US2911555A - Traveling-wave tube - Google Patents

Description

Nov. 3, 1959 s. sENslPr-:R ETAL TRAVELING-WAVE TUBE Filed Sept. 4, 1957 TRAvELING-WAVE TUBE Samuel Sensiper and Lem Wong, Los Angeles, Calif., as-` signors to Hughes Aircraft Company, Calif., a corporation of Delaware ApplicationSeptember 4, 1957, Serial No. @2,024 `11 claims. (cl. 315-35) Culver City,

This invention relates generally to microwave electron discharge devices and more specifically to'traveling-wave tubes utilizing ferrites for nonreciprocal attenuation.

Traveling-wave tubes generally comprise a slow-wave structure, such as a helix, or its electrical equivalent, for effectively decreasing the velocity .of `propagation of microwave energy along a predetermined path such as 4the axis of the helix. A stream of electrons is then projected through the helix along its length and if the stream velocity is slightly greater than that of the axial propagation of the traveling waves, a pushing or amplification may be achieved; It has been found further that more than one helix may be employed so as to carry more microwave current. wound helices having equal but opposite pitches may be utilized for greater current capacity, as well as for other advantages, for example, greater mechanical strength. An electrical equivalent of contrawound helices is a structure composed of a series of short cylinders coaxially aligned and interconnected with each other by short axial conductors secured between diametrically opposed points on the cylinders. The manner of connection of the conductors is such that alternate 'axial segments lie along one side of the slow-wave structure, while a like set of alternate axial segments lies diametrically opposite along the slow-wave structure.

Such slow-wave structures are exceedingly broadband. 'Ihere is, however, no practical scheme 'for impedance matching input and output transmission lines to provide an equivalent broadband response; that is, transmission line impedance matching devices create objectionable reflections throughout a major portion of the frequency range of the traveling-wave tube. A portion of the microwave energy amplified along the slow-wave struc- -ture may be reflected back from the output end toward the low signal level input end from whence it may be again reflected and amplified by the tube. These successive reliections may well give rise to regenerative oscillations which at least diminish the useful frequency range of the tube. Such regenerative build-up may be counteracted by providing attenuation means at some point or points along the length of the slow-wave structure in a manner to cause the feedback loop gain to be less than unity. Such attenuators normally, however, operate bidirectionally and diminish the desired forward gain also.

Ferromagneticdielectric materials, known as ferrites, disposed in the proximity of slow-wave structures such as described above, may provide a nonreciprocal attenuation. By this it is meant that backward or reliected microwave energy may be substantially eliminated, while forward traveling microwaves are not appreciably affected. In achieving nonreciprocal attenuation in this manner, a ferrite substance may slow-wave structure in regions where the radio frequency magnetic telds of the traveling waves are circularly polarized. The ferrite substance may be biased by a static magnetic field which is perpendicular both tothe plane of the radio frequency magnetic fields and to the instanbe provided along the For example, a pair of contrataneous direction of propagation. -Wheni' these conditions are met, unidirectional attenuation may be achieved,

the direction of effective attenuation being dependent upon the direction or field. t i

It is desirable for purposes of economy and size of overall package to make use of the axial static constraining magnetic eld already provided vin atraveling-wave tube for focusing and confining lthe electron stream. To use this field, however, requires means-for resolving from this longitudinal magnetic field a compolarity of the biasing magnetic ponent of magnetic field of proper sense which is trans'- verse to the axisA of the tube. In the above-described slow-wave structure consisting' of a series of cylinders interconnected by axial' segments, -the radio frequency magnetic fields are circularly polarized as they traverse points on the cylinders or rings in quadrature from the diametrically opposed points of'interconnection bythef axial segments. A selected ferrite element disposed in the proximity of these points of circular polarization and at an oblique angle-with respect to the tube axis resolves such a transverse' component and provides the desired ferromagnetic gyro resonance and consequently achieves nonreciprocal attenuation. Y'

With the arrangements heretofore known,A however,

undesired bidirectional effects are often encountered.

