US2266411A - Electron tube - Google Patents

Description

Dec.' 16, 1941.

' AfG. CLAVIER ETALv -ELECYTRON TUBE l 0rigna1 Filed May 27,v 1938 3 Sheets-Sheet 5 Patented Dec. 16, 1941 Andre Gabriel Clavier and Ernest France, assignors to International Rosts, Paris, Standard Electric Corporation, New York, N. Y.

Original 210,332. 1939, Serial No. 1937 applieationM-a 27, 193s, serial No.V Divided and this application June9, 278,206. In France May 29,

4 Claims. (Cl. Z50- 155) The present invention relates to new electron tubes and their utilisation and to circuits employed with such tubes.

This application is a application Serial No. 210,332, led May 27, 1938.

One of the objects'of the invention is to improve the output and operation of ultra-high frequency systems, for example, employing frequencies correspondingto wave lengths of the order of the decimeter, the centimeter or even of values considerably lower as well as frequencies of higher wavelength.

In order to understand the nature of the present invention, it seems well to make some remarks with regard to the output of the electron tubes employed in particular as oscillators.

The output of the normal oscillator or amplier tubes, that is to say, those in which the time of transit of the electrons remains short with respect to the period of the oscillation, is all greater if the alternating tension between electrodes is a fraction higher than the direct tension in the source of supply (the output impedance being assumed to be ohmic) By applying this reasoning to tubes in which the time of transit of the electrons is comparable to the period, there will be found a double limitation of the output of these tubes. The first is the diiiiculty in achieving output circuits of a sufficient impedance to obtain these high tensions. This limitation is not directly bound up with the use of electronic oscillators. It is simply due to the high frequencies which it isattempted to use.

The second on the other hand is directly conm nected with the method of operation of the tubes. One of the conditions necessary for the operation of the present tubes is that the time of transit of the electrons should not depart too much from. a mean suitable value related in a fixed manner to the period. Now, this type of transit depends upon the value of the alternating tension superposed on the direct tension. Inasmuch as the high frequency tension is small with respect to the direct tension, the above condition is fulfilled. If it becomes comparablev with the direct tension it considerably modifies the `time of transit of the electrons which leave at different moments in the period, and thus limits the amplitude of the oscillation. It vwill. consequently be seen that the high frequency tension must always remain small in proportion to the direct tension. In accordance with this reasoning the output of the electron tubes will thus seem theoretically limited to low values.

division of our co-pending- It is found, however, that the condition offered by normal tubes of only. being able to lead to a good 4output if the alternating high frequency tension becomes comparable with the direct tension is not inevitablein the case of electronic oscillators. This will be seen by considering not arriving at any moment on the positive electrode..

the output but the losses inthe tubes and by seeking for the condition which leads to the minimum losses, that is to maximum output.

In the case of tubes vin which the time of transit is negligible, the lossesfare defined at any moment by the productof the tension and of the instantaneous -current, or more exactly by the product of instantaneous current multiplied by the speed of the electrons (expressed in volts) Inasmuch as the time of transit of the electrons tension of this electrode.

is negligible the two. expressions `areequivalent since in this case the speed of the electrons arriving on the positive electrode is equal to the In the case in which the time of transit is comparable withthe period the speed of the electrons arriving on an electrode is not always that corresponding to the potential of thiselectrode.

This speed may be higher or lower than the speed corresponding to the tension of this electrode. The difference of speed in proportionto the case of a negligible time of transit may become great, in spite of a low high frequency tension, in the case in which the electrons oscillate several times in the high ,frequency elds before arriving on the electrode.y It will be seen that the instantaneous losses in such a tube are no longer given by the product of the instantaneous current by the instantaneoustension. They may be greater or smaller. Thisdiiference is supplied or absorbed by the oscillatory circuit. The output of the tube thus no longerdepends in the same way on the high frequency tension on the terminals of the load. The output is increased if the speed of the electrons on arrival on the electrodeis smaller th-an that corresponding to the potential electrode; it is. reduced if the speed is increased.

The present invention provides arrangements in which the electrons are systematically slowed down by one or more fields of high frequency, and thus supply energy in one or more oscillatory circuits, losing it themselves.

The present invention in accordance with one of its aspects thus permits Vthe said limitations to beV overcome; among others it provides an electron tubeparticularly adapted to the generation of ultra-high frequency waves, employing one or more electronic bundles associated with such means that the average speed of the electrons of each bundle upon their arrival on a target-electrode is less than the speed which corresponds to the difference of potential between the source of electrons and the target.

