US2394008A - Beam resonator tube - Google Patents

Description

Feb. 5, 1946.

J. R. PIERCE BEAM RESONATOR TUBE 2 Shets-Sheet 1 Filed April 9, 1941 ELECTRON STREAM M m 2 a v 6 m H I illlll fl m R x7 I E V v F J. I/IMP 1 /B IN l/E N TOR By J.R.P/ERCE ATTORNEY Feb. 5, 1946. J. R. PIERCE: 2,394,008

BEAM RESONATOR TUBE Filed April 9, 1941 2 Sheets-Sheet 2 J. R. PIERCE BY IN I/E N TOR ATTORNEY vantageously Patented Feb. 5, 1946 Telephone Laboratories,

Incorporated, New

York, N. Y a corporationgof New York Application April '9, 1941, Serial No. 387,602

"1 Claims. (c1. 25-0 27:5)

This invention relates to arrangements for coupling an ultra-high .irequency wave guide with an electron stream through a resonator to form an improved system for effecting velocity variations or some other change in the characteristic of the electron stream in response to electromagnetic energy transmitted by the wave guide. froman electrically distant source or for supplying high frequency energy from the modulated electron stream to the wave guide for transmission to a load device of any suitable kind.

The invention is particularly applicable to wave guides and resonators of a type comprising a conductive boundary surface, usually of metal, surrounding a space or cavity filled with a dielectric, which latter may consist of air.

In accordance with the invention, the wave guide and the resonator have a portion of their boundaries in common and have their interior spaces coupled together by means .of a slit or similar aperture which is located at a position intermediate between the ends of the resonator, the exact position being determined by the desired value of the impedance looking into the resonator, it generally being desirable to match the impedance of the resonator with that of the wave guide at the point of coupling. In addition to the coupling slit above described, the

resonator'is provided with a plurality of aligned apertures through which the electron stream may be projected, usually transversely to the longitudinal axis of the resonator.

It is usually convenient to make the resonator comprise a section of Wave guide one-half wavelength long with conductive closures at both ends. The. natural oscillations of which such a resonator is capable will then produce a maximum intensity of electric field midway between the ends, at which point the electron stream may be adintroduced. In order that the transit time of the electrons in passing through the resonator may be no more than a small portion of the periodic time of the oscillations, the resonator should be relatively thin transversely to its longitudinal axis. A thin wave guide of suitable dimensions for this purpose will be of relatively low characteristic impedance, the value of the characteristic impedance being determined by the ratio, in an electrically long wave guide, of the voltage appearing across the guide to the current flowing in its walls. For conveying power to or from the resonator at high frequencies with low losses, a wave guide of the kind hereinbefore mentioned forms a suitable transmission medium. For best transmission efficiency in the wave guide, the ratio of voltage appearing across the guide to current flowing in the walls should be. high. .In other words, the resonator should be :a guide of low'characteristic impedance and the transmission device should be a guide of high characteristic impedance. In a wave guide of high characteristic impedance in contrast to a iguiden f low characteristic impedance, the walls will be relatively far apart. The problem to whichthe present invention is directed is to couple the different size wave guides together in an efficient manner while at the same time pro-: viding. accessand suitable physical arrangements for introducing the electron stream at the midpoint of the resonator. A direct connection of one guide into the other, as for example by placing an open end of the smaller guide over a hole of equal size in the wall of the larger guide will not mice, 'for in that case the electric field intensity developed in the guide of low characteristic impedance is small and the coupling is inefficient. As hereinbefore mentioned, the position of the coupling aperture along the length of the resonator may be determined so as to provide within wide limits any desired impedance looking into the resonator. Thus impedance matchingbetween, the transmitting wave guide and the resonator may be achieved.

frequency oscillator employing a section of concentric conductorv transmission line as a resonator'an'dcoupled to a hollow cylindrical transmitting waveguide having substantially the same diameter as the inner conductor of the concentric line and forming substantially an extension of the said inner; conductor. In'this case the coupling between the resonator and the wave guide takes place through an annular slit communicating between their interior portions.

