US2418469A - Tuner for multiresonators - Google Patents

Description

Aprll 8, 1947-. H. D. HAGSTRUM 2,418,469

TUNER FOR MULTI-RESONATOR Filed May 4, 1944 2 Sheets-Sheet 1 F IG? INVENTOR H. D.HAGS7'RUM ATTORNEY April 8, 1947.

H. D. HAGSTRUM TUNER FOR MULTI-RESONATOR Filed May 4, 1944 2 Sheets-Sheet 2 in Q:

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lNl/ENTOR P H.D.HAG$TRUM ATTORNiV Patented Apr. 8, 1947 T7. .11

TUNER FOR MULTIRESONATORS Homer D. Hagstrum, New York, N. Y., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application May 4, 1944, Serial No. 534,019

Claims. 1 This invention relates to arrangements for tuning an electromagnetic resonator of the cavity type and especially to devices adapted for simultaneously and uniformly tuning the several cavities of a multicavity resonator. The invention is particularly applicable to microwave apparatus.

- The needfor tuning a cavity resonator may arise in many situations involving the handling of microwaves, as in the generation and transmission of such waves. It iscustomary where power outputs of several kilowatts are required, to generate microwaves in a magnetron oscillator which employs a multicavity resonator.

While the oscillating system' of the magnetron may be predesigned to operate approximately at a desired frequency, itis desirable to be able to adjust the operating frequency after the oscillator has been connected to a transmission system. One reason for this is that the operating frequency of a system made up of an oscillator and aload, which system may also include an intermediate transmission medium therebetween depends not alone upon the dimensions of the oscillator but also upon the impedance presented to the oscillator by the load and any such transmission medium. Oscillators have in certain cases been produced in quantity, inspected and tested in a standardized transmission circuit and those oscillators operating outside a prescribed frequency band have been rejected as unsatisfactory. Of the oscillators passing such a test, some operate in the test circuit at a frequency close to one edge of the hand. These marginal oscillators, when placed in the system for which they ultimately are intended, which system may differ somewhat from the test circuit in its impedance characteristics, may operate at a frequency outside the band limits, and be unsatisfactory for that reason. An oscillator which is off frequency can usually be brought to operate within the band by a small change in the resonating properties of the oscillator. Other reasons for tuning the oscillator are to permit a selection of the final operating frequency and to permit the frequency to be changed from time to time as desired. A further reason is to enable manufacturing tolerances to be relaxed while insuring a commercial product which readily can be made to operate within its prescribed frequency band.

In accordance with the invention, means are provided for altering the shape of a single cavity or of one or more of the cavities of a multicavity resonator. For tuning, over. a wide frequency the cavities of a, multicavity resonator is dc sirable as the range which may be covered .is many times that which maybe covered by tuning one cavity alone.

It is often important, in operating a multi-' cavity magnetron, to maintain as nearly as possible a symmetrical pattern of electric and magnetic fields. In this way, operating conditions in the respective individual cavities may be keptsimilar. For this purpose, means are pro-. vided in accordance with the invention whereby a plurality, preferably all, of the cavities of a multicavity resonator are tuned in a manner. that is uniform for all the cavities affected. Mechanical arrangements are shown for simultaneously tuning the several cavities.

In the drawings,

Fig. 1 is a fragmentary view of a. multicavity resonator with means for tuning one of the cavities;

Fig. 2 is a sectional view, in perspective, of a multicavity magnetron having a tuning element for simultaneously tuning the individual cavities;

Fig. 3 is a plan view, partly broken away, showing a magnetron like that of Fig. 2 together with means for adjusting the tuning element from outside the vacuum chamber of the magnetron;

Fig. 4 is a fragmentary View similar to that shown in Fig. 3 except that the tuning element is shown moved with respect to its position in' Fig. 3;

Fig. 5 is a cross-sectional view of the magnetron shown in Figs. 2, 3 and 4;

Fig. 6 is a plan view of a tuning element of a different shape from that shown in Figs. 3: and 4; and

Fig. 7 is a fragmentary view, showing a modified form of tuning system in accordance with the invention.

