US2103362A - Ultrahigh frequency magnetron oscillator - Google Patents

Description

C. W. HANSELL ULTRAHIGH FREQUENCY MAGNETRQN OSCILLATQR Dec. 28,v 1.93.7.

Filed June 13, 1935 2 Sheets-Sheet l CLARENCE w. H ANSELL #S .4MM

ATTORNEY Dec. 28, 1937. 4 c. w. HANsELL 2,103,352

ULTRAHIGH FREQUENCY MAGNETRON scILLAToR` Filed June l5, 1935 2 Sheets-Sheet 2l /IUMBZE METAL 703/176 SL /DEH /Mwmrpn INVENTOR CLARENCE W. HANSE-iv..

ATTO R N EY Patented 28, 1937 sacaste ULTRAHIGH FREQUENCY MAGNE OSCILLATR Clarence W. Hansell, Port dene-reen, N. Y., as-

le'nor to Radio Corporation ci erica, a corporation of Delaware i Application .lune i3, 11.933, derlei No. 075.5311

1c Claims.

This invention relates to the production of ultra high frequency oscillations in electron discharge devices and, more particularly, to such of these devices wherein the traveling electrons them- 5 selves and the consequent space charges about the electrodes of' the devices are primarily responslble for the regeneration required to produce oscillations.

In my United States Patent No. 2,011,133, l0 granted May 14, 1935, there is disclosed a method of producing ultra high frequency oscillations by a whistle eiect in a solid anode magnetron. In this magnetron oscillator there is provided a small central filament which is surrounded by a posi tively charged cylindrical anode. A magnetic held is applied to the spacebetween the iilament and the anode having flux lines parallel to the filament. Under these circumstances electrons are pulled out from the filament toward the anode, but due to the action of. the magnetic eld a considerable portion of them do not reach the anode and are caused to turn around and return to the vicinity of the filament. These returning electrons build up a space charge around the filament which prevents new electrons from coming out until those which previously left the filament have returned to it. The controlling eiiect of the returning electrons gives a sort of regeneration or whistle eiect which causes oscillations to take place irrespective of adjustment of the electrode circuits, although this effect may be increased if the circuits are properly tuned so that fluctuations in anodel to cathode potential m assist in producing iiuctuations in the number of this type of magnetron oscillator the frequency produced corresponds to the period required for an electron to traverse the curved path from the filament to the anode and back again.

u present invention which, however, provides a path for the electrons to travel over which is only about half as long as that described above and in this manner is believed to produce a frequency about twice is high as that obtained in the aforementioned arrangement. In addition to this whistle effect, the present invention also obtains regeneration through a time delay phenomena due to the finite velocities of the electrons themselves, a mode of operation which is described in my United States Patent No. 2,009,369, granted July 23, 1935.

In my last mentioned patent there is disclosed an electron discharge device'oscillator which has an anode substantially a half wave length ylong,

electrons leaving the vicinity of the cathode. In

The foregoing whistle effect is utilized in the` (Cl. 25d-36) the wave iength taken corresponding to the frequency of the desired oscillations. During oscillation one-half of the anode is arranged to be at a mazdm'um potential when the other half is at a minimum potential. inasmuch as the anode 6 transfers potential waves at the velocity of light, and the electrons in traveling through the cathode anode space have a much lower average velocity, it will be seen that the time required for the electrons to reach the anode will be substantially equal to the time required for the anode tov reverse its radio frequency potential. That portion of the anode which is at a maximum potential will thus tend to attract the electrons toward it, and by suitable dimensioning of the tube will be made to be at a minimum potential when the electrons impinge thereon, thereby establishing the necessary condition for sustained oscillation generation. There is thus obtained an electron discharge device in which potentials on different portions of the anode uctuate in such a manner that after a certain portion has experienced a maximum potential sufiicient to start a cloud of electrons toward it from the cathode, the voltage on that portion will have changed as the electrons are about to lmpinge thereupon with the result that the fluctuations in anode potential cause regeneration and sustained oscillation without the necessity for potential fluctuations of a control element or grid as ordinarily used. It is this time delay effect which is combined with the electron whistle eiect to aid in producing oscillations in the present invention.

