US2027017A - Electrical oscillation generator - Google Patents

Description

Jan. 7, 1936.

e. F. BRETT 2,027,017 ELECTRICAL OSCILLATION GENERATbR Filed July 19, 1932 '2 Sheets-Sheet 1 lllllllltI/llfbllllllll iig ,ia

DIRECT/01V 0F FIELD v Z 62 INVENTOR GEORGE E BRETT ATTORNEY Jan. 7, 1936. G. F. BRETT ELECTRICAL OSCILLATLON GENERATOR I Filed July 19,1932

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MAGNE 1/6 FIELD F/[ZD [0/15 INVENTOR GEORGZBRETT BY ATTORNEY Patented Jan. 7, 1936 UNITED STATES PATENT OFFICE George Fairburn Brett,

Leeds, England, assignor to Radio Corporation of America, a corporation of Delaware Application July 19, 1932, Serial No. 623,389

In Great Britain July. 28, 1931 17 Claims.

This invention relates to electrical oscillation generators and more particularly to oscillation generators for the generation of ultra high frequencies i. e. frequencies corresponding to wave lengths of the order of from 20 or 30 centimetres to 5 or 6 metres or thereabouts.

As is well known, considerable difficulties are experienced in generating such ultra high frequencies by apparatus incorporating more or less ordinary thermionic valve constructions. The present invention provides an improved high frequency oscillator wherein the self-oscillation of a cathode ray beam is utilized.

According to this invention an ultra high frequency oscillator comprises an electron gun or other source of electron beam, a first electrode system situated relatively near said source of electrons and positioned to be adjacent to the beam therefrom, a second electrode system consisting of at least two anodes, means for subjecting the electron beam to a magnetic or electrostatic field whereby said beam is caused to take a path passing adjacent .the first electrode system to the second electrode system, and means operable in dependence upon the occurrence of current flow through an anode as a result of the electron beam striking said anode, for altering the velocity of the electrons in said beam whereby said beam is caused to be incident upon another anode, whereupon the velocity of the electrons is again changed whereby said beam is caused to be again incident upon the first anode.

The invention is illustrated in and further explained in connection with the accompanying drawings, wherein Figures 1 to 3 illustrate different embodiments of an ultra high frequency oscillation generator system constructed in accordance with the principles of the present invention, and Fig. la shows a plan view of the tube of Figs. 1, 2, and 3. Figures 4 and 5 illustrate types of cathode tubes which are particularly adaptable for use in the present invention. Figures 4a and 5a are plan views of Figures 4 and 5 respectively, and Figure 6 shows, by way of example, the use of field coils for tubes such as are illustrated in Figures 4 and 4a. Figure 7 illustrates one manner of applying a constant electrostatic force in place of an electromagnetic force. Figure 8 illustrates a preferred arrangement wherein two pinches are employed for the tube instead of one,

Referring to Figure 1, which shows diagrammatically one way of carrying out the invention, a high frequency oscillator comprises a hot cathode or filament F arranged relatively close to a slitted electrode systems S so positioned that the beam from the cathode may pass through the slit therein, suitable potential differences being applied by means of a battery or other source H.T. between the slitted electrode system and the cathode; There is also provided an anode sys- 10 tem consisting of two anodes A1, A2 arranged close to one another. One of the anodes, namely A2, is directly connected to the slitted electrode system, said anode being also connected to the source H.T. through an impedance consisting of chokes C1; C2 (which prevent leakage of high frequency current to the electrode system) and a preferably non-inductive and non-capacitative resistance R, the other anode A1, being connected direct to a tap upon said source H.T. The electrodes are housed within an envelope which is evacuated and then preferably filled with a small filling of inert gas. A preferably uniform magnetic field is provided, said field being of such magnitude and arrangement as to cause the beam of electrons from F to pass through the slit in the system S and then to follow one of the approximately semi-circular paths as indicated by the broken lines SPA1 and SPAz and falling upon one of the two anodes A1, A2. In use, the electron beam oscillates back and forth between the two anodes i. e. alternates between the two paths, on the following principle:-

