US2773214A - Velocity modulation tubes - Google Patents

Description

DCC. 4, P. VOGE VELOCITY MODULATION TUBES Filed Feb. 17, 195v 4 Smeets-Sheet 1 JEH/V P. V065 BY 63W@ www@ Wma/9m Mgg@ ATTORNEY Dec. 4, 1956 J. P. voGE VELOCITY MouULATIoN TUBES 4 Sneeuw-Sheet 2 Filed Feb. 17, 1951 lNvENToR JfA/V f? V065 BY di, WM Mw?,- T

ATTORNEY? Dec. 4, 1956 J. P. voGE 2,773,214

VELOCITY MODULATION TUBES Filed Feb. 17, 1951 4 Sheets-Shes*b 3 ATTORNEY Dec. 4, 1956 J. P. voGE VELOCITY MODULATION TUBES Filed Feb. 17, 1951 4 Sheets-Sheet 4 INVENTOR Jf/V E VOGE BY Q7 l QM WM, @am @l /f ATTORNE 5 United States Patent O VELOCITY MODULATION TUBES Jean P. Voge, Paris, France Application February 17, 1951, Serial No. 211,506 9 claims; (ci. 315-6) The .present invention rela-tes to electron discharge 'tubes of the velocity modulation type, and more particularly to a novel form of klystron tube having a wide band of frequencies over which it can be tuned without alteration of the geometrical shape of its resonant cavities.

This application is a continuation in part of my copending application Serial No. 725,682, filed January 31, 1947, now Patent No. 2,614,234.

The klystron tube of my invention includes two hollow body resonators or resonant cavities of essentially prisma-tic or cylindrical shape (in the broad geometrical sense of the word cylindrical). The two cavities, termed buncher and catcher in the terminology of the art, function as wave guides Within which systems of standing waves are established by electromagnetic fields 'which have the same frequency in both, but which are of different .phase wave lengths Ain the two. The systems of lstanding waves are generated and maintained, at least in the catcher cav-ity, by an `electron beam of ribbon shape, i. e., having la two-dimensional extension, which 'is projected through the two cavities across a gap in each separating electron-permeable areas or grids in two opposite faces of the cavities. In passing through the cavity, the electron beam follows trajectories which are perpendicular to the long `dimension of these resonators,

i. e., to the generators or elements of their cylindrical or prismatic surfaces, with the breadth of the electron beam parallel to such generators or elements. In a preferred embodiment, the breadth of the electron beam is in both cavities substantially equal to an integral but different 'number of quarters of the phase wave length of the standing Wave fields existing in `the cavities.

Prior art devices of the klystron typ-e use reentrant chambers or cavities having three principal shapes: reentrant prismatic, reentrant cylindrical in the form of figures of revolution :about an axis perpendicular to the cavi-ty gaps, and reentrant cylindrical in the form of` figures of revolution about an laxis :from said gaps.

Klystrons of the iirst and second types have pencilshaped beams of electrons and klystrons of the third type have centrifugal or centripetal plane starlike Ishaped beams, i. e., beams emitted -by an axial :cathode structure and collected by a ring-shaped collector, or emitted by 'an annular cathode element and collected by an axial collector. In all three types of tube, the ultra-high freparallel to and remote quency `inputto the catcher cavity produces across its gap an electromagnetic el-d the electric vector of which is directed along the line of ,travel of the electrons. The gap areas of the resonators, i. e., the areas of the portions of opposite faces of the resonators which approach each other to form Ithe grids, are so scaled that the electromagnetic field is near its peak value over the entire area at the gaps and, in particular, has no nodes in the region of the gaps. In other words, the electron stream traverses the electromagnetic fields of the cavities near the location where thestanding wave amplitudes are maximum and over paths which, las to all `dimensions yof such paths, are very rn-uch smaller than the phase-wavelength of the oscillations in the resonant cavities.