In accordance with one feature of the inven tion these arrangements are such that the retardation of the electrons is produced in the system repeatedly under the action of theA same high frequency eld, or fields, so as to increase the total energy given by the electrons concerned to the oscillatory circuit.

In accordance with another featureof' the arrangement under consideration, the retardation of the mean speed of the` electrons., is. produced by the magnetic or electroemagnetic high frequency field sustained by the energy given up by the slowing down of the average speed of the electrons.

The invention is not limited to the generation of ultra-high frequency waves and. the tubes described here may be adapted to be employed for the generation, amplication or detection as Well as for Various other applications, such. for example, as in oscillographic systems or television systems, or for measuring apparatus.

The invention will be explained in detail in the case ofthe generation of ultra-high frequency waves and indications will be given with regard to its employ in other fields.

The4 present invention will be better understood by means` of the following description based on the attached drawings in which:

Fig. 1 represents an example of a tube, incorporating the features of. the invention in which the retardation of the electrons is ensured by means of auxiliary cylindrical electrodes;

Fig. 2. is a modification of the device. ot Fig. 1 in which the retardation of the electrons is obtained by. means of a wire wound in a conical spiral; v

Fig.V 3` shows a particular embodiment ofv the invention in. whichV the electronic bundle advances ina zig-zag path; and

Fig. 4 is a section of the `guide electrode structure of. the device of Fig. 3, along the line 4 4;

Fig. 5 shows a device in accordance with certain features ofthe invention employed in the magnetic leld to guide the bundle along the spiral;

Figs. 6 and '7 show a modification of thearrangement of Fig. 5 in which the electron emis sion takes place in one plane; and

Figs. 8 and 9 represent another modication of the device of Fig. 5 employing pole pieces of a magnet as electrodes for retarding the elec,- trons. I

Referring to Fig. 1, an envelope E in which vacuum is made contains an electron. gun. G of the usual type which supplies a bundle of elec-- trons passing through aY succession. of cylindrical electrodes L0, L1, Lz etc., of decreasing lengths and whose axis coincides with that of the bundle. These electrodesare alternately connected to the two poles of an oscillatory circuit which can alterna-tively be composed of a line having a. length` of approximately a quarter wavelength, or a whole multiple Aof a quarter wavelength. At the end of the cylindrical electrode structure is. a target electrode C. Theelectrongun G and thecathode Kv which` co-.operates therewith are respectively fedv by sources of tension S, Si.. The gun G, the middle.. point. of the oscillatory circuit EJ and the target C are connected and brought to the same direct potential. A longitudinal magnetic eld produced by the coil M Will be employed to assist in the concentration of the bundle.

Assuming that the oscillatory circuit has already acertain tension U cos wt let us consider an electron passing from the inside of the electrode L0 to the inside of the electrode L1 at the moment of the maximum of the high frequency tensionn and at the instant when the rst electrode is positive with respect to the second. The electron will be retarded by a value corresponding. involts tothe tension U. If the length of the electrode'Li is such that the electron thus retarded. passes through it in a half period it willagain--be retarded by the same value U in electron-volts, passing from the electrode L1 to the electrode L2 and so on. Finally, after hav- `ing undergone a certain number of times the same retardation it will fall on a plate C and be eliminated.

It will be seen that the length of the electrodes should decrease in accordance with the following The linear speed of the electron is:

or, taking into consideration the constants:

u 0.6 X 1081/volts. cm./sec.

It .will be seenthat for the construction of the tube it is already necessary to choose in advance the tension U in the terminals of the oscillatory circuit, or. rather the ratio between the supply tension Uu and the tension U. This ratio cletermines the law in accordance with which the lengthsof the successive electrodes must decrease.v

If all the electrons clear the interval between the electrodes- Lo and-L1 at the moment of the maximum of the retarding tension, they will finally be retarded n times the value U. The ouput of the tube would be ai U0 y Actually, the passage of the electrons takes place in a continuous manner. If we take wt=, the retardation undergone by an electron passing from the electrode n to the electrode n+1 at the moment corresponding to the phase qb we get:

AuU eos. (qa-me (0.6 108m U U in passing L1 to Lz. The electrons which have undergone an acceleration of U volts take less than a half period to pass through the same electrode and will, consequently, undergo an acceleration smaller than U volts in passing from L1-La It will be seen that on the average a retardation is, found.

The complete calculation of the operation of the tube shows that evenV oscillatory circuit different from that for which the lengths of electrodes have been established, the electronic bundle supplied energy to the oscillatory circuit. In particular, the bundle supplies energy for as small high frequency tensions as desired which indicates that the tube can be started like an oscillator.