Assume the magnetic field to be such that the beam upon being switched on strikes the anode A2. As will be obvious, the electron current striking this anode will pass through the impedance connected between this anode and the source H.T. of potential, thus giving rise to a potential drop across said impedence and therefore changing the total potential between the electrode system S and the cathode point. As a result the electron speed is somewhat decreased. The beam will therefore now follow a different path (the path SPAi) and will no longer strike the anode A2 but (if the relative electrode positions andpotentials are correctly chosen) will strike the anode A1. This, however, results in increasing the speed of the electrons and the beam shifts back to the anode A2, the speed of impedance from "about 1 mm. or

electrons being decreased again, and so the cycle of the operations is repeated indefinitely and an oscillatory current of very high frequency will be set up which is tapped ofi across the ends of the resistance R.

If the resistance R is entirely free from inductance and capacity the oscillation frequency will depend entirely on the speed of the electrons and the mutual positions and arrangement of the electrodes. The speed of the electrons is correlated with the magnetic field intensity so that the frequency obtained will in the last resort depend upon the magnetic field. In practice, however, the range of frequencies obtainable is limited by considerations of working potentials and of the geometry of the device. If the electron beam is caused to follow approximately circular paths of too small a radius of curvature, difliculty may be experienced in directing electron currents of-sufliciently high value in the required manner, while too large a radius of curvature presents obvious disadvantages from the point of view of size. The practical voltage range available extends from about volts to a few thousand volts. Within the various practical limitations the wave length range obtainable is from about 20 or 30 centimetres to 5 non-inductive resistances .of usual construction,

1. e. resistances which are not wire wound but are unsatisfactory owing to their liability to disare unsatisfactory owing to their inability to disintegration under high frequency current and owing to the difllculty that exists of obtaining such resistances capable of carrying substantial amounts of current and yet presenting, low selfinductance and capacity. For this reason it is preferred to constitute the impedance in question by a low capacity diode arrangement having the anode and cathode close together (spaced less apart) so that the transit time of electrons between the diode electrodes is very small or negligible compared with the time period of the oscillations produced. Such an arrangement employing a diode is diagrammatically represented in Figure 2 in which D is the diode having its filament heated by a battery DB, the choke 01 being duplicated as shown. The diode is designed to operate over the linear (unsaturated) portion of its current-voltage characteristic so that it behaves in use as a fixed the terminals of which the high frequency oscillations are taped oil. as in Fig. ure 1 and led to any utilization circuit e. g. a radiation system. If desired, such a diode arrangement may be incorporated in the same envelope with the electrodes of the oscillation system. thus reducing losses due to inductance and capacity in connecting leads. Instead of employing a diode, the impedance between the first electrode system and the source of anode potential may be as shown in Figure 3 constituted by a rejector circuit of suitably chosen values of capacity C and inductance L such that a high impedance is oifered to the frequency generated.

Although in the foregoing description reference is made to the use of a magnetic field to which the electron beam is subjected, the invention is, of course, not limited to the us: of a magnetic field for the purpose in question, since the said invention depends essentially on the fact that a change in electron speed results in a change in the arrival" point of the beam, and it will be obvious to those skilled in the art that an electrostatic field may be substituted for a magnetic field. A convenient and obvious manner of applying a constant electrostatic force in place of an electromagnetic force is to arrange for the beam, after issuing through the slit in the slitted electrode system, to pass between a pair of deflecting plates arranged like those ordinarily employed in oscillographs, a constant potential difference being applied between said plates. In such an arrangement which is shown in Figure 7, the path of the beam depends on its speed and on the value of the constant potential difference applied between the deflecting plates D.