I have determined by analysis and experiment that by using as cavity resonators prismatic conducting cavities traversed by .a flat ribbon-shaped electron 'beam whose width is parallel to the generators of the cylindrical surfaces to which the cavities conform, the beam having in a preferred form substantially the sam-e width as the height Iof the cavities, and by dimensioning the cavities in s-uch a way that the buncher cavity oscillates over an even number Iof quarter phase wavelengths in the direction parallel to these generators and by dimensioning the catcher cavity so that it oscillates over an odd number of quarter phase wavelengths, the bandwidth lcan be substantially increased.

.It is therefore a major object of my invention to provide an ultra-high frequency electron discharge device of the velocity lmodulated electron beam type having novel internal proportions and having unusual bandwidth characteristics.

A further object of my invention is to produce lan electron velocity modulated tube of large bandwidth without the necessity of corrugated flexible lor otherwise d-eformable walls for the cavity resonators.

A further object of my :invention is to provide a novel ultra-'high frequency device of the velocity modulation type wherein a ribbon-shaped electron beam of twodimensional extension is projected transversely through substantially the total height of the hollow prism'atic resonator means.

A further object of my invention is to provide a prismatic reentrant buncher cavity reson-ating on an even multiple of quarter-wavelengths and :a prismat-ic reentrant catcher cavity of substantially th-e same height as the buncher and resonating on an lod-d multi-ple of quarterwavelength, both chambers being traversedby 4a wide ribbon-shaped electron beam over their height.

The foregoing and other objects of my invent-ion will be best understood from the following description of a preferred embodiment thereofreference being had to the accompanying drawings wherein like numerals of reference indicate Isimilar parts throughout the several views and in which:

Fig. l is a schematic view of ,a klystron tube intended to illustrate certain theoretic-al considerations on which the -invention is based;

Figs. 2 and 3 are respectively a vertical longitudinal section and a horizontal cross-section of an electron velocity modulation tube embodying my invention, Fig. 3 being taken on line 3-J3 of Fig. 2 and Fig. 2 being taken on the line 2 2 of Fig. 3;'

Figs. 4 and 5 are respectively perspective views of the bu'ncher and catcher cavities of the klystron of Figs. 2 and 3; and l Fig. 6 is a diagram for the'calculation of the cross sectional dimensions of the cavities in klystrons ac-cording to my invention.

Referring to Fig. 1 which is idealized, and using the no-tation of Arthur E. Harrison, Klystron Tubes, Mc- Graw-Hill, 1947, the instantaneous voltage across the input gap 1 between grids lland 12 of the buncher cavity is:

E=E1 sin wifi 'i2=2111(x) sin @1oz-10) where I0 is the number `of electrons entering the cavities parameter, z2 the time of arrival in the output -gap for an electron leaving the input gap at time ti, and To the transit time from buncher to catcher for an electron with average velocity. Maximum current i2 occurs when the bunching parameter has a value of 1.84.

Let Rs be the shunt resistance .of the catcher `resonator and C the capacity between its grids 4 and 5, spaced d centimeters apart. Then,

:0.088'10-12 farads l) where A is the area of the grids .in square centimeters (perpendicular to the plane of Fig. 1). The Q of cavity 2 will then 'be vgiven by and the output voltage by:

EFRaFf-.a on

For a given amplification factor (i. e. a given Ez) and for i2 maximum (bunching parameter equal to 1.84) and i a given angular frequency w1, the Q factor will be proportional to C as shown by Equation (.3).

The invention is concerned with increasing the bandwidth of the tube. To this end it would be desirable to reduce Q by reducing C. Equation (1) implies that this can be achieved by reducing A or by increasing d. Neither of these solutions is desirable, however, because a reduction of A reduces the intensity lo of the beam and hence the intensity of i2, while increasing d introduces perturbations into the operation of the tube in View of the ei'iect of transit time between the grids 4 and 5.

