US2419895A - Ultra high frequency deflection modulated tube - Google Patents

Description

April 29, 1947.

E. J. HEFELE UHF DEFLECTION MODULATED TUBE Filed May 16, 1945 INVENTOR. EDWARD J. HEFELE A'T TORNEVS v Patented Apr. 29, 1947 ULTRA HIGH FREQUENCY DEFLECTION MODULATED TUBE Edward J. Hefele, Bronx, N. Y- assignor to Bruno Patents, Inc., Long Island City, N. Y., a combration of New York Application May 16, 1945, Serial No. 594,086

This invention relates to. means for generating, multiplying or amplifying ultra-high frequency signals and at the same time providing means for radiating into space as electrc-magnetic waves the signals so generated, amplified or multiplied.

Since the advent of ultra short or microwaves into radio and radar technique, it has been found that conventional vacuum tubes are not. a satisfactory means for generating or amplifying such short wave or high frequency signals. In the present day microwave techniques, frequencies of the order of ten billion cycles per second are common. This means that an electrical impulse reverses itself completely in one ten billionth of a second. This extremely short interval of time is a good deal smaller than the time required for the flight of an electron from the cathode to the anode of a vacuum tube.

In the use of vacuum tubes at conventional radio frequencies, the time of flight of the electron, called the transit time, is always much smaller than the time required for the electrical impulse to reverse, 1. e., which latter time is simply the numerical reciprocal of the frequency. Since this, relationship is no'longer true in the microwave technique, efiects called transit time eifects come into play which render nearly inoperative the ordinary vacuum tube. failure, new types of tubes are applied in this domain. Such new types are the magnetron and Klystron. In both these latter types of tubes, a scheme of modulation known as velocity modulation is used. This is in contradistinction to the density modulation used in the ordinary vacuum tube.

In the conventional tube there is interposed between cathode and the anode one or more open mesh structures known as grids. When signal voltages are applied upon the first grid, these voltages influence the density of the electron beam proceeding from the cathode, and hence control the beam current or beam density incident upon the anode. This type of modulation fails when the time of transit of an electron from the cathode to the grid is comparable with the time required for the electrical impulse to reverse, i. e., with the period of reciprocal frequency.

In the Klystron other means are used for modulating the beam. In this latter case an electron beam originating from a cathode passes through two closely spaced grids, through a'fre'e space region of some extent known as the drift space, and subsequently through a second pair of closely spaced grids. The first pair of grids is known as As a result of this.

4 Claims. (Cl. 315-3) the buncher and the second pair is known as the catcher. The beam of electrons proceeding from the cathode is unmodulat'ed, that is, it is purely a direct current beam. The incoming signal to be amplified or multiplied is applied between the grids of the first pair. Since the voltage of the incoming signal is in general much smaller than the velocity voltage of the electron beam, the beam is not brought to a stop at any time by this voltage. It does not, therefore, change the electron density in the beam since no electron is turned back in its flight. It does. however, change the velocity of the beam so that the, electron passing the buncher. pair of grids has a velocity which varies with time throughout the signal cycle;

Since these electrons leaving the buncher have velocities. which vary in time, this procedure of modulation is known as velocity modulation. As the electron beam drifts through the empty space between the buncher and catcher, the faster electrons overtake the slower ones and bythi's process non-uniformities in the electron density are created so that. at the. time the beam reaches the buncher ithas transformed its original velocity modulation int-o density modulation;

An equivalent of this phenomenon. is visible in every-day life in the case, fori'n'stance; of racing cars on a narrow road. The racing cars cross the starting line' in' a long'lin'e at equal can accomplishsimilar. effects. and at thesame time escape the limitations of' transit time. In the techniqueof radio and. radar utilized at the present time, the. antennae: from which the signals are eventually radiated are'alwaysseparated from the electronic density in which thesignals are generated. In the present invention the-radiiating antenna is made an integralpart of' the genera-ting; amplifying or multiplying tube.

Accordingly object of my inventionis to provide a novel oscillation for ultra igh irequencies.

A further object of my invention isto provide 3 a novel cathode ray tube ultra high frequency oscillation.

Still another object of my invention is to provide novel oscillation in which radiation is an integral part of the oscillation.

The details of the invention will become clearer with a perusal of the attached drawings in which:

Figure l is one version of the invention in which amplification 01' multiplication are involved; and

Figure 2 is another version of the invention in which the generation of self-sustained oscillations is involved.

