US2424965A - High-frequency amplifier and oscillator - Google Patents

Description

Aug. 5, 1947.' L. N. BRxLLoUlN HIGH vFREQUENCY AMPLIFIER yANDl OSCILLATOR Filedvmarch 2o, 1942 2 sheets-sheet 1 mm ms@ y @wwnmw .xw i

INVENToR. fw/ /v. /Lww/v ATIURLTY ug. 5, 1947. l L. N. BRILLOUIN 2,424,965

I HIGH FREQUENCY AMPLIFIER AND OSCILLATOR Filed March 20, 1942 2 sheets-sheet 2 Amma-Y Patented Aug. 5, 194i? einem HIGH-FREQUENCY AMPLIFEER AND OSCILLATOR Leon N. Brillouin, Madison, Wis., assignor to Federal Telephone and Radio Corporation, a

f corporation of Delaware Application March 20, 1942, Serial No. 435,521

8 Claims.

This invention relates to electron discharge apparatus and more particularly to such apparatus intended for the amplification and generation of high frequency electrical waves,

It is well known that in conventional electron discharge tubes the finite electron transit time prevents efcient operation at very high frequencies due to abnormal loading of the input circuit and consequent loss of transconductance of the tube, excessive coupling between the input and output circuits and increased losses due to the presence of large circulatory currents at high frequencies.

The principal object of my invention is to provide an improved electron discharge apparatus particularly suitable for use as an amplifier or oscillator at high frequencies.

More particularly, it is an object of my invention to provide an electron discharge device in which electron transit time is not critically related to the period of oscillation and in which high frequency losses are minimized.

The various objects and features of my invention will be more fully understood from the following detailed description of certain embodiments as shown in the accompanying drawings in which Fig. 1 is a diagram employed to illustrate the principle upon which my invention is based;

Fig. 2 is a side-sectional View of an electron discharge apparatus showing one typical method of carrying my invention into effect;

Figs. 2A, 2B, and 2C illustrate the connes of the electron beam produced by the apparatus shown in Fig. 2;

Fig. 3 illustrates alternative electrode structures which may be used in place of the electrodes shown in Fig, 2;

Figs, 3A, 3B, and 3C illustrate the confines of the electron beam produced in the arrangement of Fig. 3;

Fig. 4 shows a side sectional view of an electron discharge apparatus according to the present invention;

Fig. 5 shows a still further electrode arrangement; and

Figs. 5A and 5B illustrate the confines of the electron beam produced by the arrangement of Fig. 5.

Theoretical investigations made by myself (Physical Review, vol. 60, 1941, p. 385) and by J. P. Blewett and S. Ramo (Physical Review, vol. 57, 1940, p. 365) have shown the formation and type of motion of an electron beam traveling inside a metallic pipe under the action of a longitudinal magnetic field. Referring to Fig. 1, a metallic cylinder C is maintained at a positive potential and a constant magnetic field H is generated parallel to the axis Z of the cylinder C. Electrons enter the cylinder C with a certain longitudinal velocity o2 and rapidly build up an electronic cloud of constant density Pu whichrotates about the axis Z with a constant angular velocity wn: then WLLOHZ PO- 26W where e represents the charge of the electron, m is the mass of the electron and ,u0=% 1020 in electrostatic units, an is Larmors angular velocity.

Each electron describes a helix around the axis Z, due to the superposition of the constant velocity o2 and of the rotation wn. The space charge density Po is uniform throughout the beam and the whole electronic cloud moves like a solid body, gliding along the axis Z with a velocity o2, and at the same time spinning about the axis Z of the -cylinder C with the angular velocity wn. This represents the stable type of motion of the electron beam.

I have found that by producing periodic changes in the cross-sectional form or area of such a beam, radial vibrations are impressed upon it and result in oscillations which may be used for the purpose of amplification or generation of high frequency waves.

