US2611110A

US2611110A - Electronic discharge device of the cavity resonator type

Info

Publication number: US2611110A
Application number: US532012A
Authority: US
Inventors: Donald M Powers
Original assignee: Raytheon Manufacturing Co
Current assignee: Raytheon Co
Priority date: 1944-04-19
Filing date: 1944-04-19
Publication date: 1952-09-16
Anticipated expiration: 1969-09-16

Description

'"iled April 19, 1944 4 Sheets-Sheet l 1 1 L 1 I I Z7 A7 I1; II m EH6 26 Q l-% 27 H Sept. 16, 1952 b. M. POWERS 2,611,110

ELECTRONIC DISCHARGE DEVICE OF THE CAVITY RESONATOR TYPE fink/Hal flaw/ 0 M fbwms,

.20 w/fg Sept. 16, 1952 D. M. POWERS 2,

ELECTRONIC DISCHARGE DEVICE OF THE CAVITY RESONATOR TYPE Filed A ril 19, 1944 4 Sheets-Sheet 2 a6 a 7 Z 1 26 a6 a7 36 UI'IHI" 29 32 I I I I 1 1 1 r I 1 1 1 1 r //l t A 7"0/f.

flan 1940 Fan 4 5,

ELECTRONIC DISCHARGE DEVICE OF THE CAVITY RESONATOR TYPE Filed April 19, 1944 D. M. POWERS Sept. 16, 1952 4 SheetsSheet 5 D. M. POWERS Sept. 16, 1952 ELECTRONIC DISCHARGE DEVICE OF THE CAVITY RESONATOR TYPE Filed April 19, 1944 4 Sheets-Sheet 4 Maw/mt. fio/mw M fflmr/ra, M1,

Patented Sept. 16, 1952 ELECTRONIC DISCHARGE DEVICE OFI'IIHE Y CAVITY RESONATOR TYPE Donald M. Powers, Boston, Mass., assignor to Raytheon Manufacturing Company, Newton, Mass, a-corporation of Delaware Application April 19, 1944, Serial No. 532,012

9 Claims. 1

This invention relates to .a magnetron oscillator of .the plural-anode cavity type which is adapted to generate oscillations of hyper-frequency .having wave lengths of the order of a few centimeters or less. In such devices the wave length which is generated is dependent upon the geometricalsize of each anode cavity, and thus for their short wave lengths the anode cavities must be made correspondingly small. The amount of power which each cavity can generate is correspondingly limited. Thus in a magnetron'in which the usual number of anode cavities exists, the power-which such a magnetroncan deliver is comparatively low. Attempts to increase the amount of power which such a device can develop by increasing the number of the anode cavities have heretofore introduced considerable difficulties. For example, such a device tends to generate various spurious oscillations with a resulting decrease in efficiency. Likewise the effectiveness of anode cavities remote from the output coupling device decreases so that in some instances such anode cavities contribute -very little, if anything, to the power supplied'by 'the device.

An-object of this 'inventionis to devise a magnetron oscillator-which is-capable of generating substantially increased amounts of power of shortwave lengths.

Another .object is to devise such a magnetron in which the e'fiiciency and eiiectiveness of the device as a whole is substantially increased.

A furth'er object is to provide such a magnetron with-a comparatively large number of anode cavities, together with a common cavity resonator into which energy is :fed from a plurality of points on the anode structure.

Astill further :object is to devise an arrangement whereby .the :cavityresonator may be adjusted .to .provideifcr a substantial maximum of coupling "efiiciencywith the oscillating portions of the amagnetron, :and :also to provide means therein whereby :tuning .of :the entire device :may be accomplished through a significant range.

The-foregoing and .other objects of this invention will be best understood from'the following description of exempliiications thereof, reference being had to the accompanying drawings wherein:

Fig. -1 is a vertical cross-section of one embodiment of my invention taken along line I*! of Fig.2.;

Fig. 2is a transverse crossesection "taken-alon line? +2 of Fig. 1;

' thermionic,

.2 Fig. 3 is a. view similar to Fig. 1 of another embodiment of my invention taken along line 33 of Fig. .4;

Fig. 4 is a cross-section taken along. line 4-6 of Fig.3; and

Fig. 5 is a.diagrammaticillustration.ofa cavity resonator.

