US2724090A - Electron discharge device output coupler - Google Patents

Description

Nov. 15, 1955 N. H. MOORE 2,724,090

ELECTRON DISCHARGE DEVICE OUTPUT COUPLER Filed May 2, 1951 2 Sheets-Sheet l l N V E N TO R 24 NORMAN H. MOCRE ATTO R N EY N. H. MOORE ELECTRON DISCHARGE DEVICE OUTPUT COUPLER Nov. 15, 1955 2 Sheets-Shee Filed May 2, 1951 INVENTOR NORMAN H. MOOE ATTORNEY United States PatentO LECTRON DISCHARGE DEVICE OUTPUT COUPLER Application May 2, 1951, Serial No. 224,099 2 Claims. (Cl. S33-34) This `invention relates to output couplers and more particularly to output couplers for high frequency electron discharge devices.

In the operation of electron discharge devices having cavity resonators excited by the passage thereby `of electrons it is often desired to couple aresonator to a coaxial output line. ln general the coaxial line will have an impedance higher than the resonator so that impedance transformation is necessary for ecientoperation. Additionally, as the output is generally made by an opening from the resonator it is desirable to `havethe glass seal between the conductors ofthe coaxial line out of alignment with the opening from the resonator to prevent i damage to the seal by stray ions.

It is an object of this invention to provide anoutput coupling for `cavity resonators, such as used in electron j 2,724,090 Patented Nov. l5, 1 955 ferred embodiment of my invention applied to a multiple cavity magnetron.- The magnetron 1 comprises a body portion Z to which are connected a plurality of magnetron vanes 3 which serve to provide cavity resonators. A cathode 4 provides the electron sourcefor operation of the magnetron. The magnetic pole pieces and the tuning elements of a tunable magnetron are not illustrated since they are `not Vnecessary to an understanding of the present invention. A wave guide section 5 is provided with its outer wall 6 sealed at one end to `body portion 2. The other end of the wall 6 is closed by a metal cap 7. Intermediate the ends `of the wave guide 5 and preferably near the closed end is `provided a `tapered coaxial line section 8. The outer conductor wall 9 of coaxial line section 8 is `sealed through wall 6, the inner conductor 10 also extending into theL waveguide `S substantially half way therethrough.` Fastened to wall 9 `by brazing or welding, for example, is a sealing ring 1 1 which may be of a metal having similarcoecient of expansion to that of glass. A second` `ring -12 is provided of the same metal as ring 11, and to :this ring is fastened a glass seal 13. The other end of glass seal 13 is sealed to a metal cup 14 made of similar type metal to that of rings 11 and 12. Cup `14 is made Ito have an outer diameter substantially the same as the diameter of the inner conductor of a coaxial `line `to be discharge devices, constituting a wave guide and a1 coaxial line section which will meet the requirements outlined above.

In the study of high `frequency wave transmission, coupling circuits between a wave guide and a coaxial line have been proposed, such for example, as illustrated in Very High Frequency Techniques, vol. Il, published in 1947 by McGraw-Hill `Book Co. \\Inc.,.pages 717-736.

t t According to a feature of this invention there is provided for coupling a resonator of an electron discharge device to a coaxial line, a wave guide section having a pair of impedance transformer vanes extending within the wave guide section from a coupling opening in the resonator to a coaxial line section, the inner and outer conductors of the coaxial line section being connected respectively to ditferent ones of the impedance transformer vanes. The wave guide extension beyond the junction of the coaxial line section and the vanes may be a wave guide beyond cut-off and closed to provide a resonator reflecting a high impedance at the junction. For completing the discharge device a glass seal may be provided between the inner and outer conductors of the coaxial line section externally of the wave guide. Preferably the Wave guide section and the coaxial line section are at right angles to one another so as to provide maximum protection against ion bombardment of the glass seal.

The above-mentioned and other features and objects of this invention and the manner of attaining them will become more apparent and the invention itself will be best understood by reference to the following description taken in conjunction with the accompanying drawings, in which:

Fig. l is a sectional view of a portion of a magnetron and an output coupler illustrating my invention;

Fig. 2 is a sectional view alongthe line 2-2 of Fig. 1, and

Fig. 3 is a curve illustrating the broad band operating characteristics of a magnetron incorporating my invention.

Turning first to Figure 1, there is illustrated a prefastened to the tube.

`Rings 11 and 12 are sealed to- `gether by brazing orwelding to complete the seal of the magnetron envelope. The lower end of cup 14 is fastened as by `brazing or welding `to the tapered inner conductor 10 of ythe coaxial line section 8. A threaded connector ring 15 may `be secured to the outer surface of ring 11 to provide the desired coupling for the outer conductor of the coaxial line to serve as an energy lead from the magnetron.

