US2552040A - Electron discharge device - Google Patents

Description

A. v. HAEFF ELECTRON DISCHARGE DEVICE Original Filed April 27, 1943 May 8, 1951 2 Sheets-Sheet l .INVENTOR ANDREW V. HAEFF BY M Patented May 85 1951 ELECTRON DIS CHARGE DEVICE Andrew V. Haefi, Washington, D. 0., assignor to Radio Corporation .of America, a corporation of Delaware Application April .27, 1943, Serial No. 484,692, which is a division of application Serial No.

375,029, January .18, 1941.

Divided and this application December 5, 1947, Serial No. 789,919

6 Claims. I

My'invention relates to electron discharge devices and associated circuits for use at ultra-high frequencies and particularly to the circuits .in the form of resonant. cavity circuits or resonators.

The present application is a division of my c.0- pending application Serial No. 484,692 filed .April 27, 1943,, now Patent-No. 2,447,461, issued August I7, 1948, and assigned to the same assignee as the present application. Said .co-pending application is a division .of my earlier co-pending application Serial No. 375,029., filed January 18; 1941, now Patent No. 2,399,223., issued April 30, i946, and assigned to the same assignee as the present application. r

It has been demonstrated that tubes utilizing conventional grids for controlling current are well adapted for operation at ultra-high frequencies and retain their characteristic advantage :of possessing high transconductance. However, one of the difficulties encountered in operating amplifying tubes at ultra-high frequencies is the presence of considerable loading in the input circuit which results in an excessive amount of power being required to drive the tube. This decreases the effective power gain of the tube when operated as an amplifier.

The fundamental causes of high input loading are: (1) ohmic and radiation resistance losses due to high circulating currents in electrodes and leads; (2) electron loading which results from the interaction of the electron stream with the circuit, including degenerative or regenerative effects caused by lead impedance. V

In order to' reduce ohmic resistance losses it is necessary to use internal leads and external conductors made of high conductivity material and having large peripheries. In addition, interelectrode capacitances must be reduced as much as possible in order to minimize circulating currents. To reduce radiation losses a thoroughly shielded circuit of conventional design or closed type cavity resonators must .be used.

The principal object of my invention is to provide an electron discharge device and associated circuit having means for substantially reducing or completely neutralizing electron loading when the device is used at ultra-high frequencies.

It is also an object of my invention to provide .an electron discharge device having means for minimizing ohmic and radiation resistance losses when the device is used at ultra-high frequencies.

A still .further object of my invention is to provide improved forms of resonant cavity tank circuits or resonators suitable for use with ultrahigh frequency electron discharge devices and means for tuning the same.

The novel features which I believe to be char acteristic of my invention are set forth with particularity in the appended claims, but the-invention itself will best be understood by reference'to the following description taken in connection with the accompanying drawing in which Figs. 1 and 2 .are diagrammatic representations of electrodes and the movement of electrons between the electrodes; Figs. 3 and 4 are diagrammatic representations of conventional tubes and methods of operating the same; Figs. 5 and 6 are curves representing the relationship of the electron loading or conductance'and the transit time of the electrons of the tubes in Figs. 3 and l; Figs. '7 to 10 inclusiv are diagrammatic representations of tubes and circuits made according to my invention for practicing my invention; Fig. 11 is a longitudinal section of an electrondischarge device made according to my invention.

In order to understand better the. effect of electron loading, the mechanism of interaction between the electron stream and the electrodes to which circuits may be connected will be reviewed. Consider a system of two electrodes l0 and H as shown in Fig. 1. Assume that electrons travel from the electrode 10, which maybe a cathode, to the electrode I], which may be an anode. During electron transit an image charge appears on the electrodes equal in magnitude to the total charge present at any moment within the inter.- electrode space. The division of the image charge between the two electrodes depends, in general, upon the instantaneous distribution of charges moving within the inter-electrode space and upon the configuration of the electrodes. The current induced in an electrode due to motion of a charge is equal to the rate of time variation of the induced image charge on the electrode due to the moving charge. The total instantaneous current induced in the electrod by the electron stream will be found by summing the individual currents induced by all charges moi/=- ing within the interelectrode space. If :a voltage exists between electrodes ill and i I, the displacement current due to the interelectrode capacitance must be also taken into account.

