US2798203A - Modulated electron discharge device - Google Patents

Description

y 1957 G. H. ROBERTSON 2,798,203

, MODULATED ELECTRON DISCHARGE DEVICE Original Filed April 5. 1952 FEQBOMAGA/ET/C MA TEE/AL //v VEN r02 6. H ROBERTSON A TTORNE V United States PatentO MODULATED ELECTRON DISCHARGE DEVICE George H. Robertson, New Providence, N. J., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Original application April 5, 1952, Serial No. 280,707, now Patent No. 2,691,765, dated October 12, 1954. Divided and this application February 12, 1954, Serial No. 409,806

8 Claims. (Cl. 332-51) This invention relates to electron discharge devices and more particularly to such devices of the traveling wave tube type. c I

This application is a division of application Serial No. 280,707, filed April 5, 1952, now Patent 2,691,765, October 12, 1954.

Traveling wave tubes generally comprise a transmission line, which defines an interaction circuit, and a means for projecting an electron stream along that interaction circuit. In one known type of traveling wave tube, the interaction circuit comprises a helix to which the high frequency carrier wave is coupled; in other types of traveling wave tubes, the region of interaction may be defined by a filter-type circuit or by resonators. Amplification in these tubes occurs due to the interaction of the electromagnetic waves associated with both-the helix and the electron stream in the vicinity of this interaction region. Priorly, the high frequency carrier wave hashad the modulating signal applied thereto, external to the traveling wave tube, so that it is the modulatedcarrier that is introduced to the traveling wave tube and amplified thereice the material under the control of the modulating signal. In this manner the attenuation applied to the interaction circuit is varied under control of the modulating signal to decrease the amplification in accordance with the modulating signal, whereby the carrier wave is amplitude modulated.

It is a feature of this invention that attenuation be provided in a traveling wave tube by a magnetized element of a ferromagnetic material encompassing the interaction circuit but distinct therefrom.

It is a further feature of this invention that attenuation in a traveling wave tube be provided by a solid hollow magnetized element of a ferromagnetic material encompassing the path of the electron stream in the traveling wave tube.

It is another feature of this invention that the ferromagnetic element be magnetized to be near its ferromagnetic resonance in the frequency band of the signal to be amplified.

It is still another feature of this invention that the attenuation of the traveling wave tube be varied by an externally applied signal by varying the magnetic field through the magnetized element in accordance with the externally applied signal.

A complete understanding of this invention and of these and other features may be gained from consideration of i the following detailed description together with the acin. This, of course, requires that the steps of modulation and amplification be distinct, employing separate apparatus and interconnections therebetween.

In accordance with an aspect of this invention, a high frequency carrier wave, such as may be derived from a crystal controlled oscillator, is directly introduced into a traveling wave tube and the modulating signal applied to the carrier within the tube itself. In a specific embodiment of this invention, this is attained by varying the attenuation of the interaction circuit under the control of the modulating signal.

The amplification or gain of a traveling wave tube depends on the characteristics of the wave associated with the interaction circuit, e. g., with the helix in one known form of tube, and the interaction of that wave with the electromagnetic wave associated with the electron beam. Priorly, loss has been applied to the helix or positioned adjacent thereto to attenuate the electromagnetic wave associated with the helix so that feedback due to the signal being reflected back from the output will not occur. In accordance with a feature of this invention a ferromagnetic member distinct from the helix or interaction circuit encompasses the interaction circuit and provides attenuation in the traveling wave tube. This ferromagnetic member is magnetized and advantageously in accordance with an aspect of the invention is magnetized to be near companying drawing, in which the single figure is a sectional representation of a traveling wave tube illustrative of one specific embodiment of this invention.

Referring now to the drawing, the specific embodiment et this invention depicted comprises an envelope 10,

which may be of a conducting material and in which are positioned a cathode 11, heater element 12, and accelerating electrode 13, defining an electron gun, an electron receiver 14, and a helix 15. The ends of the helix 15 are brought out through coaxial input and output terminals 17.

,, having flanges 21 at each end encompasses the cathode 11, control electrode 13, helix 15 and collector electrode 14, leads being brought from the end of the helix 15 through apertures 22 in the cylinder 20 to the coaxial terminals 17. External to the envelope 10, which is of a non-magnetic material, is positioned a long U-shaped core member 24 having its depending portions 25 facing the end flanges 21. The core 24 need only be a segment of a cylinder, or an approximation thereof, and one or several may be employed. A coil 27 is wound around a portion of the core 24, an identical coil being thus positioned for each core utilized. A voltage source 28 and the secondary 30 of the transformer 31 are in series with the coil 27. The core 24 may be of a permanent magnetic material or of a ferromagnetic material, such as ferrite, with a superimposed direct magnetic field in either case. The field strength produced by the permanent magnet and/or the coil 27 in the ferrite cylinder 20 is adjusted so that ferromagnetic resonance occurs near the frequency band of the signal to be amplified, the occurrence of ferromagnetic resonance being dependent on both field strength and frequency. Near the ferromagnetic resonance of the ferrite, the loss in the ferrite will change rapidly with the field strength. For a narrow band of frequencies to be modulated, this variation in the ferromagnetic loss, and thus in the attenuation coupled to the carrier wave, can be controlled by a modulating signal 33 applied to the transformer 31 to vary the magnetic field in the magnetic circuit of the cylinder 20 and the core 24 and thus modulate the carrier.

As the ferrite cylinder 20 entirely encompasses the helix 15 it should also be utilized to provide magnetic chosen, so. that-itsiferromagnetic resonance. occurs, at a.

value of field strength-at. least. sufficient torfocusdhe elcc-- 'tron stream.

