US2581607A - Multisegment single cavity magnetron - Google Patents

Description

1952 c. 1. SHULMAN ETAL MULTISEGMENT SINGLE CAVITY MAGNETRON- Filed Sept. 7. 1946 INVENTORS CARLI W .SHULMAN 8; Gsqaes R. K

ILGORE' ATgRNEY Patented Jan. 8, 1952 MULTISEGMENT SINGLE CAVITY MAGNETRON Carl I. Shulman and George R. Kilgore, Princeton, N. J., assignors to Radio Corporation of America, a corporation of Delaware Application September 7, 1946, Serial No. 695,512

18 Claims.

This invention relates to electron discharge devices and more particularly to vacuum tubes of the magnetron type suitable for generating oscillations at very high frequencies.

Magnetrons in various forms have been used for producing high frequency energy in the frequency spectrum reaching several thousand megacycles. Operation at such high frequencies, generally referred to as ultra high frequencies, necessitates careful dimensioning of the tube structure in which the physical shape of the component elements determines chiefly the operating frequency. In tubes of this type the anode electrode may have the geometrical configuration of a resonant bodywith parallel plates having electrical length proportioned to the operating frequency, or the anode may form the walls of one or more resonant cavities. In either case, means must be provided for deriving the energy produced for some utilitarian purpose. Heretofore, in addition to the principal electrodes, a couplingdevice has been introduced in the tube structure in the form of a probe or loop within the resonant body. This device in effect was the output element and usually terminated in a tube prong.

The particular feature of this invention is that the high frequency energy of the magnetron constructed in accordance with the teachings thereof may be transmitted without the use of auxiliary coupling devices.

Another feature of this invention is that one of the principal electrodes, such as the cathode, may be used efficiently to perform a dual function,v serving in its normal capacity as a source of electrons as well as an output means for'the generated high frequency energy.

In" accordance with the invention the cathode electrode of the magnetron is so oriented with respect to the anode electrode as to be, at least in part, in the high frequency electric field and linked therewith. In this manner the cathode electrode together with its associated leads forms a coupling through which the high frequency energy may be: transmitted to a utilization circult.

The dual function which the cathode electrode performs by judicious placement in the high frequency electric field results in several advantages. Among these the elimination of an additional. electrode alone calls for a simplified structure easier to assemble and manufacture. The resultant symmetry in the structure assures more stable: operation and facilitates the placement in existing apparatus Other features and advantages will be apparent fromv the following description of the invention, pointed out in particularity in the appended claims, and taken in connection with the accompanying drawing in which Fig. 1 is a side view partly in cross-section of a magnetron embodying the invention in a preferred form; Fig. 2 is a perspective view showing a portion of the anode assembly and the location of the cathode therein; Fig. 3 is a top. view of the assembly shown in Fig. 2; Fig. 4 is a sectional view of a modified structure incorporating the novel features of the invention; and Fig. 5 is a sectional view showing a modified form of assembly of the component elements. Fig. 6 illustrates an anode structure similar to that shown in Fig. 1, with a shorter cathode electrode.

Referring to Fig. '1, the magnetron comprises an evacuated vessel I shown here as a glass envelope in which the anode 2 is supported in a conventional manner by means of supporting rods 3 and 3' sealed into a stem 4. A base 6 is attached to the envelope I provided with pins I and 8. Of these pins, 8 is shown conductively connected to the anode 2. The pin I, in cooperation with pin 8, functions merely as a support when the tube is placed in a suitable socket.

The anode 2 comprises a cylindrical structure completely enclosed except for centrally located openings in the top plate 9 and the bottom plate ID of the cylinder for inserting the cathode II therein. An annular series of parallel rods I2 and I 2 surround the cathode. There are eight rods shown of which four rods I2 are su ported on the top plate 9 and four rods I2 on the bottom plate Ill. The rods I2 and I 2' are grouped in alternate order whereby adjacent rods are supported on opposite plates 9 and I0 of the anode 2. The rods I2 and I2 are anode elements which divide the anode into electrical segments and are shorter than the distance between plates 9 and HI. This construction provides a gap between the end of each rod and the plate opposite to the one supporting the particular rod.