In the'drawings: Figs. 1 and 2 are diagrammatic representations of a resonator coupled to a transmission guide, with the place of introduction of the electron stream indicated; 7

Fig. 3 is a'perspective' 'view partially in. crosssection showing an electron beam tube provided with input and output resonators coupled respectively to receivingand transmitting wave guides in accordance with the invention;

Figs. 4 and 5 are cross-sectional views taken at lines 4 and 5, respectively, in Fig. 3;

Fig. 6 shows an alternative form of coupling between a resonator and waveguide; and

A feature" of the invention is an ultra-high characteristic impedance,

dicular to the paper.

ner,

Fig. 7 is a perspective view partly in cross section of an ultra-high frequency generator or projector embodying the invention.

In Fig. 1, I is a wave guide of high characteristic impedance and II a resonator of low The two structures are represented as having different thicknesses in the planeof the paper and may be of the'same or difierent dimensions in the direction perpen-l The resonator H has a total length M2 where i represents the wavelength peculiar to the operating frequency under the conditions existing in the interior of the resonator. Aligned apertures l2 and [.3 are provided for the passage of an electron stream or I beam midway between the ends of the resonator, which will be the position of a voltage anti-node. A common boundary or wall between the resonator and wave guide is indicated at I 4 and contains a slit l5 extending in the direction perpen I dicular to the plane ofthei drawing and providi ing a coupling between the interiorspaces of the guide andrresonator in a manner described in British Patent 507,473, complete specification accepted June 14, 1939. As indicated by arrows in Fig. 1 herewith, and according to the principles set forth in the British patent, the coupling befor the two line'sections always have equal nu merical values and opposite signs regardless of the particular value of 1:0. For the shorter line section, the value of tan cot

the other for the tangent terms in Equation 1,

. two expressions are obtainable which when added tween the resonator and-the wave guide is such I q thata portion of the surface current of the wave guide will flow over the edge of the slit into the resonatoras a source of current therein and con versely a portion of the surface current in the resonator will flow into the wave guide.

The value of the impedance looking into the resonatorthrough the coupling slitma be arrived at, approximately in the following man- The resonator ma beregarded as made up of two transmission lines having their input terminals connected in series. The shorter of the two line sections has a length'of 1 mission lines to be non-dissipative but allowing for the dissipation which is actually present by supposing two equal resistors R to be inserted at the ends of the resonator, respectively, as indicated schematically in Fig. '1. The characteristic impedanceof-theline II will be designated K1,

while the characteristic impedance of the .line

IOwill be designated K2, the line [0 having-the higher characteristic impedance. 1

From the well-known theory of transmission lines working at high frequencies, the sendingend impedance Z11 of a line of length L, characteristic impedance Ki'and terminated in a resistance R is as follows: l

ZH=KIR W T The two sections of line H in question are so related that their lengths add up to with the result that the trigonometric tangents together give the combined impedance of the two line sections with their inputs connected in series, the result being cot cot p Z: K1 K; K, A (2) 1+jg; cot i 1-9 cot' a By simple algebraic and trigonometric manipulation, Equation 2 may be reduced to .the following form: a

Equation 3 shows the combined impedance of the 7 sections to be purely resistive, and determines the value of the resistance as a function of :co for a resonator with given values of K1, A and R. It will be readily observed that the value of Z may be varied over an extended range by varying mo.

For example, if $0 is made'to equal 0, the imthe value of Z comes out 2R, which will be very small for small values of R. Intermediate values of will give intermediate values of Z. If then,

:00 is adjusted so that Z=K2, the line of high 7 characteristic impedance will be perfectly terminated, and in practice a substantial impedance match maybe obtainedflby proper adjustment of the value of mo.

Considering now the relative values of the voltage V1, appearing across the resonator l I, and the voltage V2 present in the line of high characteristic impedance, it is convenient to consider the power relations which hold in the presence of a substantial impedance match; The power P2 7 flowing'in line In is The power dissipated in the two resistances R together is where .112 is the current flowing inthe'resistances. As the center o! line H is distance i J i from either resister R, the voltage at the center of the resonator will be Y .vFKJR From (5) and (:6) 1o RR: Y

Equating the power flowing through the line 10 as-given byEquation 4 with the power dissipated in the resistances as given by Equation 7 enables the desired voltage ratio to be obtained as follows:

Impedance 7 Value The tabulated values give a voltage step-up ratio of ten times.

