US2530401A - Pulse-echo system utilizing an electron buncher tube - Google Patents

Description

Nov. 21, 1950 J. ROTHSTEIN 2,530,401

PULSE-ECHO SYSTEM UTILIZING AN ELECTRON sumcuma TUBE Filed Jan. 14, 1943 3 Sheets-Sheet} 44 46 A Q ARE 4o r M i TOR\ PHASE SHIFTER 45 fi l'l'l l l l-l sauAcgEt/ any- 36 GENERATOR/ llllllll ll lllllllllll "ll Illllllll l| FIG. 7

INVENTOR JEROME ROTHSTEIN BY MW FIG.3

IATTOR EY J. ROTHSTEIN Nov. 21, 1950 PULSE-ECHO SYSTEM UTILIZING AN ELECTRON BUNCHER TUBE Filed Jan. 14, 1943 3 Sheets-Sheet 2 INVENTOR JEROME ROTHS EIN ATTORNEY J. ROTHSTEIN Nov. 21, 1950 PULSE-ECHO SYSTEM UTILIZING AN ELECTRON BUNCHER TUBE 3 Sheets-Sheet 3 Filed Jan.'14, 1943 FIG. II

FIG. I2

INIENTOR JEROME ROTHSTEI N A 'I'TORN E Y system and their relation one to" i'actured and used by or for the Governme H governmental purposes, without the paymen me of any royalty thereon.

This invention relates to apparatus for ing pulses. and for utilizing same.

The primary object of my invention is,- I erally improve pulse echo systems, an mo it; especially apparatus for producing pulses i andother purposes. e v y A more particular object is to generateoi exceedingly short duration. so much'so they maybe fed directly to the radiating me hers, instead of being used merely to k y di frequency oscillator.

time in a limited region of space unoc other ponderable matter. Such a dis bu charge will be termed quasi-stationary M may be collected substantially instan n V 3 thus providing the desired short strongp To the accomplishment of the foi'fgo eral objects. andother more speciflcpfiiec will hereinafter appear, my inventio in the pulser tube elements and th are hereinafter more particularly (1 following specification. The speciil tio companied bydrawingsinwhich:

Figure 1 is a wiring diagram for crating tube embodying features o tiori'f Figures 2 and 3 are respectively pl 1 elevations showing one method ofpr tube with a magnetic ileid necessa tion; 5

Figure 4 represents an alternating I, p 4 which may be used to control the p m me h e lslltmiihe tuheris shown? the tube: a t-imp an matinmzcurrentwdiarinmtheg Figures 5 and 6 show square QCPRM milgmyziszsuppiiedzbymsumbie:

n phthe relatively eeunmuiscs iigamthenedtnlmomme be derived from the sine wave otvliisureit and? applied .to the control and collecting h ofthetube; ac? x51? n em'esor I Figure-l representsthepuisesas-manifosted in i!!! .Y the antenna or other circuit utilizing 'the sami i m mi" Figure a is a section taken in elevatin thio z i fi a pulser tube'embodyins w w flf a n e. i sa ma h: 43m g is i when I I .llgqlirmm'fiiilnichirmmf m iigg howuae1 number oi pulse:- tubes be 53 t m :1 un by a I z or 8, beingconnectedto'thesquare Figure l0 is a block diagram schematically wave generator I! by conductor 82. The other conductor 34 from square wave generator 26 is connected to the cathode 28. A suitable bias may be introduced, as is indicated by the battery 36. With this arrangement the electron stream will be intermittent, it flowing during the positive half and being interrupted during the negative half of the square wave. The resulting electron stream pulses are of proper frequency but of longduration. The use of a square wave is merely illustrative, other wave forms being suitable as described later.

Another part of the alternating current from source 24 is fed through a phase shiiter 38 and thence to another square wave generator I. The phase shifter 38 may simply reverse the phase of the alternating current, in which case a simple inverter may be used, and the square wave output from generator 40 will be 180 out of phase with the output from generator 26. If desired the square wave output of generator 40 may be rectilied to leave only the positive halves of the cycle,

its output being represented by Figure 6.

This output is fed to the collector plate It.