Referring now to Fig. 1, a fragment of a multicavity resonator It is shown, in section, including two individual resonating cavities l9. Extending radially into one of the cavities I9 is a tuning rod or screw 80, which may be adjusted to any desired position. The tuning of the cavity containing the screw is affected by the position of the screw therein and, due to the presence of coupling between the adjacent cavities IS, the position of the screw 80 is found to affect materially the tuning of the multicavity resonator as a whole. The coupling arrangement is more fully described hereinafter incon:

nection with Figs. 2, 3, 4 and 5. Provision may be made in well-known manner for retaining vacuum within the cavities of theresonator while making the element 80 adjustable from outside the evacuated space. An example is shown employing a. metallic bellows for such a purpose, in Figs. 3, 4 and '7. l

In Figs. 2,3, 4. and 5, the principal working parts of a magnetron oscillator are shown so as to more fully explain how the invention is to be embodied in an oscillator and to show how a plurality of tuners may be operated simultaneously. The oscillator has an anode it which may be a perforated metal block fitted snugly within a vacuum-tight container, the latter comprising a side wall portion II, and end plates I2 and I 3. In a central perforation H! in the anode block there may be mounted a cathode M which may contain a heating element and be supported by wires or conductive rods I5 and I5 entering the vacuum. chamber through suitable dielectric seals H and It, respectively, p

The-anode l0 comprises a multi'cavity resonator having a plurality of individual resonating cavities 19 each connected through a slot 26 with the central perforation iii, the portions H of the anode blockbetween adjacent slots 26 forminganode segments in well-known manner. End spaces 2| and 22: are: provided. between the ends of the anode. ill: and the. plates 12 and it, respec-' tively. The spaces 2! and 22, together with the slots 2%? and the anode-cathode space comprising the. perforation 1B, serve to provide electromagnetic' coupling betweenth-e individual cavities it. An. initial steady potential: difference between the anode 1e and the cathode l4 may he provided in any suitable manner as by means of a pulsing generator or other source and represented here for simplicity as a battery 23, the positive terminal of which may be connectedv to the casing of the magnetron and grounded as at 25. Heating current may be supplied to the cathode through the conductors It and i6 from a suitable source such as a. battery 25, the cathode being heated either directly or indirectly, as desired. An initial steady magnetomoti-ve force in a direction substantially parallel to the'c'athode may be supplied in any suitable manner.

A set of. connectors or straps 2%) may be used to interconnect the anode segments according to any desired scheme for the purpose of favoring one particular mode of. oscillation among several possible modes of mu'ltiresonant system, as has become customary in this art. 7

1 The magnetron oscillator shown is of the-general type disclosedin U. S ..Patent 2,0633% issued. December 8, 1935, to A. L. Samuel. Various arrangements areknown in the art for lea-ding oiT electromagnetic waves generated within an oscii-- lat'or oi this type and supplying themto a transmission system or utilization circuit. Any suitable output device may be employed with: the oscillator disclosed and will be readily sup-plied by one skilled in this art.

In the arrangement .of Figs. 2, fieand 5, a rotatable' tuning element til isprovided which passes through or projects into several, and preferablya ll',.of the individual cavities 19; The element 353 may he in the form of a ring composed of two parts joined together by screws (i-l and 3-2 as shownin Fig. 3; The ringtil is preferably assem bled. in a peripheral: 01 circurnfererrti'al' groove: 33 which may be: cut" intothe anode: hl'o'ck i9 as: by turning; in: a lathe. Bearing surfaces may be provided as by means of 1 shoulders at 81 and B2 The position of the element St in the groove 33 may be seen in Fig, 2. The groove intersects the individual tuning cavities, making a plurality of tuning openings preferably arranged in a circular array about the central axis of the opening 16. A portion or segment of the element 30 projects into the individual cavity [9. The inner edge or surface of the element 30 preferably has a non-circular outline orcontour of a pattern which repeats itself the same number of times as their individual cavities l9 so thatwhen the element 39 is rotated about the central axis of the magnetron, the amount and disposition of the material projecting into the cavity I9 is the same for each cavity but varies according to the angular position of the element 39. Figs. Band 4 show a plurality of circular scallops arranged in radial symmetry on the inner edge of the element 35, one extreme angular position being indicated in Fig. 3 in which the scallops are centered upon. the individual cavities.- Fig. 4 shows the element 38 rotated approximately 22 /2 degrees which is the correct displacement in the case ofa resonator with eight symmetrically spaced cavities as shown, to withdraw the scallopedportion of the element 36 entirely within the anodeblock Ill. By rotating the element 36, any intermediate position between those shown in Figs. Sand-4, respectively, may be obtained, the effect of rotat-- ing. the element Bil being to vary the tuning. properties of all the cavities i9 simultaneously and in the same degree.