The arrangement of the rods I2 and [2' with respect to the cathode I I can better be observed by the partial perspective view presented in Fig. 2. For the purpose of illustration, only plate ID of the anode 2- isshown. The top plate-9 is removed and the rods I2 supported thereon are shown in the position which they hold in the assembly. From Fig. 2 it is seen that the oathode II issymmetrically disposed with respect to the rods I 2 and I 2. This construction is also illustrated in Fig. 3' which is an enlarged partial top view of the cylindrical anode 2 showing the distribution of the rods I2 and I2. For a clearer illustration the plate 9 is removed and the rods I2 which it supports are shown in their respective position in the assembly.

The cylindrical anode 2 provides a cavity which, by means of the rods I2 and I 2' is divided into eight electrical segments. This construction is known in the art as a single cavity multisegment resonator. made short compared to a quarter of the resonant wavelength of the entire cavity. For this reason the rods I2 and I2 have very short electrical length as far as the operation of the system is concerned and are essentially at the same instantaneous high frequency potential of the respective plates 9 and ID. That is to say, rods I2 are at the potential of the plate It and I2 at the potential of plate 9.

The cathode II is preferably of the indirectly heated type in which a filament running axially in the cathode sleeve performs the heating function. Conducting leads I4 and I5 for the filament serve as supports for the cathode reinforced by a bead I6 which is attached to the anode structure by means of a supporting wire II. For additional support at one end, the cathode I I is also held by the lead I4 through a bridged Wire support I8 electrically divided by a glass bead I9. On the other end the cathode is connected directly to the lead I5. The leads I4 and I5 are brought out through the elongated portion of the envelope I and are connected to terminal pins 20 and 2|, respectively, sealed inthe wall of the glass envelope.

The description so far given completes the construction of a preferred embodiment of a magnetron in accordance with the invention. It may be added that the glass envelope 9 is fiattened near the anode plates 9 and I!) in order to reduce the transverse dimension of the tube. This is advantageous for the purpose of applying the magnetic field necessary for its operation in a more efficient manner. The magnet pole pieces 23 and 24 illustrate the application of the magnetic field axially to the cylindrical anode 2.

Referring again to the structural features of the anode and cathode elements, it is important to note that the cathode II is so oriented in the anode cavity that it is normal to the end plates 9 and I 3 and coaxial with respect to the high frequency electric field existing in the cavity. The reason for this is that the segments of the anode cavity formed by the rods i2 and I2 produce a high frequency electric field to which the cathode II is exposed at the gaps between the rods I2 and I2 and respective opposed plates 9 and I0. It should be noted that the direction of the high frequency electric field in these gaps is parallel to the cathode I I. The fields so created are generally referred to as fringe fields. There exists, therefore, a coupling of the electric fringe field with the cathode II at opposite ends along the length of the gaps. In effect, the cathode or the connecting wires thereto function as a probe often used in a high frequency field for the purposeof coupling.

In view of the fact that the plates 9 and III are at opposite polarity as to high frequency and the cathode is linked with the fringe fields near each plate, the coupling eifect is cumulative and opposite ends of the cathode II have an induced potential essentially equal to the potential difference between plates 9 and I9. As can be seen, the cathode II therefore will serve as an efii- The rods I2 and I2 are 4 cient coupling element for the high frequency energy produced by the magnetron and this energy may be transmitted through the conductors i4 and I5 without disturbing the heating current these conductors carry to the cathode filament.

A suitable output circuit may be provided by a simple two wire transmission line attached to the filament terminals 20 and 2|. The complete assembly shown in Fig. 1 illustrates this in a compact form. There is provided a shielding housing 26 of conducting material shaped to conform to the contours of the magnetron. In the cylindrical portion of the housing 26 is disposed a two-wire transmission line made up of tubular conducting members 21 and 28 held by the end plate 29 of the housing 26. A sliding bar 30 is provided for tuning the transmission line. In order to conduct heating current to the cathode filament, one lead is provided by the conductor I5, the member 21 and the housing 26. The other heating current conductor I4 is insulated and runs through the tubular member 28; The latter is capacity coupledto a plug 3| connected to the filament terminal 20.- The housing 26 is provided with an opening on the side having a flanged portion 32 for convenient attachment of a coaxial line. This is schematically indicated by the looped center conductor 33 which is coupled to the oscillating -magnetic field between conductors '21 and 28. Any suitable means of coupling may of course be used to derive the energy from the output circuit formed by the parallel transmission line.

