US2792520A - Ultra-high frequency discharge device - Google Patents

Description

y 1957 E. D MCARTHUR ULTRA-HIGH FREdUENCY DISCHARGE DEVICE Filed Dc. 24, 1952 Inventor. Eh'her- D. Mc Arthur; by w 4. 3

His Attorney.

United States Patent 9 ULTRA-HIGH FREQUENCY DISCHARGE DEVICE Elmer D. McArthur, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application December 24, 1952, Serial No. 327,724

7 Claims. (Cl. 315-537) This invention relates to high frequency discharge devices of the type having space charge control means.

In discharge devices utilized in frequency ranges from a few hundred to a few thousand megacycles, transit time effects may limit the efiectiveness of control grids. One ifiiculty encountered is that the currents induced in the grid by the electrons approaching it from the cathode and by electrons moving away from the grid to the anode do not cancel each other when the transit angle is substantial. Since this condition may limit the power gain of the discharge device due to power loading of the grid circuit, it is desirable to achieve grid current cancellation in devices whose operating frequency and necessary electrode spacing results in substantial electron transit time.

it is, therefore, an object of the invention to provide means for reducing the power loading of the control grid circuit of a high frequency discharge device.

it is another object of the invention to provide an improved high frequency discharge device in which the net induced grid currrent is zero.

It is a further object of the invention to provide control grid means for density modulating an electron stream at high frequencies which is not adversely affected by the electron transit time.

In accordance with my invention, a discharge device is incorporated in a concentric line input resonator, the electron discharge path being transverse to the lengthwise axis of the resonator. The control grid, which may be described as a tunnel, is an opening extending through the inner conductor of the resonator having its entrance and exit ends respectively facing the cathode and an electron permeable anode positioned on or near diametrically opposite regions on the outer conductor of the resonator. Since the transit time or transit angle for electrons in the grid-cathode space and the grid-anode space are relatively large in the desired high frequency operating range, the tunnel-type grid is also made rela tively long, so that the transit angle therethrough approaches Z'rr radians or a multiple thereof. This transit angle is preferably measured between midpoints of the cathode-grid and grid-anode gaps. Accordingly, electrons entering the tunnel grid do not emerge until almost one cycle (or an integral number of cycles) later, at which time the grid current induced by the electrons leaving the tunnel will cancel that induced by the electrons then entering the tunnel since the electric fields in the cathode-grid and grid-anode regions of the concentric conductor resonator are radially directed in opposite directions at any instant or at corresponding cyclical points. Of course, during the electron transit through the tunnel grid, the electrons within the grid are shielded from the alternating electric field by the tunnel walls. The electron stream thus modulated passes the permeable anode in the resonator Wall and is employed to excite an output resonator or other means responsive to the space charge modulation.

The features of the invention desired to be protected of oscillation employed.

are set forth in the appended claims. The invention itself, together with further objects and advantages thereof may best be understood by reference to the following specification taken in connection with the accompanying drawing, in which the single figure is a cross-section view of an electron discharge device amplifier embodying the invention.

Referring now to the drawing, an amplifier 1 is shown in which a concentric conductor input resonator 2 is modified so as to incorporate an electron discharge device therein. An output resonator 3 is arranged to be excited by the modulated electron discharge from the input resonator 2. As may be seen from the drawing, the input resonator 2 has a hollow outer conductor 4 and a hollow inner conductor 5. The resonator 2 is here designed as a foreshortened quarter wave resonator, the conductors 4 and 5 each being closed at one end and spaced from each other while at the other end an annular slidable plunger 6 having contact fingers connects the inner and outer conductors. An annular closure member 7 is suitably fastened, as by soldering, between the conductors 4 and 5 at a point beyond the position of the plunger 6 in order to support the inner conductor. Actuating rods 8, one of which is shown in Fig. 1, are fastened to the plunger or slider 6 and extend through the annular end closure 7 to provide external means for positioning the tuning slider and thus adjusting the frequency of the resonator to that of the signal source. The resonator is excited from a source of signals to be amplified, the input coupling means suitably taking the form of a concentric conductor coupling section 9 having its outer conductor attached to the tuning plunger and the inner conductor extending through an aperture in the plunger to form an inductive coupling loop within the resonator cavity.