Fig. 2 shows diagrammatically a modification of the arrangement of Fig. l in which a smoother physical termination of line ll is provided and 5 the slit i5 is shown with rounded edges, the resistances R being omitted.

Fig. 3 shows a vacuum tube amplifier of the electron velocity variation type provided with resonators each coupled to the electron stream and coupled respectively to an incoming and an outgoing wave guide in accordance with the invention. An evacuated insulating envelope i6 is shown containing in its lower portion a heating filament l1, an electron emitting cathode l8 and a collimating electrode [9, the elements l1, l8 and I9 forming an electron gun of known construction. At the upper end of the envelope i6 is shown a target or electron collector 20. The particular form of electron gun, target and envelope employed are not essential to the invention, there being many other suitable forms known to the art. v

An incoming wave guide 2| .iscoupled by means of a slit 22 with a resonator 23. The guide 21 and resonator 23 have conductive Wa'llsfpreferably metallic, for example, copper, and are conductively connected with electrodes .24 and 25. The electrodes have the form of conical frusta' with aligned apertures through which the elec- 7o tron beam from the electron gun is arranged to pass. .A second resonator 26 having similar electrodes 21- and 28, aper-tured for the passage of the electron beam, is coupled through a-slit 28 withan outgoing wave guide 30; i 76 The filament Ll may be] heated by a battery 31 or other suitable source; 'Thecollimating electrode l 9 is conductively connected to the cathode I8 and may also be connected to one side oi the filament [1. The cathode i8 is also conductively connected. to the negative terminal of anger:- celeratingbattery 32,.or other suitable source. The positive terminal of the-battery -32 isweunductively connected to the metallic system of wave guide 2| and resonator 23,'the metallic-syse tem of resonator 26 and wave guide 30, andto the electron target 20. However, other suitable biasing oraccelerating arrangements may be provided instead. Theelectrodes 24, 2.5 2'! and'28 are metallically joined to or form a part of -plates .33, 34, 35 and 36,, respectively, which plates are hermetically sealed to and extend through the walls .of the envelope 16. The plates Stand 3 form a part of the conductive resonat0r23 and the plates 35 and 36 are part of the resonator 2-5. The plates and other parts of each resonator may be welded together or joined conductively any other suitable manner. Adjustable pistons 31 and 38 are provided for tuning resonators 23 and 26, respectively.

It will be noted that the coupling slit .22 is so placed that it extends transversely to the longitudinal axes both on the wave guide 2| and the resonator 23. The slit 29 is likewise transverse to the longitudinal axes of resonator 726' and wave guide 30. In ach case the slit is preferably placed nearthe closed end of the wave guide. The position of the slit with respect to the center of the resonator in each case is determined in accordance with Equation .3 to secure a desired value of impedance looking into the resonator.

The system of Fig. .3 operates in a manner well known in its general aspects. With the electron beam properly collimated and adjusted so as to pass through the apertures in the electrodes 24, 25, 21 and 28 and strike the target .20, the arrangement may be used, for example, to amplify ultra-high frequency waves supplied through the waveguide 2|. The guide 21 is preferably designed to transmit electromagnetic waves of a type whlchwill produce longitudinal surface currents near the closed end of the guide 21 These currents will flow with a vertical component in the end wall of the guide but will also flow over the edge of the slit 22 into the interior of resonator 23 in a manner such as was explained above in connection with Fig. 1. The resonator 23 is preferably adjusted to resonate at the frequency of the incoming wave by adjusting the piston 31. With the proper adjustments, an alternating voltage at the operating frequency is impressed between the electrodes 24 and 25 and reacts with the electron stream to produce a variation in the velocities of the electrons passing between the electrodes. .A substantially fieldfree drift space is provided between electrode 24 and electrode 28 within which the electrons. of the stream, having been differentiated from each other by their velocities, tend to group themselves in bunches. The bunched electrons in passing between the electrodes 2'! and 28 tend to set up oscillations in resonator 26, particularly when the latter is tuned by means of the piston 38 to the operating frequency. The resonator 25 is coupled with the outgoing wave guide "30 by means of the slit 29 in the samemanner as has been described above in connection with the slit 22. .As is well known in the art, the wave supj greater amplitude than that -of the incoming 3 wave in guide 2|, the device thu being characvelope l6.

terized as an amplifier.

