US2617966A - Magnetron - Google Patents

Description

Patented Nov. 11, 1952 UNITED STATES ATENT OFFICE MAGNETRON of Delaware Application February 19, 1947, Serial No. 729,589

16 Claims.

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

In certain electron tubes utilizing a cathode electrode which extends into a cavity resonator, the high frequency electric field of the resonator may induce high frequency currents in the oathode. This condition is'particularly manifest in magnetron tubes of the type provided with a single cavity resonator sub-divided into a number of anode segments by means of pins or fingers uniformly disposed around the cathode. This type of tube is known as a single cavity multisegment magnetron.

In an application Serial No. 695,512, filed September 7, 1946 in the names of Carl I. Shulman and the applicant, now Patent No. 2,581,607, granted January 8, 1952 and assigned to the same assignee as the present application, it was shown how this coupling of high frequency energy to the cathode electrode may be enhanced and the cathode electrode employed in a dual function to serve also as the output coupling element of the tube. While this means of energy transfer can be efliciently used in Various circuits, it is often desirable to extract energy through a separate element removed from the cathode and its associated circuit. This is generally accomplished in the art by means of a simple coupling loop extending into the resonator. When such a coupling loop is to be used or, generally speaking, when the coupling of energy is not to be effected through the cathode electrode, it is important to avoid any inherent coupling to the cathode. Any unwanted cathode coupling results in a certain loss of energy and is considered in such cases a defect or disadvantage. Various means have been proposed to remedy this defect. However, in discharge devices utilizing a single cavity resonator, these means have not been entirely successful. In the multi-cavity type magnetron the construction inherently reduces cathode coupling to a negligible amount.

In accordance with my invention the single cavity resonator of a single-cavity multi-segment type magnetron is provided with a partition or wall dividing the resonator into two resonator portions or elements which are symmetrical with respect to the partition. These two resonator portions function as two separate resonators with oppositely-directed electric fields, so that any existing unwanted coupling to the cathode in one portion is neutralized by an equal coupling in m i rha ein t e the lwr i n- A further object of the invention is to pro-:

vide a novel resonator structure for electron tubes employing a cathode in the electric field of the resonator. V

A particular feature of the invention is that the undesirable eifect of coupling to the cathode electrode is eliminated in a manner which entails no loss of high frequency energy and Without sacrifice of efficiency.

Another feature of the invention is that the deleterious effect of coupling to the cathode circuit is neutralized in a simple manner by means of the inherent characteristics of a novel resonator structure.

Other objects and features will be apparent from the following description of the invention pointed out in particularity in the appended claims and taken in connection with the accompanying drawing in which: I

Fig. 1 is a semi-schematic sectional view showing the resonator structure of my invention and the disposition of the cathode therein;

Fig. 2 is a front elevational view of a magnetron tube incorporating the invention with the housing partly cut away to show the constructional features of the elements;

Fig. 3 is a top view with the housing along line 3-3 of Fig. 2; H

Fig. 4 is a side elevational view in cross-section taken along line 4-4 of Fig. 2;

Fig. 5 illustrates one side Wall of the resonator facing in the direction of the -magnetic field; and v a Fig. 6 is an enlarged perspective View dividing wall and the segments held thereby.

Prior to a detailed description of the constructional features illustrated in thevarious figures, attention is invited in a general senseto' Fig. 1. This figure will be used in an endeavor to .explain the problem which the invention has set out to solve and to derive a general understanding of the principles involved. The reference characters identifying the basic elements of the cut away device in Fig. 1 will be used for the samev elements appearing in the other figures in one form or another.

A closed resonator 8 of the cavity type is shown having a cylindrical cross-section and surrounding a central space in which is placed axial to the resonator an elongated cathode electrode 9. This electrode is preferably in the form of a tubular member housing a suitable filamentary heating element which is attached to conductors II and I2 in order to supply heating current to the filament.

The cathode 9 is provided on its surface with suitable material to liberate electrons when heated to a certain temperature. This is generally accomplished by spraying the cathode with a Coating of barium or strontium oxides, or other known substances, or the cathode may be made of an electron emitting substance. In any event, it is generally suificient to provide an electron emitting surface along the cathode within the confines of the resonator 8.

