adjustment of the ring 33 in a vertical direction without interference by said 7. conductor 7. The ring 33 maybe supported by a supporting arm 34 which is bent through substantially a right angle, and extends to and is supported by a nut 35. The nut 35 is carried at the outer end of a pipe 36 likewise hermetically sealed' through the-wall' of the envelope 1. The pipe 36 is provided with a thinned section 37.
When it is desired to' adjust the position-of the ring 33 relatively to the anode arms, a tool may be applied to the nut 35 so as to twist the thinned section 37. This twisting is sufficient' to give a permanent set to the section 37 to whatever position the nut 35 is turned. In this way the ring 33 can be held in any definite desired position relative to the anode arms within the tuning limits of the device. The frequency of the trans-verse oscillating mode can 'be tuned so as to bring it into exact synchronism' with the "frequency of ' the longitudinal oscillating mode. I have found for example, that in a tube which is adapted to generate oscillations having a wave length of the order of ten centimeters, the wave length of the oscillations produced by the transverse mode may be varied through about one-half a centimeter by the arrangement illustrated.
When the transverse and longitudinal 'modes are brought into synchronism, as described above, a- very remarkable increase in the efficiency of the device results. I have found, for example, that the useful oscillatory power in a device of this kind can readily be made of the order of sixty per cent of the total energy input to the tube. ' This is an extraordinarily high efficiency as compared. with those efficiencies heretofore obtainable in devices of this kind.
Of course it is to be understood that this invention is not' limited' to the: particular . details as-described above as many equivalents will suggest themselves to those skilled in the art. For example, other anode configurations .could be utilized in which a plurality, of oscillating modes might be possible. In each instance a tuning of various oscillating, modes into synchronism with each other by any suitable tuning means will result in relatively high efficiency if the principles of my invention are followed.
What is claimed is:
1. An electron discharge device comprising an electrode structure including _a, cathode and an anode, said electrode structure having a configuration, constituting capacitance and inductance elements forming, circuits which are adapted ,to have .oscillations set up therein, said oscillations being all of the same frequency, a plurality of predetermined points on said electrode structure at which in-phase voltage loops of said oscillations occur, and relatively low impedance means directly interconnecting said points and forming with portions of said electrode structure an additional oscillating circuit, the frequency of said last-named oscillating circuit being substantially equal to the frequency of said first-named oscillating circuits.
2. An electron discharge device comprising a cathode and an anode, said anode having a plurality of electron-receiving portions adjacent said cathode, and a plurality of grooved portions spaced from said electron-receiving portions forming a plurality of inductances which together with the interelectrode capacitances constitute a plurality of tuned circuits adapted to oscillate at a first frequency, relatively low impedance means directly interconnecting alternate electron-receiving portions, each pair of electron-receiving portions thus interconnected forming a tuned circuit adapted to oscillate at a second frequency, said second frequency being substantially equal to said first frequency.
3. An electron discharge device comprising a cathode and an anode, said anode having a plurality of electron-receiving portions adjacent said cathode, and a plurality of grooved portions spaced from said electron-receiving portions forming a plurality of inductances which together with the interelectrode capacitances constitute a plurality of tuned circuits adapted to oscillate at a first frequency, relatively low impedance means directly interconnecting alternate electron-receiving portions, each pair of electron-receiving portions thus interconnected forming a tuned circuit adapted to oscillate at a second frequency, the length of each of said last-named circuits being of the order of about one-half of a wave length of the oscillations of said first frequency.
4. A magnetron comprising an electrode structure including a cathode and an anode, means for producing a magnetic field about said cathode, said electrode structure having a configuration constituting capacitance and inductance elements forming circuits which are adapted to have oscillations set up therein, said oscillations being all of the same frequency, a plurality of predetermined points on said electrode structure at which in-phase voltage loops of said oscillations occur, and relatively low impedance means directly interconnecting said points and forming with portions of said electrode structure an additional oscillating circuit, the frequency of said last-named oscillating circuit being substantially equal to the frequency of said first-named oscillating circuit.
5. A magnetron comprising a . cathode and an anode, means for producing a magnetic field about said cathode, said anode having a plurality of electron-receiving portions adjacent said cathode, and a plurality of grooved portions spaced from said electron-receiving portions forming a plurality of inductances which together with the interelectrode capacitances constitute a plurality of tuned circuits adapted to oscillate at a first frequency, relatively low impedance means directly interconnecting alternate electron-receiving portions, each pair of electron-receiving portions thus interconnected forming a tuned circuit adapted to oscillate at a second frequency, said second frequency being substantially equal to said first frequency.
6. An electron discharge device comprising a cathode and an anode, said anode having a plurality of electron-receiving portions adjacent said cathode and circularly disposed around said cathode, and a plurality of grooved portions spaced from said electron-receiving portions forming a plurality of inductances which together with the interelectrode capacitances constitute a plurality of tuned circuits adapted to oscillate in a first oscillating mode, a lead-in conductor for said cathode lying in a plane extending substantially between two adjacent electron-receiving portions, alternate electron-receiving portions being directly interconnected by relatively low impedance means, said low impedance means directly connecting each of said electron-receiving portions to the two alternate electron-receiving portions with the exception of the two pairs of electron-receiving portions lying on opposite sides of said plane, each of said latter electron-receiving portions being directly connected by said low impedance means only to the alternate electron-receiving portion lying on the same side of said plane, whereby none of said low impedance means cross said plane.
7. An electron discharge device comprising a sealed envelope containing an elongated cathode, an anode structure having adjacent anode elements defining a transverse cavity resonator, the free ends of said anode arms constituting electron-receiving portions, an adjustable tuning element within said envelope, said tuning element comprising a conductive member sup-ported adjacent said free ends of said anode arms, and means connected to said tuning element for adjusting the position of said element toward and away from said cavity resonator.
8. A magnetron comprising a cathode surrounded by an anode block, said block having a central cathode space and interconnecting spaces forming coupled cavity resonators, said block also having a pair of anode arms forming opposite sides of each of said cavity resonators, the free ends of said anode arms constituting electron-receiving portions, an adjustable tuning element within said envelope, said tuning element comprising a conductive member supported adjacent said free ends of said anode arms, and means connected to said tuning element for adjusting the position of said element toward and away from said cavity resonator.
9. An electron discharge device comprising a sealed envelope containing an elongated cathode, an anode structure having adjacent anode elements defining a transverse cavity resonator, the free ends of said anode arms constituting electron-receiving portions, an adjustable tuning element within said envelope, said tuning element comprising a conductive member supported adjacent said free ends of said anode arms, and means operable externally of said envelope and connected to said tuning element for adjusting the position of said element toward and away from said cavity resonator.
10. A magnetron comprising a cathode surrounded by an anode block, said block having a central cathode space and interconnecting spaces forming coupled cavity resonators, said block also having a pair of anode arms forming opposite sides of each of said cavity resonators, the free ends of said anode arms constituting electron-receiving portions, an adjustable tuning element within said envelope, said tuning element comprising a conductive member supported adjacent said free ends of said anode arms, and means operable externally of said envelope and connected to said tuning element for adjusting the position of said element toward and away from said cavity resonator.
PERCY L. SPENCER.
source: U.S. Patent Office
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