In the above two types of oscillators described in my United States patents, supra the amount oi. power obtainable is limited by/the emission from the illament and by the maximum power dissipation allowable at the anode. The present .invention overcomes this disadvantage and makes possible the production of higher power not only by obtaining greater emission, but also by increasing the anode dissipation. At the same time the frequency'of the oscillations produced in accordance with the present invention is increased by reversing the direction of the electron travel.

A feature of this invention is the novel type of magnetron used in which the cathode is in the form of a cylinder and the anode in the form of a thin tube at the center of the cylindrical lelectron emitting element, and it is by means of this novel construction that the length of the path traveled by the electrons per cycle is only half as ,greatv as in the case of a solid anode magnetron. Consequently, for substantially the 55 same anode voltage the oscillator in accordance with the present invention will produce a fref quency approximately twice as high as that described in the prior methods.

'I'he invention, of course, is not limited to the use of a cylindrical cathode since it will be obvious that, if desired, a plurality of filaments in parallel spaced equally on a ring of a predetermined diameter may be used to surround a central metal rod anode axially positioned with respect to said ring.

Referring to the drawings, Figure 1 represents schematically a transverse section of a well known type of magnetron showing the paths taken by the electrons, and Figure 2 shows schematically a transverse section of the magnetron in accordance with the present invention also illustrating the paths taken by the traveling electrons., Figure 3 illustrates, partly in section and partly schematically, a preferred arrangement of a magnetron oscillator in accordance with the present invention. Figure 4 shows a modification of the present invention wherein there is utilized a three electrode tube for controlling the oscillator. Figure 5 showsgraphically the variations in anode to cathode potential across tube of Figure 4 with respect to time. Figure 6 illustrates another modification of thepresent invention with means for modulating the output of the oscillator, and Figure 7 shows graphically, in a manner similar to Figure 5, the variations in potential across tube of Figure 6.

In Figure 1 is shown schematically a known type of magnetron oscillator as described in my United States Patent No. 2,001,133, supra, cornprising an electron emitting cathode element I and a cylindrical anode 2 to which the electrons are attracted. This gure shows approximately the path which the electrons take at a critical plate voltage for a definite strength magnetic field set up coaxially with the cathode and at right angles to the plane of the ilgure by a field coil, not shown. 'Ihe complete path of the electronic stream from cathode to anode and back to the cathode is approximately that of a cardioid as shown in the drawings. If the anode voltage is increased all of the electrons will be attracted to the anode and if the field strength is increased none of the electrons will strike the anode. At a critical value determined by the anode voltage and the strength of the magnetic eld some of the electrons will return to the cathode and will describe a path approximately that of the cardioid indicated.

Figure 2 shows the paths of the electrons in the oscillator of the present invention wherein the outside cylinder 3 is caused to be the electron emitting cathode element while the relatively small diameter element 4 insidevthe cathode is used as an anode. It will be quite evident'that in this case the length of the path traveled by the electrons per cycle is less than half as great as in the case of the solid cylindrical anode magnetron shown in Figure l. Consequently, for substantially the same anode voltage the new oscillator shown in Figure 2 produces a frequency about twice as high as that shown in Figure 1.