A plurality of anode segments in the form of rods or bars l4 and 14' are disposed around the cathode and in alternate order are connected to electrically opposing surfaces of the resonator 8. It should be mentioned here that in speaking of opposing surfaces, this relation is considered particularly from an electrical point of View, meaning surfaces having opposite alternating potentials in cyclic variation with frequency. It does not necessarily mean opposite surfaces in a physical sense. In the conventional single cavity resonator the anode segments or rods I4 and it would be alternately connected at one end to the outer side Walls of the resonator. In accordance with my invention, the resonator 8 is divided into two portions 8A and 83 by means of the wall I5 and the segments [4 and I4 alternate symmetrically between this wall and the two outer side walls 1 of the resonator portions as to electrical connection as well as physical support.

It is intended to derive high frequency energy through an output coupling element removed from the cathode circuit. This may be accomplished in a conventional manner by means of an output coupling loop [6 which enters the resonator 8A radially through a suitable opening provided with a tubular flange It for connection to a coaxial transmission line.

In the operation of this tube a magnetic field is essential and the pole pieces marked N & S indicate in a schematic way that the magnetic field is directed parallel to the cathode 9. In practical applications this field may be produced either by a permanent magnet or an electromagnet. These magnets are separate elements, not an integral part of the tube and consequently are not included in the various figures. Of course it should be understood that for proper operation a magnetic field of a certain strength applied in the direction shown is necessary as well as an anode potential source between the resonator portions 8A and 8B and the cathode 9, and a heating current source for the filament In.

In the above mentioned copending application it was explained how fringe fields created between resonator segments and walls produce an electric field vector parallel with the cathode or its associated conductors and thereby transfer energy to the cathode circuit. Examining Fig. 1, it will be seen that the resonator 8 has the gap construction between segments and walls, which is characteristic to multi-segment single cavity resonators. In these gaps, upon excitation of the resonator, fringe fields are created in which a component of the electric field vector is in the direction of the cathode or its associated conductors. This can be seen especially when considering in Fig. 1 only one resonator portion BA, for example. The axial component of the fringe fields in the gaps between the segments 14 and the wall [5, and between the segments I l and the side wall I will induce high frequency currents in the cathode or in the conductors leading to the cathode. This applies particularly to single-cavity multi-segment anode structures wherein the anode segments are shorter than the axial dimension of the resonator. The induced currents from opposite gaps have a cumulative effect and in this manner considerable energy is transferred to the cathode circuit. When this transfer is desirable, as pointed out above, this coupling is enhanced by constructing the gaps so that the larger part of the fringe field is parallel with the cathode. On the other hand, in the construction of Fig. 1 the segments l4 and is are coextensive with the axial dimension of the resonator, therefore, the gaps extend in the direction transverse to the cathode, which markedly reduces the coupling. However, in a single cavity resonator, gap construction alone is insufficient and there remains considerable residual coupling at each gap due to stray fields radiating from the fringe fields in the gaps.

The problem is solved in accordance with the present invention by providing means for dividing the resonator 8 into portions of opposite electrical fields and so distributing the segments in these portions as to neutralize the effect of the coupling. In other words, in the operation of the tube electrons under the influence of the magnetic field are caused to sweep segments in one resonator portion creating fringe fields and simultaneously to sweep segments in another resonator portion creating equal fringe fields in opposite direction and the coupling of these fields to the cathode electrode is differentially combined, which results in zero efiective coupling.

This can be seen at a glance in Fig. 1, noting that the dividing wall I5 is symmetrical with the two resonator portions and at the same high frequency potential as segments I4 and at op-.

posite high frequency potential with respect to segments l4 and side walls 1. The segments [4 and M are short compared to a wave length to which the resonator portions are proportioned, so that the potential variations of the segments follow the side of the resonator portion to which they are attached. As an example, segments Is, being attached to the dividing wall 15, will be at the instantaneous high frequency potential of this wall, whereas segments l4, being attached to the side walls 1, will vary in accordance with the potential thereof. From this it is seen that a balanced circuit condition exists with the high frequency potential in the two resonator portions in opposite phase. Obviously, the coupling of the fringe fields is counteracting and the coupling from each field in the resonator portions to the cathode 9 is at opposite points from either the side walls I or the dividing wall [5. In a properly constructed device, this coupling is also at equidistant points from these walls in order to be equal in magnitude.

