US2350907A - Ultra short wave apparatus - Google Patents

Description

June 6, 1944. F. H. KROGER 2,350,907

ULTRA SHORT WAVE APPARATUS Filed Sept. 22, 1939 s Sheets-Sheet 1 I E i A APPROX. 2 IRON c d f If 1 9 2 71 -z z b L 5 5 4 14 [RON f5 f6 6 wpur FROM 300014 MASTER 0.90. 0/2 PRE-AMPL. -B

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June 6, 1944.

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June 6, 1944. F. H. KROGER 2,350,907

ULTRA SHORT WAVE APPARATUS Filed Sept. 22, 1939 3 Sheets-Sheet 5 ,7 STAGE N0. 3

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?D H. KROGER BY 40 0 0 ATTORNEY.

Patented June 6, 1944 ULTRA SHORT WAVE APPARATUS Fred H. Kroger, Patchogue, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Application September 22, 1939, Serial No. 296,045

13 Claims.

This invention relates to electron discharge device circuits for use particularly with ultra short waves below two meters. The invention is useful in its application to oscillation generators, amplifiers, frequency converters and detectors, although not limited thereto.

One of the objects of the present invention is to provide an improved electro-mechanical construction for an electron discharge device circuit for use with ultra short waves which will satisfy the following requirements: (1) Obtain a minimum of feed-back between output and input circuits, and (2) have the highest possible shunt impedance for the output circuit,

Another object .of the present invention is to provide a convenient mechanical arrangement of vacuum tube and associated tank circuit which permits easy replacement of the vacuum tube envelope and enclosed electrode elements.

A further object is to provide a novel mechanical construction of a vacuum tube structure and associated tank circuit which permits the assem-= bly of a multiplicity of stages which can be naturally coupled together without accessory losses and without the introduction of extraneous feedback. a

A still further object is to provide an improved electron discharge device circuit employing a beam type of vacuum tube and an associated high Q, low loss tank circuit with means external of the vacuum tube structure for tuningthe tank circuit.

In accordance with a preferred embodiment of the present invention there is employed an electron discharge device having within an evacuated envelope a cathode at one end for emitting a stream of electrons and a collector electrode at the other end for gathering the electrons after they have traversed the length of the tube. Surrounding the envelope intermediate its ends there is provided a high Q, low loss tank circuit or cavity resonator in the form of a surface of revolution with the central plane of the surface of revolution cutting the axis of the vacuum tube structure substantially at right angles. In its preferred form, the surface of revolution constituting the tank circuit is a section approximating the sector of a circle with the vertex angle as large as practical and. located adjacent the vacuum tube envelope. Generally speaking, such a structure may be said to be doughnut in form. For focusing the electrons there is provided a pair of magnetic lenses each constituted by a leakage .fleld surrounding the envelope of the vacuum may be changed to a limited extent by means of a non-magnetic sleeve surrounding the envelope of the electron discharge device structure for varying the width of the gap at the center of the surface of revolution. This non-magnetic sleeve serves as a trimmer in varying the'capacity of the gap.

An additional feature lies in the use of an iron magnetic path placed externally of and adjacent to a portion of the surface of revolution for providing the magnetic lens effect.

Other objects and features, and their advantages, will appear from a reading of the following description which is accompanied by drawings, wherein:

Fig. 1 shows, by way of example only, a diagrammatic view, in section, of a preferred form of amplifier circuit embodying the principles oi the invention;

Fig. 2 is a modification of Fig. 1, showing diagrammatically the electron discharge device circuit used as an oscillation generator;

Fig. 3 illustrates a plurality of stages constructed in accordance with the present invention coupled together in a compact assembly; and

Fig. 4 is a view of a modified form of tank circuit, shown in section, which may be used in the circuit arrangements of Figs. 1 and 2.

