US2548405A - Electron tube - Google Patents

Description

April i0, 195i R. L. sNYDER, .JR 29548945 ELECTRON TUBE Filedduly 24, 1945 IN VEN TOR.

Patented pr. 10, 19,51

ENT oie ELECTRON TUBE Richard L. Snyder, Jr., Princeton, N. J., assigner to Radio Corporation of America, a corporation of Delaware Application July 24, 1945, Serial N0. 606,812

11 Claims. (Cl. 315-12) This invention relates to storage tubes of the cathode beam type. Storage tubes have heretofore been made in which a charge pattern has been built up on the mosaic surface of the target of a cathode beam tube by a signal-modulated beam impinging on such surface under one set of conditions and discharged by an unmodulated beam impinging thereon at a later time under a different set of conditions.

It is an object oi this invention to build up an Wall coating I0 is applied electrical potential image on the scanned surface of a dielectric target of a cathode beam storage tube by signals applied to the signal plate at one side of the dielectric target as the beam is scanned over the other side.

Another object of the invention is to devise a cathode beam tube in which the electron stream is not modulated by signals repeated at the same phase of line scansionand is modulated by those repeated at changing phase.

Another object is to devise a cathode beam tube for use in a radar system in which only changes between successive wave trains of echoes are passed to the output circuit.

Another object is to devise a tube in which the echoes from xed or stationary objects are suppressed and those from moving objects are passed to the output circuit.

Other objects of the invention will appear in the following description, reference being had to the drawing, in which the single iigure is an illustration of a tube embodying the invention.

My invention may be applied to cathode beam tubes of various types, but by way of example it has been illustrated in connection with a multiplier tube such as disclosed in the Patent 2,433,941 of Paul K. Weimer, filed September 16, 1944. The tube consists of an evacuated envelope I containing a gun 2 at one end of the tube and a target 3 at the other end. The gun consists of the usual indirectly heated cathode i (the heater not being shown), surrounded by the control electrode or grid 5. Around the grid is the anode 6, the end 'l of which constitutes the first dynode of the multiplier. In the drawing the cathode1 grid and rst anode are partially sectioned to illustrate the tubular construction. The grid and rst anode have minute orices, as shown, through which the beam 8 is projected in the usual way. Tubular electrode 9 is axially placed around the front part of the gun. This electrode is often referred to as the persuaden because of its action in directing the secondary electrons into succeeding multiplier dynodes, as will be later referred to,

to the inner wall of envelope as usual.

Outside the envelope of the tube is placed the deecting unit II, consisting of two coils having their field axes perpendicular to each other and to the longitudinal axis of the tube. One of these coils deflects the beam in a vertical direction in the drawing and the other deflects it at right angles. These coils are of well-known construction and hence have not been individually shown. It will be understood that these coils will have varying voltages applied, say by av saw-tooth generator, to produce line and page scansion, or voltages may be applied thereto for producing spiral scansion of the target or line scansion only, as may be desired. In the latter case, a direct current voltage would be applied to the vertical deflector coil. The means for producing the different types of scansion of the target are well known in the art and need not be'further described.

The delecting unit II may be adjusted byrany suitable means, such as by rod I2. Outside of the envelope I an adjustable co-il I3 may be used having a field perpendicular to the axis of the tube. By adjusting this coil around the axis Vof the tube, any slight miscentering of the beam due to mechanical imperfections can be compensated for. This also is a known arrangement and need not be further described.

' Outside the coils I IY and I3 is placed solenoid I4, which produces a 'strong magnetic focusing field parallel to the axis of the tube.

