US2220556A - Ultra short wave device - Google Patents

Description

1940- H. L. THORSON 2,220,556

ULTRA SHORT WAVE DEVICE- 7 Filed March so, 1939 ll 2! 26 27 2f .28 40 I Inventor:

Harry L..Tho'rson,

His Attorney.

Patented Nov.

2,220,556 I barns snon'r WAVE DEVICE Barry L Thorson, Schenectady, N. Y assignor to General Electric Company, a corporation of 'NewYork Application March so, 1939. Serial No. 264,377 g H smaim ((1250-27) I This invention comprises improvements 'in' ultra short wave devices of the general type claimed broadly in application Serial No. 153,602, 1 filed July 14, 1937, in the name of W. C. Hahn. 5 The invention relates particularly to amplifiers, detectors, and the like, which can be used at wave lengths on the order of from live metersto five centimeters or less.,

As was pointed out in the aforesaid Hahn ap- 'plication an electron stream may be modulatedv either as to electron velocity or as to chargedensity. The first type of modulation involves.

the production of systematic irregularities in electron velocity from point to point along the 5 beam. The second involves the production of 7 charge density variations, such variations being manifested-as systematic irregularities in the electron grouping.

In the conventional design of electronic disgo charge devices, no distinction is made between these two types of modulation. In connection with' ultra short wave devices, however, it is advantageous to utilize electrodes which are capable of producing velocity modulation without simultaneously causing appreciable charge density variations. For reasons which need not be elaborated here, expedient avoids the objectionable decrease 'in'input impedance which is observed with conventional prior art devices when they are operated at extremely high frequencies. Velocity modulation produced as above specified may be subsequently converted into charge density modulation of a higher order of magnitude to obtain amplification effects. A particular mode of converting velocity modulation into charge density modulation is described and claimed in application- -Serlal No. 201,953, filed April 14, 1938, in the name of QT. Metcalf. This consists broadly in the provision 40 of means for reversing at least the lower velocity components of the velocity modulated electron stream to cause selective bunching oi the electrons which move at a common velocity. In the Metcalf application it is pointed, out that this expedient may .be used either in the'production of sustained oscillations or to obtain amplification effects. Its i'urther application to detectors is described and claimed in another application j of G. F. Metcalf, Serial No. 326,933, filed March 5 30,1940- i'My present invention comprises an improve-- ment in Metcalfs invention, especially in the application thereof to amplifiers. detectorsand the like. More specifically I have found that am- 65 plification and detectionare'greatly facilitated in a retarding fleld device if means are provided for preventing the rever'sed'component of the current-stream from returning to the vicinity' of the control electrode structure. An important aspect of my invention consists in the provision 5 of means for assuring the collection of the reversed electrons at a point which is between the region of their reversal and theregion of th originalmodulation of the beam.

The features which I desire to protect herein 10 are pointed out with particularity in the appended claims. The invention itself, together with further objects and advantages thereof,- may-best be understood by reference to the following description taken inconnection withthe l5 drawing in which Fig. l is alongitudinal section of a discharge device suitably embodying the invention-and-Flg. .la is an end view of the de- .vice shown in Fig. 1; Figs. 2, 3, 4, and 5 are graphical representations useful inexplaining the invention; and Fig. 6 illustrates an alternative embodiment thereof.'

Referring particularly to Fig. 1, there is shown an elongated' sealed glass envelope l-ll having a reentrant stem H at one end-thereof. The envelope, which is' preferably evacuated, encloses an "electron gun" for producing a relatively concentrated beam of electrons. In the particular case illustrated, the gun includes a cathode which is constituted of a heater I3 (shown in 3' dotted outline) and an emitting member .ll surrounding the heater. Electrons emitted by the cathode areaocelerated to a desired velocity by,v means of an accelerating electrode structure including a transverse conducting diaphragm I8. 35:

In order to form the electron stream into acoucentrated beam, there is provided an electrode 20 intermediate between the cathode and the diaphragm l8. This electrode may be maintained at the potential of the cathode or at a few volts positive or negative with respect thereto as required to obtain the desired lens action I The-elements so far referred to are energizedby means of lead-in conductors 2| sealed through the stem 1!. Through 7 these conductors. the cathode heater i3 is energized by means of a 'low voltage source shown as a battery 23 while the part I8 is maintained at a desired potential by means of a. tapped connection to asecond battery 25. This latter battery, which should have a' total .voltage on the order of from one to several hundred volts, serves to maintain the. accelerating electrode I8 at a high positive potential with respect to the cathode so as to'produceconsiderable acceleration of the electrons 56 emitted therefrom. If desired, additional magnetic or electrostatic focusing means may be provided in connection with the device in order to prevent undue spreading of the. electron beam.