' A feature of my invention resides, therefore, in the provision of an electron discharge apparatus comprising a means for forming the electrons emitted by a source into a beam comprising an electronic cloud of normally constant density Which rotates about a linear axis 'with a constant angular velocity and which simultaneously advances lalong this axis, and means for producing periodic changes in the cross sectional form or area of the beam at a predetermined point along the axis, means also being provided for extracting energy from the beam at another predetermined pcint along the axis.

Reference should now be made to Fig. 2, which shows one method of carrying out my invention. At one end of an evacuated envelope B there is mounted an electron emissive cathode K and a beam focusing and concentrating electrode F. A metal cylinder C is mounted in the envelope B parallel to the major axis of the envelope B, and a target or collector electrode T is mounted at the end of the cylinder C remote from the cathode K. Surrounding the envelope B and the cylinder C is a coil M for producing a magnetic field parallel to the axis of the metallic cylinder C. Near the entrance to the cylinder C adjacent the beamforming electrodes K, F is mounted a rst cylindrical electrode C1, the radius of which is slightly greater than the radius of the beam, whereby under normal conditions electrons will not strike this electrode and no current will flow to it. A second cylindrical electrode C2 is mounted within the cylinder C and adjacent its other end, such second cylinder C2 also having a radius slightly greater than the radius of the electron beam. The cylinder C is maintained at a high positive potential with respect to the cathode. The focusing electrode F is also maintained at a positive potential as is customary in electron guns, whilst the collector or target electrode I is maintained preferably at a slightly positive potential with respect to the cathode. An input circuit L1 is connected to the electrode C1, and an extracting circuit is connected to the electrode C2.

If an oscillating voltage is applied to the electrode C1 from the circuit L1, alternate radial expansions and compressions will be impressed upon the electronic beam. Fig. 2A illustrates the confines of the electronic beam in the stable condition. Fig. 2B illustrates the connes of the beam at the point where it is under the inuence of the electrode C1 when a positive half cycle is impressed thereon, and Fig. 2C illustrates the confines of the beam when under the iniluence of a negative half cycle impressed upon the electrode C1. These alternating radial vibrations travel along the beam moving in the direction of the axis Z with the longitudinal velocity v2. Since the radius of the cross section of the beam is periodically greater than the radius of the electrode C2 groups of electrons will hit this electrode C2, and yield an alternating current on it. The oscillations or vibrations impressed upon the electron beam by the electrode C1 will be large if their frequency is correctly related to the angular velocity of the beam. I have found that the frequency corresponding to the type of motion described with reference to the arrangement shown in Fig. 2 is about V2 times Larmors frequency (w=\/'2 on) With the arrangement of Fig. 2, the radial vibrations impressed upon the electronic beam o occur simultaneously in all directions of one cross section. Each cross section of the beam remains circular, but the radius of this circle is alternately larger and smaller than the normal radius of the beam. The cross section of the beam may, however, be periodically deformed by the use of other forms of electrodes. If, for example, the electrodes within the cylinder C are in the form of sets of four arcuate plates A1, Az, A3, A4, and B1, B2, Bs, B4, as shown in Fig. 3 the four in each set being disposed on each side of the electron beam, A1 opposite A2, A3 opposite A4, etc., the cross vsection of the beam during onefhalf cycle of an oscillation impressed upon the electrodes A1, A2 will be an ellipse with its major axis horizontal, as shown in Fig. 3B, and during the succeeding half-cycle will be an ellipse with its major axis vertical, as shown in Fig. 3C. These elliptic oscillations travel alom,r the beam within the cylinder C, and simultaneously rotate about the axis Z in accordance with the motion of the electron beam as described with reference to Fig. l. Before leaving the cylinder C, the beam passes between the electrodes B1, B2, and if the longitudinal velocity of the beam, the angular Velocity on, and the frequency of the oscillations impressed upon the electrodes A1, A2 are correctly chosen, the elliptic oscillations of the beam will result in a current on the electrodes B1, B2, since groups of the deiiected electrons will strike these electrodes.