Referring to Fig. 4, the modified construction shown here is particularly useful for connecting the magnetron to a coaxial line output circuit. In describing this construction, similar components of the tube structure of Fig. 1 will be indicated by similar reference characters. The anode 2 is similar to that shown in Fig. 1, particularly with respect to the rods I2 and I2. However, the anode 2 forms a completely enclosed cylindrical housing with only one central aperture which leads into. a tubular elongated stem 34 having a flange 35 which is attached to the anode plate 9. The anode so constructed eliminates the glass vessel which furnished the evacuated space. Instead, it may be evacuated through the stem 34. The cathode II is axially disposed in the anode 2' withthe cathode leads running coaxially in the center of the stem 34. The-cathode leads I4 and I5 held by the bead 3'6 act as supports for the cathode II of which one is electrically connected to the tubular inner conductor 45 of the coaxial transmission line and the other runs through this conductor and is suitably insulated. The coaxial output line comprising the tubular outer conductor 42 and the aforementioned inner conductor 45 is held on the stem 34 by an insulating sleeve 43. The line may be tuned to the operating frequency by means of a sliding block 46. The bottom plate I0 of the anode is provided with a bar 31 of magnetic material for supporting the magnets 39 and 40.

The output to a load circuit from the coaxial line may be brought out through an opening in the side of the outer conductor 42. Another coaxial line may be attached here and is indicated with the center conductor terminating at the conductor 45. The purpose of the insulating sleeve 43 is to permit the application of a direct current voltage between the cathode and anode. {The source of this voltage is shown here schematically by a battery connected between the cathode II and the stem 34-.

The modification described is particularly useful where a coaxial type of transmission line and output circuit is required. The mechanical structure lends rigidity and ease of handling. The operation is essentially the same as in the tube shown in Fig. l. The cathode is parallel to the high frequency fringe fields between the rods l2 and i2 and their respective opposed plates 5! and I0 and the coupling to said fields is effective to induce high frequency currents in the cathode. The high frequency circult from the cathode H to the output line 42, 65 comprises the coupling between the plate It! and the adjacent end of the cathode, the resonator 2, the stem 34 and the cathode lead connected to inner conductor 45.

Referring to Fig. 5, the modification shown here centers around easier assembly of the tube elements for manufacturing in large quantities. For this purpose the evacuated portion of the tube is a separate metal housing I, of cylindrical shape with an outlet 41 for exhausting the housing. A header 43 is provided as a main support on which is mounted the cylindrical box shaped anode 2. The housing I' anode and is also supported on the header 43. Axially disposed and secured to the header 48 is the tubular stem 34 in which the glass bead 36 seals the leads I and [5 for the heatin element of the cathode l and also serves as the structures here shown which illustrate merely preferred embodiments of the invention. The essential feature in all modifications is the function of the cathode element as a means for deriving energy from the high frequency fields within the magnetron. The cathode in the strict sense of the Word as a source of electrons is not to be considered as the sole medium for couplin high frequency energy out of the tube. In other words, it is not important that the active surface of the cathode be so positioned as to link the fringe fields. The cathode element itself may be shorter than the axial dimension of the anode, so that the active surface of the oathode itself does not reach the fringe fields of the anode. This is illustrated in Fig. 6. It is sufficient for exercising the invention to arrange any portion of the cathode assembly, such as the filament conductors l4 and H5 or supporting wires of the cathode in a coupling relationship with the fringe fields.

We claim as our invention:

1. A magnetron oscillation generator including anode and cathode electrodes, said anode elec trode including at least one pair of opposed surfaces spaced to form a gap across which a high frequency electric field is set up during operation of said generator, means positionin said cathode electrode to extend across said gap, whereby a high frequency current is induced in said cathode electrode by said field, and means connected to said cathode electrode for deriving output energy from said generator through said cathode electrode.