`instead, Vlet the grids f and 5 be considered as forming the two conductors of a transmission line of length L2 transverse to the `direction of propagation of the beam and supporting a system of standing waves. The line will have a characteristic impedance Ze Yand is shortcircuited at its end 6. The impedance of the line at the end opposite the short circuit is Here ,82 is the phase constant in the geometric propagation constant of the line. See Principles of Radar,

one obtains RS=QZ tan/8212. l For a given Rs, Q may be reduced by selecting 6212 as nearly to as desired. According tothe present invention one chooses for the catcher a mode of vibration such that the length of the cavity traversed by the beamis equal to an odd number of quarter phase wavelengths, i. e., so that `flzlz is equal vto K being an integer.

According to a further feature of the invention the output coupling loop is located close to the Open-circuited end of the grids 4 and S and the catcher cavity is closed oil at this end by a rounded chamber of low height, i. e. of low extension along the length of the generators of the main catcher cavity cylinder or prism.

It is known that Ithe ybunching parameter is proportional both to the drift distance and -to the peak value ot the input modulation voltage (voltage across the gap of the buncher cavity). In order to have a peak value of E1 in the buncher cavity substantially higher than the peak value of the voltage in the input line which is coupled to the buncher cavity, one chooses for the buncher cavity a `Inode of oscillation such that the height Vor length of this cavity which is traversed by the width of the electron beam is equal to an even number of quarter phase wavelengths, and the input line coupling loop is located at a node of the oscillations, i. e. either close to the bottom wall or to t-he top wall of the buncher, which is closed at both ends by a conducting plate or wall. In this way E1 can be increased, permitting -a reduction in the drift distance without changing the bunching parameter.

In Fig. l, there is shown at 7 a wide, tlat, ribbonshaped electron beam having a width equal to the cornmon heights l1 and l2 of the grids of the cavities il and 2 and of very small extension in the direction perpendicular to the plane vof the igure. 8 `represents the standingwave pattern of the electric iireld in the buncher Acavity as a half wave with nodes at the short-eircuited terminals 9 and i@ of the grids lli andiZ. i3 represents the standing wave pattern of the electric tield in the catcher cavity `as aV quarter wave with a node at the short-circui'tedterminal 6 of grids 4 ant 5 and with an anti-node at the open circuited end of these grids.

The input coupling loop Mi is located close to anode Of ,the sinusoidal standing wave pattern 3 and the output coupling loop 15 is located close to the maximum amplitude or the sinusoidal standing wave pattern 13. `lt is to be borne in mind, of course, that the dimensions of the grids are small in directions perpendicular 'to 'the plane of the iigure.

Referring now to Figs. 2 and 3, 2 l represents a vacuum tight envelope of some Asuitable material such as glass'. inside the envelope ls an electrode assembly 202 supported by a pair of standards 293 which are sealed through the wall of envelope Ztland constitute lead-in conductors to the cavity resonators for connecting them to a suitable unidirectional source of potenti-al 204, shown as a battery.

The electrode .structure 2&2 comprises a cathode. heater 205 which may for example be in the form of a helix fed from local source 2% through one pair of lead-in wires 207.

A long Hat-shaped cathode has its exterior face (Fig. 3) coated with a mixture of barium .and strontium or of other suitable thermionically emissive material. Cathode 263 is supported between insulating spaces 269 and 2l@ and is connected to lead-.in conductor 211.

i2 is a line-focussing and accelerating electrode cone Vnected to lead-in conduct-or li; and thence to a suitable voltage positive with respect to the cathode, supplied for example by a tap `on the battery 264 as shown.

To the right .of the collector Ztl/ the glass tube envelope is replacedl by a metallic membrane 2&6 sealed to the glass and provided with cooling tins 2K7.

The buncher and catcher resonators 218 and 219 are of, rectangular reentrant cross section. These cavities are bounded by a common thick metal bottom wall 220, outer smania.

lateral walls 221 .and 222, a common .separative wall 223, `front wall 224 and rear wall 225 and by walls 227 and 228. Walls 224, 223 and 22S are provided with flat rec tangular slots extending, in the embodiment shown, over the total height of the cavities and aligned lineally with p each other and with cathode 298 and collector 214. The

p with cathode and collector. This corridor and cavity 218 are further bounded by common top-wall 229.

