US2556747A - Electron discharge device of the magnetron type - Google Patents

Description

June 12,1951 w. 0. BROWN ELECTRON DISCHARGE DEVICE OF THE MAGNETRON TYPE 2 Sheets-Sheet 1 Filed March 19, 1946 mm c. a/m/m June 12, 195] r BROWN 2,556,747

ELECTRON DISCHARGE DEVICE OF THE MAGNETRON TYPE Filed March 19, 1946 2 Sheets-Sheet 2 Patented June 12, I51

ELECTRON DISCHARGE DEVICE OF THE MAGNEIRONTYPE William C. Brown, Lincoln, Mass., assignor to Raytheon Manufacturing Company, Newton, Mass, a corporation of Delaware #This invention relates to electron discharge devices, and more particularly-to such devices as are known as magnetrons.

' f This invention is particularly suitable for tuning or frequency modulating magnetrons which are adapted to generate micro-waves having a wavelength of the order of several centimeters orless.

In a co-pending application of Erich Nevin Kather, Serial No. 649,615, filed February 23,

1946, and now U. S. Patent No. 2,462,869, granted March 1, 1949, there is described and claimed a device in which the frequency thereof is modu la'ted lby a pair of electrodes located adjacentthe open ends of cavity resonators, and in which the surfaces of the modulating electrodes are good secondary electron emissive surfaces. The device in said application operates due to the fact that relatively high speed electrons, emerging from the cavity resonators, liberate secondary electrons from the surfaces of the modulating electrodes. I have found, however, that in a device iri which the power generated is relatively low, the electrons which emerge from the cavity resonators may have insufficient velocity to liberate secondary electrons in'sufiiciently large numbers to accomplish satisfactory modulation.

In other words, as the power generated by such devices falls to low values, the operation of the modulating electrodes may be unsatisfactory. An object of this invention, therefore, is to 3 Application March 19, 1946, Serial No. 655,445

' 7 Claims. (01.. 315-40) 3, a magnetic means 4 for establishing a magdevices falls to low values, the operation of the scribed and claimed in saidco-pending application which, nevertheless, operates satisfactorily at substantially all levels of power generation.

The foregoing and other objects of this inven-' tion will be best illustrated from the following description of an exemplification thereof, reference being had to the accompanying-drawings wherein:

Fig. 1 is a fragmentary, longitudinal section of an electron-discharge device incorporating the invention;

Fig. 2 is a transverse section taken along line 2-2 of Fig. 1;

Fig. 3 is a fragmentary, pers ective view with certain parts broken away showing the relationship of one of the modulating electrodes with respect to the anode arms; and I Figs. 4 and 5 are circuit diagrams representing two typical modulating circuits. g

The arrangement, as shown in Figs. 1 and 2, illustrates a magnetron indicated generally by the reference numeral I. This magnetron includes an anode structure 2, a cathode structure netic field in a direction generally perpendicular to the electron path between said cathode and anode structures and 'a pair of modulating electrodes 5 and 6. 1

The anode structure 2 preferably comprises acylindrical body I made of a highly conductive material, such as copper, and provided with a plurality of anode members in the form of interiorly extending, radially disposed vanes 8. The cylindrical body I is closed at its end by plates 9 and I0, the junction between said body and said plates being hermetically sealed as by silver soldering. The cylindrical body I is of such diameter and the number, size and relative spacing of the vanes 8 are so chosen that each pair of adjacent vanes, together with that portion of saidcylindrical body lying therebetween, defines a cavity resonator adapted to oscillate in the desired frequency range.

The cathode structure 3, which is coaxial with the anode structure 2, preferably comprises an elongated sleeve II, conventionally made of nickel or the like, and having a reduced portion I2 which is substantially coextensive with the vertical dimension of the vanes 8 and provided with a highly electron-emissive coating, for example, of the well-known alkaline earth metal oxide type. In order to support the cathode sleeve II' with respect to the anode members 8,

said sleeve may be reduced at its lower end to fit into a tubular conducting member I3 adapted to be supported from a tubular pole piece I4 hermetically sealed into the end plate 9. The pole piece I4 is provided with a bore Ma through which the cathode structure may enter the Sleeve I! in any desired manner, not shown. The

cathode sleeve Il may be heated by a filament, not shown, connected at one end I8 to said sleeve andat the other end to a lead-in conductor I9 suitably entering said device through a glass seal, not shown, in the lower end of the sleeve I1.

Current may be conveyed to the heating filament by connecting an appropriate source of voltage between the member I! and the lead-in conductor I9.

jAnother pole piece 20 is hermetically sealed into the end plate I0. The pole piece 20 is like-' wise provided with a bore 20a terminating in an insulating tubular member 2i sealed in the upper end. The pole pieces 20 and 14 are fixed, for example, at the opposite ends of a horseshoe magnet, not shown, the two pole pieces and the horseshoe magnet constituting the above-mentioned magnetic means 4 for establishing a magnetic field transverse to the electron path between the cathode and anode structures of the device.

