US3602766A

US3602766A - Traveling-wave tube having auxiliary resonant cavities containing lossy bodies which protrude into the slow-wave structure interaction cells to provide combined frequency sensitive and directionally sensitive attenuation

Info

Publication number: US3602766A
Application number: US798646A
Authority: US
Inventors: Jeffrey E Grant
Original assignee: Hughes Aircraft Co
Current assignee: Raytheon Co
Priority date: 1969-02-12
Filing date: 1969-02-12
Publication date: 1971-08-31
Anticipated expiration: 1988-08-31
Also published as: DE2134996C3; DE2134996B2; GB1325856A; DE2134996A1

Abstract

In the disclosed traveling-wave tube, auxiliary cavities which are resonant at a frequency in the vicinity of a cutoff frequency of the slow-wave structure communicate with respective slow-wave structure interaction cells. Lossy ceramic bodies disposed in respective auxiliary cavities protrude into the adjacent slowwave structure interaction cells to simultaneously provide both frequency sensitive and directionally sensitive attenuation. In a single section tube the distance of protrusion is essentially uniform for the respective lossy bodies. In a severed tube the distance of protrusion of successive lossy bodies in an amplifying section is progressively decreased as a function of longitudinal distance from the sever in order to additionally function to terminate the amplifying section.

Description

United States Patent [72] Inventor .leflrey E. Grant Los Angeles. Cdll.

[2i] Appl. No. 798,646

[22] Filed Feb. I2, 1969 [45] Patented Aug. 31, I971 [73) Assignee Ilughu Ai'cr'llt Col-poly Culver City, Calif.

[54] TRAVELING-WAVE TUBE HAVING AUXILIARY RESONAN'I CAVI'I'IB CONTAINING LOSSY BODIES WHICH PRUIRUDE INTO THE SLOW- WAVE STRUCTURE INTERACTION CELLS TO PROVIDE COMBINED FREQUENCY SENSITIVE AND DIREC'IIONALLY SENSITIVE A'I'IENUATION I6 Clnhns, 6 Drawhg Fl [52] US. Cl. SIS/3.5,

3 l 513.6, SIS/39.3

[5|] Int. Cl. H01] 25/34 [50] I leldoISeu-eh 31513.5,

(56] Reterencs Cited UNITED STATES PATENTS 3,22 l ,204 ll/l965 Hant et al. 31513.5

Primary Examiner-Herman Karl Saalbach Assistant Examiner-Saxfield Chatmon, Jr. Attorney.r.lames K. Haskell and Paul M. Coble f ABSTRACT: In the disclosed traveling-wave tube, auxiliary cavities which are resonant at a frequency in the vicinity of a cutoff frequency of the slow-wave structure communicate with respective slow-wave structure interaction cells. Lossy ceramic bodies disposed in respective auxiliary cavities protrude into the adjacent slow-wave structure interaction cells to simultaneously provide both frequency sensitive and directionally sensitive attenuation. In a single section tube the distance of protrusion is essentially uniform for the respective lossy bodies. In a severed tube the distance of protrusion of successive lossy bodies in an amplifying section is progressively decreased as a function of longitudinal distance from the sever in order to additionally function to terminate the amplifying section.

my 0 w I @J l i r F l l PATENTEU was] :91: 3.602166 sum 1 or 3 Afro/way TRAVELING-WAVE TUBE HAVING AUXILIARY RESONANT CAVITIES CONTAINING LOSSY BODIES WHICH PROTRUDE INTO THE SLOW-WAVE STRUCTURE INTERACTION CELLS TO PROVIDE COMBINED FREQUENCY SENSITIVE AND DIREC'I'IONALLY SENSITIVE ATTENUATION This invention relates generally to microwave devices, and it more particularly relates to traveling-wave tubes having means for simultaneously providing both frequency sensitive attenuation and directionally sensitive attenuation in order to increase tube stability. The invention also provides, for traveling-wave tubes of the type which are severed into a plurality of amplifying sections, a combined frequency sensitive loss introducing and amplifying section terminating arrangement.

ln traveling-wave tubes a stream of electrons is caused to interact with a propagating electromagnetic wave in a manner which amplifies the electromagnetic energy. In order to achieve such interaction, the electromagnetic wave is propagated along a slow-wave structure, such as a conductive helix wound about the path of the electron stream or a folded waveguide type of structure in which a waveguide is effectively wound back and forth across the path of the electrons. The slow-wave structure provides a path of propagation for the electromagnetic wave which is considerably longer than the axial length of the structure, and hence, the traveling-wave may be made to effectively propagate at nearly the velocity of the electron stream. The interactions between the electrons in the stream and the traveling-wave cause velocity modulations and bunching of the electrons in the stream. The net result may then be a transfer of energy from the electron beam to the wave traveling along the slow-wave structure.

