US2608618A - Cavity resonator construction - Google Patents

Description

Aug. 26, 1952 R. L. WATHEN 2,608,618

CAVITY RESONATOR CONSTRUCTION Filed Dec. 11, 1945 2 SHEETS-SHEET l INVENTOR ATTORNEY Aug. 26, 1952 R, WATHEN 2,608,613

CAVITY RESONATOR CONSTRUCTION Filed D80. ll, 1945 i 2 SHEETS-SHEET 2 INVENTOR ROBERT W/QTHLN Patented Aug. 26, 1952 UNITED STATES PATENT OFFICE CAVITY RESONATOR CONSTRUCTION Robert L. Wathen, Hempstead, N. Y., assignor to y The Sperry Corporation, a corporation of Dela- Application December 11, 1945, Serial No. 634,303

8 Claims.

This invention relates to cavity resonators which arcuseful at ultra-high-frequencies and, more particularly, to methods of constructing such cavity resonators.

In the construction of cavity resonators it is desirable. especially in electron discharge devices, that the heat that is generated in the resonator be conducted in as efficient a manner as possible to the exterior of the resonator where it may then be dissipated into the surroundings. In order to do this, it is advantageous not only to have the mass of the resonator large, but also that theheat conduction in all directions away from the cavity resonator be large. This prevents local heating from occurring and aids in maintaining all parts of the tube at substantially equal temperatures. Under these circumstances temperature com-pensation may be carried out intelligently and the problem of frequency stability of an electron discharge or other apparatus incorporating a cavity resonator may behandled with greater ease. I

Another desirable feature in the construction of cavity resonators would be the ability to assemble such cavity resonators of diiferent sizes but of the same resonant frequency.

Still another desirable feature in the construction of cavity resonators would be a method whereby the resonators, regardless of the final size and powerratings, could be assembled quickly at any convenient time from a few types of premanufactured parts.

In addition to these desirable features, it. is necessary that the resonators themselves be so constructed that tuning and removal of electromagnetic energy be easily accomplished.

In cavity resonators, which are to be used in electron discharge tubes or similar devices, it is necessary that there be openings in the resonator vide a construction and method of manufacture of [cavity resonators in which the component parts may be manufactured as units and the final resonator assembledat a later time. v

Another objectrof this invention is to provide 2 a convenient construction and method of manufacturing cavity resonators havin large mass and efficient heat conducting properties so as to maintain all parts of the resonator at as nearly an equal temperature as possible.

Still another object of this invention is to provide a novel and convenient construction and method of manufacturing cavity resonators which are to be used in electron discharge tubes In accordance with the present invention, there is provided a novel and improved method of constructing and construction for cavity resonators. This improved method consists of the manufacture of laminations which have a volume removed from them which is similar to the desired cross section of the cavity resonator; for example, toroidal shape. The laminations are preferably thin for ease in manufacture, but in many applications they may he of substantial thickness. The surface of these laminations in most applications is formed of copper or a similar metal of high electrical conductivity. This can be accomplished by electroplating or evaporating metals of high conductivity on the formed laminations, or manufacturin the laminations themselves from such materials. The laminations are stacked together so that the volumes which are removed from them form a cavity with conducting walls. semicircular end sections which may have openings in the shape of semitoroids are placed at each end of the stack of laminations to complete the cavity resonator structure. Theinner surface of these end sections is also copper or a similar metal. 'By a suitable heat treatment thelaminationsand the end sections are consolidated so as'to make one unitary cavity resonator structure. Special ar-, rangements provide for the passage of electrons through the resonator. V a

The invention in another ofits aspects relates to novel features of the instrumentalities de,'. scribed herein for achieving the principalobjects of the invention and to novel principles employed in those instrumentalities whether or not these features and principles are used for the said principal objects or in the said field.

A further object of the invention is to provide improved apparatus and instrumentalities embodying novel features and principles, adapted for use in realizing the above objects and also are adapted for use in other fields.

Gther objects of the invention will be more apparent from the following description taken in connection with the accompanying drawings in which a preferred form of the invention is shown.