Consider now a three-electrode systemformed, for example, by :a cathode H], a control grid 12 and the plate I I of a triode. Two spaces have to be considered. The total current induced in the intermediate electrode [2 (Fig. 2) is contributed by moving charges in both spaces, lit-42 rand l2! 1, and the total current is equal to the vector sum of the two currents. The power generated or absorbed by the electron stream within the spaces |0I2 and l2ll depends upon the respective current, voltage and the phase angle between the current and voltage in each space. Thus, the power generated or absorbed within the spaces 10-42 and l2-l I, will be:

In a more general case, such as a 10W-,u. triode, when there may exist considerable penetration of the electric fields from space I2-ll into space I|2, one must also consider direct-interaction between electrodes ll-lll; so that a power also must be taken into account.

In order to reduce the electron loading the total power must be reduced to a minimum. This can be accomplished by choosing currents, voltages and their respective phases in such a way ,that the total power W- 1z+W12-1o+W10-11 is a minimum.

In a conventional .negative grid tetrode operated at low frequencies the input electrode loading will be negligibly small if the driving voltage is applied in a conventional manner between the grid and the cathode so that the voltage also appears between the control grid G and the screen S. (See Fig. 3.) The radio frequency electronic current passing in the G-S space is very nearly equal and opposite in phase to the current in the C-G space so that the total driving power is ever, in a circuit shown in Fig. 4 where the driving balance the power absorbed in the C-G space.

As the driving frequency is increased the circuit of Fig. 3 will exhibit electron loading which initially will increase with frequency. This loading is due to the fact that with increasing electron transit time with respect to a period of the driving frequency the amplitudes and phases of currents in the C-G and G-S spaces change in such a manner. that the amounts. of power absorbed and generated in the two spaces no longer balance each other. For the case of a highcontrol grid when the spacings and direct current voltages are such that the G-S electron transit time is negligible compared to C-G transit time an analysis shows that the electron loading or conductance will vary with transit time as shown in Fig. 5. Here the ordinates of the curve represent the ratio G/Gmo where G=conductance of the grid G due to electron motions and G4no=transconductance of the grid G at very low or zero frequency, that is when the transit time of the electron is negligible in comparison to the time of one cycle of the frequency of the applied voltage. The abscissae represent the ratio 'r/T, that is, the ratio of the transit time of the electron to the period of oscillation of the applied alternating voltage. The electron loading increases rapidly with transit time, reaches a maximum at the value of transit time 1' equal to 0.85 of the oscillation period T and then, under ideal conditions, passes through zero and be- 'comes negative. In the case of circuit shown in Fig. 4 the variation of electron loading with transit time will be as'shown in Fig. 6. Starting T peri0d of oscillation the loading will be small even for conventional input circuits. However, the values of frequency and'operating voltages for these optimum conditions frequently lie outside the useful operating range of the tube. The tubes could be designed for this optimum condition but, in general, this may necessitate a compromise, so that high transconductance may be partly sacrificed. The present invention provides means for neutralizing electron loading for a wide range of frequencies and operating voltages without any sacrifice of the useful characteristics of the tube, such as high transconductance.

A general scheme is that in addition to the driving voltages applied between the cathode and grid, a voltage is developed between the control grid and the screen of such a magnitude and phase as to generate power in the grid-screen space and this power is fed back into the cathodegrid circuit, so that it will balance the power absorbed in the cathode-grid space.

A schematic diagram of such a circuit is represented in Fig. '7. An impedance Z2 is introduced between the screen S and the grid G of such magnitude and phase angle that the current iG-s will produce a voltage V2 across this impedance. The power W2=iG-sV2 Cos (iGsV2) generated in the G -S space is then fed to. the grid-cathode circuit Z1 by means of a coupling circuit Zn. The impedances Z1 and Z2 usually take the form of tuned circuits and the coupling impedance Zo may be the inter-electrode capacitance or an auxiliary coupling element.

A modification of the circuit shown in Fig. '7 is represented schematically in Fig. 8, where the impedance Z2 is shown introduced between the screen S and the cathode C rather than between the screen S and the control grid G. The coupling between the circuits Z1 and Z2 is provided by the controlgrid to screen capacitance or it can be supplemented by an auxiliary coupling circuit Zn. In Figures '7 and 8 conventional output circuits with output impedances (Z) connected between the anode and the screen are shown. However, other types of output circuits can be used, since the input loading neutralization scheme here proposed in no way depends upon the extraction of energy from the output circuit.

Fig. 9 shows schematically the input loading neutralization circuit in combination with an inductive type output circuit. Here the output circuit is connected between the two screening electrodes S1 and S2. The suppressor and current collecting electrodes, represented respectively by S3 and coll., are also shown. Fig. 10 represents schematically the input circuit arrangement of Fig. 8 in combination with the inductive-output circuit. In the above circuit diagrams only the essential radio frequency circuits are indicated. Blocking, grounding and by-passing condensers which are used for providing isolation of electrodes for direct current, so that different direct current voltages can be applied to different electrodes, are not shown.

