US2436397A

US2436397A - Ultra high frequency oscillator

Info

Publication number: US2436397A
Application number: US454112A
Authority: US
Inventors: Jack A Morton
Original assignee: Bell Telephone Laboratories Inc
Current assignee: AT&T Corp
Priority date: 1942-08-08
Filing date: 1942-08-08
Publication date: 1948-02-24
Anticipated expiration: 1965-02-24

Description

Feb. 24, l.

J. A. MOTON ULTRA lHIGH FREQUENCY OSCILLATOR Filed Aug. 8, 1942 f5) 2S e M5 3 Jl l l llll l Il 22 2a 2s r /f u ullnlglslellm 2/ o llllllullllllllllllll 0R TON Patented Feb. 24, 1948 ULTRA HIGH FREQUENCY OSCILLATOR .lack A. Morton, Warren Township, Somerset County. N. J.. assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New Yorls Application August 8, 1942, Serial No. 454,112

This invention relates to electronic devices for the production of high frequency electrical energy and particularly to such devices characterized by the use of hollow closed resonators and in which electron transit time is a factor of importance.

An object of the invention is to provide an efflcient oscillator capable of operation at high frequencies with relatively low direct current power supply voltages.

Another object is to provide such an oscillator incorporating the advantages o f closed completely shielded high frequency circuits.

Another object is to provide such an oscillator of which the frequency is conveniently adjustable.

Another object is to provide such an oscillator which is relatively compact.

.Another object is to provide such an oscillator having good frequency stability.

Resonant cavity type oscillators oii'er many ad vantages when energy at very high frequencies. is

to be generated. Such oscillators may employ ar f single cavity or a number of cavities and many. diiierent methods o f operation may be employed. For example, a familiar type employing two cavity resonators utilizes the first cavity to vary the velocities of the electrons in an electron stream, a drift space between the two resonators to allow the accelerated electrons to overtake decelerated electrons thus producing density varia tions in the stream and a second resonator to be excited electrically by the density varied stream. The device of the present invention differs from this and other well-known resonant cavity oseillators in several respects while incorporating the advantages of the cavity resonator type of circuit.

A resonant cavity type of circuit is employed and through a portion of the high frequency field associated with that cavity when it is energized is directed a stream oi' electrons from a cathode. By suitable electrodes and biasing potentials applied thereto' a direct current electric field is superposed' upon the portion of the high frequency field traversed by the electron stream such that it opposes the iiow of electrons tending to return them toward the cathode. Adjustments may be made so that `electrons entering the high frequency field in such" phase as to absorb energy and be accelerated will overcome the retardation of the direct current field and pass on through while electrons entering in such phase as to give up energy to the high frequency field and be de' celerated will not be able to overcome the re. tardation of the direct current eld and so will be and a dinthsoppoeite 14 Cl. (Cl. 315-6) rection. again giving up energy to the high irequency field. Thus, since the energy giving electrons traverse the ileld twice while the energy absorbing electrons traverse the field only once the energy contributions preponderate and high irequency oscillations are sustained in the cavity resonator circuit. The output and eiilciency of the device are enhanced by utilizing a resonant cavity input circuit energized by feedbackl from the output circuit to control the space charge current in a manner to eliminate from the electron stream the energy absorbing electrons which as explained above traverse the high frequency field only once and absorb A high frequency energy rather than contribute to it.

The invention will be described more fully by k\`\ output circuit a cavity input circuit with a feedtance across the annular space between members t the size of back circuit to energize it whereby the electron stream is modulated at the operating frequency and the elciency of operation enhanced, and Fig. 3 shows a modiilcation ol the Fig. 2 device in which the oscillations are produced initially in the cavity input circuit which is electron coupled to the output circuit, half of the electrons exciting the input circuit and the other half exciting the output circuit.

