US3023342A

US3023342A - Beam modulating devices and method

Info

Publication number: US3023342A
Application number: US749555A
Authority: US
Inventors: Glenn W Preston
Original assignee: General Atronics Corp
Current assignee: General Atronics Corp
Priority date: 1958-07-18
Filing date: 1958-07-18
Publication date: 1962-02-27
Anticipated expiration: 1979-02-27

Description

G. w. PRESTON 3,023,342

BEAM MODULATING DEVICES AND METHOD Feb. 27, 1962 Filed July 18, 1958 2 Sheets-Sheet 1.

INVENTOR. A G'ZE/V/V w EPA-J70 1962 e. w. PRESTON 3,023,342

BEAM MODULATING DEVICES AND METHOD Filed July 18. 1958 2 Sheets-Sheet 2 JNVENfbR. "f GLW/l 14 Ream/v- BY Wigwam United States Patent C 3,023,342 BEAM MODULATING DEVICES AND METHOD Glenn W. Preston, Oreland, Pa., assignor to General Atronics Corporation, Bala-Cynwyd, Pa., a corporation of Pennsylvania Filed July 18, 1958, Ser. No. 749,555 7 Claims. (Cl. 315-12) The invention relates to particle selecting devices and method, and more particularly devices and method for modulating a beam of electrically charged particles.

Heretofore, beam modulating devices have been provided having the form of an electron gun which have varied the intensity of a beam of electrons. However, such modulation has also varied the point of focus for the electrons and the forms of the devices have tended to reduce the life of their electron emitting cathodes.

It is, therefore, a principal object of the invention to provide a new and improved device and method for controllably selecting charged particles without substantially varying the paths of the unselected particles.

Another object of the invention is to provide a new and improved device and method for modulating a beam of charged particles without substantially affecting their point of focus. i

Another object of the invention is to provide a new and improved beam modulating device and method providing negative spherical aberration of its beam which may compensate for positive spherical aberration of the beam.

Another object of the invention is to provide a new and improved beam modulating device and method requiring low signal power and voltage for modulating the intensity of its beam of electrons.

Another object of the invention is to provide a new and improved device and method for modulating a beam of charged particles which provides optical properties of its beam which are substantially independent of the total beam current.

Another object of the invention is to provide an electron device for modulating a beam of charged particles which has a low input capacitance to its beam modulating control electrode.

Another object of the invention is to provide a new and improved beam modulating device providing uniform cathode loading of its electron gun.

Another object of the invention is to provide a new and improved beam modulating device having high transductance.

Another object of the invention is to provide a new and improved beam modulating device responsive to high frequency modulating signals and having good insulation between input electrodes.

Another object of the invention is to provide a beam modulating device and method which may readily be adapted for many varied uses.

Another object of the invention is to provide a new and improved beam modulating device and method which is highly efiicient in operation, provides low heat loss in its modulating operation, and has a high current and power capacity.

Another object of the invention is to provide a new and improved beam modulating device which may be readily utilized as an amplifier, a cathode ray tube, a klystron, and a signal combining means, in appropriately modified forms, having all the advantages stated above.

The above objects of the invention as well as the many other objects are attained by providing a beam modulating device comprising a plate member for absorbing and reflecting incident charged particles of a beam, and guide means for directing particles of the beam towards the plate member. The plate member is provided with a connection for having its potential controlled to regulate its absorbing and reflecting action for modulating the amplitude of the beam of particles produced by the device. The guide means is in the form of a magnetic field for directing incident particles towards and reflected particles from the plate member along different non-reciprocal paths.

The charged particles may be negatively charged electrons in the form of a beam derived from the cathode of an electron gun. An apertured element which electrically shields the plate member is interposed between the source of electrons and the plate member, while the magnetic field of the guide means deflects the beam of electrons through the aperture of the element so that the beam path is substantially perpendicular to the surface of the plate member when proximate the plate member. With the potential between the plate member and the element controlled to provide an electric field for regulating the ratio of absorption to reflection of electrons by the plate member, the electrons reflected by the plate member form a beam which is deflected by the magnetic field of the guide means through the aperture of the element and into a non-reciprocal undeflected path forming a predetermined angle with the'undeflected path of the beam of electrons from the source.