Fig. 4 shOWs a cross-sectional view of the res- I onator 26 and wave guide '30 at the line 4-4 in Fig. 3 and indicates that the resonator and-Wave a Fig. 5 shows a cross-sectional viewtaken through the slit 29 at the line 5-5 in Fig. 3.

3 guide may have the same horizontal dimensions I and difierent vertical dimensions, although different horizontal dimensions might also be'u'sed i if desired.

Fig. 6 shows a possible variation in the termi- Fig. 7 shows an adaptation of the coupling ar f rangement of the invention to the case of an oscillator employing a concentric cylindrical resonator and a cylindrical outgoing wave guide. 1 The electron gun elements I8 and I9 are similar to those shown in Fig. 3 and the envelope It Th resonator 40 comprises outer and cylindrical wall which is a continuation of the inner cylindrical boundary of resonator 40. The f coupling slit between the resonator and the wave guide comprises the annular space 45 between the endof the wave uide 4| and a. disc 46, .Apertu'res 41, 48, '49 and 50 are provided for the passage of the electron beam through and beyond the resonator 4|]. The guide 4| is hermetically sealed to and extends through the walls 'oi" thejen The efiective length X of the resonator is preferably a half wave-length of the operating-'frequency. The diameter Y of the wave guide' ll is preferably designed to be in the-neighborhood of eight-tenths of the wave-length of the operat ing frequency in order that it may support electromagnetic waves of the operating frequency, it

being well known that the diameter of a "wave guide of this type will set a lower limit to-the fre quency of the electromagnetic wave which may be maintained and transmitted through the guide.

Thesystem of Fig. '7 will operate as an o's'cil 1 lator provided the initialvelocity of the electrons in the electron beam is'adiusted'sothat the-electron transit timebetween electrode "49 and ele'cproper phase to supply energy to the "elect'romage netic field within the resonator 40 and thus sustain oscillations in the resonator. 'Ihu's adjusted,

the arrangement 'will generate electromagnetic Waves of ultra-high frequency which" willpass through the annular slit 45 into. the 'wave guide 1 4|: and then into the projector42' fromwhich they will be launched into space; "The waves may,

1 contains in addition to the electron gun, thetarget 20 as shown in Fig. 3. The batteries -3| and 32 are provided here also.

, ing means in the form of magnetizing coils 38 i and 39 may be used if desired. A rescinator 4o is joined conductively to a transmission line or wave guide 4| which in turn opens into a projector or horn 42 'for radiating electromagnetic j waves.

1 inne concentric conductive cylinders closed at both ends by conductive end plates 43 and 44, re-

. spectively. The wave guide 4| is bounded by a hollow conductive wave guide with walls re1a-" tively far apart in comparison with the minimum wall spacing of said resonator, said resonator and I said wave guide partially overlapping longitudinally and having a portion of their boundariesin common, said common boundary portion containing a slit interconnecting theinteriors of said wave guide and said resonator, through said common boundary at a point intermediate between the extremities of said resonator, said resonator having aligned apertures in a noncommon portion of the boundary in a line paral lel to the smallest internal dimension of said resonator, said apertures establishing a passageway through the'said resonator, and means for directing and maintaining an electron stream through said aligned apertures.