Preferably a screen or grid electrode (not shown in Figures 1, 2, and 3) is provided adjacent the surface of the anode A2, said screen electrode being connected to the anode A1. The screen or grid electrode is provided to overcome the following eifectz-Referring back to Figure l, the broken lines SPA; SPA; represent the paths of the beam between the electrode S and the anodes for each half cycle of complete oscillation. Consider for example the outer path SPA: and suppose the electrons Immediately on the arrival at the anode A: of the first electrons following this path the potential at the said anode A: will fall so that the following electrons will be moving under a modified electric field of force tending to direct them more towards the anode A1. Similarly, when the electrons change to the paths SPA1 the anode A: will immediately increase in potential this increase taking place before the majority of the electrons will have reached the anode A1 and therefore there is a tendency for electrons which should reach A1 to fall upon the anode A2. The provision of the screen electrode close to the surface of the anode A2 and connected to the anode A1 ensures a substantially unvarying field being presented to oncoming electrons so that the arrival point of these electrons will depend almost entirely upon their initial velocity, as is required by the main principle of the invention. At the same time, the grid electrode does not seriously interfere with the arrival at the anode A2 of electrons intended for it. The screen electrode over the anode A: need not be at exactly the same potential as the anode A1, the main requirement being the preservation of a substantially constant field differing not too widely from the mean potential of the anode A2. In some cases it may be advantageous to extend the grid or screen electrode to the region of the cathodeslitted-electrode-system, since this latter will also change its potential in phase with the anode A1 and will tend to modify unfavourably the path of electrons which have already passed through the slit.

As regards the general design of the cathode tube, it is desirable in the case of very high frequencies to make the radius of curvature of the electron beam small and in such a case the slitted electrode system S and the anode A: (which is directly connected thereto) may be made integrally from a single piece of metal having one aperture corresponding to the slit in the slitted electrode systemand another aperture behind which the second anode Al is placed.

A practical construction of this kind is schematically illustrated in Figure 4 wherein G represents a screen or grid electrode which is connected to the anode Al and extends over and close to the anode A2 and the slitted or aperturcd electrode system S. The anode A2 and the electrode system S may be integrally con structed. E represents the envelope or bulb which is provided with a pinch carrying four wires from whichthe various electrodes are supported and by which connection to the said electrodes is made. The filament system F consists of a small helix H of tungsten wire or oxide coated wire inside van apertured cylinder AS which is connected to one lead of the helix and through the aperture of which the electron beam is projected through the electrode system S. In Figure 4 the slit in this electrode is constituted by a short cylindrical tunnel as shown.

Where lower frequencies are in question and a larger radius of curvature of electron beam is adopted, the anode which is directly connected to the first electrode system and the said first electrode system may comprise separate electrodes joined together by wire connection within or exterior to the containing envelope. Such a construction is shown in Figure in which figure parts corresponding to parts shown in Figure 4 are indicated by like reference. It will be seen from Figure 5 that the screen G extends only over the anode A2 while the electrode system consisting of the electrodes G, A1 and A2 does not monopolize the external field to such an extent as is the case in Figure 4. The bulbs or envelopes of the arrangements shown in Figures 4 and 5 are adapted to be inserted in a solenoid or between the poles of an electromagnet in order to provide the required electro-magnetic force upon the electron stream (assuming electro-. magnetic force and not electrostatic force to be employed). Such an arrangement is illustrated, schematically, in Figure 6. Although this figure shows the use of an iron core, it will be understood that the use of such core is not essential to the practice of the present invention.

Although Figures 4 and 5 illustrate constructions embodying only .a single pinch it is preferable to employ two pinches instead of one, so as to separate the anodes A1 and A2 more completely and thus prevent leakage of the high frequency current. Such an arrangement is illustrated in Figure 8.

It will be appreciatedfrom the foregoing that it is not necessary that the path of the electrons in the beam should be approximately circular, nor when an approximately circular path is adopted that the length of said path should be approximately that of the semi-circle. The essential requirement of the invention is merely that a change in electron speed resulting in a change in the position of the arrival point of the beam shall be obtained. In many cases the semi-circular arrangement is the most convenient; when however a shorter electron path is required (e. g. for obtaining a high frequency) an arcuate pathapproximating to less than a semi-circle (e. g. a quarter circle) can conveniently be adopted the position of the anodes being correspondingly modified. Similarly an arcuate path longer than a semi-circle may be arranged for if required.

The high frequency current produced is, as above stated, tapped off from the impedance be tween the slitted electrode system and the source of anode potential.