The method as applied to a beam of negatively charged electron particles comprises subjecting the particles of said beam to a magnetic field for directing the particles along the path into an electric field parallel to the direction of the electric vector, varying the amplitude and polarity of the electric field for controlling the proportions of electrons rejected by the electric field back into the magnetic field, and utilizing said magnetic field for forming a beam of the rejected electrons along a path in a predetermined direction.

The foregoing and other objects of the invention will become more apparent as the following detailed description of the invention is read in conjunction with the drawings, in which:

FIGURE 1 is a side elevational view with portions broken away of a cathode ray tube embodying the invention,

FIGURE 2 is a side elevational view with portions broken away of an amplifier tube embodying the invention,

FIGURE 3 is a sectional view taken on line 33 of FIGURE 2,

FIGURE 4 is a side elevational view of a signal combining means embodying the invention,

FIGURE 5 is a partially diagrammatic view taken on the line 5-5 of FIGURE 4, and

FIGURE 6 is a diagrammatic representation of a klystron embodying the invention.

Like numerals designate like parts throughout the several views.

Refer to FIGURE 1 which discloses a cathode ray tube 10 embodying the invention. The cathode ray tube 10 has a glaSS envelope 12 with a first portion 14 of circular cross section having its end connected to a base 16 with connecting pins 18, and a second portion 20 of circular cross section. The first and

second portions

14, 20 are joined with their axes at an angle of degrees and forming an intermediate cylindrical portion 22 symmetrically arranged with its axis at an angle of degrees with each of the axes of the first and

second portions

14, 20 of the envelope 12. The envelope 12 is also provided with a conical enlarged portion 24 at the end of the portion 20 and has a substantially flat face area portion-26. The tube It) has its cavity within the envelope 12 evacuated in the usual manner, and is sealed.

The first portion 14 of the envelope 12 contains an electron gun 28 for producing a beam 30 of electrons of subwards the intermediate cylinder 22.

It is noted, that the electron gun 28in this case, may be designed with a slightly diverging electric field at its emitting surface for insuring increased life and dependability, whereas the field is usually converging, overloading the central portion of the cathode, in prior art beam modulating devices.

When the electrons of the beam enter the region 34 of the cylinder 22, they are deflected to the left along a curved path 36 by the field produced by the electric coil 38 positioned on the outside of the cylinder 22 about the region 34 and proximate to the first and

second portions

14, 20 of the envelope 12.

After being deflected, the beam 30 of electrons proceeds along a path 40 through an aperture 42 in a shielding element 44 and towards a plate member 46.

The shielding element 44 has the form of a cylindrical body with a wall 48 and a plane base portion 50 having the aperture 42 at its center. The shielding element 44 is maintained in position within the cylinder 22 by spring adjusting means 52. In this manner, the base 50 of the element 44 is interposed along the path 40 of the beam 30 of electrons between the magnetic field in the region 34 and the plate member 46. The shielding element 44 is made of electrically conducting material which is pervious to magnetic lines of flux.

The plate member 46 is secured within the cylinder 22 at its bottom 54 in parallel spaced relation to the base 50 of the shielding element 44. The shielding element 44 is connected to a lead 56 which, for example, may receive a positive potential of about 400 to 4000 volts with respect to the cathode of the electron gun 28. The plate member 46 is connected to a lead 58 which may be maintained at substantially cathode potential and varied positively and negatively by a modulating voltage signal. In this connection, the magnetic field produced by the coil 38, for example, may be in the order of 100 to 500 gausses to provide the required deflection for the beam. The change in intensity of the electric field between the shielding element 44 and plate member 46 produced by the modulating voltage signal on lead 58 is effectively shielded by the element 44 from the other regions within the envelope 12 of the cathode ray tube 10.

- As the beam of electrodes proceed toward the member 46 along the path 40 through the aperture 42 of the element 44, they enter the region 60 of the electric field between the shielding element 44 and the plate member 46. The lines of force of the electric field produced by this configuration are substantially parallel and perpendicular to the plate member 46. The electrons of the beam upon entering the region 60 are accelerated or decelerated in accordance with the polarity of the electric field.