Around the gun is placed a plurality of multiplier dynodes I5, I6, Il and I 8 and a collecting electrode I9, which is illustrated as a screen. The multiplier dynodes I 5, I6 and I1 are fully described in the said Weimer application and it will be suicient to say that each has a suiiciently large axial opening to iit in spaced relation over the tubular anode 6 and consists of slanting radial blades 20, somewhat like an electrical fan, held in a suitable annularframe. Infront of ythe blades is a screen ZI secured to the annular frame so as to be in electrical contact withfthe multiplier blades 20, from which it is suitably spaced. The multiplier dynodes I5, I6 and Il are partially broken away to show the blades 20 and screen ZI. The multiplier dynode I8 is the nal multiplier stage and consists of a flat annulus. The multiplier dynodes I5, I6, Il and I8 may have .anyr desired coating of active material to produce suitable emission of secondary electrons upon bombardment. Various voltages may be .applied to the electrodes of the tube, by connecting each electrode respectively to an appropriate source of potential as for example, a voltage divider 3B connected, as is shown in the drawing, across the terminals of a direct current source. By way of example I have illustrated in the drawing suitable voltages. All of the tube thus far disclosed is the same as disclosed 'in the said Weimer application.

The target 3 of my invention consists preferably of a dielectric plate 2l', such as mica or aluminum oxide, for example, which may be rectangular or circular, as desired. The signal plate 22 may be formed on the non-scanned side of the dielectric plate by depositing a metallic coating thereon, or may be produced in various other ways. If aluminum oxide is used for the target 3, one side of an aluminum plate may be anodized to produce the insulating material of the target and the other side may be left unoxidized for the signal plate.

A metal screen 23, which may be like that disclosed in the application of Harold B. Law, led March 31, 1945, Serial No. 585,925, which application is now abandoned, is in intimate contact with the target 3 on the gun side.

The signal plate 22 is connected through a resistance to a suitable voltage source indicated as ground 34, and to the output of the receiving apparatus, which is typified by a single triode 24, having its plate-anode connected by a lead 3D to the signal plate 22 and to a suitable voltage supply, the cathode being grounded. The received signals are applied to the grid of this tube 24.

Before describing the detail operation of my invention, the general theory of the action of the beam will be explained. The beam from the gun passes through the screen 23 and hits the dielectric surface of target 3 at high velocity. Secondary electrons are bombarded from the dielectric surface and, if the bombarded area is negative relative to the screen, pass through the screen towards the rst dynode 1. This causes the bombarded area of the target to become more positive, until the potential of the target area reaches that of screen 23. If the bombarded area of the dielectric target is positiverelative to the screen, the secondary emission from the area is suppressed by the negative Ifield caused by the screen and the target element becomes more'negative until it reaches screen potential. When an element under bombardment is at screen potential its voltage is in equilibrium, because if it goes negative, the number of secondaries leaving exceeds the number of primaries landing and the element becomes positive; whereas if the element goes positive, secondary emission is suppressed and the element goes negative. When the bombarded elemental area is at screen potential, there are therefore as many electrons leaving the target as land from the beam. Thus, scansion of the beam across the target brings the scanned areas to the potential of the screen. The beam will be made to have suflicient intensity to substantially instantlyvbring the potential of an elemental area to the screen potential. The emitted secondaries are drawn back to and bombard the rst multiplier dynode '1, from which new secondaries are emitted. These secondaries, guided by the De1`-' suader 9, are drawn outward by theiield from the second dynode I5 through screen 2l, which has the same potential as this dynode. This pass age of electrons from dynode 1 to the nrst mult1pl1er stage proceeds throughout the/Whole annular space around the gun and not mellly m the one path indicated in the drawing. Secondary electrons are bombarded from the inclined blades 2Il and, shielded from the potential of the previous electrodes by screen 2|, are attracted into the dynode I6 through its screen, where the process is repeated. The additional secondary electrons, aftel` being emitted from stage I1 in the same way, pass through the collector` screen I9 and produce by bombardment more secondary electrons fromthe nal dynode I8 and these are collected by screen I 9 and pass to the output terminal.

The electrons in the beam which strike the wires of the screen 23 also release secondary electrons, which enter the multiplier in the same way as other secondaries. Since the beam current is constant, the eiect produced by these secondaries is essentially constant and has little influence on the output signal.