In operation, means must be provided for modulating the electron beam so as to produce variations therein corresponding to the variations of a modulating voltage, such as a received signal. As previously indicated, satisfactory use at high frequencies is facilitated if the variations so produced comprise a maximum of velocity modulation with a minimum of attendant charge density modulation. This result may be obtained by the use of a modulating space which is sufficiently shielded from the electron source or cathode so that the application of potentials adapted to produce velocity modulation does not react on the cathode to produce corresponding charge density variations. In the particular case illustrated, such a modulating space is provided between a first transverse conducting diaphragm 24 and a second diaphragm 25 which is appreciably spaced from the first diaphragm. These diaphragms are respectively provided with openings 26 and 21 which permit the electron beam to pass through the modulating space. They are preferably maintained at the same potential by being connected to one another. for example by means of connecting sleeve 28'. The potential level of the modulating chamber as a whole may be the same as that of the accelerating electrode [8, and to this end I have shown the latter as being mechanically and electrically connected to the diaphragm 24 by means of a conducting cylinder 29.

Within the modulating space there is provided a control electrode in the form of a hollow tubular conducting member 34 which is adapted to be traversed by the electron beam without interception thereof. If the potential level of this electrode is caused to rise and fall cyclically with respect to the boundary potentials of the modulating chamber (that is, the potentials of the diaphragms 24 and 25), longitudinal velocity modulation of the beam is produced. This ef feet is a maximum when the length of the electrode 34 in the direction of the beam axis is such that the electron transit time therethrough corresponds to a half cycle of the control potential or to an odd number of such half cycles. Under these conditions, an electron which enters the modulating space at a time when the potential level of the electrode 34 is maximum, is twice accelerated: once as it approaches the electrode, and again as it leaves the electrode. Similarly, an electron which enters the modulating chamber one-half cycle later is twice decelerated as it traverses the chamber. As a consequence of these successive accelerations and decelerations, the electron beam issuing from the modulating space is velocity modulated in the sense of be-' ing characterized by successive variations in electron velocity from point to point along the beam. The potential applied to the electrode 34 may comprise a modulated signal-derived, for example, from an antenna 40. This is coupled to'the electrode through a tuned circuit comprising an inductance H and a condenser 42. A battery 43 serves to maintain the average potential level of the electrode 34 me. desired relation to that of the diaphragms 24 and 25. Although such a relationship is not necessary, it is generally convenient to have the electrode and the diaphragms at approximately the same average potential.

Assuming the device to be in normal operation,

the electron beam issuing from the opening 2'7 is velocity modulated; that is, it is characterized by successive variations in electron velocity from point to point along the beam. The degree of velocity modulation may be extremely slight if only weak control potentials are available, but it may be changed into charge density modulation of aconsiderably higher order of magnitude by conversion means now to be described.

As explained in the Metcalf application previously referred to, such means may comprise an electrode 48 positioned in alignment with the opening 21 and adapted to reflect at least the lower velocity component of the beam. This electrode, which is substantially shielded from the modulating space by the diaphragm 25, may be biased to a voltage approximately equal to or a few volts above that of the cathode. Under these circumstances, only a portion of the electron beam will be collected, the other part being reflected back along the beam axis. If the beam is velocity modulated as described above, the faster electrons will hit the electrode 48, while the slower ones will be repulsed by it. Since the faster and slower electrons are respectively segregated in alternately spaced groups along the axis of the beam, it will be seen that both the collected current and the reflected current will be charge density modulated.