The magnetron illustrated in Figs. .1 and -2 comprises a tubular anode structure I! made. of a cylinder of conducting material, such as -.cop' per. A plurality of radially-disposed plates .2 likewise formed of a conducting material, such as copper, are soldered in place along the inner surface of the hollow cylinder .1. Each pair of plates, together with the intervening portion of the cylinder I, define .anoscillatory cavity. Each of these cavitiesis small enough to generateoscillations of the desired short wave length. Although each of these cavities iscapableof generating a comparatively small amount of power,

there are provided a comparatively large .number of radial plates 2 and thus acomparatively large number of said cavities in order that the total power of the .device may reach acomparatively high value.

The inner ends of the radial, plates 2, are adapted to serve as .anode faces ,for receiving electrons emitted from the centrally located cathode 3. This cathode is preferably of the indirectly-heated, oxide-coated type having an interior heater .4 and an outer cathode sleeve '5 coated on its exterior surface with suitable electron-emitting oxides. Alternate plates 2 are preferably electrically "connected by means of conducting straps "1, 8., 9 and H3. The

straps

1 and 8 are locatedat one end of the anode structure, the strap 1 being electrically connected to the alternate plates 2, while the strap 8 is connected to the intervening alternate plates. At the other end of the anode structure the strap 9 is connected .to those plates to which the strap '8 is connected, and the strap i0 is connected tothose plates to which thestrap I is-connected. Such a'strap'arrangement decreases the tendency for the device to operate in various spurious modes, and reinforces the tendency of the tubes to oscillate in theprimary desired mode.

The energy developed within the oscillating cavities or chambers is adaptedto feed into a common cavity resonator N. This cavity resonator is formed by thespace between the cylindrical'member l and an-outer cylindrical wall The interior I I into a choke coupler device 29.

of the device is hermetically sealed by upper and lower cap members I3 and I4 hermetically soldered in place at the upper and lower ends, respectively, of the cylindrical members I and I2. A pair of upper and lower magnetic pole pieces I5 and I6 are set into and hermetically soldered in openings in the upper and lower cap members I3 and I4, respectively, thus completing the hermetically-sealed enclosure. The magnetic pole pieces I5 and I6 may be energized with a magnetic field supplied from an external electromagnet or permanent magnet in a manner as shown and described in the copending application of William C. Brown, Serial No. 503,622, filed September 24, 1943, and now U. S. Patent No. 2,416,899. In order to support the cathode 3 within the hermetically-sealed enclosure, said cathode is mounted at the upper end of a hollow conducting tube I? electrically connected to the cathode sleeve 5. Said hollow tube extends through an opening I 8 "formed in the magnet pole I6. The tube II is carried by the upper end of a hollow conducting rod I9; The upper end of the heater 4 is electrically connected to the cathode sleeve 5, while the lower end of said heater is connected to a conductor which extends through the tube II and the hollow rod IS, and passes out through a glass seal 2! carried at the lower end of the hollow rod I9. A metal sealing sleeve 22 is set into and soldered in place in an enlarged opening 23 formed in the pole piece I6 and communicating with the opening I8. One end of a glass tube 24 is sealed to the lower end of the sealing sleeve 22. The other end of said glass tube is sealed to a sealing cup 25 connected to and hermetically joined with the lower end of the hollow rod I9. By the above arrangement the cup 25 serves as the external electrical connection for the cathode, and the cup 25 together with the conductor 20 serve as the external electrical connections to the heater 4. v

In order that the energy developed by the oscillating chambers formed by the anode plates 2 may be fed into the cavity resonator I I, coupling slots 25 are formed through the wall of the cylindrical member I and connect a predetermined number of oscillating chambers disposed around the anode structure with the cavity resonator I I. In order that the impedance of the oscillating anode structure may be matched to the impedance of the cavity resonator, the slots 26 are formed as impedance transformers. For this purpose each slot 23 has a greater length looking into the oscillating anode structure, and a smaller 4 length looking into the cavity resonator I I. This provides an impedance transforming discontinuity 21 within the slot 26. By proper dimension ing, the desired impedance matching may be secured. The energy delivered to the cavity resonator II may be led out to a suitable utilization device by a proper output coupling arrangement. In the present embodiment the cylindrical member I2 is provided with an elongated slot 28, the narrow dimension of said slot appearing in Fig. 2. Said slot feeds energy from the cavity resonator This choke coupler consists of a hollow tubular conducting member 3!] hermetically soldered in place on the external wall of the cylindrical member I2. The member 30 may be provided with a central passage SI serving as a hollow Wave guide. The outer end of the member 33 may be provided with a suitable quarter-wave length choke slot 32. In order to complete the hermetic seal of the device,

a glass member 33 is sealed across the open end of the member 30. A hollow wave guide 34 presented to the end of the member 39, as shown in Fig. 2, will be properly coupled to the device in such a manner that said hollow wave guide 34 will be energized to feed energy from the oscillating tube to a suitable external consumption device. If further impedance matching is desired so as to eliminate reflection within the choke coupler 29, a conducting inset 35 may be inserted in the opening 3i so as to provide an impedance transforming discontinuity therein.

