US3838308A - Gang-tuned multicavity microwave tube - Google Patents

Abstract

A continuously tunable multicavity klystron and gang tuning apparatus therefor includes a separate tuning element in association with each klystron cavity resonator for setting the respective cavity resonant frequencies. A carriage which is translated in a generally straight line path in response to the rotation of a single tuning shaft carries a plurality of elongated deformable metal bands. These bands are variable pitch cams that are followed by cam followers coupled to the tuning elements for each of cavity resonators. Each deformable band is supported on the carriage at several discrete points along the band length, and adjustment screws are provided for setting the band height and consequent tuning element contour. Such adjustment compensates for the nonlinear tuning characteristic of the cavity resonators in order to thereby obtain a resultant substantially linear cavity resonant frequency versus tuning shaft rotation characteristic. Because of the deformable nature of the bands, a smooth and continuous cam surface is formed between these discrete points.

Description

United States Patent Merdinian et al.

[ Sept. 24, 1974 Primary Examiner-James W. Lawrence Assistant ExaminerSaxfield Chatmon, Jr. Attorney, Agent, or FirmJ. D. Slobod; D. R. Pressman; S. Z. Cole [57] ABSTRACT A continuously tunable multicavity klystron and gang tuning apparatus therefor includes a separate tuning element in association with each klystron cavity resonator for setting the respective cavity resonant frequencies, A carriage which is translated in a generally straight line path in response to the rotation of a single tuning shaft carries a plurality of elongated deformable metal bands. These bands are variable pitch cams that are followed by cam followers coupled to the tuning elements for each of cavity resonators. Each deformable band is supported on the carriage at several discrete points along the band length, and adjustment screws are provided for setting the band height and consequent tuning element contour. Such adjustment compensates for the nonlinear tuning characteristic of the cavity resonators in order to thereby obtain a resultant substantially linear cavity resonant frequency versus tuning shaft rotation characteristic. Because of the deformable nature of the bands, a smooth and continuous cam surface is formed between these discrete points.

7 Claims, 5 Drawing Figures PATENIED SEP241974 3.838.308- SHEEI 2 OF 3 GANG-TUNED MULTICAVITY MICROWAVE TUBE FIELD OF THE INVENTION The invention relates generally to electron beam tubes of the type which employ a plurality of microwave cavity resonators to interact with the electron beam. In its particular aspects the invention relates to a microwave tube having a plurality of cavity resonators which are gang-tuned.

BACKGROUND OF THE INVENTION In a multicavity electron beam tube such as a multicavity kylstron amplifier, typically an input microwave signal is coupled to an input resonant cavity to velocity modulate an electron beam. The velocity modulated beam becomes bunched as the velocity modulation causes current density modulation in the beam. The bunched electron beam excites an output resonant cavity to supply an amplified microwave signal. Generally, a plurality of intermediate buncher cavity resonators are interposed between the input and output cavities for sequential interaction with the electron beam wherein each buncher cavity increases the amplitude of electron beam modulation, thereby increasing the gain of the klystron. In such a multicavity arrangement, the input and output cavities are usually tuned to the center of a desired amplifier band, and the intermediate cavities are tuned to somewhat different frequencies about the center frequency to shape the klystron amplifier bandwidth characteristic and consequent amplifier output power by stagger tuning techniques. The input and output cavities and the intermediate cavities thus have a pattern of resonant frequencies in relation to the center frequency.

It is well known that the tuning of the resonant frequency of a cavity resonator may be effected by the provision of a movable tuning element in the cavity. The tuning element may variably influence the capacitance or inductance of the cavity or effectively vary the cavity size or shape.

One prerequisite to tuning a klystron with a structure as desired, is to provide a means to change the resonant frequencies of the cavities by substantially the same amount. This is necessary since it is required to simultaneously adjust the cavity resonant frequencies so that the spacing of each frequency about the new center frequency is substantially preserved.

