US2468928A - Electronic oscillator-detector - Google Patents

Description

May 3, 1949. w. W. HANSEN ET AL ELECTRONIC OSCILLATORTDETECTOR 2 Sheets-Sheet l Original Filed July 8, 1938 f 4 f 3 z uw /z M D M ,j IIIIIIF L a 67 @o a f f M m50 y 5f W m W Mm ,../J. v 7 vg v M 5 v w27 il.-. w., D M A W 11 Z z M ,y M z 4 /5 m /1 TTOR/VEY May 3, 1949.

Wt W.' HANSEN ET AL ELECTRONIC OSCILLATOR-DETECTOR Original Filed July 8, 1938 lNVENTORS w w HANsE/,RH VAK/Ar.' BY VAE/AN @,ORNEY l ythe resonators.

Patented May 3, 1949 UNITED STATE ATENT olf-'Fics ELECTRONIC OSCILLATOR-DETECTOR Original application July 8,A 1938, Serial No. 218,064. Divided and this application October 24, 1942, Serial No. 463,290

46 Claims.

vThis invention relates, generally, to the generation, modulation, detection, transmission and reception of electromagnetic energy, and the invention has reference, more particularly to a vnovel electron discharge 'tube apparatus adapted for such uses and operating at' frequencies of the order of 108 or more cycles. per second. The' present application is a true division of application Serial No. 218,064., filed July 8, 1938, now Patent No. 2,406,370, issued August'27, 1946.

In 4the above -copen'ding application there are described a numbery of embodiments of related inventions which have come to be known by the names, rhumbatron, klystronj buncher, and 'catcher. These names are used in the present specification. They may be dened as follows: Rhumbatron, i. e., a resonant circuit characterized by an electromagnetic field bounded by a, substantially closed conducting member, i. e., a cavity resonator, and in which energy is transferred to or from the electromagnetic eld by inductive loops or capacitive elements in the iield or by a beam of electrons projected through the el'd. "Klystron, i. e., an ultra high frequency electrical apparatus composed of one or more rhumbatronsf i. e., cavity resonators, excited and coupled by a beam of electrons projected through the fields contained in Bunchen i. e., the cavity resonator in a multi-resonator klystron nearest the emitter of the electron beam, in which the electrons are alternately accelerated and deceler- -ated at the 'frequency of oscillation of the klystron. Catcher, i. e., the cavity resonator in a klystron'farthest from the emitter of the electron beam, in which energy of the bunched electron beam is converted into electromagnetic field energy;

The principal object of the present invention isto provide a novel `electronic oscillator-detector adapted for generating, transmitting, receiving, and detecting high frequency signals.

A further object of the present invention is to provide improved: electron discharge apparatus in which an electron beam is projected through a cavity resonator and'is then reversed to re-enter the resonator for ya further exchange of energy therewith.

Another object of the present invention is to provide improved electron discharge apparatus inl which an elec-tron 4beam is projected vthrough a cavity resonaton a part 'ofthe electrons being reversed -to-reienter the` resonator vandl the reh amplification,

2 maind-er being projected further and being thereafter usefully employed.

A still further object of the invention is to produce methods yand means for detecting objects at a distance by the transmission and reception of radio Waves intercepted by such objects.

Other objects and advantages will become apparent from the specification, taken in connection with the accompanying ldrawings wherein the invention is embodied 'in concrete form.

In the drawings,

Fig. 1 is a diagrammaticl representation oi a device using two separate electron beams and useful in explaining the present invention. The device of Fig. 1 is claimed in U. S. Patent No. 2,406,370 granted August 27, 1946.

Fig. 2 is a diagram of the present invention having properties similar to those of Fig. l, Vbut with'two concentric electron beams for excitation.

Fig. 3 is a curve Yrepresenting the performance 'of the apparatus of the present invention.

Simi-lar characters of reference are used in all -of the above gures to indicate corresponding parts.

Referring nowto Fig. 1, there are four resonant circuit members or cavity resonators I, 2, 3, and il of the type shown in copending application Serial No. 214,452, filed June 18, 1938, in the name of W. W. Hansen and S. F. Varian, now Patent No. 2,242,249, issued May 20, 1941. Circuit mem*- bers I and 2 together with circuit members 3 and 4 and their associated apparatus comprise two inter-coupled velocity grouped electronic circuit means the principles of operation of which arev described incopending application Serial No. 168,355 led October 11, 1937, in the name of R. H. Varian, now `Patent No. 2,242,275, granted May 20. 1941. In the first unit comprising circuit members l and 2 there is an electron emitter 5 such as an activated oxide surface heated by a iilament 6. The emitter 5 is connected with a battery 'l for accelerating the electrons from emitter 5 into the system. Circuit member l is lprovided with a pair of spaced grids 8 and 9 and two coupling loops Il and l2. Loop ll is connected to a line I3 for coupling to circuit member 2, and loop l2 is used for coupling into 'circuit member '4. 'Members I andZ are also shown provided' with coupling loops l0 and l0 and connected antennae IB and l'". Openings 20 and 20' may be used with or in lieu of antennae I0" and 10 for receiving and radiating energy. MemberZ has a pair of spaced grids 'I4 and i5, and two coupling loops I6 and H. Loop I6 is-connected to line i3 for coupling into resonant circuit member I, and loop I1 is used to couple member 2 to member 3.

On the exterior of member 2 there is shown a novel detector arrangement which resembles in part the detector arrangement shown in Serial No. 185,382 now Patent No. 2,415,094, issued February 4, 1947, but which has certain advantages over that arrangement. In the present arrangement, two spaced grids 2| and 22 are placed near the grid I5 but at an angle with respect to the latter. Aplate isplacednear the grid 22 on the side opposite grid I5. A second plate 24 is placed as indicated about at right angles to the surface of grid I5. The surface of plate 24 is provided with fins 25 or other means for preventing secondary electron emission from plate 24. Plates 23 and 24 are connected to a push-pull transformer 26 which delivers its output to a telephone or other receiver 21. Between the emitter 5 and the grid 8 there is located a control grid 31 connected to an oscillator 39 of comparatively low frequency. Between resonators I and 2 there is a tube 38 connected to a second low frequency oscillator 39.

Circuit members 3 and 4 are arranged similarly to circuit members I and 2, respectively. Member 3 has a pair of spaced grids 28 and 29 and a coupling loop 3|. An electron emitter 32 and a battery 33 correspond to similar elements of circuit member I. Circuit member 4 has spaced grids 34 and 35 and a coupling loop 3G.