The present invention is concerned with traveling-wave tubes utilizing slow-wave structures of the coupled cavity, or interconnected cell, type. ln this type of slow-wave structure a series of interaction cells, or cavities, are disposed adjacent to each other sequentially along the axis of the tube. The electron stream passes through each interaction cell, and electromagnetic coupling is provided between each cell and the electron stream. Each interaction cell is also coupled to an adjacent cell by means of a coupling hole at the end wall defining the cell. Generally, the coupling holes between adjacent cells are alternately disposed on opposite sides of the axis of the tube, although various other arrangements for staggering the coupling holes are possible and have been employed. When the coupling holes are so arranged, a folded waveguide type of energy propagation results, with the traveling-wave energy traversing the length of the tube by entering each interaction cell from one side, crossing the electron stream and then leaving the cell from the other side, thus traveling a sinuous, or serpentine, extended path.

One of the problems encountered in traveling-wave tubes of the coupled cavity variety, and especially high power tubes of this type, is a tendency for the tube to oscillate at frequencies near the edges of the tube passband. This problem arises from the fact that for wide band operation the phase velocity of the slow-wave circuit wave and the velocity of the electron beam should be essentially synchronized over as large a range of frequencies as possible; hence, these velocities are also close to synchronism near the upper and lower cutoff frequencies of the tube. Since the interaction impedance is high and the circuibto-transmission line match is poor at and in the vicinity of the cutofi' frequencies, the loop gain for the tube, or even for a section of the tube, may be sufl'iciently large for oscillations to start.

One technique which has been used to solve this oscillation problem involves coupling to the slow-wave structure interaction cells specially designed external auxiliary cavities which are resonant at a frequency in the vicinity of a cutoff frequency of the slow-wave structure and providing lossy ceramic buttons in the external cavities in order to attenuate energy at the resonant frequency of the cavity. For further details as to this technique reference may be made to U.S. Pat. No. 3,22 l ,204, entitled "Traveling-Wave Tube with Trap Means for Preventing Oscillation at Unwanted Frequencies," issued Nov. 30, 1965 to William l-lant et al. and assigned to the assignee of the present invention. While this external lossy resonant cavity arrangement functions excellently to introduce frequency sensitive attenuation into the slow-wave structure, the introduced attenuation is relatively insensitive to the direction of propagation of the electromagnetic wave traveling along the slow-wave structure.

Accordingly, it is an object of the present invention to provide a traveling-wave tube having means for simultaneously introducing both frequency sensitive attenuation and directionally sensitive attenuation into the slow-wave structure of the tube.

It is a further object of the present invention to provide a traveling-wave tube of the type employing oscillation suppressing lossy resonant cavities coupled to slow-wave structure interaction cells and in which the slow-wave structure backward loss is increased relative to the effective forward loss, thereby increasing tube stability.

As traveling-wave tubes are designed for operation at higher and higher power levels, in order to ensure stability such tubes have been constructed in several amplifying sections, with a substantially complete sever or electromagnetic circuit wave isolation provided between adjacent amplifying sections, and the only coupling between the sections occurring by means of the velocity modulated electron stream. Since each amplifying section has a length appropriate for maximum stable gain, it is necessary to effectively terminate each section with a matched load. In the past such termination has been achieved by providing separate terminating elements either internally of the slow-wave structure, externally of the slow-wave structure, or in hybrid fashion both internally and externally of the slowwave structure. For further details as to these terminations reference may be made to U.S. Pat. No. 2,985,791, entitled Periodically Focused Severed Traveling-Wave Tube, issued May 23, 196i to David .I. Bates et al.; to U.S. Pat. No. 3,123,736, entitled Severed Traveling-Wave Tube With External Terminations," issued Mar. 3, 1964 to William H. Christolfers et al.; and to U.S. Pat. No. 3,l8l,023, entitled Severed Traveling-Wave Tube With Hybrid Terminations," issued Apr. 27, 1965 to William Hant et al., all of these patents being assigned to the assignee of the present invention.