'leferring now to Fis. l, an insulating evacuatedi envelope i contains the indirectly heated cathode 2. the grid electrodes 3 and t and the plate electrode 5, all of these being supported by and connected to the

disc members

22, 23, 2t and 2d, respectively, which are fused into'the envelope l and serve to connect the electrodes to external circuits. 'I'he cavity resonator 2l is con- `;-venlent1y made in coaxial form as shown and is bounded by members t, di. il, i2, it, it, it and d. This resonator is the sole high frequency cir cuit of the oscillator proper in Fis. l. The an nular members i2 and it are spaced ra from each other to provide direct current insula tion between electrodes d and but the capaci'- lt and It is made sufficiently large to provide a low impedance high frequency path thus effectively closing the resonator between the coamal members it and il. Members it and i2 are movable along members l0 and il. respectively so 2l and conse quently its resonant frequency may be varied."

thereby.

The cathode is heated through lead I 6 from potential source I1. The grid electrode 3 is maintained at a potential near that oi the cathode by lead I8 connecting to either potential source Il or I9; the plate electrode 5 is maintained at a potential near that of the cathode by means of lead 20 connecting to either potential source Il or I9; and the grid electrode 4 is maintained at a potential positive with respect to the cathode and the other electrodes by means of lead 2| connecting to potential source I 8.

In operation, electrons emitted from the cathde 2 proceed in the direction of the plate electrode under the influence of the grid electrode 4. Upon passing through vthe grid electrode 4 the electrons come under the inuence of the high frequency neld associated with the resonator 21 and impressed upon the space between the grid 4 and plate 5. Depending upon the phase of this field at the time an electronenters it the velectron is accelerated or decelerated and consequently some electrons are accelerated and gain energy from the iield while others are decelerated and give up energy to the eld. The electrode potentials are made such that the electron transit time between the grid electrode 4 and the plate electrode 5 is approximately the period of one-half cycle of the frequency to which the cavity resonator 21 is tuned and also such that electrons which have gained energy and been accelerated are able to pass on to the plate electrode 5 where they are collected, in spite of the retardation due to the low potential of that electrode, while electrons which have given up energy and so lost velocity are stopped before reaching the plate electrode 5 and return toward the cathode yielding still more energy to the high frequency field as they again traverse the space between the plate 5 and grid 4. During each cycle therefore more energy is given to the high frequency field than is taken from it because the electrons which absorb energy traverse the neld only once while those which give energy to the field traverse it again in the opposite direction and thus oscillations are maintained in the cavity resonator. High frequency energy thus generated in the resonator 21 may be delivered to a load circuit in any suitable manner such as through the coupling probe 28 to load resistor 23. It is desirable to dimension the tube so that the distance between grids 3 and 4 approximately equals that between grid 4 and plate 5 so that electrons returning toward the plate a second or third time will pass through the space between 4 and 5 in the proper phase.'

With a tube operated in this manner and a condition of complete space charge in the region between the cathode 2 and grid .3, 24centimeter oscillations were obtained with a bias potential of 60 volts between the grid 4 and the cathode 2 while 1li-centimeter oscillations were had with a bias potential o! 107 volts. The oscillations were easily obtained without critical adjustment of the circuit and the frequency of operation was readily changed by varying the tuning of the cavity resonator and the bias potentials. The output of the device may be varied by changing the biasing potential of the grid electrode 3 and consequently the output may be modulated by applying the modulating voltage to that electrode. It may be noted that while this device is operated with complete space charge between the cathode and the first grid electrode 3 the usual Barkhausen oscillator. where rather close coupling exists between the various regions of the tube, does not oscillate very well when space charge exists near the cathode..