Whether the ferrites are biased from the axial constraining field of the slow-wave' structure or from some other source, bidirectional attenuation may result because of the presence in the ferrite member of a component of magnetic field which is perpendicular to the desired biasing magnetic field. This undesired component inthe ferrite is due to the ever present axial kconstraining field. This effect becomes particularly deleterious inthe X-band region of frequencies Where the biasing field inthe ferrite must be higher than usual to obtain ferromagnetic resonance at such high frequencies, and where thefaxial field is particularly large, and where also the saturation magnetization of ferrites is limitation on the nonreciprocal effect which canv be achieved. v l f Some objects of the presentl invention therefore'are:

To provide a traveling-wave tube which Yhasoperation energy while at the same time preserving the useful gain of the tube;

To provide an improved non-reciprocal traveling-wavel are magnetically biased by tube utilizing ferrites which l the tubes axial constraining magnetic eld;

To provide an improved non-reciprocal traveling-wave tube utilizing ferrites in which magnetic field in the ferrites out; a

And to provide an improved non-reciprocal travelingwave tube utilizing ferrites and field compensating means combined in an easily manufactured and assembled unit.

Briefly, these and other objects are achieved in one example of the present invention by providing a travelingwave tube having a stream of electrons confined along an axial path `within the slow-wave structure by a longitudinal or axial magnetic field. A different set'of ferrite strips is disposed in each of two planes extending on opposite sides of and along the length of the Islow-waive structure. l the remainder of the set and are oblique to the axis of the undesired components of tube. Permanent compensating magnets may beplaced v Patentedy Nov. 1'959 sufficiently low toV provideaV are effectively cancelled l The ferrite strips in each set arevparallel to netic iield, they resolve a transverse component from the magnetic field. This transverse component may be paralenergyinthe. slow-wavestructure near the ferrite. Thus the transverse component biases the ferrite to .effectnonreciprocal.ferromagnetic gyroresonance absorption. of the microwave energy traversing the slow-wave structure.

The compensating magnets set up a magnetic iield in the ferrites which opposes in theferrite the component of magneticiield due to the axial field and which is perpendicular to the desired biasing eld. The resultant biasing field ,is substantially purely in the desired direction for maximum unidirectional attenuation.

The novel features characteristicof the invention, both as., to `itsorganization and methodof operation, together with -further objects and advantages thereof, will be better understood from the-following descriptioncons-idered in connection with vthe .accompanying drawing in which like reference numerals refer to like parts and in which:

Fig. v1 Ais a sectional schematic .view of a travelingwave ktube constructed in accordance with the present invention and incorporating a non-.reciprocal attenuator section;

Fig. 2 is a cross-sectional view of the arrangement of Fig. ,1, taken along section lines 2-2 of Fig. l;

Fig. 3 is a vector diagram illustrating the magnitude and directions of the static magnetic fields andcertain of their components utilized .by a device in accordance 'with the invention;

Fig. 4 is `an enlarged view of a portion of the .nonreciprocal attenuator section of the tube of Fig. 1; and

Fig. 5 is a similar view of an alternative embodiment ofthestructure shown in Fig. 4.

Referring now to Fig. l, there is shown a travelingwave tube `.10 including Van elongated glass envelope 12 lsealedto a lcollector electrode 14 at its righthand (as viewed in the drawing) extremity and housing an electron 'gun 16 within Vits enlarged lefthand end. A slowJwave structure 18 extends within the envelope 12 for substantially the length thereof between the electron gun 16 and the collector -14. Theslow-wave structure 18 is of the contrawound helix equivalent type previously described id is effectively composed of a plurality of rings 20 interconnected by axial segments 22 affixed to diametrically bpporsed points of alternate pairs of rings 20. Such a structure is l.known as uniiilar contrawound helix in that it is electrically equivalent to two contrawound helical conductors, one each being Wound in opposite directions and interconnected at each crossover.

