US2420846A - Cathode-ray tube for generating oscillations - Google Patents

Description

y 1947. M. J. o. STRUTT ET AL 2,420,846

CATHODE RAY TUBE FOR GENERATING OSCILLATIONS Filed March 25, 1943 F C C INVENTORS B '2 2 l 47 Maw/4014mm smurf 999629999999 WE/QT V/INOEA Z/EL ATTORNEY Patented May 20, 1947 UNITED STATES PATENT OFFICE CATHODE-RAY TUBE FOR GENERATING OSCIILATIONS Application March 23, 1843, Serial No. 480,196 In the Netherlands July 11, 1940 80laims. I

oscillations, whose frequency is a multiple of that of a controlling oscillation, it is already known to utilize a device comprising a cathode ray tube with deflecting means, wherein the controlling oscillation is supplied to the deflecting means and wherein the electron beam of a cathode ray tube is caused to pass over an apertured electrode behind which is arranged an electrode of strong secondary electron emissivity, which is intermittently struck by the beam. Whenever with this device the secondary emision electrode located behind the apertured electrode is struck by the electron beam, there is produced in an output circuit connected to the first mentioned electrode a current impulse whose frequency is determined by the product of the frequency or the controlling oscillation, and the number of apertures over which the beam is moved during one cycle of the controlling oscillation. Owing to the high secondary emissive character of the electrode which is intermittently struck by the beam, the current impulss are ampiifled in the output cir- 1 cult due to'the fact that every electron oi the beam causes a plurality of electrons to' issue from the secondary emissive electrode, a larger output energy being thus obtained thanwould be the case without the use of secondary emission.

With the use of the device in question for the generation of having a wavelength measurable in decimeters or centimeters, difllculties are. however, encountered with the construction of an output circuit which has a sumciently high impedance for the oscillations to be generated, so that despite the secondary emissive character or the electrode intermittently struck by the beam, the output energy to be obtained is only small.

The invention has ior its object to provide a device or the said kind with which a very much -largeroutputenergycanbeobtainedthanhas been possible with the devices known up to the 7 present.

According to the invention, this purpose is attained owing to the fact that in the path or the electrons emitted by the electrode secondary which is intennittently struck are arranged a number or secondary emissive electrodes with the aid or which the number of secondary electrons is multiplied. By repeated multiplication oi the number oi secondary electrons there may be obtained so great an amplification oi the current impulses generated by the electron beam in the flrst emissive electrode that, in spite of the very low impedance of the output (Cl. 315-12) circuit, the output energy has a considerably high value.

The invention will be explained more fully with reference to the accompanying drawing which represents, by way of example, one embodiment of the device, according to the invention, wherein the number of secondary electrons ismultiplied once.

Figure 1 is a diagrammatic showing of a cathm ode ray tube and circuit with certain parts of the tube in axial cross-section.

Figure 2 is a front elevation of the first annular targ t.

Figure 3 is a cross-section through the targets is of Figure l.

Figure 4a illustrates the sheath surrounding thereceiving electrode.

Figure 4b illustrates the electrical characteristics of Fi ure 4d.

Figures 5a and 5b illustrate modifications of the apertures 21 of Figure 2 and diflerent crosssections or the beam applied thereto.

The device represented in Fig. 1 comprises a cathode ray tube which is tically shown in axial cross-section, and usual means for generating an electron beam, constituted by a cathode I, a controlling electrode 3 and an accelerating electrode 8. The beam may be concentrate'd by means or a iocussing coil 8 excited by direct current. The electron beam representedbyadottedline2,iscausedtopassbetween two sets of deflecting plates I and 9 respectively. to which are connected oscillatory circuits represented in the flgure by condensers II and II respectively, and inductances l3 and I9 respectively, said inductances being coupled with coupling coils l5 and M respectively. The oscillatory circuits II, II and l1, l9 are tuned to the frequency oi the controlling oscillation,

coupling coils l5 and II respectively to the oscillatory circuits ll, I3 and l1, l9. These two oscillatory circuits are slightly detuned relatively to one another in such manner that the alterhating voltages induced therein (litter in phase by 90. Between the deflecting plates I, 9 there is thus set up a rotating electric field which causes a rotary motion 01' the electron beam. During this motion the beam passes over an annular electrode 25 which has a plurality of apertures 21 and forms part of a disc 23, a'tront elevation of which is shown in Fig. 2. The disc 23 further comprises an insulating ring 29, a second annular electrode 3| 0: smaller diameter 55 than the electrode 25 and an insulating disc 33.