While extremely satisfactory performance is had with the arrangement of Fig. 1 it is apparent that half of the emission of the cathode, represented by the electrons which enter the high frequency iield at 'a time to absorb energy and vbe collected at the plate electrode 5, not only do not contribute to the high frequency output but actually absorb high frequency energy. This situation is improved in the arrangement of Fig. 2 where means are provided whereby the electrons leave the vicinity of the grid 3 in groups and in the proper phase to send the groups into the held of the high frequency output circuit in the space between the electrodes 4 and 5 at the proper time to deliver energy to the oscillations. In this way the useless electrons which in the operation of Fig. 1 absorb energy from the high frequency circuit are eliminated. In Fig. 2 a cavity resonator 26 is connected .to the cathode 2 and the grid electrode 3 in the same manner as the resonator 21 is connected to the grid electrode 4 and the plate electrode 5. This resonator when energized impresses a high frequency voltage between the cathode 2 and the grid electrode 3 and the biasing potentials are adjusted so that electrons from the cathode pass the grid 3 and on to grid 4 only during the half cycles of the impressed high frequency voltage when the grid 3 is made positive with respect to the cathode 2. The resonator 26 is bounded by members 3, 23, 1, 8. 9, 6, 22 and 2. Members 8 and 9 are spaced to provide direct current insulation between the cathode 2 and grid electrode 3 land are movable along the coaxial members 6 and 1 to change the size and tuning of the resonator. As between members I2 and I3 there is suicient capacitance between members 8 and 9 to effectively close the resonator for high frequencies. 'I'he conducting sleeve member I4 which is insulated for direct current .from electrodes 3 and 4 by an insulating sleeve the field spaces of the resonators to couple therewith. The flanges 33 and 35 with the insulating spacer 34 provide direct current insulation between the electrodes 3 and 4 and at the same time provide a high frequency connection between the sections 3i and 32 of the outer conductor of the coaxial line. The length of the line must be made such that the energy is introduced into the resonator 28 in such phase relation to the energy in resonator 21 that a maximum number of electrons in each group released by the grid electrode 3 enters the space between electrodes 4 and 5 in the proper phase to give up maximum energy to the resonator 21. Ordinarily this condition is indicated by maximum high frequency output of the device. It will vbe seen that in Fig. 2 the cathode is heated and the various electrodes are biased by means .ofthe potential sources I1 and I9 generally the same as in Fig. 1 and that a load resistance 23 is coupled to the resonator 21 in the same manner in Figs. 1 and 2.

Tests of a circuit according to Fig. 2 showed a high frequency output approximately twice that of the Fig. 1 arrangement indicating the effectiveness of the high frequency control of the electron stream in increasing the output and ei'clency.

Fig. 3 illustrates a modification of Fig.. 2 in which the feedback connection is dispensed with and the relative biasing potentials are changed to alter the over-all mode of operation. With-the exception that the feedback circuit is eliminated the electrodes and the high frequency resonator circuits are arranged the same as in Fig. 2. The electrode biasing potentials, however, are different inFig. 3 than in Fig. 2, the grid 3 and plate 5 being made positive with respect to the cathode while grid 4 is made approximately the same potential as the cathode. In this arrangement high frequency oscillations are generated in the resonator 26 in much the same manner as in the resonator 21 in the Fig. 1 arrangement. Electrons which cross the space between the cathode 2 and the grid 3 in the phase of the high frequency iield associated with the resonator 26 to give up energy to it and on that account are retarded will not be able to overcome the retardation of the low potential electrode 4 and so will be returned toward the cathode and will again traverse the space between the cathode 2 and the grid 3, in the opposite direction, again giving energy to the resonator 26. The result of this multiple crossing of the space between 2 and 3 by the energy giving electrons is a preponderance of energy giving traversals of the space which sustains the oscillations in the resonator 26 in the and means for causing a flow of electrons alongat least a portion of a path extending between the manner the oscillations are sustained in resonator 21 of Fig. 1. However, the oscillations generated in resonator 26 are not coupled directly to the load circuit as were the oscillations generated in resonator 21 of Fig. 1. The electrons which cross the space between the cathode 2 and the grid 3 in the 'phase of the high frequency field to absorb energy from it are accelerated so that they are able to overcome the retardation of the low po- -tential electrode 4 and pass that electrode, after which they are accelerated and collected by the plate electrode 5. These electrons reach electrode and cross the space between 4 and the plate electrode 5 in groups at the frequency of the oscillations in the resonator 26 and, therefore, generate energy at that frequency in resonator 21. Resonator 21 then is the resonant output circuit and it is excited by the groups of electrons which have been accelerated during traversal of the space between electrodes 2 and 3 so that they arel able to pass electrode Il. 'I'he load circuit 29 is coupled to the resonator 21 by means of the probe 28 as in the other figures.