The concept of providing gang tuners" to perform this function of moving the tuning elements for various cavities in unison in response to the movement of a single tuning shaft is well known. However, since the cavity resonant frequency is typically a non-linear function to tuning element displacement, it has been difficult to provide a mechanical mechanism that will faithfully provide the required linear resonant frequency versus the tuning shaft movement. Moreover, because of the desired pattern of cavity resonant frequencies and the normal non-linear relationship, each cavity instantaneously tunes at a different rate. Consequently, in the prior art it has been difficult to gang tune resonant cavities, while at the same time preserving the shape of the amplifier bandwidth characteristics.

One prior art gang-tuned multicavity microwave tube is disclosed and claimed in U.S. Pat. No. 3,132,280, issued May 5, 1964, and assigned to the same assignee as the present invention. This prior art device utilizes a plurality of flexible strands on windless drum elements carried on a single shaft. Each of the strands is coupled to the cavity tuning elements, and upon turning the shaft, gang tune the microwave tube. This structure has given acceptable performance in previous tubes, although it has been found that for fine tuning of each element to exactly the right location over the full bandwidth, the mechanism has left something to be desired. Basically, the single adjustment on the drum elements does not provide for the known variations over the range of frequencies that are now known to exist. Also, the structure of the long strands does not lend itself well to a compact arrangement, thus making the tube assembly relatively bulky. The need for a more accurate, continuously adjustable mechanism, and one that is more compact for modern day, space limited application, has thus been identified.

Another prior art mechanism for performing the gang-tuning function is disclosed in U.S. Pat. No. 3,617,799, issued Nov. 2, 1971, and also assigned to the same assignee as the present invention. This patent shows a later attempt to solve the problem of nonlinear tuning functions of the resonant cavities and the need for simultaneously tuning the cavities in a gang by equal amounts about a central frequency. This prior structure, however, falls short of the present needs in this field, since the tuning of the various cavities cannot be continuous over a range due to the interruptions between the screw cam elements, and the range of adjustment is sorely restricted by virtue of the circumference of the tuning wheels.

OBJECTS OF THE INVENTION It is an object of the present invention to provide a new and improved gang tuned multicavity microwave tube overcoming the prior art shortcoming.

It is a further object of the present invention to provide a gang tuned multicavity microwave tube which substantially preserves a desired pattern of cavity resonant frequencies over a relatively wide range'of tube center frequencies.

It is yet another object of the present invention to provide a tuning mechanism particularly adapted for a gang-tuned microwave tube providing continuous, accurate tuning.

It is another object of the present invention to provide a gang-tuned multicavity microwave tube exhibiting a substantially linear tuning characteristic in response to the movement of a single tuning shaft.

It is still another object of the present invention to provide a gang-tuning mechanism for multicavity microwave tubes which is compactly integrated with such tubes.

SUMMARY OF THE INVENTION riage has a plurality of elongated cams mounted thereon and engages a threaded portion of a rotatable tuning shaft. Each cam, in one to one correspondence with each of the cavities. is disposed to be followed by a cam follower extension of each tuning element to effect continuous linear tuning over the entire frequency range of the tube in response to tuning shaft rotation and consequent carriage translation.

Another feature of the present invention is that the cams are deformable bands which are supported by the carriage at a plurality of discrete points along the length of eaeh band. The deformability of the bands enables setting the cam contour to obtain a linear tuning frequency versus tuning shaft rotation characteristic.

Still another feature of the present invention is the provision of adjustment screws for deforming the bands at each discrete point thereby independently setting the desired cam follower displacements. The adjustment screws also provide means for obtaining various gainbandwidth characteristics from one basic tube structure.

Other objects, features, and advantages of the present invention will become apparent upon a perusal of the following detailed description of two specific embodiments thereof taken in conjunction with the appended drawing wherein:

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic line drawing of the side view of a gang-tuned multicavity klystron in accordance with the present invention illustrating the microwave tube parts in conjunction with the tuning mechanism;

FIG. 2 is a partial cross-sectional view along the lines 22 of FIG. 1 showing the gang-tuning mechanism including a cam and cam follower;

FIG. 3 is a stepped cross-sectional view along the lines 33 of FIG. 2 showing the transverse section of the carriage and cams and cam followers;

FIG. 4 is a broken cross-sectional partial view in the same direction as FIG. 2 showing an alternate cam follower embodiment; and

FIG. 5 is a view in cross section along the lines 5-5 of FIG. 4.

