US2520383A - Ultra high frequency oscillator - Google Patents

Description

Aug. 29, 1950 P; H. CRAIGr l 2,520,383

ULTRA HIGH FREQUENCY oscILLAToR Filed oct. 1s, 1944 S Q WAVE I 1K F 8 t [O-Iii*f /Oa GENERATQQ l 1 u, n I

Patented Aug. 29, 1950 oj STA-tes `punita.xH-icm Fnaiicysouts'mn, A

RalmerHr Craig, Gainesville;FlaaassignortosI l Invex, Inc.,.a corporation oflori'da; l

.Application Qctoher 18, 1944, Serial No. 559,215

4 Claims.

This invention relates to an electronic oscillator capable of generating oscillations of ultrahigh:Lfrequencye` An object of fitheff invention i is to A.deviseaan electronic oscillator in which the frequency of the oscillations is dependent upon the speed of the electrons and is not determined by resonance of a circuit.

The invention involves an electron tube-lin. which a concentrated beam of electrons is projected through a series of aligned inductor elements each fof Whichembodiesa pickup, coil.'` The electron stream is interrupted or varied periodically so that groups or bunches of electrons` pass in succession through saidinductor elements. A voltage impulse of` yone polarity is generated in each coil by each group ,ofelectronsapproaching theinductor, and an impulse of opposite polarity" isgenerated'as eachA electron group recedes from. the inductor. The pickup coils are connected lin acommon output circuit and a `feedback.connection is provided from the output circuit to controlthe phase `relation of'the grouping `or bunchingjof they electrons 'in the stream 'in orderto secureimaxirnum amplitude of the voltages inducedinithe pickup coils.

My `invention is "illustrated inthe accompanying drawing in which Figure l is a diagrammaticrepresentationof the preferredfcrm of theoscillator circuit, the electron` tube being shown-in'- longitudinal crosssection:

Figure 2 is a sectional view ofthe magnetic core of an inductor-element showing various dimensions and- `factors controlling the operation of theoscillator; and

FiguresS and4 are diagrams illustrating the voltages `induced in the inductor elements.

Referring to the drawing, the electronic tube employed inthe oscillator is diagrammatically represented in Figure 1 and may-consister an insulating envelope l containing-a suitable cathode 2 mounted in one end thereof andlheated from a suitable source 3. An anode orwplateV P is mounted in front ofthefcathodeland `isprovided with a centralaperture or opening Pa. A control grid G'risl1interposedbetween ithevcath-f ode 2 and the plate P which `plateis maintained at a `positivepotential fwith respectuto cathode 2 by a suitable source 4. Asecond anode` Sais pro.- videdin the oppositeendiof thectube `from-...cathode-2- and maymformtm end wall :oi-:tneltubefas shown `in .Figure 1. or. itumay be separata from tained: at.` a positive potential:` `witlr` respect` cto plate f lPl byYf-meansy of source k 6. `Interposed fbee `tween .platefP and anode V5 is` la series `of `indim- Itors :embodying :magnetic Lringsi TI` arranged in .axial alignment fwithf the IaperturelPmin thefplate P and `being spaced apart at regular intervals. Each magnetic ring: --may'ibe tormedcf com pressed po'vvderedPermalloy, Mumetal,. or other suitablexmagneticzmaterial.and carries a pickup coil in; IThese pickup coils are-eonnected in serial circuit relation in an output circuit which supplies a load device 8. An uoscillator 9 of suitable.\ -constructi0n is.:connected to `supply a control wave to control grid G, and the oscillator is controlled .or synchronized and properlyphased with' respect Lto the oscillations in the output circuitby means of a feedback circuit including a. phase shifting filter I'G of V suitable construction. In the example shown inJFigure l', the lilter may be `formedA of two series .condensers 10a and 10b `in opposite-sides of the Afeedback connection and a variable'shunt resistance 10c. The function of controljgrid 'Gjis to `break `upjthe electron* stream passing through the4 inductor `elementsinto groups or bunches ofv electrons, and `for 4thispurpose I-prcfer `to use `an oscillator at9 producing-fa square-top wave, although other wave shapesmaybe employed:A Asuitableform of oscillator Vto bejused` at Swill-be found-in Termans Radio Engineering I-Iandbook ait pages 970 `and 971.