In the arrangement of Fig. 3 the load is coupled to the frequency determining circuit (resonator f ing an electron discharge tube containing at least i four planar electrodes namely an electron emitting cathode, a plate electrode, a iirst grid electrode between the cathode and the plate electrode and a second grid electrode between the iirst grid electrode and the plate electrode, a high frequency circuit comprising a substantially closed electrical cathode and the plate electrode comprising a source of velectric potential connected to each of the said electrodes and to at least one other said electrodewhereby suitable potential diierences are maintained between the various electrodes, the potential differences being such that the potential of the second grid electrode is maintained positive with respect to the cathode and to the other two electrodes and also such that the electron transit time between the second grid electrode and the plate. electrode is substantially the period of one-half cycle of the resonant frequency of the second high frequency circuit. a

2. A high frequency oscillator comprising an electron discharge tube containing at least four planar electrodes namely an electron emitting cathode, a plate electrode, a first grid electrode between the cathode and the plate electrode and a second grid electrode between the first grid electrode and the plate electrode, a high frequency circuit comprising a substantially closed electrical resonator system comprising coaxial conducting members external to the said electron discharge tube and which includes the electron emitting surface of the cathode and the first grid electrode, a second high frequency circuit comprising a. substantially closed electrical resonator system comprising coaxial conducting members external to the said electron discharge tube and which includes the platel electrode and the second grid electrode, means for connecting the two high frequency circuits in feedback relation and means for causing a ilow of electrons along at least a portion of a path extending between the cathode and the plate electrode comprising a source of electric potential connected to each of the said electrodes and to at least one other said electrode whereby suitable potential differences are maintained between the various electrodes, the potential differences being such that the potential of the second grid electrode is maintained positive with respect to the cathode and to the other two electrodes and also such that the electron transit vtime between the second grid electrode and the plate electrode is substantially equal to the period of one-half cycle of the resonant frequency of the second high frequency circuit.

3. A high frequency oscillator circuit compris,- ing an electron discharge tube containing at least four planar electrodes namely an electron emitting cathode, a plate electrode, a iirst grid electrode between the cathode and the plate electrode and a second grid electrode located substantially midway between the iirst grid electrode and the plate electrode, a high frequency circuit comprising a substantially closed electrical resonator system comprising coaxial conducting members external to the said electron discharge tube and which includes the electron emitting surface of the cathode and the iirst grid electrode, a second high frequency circuit comprising a substantially closed electrical resonator system comprising coaxial conducting members external to the electron discharge tube and which includes the plate elecv 7 trode and the second grid electrode and means for causing a flow of'electrons along at least a assedic? portion of a path extending between the cathode.'

andthe plate electrode comprising asource of electric potential connectedV to each of the said electrodes and to at least one other said electrode whereby suitable potential differences are maintained between the various electrodes, the potential differences being such that the potential of the second` grid electrode is maintained positive with respect to the cathode and to the other two electrodes and also such that the electron transit time between the second grid electrode and the plate electrode is substantially the period of oneihaif cycle of the resonant frequency oi;I the second high frequency circuit.

4. A high' frequency oscillator comprising an electron discharge tube having a planar cathode,

a planar, anode and at least one Planar electron permeable electrode located therebetween such that an electron stream passing from the cathode to the anode traverses each of the spaces between the'various electrodes, a cavity resonator comprising coaxial conducting members external to i the said electron discharge tube and connected for high frequencies to two of the said electrodes other than the cathode which are adjacent to each other such that when theresonator is energized a portion of its alternating electric field is impressed upon the space between the electrodes connected to it, means for varying the resonator frequency comprising members slidable longitudinally between the said coaxial conducting mem-` bers and means comprising a source of electric potential connected to each of the said electrodes and toat least one other said electrode for producing a stream of electrons from'the cathode to the anode and for establishing ixed potential differences between the electrodes, the potential dif.. ferences being su'ch that of the two electrodes connected to the resonator the one located nearer the cathode is the .more positive with respect to the cathode and, further, the potential dlierences and the distances between the electrodes being v and later encounter y 8 an electrode substantially negative with respect to the said permeable-positive electrode whereby'electrons are reversed and prevented from reaching the anode.