2. A magnetron oscillation generator comprising an evacuated vessel, an anode electrode supported therein, said anode electrode including at least one pair of opposed surfaces spaced to form a gap across which a high frequency electric field is set up during operation of said generator, a cathode electrode for supplying eleccovers the trons for said anode electrode, leads connected to said cathode electrode and terminating outside said vessel and sealed therein, said cathode electrode and leads forming a cathode circuit, means supporting said cathode electrode within said anode electrode with a portion of said circuit extending across said gap, whereby a high frequency current is induced in said circuit by said field during operation of said generator, and output means coupled to said cathode leads for deriving high frequency energy from said circuit.

3. A magnetron oscillation generator comprising an evacuated vessel, an anode electrode supported therein, said anode electrode including at least one pair of opposed surfaces spaced to form a gap across which a high frequency electric field is set up during operation of said generator, a cathode electrode for supplying electrons for said anode electrode, leads connected to said cathode electrode and terminating outside said vessel and sealed therein, said cathode electrode and leads being elements of the cathode assem bly of said generator, means supporting said cathode assembly within said anode electrode with at least one of said elements extending across said gap, whereby a high frequency current is induced in said cathode electrode by said field during operation of said generator, and output means coupled to said leads for deriving high frequency energy from said assembly.

l. A magnetron oscillation generator comprising an anode electrode, said anode electrode including at l ast one pair of opposed surfaces spaced to form a gap across which a high frequency electric field is set up during operation of said generator, a cathode electrode for supplying electrons for said anode electrode, means supporting said cathode electrode including conductors connected thereto for supplying heating current, said supporting means orien ing said oathocle electrode within said anode electrode and across said gap, whereby a high frequency current is induced in cathode electrode by said field during operation of said generator, and

means coupled to said cathode conductors for deriving high frequency current from said cathode electrode.

5. A magnetron oscillation generator comprising an evacuated vessel, an anode electrode supported therein having a geometrical configuration of a hollow body resonant at a predetermined frequency, plurality of anode elements dividing said body into electrically separated segments, alternate anode elements being connected at one end to one side of said body and spaced at the other end from the opposite side of said body to form gaps across which high frequency electric fields are set up during operation of said generator, a cathode electrode supported within said anode electrode and parallel to said elements and across said gaps, conductors connected to said cathode electrode for supplying heating current thereto and terminating outside said vessel and sealed therein, and an output transmission line coupled to said conductors for providing the high frequency energy output of said generator.

6. A magnetron oscillation generator comprising an evacuated vessel, an anode electrode supported therein having the geometrical configuration of a hollow body resonant at a predetermined frequency and having two opposed surfaces, a plurality of elements dividing said body into electrically separated segments, said ele ments terminating alternately on said opposed surfaces and so placed as to form gaps across which high frequency electric fringe fields are set up between said elements and said surfaces during operation of said generator, a cathode elec trode supported in said body and extending across said gaps, and output conducting means connected to said cathode electrode for deriving high frequency energy from said generator.

'7. A magnetron oscillation generator including an anode having a geometrical configuration of a cavity resonator and having two opposed surfaces forming a gap across which a high frequency electric field is set up during operation of said generator, a cathode within said anode and extending across said gap, whereby a high frequency current is induced in said cathode by said field during operation of said generator, and means coupled to said cathode for deriving energy from said cavity resonator.

8. A magnetron oscillation generator including an anode of the cavity resonator type, having two opposed surfaces forming a gap across .which a high frequency electric field is set up during operation of said generator, a cathode within said anode and extending across said gap, whereby a high frequency current is induced in said cathode by said field, means supporting said cathode in said anode, and a tunable transmission line coupled to said cathode through said supporting means.

9. A magnetron oscillation generator including an anode of the cavity resonator type, having two opposed surfaces forming a gap across which a high frequency electric field is set up during operation of said generator, a cathode within said anode and extending across said gap, whereby a high frequency current is induced in said cathode by said field, a filament within said cathode, a pair of leads connected to said filament, and a tunable transmission line coupled to said cathode through said filament leads 10. A magnetron oscillation generator including an anode of the cavity resonator type, having two opposed surfaces forming a gap across which a high frequency electric field is set up during operation of said generator, a cathode within said anode and extending across said gap, whereby a high frequency current is induced in said cathode by said field, a filament within said cathode, a pair of filament leads connected to said filament and forming a support for said cathode, a tunable transmission line coupled to said cathode through said support.