Figure 3 illustrates the preferred embodiment of the present invention wherein there is shown an oscillator comprising an envelope 5, preferably of glass 0r quartz, having surrounding it a metal shield 6 and within it a cylindrical cathode I which has at the ends thereof shielding members 8, vwhich approach more closely to a centrally located anode 9 than does the electron emitting surface. The object of using these shielding members is to obtain more nearly parallel motion of the electrons and, therefore, greater oscillation energy. Anode 9 which is maintained at a positive potential from the positive terminal of the high voltage rectifier through the medium of a metal tubing I3 connected to the anode and an adjustable slider i5 is also in the form of a cylinder and is preferably cooled by a stream of gas or liquid so that it will stand high energy dissipation. This cooling fluid may be supplied through a rubber hose I0 and passed out of the anode through a rubber hose II,.both of which connect with the anode through metal 'tubes I2 and I3 respectively. There is thus provided through the center of the vacuum tube an anode consisting of a small tube through which a cooling fluid such as water or oil or any gaseous cooling medium, such as hydrogen or air, is circulated. The anode is tuned by means of adjustable tuning sliders I4 and I5 on the metal tubes, and when the oscillator isA operated with circuits tuned to the fundamental frequency the distance from the center of the anode to each of the adjustable tuning sliders will be approximately onequarter of the wave length or odd multiples thereof. Sliders I4 and I5 are in contact with both the anode 9 and the horizontal metal plate 34 which is mounted on supports, as shown.

Horizontal plate 34 is in contact with metallic shield 6 surrounding the envelope 5. This manner of operation utilizes the presence of standing waves on the metal tubes connected to the anodes.

'I'he cylindrical cathode 'I encircling the anode is provided with energy from a power supply source 35 through transformer I6 and over leads I1 and I8 for heating the cylinder to a temperature suiliciently high to cause it to emit a considerable number of electrons. The cylinder may be made of thin metal through which a large heating current is passed at a low potential or, if desired, it may be of the heater type in which the electron emitting material is indirectly heated by means of a metal wire wound aboutit on a suitable form of refractory material in the manner commonly employed for indirect cathode heating in vacuum tubes. Preferably the cathode and its connections are also tuned for the operating frequency and this may be done by varying the length of the heating current supply leads from the cathode to a point of substantially' zero potential. If desired, a slider arrangement such as I9, I9 may be used for adjustment. It is preferred, however, that the adjustment be made in the cathode heating leads in the beginning for tuninglapproximately to the desired frequency after which all tuning in normal operation may be done by means of the anode sliders It and I5. In the drawings,` the output circuit has been shown, for purposes of illustration only, as a transmission line 20 capacitively coupled to the oscillator and extending to an antenna or radiator 2l. This radiator is preferably of a directive type. The simple radiator has been shown only for the purpose of illustration. Trombone slides 22 have been indicated for tuning the transmission line to the desired frequency in cases where the antenna does not match the characteristic impedance of the line.

Two iield coils 23, 23 are shown provided for setting up an intense magnetic eld between the vacuum tube electrodes in the direction parallel to the axis of the tube.

Although it is believed that the presence of the magnetic eld will improve the power eiiiciency and make oscillations more certain, it will be understood that in some instances the use of a. magnetic field may be undesirable. In such case its use may be eliminated. For example, in a transmitter used for airplanes the weight of a field coil and the power supply for energizing it will be considerable and for this reason it may be desirable to use either no magnetic field or a relatively weak eld to save weight.

The operation of the oscillator in Figure 3 in producing oscillations is substantially as follows:

The electrons emitted from the cylindrical cathode 'I will be propelled toward the fluid cooled central anode upon the occurrence of a positive potential thereon and these electrons will travel toward the anode with increasing velocity. Simultaneously with their movement toward the anode the electrons are subjected to the influence of the magnetic eld parallel to the axis of the tube due to the energization of field coils 23, 23, and for a certain value of iield a large portion of electrons attracted to the anode 8 will not reach it, but will be deiiected suiciently to pass close to it and return again to the vicinity of the cathode, as shawn ln Figure 2.