Each end of the slow-wave structure 18 is terminated by a diiferent matching ferrule 24and 26. An input waveguide section 28 is coupled to the input or lefthand extremity of the slow-wave structure 18, while an output section '30 is similarly coupled to the righthand extremity of slow-wave structurels. The electron gun 16 is of the well known Pierce type and includes a filamentary heater 32, a thermionic cathode 34, a focusing electrode 36 and an accelerating anode 38. A source of potential 40 is appropriately tapped at a number of points Vto provide operating voltages for the various electrodes of the traveling-wave tube. A source of potential 42 is connected between the collector electrode 14 and ground in a manner to maintain the collector at a positive potential of a few hundred volts with respect to the slow-wave structure 18 1n order to minimize the deleterious effects of electrons secondarily emitted from the collector 14. Substantially surrounding'and in axial alignment with the slow-wave structure 18 is a solenoid 44 energized by a source of direct `current 46 which provides a longitudinal focusing magnetic field.

Referring now to Figs. l, 2, and 4, it is seen that along each side of the slow-wave structure 18 is a set of elongated parallelepiped ferrite slabs or strips 48. Each of the sets lie in a plane parallel to the 'plane dctelmind by the pair of diametrically opposed sets of interconnecting axial segments 22. The ferrite strips in each set are thus arranged coplanarly along each side of the slow-wave structure. Interposed between the ferrite strips 48 of each set may be compensating permanent magnets 50. The ferrite strips each lie proximate to one of the conductive rings 20 so that there is a substantially one-to-one correlation with respect to magnets 50 and ferrite strips 48, in each set, and rings 20. The axis of elongation of each ferrite strip 48 and compensating magnet 50 is oriented at a predetermined oblique angle with respect to the axis of the rings 20. The angle chosen in a particular example is determined to a first approximation by analytical methods and then optimized empirically by considering the magnitude of axialmagnetic field, the frequency range of operation, as well as the particular composition of the ferrite strips and compensating magnets. The angle chosen is such as to provide in the ferrite a magnetic field of sufficient magnitude for gyroresonance in the frequency range of operation and which is perpendicular to the direction of propagation of microwave energy through a ring member 20 near Ithe ferrite. It is well known that in this type of slow-wave structure the fields of the microwave energy are .substantially linearly polarized'as they traverse the axialsegments 22 while they are circularly polarized as they traverse the point on the rings 20 in quadrature from the axial segments 22. The magnetic field in the ferrite is a biasing eld and, as is well known, it is made parallel tothe electric vector of -the microwave energy and thereby perpendicular to the plane of the magnetic vector. It is desirable for maximum non-reciprocal attenuation that the biasing magnetic field-be as closely as possible perpendicular tothe microwave magnetic vector and -to the direction of propagation. Deviations from this orientation of the biasing field give rise to reciprocal losses which are undesirable in that the forward gain of the traveling-wave tube is decreased.

The relationship of the magnetic iields in the ferrite may be better understood from Fig. 3, to which reference is now made. Vector H1 represents the longitudinal focusing magnetic eld provided by the solenoid 44. H2 represents its resolved component which is substantially parallel to the ferrite strips 48, while H3 represents the orthogonal component which is substantially perpendicular to the .ferrite strips. H4 represents a magnetic field in the ferrite which is opposite to and at least equal in magnitude to that represented by H3 for effectively cancelling it out. The field represented by H4 is provided across each ferrite by the set of ceramic compensating magnets 50. The magnets 50 are composed for example of ferroxdure, magnedur, or indox and are selected here in preference to metallic magnets in order that the attenuator structure may be placed closer to the slow-wave structure and thereby achieve a greater non-reciprocal attenuation with a minimum of shunting effects on the radio frequency energy. I

