US3289036A

US3289036A - Inverted magnetron having adjacent anode cavities coupled in opposite phase to a central stabilizing cavity

Info

Publication number: US3289036A
Application number: US387572A
Authority: US
Inventors: Edward T Downing; William A Bowers
Original assignee: Raytheon Co
Current assignee: Raytheon Co
Priority date: 1964-08-05
Filing date: 1964-08-05
Publication date: 1966-11-29
Anticipated expiration: 1983-11-29
Also published as: GB1088064A; NL6509998A; SE320438B; DE1491397B1

Description

1965 E. T. DOWNING ETAL INVERTED MAGNETRON HAVING ADJACENT ANODE CAVITIES COUPLED IN OPPOSITE PHASE TO A CENTRAL STABILIZING CAVITY Filed Aug. 5, 1964 F/GTJ //VVE/VTOR$ EDWARD I DUW/Vl/VG W/LL/AM A. HOWE-RS AGE/VT folz United States Patent 3,289,036 INVERTED MAGNETRON HAVING ADJACENT ANODE CAVITIES COUPLED IN OPPOSITE PHASE TO A CENTRAL STABILIZING CAVITY Edward T. Downing, Winchester, and William A. Bowers, Berlin, Mass., assignors to Raytheon Company, Lexington, Mass., a corporation of Delaware Filed Aug. 5, 1964, Ser. No. 387,572 9 Claims. (Cl. 315-3953) This invention relates to crossed-field electron discharge devices and, more particularly, to a magnetron device wherein the amode'system is within a coaxial cathode.

In order to satisfy requirements for magnetron tubes of greater power handling capability and higher frequency range, attempts have been made to construct so called inverted magnetron devices wherein the anode system is arranged within a coaxial cathode in contrast to the more conventional arrangement in which the cathode is within a coaxial anode. Reference is had to the text Crossed- Field Microwave Devices, vol. II, by E. O. Kress, Academic Press 1961, chapters 3.1 and 5.5, for a disscusion of such attempts. One of the obvious advantages to such a coaxial cathode structure is the increase of cathode emission surface area. The effective anode area presented to the cathode is also increased, since the anode segments or vanes are located outside, instead of inside, the resonant cavity structure at a greater distance from the axis of the device which permits a greater number of vanes to be employed. However, as noted in the referenced text, inversion of the magnetron with its complicated electron interaction is not as simple in theory as inversion of a tube with simpler electron trajectories, such as a tetrode or triode. Some of the difficulties associated with such inversion is that mode separation is decreased to the extent that the tube does not socillate in a stable fashion and that circuit efliciency is decreased so that the tube does not oscillate at all.

Accordingly, it is an object of the present invention to provide a magnetron device having high power handling capabilities at high frequencies with improved mode stability and operating efiiciency.

To this end, there is provided in accordance with the invention an electrode structure comprising a centrally located cylindrical stabilizing cavity of length substan tially equal to an integral number of wavelengths of the mid-band of the operating frequency, an anode structure having vanes extending radially outward from the periphery of the cavity, said anode vanes forming anode cavities therebetween, adjacent anode cavities being coupled to opposite ends of said stabilizing cavity to obtain symmetrical coupling, and a cylindrical emitting cathode facing toward the vanes. The device of the invention may be best described as an integral cavity magnetron since, unlike most magnetrons, every anode cavity is coupled to the stabilizing cavity. The RF. energy distribution in each anode cavity thus becomes equal because each anode cavity is coupled to one of two equal stabilizing cavity electromagnetic fields. Two electric and two magnetic fields with each specific field 180 out of phase with its adjacent field, exist in the stabilizing cavity because the stabilizing cavity, as aforesaid, is a full wavelength long. However, it should be noted that it is within the contemplation of the invention that the cavity length L can be made any integral number of /2 wavelength long so as to satisfy the relationship L=n)\/2 where n is an integer greater than or equal to 2. The stabilizing cavity is, in essence, symmetrically integrated to the wave structure and hence the term integral cavity.

Accordingly, it will be seen from the description to follow that the integral cavity magnetron of the in- 3,289,036 Patented Nov. 29, 1966 ice vention provides: very large anode and cathode surfaces because of the inside-out construction coupled with the one wavelength cavity structure, thus resulting in the generation of higher power at higher frequencies, as well stabilized anode cavity structure of a size and construction compatible with the use of a large number of vanes and accompanying large anode area, and symmetrical coupling by virtue of the full wavelength cavity and integral coupling arrangement, resulting in improved mode stability and operating efficiency.

Other objects, features and advantages of the invention will become apparent from the following description taken in connection with the accompanying drawings in which:

FIG. 1 is a cross section of the integral cavity magnetron structure of the invention;

FIG. 2 is an enlarged perspective view of pertinent portions of the integral cavity magnetron structure of the invention shown in FIG. 1; and

FIG. 3 is a graph plotting the quality factor Q versus the ratio of diameter to length for various cavities.

