US2578434A - High-frequency electron discharge device of the traveling wave type - Google Patents

Description

Dec. 11, I951 N, UNDENBLAD 2,578,434

HIGH-FREQUENCY ELECTRON DISCHARGE DEVICE OF THE TRAVELING WAVE TYPE Filed June 25, 1947 3 Sheets-Sheet 1 Rf. INPUT INVENTOR.

nus E. LINDENBLAD ATTORNEY Dec. 1-1, 1951 N. E. LINDENBLAD 2, 8,

HIGHJREQUENCY ELECTRON DISCHARGE DEVICE OF THE TRAVELING WAVE TYPE Filed June 25, 1947 3 Sheets-Sheet 2 .//3- soomg MPER MPER Ol-ORDER 0F 0mm l00-l250llM$ 100-125 OIIMS 1004250 1415 55mm Ill/IVDRFD INVENTOR.

o/ms NILS E. LINDENBLAD 1951 N E LINDENBLAD 2,573,434

H'IGHFREQUEN CY ELECTRON DISCHARGE DEVICE OF THE TRAVELING WAVE TYPE Filed June 25, 1947 3 Sheets-Sheet 3 m: m/pur ;9- MAGNET/L m5 FIELD COIL R. F. M/Pl/T LIA/E /8 l l l Rf. UI/TPUT ZINE INVENTOR.

NILS E LINDENBLAD BY [W83 I ATTORNEY Patented Dec. 11, 1951 HIGH-FREQUENCY ELECTRON DISCHARGE DEVICE OF THE TRAVELING WAVE TYPE Nils E. Lindenblad, Port Jefferson, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Application June 25, 1947, Serial No. 756,851

17 Claims. 1

This invention relates to improvements in electron discharge devices of the growing wave type, especially adapted for use at ultra and very high frequencies.

An object of the invention is to provide an improved electron discharge device capable of amplifying a wide band of high frequencies and which does not depend upon resonance phenomenon in the output circuit.

Another object is to provide a growing wave (sometimes called a traveling wave) type tube having an outer metallic shell or envelope sur' rounding a helical or spiral line, and Which is of such geometric configuration as to gradually change the characteristic impedance of the helical line from a relatively high value in the center of the line to a lower value near the ends of the line.

A further object is to enable the terminals of a helical conductor in a growing Wave type tube to match the characteristic impedance of connecting coaxial transmission lines.

A still further object is to provide a wide band helical line type of growing wave amplifier tube for use at high frequencies, which prevents or minimizes the occurrence of parasitics at very high frequencies outside the range of frequencies to be amplified.

A detailed description of the invention follows in conjunction with the drawings, wherein:

Figs. 1, 3 and 4 show three diflerent embodiments of the invention, and

Figs. 2a to 2 inclusive show six different types of coupling or impedance transformation circuits which can be used between the terminals of the amplifier tube of the invention and the connecting coaxial transmission lines.

Referring to Fig. 1 in more detaiLthere is shown a wide band growing wave amplifier tube of the broad general type described in my U. S. Patent No. 2,300,052, granted October 27, 1942, and in my copending application Serial No. 724,330, filed January 25, 1947, in which a helical conductor surrounds a stream of electrons and i in energy coupling relation thereto. The improved amplifier tube of Fig. 1. comprises a tubular non-magnetic metallic envelope or shell it! which surrounds a helical conductor II. A suitable cathode is provided at one end of the tube for furnishing a concentrated heavy stream of electrons which pass through the interior of the helical conductor I I and which is finally collected by a. collector electrode 2. at the other end. of the tube; This cathode is. shown, by way of example. as comprising a cylinder I4 which has only a portion l5 thereof sprayed with electron emitting material. A repeller electrode It at the cathode end of the tube serves to repel or concentrate the electrons emitted by the cathode toward the helical conductor II. A magnetic field coil I'I surrounds the tube and is energized by a direct current source I8 in series with a variable resistor I9. The field coil is so arranged that the lines of fiux extend parallel to the tube in an axial direction in order to focus the beam of electrons along the center of the tube. It should be noted that the repeller electrode it is maintained at a negative potential relative to the cathode, while the collector electrode I2 is maintained at a slight positive potential relative to the cathode. In the construction of the tube, it may be desirable for the collector electrode t be at a slight negative potential relative to the cathode or even at the same potential as the cathode. The metallic envelope iii is at ground potential which is equivalent to a positive potential with respect to the cathode. A coaxial transmission line I3 supplies radi frequency input current to one terminal of the helical conductor II, while the amplified current is abstracted from the other terminal of the helical conductor I I by an output coaxial line 20.