It is a further object of the present invention to provide, for a traveling-wave tube of the type which is severed into a plurality of amplifying sections, means for simultaneously providing both frequency sensitive attenuation and a terminating sever for respective amplifying sections.

it is a still further object of the present invention to provide a severed traveling-wave tube which for comparable power handling capabilities is more compact than severed tubes having termination arrangements according to the prior art.

it is still another object of the present invention to provide a severed traveling-wave tube which can handle more RF power than comparably dimensioned traveling-wave tubes having prior art termination arrangements.

lt is yet another object of the present invention to provide a severed traveling-wave tube which provides an improved match at the severed ends of the amplifying sections, thereby reducing undesired small signal gain variations as a function of frequency.

in accordance with the above objects, a traveling-wave tube according to the present invention includes means for providing a stream of electrons along a predetermined path and a slow-wave structure having a plurality of intercoupled interaction cells disposed sequentially along and about the electron stream path for propagating electromagnetic wave energy in such manner that it interacts with the stream of electrons. A plurality of cavities are respectively disposed externally of at least selected ones of the interaction cells and sequentially along a direction parallel to the electron stream path. Each cavity communicates with one of the interaction cells and is resonant at a preselected frequency. A body of lossy material is disposed in each cavity and protrudes into the adjacent interaction cell by a preselected distance.

In one embodiment of the invention the distance of protrusion is essentially the same for each lossy body. In this arrange ment the cavity resonances and the portions of the lossy bodies within the cavities provide frequency sensitive attenuation, while the protruding portions of the lossy bodies introduce directionally sensitive attenuation to the electromagnetic wave propagating along the slow-wave structure.

In another embodiment of the present invention the traveling-wave tube is severed into a plurality of amplifying sections. The distance of protrusion of successive ones of the lossy bodies in at least one of the amplifying sections is progressively decreased as a function of longitudinal distance from the severed end of this amplifying section. The cavity resonances and the portions of the lossy bodies within the cavities introduce frequency sensitive attenuation, while the progressively varying protrusion of the lossy bodies provides tapered attenuation which terminates the slow-wave structure amplifying section.

The foregoing, as well as other objects, advantages, and characteristic features of the present invention will become more readily apparent from the following detailed description of preferred embodiments of the invention when considered in conjunction with the accompanying drawings in which:

FIG. I is an overall view, partly in longitudinal section and partly broken away, of a single-section traveling-wave tube constructed in accordance with one embodiment of the present invention;

FIG. 2 is a cross-sectional view taken along line 2-2 of FIG. 1;

FIG. 3 is a longitudinal sectional view taken along line 3-3 of FIG. 2;

FIG. 4 is a longitudinal sectional view taken along line 4-4 of FIG. 2',

FIG. 5 is an overall view, partly in longitudinal section and partly broken away, of a severed traveling-wave tube constructed in accordance with another embodiment of the present invention; and

FIG. 6 is a perspective view of a portion of the slow-wave structure, including the combined frequency sensitive loss introducing and section terminating arrangement of the invention, for the traveling-wave tube of FIG. 5.

Referring to the drawings with more particularity, in FIG. 1 the reference numeral I0 designates generally a travelingwave tube which includes an arrangement 12 of magnets, pole pieces and spacer elements which will be described in detail later. At this point it should suffice to state that the spacer elements and interior portions of the pole pieces function as a slow-wave structure, while the magnets and pole pieces can stitute a periodic focusing device for the electron beam traversing the length of the slow-wave structure.

Coupled to the input end of the arrangement 12 is an input waveguide transducer 14 which includes an impedance step transformer I6. A flange 18 is provided for coupling the as sembled traveling-wave tube to an external waveguide or other microwave transmission line (not shown). The construction of the flange l8 may include a microwave window (not shown) transparent to microwave energy but capable of maintaining a vacuum within the traveling-wave tube 10. At the output end of the arrangement 12 an output transducer 20 is provided which is substantially similar to the input transducer 14 and which includes an impedance step transformer 22 and a coupling flange 24, which elements are similar to the elements l6 and I8, respectively, of the input transducer I4. For vacuum pumping or out-gassing the traveling-wave tube 10 during manufacture, a double-ended pumping tube 26 is connected to both of the input and output waveguide transducers l4 and 20.

An electron gun 28 is disposed at one end of the travelingwave tube 10 which, although illustrated as the input end in NO. I, may alternatively be the output end if a backward wave device is desired. The electron gun 28 functions to project a stream of electrons along the axis of the tube 10 and may be of any conventional construction well known in the art. For details as to the construction of the gun 28 reference is made to the aforementioned U.S. Pat. No. 2,985,791 and to U.S. Pat. No. 2,936,393, entitled, "Low Noise Traveling- Wave Tube, issued May I0, 1960, to M. R. Currie et al. and also assigned to the assignee of the present invention.