In Figure 1 an electron gun l of the conventional type used in cathode ray tubes or in Klystrons is located within an evacuated space 2 surrounded by a glass envelope 3. From electron gun I there proceeds an electron beam 4 which passes between a pair of vertical deflecting plates 5. The deflected beam 6 then passes through hole 1 in a paraboloid metallic reflector 8 and impinges upon a vertical wire 9. This vertical wire 9 has a carefully chosen length and becomes the actual radiating antenna of the system.

To the center of wire 9 subsequently called the doublet is attached a lead wire l which passes through a vacuum seal H to a positive source of D. C. voltage. A lead wire 12 also connects metallic paraboloidal reflector 8 with a positive source of D. C. voltage through vacuum seal I3. The cathode of electron, gun I is also connected by wire l4 through vacuum seal l to a negative source of direct current potential.

If now the direct current circuits of Figure 1 are energized, the electron beam would normally pass through the tube axially and impinge upon the center of doublet 9. If, however, voltages were impressed between the pair of deflector plates 5, the beam would be deflected either up ward or downward and strike doublet 9 in some position other than its central point, or might miss doublet 9 entirely.

In Figure 1 deflector plates 5 are shown connected through radio frequency transformer IE to an oscillator I1. If this oscillator delivers a radio frequency signal at some high frequency 1, the resulting voltages of that frequency appear.. ing upon deflector plates 5 will deflect the electron beam vertically with that frequency. Since the beam sprays electrons on. to doublet 9 at various locations, the charges will therefore flow on doublet 9. Since any straight piece of wire has certain natural frequencies of oscillation, doublet 9 will tend to oscillate at its own natural frequencies. p

As is well known, the natural frequencies of a straight piece of wire are such that the associated wave lengths bear a simple relationship to its length L. The lowest of these natural frequencies, the so-called gravest mode or fundamental frequency, is such that the associated wave length is almost exactly twice the length of the wire. Hence if the length of doublet 9 is L, the wave length of its fundamental frequency will be almost exactly 2L. When excited by any means, doublet 9 will tend to oscillate at this frequency. These oscillations at the fundamental frequency will tend to damp themselves and die out unless the exciting stimulus is repetitive, re-exciting the fundamental periodically.

In order to excite this fundamental frequency, it is necessary that components of this frequency be present in the stimulus. This can be accompllshed directly if the frequency ,f of oscillator 11 is precisely this fundamental frequency of di- 4 pole 9. In this case the relationship between the necessary frequency f of oscillator I 1 and the length L of di-pole 9 would be given by the formula where c is the speed of light.

As an example, a length L'of 5 centimeters might be chosen, in which case 2L is 10 centimeters. By' the above formula the frequency f associated therewith is 3 billion, a familiar frequency amongst microwave engineers. In this case, doublet 9 would be excited directly from the frequency of deflection of the electron beam and would therefore oscillate continuously at this frequency. Under these circumstances, doublet 9 is an efficient radiator of electromagnetic waves and would normally radiate in all directions, but most strongly in its equatorial plane. Since it is usually desirable to confine the electromagnetic radiations into a narrow beam, the paraboloidal reflector 8 is used. Doublet 9 is then placed at the mathematical focal point of paraboloid 8.

By the focusing properties of paraboloidal surfaces which are well known in the field of optics, the energy radiated from a source located at the focal point will be reflected from the paraboloidal surface into a parallel beam of crosssection equal to the largest diameter of the paraboloidal reflector. This .beam will have a small divergence angle and hence will concentrate the radiation into a very narrow cone as is desirable for most microwave radio and radar techniques.

Hole I in reflector 8 is necessary to provide access for the electron beam. This hole can be of a relatively small size compared with the extreme diameter of reflector 8 and hence will have a negligible effect upon the ray gathering efliciency of the reflector.

Such a device requires in this first version a source of alternating current of the same frequency as that to be radiated. Hence the dimculties of generating these frequencies has been laid upon the oscillator II. It is, however, not necessary that oscillator II should deliver a frequency equal to the frequency which it is desired to radiate, namely that frequency which is related to the length L of doublet 9 by the formula given previously. It will suflice if the oscillator ll delivers a frequency which is some sub-multiple of the desired frequency. In this latter case, the invention as shown in Figure 1 would be functioning as a frequency multiplication rather than merely as an amplifier as in the first-described version.