In order to assure a vacuum tight shell or envelope Ill, glass beads 21 are provided in the input and output coaxial lines at a location nearshell Ill. Obviously, the glass beads can be positioned at any suitable location.

The helical conductor I I is a plurality of wavelengths long peripherally along the helix at the center frequency of operation. The input energy supplied to the helix II by input line I3 causes the electrons passing through the interior of the helix iI to be bunched. The helix II has such dimensions as to couple properly with the electron stream passing along the axis.

The characteristic impedance of this helical conductor is of the order of several hundred ohms, whereas the characteristic impedances of the coaxial lines I3 and 2c are each of the order of 50 ohms, as an example. In order to match the impedances of the coaxial lines I3 and 29 to the characteristic impedance of the helical conductor I I, to prevent the production of standing waves due to reflections at the junction between the lines it and 20 and the conductor Ii, the metallic envelope it is tapered in diameter toward its ends so as to reduce the characteristic impedance of the helical conductor I I gradually oaxial lines to which it is connected. In order to taper the impedance of the helical conductor I I down to approximately 50 ohms, which is assumed to be the impedance of the coaxial lines, the distance between the last turn of the coil II and the siurounding tapering shell I should be of the order of the radius of the wire constituting the coil II. Because this might be difiicult to achieve in practical conditions due to the very close spacing required, it will sometimes be more convenient not to taper the characteristic impedance of the helical conductor II down as far as 50 ohms, but rather to a value of the order of 100 to 125 ohms, in which case the spacing between the last turn of the coil II and the tapering envelope I8 can be larger. In this last case, it is advisable and preferred that a transmission line link having tapering impedance be inserted externally of the tube between the last turn of the coil I I and the 50 ohm coaxial line.

Figs. 2d, 2e and 2f show three difierent arrangements for connecting a transmission line link having tapering impedance between the last turn of the coil I! and a 50 ohms coaxial transmission line shown as I3 in Figs. 203, 2c and 21. In Fig. 2d the transmission line link or impedance transformer, so to state, is labeled 25 and has an inner conductor of gradually increasing diameter. It should be noted that the length of the transmission line 25 is of the order of two wavelengths at the mean operating frequency. The inner conductor of the link 25 is relatively small at the end connected directly to the coil II and increases in diameter to a maximum at the end connected to the coaxial line I3. The gradual change in diametric ratio between the inner and outer conductors of the link 25 elfects the impedance transformation. Fig. 2c shows an arrangement equivalent to that of Fig. 2d, the difference being that this link identified as 25' has the outer conductor changing in diameter rather than the inner conductor. In Fig. 2f the transmission line link is identified as 25" and has an inner conductor which is coiled and has closer spacing between turns thereof near the helical conductor II than near the coaxial line I3. The

. radius of the spiral may also be made smaller as the pitch increases. The outer conductor diameter may also taper down in this direction. The three arrangements of Figs. 2d, 2e, and 2 are equivalent to each other and show an impedance transformation means for coupling the low impedance coaxial line I3 to the higher impedance terminal of the helical conductor II.

It should be understood that the arrangements of Figs. 2d, 2e and 2 may be used at both terminals of the helical conductor II, when the characteristic impedance of the helical conductor is not lowered to a point where it exactly matches that of the coaxial line to which it is connected. The arrangements of Fig. 1 as shown, or in combination with coupling circuits of Fig. 2d, 26 and 2f insure substantially perfect impedance matching between the helical conductor I I and the input and output lines for all frequencies which can be amplified by the growing wave tube. The helical coil I I is designed to have as low attenuation as practical without enabling undesired refiections along the coil I I to produce parasitics.

Figs. 2a, 2b and 20 show arrangements which can be connected to the input and output radio frequency carrying lines for assuring suitable ground return. In Fig. 2a the coaxial line is shown connected to a folded dipole 30. Fig. 2b shows the coaxial line connected to a suitable wave guide 3| for receiving input waves from iii 4 the wave guide or supplying amplified output waves to the wave guide. Fig. 2c shows a quarter Wave stub 32 connected between the terminal of the helical conductor II and a sleeve type antenna 33.