The system shown in Fig. 1 may be operated in either of two ways. The simpler way is to omit resonators 3 and 4 and to operate the rest of the apparatus as a complete system within itself. A second way is more complicated, and also includes the use of resonators 3 and 4 and their effects. The operation taking place when omitting members 3 and 4 being the simpler, will now be described. In this operation of the system the electrons of the beam in passing through the grids of resonant circuit member I are alternately accelerated and decelerated as explained in Serial No. 168,355 now Patent No. 2,242,275, issued May 20, 1941. As a result of the changes in velocities of the electrons of the beam they arrive at the grid I4 of member 2 in groups or bunches distributed in time at the frequency of the oscillation of the system. Energy is taken from the electrons by the eld of member 2 and this member is thereby excited to a state of oscillation. Energy of oscillation is transmitted from circuit member 2 to member I through coupling loop I6, transmission line i3, and coupling loop I I. Thus, the held of member I is maintained in a state of oscillation and the electron beam is accordingly acted upon and bunched Radiation from the fields of both circuit members I and 2 or from either one is possible. Likewise, energy can be received by either one. The resonator or circuit member 2 has stronger oscillations in it than has the resonator I, and consequently radiation from member 2 is of greater intensity than that from member I. Conversely, reception is more favorable in member I than in member 2 because a signal entering I is amplified by the bunching effect and appears with greater intensity at member 2 than a signal introduced directly into 2. Inasmuch as reception is better performed in member I, and transmission better performed in member 2, radiating elements such as either loops I9 and I0 or holes 20 and 20 or both may be used in the members I and 2.

Assuming that a modulated carrier frequency is received by member I' through either hole 2l] or antenna I0 then, the electrons of the beam 4 travel through grids I4 and I5 of member 2 and encounter grids 2| and 22. The electrons emerging from grid I5 have varying velocities depending upon the strength of oscillation in the circuit members I and 2. Some of the electrons pass through grids 2| and 22 and hit plate 23. Other electrons, i. e. the slower ones, are reflected from grids 2| and 22 to plate 24. The two grids 2| and 22 are parallel and close together. A potential difference, with grid 22 negative, is established between grids 2| and 22 by the battery 30. The resultant field between grids 2| and 22 acts like a fiat mirror insofar as the slower electrons leaving grid I5 are concerned. These electrons enter the ileld between grids 2| and 22 and their motion is opposed by this field and they are deiiected toward plate 24. The faster electrons are deflected, or rather, refracted, but they penetrate the eld between grids 2| and 22 and hit plate 23. The slower electrons are not able to penetrate the field between grids 2| and 22 and they bounce to the left as in ordinary optical reflection from grid 2| to hit plate 24. In the structure constituted by members I and 2, all the electrons leaving the grid I5-have substantially the same velocity when the system is not oscillating. As the amplitude of oscillation increases, the electrons vary in velocity, the extremes of velocity being the greater, the greater the amplitude of oscillation. The potential difference between grids 2| and 22 is adjusted either so that most of the electrons are reflected toward plate 24, or so that most of them are permitted to pass through to plate 23. The precise difference of potential between grids 2| and 22 giving the most sensitive or the most efficient detector action as `may be preferred can be found by experimental adjustment of battery 30. The detector characteristic of this system is analogous to that found in ordinary vacuum tube circuits. Since practically all the electrons emerging from grid I5 eventually strike either plate 23 or plate 24 any increase in current reaching one of the plates is accompanied by a decrease in current reaching the other plate. Hence, the current produced by electrons reaching plate 23 is 180 electrical degrees out of phase with current produced by electrons reaching plate 24, and accordingly the currents from plates 23 and 24 are appropriate to the operation of any push-pull apparatus, such as transformer 26 and receiver 21, usually used with push-pull detectors. Hence, the received signal is heard at phone 21.

The grid 31 and the tube 38 and the oscillators 39 and 39' are used to control the operation of the system as by producing modulation or for starting and stopping oscillation. The actions of grids in the location of grid 31 and tubes in the location of tube 38 have been described in Serial Nos. 185,382 and 201,898 now Patent No. 2,280,824, issued April 28, 1942. The action of these elements can be summarized by mentioning that an alternating voltage applied to grid 31 or to tube 38 accomplishes amplitude modulation with some frequency modulation. Also, in the use of grid 31 and tube 38 if the voltage is made sufficiently high the oscillation of the system can be stopped during part of every modulating cycle. The frequency of oscillators 39 and 39' may be any desired up to about 10I cycles per second, or even more if the frequency 'of the circuit members and 2 is higher than 108 or 109 cycles per second. Ordinarily, the frequencies of oscillators 39 and 39 will be well within the frequency range; of ordinary vtriode oscillators? Either grid 31 or tube 38- or both may vbe used. Ordinarily only one will be required, although in some instances it will be convenient to use' both operating at different frequencies.

'The assemblage shown in the' figure will opcrate` as a simple klystron for transmission of radio .Waves or for the detection thereof or both. It will also operate as a modulatedv oscillatortranslnitter yor as a superregenerative receiver.

In one specialized applicatiorrof the system it is set up` as a transmitter-detector. For best results-the assemblage is placedI in a suitable para'.- bol-ic or' otherA reflector as described in Serial No.. 185,382. The system is adjusted for sensitivity irr either of two modes of operation. Either the electron accelerating voltage of battery 1 is. set so'that the phase of arrival of electrons in the. circuit member 2f is such as to 'give' maximumr oscillation, andthe coupling is reducedfby -adiustingloop's II and I6 sufficiently so the oscillator-Will barely oscillate, or the electron accelerating voltage' is set so that-the phase of arrival; of thebunches in the circuitmember 2 departs considerably from. that which' gives' maximum oscillation,v and the electron current or coupling I' I-IS orA electron accelerating voltage is adjusted vjust tosustain oscillation. Experiments indicate that thealattenmode of operation is the more sensitive. Under' these vconditions of. oscillation, radiation leavingxthe system by Way of antenna I" or hole can return'by reilection from a distant objzect an-d reenter member I. The returned radiation will produce a eld in vmember `I which may have any possible phase difference relative to .thel bunching field therein. The returned radiation Will be amplified by bunching in member I, catching in member 2, and feed-back into member I in a manner analagous to that in arregenerative detector. The amplified signal will combine with the steady oscillation of the system and it will add to orsubtract from thev steady oscillation depending on the relative phase of the received signal and the steady oscillation of the system. The observed result of the action of the system-will be to receive at receiver 21 a signal of. undulating intensity as the distance from circuit ymember I to the outside reflector or object varies. The variation in distance Will cause a corresponding variation in phase of the received signal'.

