Патент USA US3068387код для вставки
Dec. 11, 1962 _ C. K. BIRDSALI.. ETAL 3,068,377 ELECTRON DISCHARGE DEVICE Filed March 7. 1955 „QQN IN VEN TORS United States Patent Oñfice 1 3,068,377 Patented Dec. 11, 1962 2 24. 3,062,377 ELECTRON DISCHARGE DEVICE Charles K. Birtlsall, Los Angeies, and George R. Brewer, Palos Verdes Estates, Calif., assignors to Hughes Air craft Company, Culver City, Calif., a corporation of Delaware Filed Mar. 7 1955, Ser. No. 492,664 1 Claim. (Cl. 315-36) Cathode 24 is maintained at a potential consider ably below ground by a source of potential 34 having its positive terminal grounded. A voltage of the order of 1000 volts with respect to ground is representative of the voltage normally impressed upon cathode 24 by source 34. Focusing electrode 28, which is connected to the negative terminal of battery 32, may have a frusto-conical internal surface of revolution disposed at an angle of 671/2 degrees from its axis of symmetry. This invention relates to microwave tubes and more Anode 30 is maintained at a potential a few hundred particularly to a high-gain traveling-wave tube amplifier. volts positive with respect to the potential of cathode v As microwave tubes find application in new fields, it isfrequently desirable to obtain as much gain as pos 24 by a connection to a tap 33 on potential source 34. sible from such tubes. A certain known but unavoid able input or electromagnetic excitation loss in a travel ing-wave tube amplifier reduces gain. The loss takes place when the total input energy divides into three for ward waves. .Only one of the waves exists as a grow ing Awave and hence vthe energy divided between the two other waves becomes a total loss. 20 It is therefore anv object of the invention to provide a relatively high-gain traveling-wave tube. , It is another object of the invention -to provide means whereby the radio-frequency input loss in a traveling wave tube- ampliiiermay be reduced. . In accordance with the present invention, a relatively» A solenoid 54 is axially positioned symmetrically about the envelope 20. An appropriate direct current is maintained in solenoid 54 by means of a potential source, such as a battery 56, so as to produce an axial magnetic field of the .order of 100() gauss within the en velope 2li to constrain the electron stream produced by gun 22. . Proceeding along from the electron gun 22 in the direction of electron ilow, there are positioned succes sively about the path of the electron stream, a matching input ferrule 58 connected by an input antenna lead 60. to an input helix 62, a principal helix 63 which is,rin turn, connected by an output antenna-lead 64 to a match-l ing output ferrule 66, and a collector electrode 68 which short input helix anda relatively long principal helix is positioned at the end of the path so as -to collect the stream electrons. Electromagnetic wave energy is cou are maintained at different average direct-current po pled from input helix 62 to principal helix 63. by means tentials in a traveling-wave tube. The potential of the input helix is maintained at a value which will provide 30 of a coupling helix 65 which is disposed about the adja maximum gain at the output end of the principal helix cent ends of input and principal helices 62 and 63. but generally at a lower potential than that of the prin Coupling helix 65, however, has a pitch angle negative.y with respect to but approximately equal in magnitudeî cipal helix in order to minimize the radio-frequency to that of input and principal helices 62 and 63 to pro-, input loss of the tube for the production of maximum gain.> The principal helix is then maintained at a po-- 35 vide the desired coupling and may be spaced about the4 tential for optimum gain. Means are also provided to outside of envelope 20 as shown. What is meant by ay negative pitch angle is that the coupling helix has op couple electromagnetic wave energy from the input helix to the principal helix. posite screw sense to that of input and principal helices The novel features which are believed to be character istic of the invention, both as to its organization and 40 method of operation, together with further objects and advantages thereof, will be better understood from the following description considered in connection with the accompanying drawing in which several embodiments 62 and 63. All of the helices, which serve as the slow-wave cir-~ cuit for the traveling-wave tube 10, preferably are made of a material such as tungsten or molybdenum, the prin cipal requirement being that they retain their