11. A magnetron oscillation generator including an anode of the multi-segment single cavity type, having two opposed surfaces between which a high frequency electric field is set up during operation of said generator, and an annular series of spaced parallel interleaved anode segments connected alternately at one end to one of said opposed surfaces and spaced at the other end from the other of said opposed surfaces to form gaps, a cathode coaxially placed in said anode and extending parallel to said interleaved segments and across said gaps, whereby said cathode is subjected to high frequency electric fringe fields between the ends of said segments and the opposing surfaces during operation of said generator, and an output transmission line connected to said cathode.

12. An electron discharge device of the magnetron type including an evacuated vessel containing a cavity resonator anode element of cylindrical cross-section and having end plates, a plurality of rods projecting inwardly in the axial d rection from and supported by one of said end plates and a plurality of similarly disposed rods supported by the other end plate, said rods being shorter than the distance between said plates and spaced in alternating order with respect to their support, each rod forming a gap between it and the plate opposite to the one supporting it across which gap a high frequency fringe field is set up when said cavity resonator anode element resonates, a cathode element coaxially disposed within said anode element and surrounded by said rods and extending substantially across said gaps, said cathode element thereby being adapted to be subjected to the influence of said fringe fields for transfer of oscillatory energy during operation of said device, leads extending from said cathode outside said vessel, said leads being adapted to conduct heating current to said cathode, and a transmission line connected to said leads to conduct oscillatory energy from said device to an utilization circuit.

13. An electron discharge device in accordance with claim 12 in which the length of said rods with reference to the resonant wave length of said rods is made short compared to a quarter wave length.

14. An electron discharge device in accordance with claim 12 in which a tubular metallic housing substantially encloses and shields said vessel, and said transmission line comprises a pair of electrically conducting within said housing and electrically connected to said leads and a slidable cross bar connecting said members for tuning said members, one of said members containing a conducting wire extending from said housing for supplying heating current to said cathode.

15. A magnetron oscillator including an elongated cathode for supplying electrons, anode elements surrounding said cathode, said cathode and anode elements being enclosed within a hollow conducting body, an output transmission line comprising a cathode lead extending externally of said hollow body and a hollow tubular member coaxial with and surrounding said lead and electrically and mechanically connected to said hollow conducting body, and means for providing a magnetic field parallel to said cathode within said hollow conducting body.

16. A magnetron oscillator including an elongated cathode for supplying electrons, a cavity resonator anode having anode elements in the form of interleaved segments surrounding and parallel to said cathode, an elongated hollow conducting body extending from and attached to said anode, a seal in said body, a lead through said seal connected to said cathode, a coaxial transmission line having a center conductor connected to said cathode lead and an outer conductor electrically and mechanically attached to said body, said line including tuning means, and means coupled to said line for deriving high frequency output energy therefrom.

17. A magnetron oscillator including a cathode for supplying electrons, a cavity resonator anode having opposed surfaces and anode elements in the form of interleaved segments surrounding said cathode, said anode constituting a vacuum envelope, said elements and opposed surfaces providing gaps across which high frequency electric fringe fields are set up during operation of said oscillator, said cathode being supported in said anode and extending across said gaps, an elongated hollow conducting body opening into and attached to said anode and through which said tubular members supported envelope may be exhausted, a seal in said body, a lead through said seal connected to said cathode, a coaxial transmission line having a center conductor connected to said lead and an outer conductor electrically and mechanically attached to said body, said line including tuning means, and means coupled to said line for deriving high frequency output energy therefrom.

18. A magnetron oscillator in accordance with claim 16 wherein said resonator anode is mounted on a header, an envelope covering said anode and sealed to said header, and an exhaust for said envelope, said hollow conducting body forming a cylindrical stem supporting said header.

CARL I. SHULMAN. GEORGE R. KILGORE.

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

UNITED STATES PATENTS Number Name Date 1,114,697 Hull Oct. 20, 1914 1,523,776 Hull Jan. 20, 1925 2,071,516 Farnsworth Feb. 23, 1937 2,144,222 Hollmann Jan. 17, 1939 2,250,698 Berline July 29, 1941 2,424,886 Hansell July 29, 1947 2,428,888 Nelson Oct. 14, 1947 2,446,826 McAl'thur Aug. 10, 1948 2,454,337 Okress Nov. 2'3, 1948 2,508,280 Ludi May 16, 1950

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