What is claimed is:

1. An oscillation generator comprising an electron gun or other source of electron beam, a'first electrode system situated relatively near said source of electrons and positioned to be adjacent to the beam therefrom, a second electrode system consisting of at least two anodes, means for subjecting the electron beam to a uniform field which is independent of said electrode systems whereby said beam is caused to take a path passing adjacent the first electrode system to the sec- 0nd electrode system, and means operable in dependence upon the occurrence of current fiow through an anode as a result of the electron beamstriking said. anode, for altering the velocity of the electrons in said beam whereby said beam is caused to be incident upon another anode, whereupon the velocity of the electrons is again changed whereby said beam is caused to be again incident upon the first anode.

2 An oscillator as claimed in claim 1 and in which the first electrode system is constituted by an electrode having a slit or other aperture therein and directly connected to one of the anodes.

3. An oscillation generator comprising an electron gun or other source of electron beam, a first electrode system situated relatively near said source of electrons and positioned tobe adjacent to the beam therefrom, a second electrode system consisting of at least two anodes, means for subjecting the electron beam to a uniform field 0 which is independent of said electrode systems whereby said beam is caused to takean arcuate path passing adjacent the first electrode system to the second electrode system, and means operable in dependence upon the occurrence of current flow through an anode as a result of the electron beam striking said anode, for altering the velocity of the electrons in said beam whereby said beam is caused to be incident upon another anode, whereupon the velocity of the electrons is again changed whereby said beam is caused to be again incident upon the first anode. 4. An oscillation. generator circuit having, in combination, within a single container, a cathode and a plurality of spaced anodes, a slitted electrode connected to one of said anodes within the electron path of said generator and adapted to enable the passage of electrons from said cathode through the slit portion thereof, individual connections having unequal impedance 'values from said respective anodes to a source of unidirectional potential located outside said evacuated container, and energizing means for said cathode.

5. A system'as defined in claim 4 characterized in this, that one of said connections include a plurality of choke coils and that means are provided for obtaining energy from said one connection.

6. An oscillation generator comprising an electron gun or other source of electron beam, a first electrode system situated relatively near said source of electrons and positioned to be adjacent to the beam therefrom, a second electrode system consisting of at least two anodes, means for subjecting the electron beam solely to a uniform magnetic field which is independent of said electrode systems wherebyv said beam is caused to take a path passing adjacent the first electrode system to the second electrode system, and means operable in dependence upon the occurrence of current flow through an anode as a result of the electron beam striking said anode, for altering v the velocity of the electrons in said beam whereby said bcam is caused to be incident upon another anode, whereupon the velocity of the electrons is again changed whereby said beam is caused to be again incident upon the first anode.

7. An oscillation generator circuit having, in combination, within a single container, a cathode and a plurality of spaced anodes, a. slitted electrode connected to one of said anodes within the electron path of said generator and adapted to enable the passage of electrons from said cathode through the slit portion thereof, individual connections having unequal impedance values from said respective anodes to a source of unidirectional potential located outside said evacuated container, one of said connections including a non-inductive resistance across which are provided means for taking ofi' high frequency potentials, and energizing means for said cathode.

8. An oscillation generator circuit as defined in claim 7 characterized in this, that said noninductive resistance constitutes a diode.

9. An oscillation generator comprising an electron gun or other source of electron beam, a first electrode system situated relatively near said source of electrons and positioned to be adjacent to the beam therefrom, a second electrode system consisting of at least two anodes, means for subjecting the electron beam to a uniform field which'is independent of said electrode systems whereby said beam is caused to take a path passing adjacent the first electrode system to the sec- 0nd electrode system, and means operable in dependence upon the occurrence of current flow through an anode as a result of the electron beam striking said anode, for altering the velocity of the electrons in said beam whereby said beam is caused to be incident upon another anode, whereupon the velocity of the electrons is again changed whereby said beam is caused to be again incident upon the first'anode, a connection including a non-inductive resistance between one anode and a source of anode potential and a connection between said other anode and source of anode potential, choke coils in said first connection for preventing leakage'of the high frequency current back to said first electrode system and said source of electron beam, and means for taking ofi high frequency potentials across said resistance.