Thus, the beam, modulated by the signal as latel` described, is passed successively to theA five multiplier stages and the signal strength is greatly increased. 4

The operation of my storage tube in a coherent pulse type of radar system will now be explained for single line scansion. I

The previous scansion of the beamover target 3 has brought thedielectric surface to the potential of screen 23. In the known coherent pulse radar system, the signal pulses are transmitted at the beginning of each line scansion at the peak of the saw-tooth-wave controlling this scansion and echoes from both moving and stationary objects are received and impressed on the dielectric target in certain .phases ofthe line scansion, depending upon the distance of the objects from the transmitter-receiver. In certain uses, the reflections or echoes from stationary or xed 0bjects, such as mountains, are not only of no interest, but they also clutter up the desired record of echoes from moving objects, such as airplanes, and make it diicult to determine which of the signals represent a moving object. 'Withv fixed objects the successive echoes arrive at the signal plate 22 always in the same phase lof the line scansion, because their distance from the transmitter-receiver does not'vary and their'amplitude is constant. The echo signals from moving objects, however, vary rapidly in amplitude, due to the well-known Doppler effect in the coherent pulse system and slowly change in phase due to their varying distance from the transmitter-receiver. This means that if an echo signal from a xed object is impressed on signal plate 22 when the beam in one scansion is on' a certain elemental area of the target, all successive signals from that same xed object will arrive while the beam is on that elemental area and will have the same amplitude as the preceding signal. On theother hand, successive trains of echoes from moving objects will produce signals of varying amplitude when the beam is on a particular elemental area, because of the Doppler eiect.

Suppose trains of echo signals from a mountain peak are constantly arrivingI While the beam ison the nth elemental area of a scanned line. Thesignal potential will be impressed on the entire signal plate 22 and the potential of the entire dielectric target 3 will be proportionally raised, say, above the potential of screen 23. The nth area will therefore receive electrons from the beaminexcess of emitted secondaries suincient to bring the surface down to thepotential of the screen. As the beam leaves the elemental area 1L, the ,Signal potential ceases to be impressed on signal plate 22 and the potential of the dielectric surface, except area n, drops down to screenpotential. The elemental area n drops in potential as far below the potential of the screen 23 as it was raised above it by the signal. Absence of signals will be assumed until the beam reaches the mth area, when an echo signal of positive potential, say, from a moving object, is impressed on signal plate 22. The potential of all areas of the surface of the target, including areav n, will again be raised by the signal. When the beam leaves the mth elemental area, the entire dielectric drops down to the potential of screen 23 except the elemental areas n and m, which drop as far below the screen in potential as they were raised above it by the signal when the beam was on area m.

On the next'scansion of this same line by the beam, it will find elemental area n just as far below the screen potential as the signal potential of the second wave train can raise it above that potential, because the signal is identical with that previously impressed on this area. Thus, the second wave train from the Xed object raises the potential of elemental area n up to the exact potential of screen 23 and no higher. Therefore, the electrons from the beam landing thereon release secondaries in a one-toone ratio to the beam electrons, so that the electron stream passing to the multiplier is not modulated. When the beam reaches the mth area, the signal arriving from the moving object has a different amplitude, because of the Doppler eiect. The beam finding the area m. below the potential of screen 23 bombards a sufficient excess of secondary electrons from its surface to bring the potential back to that of screen 23. Thus, a signal is produced by an increase in the number of returning electrons in this case. With fixed objects, in all scansions except the first one, which may be disregarded, the beam is not modulated. With moving objects, the beam is modulated during each scansion and the multiplier output from the tube contains substantially only signals from such moving objects.

It will thus be seen that with myinvention the use of radar systems in operations over or near land surfaces has been enormously increased in effectiveness, due to the elimination of all signals from stationary objects, leaving only those from moving objects which it is desired to identify'and locate.