In the drawings,

Fig. 1 is a longitudinal cross-sectional View of an electron discharge device incorporating an embodiment of this invention;

Fig. 1A is a cross-sectional view of the embodiment shown in Fig. 1 taken along line AzA thereof;

Fig. 1B is a similar cross-sectional view taken along line BB in Figs. 1 and 1A; 7

Fig. 2 is an oblique exploded view of the'cavity resonator shown in Fig. 1;

Fig. 3 is a cross-sectional view of part of a cavity resonator structure including its tuning mechanism; and

Fig. 4 is an oblique exploded view of a resonator structure incorporating a pair of cavity resonators.

Fig. 1 shows a longitudinal cross-sectional view of a reflex type of klystron, the operation of which is described with respect to Fig. 2 of U. S.

Patent No. 2,250,511. In this embodiment of the invention a substantially rectangular flat cathode I is heated by a long heater coil l I, heating current being supplied through supporting heating leads l2, which terminate in lead-in caps l3 in cathode shell 2|. leads 14 which terminate in lead-in caps l5.

' The electrons which are emitted by cathode ID pass up through the openings in the walls of cavity resonator l6 and are reflected back by a substantially flat reflector electrode ll. This reflector electrode I! is supported by rods l8, which also serve as leads to supply the reflector electrode II with suitable potential. The rods [8 terminate in reflector electrode lead-in caps is. The complete structure is enclosed in an evacuated chamber formed by reflector shell 25 and cathode shell 2| which are Vacuously sealed to the cavity resonator H3. The heater leads I2 and cathode leads [4 are insulated electrically from the cathode shell 2| by glass seals 22. In a similar manner, reflector electrode leads 58 are insulated electrically from the reflector shell 26 by glass seals 23.

The cavity resonator 56 in the above embodiment is shown in greater detail in Fig. 2. In this type of structure, preferably thin laminations 24 (sayfrom .05 to .10 inch) are used. These laminations 24 have volumes 25 and 26 removed from them, in the shape of a narrow central opening 26 and circular end openings 25, the complete openings 25, 26 being similar to the dumbbell cross-section in the conventional toroidalshaped cavity resonator such as shown in U. S. Patent No. 2,242,275. It should be understood that the complete opening 25, 25 could be of many other shapes, as desiredfor the resonator, since the resonator could be of any shape according to the characteristics desired for the device employing the resonator. Since the laminations 24 are preferably thin, aconvenient method of manufacturing would be by punching or stamping out these volumes 25 and 26. However, the invention is not concerned with the manner in which the laminations are fabricated. The volumes 25 and 26 may be removed by milling or machining or the laminations 24 themselves Cathode IE! is supported by 4 might be cast with the volumes and 26 already provided.

These thin laminations 24 are preferably made of copper or a similar metal. However, it is quite possible that they may be made of different metal than copper, but in such a case their surface is preferably of copper of a similar conductive metal.' Thus, for example, they may be constructed of steel or Invar and plated with copper or silver, or they may be cast of iron and sputtered with a good conductor.

In assembly, these thin laminations 24 are separated from one another by pairs of spacers 21 and 25. When viewed in cross section, it is seen that these spacers 21 and 28 also have volumes 29 and 30 removed from them. These volumes 28 and 30 correspond to only the circular portions 25 of the opening in the thin laminations 24. There is no spacer between the laminations 24 adjacent to the central volume 26 of laminations 24 which connects the circular volumes 25.

The spacers 21 and 28 are preferably made in a fashion similar to laminations 24. As in the case of the laminations 24, the essential feature in most applications is that the surface consists of a good conductor. An exemplary method that suggests itself for the construction of these spacers 2'! and 28 is the longitudinal drilling of a bar of copper. After the bar has a hole drilled through it, whose diameter is that of the cylindrical opening 25 of the cavity resonator desired, it is cut into sections of suitable sizes for storing and later as an assembly. Another method that lends itself quite neatly to the mass production of such pieces would be die casting. This would assure uniformity of pieces at a'minimum of cost. The thin laminations 24 and pairs of spacers 2'! and 28 are stacked alternately until a resonator 16 of desired length is obtained. In order end sections could be manufactured in any.

of several ways. One such way is by providing 1 two portions each having half the desired thickness of the complete end section. Half the semitoroidal volume 56 could be removed from each such portion. Thereafter, the two portions could be joined. This would result in a semicircular end section of the desired thickness with the semitoroidal volume 56 removed. The two halves could be preliminarily consolidated to form a unitary end section 55 or they could be merely clamped together and consolidated in a later operation.