Fig. 4 illustrates that the magnet-ferrite combination may be fabricated into a rigid sandwich consisting of coplanar, parallel strips alternately ferrite strips 48 and ceramic magnets 50. Such an arrangement facilitates reproducible alignment with the remainder of the traveling-wave tube and provides a more stable self support for the individual components of the attenuator sections. The magnets 50 and ferrites 48 are disposed parallel to each other and at an oblique angle with respect to the tube axis. Each of the magnets 50 is magnetized so that a face toward an adjacent ferrite is one pole while the opposite face is the Vother pole. In the composite sandwich, all the magnets 50 are aligned with north poles toward one end of the tube and south poles toward the other end of the tube. The rigid sandwich arrangement clearly lends itself to simple manufacturing techniques and is consequently inexpensive to produce. Each sandwich set may be readily inserted into the remainder of the travHeling-wave tube assembly without serious alignment problems as to each the sandwich.

yIn Fig. 5 is shown an attenuator section in a configuration similar to that shown in Fig. 4.v lEach of the permanent magnets 50 is relieved from its surfacesy toward one of a setof'ferrite rods 48 in a manner to receive or substantially surround half of one of the rods in each of said surfaces. The permanent ceramic magnets 50 are assembled and secured to eachother leavindividuall'cbmp'onent part of desired component of magnetic field due V tothe axial focusing field and which is perpendicular Vto gyroresonance biasing field in the ferrite.

By eliminating or cancelling out the-undesired field orthogonal to the biasing eld in the ferrite, a much greater non-reciprocal effect is achieved than has otherwise been obtainable. It is thus possible to take a further advantage of the broadband characteristic of traveling-wave tube slow-wave structures in that undesired impedance mismatch reflections ma'y be substantially eliminated without sacrice of forward gain in the travelingwave tube.

What is claimed is:

1. A traveling-wave tube comprising: a slow-wave structure of the interconnected ring type; afocusing magnet for confining an electric stream along-the axis of said slow-wave structure; an elongated ferrite member disposed near said slow-wave structure obliquely to the direction of the axis thereof for resolving from the magnetic lield of said focusing magnet a ferrite biasing component and an undesired component orthogonal thereto; and compensating magnets disposed contiguously to said ferrite member providing a magnetic field in said ferrite member substantially equal and opposite to said undesired orthogonal component.

2. In a traveling-wave tube of the character utilizing ferromagnetic gyroresonance properties of ferrites for non-reciprocal attenuation of electromagnetic waves being propagated therethrough and in which from the axial electron beam focusing magnetic field an undesired component of magnetic field is caused to exist in said ferrites, the combination with said traveling-wave tube of means for effectively cancelling said undesired component comprising: elongated ferrite membersl disposed obliquely to the direction of and spaced along the length of said traveling-wave tube, and compensative magnet means disposed contiguously to said ferrite members.

3. A traveling-wave tube comprising: a slow-wave structure including a plurality of axially registering conductive rings interconnected by two diametrically opposed sets of axial segments; means for projecting a stream of electrons along a predetermined path coincident with the axis of said rings; focusing magnet means providing an axial magnetic field along said path, non-reciprocal attenuator means including an elongated ferrite member Idisposed obliquely to the direction of said axis and near one of said rings for resolving from said axial magnetic field a ferrite biasing component and an undesired component orthogonal thereto; and compensating magnetic means contiguous to said ferrite member providing a magnetic field in said ferrite member substantially equal and opposite to said undesired orthogonal component.

4. In a traveling-wave tube of the character utilizing gyroresonance properties of ferrites for non-reciprocal the desired t 6 attenuation of electromagnetic waves beingV propagated therethrough .and in which from the axial electron beam focusing magnetic field a transverse component is resolved for biasing said ferrites,'thecombination with said traveling-wave tube of compensating magnet means for effectively cancelling'magnetic field components in the ferrite whichare orthogonal to said transverse component, the combination comprising: elongated Iferrite members disposed obliquely along said traveling-wave tube and compensating ceramic magnet means disposed contiguously to said ferrite members.