Intermediate the magnetron body 2 and the coaxial line section 8 there Vis provided within the wave guide a `pair of ramp `or vane elements 16j, 17.` These `elements 16, 17 may extend through openings in the body portion 2, their inner ends being curved to conform with the curvature of the cylindrical Wall of the magnetron body. The vane 16, 17 are spaced apart a predetermined dstance as at 18 to provide a coupling opening from one of the cavity resonators into the Wave guide. The separation between vanes 16, 17 gradually diverges to the point at which coaxial line section 3 enters the wave guide to provide an impedance matching ramp for matching the impedance of the resonator with that of the coaxial line section 8. The outer conductor 9 of coaxial section 8 is fastened to vane 16 while the inner conductor 10 is fastened to vane 17 by threaded connection for example. The portion of wave guide section 5 beyond the ends of vanes 16, 17 forms a resonator provided in the wave guide proportioned to be beyond cut-olf and so reects at the juncture of coaxial line section 8 and vanes 16, 17, a high impedance.

ln an actual construction the output coaxial line, not shown, and coaxial line section 8 have an impedance of approximately 5() ohms. The wave guide section 5 itself may have an impedance of 25 ohms: for example and the resonator impedance may be relatively small, in the order of 8-1() ohms. Separation between vanes 16 and 17 is adjusted to provide the necessary impedance match between the resonator cavity and the coaxial line section.

While the construction as described with ramps 16, 17 both fixed provides a satisfactory operation. over a relatively wide band, it is desirable in many cases to have adjustable features particularly to determine the area of the output opening 18. To this end ramp vane 17 may be provided with a xed portion 19 to which is pivoted a movable portion 20 by means of pin 21. A

rotation about pivot 21 the gap 18 may be adjusted.

Since the opening 18 is normally relatively small, for instance inthe order of 00 of an inch, and pivot 21 is adjusted, the junction point of inner conductor 10 and vane 17 no special provisions are necessary to permit this slight adjustment.

In Fig. 2 is plotted a curve 25 showing the standing wave ratio existing at an output line with respect to ,the wave length in centimeters produced by the magnetron oscillator. It will bel noted that the standing wave ratio is less than 1.3 over an operating wave length ran'geof substantially ll-23 centimeters, which repre.

sents a Vrange in the neighborhood of 800 megacycles` This; curve was plotted with a Xed ramp magnetron andfillustrates the wide band impedance matching characteristics of the magnetron output structure incorporating my invention. v

While I have illustrated my invention in connection with afmagnetron it will'be evidenced that the principles thereof are applicable to other types of coupling circuits. The impedance matching characteristics apply to any type of similar system. In addition it will be noted that any free'ions which may enter wave guide section 5 will not be able to enter coaxial section 8 and, therefore, glass seal 13 is completely protected from the bombardment by free ions so that `danger of rupture is completely eliminated.

While I have described above the principles of my invention in connection with specilic apparatus, it is to be clearlyY understood that this description is made only by way of example and not as a limitation to the Vscope of my invention as set forth in the objects thereof and in the accompanying claims.

What is claimed is:

l. In a magnetron comprising a cylindrical magnetron body, and a plurality of vanes each fastened at one end to said body to provide resonators, said body being provided with an output opening, the combination of an output coupler comprising a wave guide having a wall sealed at one end to said body about said output opening, a conductive closure memberY sealed at the other end of said wave guide, a tapered coaxial line section extending through said wave guide wall at substantially right angles thereto, intermediate said body and said closure member, an insulating seal between the outer and inner conductors of said coaxial line section externally of said wave guide, a pair of impedance transformer vanes mounted within said wave guide and extending into and substantially filling the output opening inv said body, and from said body to said coaxial line section, said transformer vanes being spacedv apart a small distance at their ends adjacent said body to provide a coupling opening between a resonator of said magnetron and said wave guide, said spacing between said transformer vanes gradually increasing from the ends adjacent said body to said coaxial line section, and means connecting one of said transformer vanes to the outer conductor of said coaxial line section and the other of said transformer vanes to the inner conductor of said coaxial line.

2. A coupler according to claim l, wherein the portion of said wave guide between said coaxial line section and said closure member comprises a wave guide beyond cut-oft' at the output frequency of said magnetron, whereby a high impedance is reflected at the junction of said coaxial line section and said transformer vanes.

References Cited in the le of this patent UNITED STATES PATENTS 1,841,473 Green Ian. 19, 1932 2,404,086 Okress July 16, 1946 2,477,633 Litton Aug. 2, 1949 2,481,151' Powers Sept. 6, 1949 2,555,349 Litton June 5, 1951 2,609,522 Hull Sept. 2, 1952 2,623,198 Hebenstreit Dec. 23, 1952 OTHER REFERENCES Very High Frequency Techniques, vol. II, McGraw- Hill Book Co., Inc., 1947.

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