The method of separating-fast and slow electrons described in the foregoing will perhaps be better understood by referring to the diagrammatic representations of Figs. 2, 3, and 4. In Fig. 2, for example, there is shown a stream of electrons which is assumed to be velocity modulated so as to comprise alternate groups of fast and slow electrons. The fast electrons are represented by the dots a, and the slow electrons by" the dots b. The electrode 48 is shown in its preferred relationship to the modulated beam. In Figs. 3 and 4 there are shown the components of the electron beam which have been respectively collected and reflected by the electrode 48. It will be seen that each of these components is characterized by successive variations in charge density and is therefore charge density modulated within the definition of that term previously given herein.

It'is believed that the foregoing discussion makes clear one manner in which velocity modulation may be converted into charge density modulation by reversing only the lower velocity components of the beam. It has been shown that such conversion can also be obtained by the process of reversing the entire beam. (In connection with the device of Fig. 1, for example, suchcomplete reversal may be accomplished by biasing the electrode 48 to a sufliciently low voltage-zero or several volts negative-as to repel all the electrons in the approaching beam.) My present invention, which is to be elaborated in the following, is applicable with either type of beam reversal.

From a consideration of the idealized situation assures occur, 7 some slow electrons being necessarily mixed with the fast groups, and vice versa. This being so, some random fast electrons are col-v lected from even the slow electron groups, and

some randomsiow electrons are reflected from the fast groups. As a result, a given amount of velocity modulation produces by'the mechani'sn': described an amount of charge density mined by the .slOpe of the ep'-i static curve of the electrode 48, as illustrated in Fig. 5.- This curve represents the variation of the collector modulation which may be considerably lower than one hundred percent and which is variable with the degree of velocity modulation involved.

The actual: relation between velocity modulation and charge density modulation is detercurrent i which is observed as the collector potential e is varied in a continuous manner. This slope, which for any given tube is fixed by the random electron velocity variations occurring in the discharge stream, may be very steep for practical tube constructions. Consequently, if

such a bias is applied that the electrode 48 operates, say at the point x, substantial amplification may be accomplished. On the other hand} if it is biased to operate at a point 'yon a. knee of the curve, detector action may be obtained.

In the arrangement of Fig. 1-, the means provided for utilizing thehigh frequency variations existing in the electron beam subsequent to the operation of the retarding field thereon comprises a circuit suitable forldetector operation.

This includes a resistor 49'connected in the output circuit of the electrode 48,the rectified potential developed across the resistor being im-- pressed on output terminals 5| through a filtering condenser 50. Obviously, by substituting a tank circuit for the resistor 49, and by adjust- I ing the bias on theelectrode 48, substantiallythe same circuit arrangement can be used for straight amplification purposes.

k Inthe use of the above described device as an amplifier or detector, I'have found that improved results are obtained it there are providedmeans to prevent the reversed component of the 1 beam from returning into the modulating space.

Such means-amay consist, for example,,of an ar=- solid portion-of the diaphragm or partition 25. A

convenient means for obtaining a retarding. field 0f the desired character is provided simply by tilting the collecting electrode 48 so thatits principal planeis not precisely perpendicular to the normal beam axis. It can readily be shown that the resulting distortion of the field exist, in between this electrode and the diaphragm I 25 will produce an angular reflection of the reversed components of theifbeam and cause them to traverse a path such as indicated by the dottedlined. The form of the electrostatic field is still fur-. ther improved with a view to obtaining resuit by the provision of a protuberant lip, 53

which partially vencirclesfthe opening 21, ,as indicated more. clearly in Fig. in, It is the-function of this lip so to distort-the electrostatic field as to assure transverse deflection of those lec-' trons which arereversed by the .electrode 4 7 im-' mediza'tely after their-passage through the opening v Y with an arrangement such as that described in the foregoing, one may obtain a marked. improvement in detector or amplifier operation over that which obtains when all or part of the reversed component'of the beam is. permitted to return into the modulating space. In the latter case-the passage of the reversed beam through the control electrode structure obviously produces coupling between the input .and output circuits of the device. This imposes a definite amplifier or detector analogous to the limitation which exists in connection with conventional regenerative receivers. However, by assuring the prompt collection of the reversed electrons.

