US2485400A - High-frequency electron discharge apparatus - Google Patents

Description

Oct. 18, 1949. E, D MQARTHUR 2,485,400

HIGH'FREQUENCY ELECTRON DISCHARGE APPARATUS Filed April 19, 1945 Fig.1.

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Inverfitor: 7 Elmer D. Mc Arthur,

His Attorney.

Patented Oct. 18, 1949 ZAtSAW HIGH-FREQUENCY ELECTRON DISCHARGE APPARATUS Elmer D. McArthur, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application April 19, 1945, Serial No. 589,231

2 Claims. (Cl. 31539) The present invention is directed to electronic tubes and is primarily concerned with the provision of a new and improved space charge control electron tube which employs the principle of sorting electrons in accordance with their velocities for increasing the trans-conductance of the tube.

It is an object of my invention to provide a new and improved electronic tube which is suitable for amplification of both low and very high frequency signals. I

It is another object of my invention to provide a new and improved electron discharge device in which the anode current therein is modulated by sorting of electrons in accordance with their velocity.

It is a still further object of my invention to provide new and improved ultra high frequency circuits employing cavity resonators.

One of the features of the invention is the employment in an electronic tube of a pair of control grids spaced between an anode and a cathode, utilizing a first of these control grids to vary the velocity of the electronic stream between the anode and cathode, and utilizing the other of the control grids to sort out electrons in the stream in accordance with their velocity.

The features of the invention desired to be protected herein are pointed out with particularity in the appended claims. The invention itself, together with further objects and advantages thereof, may best be understood by referring now to the following description taken in connection with the accompanying drawing in which Fig. 1 diagrammatically illustrates an electron discharge device and amplifying circuits suitably embodying my invention; Fig. 2 diagrammatically illustrates a modification of the electron discharge device of Fig. 1; and Figs. 3 and 4 are graphs illustrating certain operational characteristics of the device of Fig. 2.

Referring particularly to Fig. 1, there is shown an electron discharge device having an anode I and a cathode 2 arranged in end-to-end order. The anode and cathode are in the form of cylindrical members substantially coaxially aligned and having closed adjacent ends in opposed spaced relation to form electron emitting and electron receiving surfaces. Disposed between the anode and cathode are a pair of control grids 3, 4, and a focussing grid 5. The envelope within which these electrodes are enclosed comprises a series of three circular metal parts 6, 'l, and 8 which are supported in spaced relation by glass cylinders 9 and I sealed between them. The

part 1 provides a terminal for the grid 4 and a terminal for the anode is provided by a cylindrical enlargement H which is welded or soldered against the upper surface of the part 6. The grid 3 is supported from the metallic tube l2 which concentrically surrounds the cathode 2 and Which is Welded or soldered to the part 8. The focussing grid 5 is supported by a metallic tube l3 disposed between tube 12 and cathode 2. The lower end of tube I3 is provided with flange I4 which parallels the under surface of part 8, but which is separated therefrom by an insulating washer I5. Similarly, the cathode 2 extends through a central aperture in the part 8 and is provided, at its lower extremity, with a flange [6 which parallels the under surface of the part 8 but which is separated from that part by an insulating spacer l! which may be, for example, a mica washer. Preferably, the thickness of the insulating washers I5, I! is such that the cathode 2 has a high frequency connection with the part 8 through the capacity existing between this part and the flange IE, but is effectively insulated from the part 8 and the part M as far as direct currents and low frequency alternating currents are concerned. Separate connections are made to the cathode and grid 5, respectively, for direct currents and low frequency alternating currents by means of lead-in wires l8, l9 secured to the under surface of the part I2 and tercurrent to a coiled filament 24 arranged within the cathode cylinder 2. I

For the amplification of high frequency voltages, the electronic tube is incorporated into a cavity resonator forming structure which comprises an outer elongated conductive cylinder 25 having an inwardly flanged portion 26 which surrounds the base portion of the part 8, being insulated therefrom by a cylindrical insulator 21,

I a centrally disposed, conductive member 28 which abuts against the outer surface of disk 6 and is conductively connected to the anode terminal I I,

and an intermediate conductive cylinder 29 which is conductively connected to the grid disk I through a spring contact arrangement 30. In this cavity resonator, the outer cylinder 25 is insulated from the part 8 by the insulator 21, but is connected to this part for high frequency alternating currents through the capacity existing between the flange 26 and the part 8. The