5. A traveling-wave tube comprising: a slow-wave structure including a plurality of axially registering conductive rings interconnected by a pair of diametrically opposed sets of axial interconnecting segments; means for projecting-a stream of electrons along a predetermined path coincident with the axis of said rings; a focusing magnet providing an axial magnetic field along said path;

non-reciprocal attenuator means including a plurality of ferrite rods being disposed near and associated with a respective one of said rings and lying in an axial plane parallel 4to the plane determined by said sets of intercon- I necting segments, said ferrite rods being mutually parallel and lying transverse to said axis for resolving from said axial magnetic field a ferrite biasing component and an undesired component orthogonal thereto; and compensative ceramic magnets disposed parallel to and contiguously between adjacent ones of said ferrite rods and each being relieved on its surfaces towards said rods in a manner' to receive substantially half of one of said rods in each of said surfaces, said ceramic magnets providing a magnetic field in said ferrite rods substantially opposite and at least equal to said undesired orthogonal component.

6. A traveling-wave -tube comprising: a slow-wave structure including a plurality of axially registering conductive rings interconnected by a pair of diametrically opposed sets of axial segments; means for projecting a stream of electrons along the axis of said rings; a focusing magnet providing an axial magnetic field along said Y axis; non-reciprocal attenuator means including two sets of elongated parallelepiped ferrite slabs, one of saidsets of slabs lying to one side of said slow-wave structure in a plane parallel to the plane determined by said pair ,of'

stantially one to one correlation with respect to said feri rite slabs, individual ones of said ferrite slabs being co-` planarly sandwiched between adjacent ones of said cornpensating magnets.

7. In a traveling-wave tube of the character utilizing a plurality of axially registering conductive rings interconnected by a pair of diametrically opposed sets of axial segments and a focusing magnetic field along the axis of the rings, the combination therewith of a nonreciprocal attenuator comprising: two sets of elongated ferrite slabs, each of said sets of slabs lying to a different side of said slow-wave structure and each in a plane parallel to the plane determined by said pair of diametrically opposed sets of axial segments, each of said ferrite slabs in each of said sets lying parallel with the remainder of its set and proximate to a different one of said rings, the axis of elongation of each ferrite slab being at an oblique angle with respect to the axis of said rings; and a plurality of ceramic compensating permanent magnets being in substantially one to one correlation with respect yto said ferrite slabs, individual ones of said ferrite slabs being substantially coplanarly sandwiched between adjacent ones of said compensating magnets.

8. In a traveling-wave tube of the character utilizing a plurality of axially registering conductive rings interconnected by a pair of diametrically' opposed sets of axial segments and a focusing magnetic field along the axis of the rings, the combination therewith of a nonreciprocal attenuator comprising: two sets of elongated parallelepiped ferrite slabs, one of said sets of slabs lying to one side of said slow-wave structure in a plane parallel to the plane determined by said pair of diametrically opposed sets of axial segments, the other of said sets of slabs lying in a parallel plane to the other side of said slow-wave structure, each of said ferrite slabs lying parallel with the remainder of its respective set and proximate to a different one of said rings, the axis of elongation of each ferrite slab being at an oblique angle with respect to the axis of said rings; and a plurality of ceramic compensating permanent magnets being -in substantially one to one correlation with respect to said ferrite slabs, individual ones of said slabs being positioned between successive different pairs of said compensating magnets.