Referring to Fig. l in more detail, there is shown an electron discharge device amplifier circuit comprising a vacuum tube structure consisting of an evacuated glass envelope l containing within it a cathode 2, a heater 3. a grid a, ring-- like accelerator electrodes 5, a collector electrode 6 and a suppressor l. The heater 3 is supplied with energy from a suitable alternating current source, as shown, through choke coils 3. Connected to the cathode 2 and grid 5 is the input tuning circuit 9 which includes a variable condenser Hi, to which is coupled a radio frequency source of energy i I, which may comprise a master oscillator or the output of a pre-amplifier stage. The collector electrode 5 for gathering the electrons traversing the length of the glass envelope 5 is shown to be cup-shaped in form, although, if desired, it may be hemispherical, conical or of other suitable shape. Centrally located within the interior of the collector 6 there is provided a rod-like suppressor electrode 1 for gathering secondary electrons which may emanate from 5. The suppressor electrode 1 may take any suitable form according to the design of the collector electrode 6.

Surrounding the exterior of the glass envelope tube. The resonant frequency of the tank circuit l and located intermediate the two accelerator electrodes 5 there is provided the high Q, low loss tank-circuit or cavity resonator'l2 in the form of a surface of revolution whose central plane is perpendicular to the electron beam emanating from cathode 2. This tank circuit, it should be noted, is symmetrically arranged around the glass envelope '1. In order to obtain a desired high impedance across the gap 11, b of the tank circuitfor matching the impedance of the vacuum tube structure, and to-obtain the desired high Q circuit, the conflgurationof tank circuit l2, as shown by a cross-section of the surface of revolution through the axis of revolution in the plane of the drawing, should approximate two equal sectors with their vertices toward the glass envelope I.

The dimension of the tank circuit l2 as measured from the center of the glass envelope l toward the arc of the sector, as indicated in the drawing, is approximately one-quarter of the length of the communication wave corresponding to the resonant frequency. In order to vary the resonant frequency of the tank circuit to a limited degree, there is provided a non-magneticsleeve l3, such as brass, threaded for the convenience .of adjustment, as shown, for varying the width of the gap a, b with a consequent variation of the capacity between the sides of the gap. Tank circuit I2 is preferably made of a high electrical conducting material, such as copper. For focusing the electron beam there are provided a. pair of magnetic lenses in series relation constituted by gaps c, .d and e, f formed by spaced iron sleeves l4, l5 and I6 which surround the.

glass envelope I and are serially arranged with respect to an iron magnetic path. The threadsably at a givennegative bias, as shown. The

auxiliary electrodes 5 are maintained at a given positive bias. Where the grid 4 is maintained 7 at a potential sufiiciently negative to prevent the passage of electrons in the absence of radio frequency input in Ii, the initiation of radio ire-- quency input during the positive side of the wave will cause electrons from cathode 2 to pass through the interior of the glass envelope I to the collector electrode 6. The electrons immediately after passing through the apertures of grid 4 will tend to flow toward the interior surface of the first accelerator electrode 5 due to the positive potential on this electrode. In order to prevent the electrons from impinging on this accelerator electrode there is provided a magnetic lens 0, d which, by virtue of the leakage field thereacross, focuses the electrons toward the axis of the vacuum tube. As the electrons approach the gap a, b, there is a tendency toward dispersion, and it is for this reason that the additional magnetic lens e, j is required to maintain the beam in the axis of the tube beyond the second accelerator electrode 5, after which the electrons will be gathered up by the collector electrode 6 which is at a. suitable positive potential. The electrons emanating from cathode 2 will be density modulated at the frequency of the radio frequency input during the positive half cycle (ascut-off as mentioned before), and these groupsof electrons will excite the tank I2 at the group frequency as they pass the gap a, b. These groups of electrons, or pulses, traversing the gap a, b will induce. high frequency currents between the points a, b. If the excitation frequency (group frequency) is the same as the resonant frequency of the tank circuit, a high impedance will exist across the gap 0, b at this frequency, and consequently the induced currents will produce a high radio frequency voltage across the gap. If, however, the negative potential applied to the grid 4 does not normally maintain this electrade at cut-off, then electrons will emanate from 2 and pass between the cathode and the collector electrode 6 when there is no radio frequency input. In this latter case, however, as soon as there is radio frequency input the electron stream will be modulated in density in accordance with the radio frequency input, which modulation of this electron stream will in turn, induce corresponding voltages in the gap a, b. Energy from the tank circuit may be taken off by means of a coupling coil 2| which is inductively coupled to the tank I2 and which transfers the induced energy to a suitable load circuit, such as a transmission line extending to an antenna, or another amplifier stage.