form, especially with respect to the ratio of their pitches toV of the invention are illustrated by way of example. It 45 their diameters. In accordance with the present inven-l tion, input and coupling helices 62 and 65 are main is to be expressly understood, however, that the draw tained at a suitable fixed potential which may be ground., ing-is for the purpose of illustration and description Coupling helix 65 is connected directly to ground only, and is not intended as a definition of the limits whereas input helix 62 is connected to ground through of the invention. ' FIG. 1 is a sectional view of an embodiment of the 50 input antenna-lead 60 and input ferrule 58. Alterna tively, coupling helix 65 may be maintained at the traveling-wave tube amplifier of the invention shown with associated circuitry; and Y FIG. 2 is a broken section of a traveling-wave tube in which an alternative embodiment of the invention same potential as that of principal helix 63, or at a cer-A tain potential between those of input helix 62 and prin cipal helix 63. Principal helix 63 is maintained at a 55 potential somewhat positive with respect to ground by4 is illustrated. t’ Referring to the drawing, in FIG. l an embodiment a connection from output ferrule 66 to the positive ter of the microwave amplifier of the invention is shown minal of a potential source 69, the negative terminal of which is grounded. comprising a traveling-wave tube 10 including an input matching cavity 12 having a coaxial input cable 14 As previously mentioned, input and principal helices connected thereto and an output matching cavity 16 60 62 and 63 are connected to ferrules 58 and 66 by leads connected to a coaxial output cable 18. An envelope 60 and 64, respectively. Leads 60 and 64 are located 20, which provides the evacuated chamber of traveling parallel to the electric fields excited within matching wave tube 10, consists of a long cylindrical structure cavities 12 and 16. Matching cavity 12 has the con which has an enlarged portion at its left extremity as figuration of a rectangular toroid with a concentric col 65 lar 70 disposed about and spaced from matching ferrule illustrated in FIG. 1. Within the enlarged portion at the left extremity of 5S. An opening 72 is provided in the end plate of the envelope 20, there is located an electron gun 22 for cavity 12 facing the left end of input helix 62. Cavity developing an electron stream. Gun 22 comprises a 16 is similarly constructed, having a corresponding con cathode 24 with a heater 26, a focusing electrode 2S centric collar 74 arranged about and spaced from match and an accelerating anode 30. Heater 26 is connected 70 ing (ferrule 66 and an opening 76 facing the right end across a source of potential, such as battery 32, the negative side of heater 26 being connected to cathode of principal helix 63. _ The center conductor 78 of coaxial input cable 14 ex Secam? 3 tends through an aperture in the annular wall of cavity 12 and is connected to concentric collar 70 while the outer conductor of cable 14 is bonded to the periphery of the aperture. Likewise, the center conductor 80 of coaxial output cable 18 extends through an aperture in the annu lai’ wall of cavity 16 and is connected to concentric collar 74 while the outer conductor of a cable 18 is bonded to the periphery of the aperture, in the same manner as be fore, or vice-versa. Cavities 12 and 16 are fabricated ¿il second and P is the pitch angle of the helix, [P] being the absolute magnitude of the pitch angle. The pitch angles of helices 122 and 124 should therefore be approximately equal in absolute magnitude but may be opposite in sign. A helix is not, of course, the only type of slow-wave structure which may be used with the tube of the present invention. Numerous other types, such as a disc-loaded with an inner surface composed of highly conductive ma waveguide, are illustrated in chapter IV in “Traveling Wave Tubes” by J. R. Pierce, D. Van Nostrand and Co., New York, 1950. An input section and a principal sec terial and are broadly resonant so as not to limit the tion of a slow-wave structure there illustrated may be in frequency bandwidth of operation. sulated from each other, e.g. with a dielectric ring. In that case means for maintaining the sections at different The configuration shown and described for the cavities 12 and 16 in the drawing, provides suitable impedance matching from in direct-current potentials and means for coupling electro put and principal helices 62 and 63 to coaxial cables 14 15 magnetic energy from one section to