In radar systems the antenna is usually rotated to survey the entire horizon for echoes from objects. Since the radiation pattern of present directional antennas has material and variable breadth, signals from objects will vary with the field strength of this pattern. The received signals from fixed objects in one scansionA may therefore have different amplitudes from those of the previous scansion. Echoes from fixed objects thus tend to increase in amplitude from scansion to scansion as the center of the radiation pattern approaches them and to decrease from scansion to scansion as the center of the radiation pattern moves away from them. Since this change in amplitude is unidirectional over a number of radar cycles, the dilerences passed by the storage tube are all in the same direction. The output of the storage tube will therefore have a very slowly changing pattern of the differences whichcan .be removed by passing the signals throughasecond storage tube in cascade. That is, the output of one tube' may be applied to the input signal plate of another tube. Since the small output pulsesof the lirst tube will. have substantially constant phase and amplitude for any two successive line scansions for fixed objects, it will be apparent that the echoes from such objects will not produce signals. In. the cascade arrangement, however, the echoes from moving objects will produce signals in the second tube, since they are of rapidly varying amplitude in the output of the first tube.

I have described the operation of my storage tube in connection with a radar system, but this is by way of example only. The improved storage tube may be used in various other ways where storage of information is desired. Signals may be impressed on the signal plate while the beam scans a predetermined pattern over the target. The signal and beam may then be shut oir, leaving the information stored in the target. At any desired later time the beam may be turned onv and, with no new signals impressed on the signal plate, scanned kover the pattern so that the signal impressed during the first operation will be reproduced. The signals need not be recorded in one scansion and utilized in the next scansion. Signals can be stored at one time and reproduced at any later time merely by shutting off and turning on the beam at the desired times. As will be evident from the described method of operation, recorded signals may be combined with new signals, enabling one to use the tube for carrying out complex operations by suitable combination of signals.

Having described my invention, what I claim l. A cathode ray beam storage tube system comprising a cathode ray beam gun adapted to produce a beam of electrons along a path, a target having a surface positioned transversely to said beam, va screen at said surface of said target, means for scanning the beam of said gun over `elemental areas of said target surface, a signal receiver including an output terminal, means capacitively connectingy said output terminal to said target surface to apply each of successive signal potentials simultaneously to all of the scanned elemental areas, and means connected to said screen for applying an electrostatic potential thereto Ato control the secondary emission from said target surface.

2'. A cathode ray beam storage tube system comprising a cathode ray beam gun adapted to produce a beam of electrons along a path, a dielectric target having a surface facing said gun and positioned transversely to said beam path, a screen at said dielectric target surface, means for scanning the beam of said gun over elemental areas of said dielectric surface through said screen, a signal receiver including `an output terminal, means capacitively connecting said output terminal to said dielectric surface to apply each of successive signal potentials simultaneously to all of the scanned elemental areas.

3. A cathode ray beam storage tube system comprising a cathodel ray beam gun adapted to produce a beam of electrons, a target, a screen at the surface of the side of said target facing said gun, and an input signal electrode at the opposite surface of the target. means for scanning Ythe beam of said gun over elemental areas of the rst mentioned surface of the-target, and a "signal'receiver having its output terminal connected to said signal electrode forapplying signal potentials simultaneously to all said elemental areas'.

A4. A cathode Aray beamY tube systemcomprising a cathode ray beam gun adapted t'o'" provide a beam of electrons, a dielectric target, a

screen at the surface of the side of said dielectric target facing said gun, means for scanning the beam of said gun over elemental areasV of said surface, an input signal electrode at the opposite surface of the target and a signal receiver having its output terminal connected to said input signal electrode for applying signal potentials simultaneously to all said elemental areas.

' 5. A storage cathode ray beam tube system comprising va cathode ray beam gun adapted to produce a beam of electrons, a dielectric target, a screen on the surface ofthe side of said dielectric target facing said gun, and an input signal plate on the opposite surface thereof, means for scanning the beam of electrons over elemental areas of the rst mentioned' surface through said screen at high electron velocity,

and a signal receiver having its output terminal connected to said plate for applying signal potentials simultaneously to all said elemental areas.