In the operation of the system as described above in which the adjustment is critically made, the lreception of energy at the frequency of the transmitted energy, that is, the reception of energytransmitted and reflected back to the systemhas the same effect as if the rate Yof energy loss were changed by any other cause. The effect is the same as if the radiation resistance were changed, and insofar as an analysis lof operation of the system is concerned, the reflector or object outside which returns radiation to the system is in effect part of the system. Accordingly, it is convenient to consider the combined effects of transmission yand reception as if the variation in resultant detected signal were the effect of variation of radiation resistance.

In'these methods of operation grid 31, tube 38 andoscillators 39 and 39 are not used.

Another way of operating the system is to use either grid 31 or tube 38 with one of their oscillators 39 or 39 adjusted so that during part of the low frequency oscillation cycle the system Will oscillate strongly and during another part of the cycle fthe saine Will yoscillate weakly. Itis characteristic of klystrons that they are com--l frequency cycle. During other parts of thecyclezv the system can operate Withlessrestriction and. atv some parts of the cycle without anyzrestri'ction.

Thus, the system transmits pulses loffhigh fre-- quency radiation, the pulses being at the frequency of the low frequency oscillators 39 or 39', and in between pulses of radiation the system is prepared to receive radiation. If the transmitted radiation encounters a suitable reflecting body or object some radiationwill be returned to the system where it will be received and detected during the reception part Iof theA low frequency cycle. In this mode of operation, the system operates alternately as a detector and as an oscillator. Furthermore, it may operate as a superregenerative detector if adjusted properly. Thev conditions for superregeneration are, in general, fulfilled if the oscillator is all-owed repeatedly tov build up self-sustained oscillations for a period shorter than the time required for the oscillator'V to reach full oscillation, and then is stopped. The amplitude reached before oscillation `is stopped is then sensitive to incoming signals.

Thus, it will be evident by reference to Serial No. 185,382 that the system described herein 'is applicable to the uses described in that application. In general, the present invention can be used in many applications such as location of remote objects requiring an oscillator transmitter and receiver detector operating either simultaneously or alternately. When using this apparatusfor the purpose of locating remote objects a shield 4' would ordinarily be used between the transmitter antenna ID'" and the receiver antenna I0".

The operation of the system shown in Fig. f1, including use of circuit members 3 and 4 resembles that described when using members I' and 2 alone, but the use of 3 and 4 provides a novel type of control for members I and l. This novel type of control accomplishes, in eiect, feed-back from circuit member 2 to circuit member I which is non-linear, that is, feed-backin which the transfer of energy-is not proportional to the energy in the primary circuit. The use' of this type of feed-back enables the klystron to operate efficiently as an oscillator and as a detector at the same time, as will further appear.

For sensitivity in detection as an oscillatordetector the mutual conductance of the circuit should ibe substantially constant. The mutualv conductance is the ratio of the change in output load current of the system to the change in input control voltage of the system. In the ordinary klystron, the mutual conductance is constant at small amplitudes of oscillation, and then gradually decreases at large amplitudes of oscillation. This is indicated in Fig. 3 in which the mutual conductance of a circuit is indicated as ordinates and the amplitude of oscillation as abscissae. In this gure there are three curves drawn, one showing mutual conductance as a function of amplitude in a klystron with ordinary or normal excitation, a second curve showing mutual conductance as a function of amplitude in la "klystron With"over-bunched excitation, `and a third curve showing the operation of a klystron with a combination of normal feedback and feed-back through an over-hunched klystron." In the curve showing operation with this combined form of excitation conforming to Fig. 1 when resonators 3 and 4 are used, there is a region in which the mutual conductance is substantially constant over a considerable range of amplitudes. vThis is indicated on the curve by the expression operating region.

For quantitative examination of the operation of the klystron an expression for mutual conductance (Gm) is stated as follows:

Where Iozcurrent in the electron beam, f

L=bunching distance which in Fig. 1 is the distance between grid 9 and grid I4,

Vo=vo1tage, in Fig. 1 of battery l,

Vi=the effective high frequency voltage between the buncher grids,

--The ratio of electron velocity in the electron beam to the velocity of light,

7\=wave length, and

Ji=the Bessel function of Order 1. Any convenient consistent system of units can be used in the above expressions.

For small Values of :L in an ordinary klystron,

and as :L increases, Gm decreases, passing through zero and oscillating as indicated in Fig. 3. With variation of amplitudes of oscillation, the mutual conductance varies, according to an oscillating curve which is not constant for any appreciable part of its length except where :c is close to Zero.

It is only when operating with the mutual conductance very nearly constant that a small change in radiation resistance of the radiator can produce a large relative change in amplitude of oscillation, but if a large absolute change of amplitude is desired, as well as a large relative change, the oscillator must have a large amplir tude of oscillation. In the ordinary klystron, the mutual conductance is not constant when the amplitude of oscillation is large, hence we may have large relative change of amplitude with the klystron operating at small amplitude of oscillation or We now have a small relative change of amplitude with the klystron operating at large amplitude of oscillation. In the present invention there are means for producing both a large amplitude of oscillation of the klystron and a large proportionate change in amplitude as a function of radiation resistance at one and the same time. Under special conditions as represented in Fig. 3 by the curve marked overbunched excitation, the mutual conductance can either decrease or increase with change in amplitude depending on the degree of bunching. These conditions are produced in the arrangement shown in Fig. l.

Circuit members I and 2 and the elements associated with them are operated as described before substantially like an ordinary klystronf Resonators 3 and 4 operate substantially like an ordinary klystron except that the amplitude of oscillation in member 3 is greater than is usual` 8 in the buncher of a klystronf tained byy adjusting the coupling I`I-,3|. That is, the amplitude of oscillation in member 3 is greater than the normal amplitude used in member i. The greater than usual amplitude of oscillation in member 3 produces a greater than usual alternating field between grids 28 and 29. This eld imparts larger than usual changes in velocity to the electrons drawn from emitter 32v through grids 28 and 29. The result is that the electrons after leaving grid 29 become hunched to the optimum degree sooner in their transit toward grid 34 than they would with normal excitation, and by the time they reach grid 34 they have already passed through a condition in Which they would extract energy from a catcher circuit, and are progressing toward a second bunched condition in which they would deliver energy when they reach resonator 4.