Referring to the other figures of the drawing, a practical embodiment of the invention is illustrated in the form of a magnetron which can be commercially produced in quantities. The resonator portions are embedded in two solid juxtaposed anode blocks 20 and 20 supported on a header 2! by means of studs 22 and 22'.

The side walls 1 of the resonator portions, at the opening in which the cathode 9 is inserted, have a plurality of consecutive semi-circular cutouts or recesses which provide clearance holes for alternate segments [4 supported by thedividing wall Hi. The joined ends of the semi-circular cut-outs provide supports for alternate segments l4 tied to the walls 1. These segments, as mentioned before, may be simple rods and can be brazed to their respective supports. This construction is illustrated particularly in Figs. 5 and 6. For a better understanding, segments supported by the wall l5 are marked with reference character l4 and those supported by the walls I, by the same character bearing a primary index.

Output loop I6 is located on the bottom of the header 2| in a tubular sleeve 18 and protrudes into the resonator portion 8A from a radial direction. One end of the wire loop is is connected to the anode block 20 and the other end is supported coaxially within the sleeve [8 by means of the seal 24. Similarly, the cathode 9 is supported by the heater wires I l and I2 which extend through seals and 25' on the header 2|. A cover 26 over the entire assembly and welded to the header 2! completes the structure and permits evacuation of the magnetron.

The particular double cavity structure of Figs. 1 and 4, wherein the alternate rods M. are mounted on the partition I5 and extend through recesses in the two end walls I, is disclosed and claimed in a copending application of Jerome Kurshan, Serial No. 125,094, filed November 2,

1949, and assigned to the same assignee as the present application.

The magnetron herein shown incorporates the invention by way of example in a practical embodiment and various modifications will be apparent to those skilled in the art. Neutralizing of the cathode coupling in the manner disclosed may be efiectively applied to different types of magnetrons as well as to other electron tubes where such coupling may exist, without departing from the scope of the invention.

I claim:

1.An electron discharge device including a cavity resonator, a cathode extending axially of said resonator, a conducting partition extending normally of said cathode and dividing said resonator into separate portions, anode elements positioned around and parallel to said cathode, alternate elements being connected to and supported by said conducting partition, the other anode elements being supported by the walls of said resonator adjacent the ends of said other anode elements.

2. An electron discharge device including a hollow anode enclosing a cylindrical cavity resonator, a cathode mounted axial to said resonator, a plurality of anode segments surrounding said cathode, there being developed in the operation of said device fringe fields between said segments and said anode and coupling to said cathode, means for neutralizing the effect of said coupling including means dividing said resonator into coaxial portions having opposing electrical fields during operation of said device and means including said dividing means mounting said segments in said coaxial portions.

3. A magnetron including an anode member enclosing a cylindrical cavity resonator having apertured end wall, a cathode extending axially through said resonator, a plurality of anode segments in said resonator and surrounding said cathode, there being developed in the operation of said magnetron fringe fields between said segments and said member and coupling to said cathode, and means for neutralizing the effect of said coupling including means dividing said resonator into coaxial portions having opposing electrical fields during operation of said magnetron, said anode segments being mounted intermediate the ends thereof on said dividing means and spaced from said end walls of said resonator.

4. A magnetron discharge device including a hollow anode member enclosing a cylindrical cavity resonator, an elongated cathode mounted axial to said resonator, a plurality of anode segments in said resonator and surrounding said cathode, there being developed in the operation of said device fringe fields between said segments and said member and coupling to said cathode, and mens for neutralizing the eiTect of said coupling including means dividing said resonator into two coaxial portions having substantially equal and opposing electrical fields during operation of said device, said dividing means including a radially extending wall in said resonator substantially in the center thereof and normal to said cathode and said wall, said anode segments being mounted intermediate the ends thereof on said wall.

5. A magnetron including a hollow anode member enclosing a cylindrica1 cavity resonator, an elongated cathode mounted axial to said resonator, a plurality of rods extending across said anode member and surrounding said cathode, said rods separating said member into segments, there being developed in the operation of said device fringe fields between said rods and said member and coupling to said cathode and means for neutralizing the eifect of said coupling including means dividing said resonator into two coaxial portions having substantially equal and opposing electrical fields during operation of said magnetron, said dividing means including a radially extending wall in said resonator substantially in the center thereof and normal to said cathode, said rods being mounted intermediate the ends thereof on said wall.