In the particular case of a tube in which the length of the electrodes has been established for a ratio U/Un=1/12 andl having ,seven cylindrical electrodes, the output isv 13% if thel efiicient output tension is equal to ,UA/2. If the output tension is equal to 2U/\/2the output is 18%, and if the output tension is U/2\/2, the output is 3%.' If we bring the number of electrodes to thirteen, that is to say, to the maximum possible for U/Uo=1/12, the respective outputs become 13%,35% and 25%. j

Itis clear that in the case in which the total length of the tube is comparable with the wave length of the oscillation thelaw given previously for the calculation of the lengths of the successive electrodes must be modified taking into consideration the distribution of the tension along the tube. Y

In the tube shown in Fig. 1 in which-the spaces between the electrodes are short with respect to the length of the electrodes the electrons are only in the high frequency field,V during a ,small portion of their journey. If the wave length to be produced is-very short such tubes are difficult to carry out. In this case itis preferable to make use of the electric eld of a stronger wave on a tuned line. An embodiment employing this means is shown in Fig. 2. y

. In this figure the electron gun G, target C and the middle point of the tuned line are connected to the same source S so as to have the same direct potential as in the case of Fig. l.

An auxiliary concentrating magnetic eld canalso be provided.

The tuned line is composed of a wire wound in a conical spiral and associated with an outfor a tension of the ample, of a Lecher line is connected to each pair of retarding electrodes, and its middle point is connected to the electron gun G. The reflecting electrodes are connected to a source S3 of potential negative with respect to the cathode. Targets C1, C2 are placed on the two Lecher wires at the end of the structures.

The bundle of electrons F passes between the electrodes R1 parallel to the surface of these electrodes, passes through the interval between the electrodes R1 and the electrodes R2 at a certain angle different from 90, then passes between the electrodes R2. On its approach to the reecting electrode Pz at the outer edges of the electrodes R2 the bundle is returned to the space between R2 as shown, again passes between the plates R1 and is returned by the electrode P1. The bundle thus advances in zig-zag along the structure in order iinally to strike one of the targets C1 or C2.

A tension U cos wt is assumed to exist between the pairs of electrodes R1 and Rz. If the time between the two successive passages through the f interval between the electrodes R1 and R2 is a maintain the concentration of the electron bun-v side circuit 0. By means of this outside circuit stronger waves are created on thisv spiral. As the nodes (or tension loops) are at equal distances along the wire forming thefspiral the axial distance of these nodes (or loops) decreases from left to right in the example shown. We f:

thus get a highl frequency stationary axial field whose tension lloopsvarey more and more close to each other going from left to right, and the elecn tronbundle will undergo a retardation similar to that which it undergoes in the tube, Fig. 1.

Fig. 3 represents another embodiment of a device for the systematic retardation of theY electrons comprising an evacuated envelope E in which are arranged an electron gun G, two pairs of deflecting plates D1, D2 operating in the ordinary way to produce and dene an electron bundle and two pairs of metal retarding plates R1, R2 respectively associated with'metallic re fleeting electrodes P1 and P2. Fig. 4 shows a section of this figure along 'the line 4-4, Fig. 3. The oscillatory output circuit 0 composed, for exhalf period the electrode will be retarded on each journey if it has been retarded on the first journey. If the form of the electrodes is suitably chosen we then find in consequence of considerations similar to those given for the tube of Fig. l that the electrons will be retarded on the average and will consequently supply energy to the oscillatory circuit composed of the tuned transmission line 0.

If the form of the reflecting electrode P1 or P2 is suitably chosen the electro-static field between the main electrode and the reilecting electrode is such that it forms an electronic lens assisting to dle. This eld is represented schematically in Fig. 4 by means of its equipotential lines.

Fig. 5 to which we will now refer gives an embodiment of an electron retarding tube with a magnetic deflecting field;

In this drawing an envelope E in which vacuum is made contains an electron gun G associated with the pairs Aof ordinary deflectors D1 and D2, and retarding electrodes R1 andRz. An oscillatory output circuit 0 connected to the plates R1 and R2 has its middle point in the same potential as the electron gun G. 1

Each retarding electrode is formed of two plane parallel half discs close together, connected at the middle of their rectilinear edges by a Small plate serving as target C1. The half discs also support by radialconnections a target C2 at one point of -their periphery. As will be seen later on, these latter targets are notindispensable.

The operation of such a tube is as follows:

VThe two formulae relating to. the movement of the electrons in a plane perpendicular to a uniform magnetic field H and in a space devoid of electric eld are as follows:

1. The path of the electrons is the radius of a circle:

E p e H in which L p 3.37 Pcm.