2. An ultra-high frequency system comprising a hollow cylindrical wave guide and a concentric cylindrical transmission line section, said line section being substantially half a wave-length long at a predetermined operating frequency, the outer diameter of the Wave guide being substantially equal to the outer diameter of the inner conductor of the line section, said wave guide and line section being coaxiaL- said line' section being short-circuited and closed at both ends, said Wave guide extending interiorly into said line section for a portion of the length of the section and terminating therein in a conductive disc, said wave guide having an annular slit constituting a coupling for electromagnetic waves between the interconductor space of the'line section and the interior of the wave guide, said slit being located near the closed end of said wave guide, and said cylindrical transmission line section, said line sec tion being substantially half a wave-length long at a predetermined operating frequency, the outer diameter of the wave guide being substantially equal to the outer diameter of the inner conductor of the line section, said wave guide and. line section being coaxial, said line section being shortcircuited and closedat both ends, said wave guide extending interiorly into said line section for a portion of the lengthof the section, a conductive disc opposite the end of the said inwardly extending wave guide and spaced therefrom, the space therebetween defining an annular slit constituting a coupling for electromagnetic Waves between the interconductor space of the line section and the interior of the wave guide, and said line section having a plurality of aligned apertures midwaybetween the ends thereof providing a passage entirely through both conductors of the line section transversely to'the common axis of saidline section and Wave guide, and means for directing an electron stream through said aligned apertures. 7

4. An, ultra-high frequency electronic'device comprising a first wave guide of extended length and rectangular cross section with conductive walls, a second rectangular Wave guide with conductive walls, a pair of which walls are close together in comparison with the walls of said first wave guide, said second wave guide partially overlapping and being in conductive connection with said first wave guide, said first wave guide being closed by a conductive short-circuiting member at the end near said second wave guide, said second wave guide being closed at both ends by shortcircuiting members and having a length substantially a half wave-length for electromagnetic waves of a predetermined operating frequency, said second wave guide being provided with apertured electrodes forming a gap substantially in the center of said half wave-length, said overlapping portions of said wave guides containing a coupling slit interconnecting the interiors of said wave guides in said overlapping region at a position intermediate between said gap and one end of said second Wave guide, and means for passing an electron stream between said electrodes through the apertures therein.

5. An ultra-high frequency electronic device comprising a relatively thin rectangular wave guide short-circuited at both ends to form a half wave resonator at a predetermined operating frequency, a pair of apertured electrodes formed substantially at the center of said resonator, means for passing an electron stream through the apertures in said electrodes, an extended relatively thick rectangular wave guide closed at the near end by a short-circuiting member, said two wave guides overlapping longitudinally and being placed in conductive contact in said overlapping region, said overlapping and contacting region containing a slit providing a coupling for electromagnetic waves in said respectivewave guides, said slit being located intermediate between the middle and one end of said resonating wave guide.

6. An ultra-high frequency electronic device comprising an evacuated envelope of insulating material, means for maintaining an electron beam within said envelope, 2. pair of conductive plates each having an apertured electrode conductively attached thereto and said plates being hermetically sealed into and extending through the walls 1 of said envelope, conductive members attached to said plates and forming a half wave resonator of rectangular cross section for electromagnetic waves of a predetermined frequency, said resonator being partly within and partly without said envelope,- an extended wave guide having conductive walls one of which is in conductive contact with the walls of said resonator at a position intermediate between the middle and one end of said resonator, said walls being spaced apart materially fartherthan are said pair of conductive plates, the walls of said resonator and of said wave guide in conductive contact being provided with a slit intercommunicating between the interior portions of said resonator and said wave guide.

'7. An ultra-high frequency electronic device comprising an evacuated insulating envelope, a pair of parallel conductive plates, each plate having an apertured electrode attached thereto and both plates being hermetically sealed into and through the walls of said envelope, additional conductive plates external to said envelope and conductively connected with said plates and forming a rectangular shaped resonator for electromagnetic waves of a predetermined operating frequency, said resonator being extended symmetrically on both sides of said electrodes, a rectangular wave guide with conductive walls one of which walls overlaps said resonator longitudinally and makes conductive contact therewith, said resonator and wave guide being provided with an intercommunicating slit in the overlapping region at a position intermediate between the middle and one end of said resonator, and means for maintaining an electron beam within said envelope and passing through the apertures in the electrodes of said resonator.

JOHN R. PIERCE.

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