6. A multi-segment magnetron comprising an anode member enclosing a cylindrical cavity resonator, an elongated cathode mounted axial to said resonator, a radially extending wall normal to said cathode dividing said resonator into two substantially equal portions, means dividing said resonator into segments comprising a plurality of rods surrounding said cathode and extending parallel therewith, said rods being in alternate order electrically tied to said anode member and to said dividing wall, respectively, whereby in the operation of said magnetron, fringe fields are set up in opposite directions relative to the oathode between said anode member and said rods tied to said dividing wall and between said dividing wall and said rods tied to said anode member.

7. A multi-segment magnetron comprising an anode member enclosing a cylindrical cavity resonator having end plates each provided with an aperture, an elongated cathode extending through said apertures and mounted axial to said resonator, a radially extending wall normal to said cathode dividing said resonator into two substantially equal portions, means dividing said resonator into segments comprising a plurality of rods surrounding said cathode and extending parallel therewith, certain of said rods being attached at each end to said endplates; and other of said rods being attached to said wall and spaced from said end plates, whereby fringe fields existing between one end plate and said rods attached to said wall induce currents in said cathode in one direction and fringe fields existing between the other end plate and said rods attached to said wall induce currents simultaneously in the opposite direction, the combined effects of said currents tending to cancel energy transfer to said cathode.

8. A multi-segment cavity magnetron oscillator comprising an anode member enclosing a cylindrical cavity resonator, an elongated cathode mounted axial to said resonator, a radially extending wall normal to said cathode dividing said resonator into two substantially equal portions, means dividing said resonator into segments comprising a plurality of rods surrounding said cathode and extending parallel therewith, aid rods being in alternate order electrically tied to the outer wall of said resonator and to said dividing wall, respectively, whereby fringe fields coupling to said cathode in the operation of said oscillator are distributed between alternate ones of said rods and said outer wall and between the other alternate rods and said dividing wall, and the fringe fields between said rods and said outer wall are equal and opposite in direction at opposite ends of said rods.

9. A magnetron anode comprising a plurality of apertured parallel walls, wall means electrically connecting said walls together and forming therewith cavity resonators, and rods connected to alternate walls only,

10. A magnetron anode comprising a plurality of spaced, electrically connected, apertured Walls, an intermediate one of said walls being provided with spaced, internally extending projections, and rods connected to said projections and spaced from the walls adjacent said intermediate wall.

11. A magnetron anode according to claim 10, further comprising other rods parallel to and intermediate said first-named rods, said other rods being connected to said adjacent walls and spaced from said intermediate Wall.

12. A magnetron anode structure comprising a hollow conducting member, a conducting partition dividing said member into two adjacent cavity resonators and having a central aperture, and a plurality of anode segments extending through said aperture and connected to said partition.

13. A cavity resonator structure comprising a hollow conducting member, a conducting partition dividing said member into two adjacent cavity resonators and having a central aperture, and a plurality of elongated parallel conducting elements extending through said aperture, said elements being connected to said partition.

14. A cavity resonator structure comprising a hollow conducting member, a conducting partition dividing said member into two adjacent cavity resonators and having a central aperture, and a plurality of elongated parallel conducting elements extending through said aperture, alternate elements being connected to said partition and spaced from said member, the other elements being connected to said member and spaced from said partition.

15. A magnetron anode comprising a cavity resonator composed of a pair of spaced conducting walls connected by a peripheral conducting wall, each of said spaced walls having a central aperture, and parallel anode rods disposed around said apertures and alternately connected to one of said spaced walls and extending through the other of said spaced walls in spaced relation therewith, whereby the gaps between the rods and the spaced walls are oriented at right angles to the rods.

16. A magnetron anode according to claim 15, wherein each of said spaced walls has a series of radial projections and intermediate recesses disposed around said aperture, and said rods are mounted on said projections and extend through said recesses.

GEORGE E. KILGORE.

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

UNITED STATES PATENTS Number Name Date 2,145,727 Lloyd, Jr Jan. 31, 1939 2,147,159 Gutton et al Feb. 14, 1939 2,247,077 Blewett et a1 June 24, 1941 2,463,416 Nordsieck Mar. 1, 1949 2,473,828 Spencer June 21, 1949 2,477,122 Garner July 26, 1949 2,509,419 Brown May 30, 1956

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