In one embodiment of 1 actually tried out in practice, the radio frequency input was at a frequency of about 474 megacycles (approxi, mately 63 centimeters) and the tank circuit l2 had an overall diameter of approximately ten and one-quarter inches. The potential applied to the accelerator electrodes was about 3000 volts positive relative to the cathode, while the potential applied to the grid 4 was approximately minus 20 volts'relative to the cathode. The collector electrode was maintained at approximately 1000 volts positive relative to the cathde. The suppressor was maintained approximately 50 volts positive relative to the cathode. Under'these conditions, with an output of 10 watts, the average electron stream was approximately 45 milliamperes. At this output level, the input energy was 1 watt, giving a power gain of 10.

One advantage of the electron discharge device circuit of the present invention is that there is obtainable a band width which is much greater than known types of vacuum tube circuits at these high frequencies. For example, with a structure such as I have described, it is easily possible to obtain a band width of 10 megacycles in the output having a variation in response over this range of frequencies of about one and one-half decibels.

Fig. 2 shows the application of the present invention to an oscillation generator. In the main, the construction is substantially identical with that shown in Fig. 1. In order to sustain oscillations, the output coupling coil 2| is here shown suming, of course, that the grid is maintained at coupled back to the tuned input circuit 9 through a feed-back transmission line 23, which line is adjustable in electric-a1 length by means of trombone sliders -24. In one embodiment actually tried out in practice, a lecher wire system 25 was connected to the output coupling coil 2| and one end of the transmission line 23 was slidably connected to this lecher wire system, as shown, while the other end was inductively couplied to the input circuit 9. A slider 26 bridged across the conductors of the lecher wire system 25 functions to tune the output circuit. Since the circuits of Figs. 1 and 2 are identical in all respects other than those hereabove mentioned, the same parts are represented by the same reference numerals.

The oscillator of Fig. 2 has been found in practice to be extremely stable. Such an oscillator has been used successfully to generate oscillations in the range from 450 megacycles to 500 megacycles. of course, that this range of oscillations is not to be construed as a limitation upon the oscillator but merely as an illustration of some of its possibilities.

Fig. 3 illustrates the manner in which several stages of electron discharge device circuits in accordance with the invention may be coupled together in cascade. The configuration of applicants tank circuit or cavity resonator enables It should be distinctly understood,

the several stages to nest into one another, as

shown, in order to provide a highly compact and simplified arrangement which eliminates the necessity of accessory coupling elements between stages and which preserves the simplicity of the individual circuit arrangements. In the circuit of Fig. 3, the first stage is supplied with a suitable radio frequency input circuit while the second stage is coupled to the tank circuit of the first stage by means of the tuned input circuit of the next stage. Similarly, the third stage is coupled to the second stage by means of the tuned input circuit of the third stage. If desired, instead of supplying a suitable radio frequency input to the first stage, this stage may take the form of an oscillation generator such as shown in Fig, 2.

Another advantage of the present invention lies in the fact that the vacuum tube structure is easily replaceable merely by disconnecting the high voltage leads and removing the glass envelope with its enclosed electrodes from the input socket.