' In the present case the output is applied across a'resistor 42 connected in'serieswith collector It. A radio frequency choke 44 may be put in the circuit to confine the radio frequency or pulse energy to the output lead 48. It will be evident that the operation is properly synchronized, there being no collecting potential on collector l6 during the flow o! the electron stream and its formation into a ring, and there being no electron stream other than the formed ring when the ring is being collected by the potential then applied to the collector It. The instantaneous collection of the entire ring of electrons results in a single sharp pulse, marked 48' in Figure 7. The additional oscillations shown in Figure 'I take place when the pulse is fed to a radiator or other circuit tending to resonate. The pulse duration is so extremely short that in'practice the spacing between pulses will ordinarily be much greater, relative to the duration of the pulse, than is shown in Figure 7. Reverting now to Figure 8, the formation and collection of the electron ring preferably takes placewithin an electrostatically shielded space, provided in the present case by a cylindrical shield 48. The cylinder is made of a highly conductive metal and is preferably closed at the top and bottom, thereby providing a space which is shielded against electrostatic fields but not against the'magnetic field. An opening 50 is provided in the side wall of the shield near one end, and the collector plate It is a disc disposed near the other end of the shield. The leadin 52 ofvcollector I6 is insulated from the shield by means of a glass bead II. The shield 48 is supported by a lead-in 56 which also permits the application of a high positive potential to the shield (as isschematically indicated by the batteryit in Figure 1. In practice all necessary potentials may be taken from a suitable power supply pack, rather than from batteries).

The electron gun It (Figure 8) may be dis posed horizontally and aimed directly into the opening SI, but for reasons discussed later, I prefer-to dispose the gun vertically and to deilect the electron stream from vertical to horizontaldirection, as is indicated in Figure 8. The necessary deflection may be obtained by means of a curved deflecting plate 80 carried by a leadin 62, to which a suitable negative potential may be applied. Figure 1 shows a battery Blior It the electron gun were mounted horizontally at the side of the'tube, the deflecting electrode with its attendant defocussing would be eliminated. However. in such case the gun design would be far more complicated, because the magnetic field would fringe over into the gun structure and would modify .the motion of the electrons even while they were being accelerated. Moreover. the focusing action 01 the magnetic field which obtains when the electrons are projected along the lines of force would be lost.

The electron gun itself may be of conventional character (see Figure 8), it comprises the usual heating filament and leads, the-usual concave cathode 28. and appropriate focussin electrodes 66 and 68, in addition to the intensity grid or control electrode 30. Appropriate lead-in wires are provided for each of the electrodes, and these act also as supports for the same. The generally concentric relation between the tube and the solenoid l8 surrounding the same is shown in Figures 2 and 3 of the drawing.

A tube or the type described will yield a large power output. Fairly heavy beam currents are obtainable from the electron gun. The-operating voltages may be made very high because the tube is large enough to insure adequate insulation without introducing the transit time diiliculties encountered in conventional ultrahigh irequency circuits when dimensions are increased.

For a greater power output than that obtainable irom a single tube. a plurality of pulser tubes of the type here described may be used. A number of tubes may be operated in parallel, such an arrangement being shown in Figure 9, in which each of the pulser tubes with associated circuits is indicated at 88,-these being connected to a plurality of dipoles or other directive radiators 90 (only one of which is shown) by means of concentric or other suitable transmission lines 92. To ensure synchronization all of the units are preferably energized from a common alternating current source 24. All or the tubes may have common field coil excitation, and a common power-supply circuit, including the square wave generators and phase shifter. In addition, fine adjustment phase changing means may be provided to synchronize the pulses despite variations in tube parameters. If desired, the transmission lines 92 may be made adjustable in length, thereby acting as the phase adjusting meansfor the various antennas.