Any suitable mechanical means may be ,sup-' plied for rotating the element 30' from outsidethe vacuum chamber. In Figs. 3 and 4 there is shown by way of example, a tangential rod 49 with a bent end engaging a notch 4|- in the outer edge of the element 30. To maintain the vacuum, the rod may be manipulated through any suitable flexible closure such as a bellows d2, preferably of metal and sealed over an opening, d3 by which the rod 40 passes through the wall ll. Suitable. means such as a thumbscrew 44- coupled to the rod 4%! through a ring 45 rotatably secured in a groove it may be provided for controlling the motion of the rod 40 and the thumbscrew 44- may be supported as by a bracket 4,1, secured to the wall H.

It will be evident that rotation of the thumb;- s'crew' 44' will cause axial motion of. the rod 40 tangentially with respect to the element 30; which will inturn produce rotation ofthe element '30" and variation of the tuning in all thecha-Inbers l5, simultaneously. a

Figs 6 illustrates the useofatuning element 50,- similar to the element 39 except that the element has a serrated inner edge. Itwill be evident that rotation of the elementEil willeproduce simultaneous; tuning of all-the chambers!!! exactly-as in the case of the element 30, exceptthat the variation in. the tuning with respect to; the angular displacement of the rotatable element-will fol-- low a' somewhat different law. in the-two cases; 7

Fig. 7 shows another modificationo'f the tuning;

- system in which antindiv-idual tuning. rod or plunger Si] is provided projecting into-each resonating; cavity [9. In this case all-the rods are operated simultaneously by means of arotatable element 61 'containing'a series of inclinedslots 62 each of whichengages and controls thgmotion of a pin 63 attached to oneot the; rods 60. It will be evident that the element 6| mechanically 'intercouples the" rods and t1'1"a=t-'v rotation. of

the element GIIWHIZGHUIS'ET the rodste move-radially with respect to the cavities 1 9, thereby'tuning;

all the cavities simultaneously. In Fig. 7, the extreme inner and outer positions of the rods are indicated by broken lines.

It will be evident to those skilled in this art that other suitable means are known for rotating a part, such as the tuning element herein, from outside a vacuum chamber, for example, a lever arrangement supported by a flexible diaphragm may be employed. It will also be evident that the rotatable tuning element might be placed at the top or bottom of the anode plate Ill instead of being arranged in a slot 33. The tuning element would then control the size and shape of the opening between the individual cavity l9 and the adjacent end space. The element could be rotatably supported in the end space in any suitable manner. This latter arrangement would be appropriate in case it was desired to have the out,- put coupling inserted centrally into one of the cavities [9 in a radial direction, as is commonly done. a

The material of the tuning element 39, 50 or 60 may be conductive such as solid metal, or it may be any suitable material metalized or covered with a conductive coating of suitable depth to confine Within the cavity electromagnetic waves of the desired operating wavelength. On the other hand, the tuning element may be partly or wholly composed of a dielectric material so as to vary the electric properties of the space within the cavities.

What is claimed is:

l. A resonator comprising a member containing a plurality of individual resonating cavities arranged in radial symmetry about a central axis, and a tuning element rotatable about said axis, said tuning element having a plurality of non-circular portions each extending into one of said resonating cavities by a variable amount depending upon the angular position of the tuning element.

2. A resonator containing a plurality of resonating cavities each having a tuning opening, said openings being positioned in a circular array about a central axis, and a tuning element rotatably mounted with respect to said central axis, said tuning element having a non-circular contour defining a plurality of segments each extending into one of said resonating cavities through the respective tuning opening by a variable amount depending upon the angular position of the tuning element.

3. A resonator comprising a member contain ing a plurality of individual resonating cavities arranged to have radial symmetry about a central axis, and a tuning element rotatable about said axis, said tuning element having a serrated edge the respective teeth of which project each into one of the said individual cavities, whereby the tuning of the resonator depends upon the angular position of the tuning element.

4. A resonator comprising a, perforated block containing a plurality of individual resonating cavities arranged in a circular array about a central axis, and a tuning element rotatable about said axis, said tuning element having a plurality of segments each extending into one of said resonating cavities by a variable amount depending upon the angular position of the tuning element.

5. A resonator comprising a perforated cylindrical block containing a plurality of individual resonating cavities arranged in radial symmetry With their axes parallel to the cylindrical axis of said block, the block having a circumferential groove in its outer surface, said groove intersecting each of said individual cavities, and an annular tuning element rotatably mounted in said groove, said tuning element having a noncircular inner surface the contour of which has a plurality of projections as numerous as the individual cavities in the resonator, whereby rotation of said tuning element simultaneously varies the tuning properties of the several individual cavities.

HOMER D. HAGSTRUM.

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

UNITED STATES PATENTS Number Name Date 2,294,942 Varian et a1 Sept. 8, 1942 2,356,414 Linder Aug. 22, 1944 2,323,729 Ryan July 6, 1943

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