To provide the electron stream which is to be density modulated by the wave energy of the input resonator 2, a cathode It) is positioned in the outer wall 4 of the resonator at a point along the axis of the resonator where the standing wave voltage is substantial for the mode in the embodiment shown the cathode it is spaced a substantial distance from the shortcircuited end closed by the tuning plunger 6. The cathode suitably comprises a tubular nickel eyelet having a closed end facing the inner conductor 5, the eyelet being insulatingly sealed and supported from the outer resonator wall 4 by a glass sealing ring 11. A capacitor 12 be tween the cathode and outer conductor bypasses high frequency energy while maintaining direct current insulation. A heater 13 within the eyelet is arranged to heat the cathode surface to the required temperature for the desired thermionic emission, the heater terminals extending from the external end of the cathode eyelet and insulatingly sealed therethrough. Diametrically opposite the cathode is an electron permeable anode 14, which corresponds to a conventional screen grid, incorporated in the resonator wall 4. The anode14 is shown as constituting a wire mesh placed over an aperture in the outer conductor 4, although the conductor itself may be provided with apertures of suitable size and number to define an electrode which permits a substantial part of the electrons to pass therethrough.

In accordance with my invention,' a tunnel 15 through the inner resonator conductor 5 defines a path for the electrons traveling from the cathode to the anode 14 which is free of alternating fields. While in some cases the grid may be suitably defined only by the openings in either a hollow or a solid inner conductor, it is generally desirable to provide a tunnel grid having a sufiicient length to accommodate the desired electrode spacings without redesign of the inner conductorof the concentric line resonator. The tunnel is accordingly'prefera'bly defined by a section of cylindrical tubing which extends through the inner conductor 5, at right angles thereto, and is provided at either. end with a wire mesh or other apertures for current and velocity control of the electron stream. Accordingly, a first grid eyelet 16 having a wire mesh on oneend is positioned at the cathode end of the tunnel cylinder 15 and insulated for direct current potentials by means of a thin mica spacer 17. A conductor 18 is connected to the control grid and is brought out for external connection through the center of the inner conductor of the resonator. Another grid cylinder 19 is provided at the other end of the tunnel and may be suitably conductively secured thereto. The direct current potential of the grid 19 may thus be varied with respect to that of the control grid 15.

In operation, a source of heater voltage, which suitably be a battery 20, is connected to the heater 13, and a grid bias voltage, suitably supplied from a battery 21, is connected between the cathode and the control grid 16. The anode 14 is placed at a positive potential with respect to the cathode by a battery 22 connected therebetween. Since the grid 19 is at the same direct voltage potential as the anode 14, linear acceleration of electrons within the tunnel grid is provided by a potential representing the total voltage of sources 21 and 22 which is applied between the accelerating grid 19 and the control grid 16. The electron stream which passes through the electron permeable anode 14 is thus density modulated by the input signal in the cathode-grid gap of the input resonator 2.

Energy is extracted from the modulated electron stream by the output resonator 3, which suitably comprises a quarter wave section of concentric conductor transmission line axially aligned with the space charge path. Its inner conductor 23 has a planar end portion facing the anode 14 and spaced therefrom to define an excitation gap. The corresponding end of the outer conductor 24 is conductively coupled to the input resonator 2, preferably by an inner flange portion 25 thereof hermetically secured to the area of the conductor 4 around the anode 14. An annular slidable plunger 26, corresponding to the plunger 6 of the input resonator, connects the inner and outer conductors and a closure disk 7 is secured between the ends of the inner and outer conductors 23 and 24. Actuator rod 28 is employed to adjust the position of the plunger or slider and thus tune the output resonator to the operating frequency.