The cavity 219 is extended in an upward direction, i. e.

in the direction of the generators, by means of a cavity of rectangular cross-section 230. `The cavity 230 is Without nreentnant portion and is of low height or short extension `in the direction of the prismatic elements. The cross-sectional dimensions of the cavity 230 are larger than those of the cavity 219 and it is closed at the top by means of a top wall 231. The transition between the lateral walls of cavity 219 and the lateral walls of the cavity 230 is effected by means of a rounded portion 232 best seen in Fig.

All the walls bounding the cavity resonators are of copper or some `good electrically conducting material ormay be plated with a good conducting material. y

p Upper and lower insulating spacers 269 and 210 surround the cavity assembly `and are affixed to `the top and bottom walls 229 and 220 by screws 237.

On either side of the rectangular slots in the walls 224 and 225,` and at either side of the ends of the field-free drift space corridor bounded by plates 227 and 22S, there are provided vertical rod-like supports 23S of small diameter supported parallel to the generators of the prismatic cylindrical cavity v-olumes. Fine wires are wound `on these rods to form grids 233 and 234 for the buncher and 235 and 236 for the catcher. All four grids are therefore of substantially flat rectangular shape and have the same shape .and area as the cathode 208and collector 214. i

Input loop 239 extends through an opening in cavity 218 and is located near its top-wall 229. One of the ends of the loop is connected to the inner side of wall 221 of cavity 218.

`Output loop 240 extends through an opening in cavity 219 and is located at the non-short-circuited portion of grids 235 and 236, i. e. adjacent the beginning of flared wall portion 232. Loop 240 has one end connected to the inner side of wall 221 of cavity 219.

` Loops 239 and 240 are provided with conducting extensions 241 and 242, which are surrounded by tubular conductors 243 and 244, the inner ends of which are fastened to the outer side of wall 221 around the openings through which said loops project. Conductors 243 and 244 are sealed through the wall of envelope 201 and gas tight bus-hing seals 245 and 246 are l-ikewisevprovided Within them. Conductors 243 and 241 constitute the input concentric transmission line and conductors 244 and 242 constitute the output concentric transmission line through which the ultra high frequency'power is efectively led `from the'tube.

t `It the tube is to be operatedfas an amplier the input line is connected to the source of signals to be amplified while the output line is connected to a load. If the tube is to be operated as an oscillatorthe input and output lines are connected together bya transmission line of suitable length, all as is well known to those skilled in the art.V

By way of example, there will now be considered the design of a klystron amplifier according to my invention intended to operate on a centimeter wavelength and having prismatic resonant cavities 8 centimeters in height. Let the letter l represent the height of the cavities, i. e.

width of the electron beam; b their depth in the direction of the beam trajectories, and 2a the width of their reentrant portions perpendicular to the width of the beam (see Figs. 4 and 5). Let represent the length of the gap. With the subscript 1, these quantities refer to the buncher, and with the subscript 2 they refer to the catcher.

The cavity 218 must possess dimensions such that it will oscillate in a system of standing Waves having a half phase wavelength in directions parallel to its generators or elements. Since the height is to be 8 centimeters, the phase wavelength Agn is to be 16 centimeters and the cutoff wavelength )mi is givenby Consequently het: 12.64 cm.

Fig. 6 is a graphv in which .the quantity if *2b for reentrant prismatic cavities is plotted as a function of the parameter a/b for different values of the parameters The curves drawn in solid lines correspond to Curve 601'` is for If, moreover,

is to be 0.8, then C1=1.5 cm. p The abscissa .4 and the ordinate S intersect at the point 604 on the curve 602 for which @1 5;-02 and accordingly 1:02a Cm.

The` cavity 218 is thus completely determined.