In order that doublet 9 may be excited at its fundamental frequency, even though the fre-- quency of deflection of the electron beam is at a lower sub-multiple frequency, it is necessary to take measures to ensure that the stimulus 1m pressed upon doublet 9 will contain components of its fundamental frequency. This can be accomplished by utilizing the phenomenon of distortion. V As is well known amongst electrical engineers, when a sinusoidal wave of a certain frequency is distorted into some non-sinusoidal shape, it is thereby caused to contain harmonics of the fundamental frequency, namely 'to contain frequency components which are multiples of the fundamentalfrequency. In the present inven tion, distortion can readily be achieved by causing the electron beam tosweep past the ends of doublet 9. As a result of this, current would be impressed onto doublet 9 only over part of a cycle of the frequency of a deflection modulation of the electron beam, and therefore the impressed current upon doublet e would become highly nonsinusoidal.

As a result thereof, this impressed stimulus would contain frequencies which were multiples of the deflection frequency of the beam. Using a doublet f the same size as in the previous .eX- ample, suppose that he frequency f of oscillator if were not 3 billion cycles, but rather /3 of a. billion cycles, i. e., 333 megacycles. Such a frequency is somewhat below the highest which can be obtained by the use of conventional vacuum tubes and can hence be generated in a more or less conventional manner by oscillator ii.

If this frequency were now impressed upon dehector plates in such amplitude as to sweep completely be 'id the ends of doublets, the impressed stimi us into doublet (9 would contain amongst others a frequency nine times as great as the deflection frequency of the beam, i. e., it would contain a ninth harmonic. Since nine times this del ection frequency is precisely 3 bil lion cycles, i. e., 3890 megacycles, which is the nat- ..i l fundanw tal frequency of doublet 9, doublet 53 would be continuously excited this frequency and would hence carry out sustained oscillations at 3660 megacycles. the corresponding wave length, 10 centimeters, would therefore be radiated from doublet 5 reflected from paraboloid B and transmitted a narrow cone therefrom.

The version of the invention described in Figure 1 involved amplification or multiplication of impressed frequency, Another ver sion of the invention portrayed in Figure 2 provides for the self-generation of the desired frequencies. Figure 2 is therefore a self-excited 0scillator. Figure 2, 2i is a conventional electron gun emanates an electron beam easses between a pair of deflector plates impinges upon doublet 29. To the center of the doublet is attached a lead wire 3-3 which passes through vacuum seal to a positive source of D. C. potential.

From the cathode of electron gun El passes a lead wire 3% through vacuum seal 35 to a negative source of D. C. potential. To deflector plates 25 are attac ed two short straight pieces of wire equal length and having a carefully chosen length. length of doublet 29 will again be called L and the distance between the extreme ends of the two wires 25 will be call d L. 2%) will be referred to as the radiator, and the two pairs of wires 26 associated deflector plates will be referred to as the excitor. The spacing between the excitor 25, 25 and radiator 29 will be called The fundamental frequency of radiator 29 will again be related to its length by the same formula as given previously. Exciter 26 will itself have a natural frequency. Its natural frequency will now be related to the length L by the same simple formula as C at or radiator 29.

The fundemental frequency of excl-tor 25, 2t will depend not only upon the length L but also upon the spacing and area of deflector plates 25. However, it has a fundamental frequency which can be adjusted by varying the length L.

Electromagnetic waves of Doublet Suppose now that the direct currentcincuit of Figure 2 were energized. It would then be expected that the electron beam would pass axially from electron gun 12.! through deflector plates 25 impinged upon the central pointof radiator 29. Sucha condition will prevail unlesscertainquantitative relationships exist. In case these quailtitative relationships exist, this axial position of the electron beam will'be unstable. To examine into the nature of the conditions, which might cause instability of this position, it is necessary as in all stability questions, to inquire -,int0 the phenomenon subsequent to an arbitrary virtual displacement from equilibriumposition. If name- -ly;the system returnsto its originalposition after an arbitrary virtual displacement, the equilibrium is stable. If not, it is unstable. Suppose, therefore, that seine disturbance deflects the electron beam :Z i from thecentral portion of radiator 29.

In this case radiator 29 would be excited at its fundamental frequency and would emit electromagnetic waves in all directions.

These electromagnetic waves would impinge upon excitor 25, 26 and tend ,to setit into oscillation itself, particularly if the natural frequency of eXcitor 25, 2li were close to the frequency of the incident electromagnetic radiation. The .degree of excitation therefore, of eXcitor:-2,5, ,25 due to the reception of electromagnetic radiationfrom radiator 29 will. depend upon the relationship between the lengths L 'and L. Supposethatthese two lengths have been so adjusted that the two natural frequencies are very near each other. In that case, excitor 25, .25 would itself be set into vibration due to the reception of wavesemanating from radiator 29.