At the output end of the traveling-wave tube I0 there is provided a cooled collector structure 30 for collecting the electrons in the stream. The collector is conventional and may be of any fonn well known in the art. For details as to the construction of the collector, reference is made to the aforesaid U.S. Pat. No. 2,985,791 and to U.S. Pat. No. 2,860,277, entitled, Traveling-Wave Tube Collector Electrode, issued Nov. l l, P 8, to A. H. lversen and assigned to the assignee of the present invention.

The construction of the slow-wave structure and magnetic focusing system for the traveling-wave tube 10 are illustrated in more detail in FIGS. 2-4. A plurality of essentially annular disk-shaped focusing magnets 32 are interposed between a plurality of ferromagnetic pole pieces, or plates, 34. As is illustrated in FIG. 2, the magnets 32 may be diametrically split into two sections 320 and 32b for convenience during assembly of the tube. The ferromagnetic pole pieces 34 extend radially inwardly of the magnets 32 to approximately the perimeter of the region adapted to contain the axial electron stream. The individual pole pieces are constructed in such a manner that a short drift tube, or ferrule, 36 is provided at the inner extremity of each pole piece. The drift tube 36 is in the form of a cylindrical extension, or lip, protruding axially along the path of the electron stream from both surfaces of pole piece 34, Le, in both directions normal to the plane of the pole piece 34. The drift tubes 36 are provided with central and axially aligned apertures 38 to provide a passage for the flow of the electron beam. Adjacent ones of the drift tubes 36 are separated by a gap 40 which functions as a magnetic gap to provide a focusing lens for the electron beam and also as an interaction gap in which energy exchange between the electron beam and traveling-wave energy traversing the slow-wave structure occurs.

Disposed radially within each of the magnets 32 is a slowwave circuit spacer element 42 of a conductive nonmagnetic material such as copper. Each spacer element 42 has an annular portion of an outer diameter essentially equal to the inner diameter of the magnets 32 and a pair of oppositely disposed

ear portions

43 and 44 projecting outwardly from the annular portion. Each spacer element also defines a central cylindrical aperture 45 to provide space for a microwave interaction cell, or cavity, 46 which is defined by the inner lateral surface of the spacer 42 and the walls of the two adjacent pole pieces 34 projecting inwardly of the spacer element 42. The inner diameter of the spacer 42 determines the radial extent of the interaction cell 46, while the axial length of the spacer 42 determines the axial length of the cell 46.

For interconnecting adjacent interaction cavities 46 an offcenter coupling hole 48 is provided through each of the pole pieces 34 to permit the transfer of electromagnetic wave energy from cell to cell. As is illustrated, the coupling holes 48 may be substantially kidney-shaped and may be alternately disposed apart with respect to the drift tubes 36. It should be pointed out, however, that the coupling holes 48 may be of other shapes and may be staggered in various other arrangements, such as those disclosed in U.S. Pat. No. 3,010,047, entitled Traveling-Wave Tube," issued Nov. 2i, I961 to D. .l. Bates and assigned to the assignee of the present invention. In any event, it will be apparent that the spacer elements 42 and the portions of the pole pieces 34 projecting inwardly of the spacers 42 not only form an envelope for the tube, but also constitute a slow-wave structure for propagating travelingwave energy in a serpentine path along the axially traveling electron stream so as to support energy exchange between the electrons of the stream and the traveling-wave.

The axial length of the magnets 32, hence that of the spacers 42, is equal to the spacing between adjacent pole pieces 34, and the radial extent of the magnets 32 is approximately equal to or, as shown, slightly greater than that of the pole pieces 34. To provide focusing lenses in the gaps 40, the magnets 32 are stacked with alternating polarity along the axis of the tube, thus causing a reversal of the magnetic field at each magnetic lens and thereby providing a periodic focusing device. It should be pointed out, however, that although the lengths of the spacers 42 may be substantially constant, they may also be varied slightly with respect to each other so that the effective axial length of the cavities 46 is varied as a function of distance along the tube to ensure that the desired interaction between the electron stream and the traveling waves will continue to a maximum degree even though the electrons are decelerated toward the collector end of tube.