and this oscillation may be supplied thro h the 3 Behind the disc 23, viewed in the direction of travel of the electrons, and at a slight distance therefrom, is arranged a disc 35 which is parallel to and' coaxial with the disc 23. The disc 35 consists of an annular electrode 31, an insulating ring 33 and a disc-shaped electrode 4| of smaller diameter than the electrode 31. In front of the electrode 4| is arranged a grid electrode 43. The annular electrode 3| is located opposite the intervening space between the electrodes 31 and 4|. Between the discs 23 and 35, at a slight distance in front of the electrode 3| and parallel thereto, is arranged an annular grid electrode 32. The insulating portions 23, 33 and 33 serve to support the electrodes The electrode 4| is connected to the inner conductor 43 and the electrode 43 to the outer conductor 41 of a concentric transmission line which is connected at the other end to a load circuit, for example, an aerial 43.

Auxiliary voltages which are positive with respect to the cathode l are supplied from a source of direct current, for example, a battery to the electrodes 5, 25, 3|, 31, 4| and 43, while a negative bias voltage is applied to the, electrode 3 through the secondary winding of a transformer 53. The electrodes 31, 3| and 4| have a higher positive voltage according to their average diameter. that is to say, the mean value of the external and internal diameters 'of an annular electrode or half the diameter of a disc-shaped electrode, is smaller.v In the case illustrated in Fig. 1 each of the electrodes 31, 3| and 4| in this order of succession has a higher voltage than the previous one.

Under the influence of the rotating field existing between the deflecting plates 1 and 3, the electron beam 2 moves in a circular path over the electrode 25 and impinges alternately upon the electrode 25, and successively through the apertures 21, upon the electrode 31. At least on the side turned towards the disc 23 the latter electrode has a high secondary electron emitting capacity. The electrons of the beam which strike the electrode 31 liberate secondary electrons, the number of which is equal to the number of primary electrons multiplied by the coeflicient of secondary emission of the electrode 31. This coefficient may amount, for example, to about 5 so that the electron current issuing from the electrode 31 is greater than the beam current which strikes this electrode. According to the invention, a number of secondary emission electrodes (one in the practical example shown) are arranged in the path of the secondary electrons. Each of these electrodes multiplies the number of electrons by the secondary emission coefllcient of the electrode struck, with the result that the number of electrons which is finally obtained in every impact of the electron beam on the electrode 31 may be very large. The device, according to the invention, consequently permits, even with a small intensity of the beam, to obtain a high output current so that it becomes possible to obtain an appreciable output energy even with a low impedance of the output circuit.

The electrode arranged in the path of the secondary electrons is the electrode 3| which, as has previously been observed, has a higher positive voltage than the preceding electrode 31, Due to the potential difference between the electrodes 31 and 3 I, the electrons issuing from the electrode 31 travel to the last mentioned electrode and impinge thereon, thus liberating for the second time secondary electrons. These electrons are attracted and, after having passed through the grid 43, received by the electrode 4|.

For the sake of clearness, Fig. 1 shows only one annular electrode 3| with the aid of which the electrons proceeding from the electrode 31 are multiplied. Preferably, however, a plurality of such electrodes should be provided in order to insin'e a large output current. Fig. 3 represents one practical example of a construction of the discs 23 and wherein there are three of the electrodes referred to. These electrodes are denoted inthe figure by 3|, 3| and 3|" respectively, while the annular grid electrodes pertaining to these electrodes are denoted by 32, 32' and 32" respectively,

We provide means for preventing secondary emission from the electrode 31 directly to the electrode 4|. Such means includes an annular grid-electrode 32 arranged in front of the electrode 3|, viewed from the electrode 31. A positive potential equal to or slightly lower than that of the electrode 4| is applied to the grid 32. The electrons proceeding from the electrode 31 are attracted by the grid 32 and moved towards this grid. For the greater part, however, they fly through the meshes of the grid 32 and reach the electrode 3|. The secondary electronsthus liberated from the electrode 3| also fly through the grid 32 and are then attracted by the electrode 4|.