9. In a traveling-wave tube of the character utilizing a plurality of axially registering conductive rings interconnected by a pair of diametrically opposed sets of axial segments and a focusing magnetic field along the axis of the rings, the combination therewith of a non-reciprocal attenuator comprising: a pair of sets of elongated ferrite rods, one of said sets of rods lying closely to one side of said slow-wave structure in a first plane parallel to the plane determined by said pair of diametrically opposed sets of axial segments, the other of said sets of rods lying in the parallel plane symmetrically opposite said slow-wave structure from said first plane, each-of said ferrite rods lying mutually parallel with the remainder of its respective set, the axis of elongation of each of said ferrite rods being at an oblique angle with respect to the axis of said rings, and individual ones of said ferrite rods in each of said sets being proximate to and associated with different ones of said rings; and a plurality of ceramic compensating permanent magnets being in substantially one to one correlation with respect to said `ferrite rods, each of said permanent magnets being disposed parallel to and contiguously between adjacent ones of said ferrite rods and being relieved on its surfaces towards said rods in a manner to receive substantially half of one of said rods in each of said surfaces, whereby said ceramic compensating magnets substantially envelop said ferrite rods and are in a one to one correlation with respect to said ferrite rods to provide a planar structure including embedded ferrite rods.

10. In a traveling-wave tube of the character utilizing Ia plurality of axially registering conductive rings inter connected by a pair of diametrically opposed sets of axial segments and a focusing magnetic field along the axis of the rings, the combination therewith of a nonreciprocal attenuator comprising: two sets of elongated parallelepiped ferrite slabs, one of said sets of slabs lying to one side of said slow-wave structure in a plane parallel to the plane determined by said pair of diametrically opposed sets of axial segments, the other of said sets of slabs lying in a parallel plane to the other side of said slowwave structure, each of said Iferrite slabs lying parallel with the remainder of its respective set and proximate to a different one of said rings, the axis of elongation of each ferrite `slab being at an oblique angle with respect to the axis of said rings; and a plurality of ceramic compensating permanent magnets being in substantially one to one correlation with respect to said ferrite slabs, individual ones of said slabs being positioned between successive different pairs of said compensating magnets, said magnets being magnetized such that -a face of each of said magents toward one adjacent ferrite slab is one magnet pole, and the opposite face of each of said magnets toward another ferrite slab is the opposite magnet pole, all of said magnets being aligned with north poles toward one end of said traveling-wave tube and south poles toward the opposite end.

11. In a traveling-wave tube of the character utilizing a plurality of axially registering conductive rings interconnected by a pair of diametrically opposed sets of axial segments and a focusing magnetic field along the axis of the rings, the combination therewith of a nonreciprocal attenuator comprising: a pair of sets of elongated ferrite rods, one of said sets of rods lying closely to one side of said slow-wave structure in a first plane parallel to the`plane determined by said pair of diametrically opposed sets of axial segments, the other of said sets of rods lying in the parallel plane symmetrically opposite said slow-wave structure from said first plane, each of said ferrite rods lying mutually parallel with the remainder of its respective set, the axis of elongation of each of said ferrite rods being at an oblique angle with respect to the axis of said rings, and individual ones of said ferrite rods in each of said sets being proximate to and associated with different ones of said rings; and a plurality of ceramic compensating permanent magnets being in substantially one to one correlation with respect to said ferrite rods, each of said permanent magnets being disposed parallel to and contiguously between adjacent ones of said ferrite rods and being relieved on its surfaces towards said rods in a manner to receive substantially half of one of said rods in each of said surfaces, whereby said ceramic compensating magnets substantially envelop said ferrite rods and are in a one to one correlation with respect to said ferrite rods to provide a planar structure including embedded ferrite rods, each of said magnets being magnetized such that one of said surfaces toward an adjacent ferrite rod is one magnet pole, while the opposite surface is the opposite magnet pole, said magnets being aligned with north pole surfaces toward one end of said traveling-wave tube and south poles toward the opposite end.

References Cited in the file of this patent UNITED STATES PATENTS 2,798,183 Sensiper July 2, 1957 2,822,502 Sensiper Feb. 4, 1958 FOREIGN PATENTS 750,208 Great Britain June 13, 1956 UNITED STATES PATENT OFFICE CERTIFICATE CE CORRECTION Patent No., 2,911,555 'November 3, 1959 Samuel Sensper et al Signed and sealed this 26th dayiof April 1960.

(SEAL) Attest:

KARL MEINE ROBERT C. WATSON- ttesting Oicer Commissioner of Patents

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