A complete pulse echo system using the present invention is schematically illustrated in Figure 10. In this figure the alternator 24 corresponds to the source 24 in Figures 1 and 9. The transmitter 12 comprises pulser tubes with a control wave generator and a collector wave generator, all as was described in connection with Figures 1 and 9. The output of the transmitter is supplied directly to a suitable radiating system, schematically indicated at 14. While a single dipole is shown. it will be understood that a directive array of dipoles is ordinarily employed. The echo from the object intercepted by the transmitted radio energy is picked up by a directive receiving antenna or array It. The echo energy is fed to a receiver 18, the output of which is applied to the deflecting electrodes of an oscilloscope 80. A sweep wave chtained from a, sweep wave generator 84 is ap plied to the sweep electrodes of the oscilloscope 80. It will be noted that the sweep wave generator 84 is driven or synchronously controlled byalternatimenergyircmtbeprimaryscureell. "ltwlllbeunderstoodthatmoretbanoneosl'orexamp'leone arrays and receivers." If we receiving may be used for each receiver, either physically or electrically angle relative to one anand a suitable device used'io periodically one and then the other anadditional passages and insulators (not shown) for the other conductors needed to energize and to bias the various electrodes in the tube. The

bushingsandinsulatorsforthispurposearedeto the'receiver." This'provldes a so-called dual receiver! for so-called "double tracking."

A wholly or partially blocking circuit 8! may be used to help the receiver from the transmitter during radiation of the pulse.

Inasmuch ss'ule' echo is substantially a radio frequency 'peak. rather than a detected modulation offa radio frequency. carrier, the'duration of the echo pulse is exceedingly short. This will produces narrow peak on the oscilloscope screen. the trace may therefore be too faint at the To merely increase the steady intensity of the electron is not desirable as it will help shorten the life of the cathode, and

will help burn out the fluorescent coating of the oscilloscope screen. Furthermore. increasing the sweep frequency so" as to allow the peak to receive a larger fraction of the total illumination per-cycle is undesirable, for the sweep frequency is be synchronized with the pulse. rate. In accordance with a further feature of the present invention. the trace is greatly intensifled solely during reception of the echo peak.

An arrangement-for this purpose is shown in 11. in which the sweep electrodes are indicated at! while the deflecting electrodes are indicated at ill. The input signal from the reeeiver is applied to the deflecting electrodes I I! by means of conductors Ill. The electron from cathode "I. and its intensity by an intensity grid ill.

signed to withstand the necessary voltages. and are dimensioned to provide sufllcient clearances to avoid corona discharge and the like.

As an aidin computing the proper. tube dimensions and pulse frequency, I may point out that inasmuch as the electrons move in a plane perpendicular to the magneticfleld and are in an electrically held-free region. they will move ina circular path. The time taken for the electron to make one circuit is given by the formula 2: Hc/m and the radius of the path is given by in which T is the time in seconds, H is the magnetic field strength in Gauss. e/m is the ratio of the charge to the mass of an electron in emu per gram. r'is the radius in centimeters, and p is the momentum of the electron in 665 units. The period of the control wave if it is square (reciprocal of the pulse frequency) should be The is focused by appropriate focusing electrodes m. 'rrne intensity grid as is biased by' of a Ill. This bias is selected to normally keep the cathode ray at a. rela- Y t ively low' or normal intensity level. The circult of the intensity grid III is also connected to the input conductors I from the receiver. as

' by means of blocking condenser Ill and wire iil The echo peak when applied to the defleeting electrodesis a positive peak, and this positive peak when fed to the intensity grid I" greatly magnifles the intensity of the cathode ray at the critical time when it must reproduce the peak. This feature is useful in any case where the signal to be pictured on the oscillo- Ml is of very short duration compared to the period of the sweep. and where for some reason it is undesirable to use a highsweep frequency. I use a large beam current momentarily. Preferably with a persistent screen. in order to get adequate visibility for the trace.

Inasmuch as ahlgh voltage is employed on the shielding and collecting electrodes. the tube may if desired be shielded against X-rays. This is illustrated in Figure 12, in which the tube It! isenclosedwithin'aleadcasing I22.

Figure 12 also shows how the output of the tube may be connected to a concentric line. The concentric line comprises a center conductor I24 and an outer tube I". This is prefera ly enlarged at Ill to enclose the lead sheath I22.

less than or equal to but not greater than twice the needed to form one complete ring of electrons. In other words. the time may be limited so that only a fraction of a ring'is formed for each' collection on the collector, or the time may bein'creased until a complete ring is formed.

but any'greater increase is undesirable because the resulting mutual repulsion of the electrons will spread the electrons. thus spoiling the desiredinstantaneous collection which is essential for the productionof an exceedingly short pulse,

and what is even more important. causing some of the electrons to be collected by the shielding electrode 48.