6. A high frequency oscillator circuit comprising an electron discharge tube 'containing at least four planar electrodes namely an electron emit ting cathode, a plate electrode. a iirst grid electrode between the cathode and the plate electrode and a second grid electrode between the first grid electrode and the plate electrode, a high frequency circuit comprising a substantially closed electrical resonator system comprising coaxial conducting members external to the said electron discharge tube and which includes the electron emitting surface of the cathode and the rst grid electrode, a second high frequency circuit comprising a substantiallyclosed electrical resonator system comprising -coaxial conducting members external to the electron discharge tube and which includes the plate electrode and the second grid electrode,

. frequency control means comprising a movable member included with each of the said resonator` systems whereby the resonant frequency of each of the systems'may be readily varied and means for causing a fflow of electrons along at least a portion of a path extending between the cathode and the plate electrode comprising a source of electric potentialconnected to each of the said t electrodes and also such that the electrontransit tron path terminating electrodes termed cathode and anode and at least one planar electron peran electron stream passing from the cathode to the anode traverses each of the spaces between the various electrodes, a cavity resonator comprising coaxial conducting members external to the said electron discharge tube connected to two of the said electrodes which are adjacent to each other and of which one is an electron path terminating electrode such that when the resonator is energized a portion of its alternating electric held is impressed upon the space between the electrodes connected to it, frequency control means comprising a movable member included with said resonator and means comprising a source oi' electric potential connected to each of the said electrodes and to at least one other said .electrode for producing a stream oi electrons from the cathode to the anode and for establishing .anode encounter an electron permeable electrode meable electrode located therebetween such that potential diierences between the electrodes, the

time between the second grid electrode and the plate electrode( is substantially the period of one.

half cycle of theresonant frequency of the second velectron discharge tube having two planar electron path terminating electrodes termed cathode and anode and at least one planar electron permeable electrode located therebetween such that an electron stream passing from 'the cathode to the anode traverses each of the spaces between the various electrodes, a cavity Iresonator comprislng coaxial conducting members external tothe said electron discharge tube connected to two of the said electrodes which are adjacent to-each other and of which one is an electron path terminating electrode such that when the resonator is energized a portion of its alternating electric fleld is impressed upon the space between the electrodes connected to it, frequency control means comprising a movable member included with said resonator and means comprising a source of electric potential connected to each of said electrodes and to at least one other said electrode for producing a. stream of electrons from the cathode toward the anode and for establishing potential differences between the electrodes, the potential diiferences being such that. electrons traversing the path between the cathode and anode encounter an electron permeable electrode substantially positive with respect to the cathode and later encounter an electrode substantiallyv continue along the path to the anode.

l 8. A high frequency oscillator circuit comprising an electron discharge tube containing at least substantially positive with respect to the cathode 7|, four planar electrodes namely anelectron e1nit-L ting cathode, alzplate electrode, a first vgrid electrode between the cathode and the plate electrode and a second grid electrode located substantially midway between the first grid electrode and the plate electrode, a high frequency circuit comprising a substantially closed electrical resonator system comprising conducting members external to.

the said electron discharge tube which includes the electronemitting surface of the cathode and the first grid electrode, a second high frequency circuit comprising a substantially closed electrical resonator system which includes the' plate electrode and the second grid' electrode, frequency 1 control means comprising a movable member included with each of the said resonator systems whereby the resonant frequency of each of the systems may be readily varied and means for causing a flow of electrons along at least a portion of a path extending between the cathode and the plate electrode comprising a source of electric potential connected to each of the said electrodes and to at least one other said electrode whereby suitable potential differences are maintained between the various electrodes, the potential differences being such that the potential of the second grid electrode is maintained positive with respect to the cathode and to the other two electrodes and also such that the electron transit time between the second grid electrode and the plate electrode is substantially the period of one-half cycle of the resonant frequency of the second high frequency circuit.