The modulating electrodes 5 and 6 are supported adjacent the upper and lower open ends of the cavity resonators. The surface of the modulating electrode 5 facing the upper open ends of the cavity resonators is thermionically emissive. For this purpose the modulating electrode 5 consists of a hollow nickel annular member 36 containing within it a spiral heating filament 37. The filament 31 may be insulated by being coated with a suitable insulating material, such as aluminum oxide. One end of the heating filament 31 is electrically connected to the member 36. The other end of said filament passes out through an opening in the side wall of the member 36. The member 36 may be supported by a lead-in conductor 4| welded to it. The lead 4| passes out through a pipe 42 threaded and hermetically sealed in the cylindrical body I. The lead 4! is also supported by and sealed through glass sleeve 43 supported at the outer end of the pipe 42. The free end of the filament 3'! may be connected to a lead-in conductor 38 also passing out through a similar pipe 39 and glass seal 40. The lower surface of the annular member 36 is coated with an emissive oxide to emit thermionically when heated by the filament 31.

The electrode 6 is intended primarily to reflect electrons emerging from the lower open ends of the cavity resonators and thus may be made of any suitable conducting material. In some instances it may be desirable that the surface of the electrode 6 likewise be a good secondary electron'emitter so as to take advantage of the multiplyin effect of those high speed electrons which may emerge from the lower open ends of the cavity resonators. Tantalum is a suitable material for this purpose, particularly since it tends to become coated with a thin film of oxide from the main cathode. The electrode 6 is supported by a conductor 25 which passes out through a pipe 26 and a glass seal 21, similar to those described in connection with electrode 5.

When the device is generating-oscillations, these oscillations may be led out therefrom by means of a loop 28 introduced into one of the cavity resonators, said loop being supported b a pipe 29 threaded and hermetically sealed in the cylindrical body 1. One end of the loop 28 is connected to the inner end of said pipe and the other end passes out through a glass sleeve 30 supported at the outer end of said pipe.

As illustrated in Fig, 4, the cathode 3 maybe maintained at the proper negative potential by a source of such potential illustrated diagrammatically as a battery 3 I. It is desirable that the electrodes 5 and 6 be biased negatively with respect to the anode structure 2. For this purpose biasing sources of potential illustrated diagrammatically as batteries 32 and 33 may be interposed between the electrodes 5 and 6 and the anode structure 2. In series with one of the sources of biasing potential may be placed a suitable source of modulating voltage 34. The maximum amplitude of this modulating voltage is preferably related to the bias voltage 33 so that the electrode '6 never becomes appreciably positive during operation.

In accordance with my present understanding of the theory of the operation of this device, I believe that the operation is substantially as follows. When the lower surface of the annular member 36 are heated to temperature of thermionic emission, electrons will be emitted therefrom. These electrons will be impelled under the voltage existing between the electrode 5 and the anode 2 in a direction toward the open ends of the cavity resonators. The device, which under these conditions will begenerating oscillations, will have produced between the outer ends of the vanes 8 a high voltage, high frequency electrical field, Therefore, as the electrons enter this region, they will be subjected to the action of the longitudinal magnetic field as well as the action of the transverse high frequency electrical field. Under these conditions, the electrons will travel in a variable spiral path toward the lower open end of the cav ity resonator in which they find themselves. This path will besuch as to effectively prevent the electrons from being captured by the surfaces of the vanes 8. As the electrons in the particular cavity emerge from the lower end thereof, they would be quickly captured, for example, by the pole piece M or the cover 9, except for the interposition of the electrode 6. However, this electrode will intercept the electrons and, due to the bias voltage existing between the electrode 6 and the anode structure, thes electrons will .be reflected back toward the anode and will reenter the cavity resonator. The electrons will thereupon, travel toward the upper end of the cavity resonator and upon emerging therefrom will likewise be reflected by the electrode 5. Under these conditions electrons emitted from the electrode 5 will persist for long periods of time within the cavity resonators and thus a large population of electrons may be maintained within the cavity resonators with relatively small current flow from the electrode 5. The presence of these electrons varies the dielectric constant of the space within each of the cavity resonators and thus, by varying the density of this electron population, the frequency at which the cavity resonator tends to oscillate may be readily controlled. However, the paths of the electrons within each of the cavity resonators are such that substantially no energy is abstracted from the oscillating circuit, thus imparting to the device a relatively high efficiency.