The collection time is a function of the collecting voltage. the distance between the plane of ring formation and the plane of collection. and the thickness of the electron beam. If the plane of the ring is not perpendicular to the magnetic fleld, the ring will stretch axially into a' ortion of a helix. and travel either toward the collector or away from it during the formation time. Such an sheet will vitiate the operation. The extent of the harmfulness of this effect. in any particular case, is determlnedby the magnitude of the departure of the actual tube and beam geometry from the ideal. An additional electrode parallel to the collector and situated at the opposite end of the cylindrical shield will alleviate this condition. Ring .tilt" is then overcome by the provision of small suitable D.-C. potentials to the two plates during the time of ring formation. Alternative methods are to control the direction of the beam by varying the potential on the deflecting electrode. thereby to ensure the desired perpendicularity, or to provide a local distortion of the magnetic field in the region of ring formation. This last may be accomplished by putting additional turns on the soleof the field with rings of magnetic materia s.

The cathode is connected to the metal hous- Thedesired neld-distortionmaybetreated much as is f done with field distributions heretofore provided when fringing of a field was observed in focusing problems encountered in the'operation of cyclotrons and induction accelerators. A third method is to replace the simple cylindrical shield by a'more complicated one containing additional electrodes, barriers, projections, or extensions serving to give the desired electronic planar concentration. Any residual tilt will' smear the pulse somewhat, the smear being broader the larger the radius of the electron ring.

Withhigh collection voltages, small spacing, narrow beams and good geometry, pulses ofduration measured in very small fractions of a microsecond may be obtained.

The use of a square control wave is not necessary. Departure from this wave form simply yields a distribution in velocity of the ring electrons, and thus a corresponding distribution in radii of curvature of the trajectories. The circle is replaced by a spiral. A sawtooth wave, with alternate teeth blocked out, may be used. For accelerating potentials high enough to make the kinetic energy of the electrons an appreciable fraction of the rest ene y, e. g. of the order of 100 kv., a non-square wave will give a distribution in mass and thus a spread in collection time of the ring electrons. This relativistic pulse broadening is usually negligible at all practical voltages. If a gradually increasing or gradually decreasing voltage, for example, sawtooth, is employed, the period of formation may .be lengthened relative to the pulse period (the time T) because one then obtains a multiturn spiral rather than a ring. This gives a higher charge transport per. pulse, and thus a larger power output. A disadvantage is that lengthening the ring-forming time and increasing the number of electrons aggravates the defocusing effects of the mutual repulsions of the electrons, and so broadens the pulse. However, multiple turns are possible with a spiral path, but should notbe permitted at all with a circular path.

It may be desired to vary the pulse frequency in order to vary the maximum range of the pulse echo system. The time T is fixed by the field strength H, and the latter is preferably kept at a constant value because of the inconvenience of changing the fieldstrength, with its concomitant change in radius of the electron ring. As indicated above, forming multiturn spirals enables one to use a lower pulse. frequency for a longer range without changing the field strength. The larger range is automatically accompanied by a larger power output, which is a desirable feature if the radio range is to keep up with the theoretically available echo-time range.

If a higher pulse frequency (for shorter range work) than 1/ T is desired, say n/T where n is an integer, and a full electron ring rather than i/nth of a ring is to be collected in order to maintain large power output, 1; tubes may be employed instead of one. These tubes are connected in parallel as in Figure 9, the only change being that each of the 1: tubes is made to differ from its neighbor in the phase of its A.-C. excitation by Each tube has its own control andcollector wave generators. Those skilled in the art know how to obtain the desired phase splitting. As an alternative, an n-phase alternating current may be used, each phase feeding its own puller tube. For greater power, each of the 1: tubes may be replaced by a number of tubes in parallel, as described earlier in connection with Figure 9.

I prefer to dispense with shar tuning in .the receiver, and instead use an amplifier of. the linear type used for counting single particles in nuclear physics. These amplifiers are of extremely high gain, can be stabilized-are of RC type, and have a finite time constant or resolving time, i. e. for incoming pulses closer together than a certain critical amount, the output is a single large pulse. The composite transmitted pulse Should be completely keyed ofi in an interval smaller than the resolving time. This may be done by having sufiicient dipole damping. so that the oscillation amplitude drops to substantially zero during the resolving time interval. The resolving time can always be increased by adjusting the RC values inthe receiver. The receiving dipoles are preferably similar to the transmitting dipoles, this providing suflicient receiver tuning for the present purpose.

