US2542908A - Mechanical tuner for cavity resonators - Google Patents

Description

Feb. 20, 1951 P. P. DERBY MECHANICAL TUNER FOR CAVITY RESONATORS Filed April 4, 1945 Patented Feb. zo, 1951 MECHANICAL TUNER FOR CAVITY RESONATORS Palmer P. Derby, Boston, Mass., assignor to Raytheon Manufacturing Company, NewtonMass., a corporation of Delaware Application April 4, 1945, Serial No. 586,610

3 Claims. 1

My present invention relates to electron-discharge devices, and more particularly to tunable electron-discharge devices of the so-calledmagnetron type.

The main object or my' present invention is to provide means' for effecting a mechanical linkage, in a device of the general character indicated,` between tuning means located within saiddevice, and tuning control means located exteriorly of said device.

This, and other objects of my present invention, which will become more apparent as the detailed description thereof progresses, are attained, briefly; in the following manner:

As above indicated, my present invention is especially suitable for use with an electron-discharge device of the magnetron type. I prefer that said device include an anode structure, made of. highly conductive material, suchV as copper, and comprising a cylindrical body provided with a plurality of interiorly-extending, radially-disposed anode members, each adjacent pair of said anode members, together with that portion of said cylindrical body lying therebetween, constituting a resonant line.

I prefer to provide said anode structure with at least one: pair of conducting straps alternately contacting successive anode members, the straps of each pair being so disposed with respect to each other as to present a capacitance therebetween, said capacitance,` together withv the capacitance and, inductancebuilt into the device as a function of the geometry thereof, determining the natural resonantfrequency at which the de- .vicenormally operates.

I further prefer to provide the device with another conducting member, which is adapted to be introduced into the space between they straps of at least one of the4 above-mentioned pairs thereof, the introduction of this conducting member so altering the above referred, to inter-strap capacitance, and adding such other capacitance, as. to therebyv enable the tuning` of the device to a frequency other than its. natural resonant frequency.

In order to control the movement of the last above-referred to conductingV member from the exterior of the device, it is necessary to provide some mechanical linkage between the interiorlylocated tuning means and the exteriorly-located control means, and for this purpose, I. prefer to hollow at leastv one: of the magnetic polepieces associated with the` device for establishing; an appropriate magneticfield, therein, andpass said mechanical linkage through said hollowed pole piece.

In the accompanying, specication E shall describe, and in` the annexed drawing show, an illustrative embodiment of the electron-discharge devices of my present, invention. It is,

however, to be clearly understood that I do not wish to be limited to the details herein shown and described for purposes of illustration only, inasmuch as changes therein may be made withoutthe exercise of invention, and within the true spirit and scope of the claims hereto appended.

In said drawing, the single figure is a longitudinal sectional view taken substantially through the center of a tunable magnetron made in accordance with the principles of my present invention.

Referring now more in detail to the aforesaid illustrative embodiment of my present invention, and with particular reference to the drawing showing the same, the numeral 5 generally designates an electron-discharge device or the socalled magnetron type. Said device comprises an anode-structure 5, a cathode-structure l', magnetic means 8 for establishing ai magnetic eld in a direction perpendicular tothe path oi the electron-flow between said cathode and anode structures, and tuning means 9.

In. the device shown, the anode structure 5 includes a cylindrical body le made of highly conductive material, suchi as copper, said body being provided with a multiplicity of radially-disposed, interiorly-ex-tending anode members in the' form of vanes Il, each adjacent-pair of said venes, together with that portion of said cylindrical body lying therebetween, constituting a resonant line whose natural resonant frequency is, as is well known inthe art to which my present invention relates, a function of the geometry of the physical elements making up the same. I shall iurtherdescribe the anode' members l l when referring, in a later portion of this spe'cilication, to the details" of the tuning means 9.