Electrons passing through the anode 14 are collected on the end of the inner conductor 23 which serves as an anode or collector member, this member having a positive potential with respect to the cathode due to the conductive connection of the input and output resonators. The density modulation of the electron stream excites the output resonator 3 to provide a tanding wave therein having an amplitude varying in accordance with the amplitude supplied to the input resonator. The amplified output energy is coupled to the desired load by an output coupling means which may suitably take the form of a concentric conductor coupling section 29 having its outer conductor connected to the tuning plunger 26 and its inner conductor extending through an aperture in the plunger to form an inductive coupling loop within the resonator cavity. Other means of utilizing the electron current or extracting energy from the modulated stream may be substituted without departing from the spirit of my invention.

Since the discharge device must operate in vacuum, a suitable vacuum envelope is provided. By utilizing the external. conductors of the input and output resonators as parts. of the envelope, the evacuated enclosure may be simply formed by providing annular ring seals 30 and 31 of glass or other insulating material respectively positioned betweenintermediate portions of the conductors .5 and .4 and. between conductors 23 and 24.

Since the input resonator is very readily excited in its principal mode, the amplifier can be readily operated without critical adjustments. However, the transit time effects due to the width of the cathode-grid or cathodeanode gaps may be substantial where the gaps are physically large and the electron transit time is an appreciable fraction of the alternating current period. According to my invention, the transit time through the grid tunnel in the inner conductor of the resonator is itself employed to counteract these effects and thus permit operation at higher power levels (because of the larger structure permitted) or higher frequencies than otherwise available. lt may readily be seen that even if the grid were of negligible length or thickness, the transit times due to the intra-electrode spacings would still cause loading of the grid circuit. During their transit from cathode to anode, the electrons induce a current in the grid circuit in one direction while they move between cathode and grid and in the opposite sense while moving between grid and anode. Thus the total grid current is made up of two currents corresponding to the influence of electrons in these two regions. When the electron transit time is very small compared to the period of the alternating signal voltage these two currents are of equal magnitude and opposite phase. Their sum is zero and the electron loading is therefore zero. In all practical tubes operating at high frequency this transit angle is not small and the phase of the two currents is not opposed. Therefore, the induced currents generally do not cancel and there is a net current flow with consequent power loss in the input circuit.

This loss or loading is avoided according to my invention by arranging the transit time of the electrons through the tunnel grid 15 so that electrons traveling between the cathode and grid travel between the grid and anode during the same portion of a subsequent cycle of the operating frequency. The cycle-to-cycle electric field variations are, of course, generally negligible as compared to the field variations during any one cycle. This desired condition is substantially realized by making the transit angle from the mid point of one gap to the mid point of another gap equal to Zn radians (one cycle) at the operating frequency or an integral multiple of the radians. Since the transit angle of the gaps may be a relatively small part of 21:- radians while still being sufficient to adversely affect the operation of a conventional discharge device, the electrical length of the tunnel grid itself may be seen to approach 21r radians or a multiple thereof. The electrical length of the tunnel is preferably at least half the electron path length. Of course, electrons while within the tunnel grid do not induce grid currents or are they affected by the alternating fields, and hence they are in eflfect merely held for one or more cycles to be released at a time when they may cancel the transit time effects incurred before entering the tunnel grid. It should be realized, of course, that in the concentric conductor type resonator the alternating electric fields are radial and hence are oppositely directed in the two gaps of the input resonator at any given instant of time.

In order to control the transit time or transit angle within the grid without changing the mechanical dimensions of the tunnel, the bias voltage from the source 21 is adjusted to either add or subtract from the voltage from the source 22. This controls the linear static electric field directed from the grid 19 to the grid 16 at the opposite end of the tunnel.

While a specific embodiment of my invention has been shown and described, it will, of course, be understood that various modifications may be made without depare ing from the principles of the invention. The appended claims are therefore intended to cover'any such modifications within the true spirit and scope of the invention.

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

1. A concentric cavity resonator having an inner and outer conductor, an electron discharge device comprising an electron emitting cathode at the inner surface of the outer conductor, an electron permeable anode at the outer conductor at a point diametrically opposite said cathode, and a control grid comprising a portion of the inner conductor having a transverse aperture therethrough aligned with said anode and said cathode.