Now in the curves of Fig. 3 if an amplitude of oscillation is selected in which the mutual conductance of the normal klystron, I2, is decreasing, and the excitation of member 3 is adjusted so the mutual conductance-at the same amplitude is increasing, anything that occurs in the system to change amplitude will cause the mutual conductance associated with the,klystron i--2 and the electron beam thereof to change in the opposite wayfrom the mutual conductance associated with the fklystron 3-4 andthe electron beam thereof. That is, when the mutual conductance of members l and 2 increases, the mutual conductance at members 3 and fl decerases and vice versa. The resultant effect is that over a portion of the operating range of amplitudes of the system, the mutual conductance of the system is substantially constant.

Under these conditions of operation the system can oscillate and radiate at a comparatively high power output, and at the same time be sensitively responsive to an incoming signal or to a change in radiation resistance. In such a mode of operation the arrangement shown in Fig. 1 may be placed relative to a parabolic reflector as described in Serial No. 185,382 with the antenna lil yconnected to coupling loop I0 or the opening 2i] facing the mirror at the mirror focus, or it may radiate without the aid of any other apparatus. If the transmitted beam goes out into uninterrupted space the system will oscillate and radiate stably. Suitable reflectors are also shown in Figs. '7 and 8 of said Patent No. 2,406,370.

If while the system is radiating, a reecting surface is placed to intercept the transmitted beam, some radiation may be reflected back into' tent than before and this correspondingly affects circuit member which `finally reacts on member I through SE-I 2. Referring again to Fig. 3, it will be seen that the increase of amplitude of oscillation in members I and 2 results in a decrease of mutual conductance, whereas the increase of amplitude in members 3 and li results in an increase of mutual conductance. The combined effect of these changes is to retain for the system a substantially unchanged mutual conductance over a This is oblimited zonev as indicated "by the substantially horizontal portion Aor' ithercurve shown iin dash lines.

This system under the conditions-:described is, linz-th'e lregion specified, stably sensitive to -received rradiation, fto which it :responds .depending on the `rnagn'itude `and phase of ythe received signals. 'The responses-of .the apparatus to the received signal `are detected, in the electron beam emerglingv ffrom :grid 11:5, by the elements numbered :21| -Ito- .21 inclusive. 'The particular arrangement for detection shown in Fig. 1 is only oney of several that can be used. Other detection arrangements havebeen-disclosed inSer-ialiNos. f1'85,'382,193,268, inow Patent No. "2,272,165, issuedfFbruary 3, 19422, :and 2014898.

-The general principles 'involved in the operaitiorrof the embodiment-oi this invention shownin Fig. 1 are applied also in a second `vembodiment .shown in Fig. 2. In Fig. 2 son'lyitwo circuit mem- 4bers '1l land T2' are employed. Members I" 'and 2 `:have-the same grids,coupling loops-'and yother appurtenances vas in the structure of Fig. 1 'except those associated also .witlfi circuitmenibers A3 :and 4 "of that ligure which -o'f course are `not required. i

vided at the Iadjacent surfaces, fas shown, ofA cir- ;l

'cuit .members "If and i2. Grid 44 is-connected to Vmember `l"` while lgrid 45 'is insulated -from member-f2 although lsupported thereon. Grids 42 and W3 are connected toemitter 41| yandfare `maintained at a potential which is positive with respect to emitter 5. Grid '45 `is .positive Hwith respect 4to emitter 5 and negative with respectit'o emitter 4l.

In the operation of the structure of Fig. '2, electrons from emitter 5 Kare Aformed-as a cylindrical beam "45 projected along `the laids of the system. This beam vof electrons `passses through resonant circuit members LI and 2" Ias usual in the klystron providing excitation for member 22" VLfeeding 'back Athrough interconnected `loops 1'6 fand 5H to member l". 4l are yformed asabeam '411 of'annular cross section surrounding beam 146 and coaxial therewith. I'The electrons -of beam `41 vpass through member i' :and are hunched as usual, but `they vdo not enter circuit member I2". versed in transit between grids 44 and 45 "by the action Voi the latter grid, and they are `projected back through grids 9 and yil. 'The reversal of the Ielectrons ofbeaijn 41 between grids 144 and 45 is, of course, the consequence of having grid 45 negative with respect to the emitter 4l. 'The reversal lofthe electrons of beam 4l is illustrated in Fig. "2 by the doubling- -bac-k oi"- the boundary lines of beam 4l, as indicated 'by the lines 48. These electro-ns of beam '4T are acted upon lfor bunching V bymember when they `pass `initially through grids '-8 fand B in ltheir travel toward grid 44, and the bunching process ycontinues during the time the :electrons 'travel zf-rom grid lSl-through grid, 44 toward .grid .'45 .and thenbackfto tgrid 9. The energy of the hunched electrons yof -beam 41 lacts upon the .field ofy i", .these electrons being in an overbune'h'ed condition fsuch that the mutual conductance contributed fbythlis beam is increasing `with increasing amplitude.

Electrons 'from emitter Instead 'they are relrIfhe operation lofl '2 in combined itransmi'ssion and reception is similar to that :of Fig. 1 as explained before with reference to Fig. '3. The characteristic of .ordinary excitation shown .in `Fig. 3 is obtained :by the action .of the beam '46 from the emitter .5, andthe characteristic of over hunched excitation is obtained 'by the `action of the beam 4l 'fromtheemitter 411. 'The combined action of 'these two beams gives the combined eX- ctation characteristic shown in dash lines in Fig. 3, i. e. a region .in which kthe mutual conductance vchanges but little over a `definite range of amplitudes. Accordingly, Fig. i2 can `be used for those operations requiring simultaneous transmission and reception of signalsyas -described for Fig. 1, in which case the shield 4" or equivalent is employed. In Fig. 2 the lelements 2i to 2?@ inclusive shown in Fig. 1 .for signal detection have Abeen omitted for convenience, although they would be used in the same 'Way in Fig. 2 as in Fig. 1.

In Figs. 1 to 3, if desired, only asingle radiating -means suppliedfrom either the electron lgrouping circuit or on the electron absorbing vcircuit may be used both as transmitter andA receiver.