In Fig. 3, the electrode pairs A1, A2, and B1, B2, have been shown mounted on parallel diameters of the cylinder C. To avoid direct capacity effect between the pairs of electrodes A1, A2, and B1, Ba, it is preferable to arrange these pairs of electrodes along diameters at right angles to one another. As in the preceding embodiments, the frequency of the impressed vibrations should be correctly related to the angular velocity of the electron beam.

In Figure 4 the cylinder C and the A and B electrodes enclosed therein as diagrammed in Fig. 3 are shown in an envelope B similar to that shown in Fig. 2 with the connections therethrough to cathode K, electrode F, and plate T, and the solenoid M therearound to make a more complete showing of the electron discharge device according to this invention. The figure contains elements of Figs. 2 and 3 and corresponding parts have been labeled accordingly.

More complicated structures may be used for the beam deforming and energy extracting electrodes. Each of these electrodes may be constituted by 4, 6 211. arcuate plates disposed on a circle in order to excite vibrations of more complex types along the electron beam. Fig. 5 shows one example of such an arrangement in which the electrode structure upon which the input oscillations are impressed comprises six arcuate sections, alternate sectors being connected to one side of the input circuit and the remaining sectors being connected to the other side of the input circuit. The energy extracting electrode structure is similarly constituted and connected.

to the energy extracting or output circuit. With such an arrangement the cross section of the electron beam is alternately deformed according to the two shapes shown in Figs. 5A and 5B.

The arrangements described will function as ampliers of high frequency Waves. If, however, a coupling is provided between the input circuit L1 and the output circuit Le as shown by the dotted line arrow in Fig. 2 and Fig. 4, oscillations will be fed back from the output circuit L2 to the input circuit L1 and will build up, causing the Y device to generate high-frequency oscillations which may be extracted from the output circuit Lz.

While I have described my invention with reference to particular embodiments thereof, it will be understood that other modifications may be made by those skilled in the art without departing from the invention as defined in the appended claims.

What I claim is:

1. An electron discharge apparatus for amplifying a variable voltage comprising an envelope, means including a cathode positioned within said envelope for producing and directing an electron beam, a metallic tube positioned axially about the path of said beam within said envelope, means positioned about said tube for generating a magnetic eld parallel to the axis of said tube whereby said beam is rotated about the linear axis with a constant velocity, means connected to said tube for maintaining said tube at a positive potential with respect to said cathode whereby said beam is advanced through said tube, a first pair of oppcsitely directed arcuate electrodes disposed one on either side of the path of said beam and mounted in said tube adjacent the end nearest the cathode, a second pair of oppositely directed arcuate electrodes disposed one on either side oi the path of said beam and mounted in said tube at a point along axis from said rst pair of electrodes, a variable Voltage source connected to said fir 'pair of electrodes for controlling a radial dim n ,ci said beam, and an output circuit connected to said second pair of electrodes for extracting energy irom said beam in the form of said variable voltage 2. Electron discharge apparatus according to claim 1, in which said rst pair of electrodes are turned 90 about said beam with respect to said second pair of electrodes.

3. An electron discharge apparatus for amplifying alternating current waves comprising, an envelope, means including a cathode positioned within said envelope for producing and directing an electron beam, a metallic tube positioned axially about the path oi said beam within said envelope, means adjacent said tube for generating a magnetic neld parallel -to the axis of said tube whereby said beam is rotated about a linear axis with a constant velocity, means connected to said tube for maintaining said tube at a positive potential with respect to said cathode whereby said beam is advanced through said tube at a constant velocity, an even number greater than two of rst electrodes mounted in said tube adjacent the end nearest the cathode and disposed substantially in a circle about said beam, an even number greater than two of second electrodes mounted within said tube, longitudinally from said first electrodes and also disposed substantially in a circle about said beam, an input lcircuit having two terminals, one or" which is connected to alternate rst electrodes and the other of which is connected to the remaining iirst electrodes for periodically deforming the path of rotation of said beam, and an output circuit having two terminals, one of which is connected to alternate second electrodes and the other of which is connected to the remaining second electrodes for extracting energy from said beam in the form .of said alternating current waves.