One practical embodiment of my invention incorporated in a so-called inductive output tube sshown in detail in Fig, 11. .lnductive output tubes their operationare described more fully in my United States Patent 2.237.978. issued April 8, 1941, and assigned to the Radio Corporation of America. Briefly, an inductive output tube comprises a cathode for supplying a .beam of electrons and a collector for receiving the electrons. A modulating grid is placed adjacent the cathode for modulating the beam of electrons which passes to the collector. Surrounding the beam path is a resonant cavity circuit comprising a hollow member having apassageway extending therethrough through which the beam passes. The passageway is provided with a gap lying in a plane transverse to the beam path. As the modulated beam of electrons passes acrossthis gap, energy is transferred-from the beam to the resonant cavity circuit which provides the output circuit for the tube and which can be coupled to a radiator or to an amplifier.

In Fig. 11 is shown a longitudinal section of an electron discharge device made according to my invention in'which all of the resonant cavity circuits are placed outside the evacuated envelopesm. The concave spherically curved cathode H, which is indirectly heated is provided with heater leads 12 and 13, lead 13 serving also as thelead for the cathode. A control grid 14 is positioned closely adjacentthe cathode and has the same configuration, the screen and accelerating electrodes 75 and 'Hibeing supported fromthe glass envelope by means of leads l5 and 16. The collector 1'! is provided with the radiating fins l8 and the lead and support wire 9 '19. A secondary electron suppressor 89 is posilar member 99 is capacitively coupled to the extension .9] of disc .81. The cathode-control grid circuit is tuned by means of a tuning ringlM slidably mounted between the tubular members 93 and 94 and provided with an adjusting 'rod 102. The screen electrode-control grid circuit is tuned by means of the tuning ring 1.93 provided with the adjusting rod I94 and slidably supported on tubular member by means of the insulating ring-shaped members I95 and I99. To feed back energy from the screen grid-control grid circuit to the cathode-control grid circuit, I provide an L-shaped loop member 1.01 extending from the space between members 94 and 99; through apertures in members 199 and 94, into the interior of tubular member 94. Adjustment is provided by means of the rod H18. To couple the cathodegrid circuit to a driver, a loop 199 is provided extending through an aperture in the tubular member 94. The output from the output tank circuit is obtained by means of the loop H0 extending within the aperture in the member 84 of the tank circuit. To focus the electron beam through the tube, solenoids HI and H2 are provided for producing a magnetic field in the direction of the tube axis.

The grid bias voltage is obtained from the voltage source I i3 through a voltage divider -I I3, the cathode heating circuit being provided by means of a transformer H4 connected to a voltage source. The tank circuit is maintained at a highly positive potential with respect to the oathode by means of voltage source H 5 which may be greater than voltage source H6 provided with the collector.

In operation the input voltage is applied through the loop I99 to the cathodegrid tank circuit including tubular members 99 and 94. This causes the grid M to modulate the electron stream from the cathode H. This modulated beam of electrons passes by the gap 94 in the screen-control grid circuit delivering energy to the cylinder or collar 99 is slidably fitted to provide a tuning condenser for the tank circuit, the collar being provided with a radially extended lip 89 and adjusted by means of insulating rod 99 on the side of the tank circuit. The condenser cylinder is slidably supported on the electrode 96 by means of the insulating collar members 9| and 92. The leads [5 and 19' are connected to theextension 81 and the disc 89,- respectively.

The cathode-grid concentric line circuit cornprises the inner tubular member 93 which serves to shield the cathode leads, the outer tubular member 94 coaxial with and concentric with the inner tubular member 93, and the apertured shorting disc 95 electrically connecting the two tubular members. The cathode H is capacitively coupled to the inner tubular member 99 by means of the cup-shaped extension 99 electricall connected to the cathode lead 13 and insulatingly supported on the inner tubular member 93 by means of the insulating collar 91. The grid 14 is electrically connected to the outer tubular member by means of the spring contacts 99. The resonant cavity for the screen electrode-grid circuit is provided by means of the outer tubular member 99 coaxial with and surrounding member 94 and shorted by means of the apertured disc-shaped member I90. The open end of tubuthe resonant cavity circuit consisting of the cylinders 94 and 99 which energy is fed back to the cathode-control grid circuit by means of loop I01 in order to minimize the amount of driving power. The'modulated stream then passes through the accelerating electrode 15, past the gap 89' to energize the output tank circuit 82, 83, 84, the decelerated electrons being absorbed by the collector T! at a lower velocity. The output is obtained from the tank circuit by means of the loop I 1 9 extending within the tank circuit.