in the manner described,this limitation is removed. a

The precise construction which is described aboveis not essential to purposes of I the invenlimitation on the usefulness of the device as an tion, and in Fig. 6 I have shown an alternative arrangement which may be employed. In this case'there is illustrated only a fragmentary portion of the modulatingchamber (represented by a transverse-diaphragm 55) and a modulating electrode 56 which corresponds in function to the electrode 34 of Fig. 1. Reversal of theelectron beam is accomplished by means of a semiflspherical retarding electrode 51. Cooperating with this electrode there'is provided an angularly inclined diaphragm 58 which is mounted on the diaphragm 55 as to be equipotentiai therewith. Under these circumstancesthe field dis.- tribution between the electrode 51 and the diaphragm 58 will be such as to assure angular refiection of those components of the electron beam which are not collected by the electrode. The

reversed electrons will; therefore, impinge either on the solid portions'of the diaphragm 58 or on a portion of the diaphragm 55 which'is displaced from thecentral opening provided in the diaphragm. In any-,case they will be prevented from returning tothe modulating chamber.

I have in the foregoing, discussed the invention in connection with its use with a beam of electrons. Itjisobvious, however, that its. prin-' ciples are equally applicable in connection with a stream or positively. charged particles, such as positive ions. Furthermore, while I. have I exemplified the invention by reference to particular embodiments thereof, it will be understood that numerous modifications may be made by those skilled in the art; without departing from the inventlon. 1,. therefore, aim in the appended claims tocover all 'such equivalent variations as What 1 claim as newand desire to secure by Letters Patent of the United States'is:

1. -I .n--an electric discharge device, means for producing a beam of moving charges, a modulatingelectrode arranged to be traversed by the beamfmeans including the said electrode for' producing variable potential gradients acting longitudinally on the beam, thereby to-caus'e high frequency velocity variations in the components of the beam which successively traverse the electrode, means for reversing, at least the lower velocity components of the beam and for pre 1 come within the true spirit and scope ot the.

foregoing disclosure. I

venting the reversed'components of, thebeam from returning to the vicinity of the modulating electrode, and means for effectively utilizing the high frequency variations. which exist in the beam producing a stream of moving charges, means including an electrode structure for producing high frequency velocity variations in successive components of the stream, electricalfield-producing means for reversing at least the lower velocity components of the stream, said lastnamed means providing a field component at right angles to the normal axis of the stream whereby the reversed components of the stream are prevented for returning along such axis, and means for eilectively utilizing the high frequency variations which exist in the stream subsequent to the operation of the said field producing means thereon.

3. In an electric discharge device, means for producing a beam of moving charges, means for producing variable potential gradients acting longitudinally on the beam, thereby to cause high frequency velocity modulation of the beam, means for applying to the modulated beam 8. retarding field of suificient strength to reverse at least the lower velocity components thereof, the last-named means being of such character that the efiective axis of the field produced thereby is angularly inclined with respect to the normal axis of the beam, whereby the reversed components are prevented from returning along such axis, and means for eflectively utilizing the high frequency variations which exist in the beam subsequent to the operation of the retarding field thereon.

4. An electric discharge device including means for producing a beam of moving charges,

means for producing high frequency velocity modulation of the beam, means including a retarding electrode arranged in the path of the modulated beam for reversing at least the lower velocity components of the beam, the said electrode having its principal surface angularly inclined with respect to the beam axis, whereby the reversed components are prevented from returning along such axis, and means for efiectively utilizing the high frequency variations which exist in the beam subsequent to the operation of the retarding field thereon. v

5. In an electric discharge device, means for producing a beam of electrons, means for producing variable potential gradients acting longitudinally on the beam to cause high frequency velocity modulation thereof, a conductive partition having an opening therein to permit passage of the beam therethrough, said partition being arranged to be traversed by the beam after modulation thereof, field-producing means acting on the beam after its passage through the said partition to cause reversal of at least the lower velocity components thereof, said lastnamed means being of such character that the efiective axis of the field produced thereby is angularly inclined with respect to the normal axis of the beam, whereby the reversed components of the beam are caused to impinge on imperforate portions of the said conductive partition, and means for effectively utilizing the high frequency variations which exit in the beam subsequent to the operation of the retarding field thereon.

HARRY L. THORSON.

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