When a group of electrons moves from the grid 43 to the electrode 4|, a current flowing from thegrid 43 to the electrode 4| is set up in an output circuit connected between these electrodes. Whenever the electrode 31 is struck by the electron beam a current impulse is produced in the circuit between the electrodes 4| and 43. Since this circuit comprises an oscillatory circuit tuned to the frequency of the impulses it is set into oscillation by the impulses. The frequency of the generated oscillation is equal to that of the current impulses, i. e., the number of apertures in the electrode 25, multiplied by the revolution v frequency of the beam 2. With the device represented in Fig. 1 the beam performs one revolution in every cycle of the controlling oscillation, the said revolution frequency being consequently equal to the frequency of the controlling oscillation.

For optimum conditions of operation, experience and theory lead to the choice of a structure wherein the mutual distance between the electrodes 4| and 43 is determined by the transit time of an electron therebetween, this transit time being made less than one half cycle of the output oscillation. This means that for practical cases the mutual spacing of the electrodes 4| and 43 must be very small.

As shown in Fig. 1, the output circuit includes the concentric transmission line 45, 41 connecting the electrodes 4| and 43 to the aerial 43. According to the invention. a metal sheath D should preferably surround the electrode 4| in the manner shown in Fig. 4a. This sheath is connected on the one hand to the grid 43 and, on the other hand, to the outer conductor 41 of the line 45, 41, whose inner conductor 45 is connected through the intermediary of a conductor B to the electrode 4|. The sheath D and the grid 43 enclose the electrode 4| as well as the conductor B and form an oscillatory circuit tuned to the frequency of the oscillation to be generated. Fig. 4b indicates the electrical characteristics inherent in the structure of Fig. 4a. The capacity 01 exists between electrodes 4| and 43 and capacity exists at the end A of the transmission line ll, 41. The capacity C: may be formed. for example, by the capacity between the sheath D and the conductor B, and may be due to the fact that the line 45. 41 is chosen so as to be slightly longer than one quarter of a wavelength, or an odd number of quarter wavelengths of the output oscillation. Ln represents the inductance of that part of the conductor 13 which is located within the sheath, while Ln represents the inductance of the sheath D. The oscillatory circuit thus formed is tuned to the frequency of the output oscillation and is coupled via. the capacity C: with the transmission line 45, 41. Owing to the fact that the capacity 01 between the electrodes II and it constitutes part of the oscillatory circuit, a comparatively high impedance is present between these electrodes. and this is desirable in order to producethe maximum of output energy. Owing to the fact that the connections of the electrodes 4| and 43 with the line 45, 41 also form part of the oscillatory circuit no trouble is experienced from the inductance of these connectlons.

The device. according to the invention, is also suitable for the generation of modulated oscillations. For this purpose a modulating voltage may be supplied through a transformer 53 to the controlling electrode 3. By this electrode the current intensity of the electron beam, that is to say, the number of electrons which passes per unit of time through a plane perpendicular to the beam, is varied in accordance with the modulating voltage, with the result that there occurs modulation of the electron current intercepted by the electrode ll, which current determines the output energy. It modulated oscillations are generated it is preferred to give the apertures 21 the shape of slits whose width increases towards the ends, for it has been found that the variation of the current intensity of the beam by the voltage supplied to the electrode 3 principally takes place owing to the fact that the cross-sectional area of the electron beam is varied, whereas the current intensity per unit of area remains substantially constant.

With the majority of tubes the current intensity and, therefore, cross-sectional area of the beam, is a substantially linear function of the voltage applied to the controlling electrode 3. In Fig. 5a the cross-section of an aperture 21 is indicated by r for the case wherein, in deviation from Fig. 2, round apertures are utilized. s1 and s: indicate the cross-sections of the electron beam at two different values of the modulating voltage. At the greater value the cross-section s1 of the beam is larger than that of the aperture 7' so that part of the beam is intercepted by the electrode 25. As a result thereof the current intensity of the beam only increases linearly with the voltage of the control grid until the cross-sectional area of the beam is equal to that of aperture 1'. In view of a favorable operation it is undesirable to increase the aperture 1' since the controlling eflect exerted by the electrode 31 through the apertures of the electrode increases in this ease up to an undesired amount. For this reason the shape of the apertures 21 is so chosen that always a part of the cross-section of the beam is intercepted, but at the same time in such manner that with an increasing cross-sectional area of the beam the non-intercepted part of the cross-section of the beam increases proportionally. To that end the apertures may have the shape of slits whose width increases towards the ends, as shown in Fig. 5b. The shape has so been chosen that the as a hatched area) increases proportionally to the area of the cross-section.