the other may be and 18, respectively, over a range of frequencies such as, provided in accordance with the present invention. for example, from 2000 to 4000 megacycles per second. An electromagnetic wave coupled from external cir The stream electrons are intercepted by collector 68 at cuitry into a conductive helix will cause alternating-cur the opposite extremity of envelope 20 with respect to elec rent velocity modulation to exist on the beam of electrons tron gun 22. A potential of the order of 200 volts posi directed therealong. Part of the input signal energy thus tive with respect to ground may be applied to collector 68 is used to excite space charge waves on the electron in order to prevent secondary electrons, which' may be stream. These waves interacting with the stream cause produced by the stream electrons impinging on its- surface, the total tìeld to’ be represented by three forward propa from reaching principal helix 63 or ferrule 66. This po gating wavesä Approximately one-third of th'e‘input sig tential isîapplied by means of a connection from collector 25 nal energy will be found in each of these wavesv while only 68 to the positive terminal of a source 84', the negative that in the growing wave is extracted as useful output terminal of whichis grounded. energy.V An apparent “loss” in energy at the inp'ut of the In the operation of the' tube 10, an input signal to be tube is thus realized. Y amplified i's applied through coaxial input cable 14 to in As the three excited waves travel along the helix, they put cavity 12. The input wave in flowing along the ex 30 interact in such away that their total “voltage” varies posed portion of conductor 78 within cavity 12 excites an along the helixv and in addition the character ofthe totall electromagnetic field within that cavity. This ñeld in wave as evidenced by the phase relationships between the' duces a corresponding current in antenna-lead 60 connect voltage and current changes. If the helix is severed into' i'ng‘input'ferrule 58 to input helix 62 to launch a traveling two portions at some point while preservingv radio-fre' wave' along the'input helix 62. Interaction between the 35 quency continuity along the two portions of the helix, by electron stream and the traveling-wave ultimately results adjusting this inter-wave interaction a wave of any d‘e in a net transfer of energy from the stream to the wave sired character may be derived from the first portion to causing it to “grow” or be amplified. The wave suffers feed the second portion of the severed helix. The charac a relatively small coupling loss in the transition from ter o-f the wave may be modiñed to approximate the grow input helix 62 to principal helix 63. However, the com 40 ing wave on the second helix portion in which case 'a bined coupling losses will be less than the excitation loss larger proportion of the signal energy may go into the of a single helix of the same length if an appropriate length growing wave. This results in greater signal gain. The and operating potential of input helix 62 are selected. inter-wave interaction on the input helix can be further AtV the right end of input helix 62, wave energy is coupled from input helix 62 to principal helix 63 by coupling helix 65 thereby insuring the continuity of the adjusted for optimum performance by adjusting the direct current voltage of the iirst helix. ì cipal helix 63, the amplified electromagnetic wave, in flowing along output antenna-lead 64 connecting output In order to better understand the operation of the traveling-wave tube of the invention, it is desirable to re view the gain equation of a traveling-wave tube. This equation is as follows: helix 63 to output ferrule 66, excites an electric field in cavity 16. This electric field induces a corresponding out put signal on center conductor 80 of coaxial cable 18. where A` is the total loss factor of the tube; B='54'..6x1v wave traveling along on the helices. At the end of prin G=A+BCN (2) Wave energy may be coupled from the isolated input where x1 is the real part of an incremental propagation' helix 62 to the principal helix 63 in a number of ways. For example, in FIG. 2 a broken section of an evacuated constant 61 of the growing wave; C is a gain parameter of envelope 120 is illustrated housing an input helix 122 wavelengths, i.e., the length of the tube divided by the’ electronic wavelength ke'=u0/f, where uo is the direct current electron velocity, and f is frequency. Of the three waves propagated along the helix the’ 60 growing wave is the principal contributor