In order that the energy supplied through all of the slots 26 shall combine with maximum effectiveness in the cavity resonator I I, the location of said slots 23 as they enter the cavity resonator I I must be matched to the pattern of waves as established in said cavity resonator. In other words, each slot 26 is preferably located at maximum of the standing wave created in the cavity resonator, and should be in the proper phase relation with respect thereto so as to reinforce said wave. In order to satisfy the above requirements, the distance along the cavity resonator between adjacent slots 26 should satisfy the following relationship:

(Equation 1) where m is any whole number and Ag is the wave length of the Wave within the cavity resonator II. If adjacent slots 26 communicate with oscillating anode chambers which are in time phase with each other, then 114 should be an even numher, while if adjacent slots 26 communicate with anode cavities which are substantially 180 out of time phase with each other, then 111 should be an odd number.

If cavity resonator I I were provided in a completely toroidal form with no ends thereto, the location of the slots 26 in accordance with the above relationships would automatically establish the locations of the maxima of the standing wave within the cavity resonator. Under such conditions it might be diflicult to design a structure in which the relationships as described above are satisfied to a maximum degree, and therefore with a resultant maximum of efiiciency of the device. It is therefore desirable that means be provided for securing some degree of adjustment of the wave pattern within the cavity resonator II for the purpose of matching said pattern to the locations of the slots 26. For this purpose the cavity resonator II is provided with

terminal plates

36 and 31 formed of conducting material extending across and substantially completely closing the cross-sectional area of the cavity resonator. The position of the

plates

36 and 31 may be adjusted by

links

38 and 39 pivoted to the backs of said plates, respectively. Both

links

38 and 33 are also pivoted to the lower end of an adjusting rod 43. The adjusting rod 43 is carried by the lower end of a hermetically-tight bellows 4| sealed in the walls of a tubular housing 42, the lower end of which is hermetically sealed and may be provided with a knurled edge for ready rotation and adjustment of the screw 43. By rotating the adjusting plate 44, the rod 40 is moved longitudinally, thus adjusting the posiacrmro tions of the. plates 36'andf 37. In. order to guide the.

plates

36, and 31; in. their. motion, the. plate 3.6. may be" provided. with a curved rod 316 fitting into a. correspondingly curved sleeve. 37" carried by the plate 31.;

Since the deviceas described; above. is, capable of generating and. delivering large amounts. of power,, it may be desirable. to provide. means for coolingthe device. For. thispurpose holes 45 may be. drilledfllongitudinally throughthe walls of. the cylindrical member. I. These holes teed.v into common passages 46 and 4.1 at the. upper. and lower ends respectively or said cylindrical memberv I'.. Pipes. 48 and 49. may. be. connected to the structure for supplying and. carryingaway the necessary cooling fluid'.. In this way, acooling medium, such as. water. or air, may be. supplied to the device. to keep" its. temperature within reasonableliinits.

The cavity resonator. H is substantially equivalent toa. cavity resonator having. the simple form. asillustrated. in Fig. 5.. Thislcavity resonator has .a length] andialtransverse. dimension 17. The equations relating the dimensions b and l, the free, space wave length. and. the wave. length. Xg within the cavity. resonator. are

I (Equation 2') where. n. an. integer. Also c" A Where c' is substantially the velocity of light, and f is the frequency of" the oscillations generated within the anode structureof the tube..

In order that the. conditions of Equation 1 shall be satisfied, Xg should have. a. particular length dependent upon the spacing between. the slots 26. From Equation 3 wesee that the value of M7 maybe adjusted by varying 1; Such a variation is provided by the. adjustment of the positions of

theplates

36 and 31, as described above, between the surfaces of said plates through the cavityresonaton.