The tank circuit of Figs. 1, 2 and 3 has been found to be superior in practice to other forms of tank circuit mainly because of .the higher shunt impedance possible at the gap, which is of prime importance where wide band width is required. Moreover, this particular construction enables the minimization of feed-back between the output and input circuits. Other advantages of this particular tank circuit, such as the convenience of replacing the vacuum tube structures and the enabling of a compact practical assemblage of stages with low feed-back and the absence of accessory losses, have been mentioned above. In the embodiment tried out in practice, the acute angle formed between the inner converging symmetrical surfaces of the tank circuit on the same side of the central plane was approximately 87", as shown in Fig. 1, although it will be appreciated that the invention is not limited to this particular angle.

Fig. 4 shows a modification of the tank circuit which may be used but lacks many of the advantages inherent in the preferred form of tank circuit shown in Figs. 1, 2 and 3.

It should be distinctly understood that the invention is not to be limited to the precise arrangements illustrated in the drawings and described in the specification, since various modifications may be made without departing from the spirit and scope of the invention. For example, although the iron magnetic path has been illustrated as being in the plane of the drawings, in practice it may be preferred that this path be rotated 90 from the position shown in the drawings.

What is claimed is:

1. An electron discharge device circuit including a cavity resonator in the form of a surface of revolution having a gap, a source of electrons for projecting a stream of electrons across said gap, a magnetic lens having a gap registering with the gap of said cavity resonator, and an adjustable non-magnetic sleeve on one side of said resonator gap and surrounding a portion of the path of said stream for varying the effective width of said resonator gap without moving any part of said cavity resonator and without varying the width of the magnetic lens gap.

2. An electron discharge device circuit including a cavity resonator in the form of a surface of revolution having a gap in the center thereof, means for projecting a stream of electrons across said gap at right angles to the central plane of said surface, and an adjustable non-magnetic metallic sleeve on one side of said resonator gap and surrounding the path of said stream for varying the capacity between the sides of said resonator gap with a consequent variation of the resonant frequency of said resonator but without moving any part of the resonator, said sleeve being in contact with said surface of revolution and adjustable in a direction parallel to said stream.

3. An electron discharge device circuit including a cavity resonator in the form of a surface of revolution having a gap in the center thereof, means for projecting a stream of electrons across said gap at right angles to the central plane of said surface, and a pair of spaced magnetic lenses in series relation surrounding the path of said stream for focusing said electrons, each of said lenses having a gap, the gap of one of said pair of lenses substantially registering with the gap in the center of said surface of revolution, and nonmagnetic means adjacent the resonator gap for varying the effective width of said resonator gap without moving any part of said resonator.

4. A cavity resonator in the form of a surface of revolution having an aperture in the center thereof providing a gap, an electron discharge device having within an evacuated envelope a source of electrons near one end and an electron collector near the other end, said envelope being located within said aperture of said resonator with said gap located between said source and said collector and adapted to be traversed by the electrons projected from said source, an accelerator electrode within said envelope located between said source and said gap, and another accelerator electrode within said envelope between said gap and said collector, and means adjacent to and surrounding said envelope for producing a pair of spaced leakage fields in the form of magnetic lenses for focusing the electrons toward said collector, each of said lenses having a gap, the gap of one of said pair of lenses substantially registering with the gap in the center of said surface of revolution, and non-magnetic means adjacent the resonator gap for varying the effective width of said resonator gap without moving any part of said resonator.

5. A cavity resonator in the form of a surface of revolution having an aperture in the center thereof providing a gap, an electron discharge device having within an evacuated envelope a source of electrons near one end and an electron collector near the other end, said envelope being located within said aperture of said resonator with said gap located between said source and said collector and adapted to be traversed by the erator electrode within said envelope located be tween said source and said gap, and means adjacent to and surrounding said envelope for producing a leakage field in the form of a magnetic lens having a gap registering with the resonator gap for focusing the electrons emanating from said source, and adjustable non-magnetic metallic means for varying the effective width of the resonator gap wtihout varying the eifectiveness of said magnetic lens and without moving any part of said resonator.