to the useful> which is disposed about a principal helix 124. The en vlelopeV 120 is contracted at its _right end whereby it is disposed contiguously about both helices 122 and 124, input’ helix 122 having a larger diameter than that of principal helix 124. Input helix 122 may be disposed contiguous to a portion of principal helix 124 to provide optimum electromagnetic coupling. Both of the helices the tube; and N is the length of the tube 1n electronic output power of the circuit or helix at the output end of the traveling-wave tube. v ` n . . The loss factor A of the traveling-wave tube 10' 1s given 122l and 124 may then be appropriately tapered at their mutual coupling ends. It is to be noted that input helix 65 122 has a negative pitch with respect to principal helix where A1 is the apparent loss suffered by the input signal 124; in modulating the electron stream, A2 is the loss suffered The principal requirement in coupling wave energy in by the output wave because not all of the energy stored this manner is that all helices must propagate waves of in the electron stream can be coupled out to the helix frequencies within the operating frequency band at sub 70 and thus to the load, and, A3 is the coupling loss between stantially the same velocity. The propagation velocity helices. v1', is given approximately by When designing the amplifier of the invention, helices 62, 63 and 65 may'have approximately the same absolute (1) pitch. Helices 62 and 63 may have equal diameters. where cis the velocity of light or 3 X1010 centimeters per 75 The actual pitch and diameter of helicesV 62 and 63 will 3,068,377 5 6 gun including a cathode maintained at a predetermined reference potential for producing an electron stream, means for directing said stream along a predetermined path, a collector electrode disposed opposite said electron gun to intercept the stream electrons, an input helix be determined by the operating frequency range oir band fof the traveling-wave tube 10. The length of principal helix 63 will generally be determined by the radio-fre quency power output or gain required of the traveling wave tubelt). Principal helix 63 will be maintained at a potential to produce `a maximum x1 in order to obtain disposed about said path adjacent said electron gun for propagating an electromagnetic wave at a predetermined maximum gain from the tube 16. A2 is unaffected by changes in the length or potential velocity, said predetermined velocity being small in com parison to the velocity `of light, a principal helix electro optimum length iand direct-current potential of input 10 magnetically coupled to said input helix and disposed be tween said input helix and said collector electrode for helix 62, it is necessary to plot the length of input helix propagating said electromagnetic wave, means for main 62 as a `function of taining said principal helix at a predetermined direct~ of input helix 62. However', in order to determine an current potential producing maximum amplification of If a family of curves are thus plotted for ditïerent values said electromagnetic wave, and means for maintaining said input helix at a predetermined direct-current potential minimizing the coupling loss to Said input helix and be tween both of said helices with regard to the growing wave portion of said electromagnetic wave. of the direct-current potential of input helix 62, then minimum loss, A40, may be plotted as `a @function of tube length. In this manner, an optimum length for the helix 62 may be found where A40 is itself a minimum. By using the optimum length, loss A4 may again be plotted as a function of the direct-current potential of the input helix 62. in this manner, an optimum direct-current potential may ybe ascertained making signal gain a maximum. It has been determined experimentally that when two helices having an electromagnetic coupling, such as the 25 helices 62 `and 63, having coupling helix 65, are insulated References Cited in the tile of this patent UNITED STATES PATENTS 2,588,831 2,660,689 2,694,159 Hansell _____________ ._ Mar. l1, 1952 Touraton et al _________ __ Nov. 24, 1953 Pierce ________________ __ Nov. 9, 1954 1,053,556 France ______________ __ FOREIGN PATENTS from each other in a traveling-wave tube, a substantial improvement in the gain of the tube may be obtained. The invention is thus borne out both in theory and in practice. What is claimed is: A traveling-wave tube ampliñer comprising yan electron 30 ept. 30, 1953 OTHER REFERENCES Article by P. D. Lacy, pages 132 to 135, Electronics for November 1954.