10. An oscillation generator circuit having, in combination, within a single container, a cathode and a plurality of spaced anodes, a slitted electrode connected to one .of said anodes within the electron path of said generator and adapted to enable the passage of electrons from said cathode through the slit portion thereof, individual connections having unequal impedance values from said respective anodes to a source of uni-direc tional potential located outside said evacuated container, one of said connections including a parallel resonant circuit tuned to the working frequency across which are provided means for taking oi! high frequency potentials, and energizing means for said cathode.

11. An oscillation generatorclrcuit having, in combination, within a single container, a cathode coil and a plurality of spaced anodes, an elec-- trode in the form of an apertured cylinder connected to one of said anodes within the electron path of said generator and adapted to enable thepassage of electrons from said cathode through the apertured portion thereof, said cathode coil being situated within said apertured cylinder, individual connections having unequal impedance values from said respective anodes to a source of uni-directional potential located outside of said evacuated container, and energizing means for said cathode.

12. An oscillation generator circuit having, in combination, within a single container, a cathode and two spaced anodes, an apertured electrode formed integrally with one of said anodes within the electron path of said generator and adapted to enable t-e passage of electrons from said cathode through the apertured portion thereof, said other anode being situated behind a gap which lies within that portion of the integrally formed structure which forms the anode and that portion which constitutes the apertured electrode, individual connections having unequal impedance values from said respective anodes to a source of uni-directional potential, and energizing means for said cathode.

13. An oscillation generator circuit having, in combination, within a single container, a cathode and a plurality of spaced anodes, a slitted electrode connected to one ofsaid anodes within the electron path of said generator and adapted to enable the passage of electrons from said cathode through the slit portion thereof, individual connections having unequal impedance values fromsaid respective anodes to a source of unidirectional potential located outside said evacuated container, a screen connected to one of said anodes and extending over said other anode, and energizing means for said cathode.

14. An oscillation generator circuit having, in combination, within a single container, a cathode and a plurality of spaced anodes, a slitted electrode connected to one of said anodes within the electron path of said generator and adapted to enable the passage of electrons from said cathode through the slit portion thereof, individual connections having unequal impedance values from said respective anodes to a source of uni-directional potential located outside said evacuated container, a screen extending over one of said anodes,'m'eans for applying a potential to said screen such that a substantially unvarying field is presented to the oncoming electrons, and energizing means for said cathode.

15. An oscillation generator circuit having, in combination, within a single container, a cathode and a plurality of spaced anodes, a slitted electrode connected to one of said anodes within the electron path of said generator and adapted to enable the passage of electrons from said cathode through the slit portion thereof, individual connections having unequal impedance values irom said respective anodes to a source of unidirectional potential located outside said evacuated container, and energizing means for said cathode, and a magnetic field adjacent said container for influencing the electrons emanating from said cathode.

v 16. An oscillation generator comprising an electron gun or other source of electron beam,

a first electrode system situated relatively near said source of electrons and positioned to be adjacent to the beam therefrom, a second electrode system consisting of at least two anodes, means for subjecting the electron beam solely to an electrostatic field of uniform intensity whereby said beam is caused to take a path passing adjacent the first electrode system to the second electrode system, and means operable in dependence upon the occurrence of current flow through an anode as a result of the electron beam striking said anode, for altering the velooity of the electrons in said beam whereby said beam is caused to be incident upon another anode,

whereupon the velocity of the electrons is again changed whereby said beam is caused to be again incident upon the first anode.

17. An oscillation generator circuit having, in combination, within a single container, a cathode and a plurality of spaced anodes, a slit electrode connected to one of said anodes within the electron path of said generator and adapted to enable the passage of electrons from said cathode 10 through the slit portion thereof, individual connections having unequal impedance values from said respective anodes to a source of uni-directional potential located outside said evacuated container, one of said connections including a non-inductive and non-capacitive resistance across which are provided means for taking of! high frequency potentials, and energizing means for said cathode.

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