4. An electron discharge apparatus comprising a metallic tube, means adjacent said tube for producing a substantially solid, generally cylindrical electron ibeam and directing it axially through said tube, means positioned in the vicinity of said metallic tube for generating a magnetic eld parallel to the axis of the said tube whereby said beam is rotated, a rst electrode mounted in said tube along the path or said beam, electrodes mounted within said tube and spaced from and co-axial with said rst electrode and normally outside the path of said beam, a connection to said iirst electrode for applying thereto a variable voltage of frequency different from and bearing a predetermined relation to the frequency of the rotation of said beam for periodically deforming the path of rotation of said beam whereby electrons periodically strike said electrodes, and an energy extracting circuit connected to said electrodes adapted to remove energy from said electron beam.

5. Electron discharge apparatus comprising, an envelope, a metallic tube within said envelope, means in said envelope for producing an electron beam having a predetermined cross-sectional area and for directing said beam axially through said tube, means positioned in the vicinity of said metallic tube for generating a magnetic iield parallel to the axis of said tube whereby said beam is rotated, radially displaced electrodes mounted in said tube in a position about the path of said electron beam, means positioned in said tube intermediate said electrodes and said beam producing means for periodically enlarging the crosssectional area of said beam at a frequency dii ferent from and bearing a predetermined relation to the frequency of the rotation of said beam whereby electrons periodically strike said electrodes, and an energy extracting circuit connected to said electrodes.

6. Electron discharge apparatus comprising an envelope, a metallic tube within said envelope, means in said envelope for producing an electron beam having a predetermined cross-sectional shape and for directing said beam axially through said tube, means positioned about said tube for generating a magnetic field parallel to the axis of said tube whereby said beam is rotated, electrodes mounted in said tube in a position normally outside the path of said electron beam, means in said tube intermediate said electrodes and said beam producing means for periodically deforming the cross-sectional shape of said beam at a frequency different from and Ibearing a predetermined relation to the frequency of the rotation of said beam whereby electrons periodically strike said electrodes, and an energy extracting circuit connected to said electrodes.

'7. Electron discharge apparatus for generating high frequency oscillations comprising, an envelope, means in said envelope for producing and generally directing an electron beam including a biasing electrode, a metallic tube positioned about the path of said beam, means positioned about said tube for generating a magnetic eld parallel to the axis of said ltube for substantially the entire length ci said beam whereby said beam is rotated, a iirst electrode mounted Within said tube and within said envelope, a second electrode mounted within said tube intermediate said first electrode and said beam producing means, a resonant input circuit connected to said second electrode for controlling a radial dimension of said beam, said resonant input circuit being tuned to a frequency diierent from and bearing a predetermined relation to the frequency of the rotation of said beam, a resonant extracting circuit connected to said first electrode, and means connected to said input and extracting circuits coupling said input and extracting circuits whereby said high frequency oscillations are generated and extracted.

S. An electron discharge apparatus comprising an envelope, a metallic tube within said envelope, means positioned in the vicinity of said tube and including a cathode for producing an electron beam and directing said beam through said tube, means positioned in the vicinity of said tube for rotating said beam about a linear axis with a normally constant velocity, a first pair of oppositely directed arcuate electrodes disposed one on either side of the path of said beam and mounted in said tulbe adjacent the end nearest the cathode, a second pair of oppositely directed arcuate electrodes disposed one on either side of the path of said beam and mounted in said tube at a'point along its axis removed from said rst pair of electrodes and turned about said axis lwith respect to said first pair of electrodes, a variable voltage source connected to said iirst pair of electrodes for controlling a radial dimension of said beam whereby electrons periodically strike said second pair of electrodes, and an output circuit connected to said second pair of electrodes for extracting energy from said beam in the form of said variable voltage.

The following references are of record in the LEON N. BRIILOUIN.

REFERENCES CITED file of this patent:

Number UNITED STATES EATENTS Name Date Haei i Dec. 15, 1936 Number

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