By varying the extent to which the electrons between either or both of the electrodes 5 and 6 and the anode 2 are reflected into the 'cavity resonators, the density of the electron concentration in the cavity resonators readily may be controlled. Thus, for example, by interposin the modulation voltage 34 in the connection extending to the electrode 6, the frequency modulation described above may be obtained.

lectrons which pass directly from either of the electrodes 5 and 6 to the upper ends of the vanes 8 constitute an ineffective fiow of current and thus it is desired that such flow be reduced to a minimum. For this purpose, electrodes 5 and 5 may each be provided with an electrical shielding member 35 supported by each of said electrodes. This shielding member 35 is provided with a plurality of inwardly extending radial arms which are closely spaced from and substantially cover those surfaces of the vanes 8 which tend to intercept the electrons. In this way the electron flow is constrained to pass be tween the anode arms 8.

Although only the electrode 5 has been described as being 'thermionically emissive, in

some instances it might be desirable to have the electrode 6 constituted in the same way.

Instead of modulating the voltage on but one of the electrodes 5 and 6, various other circuit arrangements may be devised. For example, in Fig. 5 there is illustrated an arrangement in which the voltage on both of these electrodes is modulated. The electrodes 5 and 6 may be connected together and a connection extending from the common lead to the anode structure may include a biasing battery 44 and a source of modulation voltage 45. In this instance likewise the biasing battery 44 is so polarized as to tend to maintain the electrodes 5 and 6 negative with respect to the anode structure 2. Such an arrangement likewise produces the desirable frequency modulation.

Of course it is to be understood that this invention is not limited to the particular details as described above inasmuch as many equivalents will suggest themselves to those skilled in the art.

What I claim is:

1. An electron discharge device comprising a cathode, an anode structure spaced from said cathode and including a pair of anode faces interconnected by a cavity resonator open at both ends, means adjacent said cathode for maintaining a magnetic field through said cavity resonator in a direction extending between said open ends, a thermionic electron-emitting electrode facing one of said open ends, and an electron reflecting electrode facing the other of said open ends.

2. An electron discharge device comprising a cathode, an anode structure spaced from said cathode and including a pair of anode faces interconnected by a cavity resonator open at both ends, means adjacent said cathode for maintaining a magnetic field through said cavity resonator in a direction extending between said open ends, and a pair of electrodes, at least one of which is a thermionic electron-emitting electrode, facing said open ends.

3. An electron discharge device comprising a cathode, an anode structure spaced from said cathode and including a pair of anode arms which, together with that portion of the anode structure lying therebetween, defines a cavity resonator open at both ends, a thermionic electron-emitting electrode facing one of said open ends, an electron reflecting electrode facing the other of said open ends, and means, intermediate said anode arms and said thermionic electronemitting electrode, for shielding the surfaces of the anode arms adjacent said thermionic electron-emitting electrode from electrons emitted from said thermionic electron-emitting electrode.

4. An electron discharge device comprising a cathode, an anode structure spaced from said cathode and including a pair of anode arms which, together with that portion of the anode structure lying therebetween, defines a cavity resonator open at both ends, a pair of electrodes, at least one of which is a thermionic electronemitting electrode, facing said open ends, and a shielding member intermediate said anode arms and said last-named electrode for shielding the surface of the anode arm adjacent said last-named electrode from electrons emitted from said last-named electrode.

5. A frequency modulating oscillator system including an electron discharge device comprising a cathode, an anode structure spaced from said cathode and including a pair of anode faces interconnected by a cavity resonator open at both ends, means adjacent said cathode for maintaining a magnetic field through said cavity in a direction extending between said open ends, a pair of electrodes, at least one of which is a thermionic electron-emitting electrode, facing said open ends, means, connected intermediate said electrodes and said anode structure, for biasing each of said electrodes negatively with respect to said anode structure, and means, connected in series with said biasing means, for superimposing a modulating signal voltage on at least one of said electrodes.

6. An electron discharge device comprising a cathode, an anode structure spaced from said cathode and including a pair of anode faces interconnected by a cavity resonator open at both ends, means adjacent said cathode for maintaining a magnetic field through said cavity 9 resonator in a direction extending between said open ends, a thermionic electron-emitting electrode facing one of said open ends, and an electron reflecting electrode facing the other of said open ends, said electron emitting and reflecting electrodes being electrically isolated from said cathode.

7. An electron discharge device comprising a cathode, an anode structure spaced from said cathode and including a pair of anode faces interconnected by a cavity resonator open at both ends, means adjacent said cathode for maintaining a magnetic field through said cavity resonator in a direction extending between said open ends, and a pair of electrodes, at least one of which is a thermionic electron-emitting electrode, facing said open ends, said electrodes being electrically isolated from said cathode.

WILLIAM 0. BROWN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,063,342 Samuel Dec. 8, 1936 2,163,157 Samuel June 20, 1939 2,338,237 Fremlin Jan. 4, 1944 2,413,385 Schmidt Dec. 31, 1946 2,462,137 Smith Feb. 22, 1949 2,462,869 Kather Mar. 1 1949

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