US2688107A

US2688107A - Electron beam device

Info

Publication number: US2688107A
Application number: US140530A
Authority: US
Inventors: Winfield W Salisbury
Original assignee: Collins Radio Co
Current assignee: Collins Radio Co
Priority date: 1950-01-25
Filing date: 1950-01-25
Publication date: 1954-08-31
Anticipated expiration: 1971-08-31

Description

1954 w. w. SALISBURY ELECTRON BEAM DEVICE Filed Jan. 25, 1950 INVENTOR.

.W/NF/fLD Win/55am I A rromve v Patented Aug. 31, 1954 ELECTRON BEAM DEVICE Winfield W. Salisbury, Cedar Rapids, Iowa, as-

signor to Collins Radio Company, Cedar Rapids, Iowa, a corporation of Iowa Application January 25, 1950, Serial No. 140,530

2 Claims. 1

This invention relates in general to electronic devices and in particular to extremely high frequency electronic apparatus.

It is an object of this invention to modulate an electron beam at very high frequencies as, for example, between 25,000 to 500,000,000 megacycles, and this frequency range will be referred to as the extremely-high range in this specification.

To produce standing waves by optical means and thus transfer energy between electro-magnetic waves and an electron beam is an object of this invention.

Another object of this invention is to provide an electronic device which will amplify signals in the extremely-high frequency range. Yet another object of this invention is to provide a mixer which will mix together two signals which are in the extremely-high frequency range.

A feature of this invention is found in the provision of an electron gun which passes a beam of electrons through a pair of tunable modulating members. When used as an amplifier, the first modulating member is placed closely adjacent to an external modulating signal source. A signal from the source impinges upon the first modulating member to set up a standing wave pattern therein. The electron beam passing through the first modulating member is modulated in response to the modulating signal before passing out into a drift space. A second modulating member is tuned to substantially the same frequency as the modulating signal, and as the bunched electron beam passes there-through, the

modulation is amplified and energy is removed from the beam. The output has substantially the same frequency as the modulating signal but is greatly amplified.

Another feature of this invention is the provision for mixing extremely-high frequencies between 25,000 megacycles to 500,000,000 megacycles. An electron beam once more passes a beam of electrons through two modulating members which are tuned respectively by means of a standing wave pattern to the frequencies that it is desired to mix. A drift space is provided between the modulating members and the output from the second modulator contains the mixed signal.

Further objects, features, and advantages will become apparent from the following description and claims, when read in the light of the drawings, in which:

Figure l is a schematic view of this invention when operating as an amplifier, and

Figure 2 is a schematic view of the apparatus of this invention when operating as a mixer.

Referring to Figure 1, an electron gun produces a steady beam of electrons, in a wellknown manner. The velocity of the electrons from the electron gun varies as the accelerating voltage. Thus for a particular accelerating voltage there will be an associated velocity. This average velocity of the electrons will be referred to herein as the electron velocity.

The phase velocity of waves in an electron beam is defined by the equation:

( c I 1 i w2 Eo where w is equal to the angular frequency, n is equal to the number of electrons per cubic centimeter, e is equal to the voltage of the electrons, E0 is equal to the dielectric constant of the medium through which the beam is passing, m is equal to the mass of the electron, and c is the speed of light.

Adjacent the electron gun is a first modulating means, designated generally as H. The modulating member ll comprises a pair of reflecting members l2 and IS. The members 12 and I3 may be moved relative to each other to vary the angle between them. This may be accomplished by pivoting the member l3 with the shaft l4 and connecting the threaded screw l5 to the member l3. The member I2 may be a diffraction grating. As is well known to those skilled in the art, a diffraction grating may be constructed by placing a multiplicity of spaced lines on a glass sheet. The number of lines per unit length and the width of each line should be chosen in accordance with the desired range of the output radiation frequency. For example, 10,000 lines per centimeter may be used to give an interlined spacing of .001 millimeter. The member [3 should have a highly reflecting surface and may be a mirror. As the reflector I3 is rotated about the axis I4, a standing wave pattern will be set up between the grating and. reflector and the frequency depends upon the angle between them. The reflector picks up one wave-length from the diffraction grating and reinforces it to obtain a standing wave pattern between the grating and reflector. This is true even through there be no auxiliary exciting source 22, in that all bodies above a temperature of absolute zero radiate energy. This radiant energy will be sufiicient to set up standing waves. An excitation source 22, which might be, for example, a tungsten filament heated to a light emission temperature, is placed so as to throw energy upon the reflecting surface [3. If any of the energy given off by the source 22 is at the resonant frequency of the members 12 and [3, then the standing wave pattern between these members will be reinforced and as the intensity of the energy at the resonant frequency from the member 22 is varied, the amplitude of the standing wave pattern between the members 12 and I3 will be varied.