'Ihe anode structure is closed at its ends, for example, by end plates l2 and |13, with the junctions betweenthe cylindrical body Eil of said structure,` and` said plates l2 and t3, hermetically sealed, as at M,

'I-'he cathode structure l, which. is coaxial with the anode structure li, includes a cathode sleeve I5, conventionally made` ot nickel, or the like, provided: with a reduced portion l 6 whose length, preferably, is coextensive with the width` of the anode` members lll, said reduced portion' t6 being provided with av highly electron-emissive coating lli, for example, of the well-known alkaline-earth metal oxide type.

In order properly to support the cathode sleeve t5 with` respect to the anode members ll, said sleeve may beA reduced, as at i3, to fit into an elongated, electrically-conductive tubular member i9 having, at its outer end, a ferrule closed by a glass seal 2|. Said seal, together with one or more glass beads 2,2 disposedwithin thev tubular member I9, supports a lead-in conductor 223 which` passes through saidmember It` and has its upper end connected, as at 24, to one terminal of a cathode heating filament 25. The other terminal of said filament may be connected, as at 26, to the cathode sleeve I5.

In order to convey current to the lamentz, the lead-in conductor 23 is connected by a conductor 21 to one terminal of a suitable source of electromotive force (not shown), the other terminal of said source of electromotive force being connected by a conductor 26 to a heat-dissipating member 29 fixed upon the lower end of the tubular member I9.

In order properly to support the cathode structure 1, and insulate the same from the anode :structure 6, the tubular member I9 may have VVfixedY thereto a cup-like bushing 3i) sealed into one end of a glass tube 3i, the other end of said `glass tube having sealed therein a tubular bushing 32, in turn, secured to a tubular pole piece 36, constituting one of the components of the magnetic means 3.

Said pole piece 33 may be hermetically sealed, as atr34, into the end plate I2, and be provided Vwith a central bore 35 whereby the cathode structure l may enter the device.

Another tubular pole piece 36 may be hermetically sealed, as at 3l, into the end plate I3, said pole piece and the pole piece 33 being fixed, for example, to the opposite ends of a horseshoe magnet (not shown), whereby an appropriate magnetic eld may be established, as previously indicated, in a direction perpendicular to the path of the electron-flow between the cathode structure 'I and anode structure 6.

Now, by suitably heating the cathode, and applying a proper potential difference between said cathode and the anode, the device can be made to generate electrical oscillations of a wave length determined, primarily, by the capacitance and inductance built into said device as a function of the geometry thereof, and more especially, of the dimensions of the above referred to resonant lines defined by the anode structure.

In order to extract power from the device I may, for example, introduce a loop- 39 between the anode members II defining one of said resonant lines, said loop coupling with the magnetic component of the above-mentioned electrical oscillations. Said loop may, in turn, be connected to a conductor 46 supported in a glass seal 4I fused into an outlet pipe 42, said pipe being threaded and hermetically sealed into the cylindrical body I6 of the anode structure 6.

In the device as thus far described, there is no external control over the frequency of the generated oscillations and, furthermore, because of Vthe numerous paths which the oscillating energy can follow within the anode structure of said device, spurious oscillations are present which reduce the eiciency of the device.

In order to eliminate these disadvantages, I proceed as follows:

Each anode member II is provided, preferably, in both its upper and lower edges, adjacent its inner end, with cut-away portions or slots 43, said slots being receptive of two pairs of concentric conducting straps 44 and 45, and 45 and 4i, the straps of each pair thereof alternately contacting successive anode members II. Said straps present therebetween capacitances entering into the determination of the natural resonant frequency of the device.

It has been found that when alternate anode members are electrically inter-connected as just Vdescribed by theV straps 44 to 41, inclusive, the

4 spurious oscillations above referred to become suppressed.

It has also been found that inasmuch as the straps of each pair thereof have a capacitance therebetween, they may be considered the plates of a capacitor, and by varying said capacitance, and introducing additional capacitance in parallel therewith, the device can be tuned, and this may be accomplished as follows:

A plunger 48, made of highly conductive material, such as copper, is slidably mounted in the bore 49 of the tubular pole piece 36, the inner end of said plunger being recessed, as at 56, to accommodate the upper end of the cathode structure 6, and the extremity thereof being cupped to provide a conducting annulus 5I, which, Ywhen moved, for example, intermediate the straps 44 and 45, constitutes, together with said straps, a Variable capacitor. In order to maintain the device air-tight, Ii provide an apertured flexible diaphragm 52, hermetically sealed, at its periphery 53, to the cylindrical body I6 ofthe anode structure 6, and similarly sealed, at its central aperture 54, to said plunger 48.