6. A cavity resonator in the form of a surface of revolution having an aperture in the center thereof providing a gap, an electron discharge device having within an evacuated envelope a source of electrons near one end and an electron collector near the other end, said envelope being located within said aperture of said resonator with said gap located between said source and said collector and adapted to be traversed by the electrons projected from said source, an accelerator electrode within said envelope located between said source and said gap, a non-magnetic sleeve adjacent one side of said gap and surrounding said envelope for varying the width of said gap, and means in the form of a magnetic lens adjacent to and surrounding said envelope for producing a leakage field for focusing the electrons emanating from said source.

7. An electron discharge device circuit including a cavity resonator in the form of a surface of revolution having a gap in the center thereof, means on one side of said gap for projecting a stream of electrons across said gap at right angles to the central plane of said surface, first, second and third spaced magnetic sleeves surrounding the path of said stream of electrons, a closed magnetic path between said first. and third sleeves, and a coil for producing an electric field in said path, wherebythe leakage field between said first and second sleeves and between said "second and third sleeves serves to focus said stream of electrons, and a metallic non-magnetic sleeve for varying the eifective distance across the gap of said resonator circuit without moving any part of said resonator.

8. A multi-stage ultra high radio frequency electron discharge device circuit, each stage having a cavity resonator in the form of a surface of revolution whose central plane is perpendicular to the path of the stream of electrons of that particular stage, said surface of revolution constituting a section approximating the sector of a circle with the vertex angle located adjacent the electron stream, with the central plane of each stage substantially perpendicular to the central plane of the surface of the succeeding stage. 1 v

9. A multi-stage ultra high radio frequency electron discharge device circuit, each stage have ing a cavity resonator in the form of a surface of revolution whose central plane is perpendicular to the path of the stream of electronsof that particular stage. said surface of revolution constituting a section approximatingthe sector of a circle with the vertex angle located adjacent the electron stream, with the central plane of each stage substantially perpendicular to the central planes of the surfaces of the preceding and succeeding stages.

10.-A- cavity resonator having an aperture therein forming a gap, anelectron discharge device having within an evacuated envelope a source of electrons near one end and an electron collector near the other end, said envelope being located within said aperture of said resonator with said gap located between said source and said collector and adapted to be traversed by the electrons projected from'said source, an accelerator electrode within said envelope located between said source and said gap, an adjustable non-magnetic sleeve adjacent one side of said gap and surrounding said envelope for varying the width of said gap, and means in the form of a magnetic lens adjacent to and surrounding said envelope for producing a'leakage field for focusing the electrons. emanating from said source.

11. A multi-stage ultra high radio frequency electron discharge device circuit, each stage having a cathode and a cavity resonator whose central plane is perpendicular to the path of the stream of electrons emanating from the cathode of that particular stage, said resonator constituting in cross-section a pair of oppositely positioned V-shaped segments whose vertex angles are located adjacent the electron stream, with the central plane of each stage substantially perpendicular to the central plane of the cavity resonator of the adjacent stage.

12. A multi-stage ultra high frequency electron discharge device system, each stageof which has a hollow body resonator with re-entrant midportions and an envelope passing through said mid-portions, adjacent stages having th ir resonators at right angles to each other 'th the mid-points of said resonators in a common plane,

. there being means in the envelope of each stage for producing a stream of electrons at right angles to the central axis thereof.

13. An electron discharge device circuit comprising a hollow body resonator with re-entrant midportions, a magnetic lens having elements engaging said re-entrant midportions, non-magneticelectron permeable elements secured to said midportions and movable relative to each other for varying the distance between said midportions with a corresponding variation of the tuning of the resonator but without moving any part of said resonator or any part of said magnetic lens, and means for projecting a stream of electrons through said electron permeable elements and through the interior of said resonator.

FRED H. KROGER.

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