In operation, the polarity of the electric field is adjusted to retard and decelerate the incident electrons in their motion towards the intercepting surface 62 of the plate member. 7 It is also noted that the path 40 of the beam of electrons is substantially parallel to the electric field vector so that there is no component of lateral acceleration or velocity and the path 40 is substantially perpendicular to the intercepting surface 62 of the plate member 46. If the voltage on the plate member 46 is sufliciently above cathode potential, most of the electrons in the path 40 will reach the plate member 46 and be absorbed. However, as the potential of the plate member 46 is reduced a decreasing number of electrons will reach the plate member 46, while the remaining electrons will have their velocity reversed before they reach the plate member 46 and be rejected from the region 60 along a path 64 coincident with the path 40. The electrons will move along the path 64 through the aperture 42 and into the region 34 of the magnetic field produced by the coil 38. At this time, since the direction of the electrons along their path 64 is reversed from that along the path 40, the magnetic field deflects the electrons along a non-reciprocal curved path 66 into the undeflected path 68. The rejected electrons form a beam 70 along the path 68 proceeding axially along the portion 20 of the envelope 12 towards the enlarged end portion 24.

It is noted that the boundaries of the magnetic field in the region 34 transversed by the electrons of the beam 30 are substantially plane and parallel to the intercepting surface of the plate member 46 and oriented at an angle of substantially 45 degrees to the direction of the

undeflected beams

30 and 68. This angle of the boundary of the magnetic field within the region 34 acts to broaden the beam 30 as it enters the magnetic field. This is due to the fact that the electrons in the beam to the left are acted upon earlier than the electrons to their right along the cross section of the beam. The broadening of the beam serves to decrease the electron density of the beam, and thereby, increase the efiiciency of the'reflecting operation of the device. It is noted that, since the beam is doubled back upon itself along the paths 40, 64, this tends to maintain the beam density at a value substantially equal to that of the beam along the path 32.

As the beam is deflected along path 66 and leaves the magnetic field in the region 34 it is directed into a path 68 which is also at an angle of substantially of 45 degrees with the boundary of the magnetic field. This has the effect of sharpening or narrowing the beam and increasing its density to a value that is substantially the same as that of the beam 30 along the path 32 when the beam is unmodulated. As previously noted, however, the beam 70' may have introduced therein negative spherical aberration due to the reflecting process undergone by its electrons.

The proportion of electrons absorbed to those rejected or reflected is a function of the potential of the plate member 46. Therefore, as the modulating signal varies the voltage on the plate member 46 the intensity of the beam 70 formed of reflected electrons varies in a corresponding manner. Since the incident electrons move perpendicular to the intercepting surface 62 of the plate member 46 the electrons which impinge upon and are absorbed by the member 46 have lost most of their energy, thereby minimizing the heat produced in the member 46, and the energy and power required to operate the device. It is also noted that the electrons which are reflected or repelled by the electric field 60 do not lose any of their energy, which is regained by their passage in the opposite direction through the electric field in the region 60.

Since this device does not utilize the grids commonly used in electron devices, the partition noise resulting therefrom is eliminated, thereby increasing the signal to noise ratio obtainable. This structure also provides a high transconductance for the tube 10 as well as a low capacitance to the input lead 58 of the plate control member 46 receiving the beam modulating signal, because of the relatively large separation between the base 50 and the plate member 46.

The modulating device also provides an electron beam 70 which, while having its amplitude modulated, does not vary its focal point. The reflecting method of the structure also provides a negative spherical aberration which may compensate for the positive spherical aberration usually present due to the focusing and other means of the cathode ray tube 10. The optical properties of the beam are, thus, independent of the total current of the beam. This is a very highly desirable property.

As the beam 70 of electrons proceeds along its path 68,

itpasses through an aperture 72 in the transverse wall portion 74 of a focusing cylinder 76 positioned within the portion 20 of the envelope 12. The beam 70 passes through the focusing cylinder 76 and between the horizontal and vertical deflecting plates '78, 80. The deflecting

plates

78, 80 provide for horizontal and vertical deflection of the beam 70 which proceeds towards the face portion 26 of the cathode ray tube 10 and impinges upon its electron collecting surface.

In summary, the tube 10 produces a beam of electrons 108 of the shielding element 102.

