US2697799A - Amplifying device for microwaves - Google Patents

Description

Dec. 21,1954

R. H. SVENSSON 2,697,799

AMPLIFYING DEVICE FOR MICROWAVES Filed Dec. 1, 1948 i1 2 '6 F- I FIG. 1.

7 Q Q INVENTOR. 7'

Al 1m MNARHQLMFRIDSVNSON FIG f a ATTORNEYS United States Patent AMPLIFYING DEVICE FOR MICROWAVES Regnar Holmfrid Svensson, Hammarbyhojden, Sweden,

assignor to Telefonaktiebolaget L M Ericsson, Stockholm, Sweden, a company of Sweden Application December 1, 1948, Serial No. 62,809

6 Claims. (Cl. 31539) The present invention refers to an amplifying device for micro-waves. Electromagnetic waves, especially waves with a short wave-length, so called micro-waves, have the particularity, that they readily follow the surface of metallic conductors. A micro-wave, which is caught by a wave-guide, can be made to follow a helically wound metallic wire outgoing from such a wave-guide. It is known to enclose a helically wound metallic wire in a high evacuated glass tube together with an electron gun emitting an electron beam along the axis of the helix towards a collecting anode. If the pitch and length of each turn of the helix is chosen so that micro-waves following the surface of the metallic wire are propagated along the axis of the helix with the same speed as the electrons in the electron beam, the micro-waves will actuate the electrons in the electron beam and these will, due to electrostatic induction, produce an amplified electromagnetic oscillation having the wave-length of the incoming micro-waves, which oscillation can be collected by a wave-guide at the farthest end of the helix.

It is not necessary to wind the metallic wire conducting the micro-waves as a helix, it can also be formed as a plane wave-shaped line in which the pitch and length of the individual waves is such that the component of ad vance of the micro-waves along the axis of the line substantially corresponds in velocity to that of the electron beam, or consist of a zig-zag-shapcd cutting in a sheetmetal band, along which the electron beam from the electron gun passes at the rate just defined.

The present invention refers to an amplifying device for micro-waves, in which the micro-waves are made to follow a curved conductor enclosed in an evacuated receptacle.

A tube according to the invention is provided with an elongated electron-emitting cathode arranged inside the evacuated receptacle alongside the conductor and with its axis parallel to the axis of the conductor. When working this tube is arranged in a magnetic field perpendicular to the axis of the cathode. The electrons produced by the cathode are forced by the magnetic field to move along the axis of the cathode with a speed corresponding to the speed with which the micro-waves proceed along the axis of the cathode. They are thus influenced by the micro-waves (accelerated or retarded) and may by electrostatic induction produce an amplified electromagnetic wave having the same wave-length as the micro-waves.

The invention will be more clearly described below wiah reference to the accompanying Figures 1, 2, 3, .4 an 5.

Fig. 1 shows an application of the invention for the amplification of microwaves entering through a co-axial cable.

Fig. 2 shows a section A-B in Fig. 3 of an amplifying device according to the invention.

Fig. 3 shows an application of the invention for the amplification of micro-waves caught by a wave-guide.

Fig. 4 shows in plan a wave guide comprising the edges of a sinuous slot in a sheet metal strip.

Fig. 5 is a view similar to Fig. 1 but showing in reduced scale the whole length and both ends of the amplifying device.

In Figs. 1, 2 and 5, 2 is a highly evacuated glass envelope enclosed in a metal tube 1 screening the amplifylng device from the surroundings. Only half of the amplifying device is shown, since it is symmetrical with respect to the line A--B. At each end of the glass envelope 2, there is a narrow, fused metallic tube 3, in the center of which an electron-emitting filament 4 is kept in position by a glass pearl 13 sealing the metallic tube 3. The filament 4 is the cathode of the tube. A co-axial cable with an outer conductor 6 and an inner conductor 7 is connected to each end of the tube. The outer conductors are connected to the metallic screen 1 and each of the inner conductors connected to the ends of a helically wound or wave-shaped wave-guide 8, the axis of which is parallel to that of the cathode 4 and which reduces the propagation speed of the micro-waves along the cathode to below the speed of light. The device is arranged in a transverse magnetic field, like that which appears from Fig. 2, which shows a section of Fig. 3 at AB. 12 is a magnet with the poles N and S. In Fig. 1, there is further an impedance-transformer 9 matched by means of the piston 10, and a piston 11 for matching of the metallic screen 1 to the co-axial cable and its tension. The piston 11 consists of two metallic rings insulated from each other by means of a cylindrical insulating filler. .One of the metallic rings makes contact with the screen 1 and the other with the metallic tube 3.

The device acts in the following manner. By means of devices, which are not shown in Fig. 1 but are indicated in Fig. 3 by battery 14, the cathode 4 is given a negative voltage in relation to the conductor 8. Electrons emitted from the cathode 4 are obliged by the magnetic field to move along the axis of the cathode toward the right of Fig. 1. They form cycloid-like curves. A micro-wave which enters through the co-axial cable, propagates along the conductor 8, which has such a length and pitch of individual wave bends, that the micro-wave will move with a component in the longitudinal direction of the tube 2 with substantially the same speed as the electrons emitted from the cathode. The micro-wave will influence the free electrons so that they are accelerated or retarded. If an electron is accelerated, it will return to the cathode,

. but if it is retarded it will continue along the cathode and either go to the conductor 8 or be caught by a collecting anode 20, Fig. 5, at the far right end of the tube. This collecting anode may otherwise consist of a part of the conductor 8, e. g. one or several narrow windings in a helix around the cathode 4. ,By electrostatic induction the electrons will react on the micro-wave along the condulftozr 8 so, that it will be amplified when leaving the tu e In order to increase the efficiency of the amplifying de- .vice, a focusing electrode 5 in Figs. 1 and 2 is inserted,

which electrode consists of a bar or trough stretching along the cathode and connected to the same voltage as the cathode or a negative voltage in relation to the cathode. The focusing electrode is placed so that the electrons are reflected in a direction perpendicular to the magnetic field. The focusing electrode is fixed to and metallically connected with the metal tube 3.