It is to be understood, of course, that the members l2 and I3 are resonant at only one frequency, depending upon the angle between them and the interlined spacing on the diffraction grating. The source 22 might provide a monochromatic radiation which has a frequency equal to the resonant frequency of the members 12 and 13. However, radiation over a relatively broad band will not prevent operation of the device in that only the resonant frequency from the excitation source 22 will cause amplification of the standing waves between [2 and it. Thus, there is provided means for varying the amplitude of the standing wave pattern between the members [2 and I3. The electron beam from the gun Ill passing between the members l2 and i3 interacts with the electromagnetic waves produced by the grating and, as a result, the beam of electrons tend to group or bunch. If the angle between the members l2 and I3 is designated as on the phase velocity of the standing Wave between them will be defined as:

cos a and the group velocity will be defined as:

where c is equal to the velocity of light and w is defined above. It is to be noted that the phase velocity multiplied by the group velocity is equal to the speed of light squared.

1) (phase) 22 (group) :0 cos 0:

When the electron velocity is slightly greater than the group velocity of the electronic medium, and the phase velocity of the medium and the phase velocity of the modulating member match, amplification will occur. Stated otherwise, if the voltage of the electron beam is such that the electron velocity is greater than the group velocity, and the modulating member is tuned to a frequency having a phase velocity in the modulating member equal to the phase velocity of the electron beam, amplification will occur.

Referring once again to Figure 1, a second modulating member, designated generally as i6, is placed longitudinally from the first modulator and the electron gun It. A drift space is provided between the modulating means H and [6. The second modulating member comprises the members I! and I8 which are angularly movable relative to each other to allow tuning. The member ll comprises a diffraction grating with the same physical characteristics as the diffraction grating I2, and the member [8 comprises a reflecting surface. Thus, a standing wave pattern will be set up between the members H and I8 whose frequency depends upon the angle a between them. The member H3 is pivotally supported by shaft l9 and screw 20 adjusts its position. A collector plate 2| is placed adjacent the v (phase) 1; (group): X0 cos (2 0 end of the modulator I6 and collects the electrons after they have passed through the second modulating means. If an input signal is furnished to the first modulating means II from a modulation source 22 in such a manner that a standing wave pattern will be set up in the first modulating means, the electron beam passing through the first modulating member will be bunched in the drift space in response to the input signal. It is to be understood, of course, that this first modulating member is tuned to substantially the same frequency as the incoming modulating signal. The modulating signal may be a monochromatic light source. Message modulations of variable intensity or a frequency or phase variation may be used.

It is to be realized, of course, that the apparatus of this invention is enclosed in a suitable envelope 2t which might be made of glass, for example. Support members 25 extend from the envelope and support the electron gun It. Stand-offs 26 and 3|, respectively, support the members 12 and H, and stand-

offs

21 and 30, respectively, rotatably support the members l3 and i8. Stand-

offs

28 and 29 support the

screws

15 and 20. The modulation source 22 and the resonator 23 are pivotally supported by stand-cits 32 and 33, respectively.