In order to minimize any tendency for the traveling-wave tube to oscillate at frequencies near the edges of the slowwave circuit passband, frequency selective attenuation is provided to substantially decrease the gain at these frequencies and, thereby, suppress the oscillations. This attenuation takes the form of lossy ceramic bodies disposed in cavities which are coupled to the slow-wave structure interaction cells and which cavities are made resonant at the frequencies to be attenuated. Thus, as is shown in FIGS. 2 and 4, a slow-wave structure spacer element 42 may define a pair of

cylindrical cavities

50 and 52 which are respectively disposed in the projecting ear portions 43 and 4-4 of the spacer element 42 and have their longitudinal axes disposed parallel to the longitudinal axis of the traveling-wave tube I2. The cavities and 52 have a length equal to the thickness of the slow-wave structure spacer element 42 and are designed to resonate at a frequency at which loss is to be introduced into the circuit. Although the cavity resonant frequency is preferably at or near either the upper or lower cutoff frequency of the slow-wave structure, it is to be understood that the resonant loss frequency may be any preselected frequency. Cylindrical buttonlike bodies 54 and 56 of a mixture of ceramic and lossy materials are disposed in and substantially fill the

respective cavities

50 and 52 in order to provide the desired loss. For further details as to the

resonant cavities

50 and 52 and the lossy bodies 54 and 56 reference may be made to the aforementioned US. Pat. No. 3,221,204.

As is illustrated in FIG. 2, the lossy bodies 54 and 56 protrude into the adjacent interaction cell 46 by a preselected distance d. The distance of protrusion d is preferably between percent and 30 percent of the distance from the edge of the interaction cell 46 to the center of the stream of electrons, ie the radius r of the interaction cell.

In the embodiment of FIGS. 1-4, the traveling-wave tube has a single amplifying section, and the distance of protrusion d of each of the lossy bodies 54 (or 56) is essentially the same. Thus, essentially uniform distributed attenuation is introduced to the slow-wave structure. This distributed loss attenuates electromagnetic waves traversing the slow-wave structure in the backward direction, i.e. from the collector 30 toward the electron gun 28, by two to three times more than it attenuates electromagnetic waves traveling in the forward direction, i.e. from the electron gun 28 toward the collector 30. Thus, the

resonant cavities

50 and 52 and the protmding lossy bodies 54 and 56 function to provide both frequency sensitive attenuation at the cavity resonant frequency and directionally sensitive attenuation in favor of forwardly traveling electromagnetic waves, thereby increasing the stability of the tube.

In the embodiment of the invention illustrated in FIGS. 5 and 6, the traveling-wave tube is severed into a plurality of amplifying sections. Since the traveling-wave tube of FIGS. 5 and 6 is very similar to that of FIGS. 14, components in the embodiment of FIGS. 5-6 which are the same as corresponding components in the embodiment of FIGS. I4 are designated by the same second and third reference numeral digits as their corresponding components in FIGS. 1-4 but with the addition of the prefix numeral l."

In the embodiment of FIGS. 5-6 the traveling-wave tube I10 is illustrated as having three amplifying

sections

162, 164 and 166, although it is understood that three such sections are shown solely for illustrative purposes. Each of the amplifying sections is isolated from the adjacent section or sections by means of an isolator device. Thus, in the traveling-wave tube shown in FIG. 5, the first and second amplifying

sections

162 and 164, respectively, are isolated from each other by isolator device I68; while the second and third amplifying sections I64 and 166, respectively, are isolated from one another by means of isolator device 170. The isolator devices 168 and I70 provide a substantially complete sever between adjacent amplifying sections of the traveling-wave tube IIO for electromagnetic waves traveling along the slow-wave structure, and which waves are hereinafter referred to as electromagnetic circuit waves. At the same time the electron stream is allowed to pass through the entire length of the traveling-wave tube 110. The electron stream is modulated in each amplifying section, and hence, as it enters the subsequent amplifying section it launches a new electromagnetic circuit wave therein which is amplified by interaction between the new electromagnetic circuit wave and the electron stream. Thus, unidirectional coupling adjacent amplifying sections is provided by means of the electron stream.

FIG. 5 is broken away in the region of isolator device 170 in order to illustrate the interior construction thereof, it being understood that isolator device I68 is constructed in an identical manner. Isolator device 170 comprises a modified pole piece, or plate, 134 which differs from the remaining pole pieces 134 in that no coupling hold for electromagnetic circuit waves is provided in the pole piece I34. This prevents electromagnetic circuit waves in amplifying section 164 from passing into the section 166, and vice versa, thereby achieving electromagnetic circuit wave isolation between the

sections

164 and 166.