It will thus be apparent that by means of the construction shown in Fig. 11 that losses due to the electron loading effects in the input circuit are reduced to a minimum by my invention. Ohmic and resistance losses due to high circulating current in electrodes and leads are reduced to a minimum due to the fact that concentric lines and resonant cavities used are of high conductivity material and large diameter and due to the efiective by-passing of the radio frequency currents. Radiation losses are reduced to a minimum because of the shielded circuits. Thus, all three objects contemplated by my invention are practiced to provide a tube particularly suitable for use at ultra-high frequencies.

While I have indicated the preferred embodiments of my invention of which I am now aware and have also indicated only one specific application for whichmy invention may be employed, it will be apparent that my invention is by no means limited to the exact forms illustrated or the use indicated, but that many variations may be made in the particular structure used and the purpose for which it is employed without departing from the scope of my invention as set forth in the appended claims.

What I claim as new is:

1. A resonant cavity tank circuit comprising a first tubular member and a second tubular member surrounding said first tubular member, said tubular members being electrically connected toand the second tubular member, and movable longitudinally of said tubular members for tuning the tank circuit.

2. A resonant cavity tank circuit comprising a first tubular member, a second tubular member surrounding said first tubular member, said tubular members being electrically connected together to provide a coaxial line tank circuit and tuning means for said coaxial line tank circuit including .a conducting member within said second tubular member surrounding and slidable longitudinally of the first tubular member, said conducting member comprising an annular-shaped conducting member and a pair of oppositely disposed annular-shaped insulating members surrounding said inner tubular member and supporting said annular-shaped conducting member in spaced relationship with respect to said tubular members.

3. A coaxial line resonant cavity tank circuit including an outer tubular member and an inner tubular member, said tubular members being electrically connected together, and means for tuning said resonant cavity tank circuit including an annular-shaped member of conducting material, a pair of insulating collar-like members slidably mounted on the inner tubular member and provided with flanges lying parallel to the longitudinal axis of said tubular members and engaging said annular conducting member and supporting said annular conducting member in spaced relation to said tubular members.

4. A cavity resonator structure adapted for use with an electron discharge device having an envelope containing a cathode structure at one end for directing a beam of electrons along said en- ,velope and another electrode toward which said electrons are directed, said cavity resonator structure including a first cavity resonator comprising inner and outer hollow tubular members coaxial with each other and having a, member extending between said coaxial members at one end and tering with the passage'through the inner tubular member, said resonators being adapted to receive said electron discharge device within the inner tubular member to extend through said apertures.

5. A cavity resonator structure adapted for use with an electron discharge device having an elongated envelope containing a cathode structure at one end for directing a beam of electrons along said envelope and another electrode toward which said electrons are directed, said resonator structure including a first cavity resonator comprising inner and outer hollow tubular members coaxial with each other and having a conducting member extending between said coaxial members at one end and providing an enclosed space between said coaxial members and a second cavity resonator at the opposite ends of said coaxial tubular members and comprising a pair of spaced disc-like members closed at their peripheries-and having apertures centrally thereof registering with the passage through the inner tubular member, said resonators being adapted to receive said electron discharge device within the inner tubular member to extend through said apertures, with the cathode end of said envelope within said tubular member.

6. A cavity resonator structure adapted for use with an electron discharge device having an envelope containing a cathode structure at one end for directing a beam of electrons along said envelope and another electrode toward which said electrons are directed, said cavity resonator structure including a coaxial line comprising inner and outer hollow tubular conductors coaxial with each other, and a cavity resonator at one end of said coaxial tubular members and comprising a pair of spaced plate-like members lying in planes transverse to the longitudinal axis of said tubular members and closed at their peripheries and having registering apertures registering with the passage through the inner tubular member, said coaxial line and said cavity resonator being adapted to receive said electron discharge device Within the inner tubular member to extend through said apertures.

ANDREW V. HAEFF.

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

UNITED STATES PATENTS Number Name Date 2,272,211 Kohler Feb. 10, 1942 2,287,845 Varian et a1 June 30, 1942 2,353,742 McArthur July 18, 1944 2,399,223 Haeif Apr. 30,1946 2,400,752 Haeff May 21, 1946 2,411,424 Gurewitsch Nov. 19, 1946 2,412,055 Meahl Dec.-3,- 1946

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