T phase of th vi ra i set up inexcitor 25, 2&3 will depend upon several factors, among which is the distanced betweenthe radiator 29 and , excitor 25, ,26. The ,oscillations set ,up in excitorfifi, .26 by the receipt of radiation from radiator 29 will cause voltages to .exist between the deflector plates .25, which voltages will of themselves tend to deflect electron beam ;2-.4 and therefore to alter the point of impact of electron beam 24 on radiator 29, i. e., to influence the stimulus incident upon radiator 29.

Whether this influence tends to aid or to cancel the original arbitrary virtual stimulus depends upon the phase relationship existing between this secondary and the primary stimulus. This phase relationship depends amongst other things upon the precise natural frequency of the excitor and upon the distance between the excitor and. the radiator d. It is therefore possible to adjust these perimeters so that this phase relationship is such that the secondary stimulus is in the proper direction to aid the primary virtual stimulus.

This entire scheme of creating instability is a novel version of the conventional feedback used in all self-oscillating arrangements. Instability and hence self-sustained oscillations will be created if these perimeters are so adjusted that the feedback is in the proper phase and if in addition the strength of the feedback is sufficient to overcome the dissipation and radiation losses of the system. The strength of this feedback will depend amongst other things upon the intensity of the electron beam 24. If this intensity is sufiicient and if the spacing at is correct, and if the length L of excitor 25, 26 bears the proper relationship to the length of radiator 29, then all the conditions for self-sustained oscillations will be met and the version of the inveninvention therefore is a source of electromagnetic radiation of extremely short wave length wherein radiation is accomplished directly without the necessity for circuits connecting the generator of the electrical oscillations with the antenna which radiates the waves. Both functions are carried out simultaneously by the invention as portrayed in Figure 2.

Referring again to Figure 1, the paraboloidal reflector 8 could at will be replaced by a. reflecting array of parasitic antennae. Such parasitic arrays are now common in short wave techniques.

In both versions of the invention portrayed in Figures 1 and 2, it would be feasible to coat the end of the tube with a fluorescent coating which although functionally unnecessary, would assist in the alignment of the electron beam, since then it would be immediately possible to observe whether the electron beam was incident upon the radiating doublets or not.

This invention therefore utilizes a novel means of modulating an electron beam, namely the means of deflection modulation in contradistinction to density or velocity modulation, and also accomplishes direct radiation of electromagnetic waves without additional circuit arrangements.

Many modifications of the specific forms of my invention will now be obvious to those skilled in the art. Accordingly, I prefer to be bound not by the specific disclosures herein, but only by the appended claims.

I claim:

1. In an oscillator, an electron gun having an relectron beam emitter, means for deflecting said beam, means including the elements of said gun ;for setting up ultra high frequency oscillations,

,-said means comprising a parabolic reflector and electron beam emitter having a source of direct current potential applied thereto, means for deflecting said beam, means including the elements of said gun for setting up ultra high frequency oscillations, said means comprising a reflector and a dipole of predetermined length, and means for applying a positive charge to said reflector.

3. In an oscillator, an electron gun having an electron beam emitter having a source of direct current potential applied thereto, means for deflecting said beam at a predetermined frequency, means including the elements of said gun for setting up ultra high frequency oscillations, said means comprising a reflector and a dipole of predetermined length, and means for applying a positive charge to said reflector, whereby oscillations of the natural frequency of the length of the dipole are generated.

4. In an oscillator, an electron gun having an electron beam emitter having a source of direct current potential applied thereto, means for deflecting said beam at a predetermined frequency, means including the elements of said gun for setting up' ultra high frequency oscillations, said means comprising a reflector and a dipole of predetermined length, and means for applying a positive charge to said reflector, whereby oscillations of the natural frequency of the length of the dipole are generated and radiated.

EDWARD J. HEFELE.

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

UNITED STATES PATENTS Number Name Date 1,969,578 Rice Aug, 7, 1934 2,071,311 Linder Feb. 16, 1937 2,205,475 Hollmann June 25, 1940 2,215,779 Clavier et a1 Sept. 24, 1940 2,291,767 Shore Aug. 4, 1942 2,391,914 McElhannon Jan. 1, 1946

Images