As many changes could be made in the .above construction and many apparently widely Adii-*fenent embodiments v'of this invention could be made without departing from the scope thereof, it is intended that all matter -contained in the` above y.description or shown in the accompanying drawings `shall be interpreted 'as illustrative and not in a limiting sense. l

What is claimed is:

1. An electronic device comprising an apertured` thermionically emitting structure, van accelerating electrode, a second thermionically emitting structure on the opposite side 'of said first structure from vsaid electrode, and potential lsupply means coupled` to said electrode and said kstructures forv electrically biasing said rst emitting structure with respect to said second emitting structure and for biasing said electrode with respect to .said Yiirst structure to :draw thermions from said second ,structure through Asaid irst structure toward said 4accelerating electrode and also from said .first structure toward said electrode.

2. An electronic `device as defined in claim 1, comprising an apertured electrode positioned beyond said accelerating electrode, andmeans connecting said last apertured electrode to said potential supply means to bias said electrode to turn back thermons from sai-d first emitting structure while causing thermions from said second emitting structure to continue therethrough.

3. An electronic device .as in claim 1', in which an apertured internally resonant hollow body is positioned beyond said accelerating electrode in the path of the thermions from both of said thermionically emitting structures, and means 'beyond said body for turning the thermions from lsaid first structure 'back into said internally vresonant hollow body after said 'thermions have initially passed outwardlythereoi..

4. An oscillator comprising means including a cathode for producing a uniform-velocity electron beam, means including a cavity resonator providedV with openings in the path of said beam topermit passage Ofvsaid beam therethrough `for imparting lvelocity modulation to said bea-m, and means in the path o-f saidbeam beyond said resonator for producing a reversing eld acting on said beam to convert its velocity modulation into .charge-density modulation and to return a por- `tion of the energy of the charge-density--modulated part of the beam into said resonator.

5. An oscillator comprising means for producing a substantially uniform-Velocity beam of electrons, means including a cavity resonator having openings in the path of said beam to permit passage of the beam therethrough for imparting velocity modulation to the beam, and means including an electrode in the path of said beam for reversing at least the lower velocity components of the beam after its passage through said resonator and for returning the reversed components into energy-exchanging relation with said resonator.

6. High frequency electron discharge apparatus, comprising a cavity resonator having electron permeable Walls and adapted to contain an oscillating electromagnetic eld, means comprising a cathode on one side of said resonator and spaced therefrom for projecting electrons through said resonator whereby said electrons and said field interchange energy, and means in the path of said electrons beyond said resonator for reversing the night of said electrons to further interchange energy with said field.

7. An oscillator comprising means including a uniform-velocity cathode for producing an electron beam, means including a cavity resonator spaced from said cathode and provided With openings in the path of said beam for imparting Velocity modulation to said beam, and means along the path of said beam beyond said resonator for producing a reversing eld acting on said beam to return a portion of the energy of the beam into said resonator.

8. An oscillator comprising means for producing a uniform-Velocity beam of electrons, means including a cavity resonator having openings in the path of the beam for imparting velocity modulation to the beam, means along the path of said beam beyond said resonator for causing the electrons of said beam to become bunched, and means including an electrode in the path of said beam for reversing said bunched beam and for returning said beam to said resonator into energy-exchanging relation therewith, whereby oscillations are sustained in said resonator.

9. High frequency apparatus comprising a cavity resonator means adapted to contain an oscillating electromagnetic field, means aligned with said resonator for projecting an electron beam through said resonator, means along the path of said beam for returning a portion of said beam through said resonator for further interaction with said field, and means along said path comprising an additional cavity resonator means for abstracting high frequency energy from the remainder of said beam.

10. High frequency apparatus comprising means for producing an electron beam and for passing said beam through an oscillating electromagnetic eld, means along the path of said beam for returning aV portion of said beam for further interaction with Said field after passage therethrough, and means along said path for extracting high frequency energy from the unreturned remainder of said beam.

11. High frequency apparatus comprising means including a cathode for producing a uni form-velocity electron stream, a cavity resonator in the form of a figure of revolution about a predetermined axis extending along the path of said stream, said resonator having a pair of electronpermeable walls adjacent said axis, and spaced -from said cathode, and a reflector electrode in 12 the path of said stream beyond said resonator and spaced therefrom for returning electrons of said stream into said resonator for sustaining oscillations therein.

12. HighV frequency apparatus comprising a cavity resonator in the form of a figure of revolution about a predetermined axis, and having a pair of electron-permeable Walls adjacent said axis, a cathode adjacent one of sai-d walls and outside said resonator, and a reiiector electrode adjacent the other of said Walls and outside said resonator.

13. High frequency apparatus comprising a substantially toroidal cavity resonator having a pair of electron-permeable walls adjacent the axis thereof, a cathode opposite one of said walls and outside said resonator, and a reflector electrode opposite the other of said Walls and outside said resonator.

14. High frequency apparatus comprising a. cavity resonator in the form of a figure of revolution about a predetermined axis and having a pair of closely adjacent electron-permeable walls along said axis and forming a narrow gap therebetween, a cathode opposite one of said walls along said axis and outside said resonator, and a reflector electrode along said axis opposite the other of said walls and outside said resonator.

l5. High frequency apparatus comprising an axially symmetrical reentrant cavity resonator having a pair of closely spaced electron-permeable walls along the axis of symmetry thereof, a cathode adjacent one of said Walls outside said resonator, and a reflector electrode adjacent the Aother of said Walls outside Said resonator.

16. High frequency object-detecting apparatus comprising means for producing an electron stream, a cavity resonator having apertured walls in the path of said stream, means coupled to said resonator for supplying received energy thereto, a second cavity resonator spaced from said first resonator and also having apertured walls in `said stream path, means coupled to said second resonator for radiating energy from said second resonator toward an object to be detected, whereby a part of said radiated energy may be reflected from said object and supplied to said first resonator, means coupling said two resonators together, said apparatus including means for maintaining substantially constant mutual conductance between said resonators to permit oscillations at high amplitude for transmission and to render said apparatue simultane-A ously sensitive to small received signals, said lastnamed means comprising a reflecting electrode between said resonators for reflecting a portion of said beam back into said rst resonator in overbunched condition.