If the flow of a large number of electrons is started toward the anode 9 their arrival inthe Avicinity of the anode will set up a negative space charge around it which will balance out the inuence of the anode potential upon the electron emitting surface and no more electrons will be pulled out of the cathode 'I until thosel already in the space between the anode and the cathode have completed their travel past the anode and are returning again to the cathode. As soon as all of the electrons in the space have left the vicinity of thev anode, the electrostatic attraction at the cathode will again become effective and a new group of electrons will start out. action, recurring at intervals corresponding to the time of the travel of the electrons, is equivalent to a radio frequency oscillation, energy from which is taken out by tuning and coupling any suitable utilization circuit, such as a transmission line. 20 andantenna 2|, to the anode cathode circuit. If the electrode circuits are tuned, such as by adjustable sliders Iii, I and tuning elements I9, I9, the action of the tube in producing oscillations may be considerably increased, although in this case it may be necessary to make some readjustment in the anode potential. This will be evident from the mere observation that the arrival of the groups of electrons in the vicinity of the anode is accompanied by the impact of some of the electrons upon the anode surface, the total number of the impacting electrons corresponding to the D. C. input current. These impacting electrons, in combination with oscillations in the anode circuit, serve to reduce the anode potential during the time when it is desired to have a minimum number of electrons leaving the cathode. A half cycle later, at the time when maximum emission from the cathode is desired, the anode will have oscillated to a maximum positive potential of a value greater than the direct current potential by an amount corresponding to thestrength of the oscillations on the anode. It will thus be seen that there is obtained a cooperative effect between the electron whistle principle and the emitter of electrons.

This

time delay principle, both of which are described above in connection with my United States patents, supra.

Figure 4 illustrates another embodiment of the present invention wherein a three element vacuum tube 24, having an anode 33, a grid 2I and a cathode 39, is used to control the production of oscillations in the oscillator 25. In this figure controltube 24 has a low resistance most of the time so that the voltage on the oscillator tube is equal to that existing between terminals B and C of] the anode current supply source 26, less the relatively small voltage drop in the control tube. As indicated in the drawings, this voltage may be of the order of 2000 volts. Under such conditions there will be suiiicient current and anode Power lost in the oscillator tube 25 to heat the anode 36 to a temperature where it become's an Then, periodically, the control tube is caused to cut oi its current by having the potential on its grid 2l swing negative whereupon the voltage impressed upon the oscillator tube 25 is that between terminals A and B of supply source 20, less some current voltage drop due to the resistance 28 in series with the lead to terminal A, in this case around 1000 volts. The voltage applied to the oscillator tube from terminals A'and B is arranged to be opposite in polarity from that previously applied from terminals B and C. Thus, the cathode 40 of the tube 25 will be made positive and, due to the emission from the anode l36 of tube 25, a reversed current will ow in the tube. This, it will be seen, is the precise condition required for setting up oscillations in the manner previously described in connection with Figures 2 and 3, provided all other conditions and adjustments have been previously made. Thus there may be employed an ordinary vacuum tube for oscillator 25 by passing current through it in a normal direction suiliclent to heat the anode until it will emit electrons and then reversing the anode to cathode potential. By rapidly reversing the p0- tentials, modulated ultra high f'. equency oscillations can be produced. The relatively small proportion of the time during which oscillations take place keeps the average energy dissipation on the small central portion of the tube within its energy dissipation limits, otherwise the conditions for obtaining any oscillations at all might betoo severe for the tube towithstand.

Commutator 29, which is driven, by means not shown, over its drive shaft, is illustrated in the drawings, `by way of example only, as one way of controlling the potential on the grid 21 of the control tube 24 whereby there is caused the desired condition for oscillations to occur at short periods at a rate determined by the Commutator. For commercial purposes it would probably be necessary that the condition for oscillations occur at the rate of from 250 to 2500 times per second or higher, whereas for testing purposes interruptions at the rate of 120 per second or so would be in order. In the latter case an electromagnetic relay may be used.