we claim:

1. A cathode ray tube generator having a plurality of target electrodes arranged in parallel planes, a receiving electrode, a grid-like electrode in front of said receiving electrode, and parallel thereto, an output circuit connected between the two, electrodes last mentioned, an apertured conductive sheath surrounding the receiving electrode, and a conductor extending through an aperture in said sheath and connected to the receiving electrode, said generator being further characterized in that the capacity between the said electrodes and the capacity between the sheath and the conductor form, jointly with the inductance of the sheath and of that part of the conductor which is located within the sheath, an oscillatory circuit which is tuned to the frequency of the output oscillation.

2. A device as claimed in claim 1, wherein modulated oscillations are generated owing to the supply of a modulating voltage to the controlling electrode of the device for generating the electron beam, and characterizedin that the apertures of the apertured electrode have the shape of slits whose width increases towards the ends.

3. In a cathode ray tube having an electron gun, a first target electrode having apertures through difierent ones of which an electron beam, upon deflection, may be successively projected, a second target electrode arranged to receive primary electrons after they have been projected through said apertures. a third target electrode insulated from and coplanar to said apertured electrode, a fourth target electrode insulated from and coplanar to said second target electrode, a direct current source and connections therefrom to diiferent electrodes, including those of the electron gun and of said target electrodes, for causing oscillations to be generated in said cathode ray tube, and, further, for producing secondary emission from the second and third target electrodes, a grid-like electrode the mesh of which is disposed in the electron stream between the third and fourth target electrodes, and a coaxial transmission line the inner and outer conductors of which are connected respectively to said fourth target electrode and to said grid-like electrode.

4. A device according to claim 3 and including a dipole antenna the arms of which are fed with energy transmitted through said coaxial transmission line. I

5. A device according to claim 3 and including a conductive sheath which serves to connect said rid-like electrode to the outer conductor of said transmission line, said fourth target electrode being substantially surrounded by the assembly of said sheath and grid-like electrode. and being capacitively related thereto.

. 6. A cathode ray tube comprising means to generate an electron beam, a first target annular electrode facing the electron beam and having a plurality of annularly arranged apertures through which the electron beam may be successively proiected, a second target annular electrode spaced from said first target electrode and arranged to receive primary electrons after they are pro jected through said apertures, and having a secondary electron emiasive surface, a third target electrode insulated from and arranged within and coplanar to said apertured electrode, and

through said apertures and having a secondary electron emissive surfaceja third target electrode insulated from and arranged within and coplanar to said apertured electrode and having a secondary electron emissive surface, a fourth target electrode insulated from and arranged within and coplanar to said second target electrode, and a grid-like electrode interposed between the said second and third electrodes.

8. A cathode ray tube comprising means to generate an electron beam, means to vary the intensity of said beam, a first target annular electrode facing the electron beam and having a plurality of annularly arranged apertures through which the electron beam may be successively projected, a second target annula electrode spaced from said first target and arranged to receive primary electrons after they are projected through said apertures and having a secondary electron emissive surface, athird target electrode insulated from and arranged within and co-planar to saidapertured electrode and having a secondary electron emissive surface, a fourth target electrode insulated from and arranged within and c0- planar to said second target electrode, a grid-like electrode interposed between the said third and fourth electrodes, and output coupling means for said tube connected to the said grid and fourth electrodes.

JULIUS O'I'I'O STRUTI.

ALDERT vm mm ZIEL.

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

UNITED STATES PATENTS Number Name Date 1,920,863 Hopkins, Jr Aug, 1, 1933 2,194,547 Haines Mar. 26, 1940 1,955,126 Heintz Apr. 17, 1934 2,026,892 Helntz Jan. 7, 1936 2,053,268 Davis Sept. 8, 1936 2,086,904 Evans July 13, 1937 2,164,595 Siebertz July 4, 1939 2,173,193 Zworykin Sept. 19, 1939 2,185,684 Bennett Jan. 2, 1940 2,185,693 Mertz Jan. 2, 1940 2,250,527 Gray July 29, 1941 2,250,528 Gray July 29, 1941 2,250,529 Gray et a1 July 29, 1941

Images