9. A high frequency oscillator comprising an electron discharge tube containing at least four planar electrodes namely an electron emitting cathode, a plate electrode, a first grid electrode between the cathode and the plate electrode, arid a second grid electrode between the first grid electrode and the plate electrode, a high frequency circuit comprisinga. substantially closed electrical resonator system comprising coaxial conducting members external to the said electron discharge tube which includes the plate electrode and the second grid electrode, means for causing a flow of electrons along at least a portion of a path extending between the cathode and the plate electrode comprising a source of electric potential connected to each of the said electrodes and to at least one other said electrode wherebyI suitable potential differences are maintained between the various electrodes, the potential differences being such that the potential of the second grid electrode is maintained positive with respect to the cathode, and to the other two electrodes and means comprising the first-grid electrode for controlling at low frequency the high frequency output of the oscillator.

10. A high frequency oscillator comprising an electron discharge tube containing an electron emitting cathode, a plate electrode, a rst grid the electron emitting surface of the cathode and v the first grid electrode, a. second high frequency circuit comprising a substantially closed electrical resonator system which includes the plate electrode and the second grid electrode, means comprising a movable member included with each of the said resonator systems for varying the resonant frequency of the two resonant systems and electric potential sources connected to the cathode and other said electrodes for maintaining suitable assess? Potential differences therebetween and 'for causing a ow of electrons along at least a portion of a path extending between the cathode and the plate electrode, the said potential differences being such that the first grid electrode and the plate electrode are maintained at potentials positive with respect to the cathode and the secondgrid electrode is maintained at a potential negative with respect to the first grid electrode and the plate electrode. v

11. A high frequency oscillator comprising an electron discharge tube having two planar electron path terminating electrodes, one being a cathode and one an anode, and at least one planar electron permeable electrode located therebetween such that an electron stream passing from the cathode to the anode traverses each of the spaces between the various electrodes'. a cavity resonator comprising coaxial conducting members external to the said discharge tube connected to two of the said electrodes which are adjacent to each other and of which one is an electron path terminating electrode such that when the resonator is encrlgized a portion of its alternating electric field is impressed upon the space between the electrodes connected to it, means for varying the resonator frequency comprising members slidable longitudinally between the said coaxial conducting members, `electric potential sources connected to the said electrodes for producing a stream of electrons from the cathode to the anode and for establishing potential differences between the electrodesl the potential differences being such that electrons traversing the path from the cathode toward the anode encounter an electron permeable electrode substantially positive with respect to the cathode and later encounter an electrode substantially negative with respect to the said permeable positive electrode,

12. A high frequency oscillator comprising an electron discharge tube containing at least four planar electrodes namely an electron emitting cathode, a plate electrode, a rst grid electrode between the cathode and the plate electrode and a second grid electrode between the first grid electrode and the plate electrode, a high frequency circuit comprising a substantially closed electrical resonator system comprising conducting members preponderantly external to the said electron discharge tube and which includes the electron emitting surface of the cathode and the first grid electrode, a second high frequency circuit comprising a substantially closed electrical resonator system comprising conducting members preponderantly external to the electron discharge tube and which includes the plate electrode and the second grid electrode, frequency control means comprising a movable member included with each of the said resonator systems whereby the resonant frequency of each of the systems may be readily varied and means for causing a flow of electrons along at least a portion of a path extending between the cathode and the plate electrode comprising a source of electric potential connected to each of the said electrodes and to at least one other said electrode whereby suitable potential differences are maintained between the various electrodes, the potential differences being such that the potential of the second grid electrode is maintained positive with respect to the cathode and to the other two electrodes.

13. A device according to claim 5 in which the said resonator includes the said anode.

14. A device according to claim 5 in which the said potential differences and the distances between fhe electrodes are suchiliatflie .*letxon l transit time between the electrodes connected to the resonator is s. period substantially equal to the electric eld.

MORQN,

Name Date v Linder -1-1.--- Mar. 23. 1943 Southworth Apr. 11, 1939 Chev1gny,y--.-..-..-.'.. June 20, 1944 e Dallenbach Aug. 30, 1938 Varian July 29, 1941 Morton Mar. 31. 1942 -'Linder .........;.----e.. Aug. 18. 1942 Aus. 18, 1942 *K