The introduction of the annulus 5I into the space between the straps 44 and 45 does two things. First, it reduces the effective area of the surfaces of said straps between which the above-mentioned capacitance exists, but inasmuch as this capacitance is small to begin with, the overall eifect on the frequency of the device is, likewise, small. Second, it forms, together with said straps, two capacitors, connected vin series, which did not, before, exist. Inasmuch as the gaps between said annulus and said straps are small, the total capacitance of the newly formed capacitors is relatively large, and this capacitance, added in parallel with what remains of the original capacitance, has a considerable effect upon the frequency of the device.

There remains to be described the control mechanism of the tuning means 9, by means of which the penetration of the annulus 5I into the space intermediate the straps 44 and 45 may be varied.

While not limited thereto, I prefer to construct such tuning control means as follows:

Secured on the upper end of the plunger 46 is a threaded bushing 55, engageable in a disk 56 whose periphery may be provided with a V-cut 57, constituting a ball-bearing race. Surrounding said race is another race comprised of two cooperating bevelled rings 58 and 59, the ring 5B being carried by a disk 66, and the ringY 59 being pressed into cooperation with said ring 58V by an annular spring 6I. The races are receptive therebetween of bearing balls 62, and the spring 6I is afiixed to the disk 6I) by a flat retaining ring 63 and bolts 64.

The disk 6D is maintained against rotation by being bolted, as at 65, to a plate' fixed, at its center, to the pole piece 36, the plate 66 being provided with bearings (not shown) Yin which is journalled a shaft 61. Mounted upon the shaft 6'! is a worm gear 69 engageable with a worm wheel 'I9 secured to the disk 56 by means of bolts il. The shaft 67 is provided, at one end, with a pinion 12, whereby the same may be manually or otherwise rotated, slidably to move the plunger 43 with respect to the pole piece 36, and 'thus vary the capacitances between the straps 44 and 45, and the annulus 5I and saidstraps.

This completes the description of the aforesaid have provided, in a tunable magnetron, simple means for effecting mechanical linkage between the tuning means located within the magnetron, and the control means therefor, located outside of said magnetron Other advantages of my present invention will readily occur to those skilled in the art to which the same relates.

What is claimed is:

l. An electron discharge device comprising a hollow body dening a portion of an enclosing vessel, an anode and a cathode within said vessel, said anode having portions dening a cavity resonator, conductive members connected, re spectively, to points of opposite polarity on said cavity resonator, a mounting member joined to said body, a guide supported by said mounting member, a driving member slidably tted Within said guide for motion toward and away from said anode, a carrier mounted by said driving member, a tuning member supported by said carrier and extending intermediate said conductive members, means including a flexible bellows forming a hermetic seal between said carrier and said enclosing vessel, and means coupled to said driving member for actuating it to displace said carrier and said tuning member, thereby to tune said cavity resonator.

2. A tunable electron discharge device comprising: an anode structure incorporating a cavity resonator; a pair of conductors connected, respectively, to points of opposite polarity on said cavity resonator; a pole piece carried by said anode 6 structure and provided with a bore; a plunger mounted for reciprocation in said bore a third conductor disposed intermediate said pair of condnctors; and means extending from said plunger and supporting said third conductor.

3. An electric discharge device of the magnetron type comprising a generally cylindrical envelope, a resonant anode structure supported Within said envelope, a `cathode supported from one end of said envelope and a tuning mechanism supported from the other end of said envelope, said cathode and said tuning mechanism being carried, respectively, by magnetic pole pieces which extend through opposite ends of said envelope from the exterior to the interior thereof.

PALMER P. DERBY.

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

UNITED STATES PA'I'ENTS

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