After stacking laminations 24, spacers 21 and 28, and end sections 55 together, they are given a suitable heat treatment (i. e., soldering, brazing, etc), so that the component parts consolidate to form a unitary structure. The resonator I6 thus formed can then be used in an electron discharge tube such as shown in the embodiment in Fig. J

As is seen in Fig. 1A, because of the present novel structure, it is possible to have a large unobstructed area 3| across which electrons may flow formed by the separation between the pairs of spacers 2'! and 28. Since this construction permits only a minimum number of electrons which are emitted by the cathode [0 to be intercepted as they pass thru the alternating electromagnetic field of the cavity resonator it allows the usable power or the electron discharge tube to beincreased. l i The cavity resonator 16 thus formed has many of the features which are considered desirable in resonatorconstruction. It has been constructed of components which are themselves quite easy to manufacture. The resulting resonator assembled from these premanufactured partshasa considerable mass surrounding the cavity res onator, such mass having high heat conductivitywhichaids in maintaining all parts of the cavity resonatorat substantially equal temperatures. i As has been discussed, an electron beam of large cross-sectioncan be projected into the alternatin electromagnetic field of the cavity resonator. Since a minimumnumber of electrons in the beam are intercepted the usable power of-the electron tubes usingthis construction is large. Furthermore, tubes of different amounts-of power butwith the same frequency could be assembled as desired merely by stacking a suflicient number of laminations and spacers together until the correct cavity resonator dimensions are obtained, since the resonator frequency is determined by the shape ofthe opening 25, 26 and not by the overall resonator length. Such a cavity resonator, used with a cathode and reflector plate or comparable dimensions, would thus result, when assembled, in a reflex k-lystron of a power output predetermined by the number of laminations used, and Ofcorrect frequency. Thus, by having stock cathodes and reflector plates of different sizes and laminations, spacers, and end sections as described, reflex klystrons could be assembled quickly and con veniently having predetermined power outputs covering a large range, all such klystrons having thesame desired frequency. For different frequencies, different laminations, spacers and end: sections are used, but with the samecathodes and reflectors.

If it is desired to construct a cavity resonator which is not to be used in electron discharge devices, the spacers 21 and 28 can be omitted. In this way, by stacking a sufiicient number of identical laminations 24 and usin two end sections 55, it is possible to quickly and conveniently assemble a cavity resonator from premanuiac-- tured units.

In order to remove electromagnetic energy from the "cavity resonator, coupling loops are used.. Such a coupling loop is constructed in one of the spacers 32, shown in Fig.2. The crosssection of such a spacer 32 is shown in Fig. 1A and in Fig. 1B. A small loop 33, which links the magnetic field in the cavity resonator I6, is constructed within the spacer 32. This loop 33 terminatesin a coaxial line 34 sealed into the rear of spacer 32. vacuum system, the coaxial line glass-t'o-metal seal 35.

Tuning cavity resonators made in accordance 34 includes a 'witht'his invention may be accomplished in a rod 36' is shaped so that a portion ofit forms a continuation of theirmer circular portion of the since the resonator is part of a 6 cross-section of the cavity "resonator 16. As rod 36 is rotated about its axis 38 by knobil, shown in Fig. 1A, the cross-section of the reednator IS-is changed. The resulting fielddis turbancescause a change in resonant frequency.- Knob 39 is sealed to a cylinder which in turn is sealed to the resonator cavity, to maintain the vacuum envelope. If the tuning mechanism is to be used merely as atri'mmer in adjusting the resonant frequency of the cavity resonatorii over small amounts, and quite infrequently, the

walls of'the cylinder 60 may be made of a ductile metal. However, if the tuningmechanismisto be used'r'epeatedly and-over large ranges, it is preferable that the walls of the cylinder be of resilient metal. In such a case, it is necessary to provide some sort of a locking fixture to the tuning'mechanism, such as a lock nut 6| which moves on threads 62 provided on the outside walls of cylinder to. against the face 63 of the end section and maintains the rod 36 in the proper angular post tion after it is turned by knob 39.