Operation of Figure 1 `is as'follows: Th'eelectrons emitted from cathode `2 are drawn towards 'the plate P -by source' 4 fand Athe velocity of the 4electrons passing through the aperture Pa Awill be determinedbythehvoltagerof the plate-=P with `respect to the cathode 2. Suitable focusing coils or `electrodes maybe used to concentrate the electrons on the aperture -Pa- `if desired. The grid lGr serves to interruptor vary `thestreamfo electro-ns which passes-.through the aperture-` Pa so that the stream `passing" through fthe-aperture is formed-- of a series- `of `successive 1 groupsror bunches of `electrons Awhich are-projectedvalong the common axis of the inductonrings 1.' If 1desired, conventional. electron focusing coils or electrodes may be employed to concentrate and direct the stream along. the:,axis :of i the inductor elements. As` each electronzgroup or bunch :ap-.- proaches.; and:` passes.l through i each inducton a complete.; cycle of voltage' is;` generated inil the associated` pickup.; coil;'la,;and the duration` of the induced cycle i will be dependentV upon;` the speed at which the electron bunch isftravelling, Since all of the pickup coils are connected to a common output circuit; each bunch of electrons will inducen:voltagetcvcleineach .pickup coil it passes from plate P to anode 5. In other Since the magnetic circuit of ring 'lis uniform Words, in the example shown in Figure 1, each in cross-section and is symmetrical about the axis bunch of electrons will induce ten complete of the ring, Equation 1 may be stated in terms of cycles of voltage in the output circuit in passing a, b, :c and y as follows:

from plate P to anode 5, and the separation be- 5 tween the successive cycles of voltage will be VQ-Fj dependent upon the speed at which the electron H=-22-'J=VQ 2y-2 (3) bunch is travelling and upon the distance of x 'i'y (x iw) separation between adjacent inductor units. The total flux induced in the magnetic circuit Accordingly, by properly spacing the inductor 0f ring 1 now becomes: units and by adjusting the speed of the electrons, the frequency of the voltage impressed Imis-u 2+!) y'ia--gimdydx upon the output circuit may be controlled. I b V (x 'i'y With a given spacing between the inductor units, =[Sinh l x Sinh 1 j Ti'buVQ the frequency may be varied by varying the voltl/-a 11H-a I-b age of the source 4 or of the source 6 or of both. z+1, b

In order that the succeeding bunch or group =VQ|:S1nh'1 y asmh"1 23" of electrons shall have the proper phase relation z+1) z b to augment the voltage induced by a given bunch sinh-1 +a+sinh1 E .o f electrons, it is important that the groups or Y' f 'f Y s yr y l bunches of electrons shall be released by the grid (4) ,G in a predetermined phase relation with respect The electromotive force induced in any pickup to the oscillations in the load circuit. For this loop wound around ring 1 will be:

purpose, a feedback circuit including phase From Equation 5 it will be seen that the inshifter l0 is provided for controlling the phase 35 duced voltage varies as the square of the velocity relation of the pulses generated by control genof the approaching charge, and directly with the erator 9 in timed relation with the oscillations in value of the charge, the number of turns o'n a. the load circuit. The proper phase relation may pickup coil, the permeability and dimensions of be secured by adjusting the values of the elements the inductor core, and the instantaneous posiin phase shifter I0 until maximum output is ob- 40 tion of the charge along the inductor axis. tained in the load circuit. Upon examining the term within the brackets Since energy will be absorbed from each elecand designating it as F(), it will be found that tron charge or group as it passes through each as a: is varied, the general shape of this funcinductor element, the speed of the charge will be tion is shown in Figure 3. This figure also repslowed down, and in order to compensate for this resents the shape of the induced electromotve loss in velocity, the anode 5 is maintained at a force. As the charge Q approaches the magnetic positive potential with respect to plate P by ring yfrom the left, the induced E. M. F. Vin the Ameans of source 6. Additional accelerator pickup coil increases to a maximum at a definite anodes (perforated anodes) may be inserted at distance 5cm from the center of the magnetic .different points along the series of pickup units ring, and then reduces in value to zero at the in order to compensate for the loss in energy, and plane of the ring and thereafter increases to a these additional anodes would be connected to maximum value in the opposite direction at +m.

intermediate points on the source 6. One such and then decreases towards zero as the charge i accelerating anode is shown at 5. continues to the right of the ring along the axis. The wave form of the electromotive force which Where Several of the inductors are connected is induced in each pickup coil may be understood in series and are spaced apart by equal distances, from the following. Referring to Figure 2, if Q the individual voltage cycles generated in the represents la charge moving at a given velocity different coils are represented by the solid, line V along the axis of magnetic ring '1, then the curves in Figure 4, and the resultant alternating field H of this moving charge at the point S lo- 50 voltage produced by a group of electrons passing cated at a distance 1' from QY and at an angle through the four coils is represented bythe dot- 0 with respect to V may be determined from the ted line curve in this figure. following equation: If more than one group of electrons is passing Y 2 through the series of pickup units at the same H VQ Sme o/T (l) 55 time, the resultant Voltage induced in the circuit In Figure 2 the point S has been taken at the Will depend UDCH the TeleiVe SDaCIlg 0f the center of the magnetic path of the ring 'I which g'IOllpS- It iS implienb therefore that the Spachas a cross-section of 2b 2a and a mean diameing 0I phasing 0f the eleCtI'On gIOuDS be propter of 2y. The charge Q is located at a, distance erly controlled. The groups should be released in :1: from the central plane of the ring 'I passing I timed felation Such that they are Separated by a through the point S The iiux induced in the distance equal to the spacing between adjacent ying by the eld H Wi11 be; units or anyrmultiple of this spacing. The propp fuH'd (2) er phasing Aof the electron groups or bunches is determined bythe phase shifter lll; The fre- -where u is the permeability of the ring. quency of the electron groups, or the numberof groups per second which pass through aperture Pa, may be equal to the frequency of the generated voltage in the load circuit, or it may be any sub-multiple of this frequency.