The interior portion of slow-wave structure amplifying section 164 adjacent isolator device I70 is illustrated in FIG. 6. It may be seen that the distance of protrusion of successive lossy bodies 1540, 154b, I54c and 154d (also 1560, 156b, l56c and 156d) disposed in respective spacer elements 142a, I42b, I42c and 146d into respective interaction cells 146a, I46b, l46c and 146d decreases as a function of longitudinal distance from the isolator pole piece 134. The distance of protrusion can be varied by varying the radial location of successive lossy bodies with respect to the tube axis. However, in a preferred arrangement, illustrated in FIG. 6, the successive lossy bodies are axially aligned with one another and their distance of protrusion into the respective interaction cells is varied by removing varying portions of the lossy bodies on the side facing the stream of electrons. Thus, in FIG. 6 lossy bodies I54b, 154a and 154d (also 156b, l56c and 156d) define respective flat, or planar, lateral surfaces b, ISSc and I55d (I57b, 157C and 157d) facing the stream of electrons in respective planes perpendicular to the plane passing through the longitudinal axes of the lossy bodies and the electron stream path. The distance between the respective planes of the surfaces 155b, 1556 and 155d (also 157b, l57c and 157d) and the outer edge of the respective interaction cells 146b, 1460 and 146d is progressively decreased as a function of longitudinal distance from the isolator pole piece I34. In a preferred embodiment of the invention the distance of protrusion d of the successive lossy bodies is decreased essentially linearly as a function of longitudinal distance from the isolator pole piece 134', although it should be understood that other relationships are possible and may be employed.

Since the distance of protrusion of the lossy bodies determines the amount of attenuation introduced to the slow-wave structure, with the greater the protrusion the greater the loss, the arrangement of FIG. 6 provides progressively increasing attenuation as a function of distance toward isolator pole piece 134'. Thus, the end of the amplifying section I64 adjacent the isolator pole piece I34 is effectively terminated with minimum reflection of electromagnetic circuit wave energy back toward the electron gun 128. As a result, undesired small signal gain variations as a function of frequency are minimized. In addition, since the auxiliary resonant cavities and the protruding lossy bodies perform the combined functions of providing both frequency sensitive attenuation and a terminating sever (which functions required separate attenuating and terminating elements in the prior art), a severed traveling-wave tube according to the present invention requires fewer parts and is more compact than prior art severed tubes with comparable power handling capabilities. Moreover, a severed traveling-wave tube according to the invention is able to handle more RF power than comparably dimensioned severed traveling-wave tubes according to the prior art.

It is pointed out that the arrangement illustrated in FIG. 6 is designed to provide a termination for forwardly traveling electromagnetic circuit waves in amplifying section 164. The same arrangement may be employed at the end of amplifying section 162 adjacent isolator device 168 to provide a termination for forwardly traveling electromagnetic circuit waves in the section 162. Moreover, a similar arrangement can be sued in each of the

sections

162, 164 and 166 to provide a termination for backwardly traveling electromagnetic circuit waves. In such an arrangement the distance of protrusion of successive lossy bodies would be decreased as a function of distance from the ends of the respective amplifying sections nearest the electron gun l28 in a direction toward the collector 130. Thus, in

sections

162 and 164 the lossy body protrusion would be the greatest at both ends and smallest at the longitudinal centers of these amplifying sections.

Although the present invention has been shown and described with reference to particular embodiments, nevertheless various changes and modifications which are obvious to a person skilled in the relevant art are deemed to lie within the purview of the invention.

What l claim is:

l. A traveling-wave tube comprising: means for providing a stream of electrons along a predetermined path, slow-wave structure means defining a plurality of intercoupled interaction cells disposed sequentially along and about said predetermined path for propagating electromagnetic wave energy in such manner that it interacts with said stream of electrons, means defining a plurality of cavities respectively disposed externally of at least selected ones of said interaction cells and sequentially along a direction parallel to said predetermined path, each of said cavities communicating with one of said interaction cells and being resonant at a preselected frequency, and a body of lossy material disposed in each said cavity and protruding into the adjacent one of said interaction cells by a preselected distance.

2. A traveling-wave tube according to claim I wherein said cavities and said bodies are of essentially cylindrical shape and have their longitudinal axes disposed parallel to said predetermined path.

3. A traveling-wave tube according to claim 1 wherein said preselected distance of protrusion is between essentially 5 percent and essentially 30 percent of the distance from the edge of said interaction cell to the center of said stream of electrons.

4. A traveling-wave tube according to claim 1 wherein said preselected distance of protrusion is essentially the same for each of said bodies.

5. A traveling-wave tube comprising: means for providing a stream of electrons along a predetermined path, a plurality of axially aligned essentially annular electrically conductive spacer elements sequentially disposed along and encompassing said predetermined path, a plurality of electrically conductive plates each mounted between a pair of adjacent spacer elements to define in conjunction with said spacer elements a plurality of interaction cells, said plates defining aligned apertures in their central regions to provide a passage for said electron stream and further defining coupling holes in regions radially outwardly of said central regions for interconnecting adjacent interaction cells whereby a propagation path is provided for an electromagnetic wave in a manner to provide interaction between said electron stream and said electromagnetic wave, at least certain ones of said spacer elements each defining a cavity disposed externally of and communicating with the interaction cell defined by the said spacer element, each of said cavities being resonant at a preselected frequency, and a body of lossy material disposed in each said cavity and protruding into the adjacent interaction cell by a preselected distance.