1'?. High frequency object-detecting apparatus comprising means for producing an electron stream, means in said apparatus for receiving a radiated high frequency signal, means in said apparatus responsive to said signal for periodically varying the velocity of the electrons of said stream, means in said apparatus for causing said velocity-varied stream to become hunched, means in said apparatus spaced from said velocityvarying means for extracting high frequency energy from said bunched stream, means coupling said velocity-varying means to said energy-extracting means to sustain oscillations within said energy-extracting means, means in said apparatus for radiating a portion of said extracted energy toward an object to be detected, whereby a part of said radiated energy may be reflected iffrom :said object and deceived :by :said :receiving rmeans, .and means-in said v.amparatus `forfmaintaining substantially constant mutual conductfance between `said f velocity-Varying -means and fsaid venergy-,extracting zmeans rto permit loscilla- '.tion athigh-amplitude:for-producing said radiated venergy and 'gto render said :apparatus simultaneouslyssensitive to.smallzreceivedrsignals, said lastznamedl means 'comprising-means fiorv reflecting .1a aportion of .fsaid "velocity-varied rbeam back into ssaid'zvelocityevaryingmeans;in over-.hunched con- Idition.

L18. High .frequency fapparatus comprising mica-ns vvfor producing an electron i'stream, :means valong the pathlofsaidstream .for velocity-modulatingzsaidfelectrongstream;means along saidpath ffnrfextracting high frequency energy .from said modulated stream, means couplingsaid modulat- :ing'means and said :extractingmeansxtogether to `@sustain-10scillationstin'saidextracting means, said g.

apparatus also including means Ifor` maintaining :substantial-ly :constant zmutual .conductance .be- .tween isaidxmodulating; means and said extracting means,aid;lastenamedmeans comprising means :along :said .pat-h frorrelecting Va portion vof said i ,hear-n fback `'througli said vvelocity-modulating imeansiinzoverbunchedcondition.

;19. ,High `@frequency electron :discharge `appafiatus acomprising mean-s ifor producing an elecztron z stream, v`a .pair cof electron f, permeable electtrodes in .the1path of tsaid Vstream x and defining .ragga-pftherealong,ttunedfrcircuit` means. coupled-to said -electrodes for 4 producing a .high frequency falternating'electric field iacross said gap, a furitherfe'lectron permeable felectrode .in said path,

:said i apparatus :including -means 'deiining-a viiel'd :free 'spa-ce :between said further :electrode and :saidvfgapaafreector electrode in saidpath beyond said .furtherelectrode, and biasing means f, coupled l to said reflector electrode for maintain- .,ingf-saidrreflector electrode at a negative poten- .itial` with respect'to-said further electrode, :wherei-by :.the electrons of said 1 stream are reiiected ato freenter said gap-andxniaintainy said eld.

20. High frequency electron discharge v'appa- .fratuscomprising means'ior producing :an elec- :tron'strea-m, v.meansin the path of `said stream for producing Van axially extending alternating electric field-for velocity modul-ating said stream,

.said apparatusiincluding-i-rneansfdening `a eldf1ee.-s1: ac,eV surrounding *the path of said stream .beyond "said el'd-producing imeans, Vand means aforfdeningal reflecting -electricifeldzin the path ,cof Isaid ,-strearn adjacent toeandbeycnd said eld- :'lfree-spaee-dening vmeans, whereby said elecz i stron ,streamfisreversed to ymaintainsaid alter- ',nating eld. f

:.21. ,-I-Iigh .frequency --electron discharge .appafratus ,comprising means for lproducing 1 an velec- .-,tronrstream, a cavity resonator having apairfof y apertured vwalls in the -fpath of. said stream, .fan @electron-permeable .electrode in said path,sai'd capparatusincludingmeans defining a field-'free -space bet-Ween said rcsonatorandsaid electrode,

fa .reiiector electrode in Asaid :path beyond said lrst electrode, andfbiasing; means coupled to; said :reflector electrode for `maintainingsaid reflector @electrode vata, negative Vpotentialzwith respect to said first electrode, whereby the electrons -of Isaid 'permeablewwallsiinlthe path.:.of-. said:.streamnsaid ;apparatus including means defining a eldefree space-surrounding the; pathrof. said stream beyond said 'resonatcr, and a "reiiector .electrode v in :the rpath.y of ,i said :stream '..heyond #said field-.free .space for refieeting .the electrons of said-stream torre- ;eni-erfsaid resonator.

1123. High :frequency i electron discharge appafratus @comprising :means for w producing an y.electron stream.: a :cavity:resonator` having electron.- iperrneableawallsi in the path :of A said stream, `arreiilector yelectrodezin at'he path `of :said stream .':befryond .said :resonator i:for -re`ecting rthe electrons of :said .-f-stream torreenter `said resonator, and ea further electron-permeable :electrode vpositioned :alongthepathg-of saidistream between said res- "Onator and :said 'reiiector' electrode YYfor further lcontrollingsaid stream.

.2.4. :High @frequency apparatus, comprising sa cathode. a pairfoflgrids and a reflector :elec- -t-rode, .all' said electrodes v being aligned along :an i-electronstream path, and means .f-coupledftofsaid :grids and defining a :cavity f resonator ytherewith .adaptedrtohave-an-.electric eld extending along .said path -between .f said grids and -spaced Vfrom ...saidfcathodefand reector.

I25. fApparatusfasfin .claim 24, further comprising potential sourcez means coupled between said -cathode and resonator ,for -frnaintaining said cathode :negative V,with irespect :tosaid resonator, whereby @electrons from said cathode are V`accel eerated (.towar'd and ;.thro ugh l*said grids, fand fur- .ther including potentialA source: meanscoupled'zto said reflectornelectrode for maintaining said reiiector lelectrode negative -.with respect -to said gridsl .wherehyss-aid .electron-s are v repelledi and re- -iversed .by -fsaid reflector electrode and caused Pto lreenter saidresonatorlcy way of-sa`id grids.

26. Apparatusas in .claim 24, .further including ,'another ,grid "electrode between -said reflector electrodefand-said pair of grids.