In its prismatically reentrant portion traversedrby the beam, the cavity 219 must oscillate in a system of standing waves one quarter of a phase wavelength long parallel to the: generators of the cavity. Since its height or length `is 8 centimeters, its phase wavelength Mp2 Vwill be 32 l. centimeters and it's -cutolf wavelength )tez will be given by M2: 10.52 cm. In order to employ for both cavities the same lateral exterior 'walls Vand the same walls for the drift space corridor, i, e. vto make 2521, 2'2'2, 227 and 228 common to the two cavities, one chooses` The abscissa t2 and the ordinate 2.1 intersect at the point 605 through which passes the solid line curve 606 corresponding to This gives 62:0.85 cm. and the cavity 219 is completely etermined as to its prismatically reentrant portion.

`The magnitude of the short dimension e for the rectarb gular cavity 230 which closes the cavity 219 at its upper Vextremity is chosen so as to give to the cavity 230 a cutoff Wavelength 2e' greater than l() centimeters. For example, e=6 cm; will be a suitable value. The two portions 219 and 230 of the catcher cavity are coupled by means of the curved boundary 232. Y

Operationrof my klystron is as follows:

Referring to Figs. 2 and 3, heater 205 raises cathode 208 to a temperature at which it emits electrons. These electrons are accelerated under the action of the positive potential applied to electrode 212 into cavities 218 and 219 and pass through the gap between grids 233 and 234. Across this gap, electrons are modified as to velocity by the input field in chamber 218 and continue their travel through the field-free corridor between plates 227 and 22S with the electrons having normal or unaffected speed overtaking previously dispatched slower electrons and, in turn, being overtaken by speeded-up electrons started at a later moment. ln accordance with classical theory, the proper bunching of electrons takes place across gap between grids 235 and 236. The electrons accordingly represent a concentration of energy in the said gap and give up energy to resonator chamber 219 which oscillates with a reduced VQ without sacrificing the shunt resistance as set forth above.

InV the foregoing ydescriptive specification I have describcd'a particular embodiment of the principles of my invention, but these principlesrare capable of application in many alternative forms, which will be evident to those skilled in the art. For example, I have described the buncher cavity as resonating upon half a wavelength and Vthe catcher cavity as resonating upon a quarter-Waveclosed by conducting material and conforming substantially to a prism whose principal section is a reentrant polygon, a pair of parallel electron-permeable grids vof similar and equal rectangular shape one formed in a reentrant face of the buncher cavity and the other formed in a face of said buncher cavity opposite the said reentrant face, said grids extending in the direction of the buncher cavity prism elements over that proportion of the height of the buncher cavity prism represented by a simple fraction whose numerator and denominator are small integers, an input coupling loop in the buncher cavity located distant from one end thereof by a simple fraction of the said prism height, the numerator and denominator of the said fraction being small integers, said numerator being a multiple of two and said denominator being a multiple of four, a catcher cavity substantially enclosed by conducting material and conforming except at `one end substantially to a prism whose principal section is a reentrant polygon, the cross-section of said catcher cavity being different from the cross-section of said buncher cavity, a pair of electron-permeable grids in opposite faces of the prismatic portion of the catcher cavity of substantially the same size, shape and disposition as the buncher cavity grids, a non-reentrant supplementary cavity of greater cross section than that of the prismatic portion of the catcher cavity closing one end of the catcher cavity, means to support the buncher and catcher cavities parallel with their grids in alignment, means t0 generate an electron beam of two-dimensional extension having a width substantially equal to the height of said grids, means to accelerate said beam through all of said grids, an output coupling loop in the catcher cavity located adjacent the junction between the supplementary cavity and the prismatic portion of the catcher cavity, said catcher cavity having in its prismatic portion such cross section and height that an electromagnetic iield of the frequency of a eld which in the buncher cavity will have a phase wave length of whose quarter the height of the buncher cavity is an even multiple will in the catcher cavity have in propagation down the catcher cavity a phase wave length of whose quarter the prismatic height of the catcher cavity is an odd multiple.