30, preferably by providing a diverging electric field at the emitting surface of the cathode. The beam 30 proceeds towards the region 34 of the cylinder 22, where it is broadened at the boundary of the magnetic field of coil 38 and deflected to the left along the circular path 36 into path 40. The path 40 proceeds through the aperture 42 of the shielding element 44 into the electric field of the region 60. Depending upon the potential difference and the resulting electric field produced by the plate member 46 and the shielding element 44, a greater or smaller proportion of electrons will be absorbed by the plate 46, with the remaining electrons being rejected or reflected back through the aperture 42 along the path 64. When the electrons move through the magnetic field in the region 34 they are deflected along the nonreciprocal circular path 66 into the path 68. The beam is narrowed at the boundary as it emerges from the magnetic field. The electrons along the path 68 form a beam which is modulated in intensity and proceeds to the right making an angle of 90 degrees with the beam of incident electrons along the path 32.

The electrons approach the plate member 46 substantially perpendicular to its intercepting surface 62, thereby, minimizing the energy dissipated by the impinging electrons, While the reflected or rejected electrons regain their initial kinetic energy and are focused at the same point, which is not dependent upon the beam intensity or the modulating signal. The shielding element 44 serves to shield the modulating electric field from the remaining portions of the envelope 12.

The modulated beam 70 proceeds along the portion 20 of the envelope 12 being focused by the cylinder 76 and deflected by the

plates

78, 80 in the usual manner. The negative spherical aberration produced by the beam modulating structure within the cylinder 22, compensates for and counteracts the positive spherical aberration produced by the focusing cylinder 76.

Refer to FIGURES 2 and 3 which illustrate an electron tube 82 which is a modification of the device shown in FIGURE 1. The electron tube 82 has a glass envelope 84 providing an evacuated cavity. The left end portion 86 of the envelope 84 has its end connected with a base 88 with pins 90. A cathode ray gun 92 is positioned within the end 86 of the envelope 84 for producing a beam of electrons 94 which proceeds along an axial path 96 towards the second end 98 of the envelope 84.

i The central portion 100 is provided with a cylindrical metallic shielding element 102 which is axially aligned with the axis of the envelope 84'. A portion of the circular wall of the shielding element 102 is deformed to provide a flattened region 104 having a central aperture 106. The right end of the shielding element 102 is enclosed by a base. portion 108 having a central aperture 110.

The central portion 100 of the envelope 102 receives about it a magnet 112 having

poles

114, 116 providing a field therebetween shown within the dotted region 118 with lines of flux substantially parallel to the plane of the deformed portion 104 of the shielding element 102. The magnetic ficldin the region 118 is symmetrically positioned on each side of the aperture 106 with its flux lines perpendicular to the plane of FIGURE 2.

A pair of

magnetic coils

120, 122 are symmetrically positioned about the outside of the envelope 12 at its central portion 100 on each side of the magnet 112 with their bottom ends 124, 126 spaced further apart than their top ends 125, 127. V p

Collecting plate 128 is positioned at the end of the portion 98 of the envelope 84 in spaced relation to the base The collecting plate 128 is connected with a lead 130 which may be returned to ground potential through a load 132.

A plate member 134 is positioned outside the shielding element 102 in spaced relation to its deformed portion 104 and is connected externally to a lead 136.

The tube device 82 operates in a manner similar to that of the device 10 of FIGURE 1. A beam 94 formed of electrons emitted from the electron gun 92 proceeds along the path 96 until it enters the magnetic field produced by the magnetic coil in the region 138 within the envelope 84.

Since the beam 94 enters the magnetic field at its boundary at an angle differing from 90 degrees, the beam is broadened. The electrons within the magnetic field, since their path is substantially perpendicular to the lines of magnetic flux, are deflected along substantially circular paths 140 and into substantially linear paths 142 as they emerge from the region 138. When the beam of electrons along the path 142 enter the region 118 of magnetic flux produced by the magnet 112, they are again deflected along substantially circular paths 144 and through the aperture 106 towards the intercepting surface of the plate member 134.

The beam of electrons, as it approaches the plate member 134, proceeds along the path which is substantially perpendicular to the intercepting surface of the member 134. The region 146 between the deformed portion 104 of the shielding element 102 and the plate member 134 is provided with a retarding electric'field of varying intensity controlled by the relative potentials of the shielding element 102 and the plate member 134. As an example, the potential of the shielding element 102 may be maintained at a positive voltage with respect to the cathode of the electron gun 92 of about 20 to 400 volts for use of the tube device 82 as an amplifier, while the plate member 134 may be maintained at substantially the same potential as the cathode of the electron gun 92 and varied about this potential by a beam modulating signal delivered to the terminal of a lead 136 for varying the intensity of the electron beam reflected by the plate member 134.