DETAILED DESCRIPTION OF THE DRAWING Referring to FIG. 1, the multicavity microwave tube of the invention is seen to comprise a klystron portion in association with a gang-tuning mechanism 11 which includes a carriage 12 (see also FIG. 2). The carriage 12 is translated horizontally (into or out of the page viewing FIG. 1) on wheels 14 to effect, by means which will be fully understood as the discussion proceeds, simultaneous vertical motion of the tuning elements 17 for the various klystron re-entrant cavity resonators 16.

The multicavity klystron portion 10 is of the same general configuration as disclosed in previously cited U.S. Pat. No. 3,617,799 and includes an electron gun portion 18 for forming and projecting a beam of elec trons 20 over an elongated horizontal path to a collector electrode 22. Electron gun 18 includes a thermionic cathode 24 from which electrons are emitted. To fully accelerate the electrons in a relatively short space. the tube is provided with a centrally apertured anode electrode 21 downstream from the cathode 24. The beam 20 passes through the anode aperture and thereafter passes sequentially through apertures in each of the cavity resonators 16 prior to the beam impinging upon the collector 22. Anode 21 and collector 22 are at ground potential while cathode 24 is maintained at negative potential with respect to ground by dc. power supply 23. As is usual. a magnetic focusing structure (not shown) coaxial with the electron beam 20, provides an axial magnetic field along the beam 20 to confine the cross section of beam 20 during its passage through the region including all of the cavity resonators 16.

The first cavity resonator encountered by electron beam 20 is the input cavity 26 to which an input microwave signal is coupled via input line 28 to velocity modulate electron beam 20. A plurality of buncher resonant cavities 30 are sequentially encountered by electron beam 20 which thereafter encounters output cavity resonator 32. Each buncher cavity increases the microwave modulation of the electron beam to increase the gain of the klystron l0 and consequentlythe amplitude of the output microwave signal which is extracted from the output cavity resonator 32 via coupling 34.

The various cavity resonators 16 are not generally tuned to exactly the same microwave resonant frequency, but rather are tuned to slightly different frequencies about a microwave center frequency to shape the gain-bandwidth characteristic of the amplifier by stagger tuning techniques. Typically, the input and output cavity resonators 26 and 32, respectively, are tuned to the microwave center frequency and the buncher cavity resonators 30 are tuned to various microwave frequencies about the center frequency to generate the intended passband of klystron amplifier l0.

Tuning elements 17 for changing the cavity resonant frequencies are preferably plungers which project into the cavity resonators l6 and which are mounted for vertical movement. In particular, the tuning elements 17 are preferably sliding shorts for changing the electrical length of the cavity resonators 16. A suitable sliding short-type tuning plunger is disclosed and claimed in U.S. Pat. No. 3,618,518, issued Oct. 19, 197], and assigned to the same assignee as the present invention. Other tuning elements which are essentially probes for influencing the cavity resonator inductance or capacitance are suitable or the purposes of the invention. In addition, tuning elements of the type which bear upon and deform a wall of the cavity resonators may be used. Whatever tuning element type is used, an actuating rod portion or equivalent 36 is fixedly attached to the tuning element for moving the element vertically in the orientation of the figures and perpendicularly to the beam 20. The rods 36 protrude vertically through an aperture 37 in the cavity resonators 16. Each actuating rod 36 also passes through a vacuum sealing bellows 38.

At the bottom ends of the actuating rods 36 are carried cam following rollers 40. Each roller 40 rides upon an associated inclined cam 42 carried by the carriage 12. As the carriage is translated horizontally and perpendicularly to the beam 20, the cam following rollers 40 for each actuating rod are driven in unison, but by different amounts as adjusted. Responsively, the plungers 17 are moved in a manner to change the center frequency of the tube while substantially preserving the intended frequency spacing between the various cavity resonant frequencies, thereby substantially preserving the intended gain-bandwidth characteristics of the klystron 10.