Since the

plates

35 and 31 are formed of conducting material, itisclear that the wave pattern set up-within the cavity'resonator it will have minima at saidplates. We have already seen from the above discussion that the distance between said plates through the cavity resonator H is equal to an integral. number of halfwave lengths. Therefore, the location of the" plates 35 and. 3? also establishes'the positions of the maxima of the wave within the. cavity resonator; Thusa shifting of the .

plates

32 and 3?: a unit around the wave guide will. shift the entire pat ternrofzthezwavetherein, sothatmaxima of said wave may occur attheslots 26. Such a matching of: the. maxima: with the slots: 26 may be accomplished bypredetermining. the position of the pair of plates. 36 and 3.1 in the. initial constructionot the. tube- Also a certain: degree of adjustment can. be secured. by bending the ad justing: screw. 432 so as to displace the plates 3%: and 31' to oneside or-the other of the of the housing 42;

Since the dimension D- appearingin Equation 2 is fixed by the distancebetween the inner sur faces of the caps l3 and Hi, we see from said (Equation) 6 equation thatithe value of'lig; as called; iorbythe adjustment .011 the plates 36' and 31,.wi1l-i'nturn require a particularvalue ofx," and thus a particular value'of as required byllquation 4; For maximum effectiveness; therefore, the anode structure should be designed so that iii-normally tends to oscillate at sucha frequency. If, however; theirequency at which the: anode normally tends to oscillate difiers somewhat from the frequency. as. required bylthev adjustment: of the plates. 35' and; 31, the cavity; resonator M will reflect asuincient" amount ofireactive impedance into. the oscillating anodastructure to pull the frequency. thereof, into' agreement" with the fre-- quency calledlfor' by the value ofil resulting from the. positioning of the

plates

36 and, 31. However, for maximum effectivenessit' is desirable that the normal. frequency'of the anode structure should agree withv the-frequency, as required by that value of. l inwhich the wave pattern within, the cavityresonator I t is matched to the positions of" the slots 26;

A certain degree of tuning or variation in the frequency" of the oscillator may be secured by adjustment of the: positions of the

plates

38 and 31. A variation irrl. varies Ag; and fromEquation 2: we see that with a. fixed value of 5; such a variation should produce a variation-in R. However; attempts to vary' the positions of the

plates

36 and 31 away from a conditionin which the wave pattern in thecavity resonator: ii is matched with the positioned the slots 25 will decrease the efiectiven'ess of" the transfer of energy from. the anode structure to; the cavity resonator. 'I'hus only a comparatively slight degreeof this type-of tuning canbe tolerated in the tube:

If it' i's desired t'o'secure a greater degree of tuning and flexibility of adjustment than: that possible with the embodiment as describedzabove, the arrangementas shown-in Figs. 3; and. 4. may be utilized. In: these: figures the samereferen'ce numerals. which appear in. Figs. 1 and 2. areapplied where the el'ementsare. identical. In the arrangementasshownjinFigszBand 4 the commoncavity'resonator:isformed as a chamber 53 formed by the spacesv between the cylindrical member and. theeouterscylindrical wall member 5| formed of a. suitable conducting; material. The cylindrical wall member 5| eXtends-to'substantially'beyondithe. upper end of.' the cylinder 1, and is hermetically sealed by a cap 52* hermetically soldered in place in the top of said cylinder 51.. The. cap 52- has a central opening a'crcssswhichis sealed a flexible: diaphragm 53. The;di'aphragm1 53 has. rigidly secured to its center a rod. 54. which carries a, tuning member 55; at. its lower end, This tuning member is formed; of conducting; material having a lower ring;-shap e d surface. 56; whichfits into the annular: spacebetween. the'members I. and 5.! and defines the upper s-urface'of the cavity resonator 5.0: The upper end of. the cylindrical member i may: be. closed bya cap 51- soldered in. place thereon. In. order to adjust. thepositionof the surface-56, the;diaphragm 53 has secured. to the center thereofathreaded. stub 58. extending outwardly from.thedevice. The stub. 58 is received in a. threaded. hub 59 of an adjusting p-l'atefit. l'he hub, 5.! is.rotatably mountedjin the cover member 61' bolted onto. the. cap 52. The. adjustingplate. 60. preferably extends beyond. the edges ofthecovermember 6| andis knurled so. as to provide for. a ready rotation of said plate with the consequent adjustment of the position of the surface 56; An upper pole piece 62 maybe placed 7 adjacent the upper end of the structure cooperating with the pole piece It to create a magnetic field within the device, as described in connection with the pole pieces l5 and iii of Fig. 1.

Instead of coupling the oscillating chambers within the anode structure to the cavity resonator 50 by means of slots, the alternative arrangement as shown in Figs. 3 and 4 may be utilized. In this arrangement a coupling loop 63 is placed in each of certain anode chambers.