' anode cylinder 28 is supplied with unidirectional currents over a lead-in conductor or rod 3|. An extension 32 of the anode cylinder 23 concentrically surrounds the rod 3|, being insulated therefrom at one end by an insulating washer 33 disposed between the adjacent ends of parts 28 and 32 and at its opposite end by a washer 34 which, in conjunction with a nut 35, serves as means for clamping the parts 28 and 32 and maintaining them in axial alignment. The structure thus described forms a pair of cavity resonators, one defined by the cylinders 25 and 29 and coupled to the space between the grids 3, 4" and the other defined by the cylinders 28, 32 and intermediate cylinder 29 and coupled to the. space between anode and grid 4. The dimensions: of these cavity. resonators may be adjusted by means of sliding plungers 36, 3'! and rods 38, 39 connected to these plungers.

The D. C. connections for the discharge device may be made in various ways and, in the arrangement illustrated, the anode is maintained at a potential above ground being. supplied with that potential by a lead-in conductor 4|! connected to the rod 3|, while the cathode is maintained at essentially ground potential. The focussing grid is maintained slightly negative with respect to the cathode 2 by means of a lead-in conductor 4| connected to prongs 2|. For purposes to be explained later, the second control grid 4 is maintained: at or near ground potential, while the first control grid 3 is maintained at a. positive potential. with respect to the cathode, being connected by means of lead 42 to a suitable source of voltage, such as the battery 43.

Signals to be amplified are supplied to the cavity resonator formed b the cylinders 25, 29 over a concentric transmission line comprising a tubular outer conductor 44 and a centrally disposed inner conductor 45 terminating in acapacitive coupling plate 46 disposed within this cavity resonator in spaced relation with the outer surface of intermediate cylinder 29. Amplified signals may be extracted from the cavity resonator coupled with the anode-grid 4 space, for utilization in an external circuit by means of a coupling loop 41 which extends into. this anode-grid cavity and which is supported from a hollow tubular conductor 48 extending outwardly through the plunger 31. A Wire 49, which connects with one extremity of the coupling. loop 41 is arranged within the conductor 48 and forms with it a coaxial transmission line.

In the operation of the system of Fig. 1, for the amplification of signals supplied. over input transmission line 44, 45', the dimensions of the cavity resonator defined by the members25, 29 are; adjusted by positioning of the plunger 36 to resonate at the frequencies of the, input signals. The grids 3, 5 preferably are aligned, and the grid 5 is supplied with a focussing potential so that electrons from th cathode 2 do not strike the. wires of the grid 3. The grid 3 is maintained at a positive potential to accelerat electrons emittedby the cathod 2. As the'focussed electrons from the, cathode 2 traverse the region between the wires 3 and 4,. they are either further accelerated or decelerated by the electromagnetic fields existing between. these wires. The grid 4 is maintained at a potential which is substantially that of the cathode 2 or slightly negative with respect to the potential of thi cathod in order to refiect those electrons which are decelerated' in traversing the region between the grids 3', 4. As a result,,on1 e1ectrons which are accelerated in this region pass, through the grid .4 4 to excite the output cavity defined by the members 28, 29 and supply energy to the output coupling loop 41.

In the modification of my ultra high frequency system shown in Fig. 2, the electron discharge device th-ere employed differs from that of the device of Fig. 1 in that it is so constructed that inputs signals may be impressed between the cathode 5D and a first grid or control electrode The electron discharge device of this system includes, in addition to the mentioned electrodes, an anode 52 and two additional grids or control electrodes 53, 55 supported between the electrodes 5| and the anode 52. The grids 53, 54 are provided, respectively, with supporting disks 55, 56, while the grid. 5! is supported with a cup-shaped metallic disk. 51. The disk 57 may be soldered or Welded to a metallic sleeve 58 which concentrically surrounds the cathode 58, being spaced therefrom by a disk insulator 59. The sleeve 58 has an outwardly directed flange 60, and insulating. cylinders GI, 62, sealed respectively between the members 65, 55 and 55, 56, support the grids 5|, 53, 54. in spaced relation. An additional insulating cylinder 63. is sealed between the disk 56. and an enlarged flange portion 64 of the anode 52 to complete the enclosing envelope of the. discharge device. The cathode 50 isheated by a filament 65 whichis enclosed within the cylinder which forms the cathode.