In FIGS. 1 and 2. there is shown a magnetron structure 10 comprising a hollow anode cylinder 14, forming a cavity 12, and which may be of any desired conductive material, such as copper. Extending radially outward from cylinder 14 are a plurality of anode elements 16, which, in this embodiment though not by way of limitation, comprises substantially rectangular plates with surfaces parallel to the longitudinal axis 15 of cylinder 14. One end of cavity 12 is sealed off from the atmosphere by a microwave window 24 which is transparent to electromagnetic energy and comprised of suitable dielectric material. The remaining end of cavity 12 is sealed by solid support piece 21 of cylinder 14. In cavity 12 and suspended from microwave window 24 is a coupling iris 19 located a distance nh/Z from surface 40 of cavity 12. It should be noted that X represents the wavelength of the mid-band of the frequency of the energy propagated in the cavity, and n is an integer greater than or equal to 2. It is further noted that iris 19 instead of being suspended from window 24 could alternatively be supported by a thin rod extending from surface 40 if desired. Iris 19 is formed of metal such as copper and partially closes one end of cavity 12 while permitting a predetermined portion of the energy propagated in the cavity to egress through microwave window 24. It is further noted that output ports could be provided at either or both ends of cavity 12 as desired and the invention is not to be limited to the particular manner of extracting energy shown herein.

Concentric with and encircling the window end of cylinder 14 is a magnetic pole piece 13 which has its central opening extending axially therein concentric with waveguide 11 to enable R.F. energy from the magnetron structure to be coupled out through window 24 to a utilization device, not shown. A second magnetic pole piece 23 is provided in concentric encirclement of support piece "21. Concentric insulative discs 30' and 31 are provided intermediate the pole pieces and the support piece 21 and waveguide 11 to vacuum seal the ends of the magnetron interaction space 17. A cathode cylinder or ring 22 coated with electron emissive material is provided encircling the axis of inner cylinder 14 and coaxial to the anode vanes 16. Cathode 22 is supported by insulative member 41 disposed

intermediate pole pieces

13 and 23.

The integral cavity magnetron of FIGS. 1 and 2 thus obtained may be looked upon descriptively as formed from two inverted coaxial magnetrons placed end-to-end so that their axes coincide in a common axis 15.

The stabilizing cavity thus formed is a full wavelength cavity containing two electric fields illustrated by dotted 3

lines

32 and 33 and two magnetic fields illustrated by solid lines 34 and 35 with each field 180 out of phase with its adjacent field. Since the stabilizing cavity is a full wavelength cavity, two fields of opposite polarity exist therein. The fields in one-half of the stabilizing cavity 12 are connected to alternate vane resonators or interaction spaces formed by the vanes and cathode structure by means of coupling slots 18. The fields in coupled alternate resonators are phased by the cavity; hence alternate resonators which are all fed from the same half of the cavity will all be in phase. The remaining resonators which are fed from the remaining half of the cavity by means of slots disposed into the remain ing half of the cavity will be of opposite phase polarity. Therefore, in the integral cavity magnetron, unlike the prior art structures, every vane or anode resonator is coupled to the stabilizing cavity. The R.-F. energy distribution in each resonator is equal because each resonator is coupled to one of the two stabilizing cavity fields and these cavity fields are intimately coupled together. The stabilizing cavity is, in essence, symmetrically integrated to the vane structure; therefore, the device is called an integral cavity magnetron. Such intimate and symmetrical coupling between the vane structure and stabilizing cavity results in a tube with less tendency towards moding and with better starting characteristics.

Furthermore, the integral cavity feature results in an overall increase in efficiency resulting from the higher unloaded Q of the stabilizing cavity. This feature of the invention may best be appreciated from an analysis of FIG. 3 which is a plot of the ratio of the cavity diameter D to cavity length L versus the normalized Q of a full wavelength cavity (curve a) operating in the TE mode and a half wavelength cavity (curve 12) operated in the TE mode. It may be seen that in both curves a and b the optimum Q occurs when the ratio of D/ L is unity. At that point in the curve the Q of the full wavelength cavity is about 20% higher than the Q of the half Wavelength cavity. A higher unloaded Q will provide improved circuit efliciency; hence, the circuit efficiencies will be higher in the full wavelength integral cavity of the invention for a given loaded Q.

Although there have been described what have been considered to be preferred embodiments of the present invention, various modifications and adaptations thereof will be apparent to those skilled in the art. For example, the integral cavity magnetron may be-employed to obtain considerable amplification of an input signal since the stabilizing cavity geometry is such that it may or may not be constructed as reentrant, depending on the application desired. To obtain amplification an input cavity is isolated from an output cavity or cavities by means of a metallic wall perpendicular to the axis of the output cavities and filling the cross-sectional area bounded by the cylindrical cavity wall. The coupling slots in the input cavity couple input energy onto the vane structure where amplification is obtained by magnetron type interaction. The output cavity or cavities couple the RF. energy to the output and define the pass band of the system. A plurality of cavities may be employed, stagger-tuned to increase the pass band and the gain. In this instance over-all gain may be defined in terms of the anode length which will ultimately be dependent upon the number of cavities employed. Accordingly, it is desired that the invention not be limited except as set forth in the appended claims. I

What is claimed is:

1. An electrode structure comprising:

an anode cylinder having inner and outer longitudinal surfaces and defining an integral stabilizing cavity;

a cathode cylinder encircling said anode cylinder;

a plurality of anode vanes attached to an outer surface of said anode cylinder and forming resonant anode cavities between said vanes;

a first plurality of slots extending through said anode cylinder and coupling alternate anode cavities to the upper portion of said stabilizing cavity;

and a second plurality of slots extending through said anode cylinder and coupling the remaining anode cavities to the lower portion of said stabilizing cavy;

adjacent slots of said first and second pluralities being spaced apart axially of the anode cylinder.