:27. ,High ,frequency apparatus icomprising .a cathode, a redenen-electrode spaced Atherefrom sanda: cavi-ty. resonator rbetween; and f spaced i from `looth said icathode yand ,reflector -electrode .and .,adaptedto-,sustaina high frequency electric field extending in a region between said-cathodezand freflector elect-rodeuponrexcitation of said resonaton 28. A .high .frequency ielectronic .device corn- .prsing a. hollow l cavity lresonaton capable of 'be- `higiene*rg-izedto support highirequency electricaL oscillations to producetaJ high f frequency elec- ;,trc Jield, Aa Isource of `electrons and means for .causingelectrons-,from the source .to ytraverse yat llleast portions v of a path extending .fin alignment ,with .the .electron source .and Athe resonator, the 'traversed portionsoftheipath including va region `Qccupiedhy thehighfrequency electric fieldfand lincludingtalso. spaces-.on yeach sidev of i, thatiregion .Which...are free 'frpm .thehighffreqnency weld, ifor permittingelectrons .to ypass through said spaces Without influencing said ,'eld, -said means -com- ;prisi'ng .an .accelerating :electrode ,located along the .said path andsozpolarizedsas'to propel elec- .trons f. through .the high .frequency eld region `in .the direction, away from the-.electron source,-and ta :retard-ing f and reversing electrode located along V-the gpathon the sideofithe high ifrequency feld :stream ;are';:reflected-',to.reenter-said resonator to im .region ppposite theaelectronysource and so .polarexchange energy' with the electromagnetic afield ttherein.

22. fHigh :frequency -electron discharge riaipparatus :comprising :means for producing :an electized .fas ,to propel electron-s: through the high frequ'ency feld y.region in the i.direction :toward --tne ele ctrcn asonrce.-

:1.29. .+highzfrequency :devices comprising a 1h01- ttmn.strean1,.;a:cavi ty resonator .having electron- 1.15 ginwfpavityrresonatqr.-apable--Qffbeingz'energizedito support high frequency electrical oscillations to produce a high frequency electric field, a source of electrons external to the resonator, an electron collecting electrode spaced from the electron source, the resonator being located between the electron source and the collecting electrode and having an opening in its structure such that electrons traversing the path between the electron source and the collecting electrode pass through the high frequency electric field associated with the resonator in the vicinity of the opening and through regions on each side of the high frequency field region which are free of high frequency eld, an electron accelerating electrode located along the said electron path and polarized such as to propel electrons through the high frequency field in the direction away from the electron source and an electron retarding and reversing electrode located along the electron path on the side of the resonator op- .posite the electron source and polarized such as to propel electrons through the high frequency field in the direction toward the electron source.

30. A high frequency electronic device comprising a hollow cavity resonator capable of being energized to support high frequency electrical oscillations, a gap in the structure of the resonator such that electrons projected across the gap will pass through the high frequency electric iield associated with the resonator when it is energized, a space on each side of the gap which is free from the high frequency field, a source of electrons external to the resonator, an elec tron accelerating electrode so positioned and polarized with respect to the electron source as to propel electrons from the source through the Vhigh frequency electric iield across the said gap in the direction away from the electron source,

an electron retarding and reversing electrode positioned along the path of the above-mentioned electrons on the side of the gap opposite the electron source and so polarized as to stop, reverse and propel at least some of the electrons through the high frequency eld across the said gap in the direction toward the electron source,

and electric potential means for polarizing the said electrodes.

31. In a high frequency amplifier, a resonant cavity input circuit, a resonant cavity output circuit, an electron emitting cathode, an electron collecting electrode spaced from the cathode, means for causing a stream of electrons to leave the cathode and traverse at least portions of the Vpath between the cathode and the collecting electrode, the input and output resonant cavities having openings in their structures and being so placed along the electron path between the cathode and the collecting electrode that electrons from the cathode pass first through the high frequency electric field associated with the input cavity in the vicinity of the opening in that cavity then through the high frequency electric field associated with the output cavity in the vicinity of the opening in that cavity, there being also regions along the electron path on each side of the last-mentioned opening which are free of high frequency field, the said means for causing electrons to traverse the said paths comprising at least one electron. accelerating electrode so polarized as to propel electrons in the direction away from the cathode through the high frequency eld and the regions free of high frequency field in the vicinity of the opening in the output cavity, and at least one accelerating electrode so `polarized as to propel electrons inthe direction toward the cathode through the high frequency field and high frequency iield free regions in the vicinity of the opening in the output cavity, means for transferring high frequency energy from the output cavity to a utilization circuit, and means for energizing at high frequency the input cavity whereby high frequency variations are impressed upon the electron stream from the cathode as it passes through the high frequency field associated with the input cavity in the vicinity of the opening in the input cavity structure.

32. An amplifier according to claim 31 in which the means for impressing the high frequency variations upon the electron stream as it passes through the high frequency field associated with the input cavity are means for producing variations in the electron velocities.

33. An amplifier according to claim 31 in which the means for impressing the high frequency variations upon the electron stream as it passes through the high frequency field associated with the input cavity are means for producing Variations in the charge density of the electron stream.

34. A high frequency electronic device, comprising a hollow cavity resonator capable of being energized to support high frequency electrical oscillations to produce a high frequency electric field, a source of electrons external to the resonator. and means for causing electrons from the source to traverse at least portions of a path extending from the source and including a region occupied by the high frequency electric field and including also spaces on each side of that region which are free from the high frequency field, said means comprising an accelerating electrode located along said path and so polarized as to propel electrons through the high frequency field region in the direction away from the source and a retarding and reversing electrode located along the path on the side ofthe high frequency eld region opposite the electron source and polarized to repel electrons through the high frequency eld region in the direction toward the electron source.

. 35. An amplifier comprising means for producing an electron stream, input and output circuits comprising hollow resonators having apertures to permit passage of at least portions of the electron stream through a portion of the electric eld associated with the excitation energy of each of the resonators, means for exciting the input circuit whereby the interaction between the electron stream and the electric field of the input circuit resonator produces variations in the velocities of the electrons in accordance with the excitation energy, means at a point in the path of the electron stream following the place of its interaction with the field of the input circuit resonator (but in advance of the place of its interaction with the field of the output resonator) for producing a retarding field to turn back at least some of the electrons which have had their velocities reduced by the said interaction and allow other higher velocity electrons to pass on through the said portion of the electric field of the output circuit resonator and transfer energy thereto in accordance with the excitation of the input circuit resonator.

36. An amplifier comprising an input circuit an output circuit comprising a hollow electrical resonator, means for producing an electron stream, means for energizing the said input circuit, means for varying the velocities of the electrons of the said stream at a point along its course in accord with the `eXcitati-onof 4the input circuit, ,means ata subseqnent-.pointf-along :the course of the stream for setting up a retarding electric eld to turn back lower velocity electrons while allowing higher "velocity yelectrons topass and excite in accord with the excitation of the input circuit the hollow resonator of the output circuit which is positioned at a point still farther along the stream.