The brush arrangement shown for connecting the grid 21 of tube 24 to the bias source of potential 32 is one which is adequately described in United States Patent No. 1,963,587, granted June 19, 1934, to Richard E. Mathes. In. this arrangement the brushes are short circuited by the commutator bars extending longitudinally of the revolving drum at intervals depending upon the speed of the drum and the width of the bars. By making the brushes movable along the commutator and by tapering the width of the bars any desired relative length of time for potentials in one direction or the other may be readily obtained. l

Figure 5 illustrates diagrammatically the variations in anode to cathode potential of tube 25 with respect to time. In this gure thel positive potential sign indicates the condition for heating the anode of the tube and the negative potential sign indicates the condition for reversing the functions of anode and cathode to produce oscillations.

In Figure 6 there is shown a two electrode, tube 30, having an anode 31 and a cathode 38, which may be used as a magnetron oscillator having magnetic flux parallel to the axis of the tube provided by coils in a manner indicated in Figure 3. This magnetron will give oscillations when the cathode 38 is positive with respect to the anode 31 of the tube. The anode 31 is heated by electron bombardments from the D. C. voltage and current until it becomes an emitter of electrons,

at which time suilicient keyed or modulated alternating current voltage is superimposed upon the direct current voltage to cause a reversal of the anode-cathode voltage for part of the time. The ultra high frequency oscillations will thus take vplace during the interval of reverse potential. For utilization purposes there is shown an antenna 3l which is electromagnetically coupled to the anode lead of tube 30. The operation of the circuit, it is thought, will be obvious from the foregoing description.

Figure 7 indicates the variations in potential across the tube 30 in Figure 6, with respect to time in the same way that Figure 5 illustrated the potential across tube 25 in Figure 4.

It will, of course, be understood that this new type of oscillator hereinabove described may be modulated by varying its electrode potentials or the strength of magnetic field by any of the means already well known in the art. The output of the circuit may, if desired, also be modulated by variably absorbing the output energy, or by Varying impedances in the output circuits in .known manner. In practice, any of these modulating means may be employed, according to service requirements.

I claim:

1. An oscillation generator comprising an electron discharge device having a cylindrically shaped electron emitting element, a source of heating energy for said element and leads extending from said source to saidelement, an electron collecting element at the center of the electron emitting element and positioned along the axis thereof, and means for tuning said leads and the eifective length of said electron collecting member.

2. An oscillation generator system comprising an electron discharge device having a cylindrically shaped electron emitting element, a source of heating energy for said element and leads extending frcm said source to said element, and an electron collecting element at the center of the electron emitting element and positioned along the axis thereof, means for tuning each of said leads and for making the eifective length of said collecting member to be an odd multiple of half the wave generated by said system, and means for producing a magnetic field having ux parallel to the axis of the emitting element.

3. An oscillation generator system comprising Within an envelope an electron discharge device having a solid cylindrical cathode, a rod-like anode axially positioned in the center of said. cathode and along the axis thereof, a shield surrounding said envelope, and a tuning slider connected with each end of said anode and said shield for tuning said anode, whereby the distance from the center of said anode to each slider is approximately an odd multiple of a quarter wave length When said system is tuned to the fundamental frequency.

4. An oscillation circuit comprising an electron discharge device having a cylindrical cathode, an anode axially positioned in the center of said cathode and extending lengthwise on both sides of said cathode, metallic tubular conductors connected to both ends of said anode, means for causing the presence of standing waves thereon, said means including metal sliders in contact with said tubular conductors and in circuit with said cathode for tuning the eifective lengths of said tubular conductors, whereby the frequency of the oscillations generated may be changed.

5. The combination with an oscillation circuit comprising an electron discharge device having a solid cylindrical cathode of appreciable Width and a, concentrically positioned rod-like anode at the axis of said cathode, of means for cooling said anode, and means for adjustably tuning the effective length of said anode.

6. The combination with an oscillation circuit comprising an electron discharge device having an envelope, a hollow cylindrical cathode of imperforate material Within said envelope and an anode tube concentrically positioned along the axis of said cathode, of metallic tubing connecting with both ends of said anode and extending outside of said envelope for enabling the existence of standing Waves on said metallic tubing, tuning elements for said anode located on said metal tubing and coupled back to said cathode, andr a utilization circuit capacitively coupled to said anode.