The input circuit of the system of Fig. 2 comprises a cavity resonator of the concentric conductor type constituted by an inner conductor 66 which slides over the cathode cylinder 59 and a tubular outer conductor 61 which slides over the metallic sleeve 58. and the cathode cylinder 56 form a portion of this cavit resonator. The dimensions of the resonator may be adjusted by means of a plunger 68 and input signals may be supplied over a concentric transmission line comprising a tubular outer conductor 69 and a centrally disposed inner conductor 18 terminatingin an input. electrode or probe H of the capacitive type. The output circuit of the system likewise is in the form of a cavity resonator of the concentric conductor type and' comprises an inner conductor 12 and capacitively coupled through an insulator 13 with a cylindrical enlargement 14 attached to the outer surface of the anode. The outer conductor of the output resonator is in the form of a metallic cylinder 15 having resilient fingers 16 engaging the disk 56. The dimensions of this output cavity resonator may likewise be adjusted by means of plunger H to adjust the resonance frequency of the resonator. Energy may be extracted from the resonator by means of an output coupling loop 18.

Unidirectional potentials for operating the device 2 are supplied to the anode 52 over a conductor 19. The cathode 5|] is preferably maintained at ground potential and a negative potential is supplied to the grid 5| over a conductor connected with the sleeve 53, the sleeve 58 and the outer conductor 61 of the input resonator being insulated by a cylindrical insulator 8! to permit the impression of unidirectional potentials between the cathode 59 and the electrode 5|. The control electrode 53 is provided with positive potential by means of a conductor 82 connected to the disk 55. The reflecting electrode 54 preferably is operated at the potential of the cathode or slightly negative with respect thereto, such potentials being supplied directly to the supportingdisk 56 for this electrode.

In this way, the sleeve 58v In the operation of the system for amplification of signals supplied to the input circuit over the transmission line 69, 10, the grid 53 is maintained at a positive potential to accelerate electrons emitted from the cathode 50 and the grid 54 is maintained substantially at the potential of the cathode or slightly negative with respect to the potential of this cathode in order to repel or reflect the emitted electrons. Thus, between the grids 53, 54, there are present electrons flowing in both directions. Both the quantity of electrons and the transit angle inthe region between these control electrodes may be controlled by the magnitude of the positive potential applied to the grid 53 so that the system does not oscillate.

The condition which exists when a signal to be amplified, is supplied to the input resonator may best be explained by reference to the curves of Figs. 3 and 4. The current flow, i in the plane of the grid 53 is shown by the curve 83 of Fig. 3. This current of course varies in magnitude with the potential impressed between the cathode and grid 5| that is, in accordance with the variations in the electromagnetic field in the input resonator. The average value of the current, Iav, is indicated by the line 84 of Fig. 3. The velocity of the electrons, which varies with the accelerating fields existing between the cathode and the grid 5|, is shown by the curve 85 and the average velocity of the electrons in the plane of grid 53 is shown by the straight line 86. If the voltage on grid 54 is made such that electrons having a velocity Dav cannot pass grid 54, then those electrons arriving at the grid 54 between the times t1 and t2 pass through the plane of grid 54 to the anode, while those which arrive at the plane of grid 54 between the time t: and the time its are reflected and returned partly to the grid 53 and partly to the cathode 50.

Those electrons which pass through the grid 54 give a current flow at the anode which is shown by the curves of Fig. 4. The overall effect at the anode of the accelerating potential applied to the grid 53 and the reflecting potential applied to grid 54 is to provide a large flow of current during positive halves of each cycle and zero flow of current during negative half cycles so that, for all purposes, a very large trans-conductance of the electronic tube is obtained.

Since the time of transit of electrons between the planes of the various electrodes is an appreciable part of and frequently more than a cycle, the voltages impressed may be so related with respect to the frequencies of the signals to be amplified that electrons reflected at grid 54 reenter the spacing between grid 5| and the cathode on a subsequent retarding half cycle of the excitation voltage. With this relation between transit time and potentials, the presence of these returning electrons in the cathode-grid 5| space increases the space charge with a resultant decrease in the velocity of forward moving electrons, thus essentially increasing the modulating effect of the excitation signals on the electron stream of the device. The effect, therefore, of introducing signals into the input cavity is to modulate the electron stream passing between the cathode 5|! and the control electrode 54, that is, electrons of this stream are sorted in accordance with their velocities. On positive half cycles, current pulses penetrate the grid 54 and flow to the positively charged anode. The modulated current which flows between the grid 54 and the anode excites the output cavity defined by the cylinders I5, and

12, 13 and is suppliedto utilization circuits by means of the output coupling loop 18.