Modulating. the carrier wave by thisspecific. illustrative embodiment of this. invention. other than, by theaother embodiments set forth in the parent application can. best beutilizedfor relatively low modulating; frequencies at. which. the hysteresis etfectswithin-the. ferromagnetic cylinder 5.0 will not be, a limiting factor..

While this invention hastbeendescrihed-with referenceto modulation ofthe-carrier wave-.in;accordancewith-a modulating signal,.i.t;is to beunderstoodjthat the impedi ance" value of} the variable,- impedance: elernenttinzenergy, coupled: relationship: may be; varied tov vary the; attenun ation at a given point or along the interaction circuit; inaccordance; with. other-than: modulating; signals... Sim: ilarly, although the; specific;-embedirnentaofithisiinvention. described above has,inc.or.p.orated.a helix as. defining the; interaction circuit, this invention is equally applicabltc to ether types .of traveling-wave. tubes wherein the electromagnetic wave'may be; slowed downin othergmanners. and the region. of interactionv thusdefined by. other struc tures, such as. by filter-type circuits. or. resonators. N r. is this invention to be considered limitedll-to, the manner; of. introduction of the.- carrier wave-inttx-the; device; as this will depend on anumbercf considerations; such: as: carrier frequency. Thus the carrier; wave. may be; con: pled to the; interaction circuit. not: only. by coaxiai tor: minals, but by wave. guides, resonatorsrgridst electron. streams, or in othergmanners knowninthevart...

Further, this invention. is not: limited to:- the inclusion with the magnetized ferromagnetic attenuating'memher of elements to vary thev attenuation ofztheiferromagnetic. member.

Itis tobe understoodthat the ahoveadescribed;arrangements are illustrative of. the-application. of the: principles. of this invention. Numerous; other arrangements, maybe devised by those skilled in the art without departing: from the; spirit and scope of; the invention.

What is claimed is:

1. An; electron discharge. device; comprising-:mcans. for. propagating a traveling. electromagnetic wave; along; an. extended path, mcansfor, projectinga streantof; electrons along said. path, means. distinct. from; said propaga ing means. for providing. attenuation along: said. path. said:

attenuation means including-fa. magnetized; element: of:

ferromagnetic material encompassing: said: path. anti-in: energy coupled relationship. with the.electromagnetictfieltl;

of said wave, and means for; applying-1 11 magnetic. field to said element. such that. the magnetic field strength;

along said path issufficient to, focus said; electron; strearnt.

2. An electron discharge device. comprising; means. for propagating a traveling electromagnetic wave along. an extended path, means for, projecting a stream; of electrons. along said path, means for providingattenuation along said path, said last-mentioned. means including a solid; hollow magnetized element of ferromagnetic. material encompassing said path, and means applying; a magnetic. field to said element to focus saidelectron; stream, whereby said hollow element. both. provides. said. attenuation and serves as a flux. guide. for. the focusing magnetic. field.

3. A, traveling wave tube comprising electrical con: ductor means defining an interaction circuit, means for projecting a stream of electrons along said circuit, means for introducing a carrier wave to said circuit, and means for providing attenuation of said wave along said circuit, said last-mentioned means including a magnetic member encompassing said-conductor and means for magnetizing said magnetic n1embe r,. said, magnetizing, means. includingmeans for-providing aisufilcient field strengthin said member for focusing saidelectronstream.

4. A traveling wave tube in accordance with claim 3 wherein said magnetic member is of, a ferrite material.

5. A traveling wave tube in accordance with claim 3 wherein said'means for magnetizing said magnetic member comprises means for providing a magnetic field strength in said member-such that. said'member is near ferromagnetic resonance.

6. Anaelectron discharge. evi cmpr singmeans defining -;an. interaction. circuit, me ns. f prei ting. a

stream of electrons along said circuit, means for; intro-.

ducinggalcarrier; wavete said; circuit, n me n for: ying the amplitude; oh said carrier; wave, saidlast-mentioned means comprising a first magnetic element having a variable, ferromagneticloss characteristic in energy coupled relationship-with. the electromagnetic field, of

said carrier, fl2SC Ildt i gI1Q element. a j n id: fir magnetic element-and; defining; a magnetic; circuit therewith,;and; means-for varying themagnetic field strength in said magnetic, circuit to; vary-the.- ferromagnetic loss, insaidfirst. magneticelementi' 7'. Anelectron discharge deyice-compr-ising means defining an; interaction, cir uit-cmeansfor: projectinga stream of; electrons.v along said cireuiti means f r. introd cing a carrier: Wave to, said cireuit, and'means, for; varying the attenuation along said circuit, saidlast-mentioned meanscomprising; at ferrite; member having a variable, ferromagnetic lossmharacteristicnfiarferromagnetic resonance, saidferrite mom-hen being adjacent said circuit, a, magnetic"memberaadjacent,said ferromagnetic member; and defining a magnetiocircuit therewith, means for providing a magnetic field, strength. in said magnetic circuit such thatsaildrfenritei member. is; near: ferromagnetic resonance, anti-means for;-varying-said field strength.

8. An electron, discharge, device; comprising means defining an-;interactioni circuit-,electrOn gunmeans for projecting. astreanr-of'electrons along said circuit, meansforintrodncinga carrierwayejto said; circuit; and. means for: varying the. attenuation. along said circuit, said last-.

References; Cited in the-file. of this patent UNITED STAT ES PATENTS 2,197,123 King; Apr. 16, 1940 2,602,148 Pierce July 1, 1952 2,629,079 Miller etal. Feb. 17, 1953 2,645,758 'Lindt" July 14, 1953.

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