The system has the advantage that the UHF is supplied without the use of resonant circuits or conventional oscillators with their accompanying design, adjustment and power output difliculties and limitations. The pulse is the equivalent of a band of frequencies clustered about a mean frequency given by j=1/t where t is the duration of the pulse-consequently length and spacing of the dipoles are not as critical as is the'case where a conventional oscillator is employed. Transmitter circuits are considerably simplified. The keyer' is replaced by a control wave generator,.and amplifiers, oscillators, limiters, pulse sharpeners, etc. are eliminated. A rather large power output per tube is obtained because distributed and tube capacitance, transit time, etc. do not limit the size of the tube. Also, with proper design, high voltages can be-usod and heavy beam-currentsare obtainable.- Plate dissipation can be spread over a. plate of large area, and lasts for a period of time much shorter than pulse durations currently employed, thus permitting higher .power' output per tube per pulse. No dimculties with respect to feed-back between output and input, parasitics, distributed capacitance and inductance of leads, etc., prwent themselves.

It is believed that the construction and operation of my improved pulser tube and pulse echo system, as well as the many advantages thereof, will be apparent from the foregoing detailed description. It will also be apparent that 7 while I have shown and described my invention in several preferred forms, many changes and modifications may be made without departing from the spirit of the invention as sought to be defined in the following claims. In the claims the term "antenna is intended to include other directive radiators such as an electromagnetic horn, as well as the use of reflectors, directors, lenses, etc.,' associated with radiating elements.

I claim:

1. In the operation of an electron tube comprising an electron source and an electron collector, the method of producing pulses which ineludes the steps of forming and storing a mobile charge distribution during a certain period of time, causing said charge distribution to remain juxtaposed to said collector at a fixed distance therefrom during said period of time. and then collecting said mobile charge distribution in atime shorter than the formation time by suddenly assault creating an m chmto tie new in the renlentt teeneleetrenetrenme umenlaneeneeednem thecollector. shitting the phase oi another poralternating current by apteiydililf'deriving a collector wave from ti omgimat ofi 5 n r ;shii d alternating current wave, and anulaw wmcnuneiuaeemdweemmwi twWa r tfle' rgiute portion or the collector wave bmag'neti'c neld, a me"; to'j'a iggl'd" collector. whereby all of the elecdirection p dicular to "f q: the relatively long electron whereby taeeuetnrle m'dii e isllnje gnh g r nm at r pulses egathered almost simultaneously man el alternating 'desired pulse frequency. th. 9

in l 1 .tc t'lle magneueneld 9 p. .tlllifiinaplanemba rrm mt substantially parallel to the collector. substantially shifting the phase of another portion of the aforesaid alternating current. deriving a collector wave from the phase-shifted alternating current. and 09 7 8 the collector wave to the collector.

6. In the operation 0! an electron tube comprising an electron gun, a control grid. and an electron collector all surrounded by a solenoid, the method of generating extremely short pulses which includes generating an alternating current having the desired pulse frequency, deriving a controlwave from a portion oi the alternating current. so applying the control wave to the control grid' of the electron gun that intermittent long-duration pulses of electrons are discharged iromthegmguidingtheelectronstreamsina direction generally perpendicular to the magnetic fleidatapolntspacedi'romthecollectonsothat w de the iorm relatively powerful and grating tube comprising an elecco trol electrode. a cylindrical eleccl d at both ends but having an ear one end. a collector withthe opposite end, means to pply -a potential to the control elecmake the electron stream interectrostatic shield having an open- ;near one end, a collector within the opposite end, means generatmagne' tic ileld within the shield, means to electron stream into the opening in a U M la potential to the control r; ider to make the electron stream tten means to periodically app y a ve to the collector in order to colof each stream substanthe periodic potentials bet usbut outot phase.

enerating tube comprising an c rol rid. a cylindrical electrostatic shield having an. opening in the side .of

one end, a collector disc withcylinder near the opposite end, means to electron stream into the opening in a erse to the axis of the cylinder, a field in the direction or the aids or the cylinder, means to apply a periodic potential to the control grid in order to make the electron stream intermittent. and means to apply a periodic positive potential to the collector in order to collect all of the electrons of each stream substantially instantaneouslln. the n rlodic potentials being synchronous but out of phase.