The foregoing considerations apply of course only when the electron discharge device is operated as a space charge limited electronic tube. The modulation of electron velocity takes place in the interaction space between the cathode 50 and the control electrode 5|, while the reflection of electrons having a velocity less than the value Dav is effective between the grid 53 and the grid 54. As a result of these eifects, there are many more than the normal number electrons or charges between the cathode 50 and the grid 54. This increase is due to the fact that electrons are both traveling from the grid 54 to the cathode and returning to the cathode from the grid 54. It is apparent of course that the number of electrons between the cathode and the control grid 53 establishes the magnitude of the current whic flows to the anode- In the foregoing, the system of Fig. 2 has been described as an amplifler.- It is apparent, of course, that the systems of both Figs. 1 and 2 may be employed as a source of oscillations. This is indicated in Fig. 2 by the dotted feedback connection, as shown by a coupling probe 81 and the input probe 1 the feedback being made over a concentric transmission line connecting these two probes. In the operation of the structure as an oscillator, the grid 5|, being maintained at a negative potential, operates to focus the electron beam emitted by the cathode 50. One of the advantages of the structure is that concentration of the electrons in the interelectrode space into a beam through the action of the negative focussing electrode 5| results in a reduction of current at the positively charged electrode 53. The overall efiect is to increase the space charge density and to provide higher power output for the oscillator.

It is apparent also that the principles which are employed in the systems of Figs. 1 and 2 for the amplification of high frequency signals are applicable also to the generation or amplification of low frequency signals, the result being obtained by sorting of electrons in accordance with their velocities to permit only those having a velocity greater than a threshold level to travel to the anode of the device.

While I have shown and described my invention as applied to particular systems embodying various devices diagrammatically shown, it will be obvious to those skilled in the art that changes and modifications may be made without departing from my invention and I aim in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An ultra high frequency circuit comprising an electron discharge device having an anode cylinder and a cathode cylinder coaxially aligned therewith, said cylinders having adjacent closed ends in opposed spaced relation, three control grids positioned between said ends, three transverse conductive members connected respectively to said anode and two of said control grids, a pair of cylindrical insulating members surrounding said anode and cathode cylinders and sealed respectively between said transverse conductive members, a conductive cylinder surrounding said cathode supporting the third of said grids, means connected to said third grid for maintaining said grid at a negative potential with respect to said cathode fito ifoc'us electrons remitted therefrom, means connectdfltothe said two of. said "control gi ids forasupplysing afi high 'frequency :signal r-to" be amplifiectb'etween said twoz'grids;meansconnecteclztd theione' ef saidtwo grids a'djacent said cathodei f ormaiintaining said-'grid at a positive'potential WV-1th i 'respect' -to salicl cathode to accelerate electrons emitted therefromgmeans connected to thenether df-=Said1two grids for: maintaining said grid. substantially #atLthe potential of said cathode to sso'rt electrons r-passin'g between =said cathode andaanode: in accondance withtheir velocities.

i2. kAn electrcn dischargeudevice 'com'prising' an anode an'dua cathdd'e having planar surfaces in opposed spaced relation, a pair-of:grids'interposed between said surtacesi tl-iree transverse conductive men i'bers'con d-uctivly supportingxsaid anode and said gridsrinz spaced relation and a'fiording extemri'aily :=a'cces'sib1e terminals therefor, -means maintaining said transverse members in spaced reiatiomlapcyliinderrexteriding'inea direction transversettot sai'd canductive membersconstituting a -REFERENGES .GIlT ED "The f o'llowing" references are 6f "record in the file ("if this patent:

UNITED STATES PATENTS Number Name Date ::2',2'Z2;374 Kallmannet al -J'Fb. 10, I942. "2,278,210 "Morton ='Mar. 31, 1942 "2,353,743 *McArtnur July 18, 1 944 2,395,043 Goodchild Feb. 1 9, 19.46 914002753 Haeff May '21, 1946 2,402, 6I2 Dod i ngton J-u1y' "25, 1946

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