6. A traveling-wave tube according to claim 5 wherein each said cavity and each said body is of essentially cylindrical shape and has its longitudinal axis disposed parallel to said preselected path.

7. A traveling-wave tube according to claim 5 wherein said preselected distance of protrusion is between essentially 5 percent and essentially 30 percent of the radius of said interaction cell.

8. A traveling-wave tube according to claim 5 wherein said preselected distance of protrusion is essentially the same for each said body.

9. A traveling-wave tube of the type which is severed into a plurality of amplifying sections, each isolated from one another with respect to electromagnetic circuit wave energy, comprising: means for providing a stream of electrons along a predetermined path, slow-wave structure means extending through each of said amplifying sections and defining a plurality of intercoupled interaction cells disposed sequentially along and about said predetermined path for propagating elec tromagnetic circuit wave energy in such manner that it interacts with said stream of electrons, means disposed between each pair of adjacent amplifying sections for precluding the passage of electromagnetic circuit wave energy between said adjacent amplifying sections while permitting the passage of said stream of electrons therebetween, means defining a plurality of cavities respectively disposed externally of at least selected ones of said interaction cells and sequentially along a direction parallel to said predetermined path, each of said cavities communicating with one of said interaction cells and being resonant at a preselected frequency, and a body of lossy material disposed in each said cavity and protruding into the adjacent one of said interaction cells by a preselected distance, the distance of protrusion of successive ones of bodies in at least one of said amplifying sections progressively decreasing as a function of longitudinal distance from the end of said one amplifying section adjacent said precluding means.

10. A traveling-wave tube according to claim 9 wherein the distance of protrusion of successive ones of said bodies in said one amplifying section decreases essentially linearly as a function of longitudinal distance from said end of said amplifying section.

ll. A traveling-wave tube according to claim 9 wherein said cavities and said bodies are of essentially cylindrical shape and have their longitudinal axes disposed parallel to said predetermined path.

12. A traveling-wave tube according to claim ll wherein at least selected ones of said bodies in said one amplifying section each define a planar lateral surface facing said stream of electrons and in a plane essentially perpendicular to the plane passing through the longitudinal axes of the said body and said predetermined path, the distance between the plane of said surface and the edge of the interaction cell into which the said body protrudes progressively decreasing as a function of longitudinal distance from the end of said one amplifying section adjacent said precluding means.

13. A traveling-wave tube comprising: means for providing a stream of electrons along a predetermined path; a wave propagating structure divided into at least first and second amplifying sections and disposed along and about said predetermined path, each of said sections including a plurality of axially aligned essentially annular electrically conductive spacer elements sequentially disposed along and encompassing said predetermined path, a plurality of electrically conductive plates each mounted between a pair of adjacent spacer elements to define in conjunction with said spacer elements a plurality of interaction cells, said plates defining aligned apertures in their central regions to provide a passage for said electron stream and further defining coupling holes in regions radially outwardly of said central regions for interconnecting adjacent interaction cells whereby a propagation path is provided for an electromagnetic circuit wave in a manner to provide interaction between said electron stream and said electromagnetic circuit wave; an isolator electrically conductive plate similar to the plates of said plurality but not defining any electromagnetic circuit wave coupling hole disposed between said first and second amplifying sections and axially aligned with the remainder of said plates, whereby the passage of electromagnetic circuit waves between said first and second amplifying sections is precluded while the passage of said electron stream therebetween is permitted; at least certain ones of said spacer elements each defining a cavity disposed externally of and communicating with the interaction cell defined by the said spacer element, each of said cavities being resonant at a preselected frequency; and a body of lossy material disposed in each said cavity and protruding into the adjacent interaction cell by a preselected distance. the distance of protrusion of successive ones of said bodies in at least one of said amplifying sections progressively decreasing as a function of longitudinal distance from said isolator plate.

14. A traveling-wave tube according to claim 13 wherein the distance of protrusion of successive ones of said bodies in said one amplifying section decreases essentially linearly as a function of longitudinal distance from said isolator plate.

15. A traveling-wave tube according to claim 13 wherein said cavities and said bodies are of essentially cylindrical shape and have their longitudinal axes disposed parallel to said predetermined path.