One end of the coupling loop is mechanically and electrically connected to the inner wall of the cylinder l. The other end of the coupling loop extends out through openings in the cylindrical member I into the cavity resonator 50 so as to form probes 64 therein. The relationship of the probes 54 to the cavity resonator 50 should be substantially as described in connection with the relationship between the slots 26 in the cavity resonator H of Figs. 1 and 2.

Instead of using the type of output coupling as described in connection with the previous embodiment, this second embodiment may be provided with an alternative output coupling arrangement, as shown in Fig. 4. In this arrangement a probe 65 formed as the extension of a conductor 66 extends into the cavity resonator 50. The conductor 58 extends through pipe 6"! and passes out through a glass seal 63 carried by the outer end of said pipe. The pipe 6'! is likewise hermetically sealed in the wall of the cylindrical member 5|. An additional hollow conducting pipe connected to the pipe 81 may surround the conductor 66 so as to form a concentric transmission line through which the energy may be led to a suitable utilization device. The probe 85 should be located at a maximum point on the standing wave within the cavity resonator 50 so as to receive a maximum amount of energization.

When the device as described above is energized, oscillations will be generated in the anode structure, will pass by means of the probes 64 in the cavity resonator 50, and will be led out through the concentric transmission line, including the conductor 66. Since the tuning surface 56 must be free to move up and down in the annular space between the cylinders I and 5| for tuning purposes, there will necessarily be a small space between the walls of these cylinders and the side walls of the depending annular portion of the tuning member 55. However, there will be very little tendency for any of the high frequency energy to be propagated through these spaces. members, a relatively high capacity will exist across the above-mentioned gaps. This high capacity will present a relatively low impedance to the hyper-frequency energy, and thus will substantially short-circuit the gaps. In order to insure against the loss of any hyper-frequency energy through the gaps, the walls of the depending annular portion of the tuning member 55 may be provided with quarter-wave length choke slots extending around the entire circumference of the outer and inner gaps existing between the member 55 and the cylindrical members El and I, respectively. These choke slots therefore present a low series impedance so as to assist in the short-circuiting of the gaps.

The cavity resonator 50 is again equivalent to the cavity resonator as diagrammatically illustrated in Fig. 5, and the Equations 1-4 apply with equal force. In the case of this latter embodiment, the adjustable surface 56 enables the di- Due to the close spacing between these mension b to be varied, while the plates 36 and 3'! enables the dimension Z to be varied.

If we now adjust I so as to match the wave pattern in the cavity resonator 50 to the position of the probes 64 and with a given value of b, the normal frequency of oscillation of the anode structure produces a value of A which does not satisfy Equation 2, the value of b can be adjusted until said equation is satisfied. In this way the system can always be adjusted to a point of maximum efliciency since the anode structure can be permitted to oscillate at its normal unrestrained frequency.

If it is desired to tune the frequency of the device, such a tuning arrangement is also possible. For this purpose the value of l is fixed by the position of the

plates

36 and 31 so as to produce the desired matching of the wave pattern with the positions of the probes 64. This likewise fixes the value of Ag. If new the tuning surface 56 is varied so as to change the value of b, it will be noted that Equation 2 will require a corresponding change in the value of x. This will require a corresponding change in the value of f pursuant to Equation 4. Under these conditions the cavity resonator 50 will re fleet a sumcient amount of reactive impedance into the oscillating anode structure to pull the frequency thereof into accord with the frequency called for by the adjustment of the tuning surface 56. It will be noted, however, that such a tuning adjustment does not disturb the matching of the wave pattern within the cavity resonator to the position of the probes therein.

Of course it is to be understood that this invention is not limited to the particular details as described above as many equivalents will suggest themselves to those skilled in the art. It is accordingly desired that the appended claims be given a broad interpretation commensurate with the scope of the invention within the art.

What is claimed is:

1. A high frequency oscillator comprising an electron discharge tube having a plurality of oscillatory chambers therein, a cavity resonator adapted to be excited by said oscillatory chambers, a plurality of said oscillatory chambers being coupled directly to said cavity resonator at a plurality of points spaced along the length of said cavity resonator, said resonator incorporating adjustable means for shifting the position of the standing wave pattern established therein by said excitation, said resonator having a substantially rectangular cross-section with a dimension axially of said resonator greater than the Width thereof, and means coupled to said resonator for adjusting said axial dimension for tuning said oscillator.