6.'A cathode ray beam storage tube system comprising a cathode, a grid, an anode having a beam aperture, a multiplier dynode at the side of the aperture, a target having one surface facing said aperture, a screen at said target surface, an input signal electrode at the opposite surface of the target, a direct current potential source having negative potential terminals connected to said grid and cathode, positive potential terminals connected to said anode and said screen and a terminal of still higher positive potential connected to said dynode, whereby a beam of electrons issues from said aperture, means for producing a focusing eld for said beam, means for scanning said beam over a line of said target, and a signal receiver having its output terminal connected to said input signal electrode for applying signal potentials simultaneously to all elemental areas of said line.

7. A storage cathode ray beam tube system comprising a cathode, a grid and an anode having a beam aperture and an electron multiplier surface therearound, a dielectric target having one surface facing said aperture, a screen at said surface, an input signal electrode at the opposite surface of the target, means for producing a magnetic focusing eld in the tube, a direct current potential source having negative potential terminals connected to said grid and cathode, positive potential terminals connected to said anode and said screen and terminal of still higher positive potential connected to said multiplier dynode,V whereby a beam `of electrons issues from saidy aperture, means fory scanning said beam of electrons over a line of said target, and a signal receiver having its output terminal connected to said signal electrode for applying signal potentials simultaneously to all elemental areas of said line.

8. A storage cathode ray beam tube system comprising a cathode, a grid, an apertured anode, a dielectric target, a screen atl one surface of said target, an input signal electrode at the opposite surface of the target, a direct current source adapted to apply voltages to said cathode, grid, anode, and screen to produce a beam of electrons through said apertured anode of suicient velocity to bombard secondary electrons from said target at greater than unity ratio and to produce a voltage between said screen and said anode to bombard secondary electrons from said anode at (greater than unity ratio, means for producing a magnetic focusing field in said tube, means for v facing said gun, means for scanning the beam of said gun over elemental areas of said target, a conducting plate on the other face of said target and a conductor connected to said plate for applying each of successive signal potentials simultaneously to all of the scanned elemental areas of the target. v

10. A signal storage device comprising, an electron gun adapted to produce a beam of electrons along a path, said beam being of sufcient energy to initiate secondary electron emission from a dielectric surface, a target electrode mounted transversely to said beam path, said target electrode including a surface of dielectric material facing said electron gun and an input signal electrode capacitively connected to said dielectric surface, means for scanning said electron beam over said dielectric surface to produce a secondary emission therefrom, an electrode spaced from said dielectric surface for collecting the secondary emission therefrom, a screen electrode adjacent said dielectric target surface between said electron gun and target, a signal receiver including an output terminal. means connecting said output terminal to said signal electrode, andrmeans connected to said screen and said signal electrode for applying a common potential thereto to control the secondary emission from said dielectric target surface.

11. A signal storage device comprising an envelope, an electron gun within said envelope adapted to produce a beam of electrons along a path and of sufcient energy to initiate secondary electron emission from'a dielectric surface, a target electrode mounted transversely to said beam path, said target electrode including a surface of dielectric material facing said electron gun and an input signal electrode capacitively connected to said dielectric surface, a screen electrode in contact with said dielectric target surface. and positioned betweenv said electron gun and said target, a lead connected to said input electrode for connecting said input signal electrode to a signal source, and lead means connected to said screen electrode and said signal electrode for applying a common potential thereto to control the secondary emission from said dielectric target surface.

RICHARD L. SNYDER, JR.

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

UNITED STATES PATENTS Number Name Date 2,160,022 Kaufmann May 30, 1939 2,213,178 v f Iams Aug. 27, 1940 2,301,743 Nagy et al. Nov. 10, 1942 2,425,657 Tunick et al Aug. 12, 1947 2,454,410. .Snyder Nov. 23,1948

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