16. A traveling-wave tube according to claim l5 wherein at least selected ones of said bodies in said one amplifying section each define a planar lateral surface facing said stream of electrons and in a plane essentially perpendicular to the plane passing through the longitudinal axes of the said body and said predetermined path, the distance between the plane of said surface and the edge of the interaction cell into the said body protrudes progressively decreasing as a function of longitudinal distance from said isolator plate.

Claims

1. A traveling-wave tube comprising: means for providing a stream of electrons along a predetermined path, slow-wave structure means defining a plurality of intercoupled interaction cells disposed sequentially along and about said predetermined path for propagating electromagnetic wave energy in such manner that it interacts with said stream of electrons, means defining a plurality of cavities respectively disposed externally of at least selected ones of said interaction cells and sequentially along a direction parallel to said predetermined path, each of said cavities communicating with one of said interaction cells and being resonant at a preselected frequency, and a body of lossy material disposed in each said cavity and protruding into the adjacent one of said interaction cells by a preselected distance.

2. A traveling-wave tube according to claim 1 wherein said cavities and said bodies are of essentially cylindrical shape and have their longitudinal axes disposed parallel to said predetermined path.

9. A traveling-wave tube of the type which is severed into a plurality of amplifying sections, each isolated from one another with respect to electromagnetic circuit wave energy, comprising: means for providing a stream of electrons along a predetermined path, slow-wave structure means extending through each of said amplifying sections and defining a plurality of intercoupled interaction cells disposed sequentially along and about said predetermined path for propagating electromagnetic circuit wave energy in such manner that it interacts with said stream of electrons, means disposed between each pair of adjacent amplifying sections for precluding the passage of electromagnetic circuit wave energy between said adjacent amplifying sections while permitting the passage of said stream of electrons therebetween, means defining a plurality of cavities respectively disposed externally of at least selected ones of said interaction cells and sequentially along a direction parallel to said predetermined path, each of said cavities communicating with one of said interaction cells and being resonant at a preselected frequency, and a body of lossy material disposed in each said cavity and protruding into the adjacent one of said interaction cells by a preselected distance, the distance of protrusion of successive ones of bodies in at least one of said amplifying sections progressively decreasing as a function of longitudinal distance from the end of said one amplifying section adjacent said precluding means.

11. A traveling-wave tube according to claim 9 wherein said cavities and said bodies are of essentially cylindrical shape and have their longitudinal axes disposed parallel to said predetermined path.

12. A traveling-wave tube according to claim 11 wherein at least selected ones of said bodies in said one amplifying section each define a planar lateral surface facing said stream of electrons and in a plane essentially perpendicular to the plane passing through the longitudinal axes of the said body and said predetermined path, the distance between the plane of said surface and the edge of the interaction cell into which the said body protrudes progressively decreasing as a function of longitudinal distance from the end of said one amplifying section adjacent said precluding means.

13. A traveling-wave tube comprising: means for providing a stream of electrons along a predetermined path; a wave propagating structure divided into at least first and second amplifying sections and disposed along and about said predetermined path, each of said sections including a plurality of axially aligned essentially annular electrically conductive spacer elements sequentially disposed along and encompassing said predetermined path, a plurality of electrically conductive plates each mounted between a pair of adjacent spacer elements to define in conjunction with said spacer elements a plurality of interaction cells, said plates defining aligned apertures in their central regions to provide a Passage for said electron stream and further defining coupling holes in regions radially outwardly of said central regions for interconnecting adjacent interaction cells whereby a propagation path is provided for an electromagnetic circuit wave in a manner to provide interaction between said electron stream and said electromagnetic circuit wave; an isolator electrically conductive plate similar to the plates of said plurality but not defining any electromagnetic circuit wave coupling hole disposed between said first and second amplifying sections and axially aligned with the remainder of said plates, whereby the passage of electromagnetic circuit waves between said first and second amplifying sections is precluded while the passage of said electron stream therebetween is permitted; at least certain ones of said spacer elements each defining a cavity disposed externally of and communicating with the interaction cell defined by the said spacer element, each of said cavities being resonant at a preselected frequency; and a body of lossy material disposed in each said cavity and protruding into the adjacent interaction cell by a preselected distance, the distance of protrusion of successive ones of said bodies in at least one of said amplifying sections progressively decreasing as a function of longitudinal distance from said isolator plate.

16. A traveling-wave tube according to claim 15 wherein at least selected ones of said bodies in said one amplifying section each define a planar lateral surface facing said stream of electrons and in a plane essentially perpendicular to the plane passing through the longitudinal axes of the said body and said predetermined path, the distance between the plane of said surface and the edge of the interaction cell into the said body protrudes progressively decreasing as a function of longitudinal distance from said isolator plate.