In the arrangements of Figs. 2a to 21 inclusive only those portions of the growing wave amplifier tube of the invention have been shown which are necessary for an understanding of the principles involved. Thus, in these figures the conical tapering end of the metallic shell has been shown and only a few turns of the helical con ductor II near one of its terminals. It will be understood that the remaining portion of the growing wave amplifier tube not shown in these figures may take the form shown in Fig. 1, or those of Figs. 3 and 4 described hereinafter.

In constructing the growing wave vacuum tube in accordance with the invention, it is advanc tageous to provide a coil II which has no loss at the frequencies to be amplified, so that as much as possible of the kinetic energy of the bunched electrons can be transferred to the working load. At other frequencies, it is of course irnmaterial whether a loss occurs internally or ex ternally of the tube. The arrangement, however, should be such that sufiicient loss is introduced to prevent parasitic oscillations, and one way that this can be done is by employing external trap circuits or deflecting circuits which will connect artificial loads (damping circuits) to the tube.

Fig. 3 shows an arrangement employing the principles of the invention, wherein parasitics can be prevented at very high frequencies out--' side the range to be amplified at which the conducting metallic shell IU may provide undesired. cavity resonance conditions. This is done by employing reactive impedance elements in the form of absorber resistors 5s connected to ca-' pacity pick-up plates 5|. These pick up' plates- 5] are uniformly distributed along at least a substantial portion of the length of the helical conductor II and have such dimensions that their reactance is very high in the operating frequency range but becomes low at frequencies higher than the highest operating frequencies. At these frequencies higher than the operating frequency, the low reactance between the helical conductor I I and the capacity pick-up plates will. permit sumcient current to pass into the resis tors 50 to introduce the desired damping effect to prevent the production of standing waves on the conductor II.

The tube, with reactive impedance elements distributed along the helical conductor, as shown in Fig.3, is claimed in my divisional applica' tion Serial No. 229,072, filed May 31, 1951.

Fig. 4 shows another embodiment of the in-' tor II is connected to the input coaxial line.

I3, while the other end is terminated by a resistor I0 whose value matches the characteris tic impedance of the helix II at that end. A suitable metallic partition having an aperture BI therein serves to separate the twochan bers. cathode 81! provided with a repeller electrode III,

The output chamber includes a second.

ductor along the axis of said tube, means for projecting a stream of electrons coaxially with respect to said helical conductor, a hollow cylindrical non-magnetic metallic element also positioned coaxially with respect to said helical conductor and spaced therefrom and extending over substantially the entire length of said helical conductor, the spacing between said cylindrical metallic element and said helical conductor decreasing from a point intermediate the ends of said helical conductor toward one terminal of said helical conductor, whereby the characteristic impedance of said helical conductor changes over that portion of the length thereof measured from said intermediate point toward said one terminal, and a line adapted to carry radio frequency currents coupled to said one terminal.

7. An electron discharge device comprising a helical conductor, means for projecting a stream of electrons through the interior of said helical conductor, a metallic shell surrounding said helical conductor over substantially the entire length thereof and spaced therefrom, the spacing between said shell and said helical conductor increasing from both ends of said helical conductor toward spaced points intermediate the ends of said helical conductor, the diameter of said shell being uniform between said spaced points, means for producing a magnetic field having fiux lines running parallel to the axis of said helical conductor, and coaxial transmission lines having characteristic impedances different from that of said helical conductor coupled to-both ends of said helical conductor.

8. An electron discharge device as defined in claim 7, wherein said shell is the outer envelope of said device, and means are provided for sealing said envelope at the locations where said transmission lines join with said envelope.

9. An electron discharge device comprising first and second chambers placed longitudinally end-to-end, the side walls of said chambers being constituted by a continuous cylindrical inetallic tube, means for projecting a stream of electrons from one chamber into and through the other chamber, a helical conductor in each of chambers in energy transfer relation to said stream, the side walls of each chamber being spaced from the helical conductor contained therein, the spacing between the side walls of each chamber and the enclosed helical conductor being non-uniform and increasing from one terminal of the helical conductor toward a point intermediate the ends of said helical conductor, and a radio frequency carrying medium coupled to said one terminal. Y

10. An electron discharge device comprising first and second chambers placed longitudinally end-to end, the side walls of said chambers being constituted by a continuous cylindrical metallic tube, means for projecting a stream of electrons from one chamber into and through the other chamber, a helical conductor in each-of said chambers in energy transfer relation to said stream, the side walls of each chamber being spaced from the helical conductor contained therein, the spacing between the side Walls of each chamber and the enclosed helical conductor being non-uniform and increasing from one terminal of the helical conductor toward a point intermediate the ends of said helical conductor, a radio frequency input coaxialline coupled to said one terminal of one helical conductor, and a radio frequency output coaxial-line coupled to said one terminal of the other helical conductor.