2. The apparatus of claim 1 wherein the electrical length of the anode cylinder is substantially equal to ilk/2 wherein n is an integer greater than or equal to 2 and A is the wavelength of the midband of the operating frequency.

3. In a crossed field device:

a cathode cylinder coaxial to and encircling said anode cylinder;

a plurality of anode vanes attached to an outer surface of said anode cyhnder and forming resonant anode cavities between said vanes;

a first plurality of slots extending through the inner surface to the outer surface of said anode cylinder coupling every other anode cavity to the upper portion of said stabilizing cavity;

a'second plurality of slots extending through the inner surface to the outer surface of said anode cylinder coupling the remaining anode cavities to the lower portion of said stabilizing cavity;

and means at at least one end of said anode cylinder forfcoupling energy from the stabilizing cavity to a load device.

4. An inverted magnetron having a cathode electrode coaxial to and encircling a vaned anode cylinder forming a plurality of resonant anode cavities between the vanes in which means are provided for coupling alternate anode vane cavities to the upper half of an interior cylindrical cavity formed by said anode cylinder and for coupling remaining anode vane cavities to the lower half of said cylindrical cavity whereby every anode vane cavity is coupled alternately to the upper and lower portions of said cavity.

5. The apparatus of claim 4- wherein the coupling means comprises a first plurality of slots located adjacent each other along the circumference of said cylindrical cavity and a second plurality of slots spaced apart axially from said firs-t plurality of slots. 6. The apparatus of claim 4 in which the efiective length of the interior of said cylindrical cavity is equal to nA/Z wherein n is an integer greater than or equal to 2 and A is the wavelength of the midband of the operating frequency of said magnetron.

7. An electrode structure comprising:

a hollow cylindrical anode structure forming a stabilizing cavity in the interior thereof, said anode structure having vanes extending radially outward from the periphery of said structure forming anode cavities therebetween, adjacent anode cavities being coupled to opposite ends of said stabilizing cavity for symmetrically coupling energy therebetween, said stabilizing cavity of length substantially equal to an integral number of wavelengths of the midband of the operating frequency; A

and a cylindrical emitting cathode coaxial to and encircling said vanes.

- 8. An electrode structure comprising:

a hollow cylindrical anode structure forming a stabilizing cavity in the interior thereof, said anode structure having vanes extending radially outward from the periphery of said structure forming anode cavities therebetween, adjacent anode cavities being coupled to opposite ends of said stabilizing cavity for ymmetrically coupling energy therebetween, said 3,289,086 5 6 stabilizing cavity of length substantially equal to an References Cited by the Examiner integral number of Wavelengths of the midband of UNITED STATES PATENTS the operating frequency;

1i 0 th d t d 2,815,469 12/1957 Sixsrnit-h 31539.77 1; 12:21P Ca 0 e coaxial 0 an enclrchng 5 3,096,462 7/1963 Feinstein 315-4915 and means disposed at, at least, one end of said sta- References Cited by the Applicant bilizing cavity for extracting predetermined portions UNITED STATES PATENTS of the energy in said cavity therefrom. 9. The apparatus of claim '8 wherein the means for extracting energy from the stabilizing cavity comprises 10 HERMAN KARL SAALBACH Primary Examiner an iris dependent from a microwave Window sealing off an end of said Stabilizing cavity P. L. GENSLER, Asszstant Examiner.

2,419,172 4/1947 Smith.

Claims

1. AN ELECTRODE STRUCTURE COMPRISING: AN ANODE CYLINDER HAVING INNER AND OUTER LONGITUDINAL SURFACES AND DEFINING AN INTEGRAL STABILIZING CAVITY; A CATHODE CYLINDER ENCIRCLING SAID ANODE CYLINDER; A PLURALITY OF ANODE VANES ATTACHED TO AN OUTER SURFACE OF SAID ANODE CYLINDER AND FORMING RESONANT ANODE CAVITIES BETWEEN SAID VANES; A FIRST PLURALITY OF SLOTS EXTENDING THROUGH SAID ANODE CYLINDER AND COUPLING ALTERNATE ANODE CAVITIES TO THE UPPER PORTION OF SAID STABILIZING CAVITY; AND A SECOND PLURALITY OF SLOTS EXTENDING THROUGH SAID ANODE CYLINDER AND COUPLING THE REMAINING ANODE CAVITIES TO THE LOWER PORTION OF SAID STABILIZING CAVITY; ADJACENT SLOTS OF SAID FIRST AND SECOND PLURALITES BEING SPACED APART AXIALLY OF THE ANODE CYLINDER.