As explained in connection with the tube device 10, the proportion of the reflected or rejected electrons, which are not absorbed by the plate member 134, is controlled by the potential signal delivered to the plate member 134. The reflected or repulsed electrons pass along a path substantially perpendicular to and in a direction away from the plate member 134, through the aperture 106, then along a substantially circular path 148 in the region 118 of magnetic flux. Since the direction of the repulsed electron is oppositeto the direction of the motion of the electrons incident to the plate member 134, the magnetic field in the region 118 acts to deflect the electrons to the right into a non-reciprocal path 150. The electrons move to the right along the path 150 until they enter the magnetic field produced within the shielding element 102 by the magnetic coil 122. This field, which has its lines of flux substantially perpendicular to the velocity of the electron beam, deflects its electrons along substantially circular paths 152 into an undeflected path 154 which can be aligned with or made substantially parallel to the direction of the beam of electrons 94 as emitted by the electron gun 92.

When the beam of electrons along the path 152 emerges from the region 156, its path 154 forms an angle with the boundary of the magnetic field which operates to narrow or sharpen the beam providing a cross section which is substantially similar to that of the original beam 94 emerging from the electron gun 92.

In the tube device 82 each of the magnetic fields produced by the magnet 112, and

magnetic coils

120, 122 may have a magnetic field intensity of approximately 50 gausses to provide the required deflection of the beam of Thus, the electron tube device 82 may be used as an amplifying device by delivering an input signal to the lead 136 of the plate member 134 which in turn modulates the intensity of the beam of electrons which electrons are delivered to the collector plate 128 producing an output signal. The tube device, in this manner, may be used for voltage or current amplification.

As previously noted many advantages are provided by this structure because of the low input capacitance and high transconductance achieved by the device. The device also provides high efliciency with low power dissipation, high reliability and long tube life.

Instead of providing a collector plate 128, the device 82 may be provided with focusing and deflecting means and a fluorescent screen to form an in line type of cathode ray tube instead of the bent cathode ray tube 10 shown in FIGURE 1. Of course the modulated beam produced by the device may be utilized to form many other electronic devices having many if not all of the enumerated advantages.

The invention may be adapted to utilize charged partioles other than electrons embodying the basic features disclosed herein. For example, the method of the invention may be applied by subjecting a charged particle or a beam of charged particles to a magnetic field for deflecting the particles along a predetermined path into an electric vector field, varying the vector intensity of the electric field for controlling the proportion of particles rejected by the electric field, and forming the electrons rejected by the electric field into a beam of particles. The beam of rejected particles may also be further deflected by a magnetic field into a desired non-reciprocal path. The intensity vector of the electric field is directed parallel to the path of the particles for reflecting or rejecting the panticles from the electric field along a path substantially identical in direction to the path of the incident particles. The method of the invention, it will be noted, may readily be applied to removing or absorbing particles for modulating the intensity of the beam comprising positively or negatively charged particles having a mass greater or smaller than that of the electron.

Refer to FIGURES 4 and 5 which shows a signal combining means 160 comprising a substantially cylindrical glass envelope 16-2 having a cylindrical wall 164 and top and

bottom walls

166, 168. The envelope 162 has its chamber evacuated and sealed in the usual manner.

A cylindrical shielding element 170 is positioned by a plurality of radially extending spacing means 172 within the envelope 162 with its axis aligned with the axis of the envelope 162. The spacing means may be in the form of springs to adjust for relative expansion and contraction of the envelope 162 and shielding element 170. The spacing means 172 also provides a peripherial annular region 174 between the side wall 164 of the envelope 162 and the shielding element 170. A cathode 176 is positioned within the annular region 174, and is associated with a heating element 178. The cathode 176 may be returned to ground potential while the heating element 178 may be energized by an appropriate current source.