Figs. 2-3 show an application of the invention for a radio transmission system with micro-waves. The highly evacuated glass tube 2, the metal tubes 3, the cathode 4, the glass pearl 13, the focusing electrode 5 and the magnet 12 are the same as in the description of Fig. 1. Fig. 2 shows a section at AB through the device according to Fig. 3. The tube is screened by two metallic tubes 1a and 1b connected to each other by means of flanges between which a metallic plate 7 fused in the wall of the glass tube 2 is rigidly fixed. A wave-guide 6 and a short metallic tube 9 with an adjustable piston 10 for matching the wave-guide to its outer impedance are furthermore fastened to the metallic tube 1a. In the metallic tube 1b there is also a piston 11 made as described above for the piston 11 in Fig. l and intended for matching of the screen 1a--1b to the wave-guide 6. The device is symmetric with regard to the line A-B, as clearly shown in the small scale view of Fig. 5.

The amplifying device according to Fig. 3 acts in the following manner. A micro-wave, which has been caught by the wave-guide 6, follows the plate 7 and the conductor 8 to a transmitter wave-guide (not shown) corresponding to the wave-guide 6 and arranged at the opposite end of the metallic tube 1a. The voltage source 14 keeps the cathode 4 negative in relation to the screens 1a and 1b and the plate 7 and plane, sinuous conductor 8. Electrons emitted from the cathode and caused to proceed in cycloid-like curves along the cathode by the magnetic field from the magnet 12 in Fig. 2 are accelerated or retarded by the micro-waves propagating along the conductor 8. The electrons, which have been accelerated, return to the cathode, whilst electrons, which have been retarded, are caught by a plate corresponding to the plate 7 in Fig. 3 in the opposite end of the glass tube 2. Said plate 7 is shaped as a collecting anode. Part of the electrons will part from the cathode to the conductor 8. By means of electrostatic induction the electrons will amplify the micro-wave proceeding along the conductor 8.

Besides the two embodiments according to Fig. 1 and Fig. 3, combinations can be obtained by shaping the receiving or emitting half of the amplifying device e. g. according to Fig. 1 and the other half according to Fig. 3. It is thus possible to transmit amplified micro-waves from a coaxial cable to an antenna array or to transmit anlljplified micro-waves from an antenna array to a coaxial ca le.

Furthermore the shape of the wave guiding conductor 8 may be changed from the helix of Fig. l and the plane, sinuous conductor of Fig. 3 to the form shown in Fig. 4. Here the micro-waves are guided by the edges of a sinuous slot 8 in a plane metal strip 16 positioned above the reflecting trough 5 and the cathode 4, in the manner shown for the waving conductor 8 in Fig. 2. In Fig. 4 the connector plates 7 are shown electrically connected to the respective ends of the slot 8 in strip 16.

' means outside said receptacle producing a magnetic field perpendicular to said two axes to direct a beam of elec trons from the cathode parallel to said axes and between the cathode and wave guide, means for delivering microwaves to one end of said guide for passage therealong, means to take off amplified micro-waves from adjacent the other end of the wave guide, the length and pitch of the curves of the wave guide conductor being such that 1 the component of advance of the micro-waves parallel with said axes corresponds substantially to the rate of travel of the electronbeam along said axes.

2. The electron discharge apparatus as claimed in claim 1 in which said wave guide comprises the edges of a sinuous slot in a sheet metal strip lying wholly in a plane parallel to the direction of the magnetic field.

3. An electron tube for amplification of micro-waves comprising, in combination, a plane surface wave guide for micro-waves having wave shaped edges disposed about an axis of symmetry in said surface, an electron emitting cathode having an axis extending parallel to said axis of the guide and in all parts adjacent to said guide, a troughlike focussing electrode extending longitudinally of and adjacent to said cathode, an evacuated receptacle enclosing said guide, said cathode and said focussing electrode, means outside said receptacle producing a magnetic field perpendicular to said axis and said cathode and parallel to said surface to cause a beam of electrons emitted from said cathode to propagate along said axis between the cathode and the said guide, means delivering micro-waves to one end of said guide for passage therealong and means leading away the micro-waves from the other end of the guide, the pitch and length of the individual Waves of said edges being such that the component of advance of the micro-waves along said axes substantially corresponds in velocity to that of the electron beam.

4. In an electron tube for amplification of micro-waves as claimed in claim 3, said guide for micro-waves consisting of a zig-zag shaped conductor.

5. The electron discharge apparatus as claimed in claim 3 wherein said wave guide lies wholly in a plane surface parallel to the direction of the magnetic field.

6. The electron discharge apparatus as claimed in claim 1 5 in which said guide comprises a conductor outlining the slnuous wave form.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,013,773 Weihe Sept. 10, 1935 2,122,538 Potter July 5, 1938 2,241,976 Blewett et al May 13, 1941 2,289,756 Clavier et al. July 14, 1942 2,300,052 Lindenblad Oct. 27, 1942 2,414,121 Pierce Jan. 14, 1947 2,428,612 Blewett Oct. 7, 1947 2,511,407 Kleen et al. June 13, 1950 2,559,581 Bailey July 10, 1951 2,566,087 Lerbs Aug. 28, 1951 2,582,185 Willshaw Jan. 8, 1952 2,600,509 Lerbs June 17, 1952

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