2. An electron discharge tube of the velocity modulation type including buncher and catcher cavities, a cathode and a collector electrode, input coupling means linking with the volume of the buncher cavity and output coupling means linking with the volume of the catcher cavity, the buncher cavity conforming substantially to a cylindrical solid, a pair of electron-permeable grids occupying substantially equal areas on opposite faces of the buncher cavity cylinder, said areas having in the direction of the generators of the buncher cavity cylinder a dimension substantially equal to an even number of quarters of the phase wave length of a eld of given frequency vibrating in a fundamental mode of the buncher cavity cross section, the height of the buncher cavity cylinder being substantially equal to an even number of quarters of the said buncher cavity phase wave length, said input coupling means being located in thebuncher cavity adjacent a node of the standing Wave pattern of radiation having said buncher cavity phase wave length, the catcher cavity including a re-entrant cylindrical cavity closed at one end by a right section of said catcher cavity cylinder and closed at Athe other end by a non-reentrant supplementary cavity, the catchercylindrical cavity having such length and cross section that radiation of the Asaid given frequency vibrating Withinlthe catcher cavity according tothe said mode vhas a phase wave length whose quarter is an odd submultiple of the cylindrical catcher cavity length, and said output coupling means being located remote from said one end of the catcher cylindrical cavity an odd number of quartersof said catcher cavity phase Wave length.

3. An electron velocity modulation'discharge device comprising in combination narrow rectangular cathode and collector electrodes, rbuncher vand catcher reentrant prismatic cavity resonators of substantially the same height with each other and with said cathode and collector electrodes but of different cross sections, said resonators being adapted to have a. ribbon-shaped electron stream emitted by said cathode pass through narrow electron permeable sections in said resonators extending overthe total height thereof, said buncher cavity being shortcircuited at both ends and said catcher cavity being shrtcircuited at one end only, a non-re-entrant supplementary cavity coupled to the other end of the catcher cavity, the buncher cavity being adapted to oscillate in a system of standing waves having a half-phase-wavelength equal to its height and the catcher cavity being adapted to oscillate in a system of standing Waves having a quarter-phase wavelength equal to its height, and means for applying input energy to the buncher and for extracting output amplified energy from the catcher.

4. A velocity modulation electron discharge device comprising in combination narrow rectangular cathode and collector electrodes, ybuncher `and `catcher reentrant prismatic cavity resonators of different cross sections but of substantially the same height with each other and with said cathode and collector electrodes and adapted to have a ribbon-shaped electron stream emitted by said cathode pass through narrow electron permeable sections extending over the total height thereof, the buncher resonator being short-circuited at both ends and the catcher resonator being short-circuited at one endV only, a supplementary cavity resonator coupled to the other end of said catcher resonator, the buncher resonator being adapted to oscillate in a system of standing waves having a half-phase-wavelength equal to its height and the catcher resonator being adapted to oscillate in a system of standing waves having a quarter-phase-Wavelength equal to its height, means for applying input energy to said buncher resonator located near one end thereof, and means for extracting output amplified energy from the catcher resonator located near the junction of the catcher and supplementary resonators.

5. An electron discharge tube comprising two cavity resonators each conforming at least in part substantially to a cylinder whose principal section is a plane figure having a re-entrant portion, the principal sections of said two resonators being of unequal areas, each said resonator having on one of its re-entrant faces and on an exterior face a substantially rectangular electron-permeable grid, all four of said grids extending over substantially equal lengths parallel to the elements of the cylinders, the first of said resonators being short-circuited at both ends, the second of said resonators being short-circuited at one end only, a supplementary cavity resonator coupled to the other end of said second cylindrical resonator, said cylindrical resonators being supported with their cylindrical elements parallel and with said four grids in line with each other, a cathode adjacent a first one of said cylindrical resonators adapted to generate a ribbon-shaped electron beam having a width substantially equal to the length of said grids, and means to accelerate said beam through all of said grids, the first of said cylindrical resonators having a cross section adapted to provide over the length of said first cylindrical resonator for energy of a frequency at which said first cylindrical resonator resonates a path substantially equal to an even number of quarters of the phase wave length of such energy in propagation lengthwise of said first cylindrical resonator and said second cylindrical resonator having a cross section adapted to provide over the length of said second cylindrical resonator for energy of the said frequency a path substantially equal to an odd number of quarters of the phase wave length of such energy in propagation lengthwise of said second cylindrical resonator.