A plurality of

plate members

180, 182, and an electron collecting plate 184 are angularly positioned in spaced relationship within the annular region 174 of the envelope 162. The

members

180 and 182 may be oined to respective

external terminals

186, 188 which are each adapted to receive input signals, while the collector plate 184 is connected to an external lead 190' which is joined to a terminal 192 maintained at an appropriate potential through a load 194. A lead 195 connects the shielding element 170 to a terminal 197 for being maintained at an appropriate voltage which is positive with respect to the cathode 176. For example, the device may be operated with a positive potential of 100 to 500 volts on 11 6 te minal 197 of the shielding element 170.

The shielding element is provided with a plurality of

apertures

196, 198, 200 and 2.02 each respectively positioned proximate the cathode 176,

plate members

180, 182 and the collector plate 184.

A substantially uniform magnetic field is produced in the region 204 inside the shielding element 170. The lines of flux of the magnetic field are parallel to the cylindrical axis of the shielding element 170 and perpendicular to the plane of FIGURE 5. The magnetic field is produced by a magnet 206 having the faces of its

poles

208, 210 respectively parallel and proximate to the top and

bottom walls

166, 168 of the envelope 162.

In operation, the electrons emitted by the heated cathode 176 are accelerated towards the shielding element 170 because of its higher potential. T he'elect'rons which pass through the aperture 196 in the element 178 form a beam of electrons 212 which are deflected into a substantially curved path 214 by the magnetic field within the region 204. The path 214 is substantially circular since the velocities of the electrons are perpendicular to the lines of magnetic flux. The electrons along the path 214 pass through the aperture 198 of the shielding element 170 towards the plate member 180 in a direction perpendicular to its electron intercepting surface.

As previously explained in connection with the

devices

10 and 82 the electric field produced between the shielding element 170 and the plate member 180 acts upon the electrons to decelerate them. As the modulating signal delivered to the terminal 186 varies the potential of the plate member 180 about substantially ground potential, the proportion of electrons repelled and not absorbed by the member 180 is correspondingly controlled. The repelled or reflected electrons, like the incident electrons, move substantially parallel to the lines of force of the electric field and pass back through the aperture 198 forming a beam 216 with a modulated amplitude within the region 204 of the device 160.

The magnetic field within the region 2% acts upon the beam 216 to deflect the electrons along a non-reciprocal substantially circular path 218 which proceeds to the right and causes the electrons to pass through the aperture 200 into the electric field between the shielding element 170 and the plate member 182. As before the variation of potential of the plate member 182 by the application of an input signal to its terminal 188 varies the electric field acting upon the electrons. In this manner, the ratio of electrons which are absorbed to those reflected is controlled. The reflected electrons pass back through the aperture 200 forming a beam of electrons 220 in the magnetic field of the central region 204 of the device 160. The beam 220, however, has an amplitude which is further modulated by the signal delivered to the terminal 188.

The beam 220 is deflected by the magnetic field along a non-reciprocal circular path 222 and through the aperture 202 toward the collector plate 184. Since the collector plate 184 is maintained at a potential which is substantially above ground potential, it absorbs substantially all of the electrons of the beam 220. This produces an output signal across the load 194. The output signal produced is related to the amplitude of the beam 220 which has been appropriately modulated by the several input signal delivered to the

terminals

186 and 188.

Although the device 160 has been described with two plate members, many such members may be arranged within the annular region 174 for combining a plurality of input signals. In order to reduce the magnetic field necessary to sharply deflect the beam of electrons, the plate members may be spaced about the periphery so that the beam passes from one plate member to a non-adjacent plate member and makes more than one revolution about the central region 204 before it impinges upon the collector plate. By this means a highly compact signal combining device may be provided which is adapted to receive a plurality of signals.

As noted in connection with the devices and 82, the signal combining device 160 has a low input signal capacitance and provides good insulation between input electrodes while using one magnetic field for particle deflection. Such devices can be especially useful in conreceive a plurality of input signals.

The FIGURE 6 is a diagrammatic view of a klystron device 224 embodying the invention. The device 224 comprises a tubular envelope 226 having a first end 223 and a second 230. The first end 228 of the device 224 is substantially similar to the beam modulating device 82 of FIGURE 2 except that the distance between the shielding element 102 and the collector plate 231 is greatly enlarged.