U being the speed of the electrons in electron volts and H the magnetic field in gauss.

2. Their angular velocity is:

1:1176 X 10'H sec-1 "'LIt is independent of the speed of the electrons employed: w z. i

The two electrodes Ri and Rz are placedA in a uniform magnetic field H perpendicular'to the planeof theelectrodes. Thefrequency proper f of the oscillatory circuit B is equal to:

An electron bundle F is thrown perpendicularly into the magnetic field and tangentially with respect to the circle formed by the Atwo electrodes. The speed of the electrons ofthe bundle is given in electron-volts by:

r being the external radius'of the electrodes.

Let us recall the term: w=1.'76I-I 107. The electrons will describe a semi-circle in the period l 7F 2f independent of their period. If an electron has crossed the separation between the two electrodes at 4the moment t1, it will kpassv a second time through Vthe separation of theother-side of the electrode of half period later and so on, that is tosay, it willpass the separations at the same moment of the period. Y

If the electron passes the first time from one electrode to the other atthe moment when it-is retarded, it will be retarded-'iri-all` the successive journeys. As moreover,its speed decreases on each journey the radius of its path also decreases and it will describe a spiral which will get nearer to the centre of the electrodes;

If, on the vother hand,-the electron passes the separation the first time atthe moment when it is accelerated it will be accelerated each time it passes by `the same value, in volts; it will describe aspiralwhich gets further and further from4 the centre ofthe electrodes. This acceleration takes place at the expenseI of the energy of the oscillatory circuit in the same way that the retardation takes place to the benet of the energy in the oscillatory circuit.

It is suicient to limit the diameter o f the paths of the electrons in order to limit the energy taken up by the accelerated electrons. This limitation takes place automatically by the limited diameter of the electrodes, but it can'also be obtained by placing targets `in the path of the accelerated electrodes. It is also possible to fix a lower limit to the speed of the electrons by means of targets C1 in the path of the retarded electrons.,

other half retarded the theoretical output of this In order that this may be upheld it is necessary that:

which is easily realised.

If vthis .latter condition is fulfilled as well as the conditionswhich relate theintensity of. the iield to the proper frequencyof theoscillatory circuit, and the feed tensionto the magnetic field and to the external radiusofthe retarding electrodes, the electrons supply energy Vto the oscillatorycircuit. 2. fu.

`Figsand 7 represent another embodiment incorporating features of theinvention.r l.

A-n evacuating. envelope Econtainsa hot circular k.cathode K-ofF any known suitabley type, placed between two` annular plane reflecting electrodes P1 and P2 4concentric with the cathode. Between the plane of the cathode and the refleeting electrodes are arranged-two electrodes R1 andRz` similar to those of Fig. 5, and provided This latter target Cif thus determines the l smallest radius ofcurvature of the paths in the retarded electrons. The ratio between the speed of the electrons before entering the retarding system and thesp'eed of theelectrons on the arrival at the'internal target C1 is given by:

U0 VT2 m. 1lzruu.

rmin. being the distance at the centre of the retarding system to the edge of the target C1.

In the same way the: maximum speed of the accelerated electrons is given by:

internal Yedges of fthe targets C2.

As half the electrons'are accelerated and the with central targets C1 and'peripheral-targets C2. The oscillatory circuit` ilv is connected :to the half-discs Ri and R2 and its-middle` point is connectedl to the positiveside of the -direct source S2. The source S3 maintains theelectrodes P1 and P2 at a negative potential with respect to the cathode. lThe whole of-the device is placed in a uniform magnetic eld of suitable intensity perpendicular to the plane of the electrodes.; v- I The operation of the device is similarto that of the device of Fig. 5 with the exception that the cathodic emissionl takes placeinxthe plane of the cathode towards the centre.` Theeletrodes P1, and Pz serve to prevent thejemission of the electrons outside the .planeof the cathode,

Fiss. 8 and9 showanother mQdi-atonthe tube Structure. shown. infie.