2. An electron discharge device comprising a cathode, a control grid electrode, and an electron permeable anode aligned in that order along a discharge path, means coupling said cathode and anode in parallel for high frequencies, means for providing a high frequency signal voltage between said grid and said coupled cathode and anode to modulate an electron beam between said cathode and said anode, and an output means coupled to and positioned beyond said electron permeable anode for producing an output signal responsive to the modulation of said electron beam, said grid comprising a shielded chamber having a length along said discharge path which is a substantial portion of said path length.

3. An electron discharge device comprising a cathode, a control grid electrode, and an electron permeable anode aligned in that order along a discharge path and defining a cathode-grid gap and a grid-anode gap, means coupling said cathode and anode in parallel for high frequencies, means for providing a high frequency signal voltage between said grid and said coupled cathode and anode to modulate an electron stream between said cathode and said anode, and an output means coupled to and positioned beyond said electron permeable anode for producing an output signal responsive to the modulation of said electron stream, said grid comprising a shielded chamber having a length along said discharge path which is a substantial portion of said path length, the transit angle for electrons of said electron stream between the mid-points of the cathode-grid gap and the grid anode gap being an integral multiple of two pi radians.

4. A high frequency amplifier comprising an input resonator, having an inner conductor and a hollow outer conductor concentric therewith, an electron discharge device comprising a cathode electrode and an electron permeable anode electrode positioned at diametrically opposite regions on said outer conductor, said inner conductor being apertured to provide a control electrode tunnel extending at least half the length of the electron discharge path between said cathode and said anode, means for coupling said input resonator to a source of signals to be amplified whereby high frequency oppositely directed radial electric fields are provided between said grid and cathode and between said grid and anode, and an output resonator coupled to said input resonator and adapted to be excited by the electron discharge passing through said anode.

5. A high frequency amplifier comprising an input resonator, having an inner conductor and a hollow outer conductor concentric therewith, an electron discharge device comprising a cathode electrode and an electron permeable anode electrode positioned at diametrically opposite regions on said outer conductor, said inner conductor being apertured to provide a control electrode tunnel extending at least half the length of the electron discharge path between said cathode and said anode and defining interelectrode gaps, means for coupling said input resonator to a source of signals to be amplified whereby high frequency oppositely directed radial electric fields are provided between said grid and cathode and between said grid and anode, and an output resonator coupled to said input resonator and adapted to be excited by the electron discharge passing through said anode, the electron transit time between the mid-points of the interelectrode gaps being an integral number of cycles at said high frequency.

6. An electron discharge device comprising a cathode, a control grid structure, and an electron permeable anode aligned in that order along a discharge path, means coupling said cathode and anode in parallel for high frequencies, means for providing a high frequency signal voltage between said grid and said coupled cathode and anode to modulate an electron beam between said cathode and said anode, an output means coupled to and positioned beyond said electron permeable anode for producing an output signal responsive to the modulation of said electron beam, said control grid structure comprising a shielded chamber having a length along said discharge path which is a substantial portion of said path length, and a source of potential coupled to said control grid structure to cause the transit angle for electrons of said electron beam between the mid-points of said cathodegrid gap and the grid anode gap to be an integral multiple of two pi radians.

7. A high frequency amplifier comprising an input resonator, having an inner conductor and a hollow outer conductor concentric therewith, an electron discharge device comprising a cathode electrode and an electron permeable anode electrode positioned at diametrically opposite regions on said outer conductor, said inner conductor being apertured to provide a control electrode tunnel extending at least half the length of the electron discharge path between said cathode and said anode and defining interelectrode gaps, means for coupling said input resonator to a source of signals to be amplified whereby high frequency oppositely directed radial electric fields are provided between said grid and cathode and between said grid and anode, an output resonator coupled to said input resonator and adapted to be excited by an electron discharge passing through said anode, and a source of potential coupled to said control electrode tunnel to cause the electron transit time between the mid-points of the inter-electrode gaps to be an integral number of cycles at said high frequency.

References Cited in the file of this patent UNITED STATES PATENTS 2,383,343 Ryan Aug. 21, 1945 2,423,327 Lafferty July 1, 1947 2,662,937 Horvath Dec. 15, 1953

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