Another method of tuning that may be use'din a resonator constructed according to this inverttion is shown in Fig. 3, which is a cross-section of one of the spacers 28. In this method or tuning; a metal bar 40 which extends the length of the" resonator Hi is supported ina recess *whltih is in addition to the removed voluni'e3ll of the spacer 2B and the removed volume 25 of the thin lamination 24. The inside face 42 of the metal bar 46 ordinarily forms a smooth continuation of the resonator wall. By the use of a rod orrods 43 which pass through a vacuum seal' 44 of the bellows type, the metal bar 40 may be moved sideways into the resonator I6, distortingth field therein and causing a change in the resonant frequency.

Although the embodiment of the present iiivention described above uses but a single cavity resonator, it is quite possible to construct mul tiple resonators in the same manner. Fig.4 shows an oblique exploded view of parts for a two-resonator structure. The thin laminations 45 have twovolumes 46 and 41 removedfrohi them. These volumes 46 and 41 are similar to volumes 26 and 25 of the thin lamination- 14" shown in Fig. 2'. Pairs of spacers 48 and 45 have tions 50 and 5| of the spacers 48 and 49,. and the portions 53 i and 54 of the end section 52, are I spaced from one another insuch a manner so ac to provide a drift space of the proper dimensions to allow for proper bunching. of the electronsas they pass up through the space betweenspacers 48 and 43. If internal coupling between the two resonators is desired, one or more of the laminations 45 may have a further opening 10' joining the circular openings 41, 46.

Thus, the manner of manufacture and assent bly of a double resonator is the same as that of a single resonator. The component parts, whose surfaces in most applications are good conductoiui',v are consolidated by proper heat treatment and the resulting structure is a double cavity reso' nator formed of premanufactured parts. Methods of tuning and coupling of electromagnetic energy used in the single cavityresonator may This locking nut 6i shoulders easilybe applied to such a, double cavity reson r. l

;-Thus it can be seen that in accordancewith this invention, a cavity resonator may becon: structed using premanufactured elements and having: any desired length, corresponding to a predetermined power capacity. The mass sur: rounding the cavity resonator would be of sufiiciently high conductivity to allowthe heat which is, generated in the resonator to be quickly conductedtothe exterior, keeping all parts ofthe resonator at substantially equal temperatures. Thus temperature compensation can easily be accomplished with the resultant increase in frequency stability. Furthermore, cavity resonators constructed according to this invention provide means whereby beams of electrons of large crosssection can be projected into the alternating electromagnetic field ofthe cavity resonator with a minimum number of such electrons beingintercepted by the cavity resonator itself, thereby increasing the usable power. Y

Since many changes could be madein the above construction and many apparently widely difierentembodiments of this invention could be made without departing from the scope thereof, it is intendedthat all matter contained in the above description or shown in the accompanying drawin gs shall "be interpreted as illustrative and not in a limiting sense. I

v What is claimed is: L A unitary cavity resonator for supporting electromagnetic oscillations formed of a plurality of thin conductive-surface,laminations having a relatively long dimension, a plurality of relatively said laminations, and a pair of conductive-surface end sections, each of said laminations and end sections having corresponding openings therein, each of said spacers having an opening therein which corresponds to at least part of the opening in saidv laminations ,andend sections, pairsof said spacers being disposed between successively spaced laminations, each pair of said spacers comprising one spacer between adjacent ends: of two laminations and the other spacer between the other endsof said two laminations, said openingsin said spacers being in register with the corresponding part of said openings in said laminations. and forming continuous passages therewith, said successively spacedlaminations and said pair of spacers therebetween'defining gaps surrounded at least substantially by said passages;- said laminations and s'pacers'and end sections being consolidated to forms, unitary structure in which said openings and said passages define a smooth-walledunitary cavity with conductive walls, said unitary cavity being r850 nant at a predetermined frequency for electromagnetic oscillations i 2.- A unitary cavity resonator structure adapted to contain ultra high frequency electromagnetic oscillations, said structure being formed of a plurality of conductive-surface laminations, a plurality of conductive-surface spacers and a pair of conductive-surface end sections, each of said laminations and end sections having corresponding openings therein, each of said spacers having an opening therein which corresponds to at least part of the said openings of said laminations and end sections, said laminations, spacers and and sections being consolidated toform a unitary structure in which said openings define a unitary cavity with conductive walls, said laminations consolidated in said unitary structure defininga plurality of regularly spaced passages parallel to said laminations and transverse the unitary cavityfor' the passage of an I electronstream transverse the, cavity, said unitary cavity being resonant at a predetermined frequency; 7