37. An amplifier including anfelectronemitting cathode, an electron collector, `means for produci-ng yan velectron stream :along .a vpath from the cathode to the collector, a resonant cavity, means comprising a pair of electrodes bounding a gap in the `resonant cavity and positioned along .the path of the electron stream between the cathode and the collector for varying the velocities of the electrons traversing thegap .between theeletrodes, .a second resonant cavity, means comprising a second pair of electrodes .bounding a .gap in the second resonant cavity and positioned along the path of the electron stream between the first-mentioned pair of electrodes and the collector whereby density variations in the electron stream traversing the gap between the second pair of electrodes may excite electrically the second resonant cavity, and means comprising a retarding electrode positioned along the electron stream and between the two said pairs of electrodes for producing a retarding field to turn back electrons which have had their velocities reduced during traversal of the gap in the rst cavity while allowing higher velocity electrons to pass on and cross the gap in the second cavity whereby the electron stream traversing the gap in the second cavity is density varied and the second resonant cavity is excited thereby in accordance with the velocity variations impressed upon the electron stream as it traverses the gap in the first resonant cavity.

38. In combination, a pair of hollow electrical resonators having apertures such that an electron stream may be projected through portions of the space of both resonators in series, means in said combination for projecting an electron stream therethrough, means external to it for exciting at high frequency the said resonator first traversed by the electron stream to produce variations in the velocities of the electrons in the stream, means in said combination for producing a retarding field located between to reduce the velocities of all of the velocity varied electrons and to turn back electrons having had a negative velocity variation permitting others to pass on into the space of the other resonator to excite it at the said high frequency, and a high frequency load circuit coupled to the said other resonator.

39. In combination, means for producing an electron stream, means for varying the velocities of the electrons of said stream, means for producing a retarding field beyond the velocity variation Zone to reduce the velocities of all the electrons in the stream and to turn back electrons having had a negative velocity variation, thereby dividing the stream into two parts each having density variations in accordance with the impressed velocity variations, one part consisting of the electrons turned back by the retarding iield and the other part consisting of the electrons which continue on through and past the retarding field, and a hollow resonator having an aperture in line with one of the density varied parts of the electron stream to permit the resonator to be excited thereby.

40. In combination, means for producing an electron stream, means comprising an electrical circuit excited from a -source external to it for varying the velocities of the electrons of said stream, means for producing `a retarding iield beyond the velocity variation Zone to reduce the velocities of all the Velectrons in the stream and to turn back electrons having had a negative velocity variation and to pass on other Velectrons of said'stream beyond said `retarding field, thereby dividing the stream into two par-ts -each having density variations `in accordance with the impressed velocity'variations, one part consisting of the electrons turned back by the retarding eld and the other lpart consisting of the electrons which continue on through and past the retarding held, and a hollow resonator having an aperture in lline with one 4of ythe density varied parts of I'the electron vstream to permit the resonator to ybe .excited thereby.

41. 11n combi-nation, means for Iproducing an electron stream, means vin said combination -ior var-ying the velocities of the electrons of said stream, means in said combination for producing' a retarding field beyond the velocity variation zoneto reduce the Avelocities of all electrons in the stream and-ltofturn back electrons having had a negative velocity variation and a cavity resonator beyond the zone of the retarding field having an aperture in line with the electron stream to permit the resonator to be excited by electrons which received a positive velocity variation.

42. In combination, means for producing an electron stream, means in said combination comprising an electrical circuit excited from a source external to it for varying the velocities of the electrons of said stream, means in said combination for producing a retarding field beyond the velocity variation zone to reduce the velocities of all electrons in the stream and to turn back electrons having had a negative velocity variation, and a cavity resonator beyond the zone of the retarding eld having an aperture in line with the electron stream to permit the resonator to be excited by electrons which received a positive velocity variation.

43. Apparatus including means for producing an electron stream, means in said apparatus for varying the velocities of the electrons of said stream at a point along its course, means at a subsequent point along the course of the stream for setting up a retarding electric field to turn back lower velocity electrons while allowing higher velocity electrons to pass, and a cavity resonator positioned at a point still further along the course of the stream to be excited by the higher velocity electrons which succeed in passing beyond the retarding field means.

44. Apparatus including means for producing an electron stream, means in said apparatus comprising an electrical circuit excited from a source external to it for Varying the velocities of the electrons of said stream at a point along its course, means at a subsequent point along the course of the stream for setting up a retarding electric field to turn back lower velocity electrons while allowing higher velocity electrons to pass. and a cavity resonator positioned at a point still further along the course of the stream to be excited by the higher velocity electrons which succeed in passing beyond the retarding field means.

45. Apparatus including means for producing an electron stream, means in said apparatus comprising a rst cavity resonator adapted to be excited from a source external to it for varying the velocities of the electrons of the said stream at a point along its course, means at a subsequent point along the course of the stream for setting up a retarding electric eld to turn back lower velocity electrons While allowing higher Velocity electrons to pass, and a second cavity resonator positioned at a point still further along the course of the stream to be excited by the higher velocity electrons which succeed in passing beyond the retarding eld means.

46. In combination, means for producing an electron stream, means in said combination for varying the velocities of the electrons of said stream, means in said combination for producing a retarding eld beyond the velocity variation zone to reduce the velocities of al1 electrons in the stream and to turn back only electrons having had a negative velocity variation, and a cavity resonator beyond the Zone of the retarding eld having an aperture in line with the path of the electron stream to permit the cavity to be excited by electrons which received a positive Velocity variation.

WILLIAM W. HANSEN. SIGURD F. VARIAN. RUSSELL H. VARIAN.

REFERENCES CITED UNITED STATES PATENTS Number Name Date Re. 22,506 Hahn June 27, 1944 1,971,902 Clavier Aug. 28, 1934 2,128,232 Dallenbach Aug. 30, 1938 2,128,236 Dallenbach Aug. 30, 1938 2,129,713 Southworth Sept. 13, 1938 2,167,201 Dallenbach July 25, 1939 2,170,219 Seiler Aug. 22, 1939 2,170,657 Herzog et al Aug. 22, 1939 2,190,511 Cage Feb. 13, 1940 2,220,839 Hahn Nov. 5, 1940 2,245,627 Varian June 17, 1941 2,250,511 Varian et al July 29, 1941 2,259,690 Hansen et al Oct. 21, 1941 2,278,210 Morton Mar. 31, 1942

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