, ll. Pulse generating apparatus comprising an electron source, a control electrode, a collector plate, a magnet providing a magnetic field, means to guide the electron stream in a direction perpendicular to the said iield, an alternating current generator having the desired pulse irequency. a control wave generator driven thereby. connections applying said control wave to the aforesaid control electrode. a phase shifter for a portion oi the aforesaid alternating current, a collector wave generator driven by the phaseto the magnetic field, means applying the resulting collector potential to'the collector.

12. Pulse generating apparatus comprising an electron source, a control grid for, said source, a cylindrical electrostatic shield having an opening in the side near one end, a collector near the opposite end, means to provide a magnetic field in said shield, means to guide the electron stream into the opening in a direction perpendicular to the field, an alternating current generator having the desired pulse frequency, a control wave generator driven thereby, connections applying said control wave to the aforesaid control electrode, a phase shifter for a portion of the aforesaid alternating current, a collector wave generator driven by the phase-shifted alternating current, and connections for applying the resulting potential to the collector.

13. Pulse generating apparatus comprising an electron gun, a control grid, a cylindrical electrostatic shield having an opening in the side near one end, a collector disc near the opposite end, means to guide the electron stream into the opening in a direction parallel to the collecting disc, a solenoid surrounding the tube with its axis in the direction of the axis of the cylinder, an alternating current generator having the desired pulse frequency, a square wave generator driven y. connections app y said square wave to the aforesaid control grid, 8- phase reverser for a portion of the aforesaid alternating current, a square wave generator driven by the a pulse generator as defined in claim '11 connected to said antenna, at least one directive receiving antenna, a tracking oscilloscope energized from said receiving antenna, and a sweep wave generator for the oscilloscope, said sweep wave generator being driven by a portion of the alternating current referred to in claim 11, whereby all parts of the system are maintained in synchronism.

15. A pulse echo system for locating and ranging, said system comprising a directive antenna, a pulse generator as defined in claim 12 connected to said antenna, at least one directive receiving antenna, a tracking oscilloscope enerin synchronism. Y

gized from said receiving antenna, and a sweep 16 A pulse echo system for locating and ranging, said system comprising a,directiv.e antenna, a pulse generator as defined. in claim 11 connected to said antenna, .at least one directive receiving antenna, a tracking oscilloscope having deflection electrodes energizedfrom said receiving antenna, a sweep wave generator for the sweep electrodes of said oscilloscope,,-s'aid sweep wave generator being synchronized bya portion of the alternating current referred to in claim 11, a control or intensity grid in said oscilloscope, and means so connecting the receiving antenna to said intensity grid as to increase the intensity of the trace during reception of the echo.

17. A pulse echo system for locating and ranging, said system comprising a directive antenna, an untuned pulse generator as defined in claim 11 connected to said antenna, at least one directive receiving antenna, and an untuned receiver connected to said antennas.

18. A pulse echo system for locating and ranging, said system comprising a directive antenna, an untuned pulse generator as defined in claim 11 connected to said antenna, at least one directive receiving antenna, and an untuned receiver connected to said antenna, a tracking oscilloscope energized from said untuned receiver, and a sweep wave generator for the oscilloscope, said sweep wave generator being driven by a portion of the alternating current referred to in claim 11 in order to maintain all parts of the system in synchronism.

JEROME RUIHSTEIN.

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

UNITED STATES PATENTS- Number Name 7 Date 1 2,032,620 Langmuir Mar. 3, 1936 2,037,977 Hansell Apr. 21, 1936 2,143,035 Smith Jan. 10, 1939 2,218,549 Philpott Oct. 22, 1940 2,227,598 Lymanet al. Jan. 7, 1941 2,289,319 Strobel July 7, 1942 2,362,209 Litton Nov. 7, 1944 2,372,210 Labin Mar, 27, 1945

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