The second end 230 of the envelope 226 is provided with a pair of spaced resonating

units

232, 234 having their

central portions

236, 238 extending into the envelope 226 forming

respective apertures

240, 242 along the linear path of the beam of electrons. The resonating

units

232, 234 are of the usual type made of a conducting material and having annular cavity regions 244. The resonating unit 232 which precedes the unit 234 along the beam of electrons is connected to a terminal 246 for receiving input signals which may be of radio frequency, while the resonating unit 234 is connected to a terminal 248 for delivering an output signal.

In operation, the beam produced by the device 224 is modulated by the input signal delivered to the terminal 136 of the plate member 134. This beam which has its amplitude modulated passes through the opening 240 of the resonating unit 232 which accelerates and decelerates the electrons in accordance with the input signal delivered to its terminal 246. When the beam of electrons pass through the opening 242 of the resonating unit 234 they induce an appropriate signal therein which is delivered to terminal 248. This output signal, thus, is modulated by the input signals to the

terminals

136 and 246. The electrons which emerge from the opening 242 impinge upon and are removed by the collector plate 231 which is returned to a positive potential.

The device 224 provides a beam of electrons which is not defocused by the modulating input signals and has the further advantage of being driven by a small input signal voltage and requiring low power. The construction also reduces the noise output which would be produced by partition noise caused by collisions of the electrons of the beam with electrodes in the beam path.

Although the above devices illustrate some of the forms of the invention and some of its uses, the invention may be utilized in other devices such as backward traveling wave tube as well as various other forms of amplifiers and signal generating and combining means.

While only a few representative embodiments and methods of practicing the invention disclosed herein, have been outlined in detail, there will be obvious to those skilled in the art, many modifications and variations accomplishing the foregoing objects and realizing many or all of the advantages, but which yet do not depart essentially from the spirit of the invention.

What is claimed is:

1. A system for modulating the intensity of a beam of electrically charged particles, said system comprising: means for projecting said beam along a predetermined path; means for magnetically deflecting said beam into a different path at an angle to said predetermined path; and means for reflecting along a reciprocal of said different path a fraction of the particles in said beam while absorbing the remainder of said particles.

2. The system of claim 1 further characterized in that said reflecting means comprises means for establishing in said different path an electric field having lines of force parallel to said last-named path and of such polarity as to retard particles entering said electric field from the direction of said magnetic field.

3. The system of claim 2 further characterized in that said means for projecting said beam comprises an electric accelerating field of predetermined strength, said system further comprising means for varying the strength of said retarding electric field over a range of values extending both above and below that of said accelerating electric field.

4. A system for modulating the intensity of a beam of electrically charged particles, said system comprising: an electrode for emitting said particles; means for forming said particles into said beam and projecting said beam along a predetermined path; means for establishing a magnetic field transversely to said path whereby said beam is deflected into a different path; and means for reflecting back into said field along a reciprocal of said dilferent path a controllable fraction of the particles in said beam while absorbing the remainder, said last-named means comprising an electrode disposed in said different path and means for varying the potential of said electrode over a range of values extending both above and below the potential of said emitting electrode.

5. The system of claim 4 further comprising an electrode for shielding said electrode of variable potential from other electrodes affecting said beam.

6. The system of claim 4 further comprising means for increasing the cross-section of said projected beam before traversal of said magnetic field.

7. The system of claim 6 further comprising means for reducing the cross-section of said reflected beam after traversal of said magnetic field.

References Cited in the file of this patent UNITED STATES PATENTS 2,159,534 Ruska May 23, 1939 2,205,071 Skellett June 18, 1940 2,332,876 Uhlmann Oct. 26, 1943 2,416,302 Goodall Feb. 25, 1947 2,416,303 Parker Feb. 25, 1947 2,452,075 Smith Oct. 26, 1948 2,460,402 Sziklai Feb. 1, 1949 2,651,000 Linder Sept. 1, 1953 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,023,342 February 27, 1962 Glenn W. Preston that error appears in the above numbered pat- It is hereby certified that the said Letters Patent should read as ent requiring correction and corrected below.

lines 47 and 48, for "transductance" read Column 1, transconductance column 8, line 75, after "of" insert input column 9 line 6, for "receive a plurality of read nection with electric computers input signals Signed and sealed this 2nd day of April 1963.

(SEAL) Attest:

ESTON G. JOHNSON DAVID L. LADD Attesting ()fficer Commissioner of Patents