2. A high frequency oscillator comprising an electron discharge tube having a plurality of oscillatory chambers therein, a cavity resonator adapted to be excited by said oscillatory chambers, said resonator having a pair of closed ends defining a predetermined length of said resonator, a plurality of said oscillatory chambers being coupled directly to said cavity resonator at a plurality of points spaced along said length of cavity resonator, means in said resonator for adjusting the position of said ends relative to each other for adjusting said length, said resonator having a substantially rectangular crosssection with a dimension axially of said resonator greater than the width thereof, and means coupled to said resonator for adjusting said axial dimension for tuning said oscillator.

3. A high frequency oscillator comprising an electron discharge tube having a plurality of oscillatory chambers therein, a cavity resonator adapted to be excited by said oscillatory chambers, said resonator having a pair of closed ends defining a predetermined length l of said resonator, I being substantially equal to where n is a whole number and mg is the wave length of the radiations in said cavity resonator, a plurality of said oscillatory chambers being coupled directly to said cavity resonator at a plurality of points spaced along said length of cavity resonator, and separated from each other by a distance of where m is a whole number, said resonator incorporating means for adjusting the position of said ends relative to each other for adjusting said length Z, said resonator having a substantially rectangular cross-section with a dimension axially of said resonator greater than the width thereof, and means coupled to said resonator for adjusting said axial dimension for tuning said oscillator.

4. A high frequency oscillator comprising an electron-discharge device having a plurality of oscillatory chambers therein, and a cavity resonator adapted to be excited by said oscillatory chambers, a plurality of said oscillatory chambers being coupled directly to said cavity resonator, and said cavity resonator being provided with adjustable means for shifting the position of the pattern of the standing wave established therein by said excitation, whereby selected points along the length of said pattern may be selectively located with respect to the points of coupling between said oscillatory chambers and said cavity resonator.

5. A high frequency oscillator comprising an electron-discharge having a plurality of oscillatory chambers therein, and a cavity resonator adapted to be excited by said oscillatory chambers, a plurality of said oscillatory chambers being coupled directly to said cavity resonator at points spaced from each other by a distance where n1 is a whole number and 1g is the wave length of the oscillations in said cavity resonator, said cavity resonator being provided with adjustable means for altering the electrical length Z thereof such that the position of the pattern structure; an anode structure, spaced from said cathode structure, and provided with a plurality of oscillatory chambers therein; a cavity resonator surrounding said oscillatory chambers and being coupled to selected ones thereof, whereby said oscillatory chambers excite said cavity resonator; and means extending into said cavity resonator for shifting the position of the pattern of the standing wave established therein by said excitation, whereby predetermined points along the length of said pattern are matched to points of coupling between said oscillatory chambers and said cavity resonator.

7. In an electron-discharge device: a cathode structure; an anode structure, spaced from said cathode structure, and provided with a plurality of oscillatory chambers therein; a cavity resonator surrounding said oscillatory chambers and being coupled to selected ones thereof, whereby said oscillatory chambers excite said cavity resonator; and a pair of coacting shorting plates movable in said cavity resonator for shifting the position of the pattern of the standing wave established therein by said excitation, whereby predetermined points along the length of said pattern are matched to points of coupling between said oscillatory chambers and said cavity resonator.

8. An electric discharge device comprising a substantially cylindrical envelope having an open end, a space resonant anode structure supported within said envelope, a structure for tuning said anode comprising a hollow metallic cylinder having an apertured end wall for the reception of a portion of said space resonant anode, and a flexible vacuum-tight connection between a second wall of said tuning structure and said envelope.

9. An electric discharge device comprising a substantially cylindrical envelope having an open end, a space resonant anode structure supported within said envelope, a structure for tuning said anode comprising a hollow metallic cylinder having an apertured end wall for the reception of a portion of said space resonant anode, and meansv connected with said tuning structure for producing relative movement between said anode structure and said tuning structure.

DONALD M. POWERS.

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

UNITED STATES PATENTS Number Name Date 2,190,668 Llewellyn Feb. 20, 1940 2,247,077 Blewett et al June 24, 1941 2,261,130 Applegate Nov. 4, 1941 2,280,824 Hansen et al Apr. 28, 1942 2,284,405 McArthur May 26, 1942 2,404,261 Whinnery July 16, 1946 2,409,640 Moles Oct. 22, 1946 2,411,953 Brown Dec. 3, 1946 2,419,172 Smith Apr. 15, 1947 FOREIGN PATENTS Number Country Date 509,102 Great Britain July 11, 1939