3..A, unitary r nu1tiple resonator structure adapted, to containultra high frequency electromagnetic oscillations, said structure being formed of a plurality of conductive-surface laminations, a plurality ot conductive-surface spacers and a pair of conductive-surface end sections, each of said laminations having a plurality of separate openings therein, each of said end sections having a similar plurality of separate openings therein which correspond to said first separate openings, each of said spacershaving a plurality of separate openings therein which correspond to at least part of said openings, of said laminations and endsections, said laminations, spacers and end sections being consolidated to form a unitary structure in which said openings define a plurality of cavities of a fixedand predetermined separation, open spaces being provided at regular intervals between successive spaced portions of said laminations in said structure whereby multiple parallel passages extend transverse said cavities through which an electron stream mayv pass to provide tandem interactions with said, cavities, each of said cavities being-resonant at a predetermined frequency. 4. A unitary cavity resonator structure adapted to contain ultra high frequency electromagnetic oscillations, said structure being formed of a plurality, of conductive-surface .laminations, a plurality of conductive-surface spacers and, a pairlof conductive-surface endsections, eachoi saidlaminations and end sectionshavlng Corre-- sponding openings therein, each of said spacers having an opening therein corresponding to at least part of said laminations and end sections, one or more of said spacers having a coaxial line sealed to it, one end of said coaxial line terminating in a coupling .100p located inside of removed portions ;of said spacers, said laminations, spacers and end sections, being consolidated to form a unitary structure in which said .removed portions define a unitary cavity with conducting walls and resonant at a predetermined frequency, said unitary structure including plural parallel passages therethrough along lines'surrounded by said-conducting walls of said unitary cavity, each passage being bounded on two sides by parallel surfaces of successive laminations and being bounded at its two ends by the inner ends of a pair of spacers between the successive laminations defining the-passage. 5. A unitary cavity resonator structure adaptedto contain ultra high frequency electromagnetic oscillations, saidstructure being formed .of a plurality of conductive-surface laminations and a pair of conductive-surface end sections, each of said laminations and end sections having corresponding openings therein, .said laminations and end sections being. consolidated to form a unitary cavity with conducting walls and res o-. nant'at a predetermined frequency,a tuning rod ofnoncircular' cross-section extending through said openings and perpendicular to said lamina,- tions, and'means for imparting rotationa1 dis-' placements to sai'd'rodiabout its longitudinal axis,

whereby said resonant, frequency is correspond oscillations, said structure being formed of a plurality of conductive-surface laminations, a plurality of conductive-surface spacers, and a pair of conductive-surface end sections, each of said laminations, spacers and end sections having corresponding openings therein, said laminations, spacers and end sections being consolidated to form a unitary structure in which said openings define a unitary cavity with conductive walls and resonant at a predetermined frequency, said unitary cavity having at least one straight portion of appreciable length extending transversely through a multiplicity of said laminations, a tuning rod extending an appreciable distance along said straight portion of said cavity. the

longitudinal axis of said rod being parallel to said straight cavity portion and perpendicular to said laminations, and means for varying the less tubular cavity being open to define an endless narrow gap therealong, and a plurality of spaced cross-members extending transversely between said parallel passages and each having a slot extending therealong interconnecting said parallel passages at the narrow gap thereat,

whereby the spaces between successive crossmembers define electron permeable electrode 10 structure surrounded by said endless tubular cavity.

8. Electron discharge tube apparatus, comprising conductive means having an endless tubular cavity, said tubular cavity comprising two oppositely disposed and parallel tubular passages, and two curved tubular end section passages, the innermost circumferential surface portion of said endless tubular cavity being open to define an endless narrow gap therealong, and a plurality of REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date Re. 22,990 Hansen Mar. 23, 1948 2,352,190 Foote June 27, 1944 2,418,469 Hagstrum Apr. 8, 1947 2,433,368 Johnson Dec. 30, 1947 2,440,851 Donal May 4, 1948 2,445,771 Fremlin July 27, 1948 2,450,023

Spencer Sept. 28, 1948

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