Likewise, the modulating means I6 is tuned substantially to the modulating signal. The electron beam passing through the first modulating member I l interacts with the standing wave pattern caused by the modulating source 22. This causes the electron beam to bunch in the space between the modulating members II and Hi. When the beam passes through the member IS, the modulated beam causes a standing wave pattern to be set up. The output is removed by coupling energy therefrom as, for example, by reflecting energy from the member It to a resonator 23. The output removed will be at the same frequency as the modulating signal, but will be substantially amplified. Thus it becomes possible to modulate and amplify extremely-high frequency signals. This may prove of great value in detecting extremely-high frequency radiations for astronomical work, for example. Another possible use of such a device is for amplifying infra-red radiations so that they may be easily and accurately detected. Frequencies which have heretofore been unavailable to electronic engineers may thus be made available by the apparatus of this invention.

Figure 2 illustrates the manner in which the modulating means I l and l 6 in combination with a gun It! may be used as a mixer.

Once again the electron beam is produced by the electron gun and passes through the modulators II and IS. The modulators and their standing wave patterns are tuned, respectively, to frequencies which it is desired to mix, as, for example f1 and f2. Frequencies f1 and are selected by varying the angle a of the respective modulators. The output removed will contain the frequencies f1 and f2 and the various side bands. When the electron beam passes through the modulating member H, the resonant frequency of the member will be excited to set up a standing wave pattern which will interact with the electron beam. The electrons of the beam will be bunched in response to this standing wave before passing into the second modulating member [6. Standing waves will be set up in member l6 and the electron beam will emerge with frequencies of f1, f2, fl-fz and n+1: superimposed on it. The member 23 will be placed so as to intercept energy from the reflector 18. If the response of the member 23 is such that it is energized by only one of the mixed signals then its output will contain only the particular mixed component. For example, assume that ii in the above example is equal to 100,000,000 megacycles and I2 is equal to 50,000,000 megacycles. If the member 23 is responsive to 150,000,000 megacycles only, this frequency will appear in the output of member 23. It is to be understood, of course, that suitable filters may be used to filter out the undesired frequencies. For example, if the apparatus is. operating in the visible spectrum, filters of colored glass may be used to remove undesired frequencies.

It is seen, therefore, that this invention provides a device for amplifying and mixing signals in the extremely high frequency range. Many applications of this invention may be imagined and foreseen Although this invention has been described with respect to a preferred embodiment thereof, it is not to be so limited since changes and modifications may be made therein which are Within the full intended scope of the invention as defined by the appended claims.

I claim:

1. Extremely high frequency energy producing means comprising, an electron gun for producing a beam of electrons, a first modulating means mounted in the path of the electron beam so that it passes therethrough, said first modulating means comprising a first pivotally supported reflecting surface and a diffraction grating, a second modulating means with the electron beam passing therethrough, said second modulating means comprising a diffraction grating and a refleeting surface pivotally supported so as to be angularly adjusted relative to the diffraction grating, a collector plate for intercepting said;

electron beam, a modulation source mounted adjacent the first modulating means and furnishing energy to the first modulating means, a resonator mounted adjacent the second modulating means and positioned so as to intercept energy from the reflecting surface of the second modulating means.

2. An extremely high frequency electron modulating means comprising, an envelope, an electron gun supported at one end of said envelope for producing a beam of electrons, a collector plate mounted to the opposite end of said envelope and intercepting said beam of electrons, first and second modulating means supported by said envelope with the electron beam passing therethrough, said modulating means comprising, respectively, a diffraction grating, and a reflection means pivotally supported by the envelope, said diffraction grating and reflecting means mounted on opposite sides of the electron beam and tunable by varying the relative angle therebetween, a modulation source adjacent the first modulating means for supplying energy to the reflecting means so as to excite the first modulation source with a standing wave pattern, and a resonator mounted adjacent the second modulating means and positioned so as to receive energy from the reflecting means of said second modulating means.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,280,824 Hansen et a1. Apr. 28, 1942 2 ,281,717 Samuel May 5, 1942 2,362,209 Litton Nov. '7, 1944 2,425,748 Llewellyn Aug. 19, 1947 2,444,434 Feenberg July 6, 1948 2,484,643 Peterson Oct. 11, 1949 2,608,669 Hurvitz Aug. 26, 1952