6. An electron discharge tube according to claim including input coupling means located distant from one end of the first cylindrical resonator by an even number of quarters of the phase wave length of energy of said frequency in propagation lengthwise of said first cylnd drical resonator and including output coupling means located distant from said one end of said second cylindrical resonator by an odd number of quarters of the phase wave length of energy of said frequency in propagation lengthwise of said second cylindrical resonator.

7. An electron discharge tube comprising two cylindrical cavity resonators of substantially the same height and of diierent re-entrant cross sections, the first of said resonators being short-circuited at both ends and the second being short-circuited at one end thereof only, a supplementary cavity resonator coupled to the other end of said second cylindrical resonator, said supplementary cavity having a greater cross section than said second cylindrical resonator, said cylindrical resonators having each two electron-permeable grids formed in opposite faces thereof, said grids extending over substantially the total height of said cylindrical resonators, means sup* porting said cylindrical resonators with their grids in line and parallel to each other, a cathode adjacent a first one of said cylindrical resonators adapted to generate a ribbon-shaped electron beam having a width substantially equal to and aligned with the length of said grids, means to accelerate the beam through all of said grids, means to couple a radio frequency field into said first cylindrical resonator, and means located adjacent the junction between the second cylindrical resonator and the supplementary resonator to couple out radio frequency energy from. the second of said cylindrical resonators. v

8. An electron discharge tube comprising a buncher cavity resonator conforming at least in part substantially to a prism having lateral, top and bottom walls of conductive material and having a re-entrant cross-section adapted to provide over the length of said buncher resonator between its top and bottom walls for energy of a frequency at which said buncher resonator resonates a path substantially equal to an even number of quarters of the phase wave length of such energy in propagation lengthwise of said buncher resonator, a catcher cavity resonator conforming at least in part substantially to a prism of the same length as said buncher resonator, said catcher resonator having lateral and bottom walls of conductive material and being open-ended at its top and having a re-entrant cross-section adapted to provide over the length of said catcher resonator for energy of said frequency a path substantially equal to an odd number of quarters of the phase Wave length of such energy in propagation lengthwise of said catcher resonator, a non-reentrant supplementary cavity resonator, of conductive material joined to said catcher resonator at the top thereof, said supplementary resonator having a greater crosssection than that of said catcher resonator, four electronpermeable grids disposed two on each ofthe buncher and catcher resonators and extending over substantially the total lengths of said buncher and catcher resonators parallel to their prismatic elements, means to support said buncher and catcher resonators with their prism-atie elements parallel and with said four grids in line, a cathode adjacent said buncher resonator adapted to generate a ribbon-shaped electron beam having a width substantially equal to the common length of said buncher and catcher resonators, means to accelerate the electron beam from said cathode through all of said grids, means to couple a radio frequency held into said buncher resonator, and means located adjacent the junction between the supplementary resonator and the catcher resonator to couple out radio frequency energy from the catcher resonator.

9. An electron discharge tube according to claim 8 in which the means to couple the radio frequency iield into the buncher resonator is located distant from one end of the buncher resonator by an even number of quarters of the phase wave length of energy of said frequency in propagation lengthwise of said buncher resonator.

(References on following page) References Cited in the le of this patent UNITED STATES PATENTS Litton Oct. 13, 1942 yLitton Dec. 22, 1942 Fremlin Nov. 26, 1946 Marsh et al. Mar. 29, 1949 1,2 Woodyard et a1 Apr. 5, 1949 Harries Apr. 26, 1949 Law May 24, 1949 Harrison Sept. 27, 1949 Sunstein May 30, 1950 Bonne et al. Nov. 6, 1951

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