The electrongun `Ceandthe pairs of deflecting plates Di and D2 supply .a thermionicbundle whichmay be exactly directed towards and. toy one sideof a gap betweenv-itwo pole-pieces witnpref.- erably circular. sections Ti and T2. Qfa magnetic substancecovered lwith alayer of good Lconducting metal such as copper, silver etc.; .these pieces are of such shape that at the same .tmetheyconstitute the retarding `electrodes r,corresponding xto the electrodes R1v and R2 of .Fig 5, andtwoituned transmission lines: forming anoutput oscillatory circuit. For this, purpose thepieces T1. andrTz are longitudinally split..assl iown.. TheJength of these-splits is approximately equal to a quarter or to awhole multiple of a quarter ofthe' operative wave length. Targets C1 preferably-of nonmagnetic material, `are-,provided near the centre of the air-gap. Targets simil-arto thetarg-etsCz in Fig..5 can also be .provided ',outsidelfthega The pole pieces Tiqand Tgpassyiirvacuu tight fashion through 'uthep-walls ofthe envelope Eg.; -A magneticfieldis produced inV the;airgap-,either by means of an velectro-magnet .Orby means of permanent magnets. The source S Iis connected between the cathode K' and the electron. gun G which is directly connectedto the .body .of thetwo pole'pieces. Y l .v s.-

The coupling with a loading circuit, such for example asar dipole antenna, can becarried out in any position alongthe tunedv oosillatory cire cuit-T1 or Tzgwhich permits a choicelofithelloading impedance and of the oscillatory circuit by simple adjustment of said position.

The path of the bundle of electrons is indicated at F. The operation of the device is similar to that of the device of Fig. 5.

In the systems employing a magnetic field for the guiding of the bundle the retarding electrodes shown are constituted by discs cut along a diameter, but it is clear that such electrodes can be provided according to the requirements in the form of a certain number of identical sectors, preferably even in number. These sectors may, of course, be such that once assembled they give a polygonal ligure instead of a circumference. These sectors must be alternately connected to the tWo poles of the oscillatory circuit. The relation between the ffrequency of the oscillatory circuit and the intensity of the magnetic eld is changed, the intensity of the eld decreasing in inverse ratio to the number of pairs of electrodes.

When We produce an oscillator device by the means which have just been described We have at our disposal a negative resistance effect which can be utilised in the amplification of electrical oscillations, vfor example, of the same order of magnitude as that of the oscillations Which can be produced by the tube, when the conditions of operation are adjusted to be outside the range of conditions in which self-oscillation occurs.

In the case in which it is desired to employ such tubes as modulated oscillation generators it is possible to provide inside the tubes which have just been described electrodes having an influence on either the intensity or the direction of the electronic bundle or bundles employed.

Other arrangements within the spirit of the invention and Within the scope of the appended claims Will be apparent to those versed in the art. f

What is claimed is:

l. An electron tube comprising an annular electron source, retarding electrodes having at least one substantially flat surface and overlying a substantial portion of the space encircled by said annular source, said electrodes being on each side of said source and the flat surfaces thereof being in planes substantially parallel to the plane of said source, means for connecting retarding potentials to said electrodes, means for establishing a magnetic field perpendicular to the plane of said electron source, whereby electrons from said source are directed toward the center of the space encircled by said source, and a target electrode positioned at the center of said space and between said electrodes, said target electrode extending a predetermined distance away from the center of said space.

2. An electronl tube comprising an annular electron source, retarding electrodes having at least one substantially flat surface and overlying a substantial portion of the space encircled by said annular source, said electrodes being on each side of said source and the fiat surfaces thereof being in planes substantially parallel to the plane of said source, means for connecting retarding potentials to said electrodes, means for establishing a magnetic eld perpendicular to the plane of said electron source, whereby electrons from said source are directed toward the center of the space encircled by said source, and a target electrode positioned beyond the periphery of said retarding electrodes and Within the space bounded by the planes of said retarding electrodes.

3. An electron tube comprising an annular electron source, retarding electrodes having at least one substantially iiat surface and overlying a substantial portion of the space encircled by said' annular source, said electrodes being on each side of said source and the flat surfaces thereof being in planes substantially parallel to the plane of said source, means for connecting retarding potentials to said electrodes, means for establishing a magnetic field perpendicular to the plane of said electron source, whereby electrons from said source are directed toward the center of the space encircled by said source, and circular reflecting electrodes on each side of said electron source and in planes substantially parallel to the plane of said source.

4. An electron tube comprising an annular source, retarding electrodes having at least one substantially flat surface and overlying a substantial portion of the space encircled by said annular source, each of said retarding electrodes comprising a pair of semi-circular coplanar plates, the plates of each electrode having their linear edges adjacent each other and being on opposite sides of the center of the space encircled by said source, means for connecting retarding potentials to saidelectrodes and means for establishing a magnetic field perpendicular to the plane of said electron source, whereby electrons from said source are directed toward the center of the space encircled by said source.

ANDRE GABRIEL CLAVIER. ERNEST RosTs.

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