11. An electron discharge device comprising first and second chambers placed longitudinally end-to-end, an apertured partition between said chambers for enabling electrons to pass therethrough, a cathode near that end of said first chamber farthest removed from said partition, and a cathode in said second chamber at a location near said partition and shielded by said partition from said first cathode, whereby the electrons emanating from the cathode in said second chamber add to the electrons emanating from said first cathode and passing through said partition.

12. An electron discharge device comprising first and second chambers placed longitudinally end-to-end, an apertured partition between said chambers for enabling electrons to pass therethrough, a cathode near that end of said first chamber farthest removed from said partition, and a cathode in said second chamber at a location near said partition, whereby the electrons emanating from the cathode in said second chamber add to the electrons emanating from said first cathode and passing through said partition, means for focusing the electrons from said cathodes into a stream passing in one general direction, and a helical conductor in each of said chambers positioned to be in energy coupling relation to said stream.

13. An electron discharge device comprising first and second chambers placed longitudinally end-to-end, the side walls of said chambers being constituted by a continuous cylindrical metallic tube, a helical conductor in each of said chambers positioned around the axis thereof, said chambers being separated by an apertured partition for enabling electrons to pass therethrough, a cathode in said first chamber arranged to pass a concentrated stream of electrons through the interior of the helical conductor in said first chamber and through the apertured partition, and a cathode in said second chamber located near said partition for producing additional electrons which add to the electrons from said first chamber for passing through the interior of the helical conductor in said second chamber, said helical conductors being in energy transfer relation to said electron stream, an input circuit coupled to the helical conductor in said first chamber, and an output circuit coupled to the helical conductor in said second chamber.

14. An electron discharge device as defined in claim 9, wherein said means for projecting a stream of electrons includes a cathode in each of said chambers.

15. An electron discharge device adapted to operate over a predetermined frequency range comprising a helical conductor, means for projecting a stream of electrons through the interior of said helical conductor, said helical conductor being positioned to be in energy coupling relation to said stream, a metallic shell surrounding said helical conductor and spaced therefrom, a transmission line having a characteristic impedance different from that of said helical conductor and coupled to said helical conductor, the spacing between said shell and helical conductor gradually decreasing from a point intermediate the ends of said helical conductor to the junction point of said line and helical conductor, a plurality of spaced capacity pick-up elements spaced from said helical conductor and connected to said shell through absorber elements, the re-- actance values of said pick-up elements being relatively high in said operating range of said discharge device and relatively low at frequencies higher than the highest operating frequency of said range.

16. An electric tube comprising a helical conductor effectively divided into two parts, means for projecting a stream of electrons coaxially with respect to said helical conductor and over substantially the entire length thereof, a hollow metallic shell surrounding said helical conductor and spaced therefrom, the diameter of said shell increasing from opposite ends of said helical conductor to spaced points intermediate said opposite ends, the diameter of said shell between said points being uniform, an input circuit coupled to one end of said helical conductor and an output circuit coupled to the opposite end of said helical conductor.

17. An electron discharge device comprising first and second chambers placed longitudinally end-to-end, an apertured partition between said chambers for enabling electrons to pass therethrough, a cathode near that end of said first chamber farthest removed from said partition, and acathode in said second chamber at a loca- 10 tion near said partition and shielded by said partition from said first cathode, whereby the electrons emanating from the cathode in said second chamber add to the electrons emanating from said first chamber and passing through said partition, means for focusing the electrons from said cathodes into a stream passing in one general direction, and a helical conductor in each of said chambers positioned to be in energy coupling relation to said stream.

NILS E. LINDENBLAD.

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

UNITED STATES PATENTS Number Name Date Re. 21,739 Llewellyn Mar. 4, 1941 2,103,507 Zworykin Dec. 28, 1937 2,233,126 Haeff Feb, 25, 1941 2,289,756 Clavier et a1. July 14, 1942 2,300,052 Lindenblad Oct. 27, 1942 2,367,295 Llewellyln Jan. 16, 1945 2,409,913 Tonks Oct. 22, 1946

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