7. The combination with an oscillation circuit comprising an electron discharge device having an envelope, a hollow cylindrical cathode of imperforate material within said envelope and an anode tube concentrically positioned along the axis of said cathode, of metallic tubing connecting with both ends of said anode and extending outside of said envelope for enabling the existence of standing waves on said metallic tubing, tuning elements for said anode located on both sides of said cathode and approximately an odd multiple of a. quarter wave length from the center of said anode, said elements being connected to said tubing and coupled back to said cathode, and a utilization circuit coupled to said anode.

8. In an electron discharge device oscillator having a cathode and an anode, the method of generating oscillations which includes attracting electrons from said cathode to portions of the anode only at times when' the portions are subjected to a maximum anode potential, decreasing the anode potential on the portions as the electrons arrive, and periodically interrupting the stream of electrons.

9. In an electron discharge device oscillator having a cathode and an anode, the method of generating oscillations which includes propelling electrons from said cathode to portions of said anode only at times when the portions are subjected to a maximum anode potential, decreasing the anode potential on the portions as the electrons arrive, periodically interrupting the stream of electrons, and generating a magnetic eld to deflect the path of the electrons.

10. In an electron discharge device, the com- @,id v f tential to said anode with respect to said cath- 4 suitable polarizing potential to the other of said electrodes with respect to said cathode, in order to heat said other electrode to enable same to emit electrons, the method of producing oscillations which includes reversing the polarization of said electrodes whereby the direction of current ow from the other electrode to the cathode simultaneously reverses.

12. In combination,` an electron discharge device having an anode and a cathode, another device having an anode, cathode and control electrode, the anode of said last device being connected to the cathode of said first device, a source of potential having positive and negative termi- 'nais and a third terminal, the potential between said negative and third terminals being greater than the potential between said positive and third terminals, a connection including a resistance from said positive terminal to the anode of said last device, a direct connection from the anode of said rst device to the third terminal oi' said-source, a connection including al resistance from said positive terminal to said control electrode, a connection from said negative terminal to the cathode of said second device, and means for periodically applying a negative bias to the control electrode of said second device whereby said last device is made inoperative.

13. In anl electron discharge device oscillator having an anode and a cathode substantially concentrically positioned with respect to each other, and means for applying a suitable polarizing poode to heat said anode to enable same to emit electrons, the method of producing oscillations which includes periodically reversing the polarization of said anode and cathode at an audio frequency rate of at least 250 times per second,

whereby the directionl of current dow from the anode to the cathode is reversed. at said rate.

14. An electron discharge device having an inner cathode and an outer anode surrounding said cathode, a source of energy for maintaining said anode at a positive potential relativeA to said cathode for causing said anode to be heated to emit electrons, and means including switching mechanism for reversing the relative polarities of said anode and cathode whereby electrons ow from said anode to said cathode.

15. In combination, a magnetron oscillator i having a cathode and an anode within an envelope and an external magnetic eld surrounding said envelope, a source of potential between-said anode land cathode for maintaining said anode at a potential sulciently positive relative to said cathode to enable said anode to be heated to emit electrons, and periodically operating keying mechanism including another source of potential for superimposing energy uponvthe circuit connections from saidanode and cathode to said rst source of a` value suiilciently high to cause a reversal of the relative polarities of said electrodes. whereby electrons emanating from said anode are collected by said cathode.

16. An oscillation generator comprising an electron discharge device having means substantially arranged in the ,form of a hollow cylinder for emitting electrons, a source of heating energy and .leads extending from said source to said means,

an electron collecting element at the center of said means and positioned substantially along the axis thereof, and means for tuning said leads and the eiective length oi' said electron collecting element.

CLARENCE W. HANSELL.

Images