The value of the resultant voltage generated in the series of pickup coils will also be dependent upon the length of each electron group or bunch passing through the series of pickup units. For most eicient operation the electron groups should have a length equal to half the distance of separation of adjacent pickup units. Other lengths are possible, but it is preferred to have the electron groups of a length of one-half the distance of separation between adjacent pickup units or an odd multiple of this length, The importance of the length of the electron group will become apparent when it is considered that the approaching end of the group induces a pulse of one polarity in a given inductor unit while the receding end of the group induces a pulse of opposite polarity in the same unit. The length of the individual electron groups or bunches will be determined by the shape of the control wave applied to the grid G from the source 9.

The length of the inductor element along the electron path is also a factor in the shape of the current pulse generated in the pickup coils. Preferably, the inductor elements have a relatively narrow dimension in the direction of the electron stream with respect to the length of the path between the plate P and the anode 5, and the inductor elements should not have a width along this path greater than one-half the distance of separation of adjacent units.

A condenser Il may be connected across the load circuit to form a resonant combination with the pickup coils. This will reduce the effect of the inductance of the pickup coils in the output circuit. If desired, small condensers may be connected in series with the circuit between the inductor elements, or the condensers may be connected in parallel with the pickup coils. Such condensers may be located either inside of the tube or outside and would serve to tune each coil or a group of coils to a particular frequency. Furthermore, it is not essential that the pickup coils be connected in serial circuit relation to the output circuit, but they may be connected in parallel relation to the output circuit.

An amplifier may be inserted in the feedback connection either in front of or behind the phase shifter IU, or the necessary amplication may be obtained in the control generator 9.

It will be obvious that the details of construction of the oscillator tube may be varied in different ways. For example, instead of forming the inductor elements of magnetic rings with pickup coils wound thereon, these elements may be formed without magnetic cores and the pickup coils would surround the path of the electron groups and would be spaced apart in the same manner as the magnetic rings. Also, the pickup elements may be spaced apart by progressively decreasing distances in order to compensate for the loss in Velocity of the electron groups as they move from the beginning towards the end of the series.

I claim:

1. An electronic oscillator comprising, in combination, a source of electrons, means acting on said source and producing a stream of electrons therefrom directed along a predetermined path, means periodically interrupting said stream to form a succession of electron groups along said path, a plurality of separate inductor elements mounted in spaced relation along said path and in inductive relation to said electron stream, each of said inductor elements including a coil, and an output circuit including said coils connected therein in series relation.

2. An electronic oscillator comprising in combination, a source of electrons, means producing a stream of electrons from said source and directed along a predetermined path, means periodically interrupting said stream to form a succession of electron groups along said path, said groups being of uniform lengths, a plurality of inductor elements mounted in spaced relation along said path and in inductive relation to said electron groups passing along said path, each inductor element including a coil, said inductor elements being spaced apart by distances of the order of twice the length of an electron group, and an output circuit having said coils connected therein in series circuit relation.

3. An electronic oscillator according to claim 1 wherein said inductor element comprises a magnetic ring surrounding said path, and a pickup coil wound on said ring.

4. An electronic oscillator comprising in combination, a source of electrons, means producing a stream of electrons from said source and directed along a predetermined path, means periodically interrupting said stream to form a succession of electron groups along said path, a plurality of inductor elements mounted in spaced relation along said path and in inductive relation to the electron stream, each of said inductor elements including a coil, an output circuit including said coils connected in series relation, and a feedback connection from said output circuit to said interrupting means for controlling the phasing of said interrupting means.

PALMER I-I. CRAIG.

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

UNITED STATES PATENTS Number Name Date Re. 21,739 Llewellyn Mar. 4, 1941 2,009,457 Sloan July 30, 1935 2,074,478 Linder Mar. 23, 1937 2,197,338 Fritz Apr. 16, 1940 2,284,751 Linder June 2, 1942 2,295,680 Mouromtseff et al. Sept. 15, 1942 2,299,792 Bouwers et al l- Oct. 27, 1942 2,300,052 Lindenblad Oct. 27, 1942 2,272,605 Hesing Feb. 10, 1942 2,305,883 Litton Dec. 22, 1942 2,372,193 Fisk Mar. 27, 1945

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