Referring next to FIGS. 2 and 3, the mechanical parts of the gang tuning mechanism will be better understood. The mechanical parts of the gang-tuned klystron are enclosed in a housing 44 of a non-magnetic material, so as not to influence the electron beam direction. Similarly, all mechanical parts are preferably nonmagnetic.

The carriage 12 comprises an elongated plate 46 which carries the plurality of spaced apart elongated inclined cams 42, with each cam 42 disposed below one of the cam following rollers 40. A threaded block 48 is fixedly attached to the bottom of plate 46 by screws 50. A rotatable tuning shaft 52 passing through the block 48 is journalled at opposite sides of the housing and is driven by a crank type tuning knob 54 external of the housing to effect translation of the carriage 12. The majority of the shaft 52 is externally threaded for translating the block 48 and consequently the carriage 12 parallel to the tuning shaft 52. At the point where the tuning shaft 52 exits the housing 44, the tuning shaft passes through a collet member 56 retained by the housing. The member 56 may be tightened upon the tuning shaft by a coaxially surrounding conically apertured locking knob 58. This combination locks the angular position of the tuning shaft, and consequently the position of the carriage 12 along its horizontal path of movement. The cams 42 are inclined (see FIG. 2) in the direction of carriage movement for vertically moving the actuating rods 36 as the carriage is translated.

Any tendency for horizontal movement, such as the downward pushing force of the rollers 40 on the in clined bands, is prevented by the locking knob 58 when activated.

Below the plate is fixedly attached the shafts 60 for the four wheels 14. The wheels 14 ride upon atop horizontal surface 62 provided by two laterally spaced apart blocks 63. Blocks 63 are supported by the base of the housing 44 and one of the blocks 63 is provided with an elongated slot 64 in the surface 62 running the length of intended carriage translation. The two wheels on the side of'the carriage above the one block are pro vided with a radial flange 66 which projects into the slot 64 to provide a track for laterally guiding the carriage 14.

Above the carriage plate 12 are a plurality of spaced apart cam carrying blocks 68. The cam carrying blocks 68 are each supported at opposite ends on the tops of screws 70, which are threaded vertically upward into the plate 46. Screws 71, threaded into block 68 from the underside of plate 46, draw the blocks 68 downward against the screws 70. The screws 70 permit the independent adjustment of the general or concerted incline of each of the blocks 68, and consequently the gang adjustment of the cams 42 carried by the blocks.

The earns 42 are pinned to the block at opposite ends 73 with pins 72 and springs 76 are stretched between the pins 72 and corresponding pins 74 fixedly carried by the plate 46. This arrangement forces the block 68 against the inclined setting screws 70 during the time when screws 71 are loosened to permit adjustment. Consequently, the cam follower displacement at the two end points of the cam may be independently set by simply adjusting the screws 70.

The elongated earns 42 are each relatively thin deformable metal bands. At a plurality of intermediate points 77 along the cams 42, projections are provided on the underneath side, and threaded support rods 78 are pinned to the cam. This structure provides a means for deforming the shape of the cams to the nonlinear but smooth contour required to continuously compensate for the inherent nonlinearity in each independent cavity tuning characteristic. This unique combination of elements allows independent setting of the cam follower displacement at these intermediate points, and thus the infinite range of contours required.

Axially bored screws 79 are internally, as well as externally, threaded with threads of slightly different pitches. The outer threads engage correspondingly threaded holes in the block 68. Each of the support rods 78 is threaded by engaging the internal threads of a corresponding screw 79. Rotation of the screws 79 permits a very fine vertical adjustment of the height of each of the points 77 with respect to the block 68. Consequently, utilizing adjustment screws and 79, the vertical height of the cams at a plurality of discrete points along the cam length may be adjustably set to gain the variable relationship required non-linear compensation described above.

To explain further, it is convenient to consider the horizontal surface 62 on which the wheels of the carriage ride as a reference plane. [t is clear that the various adjustment screws carried by the carriage 12 provide means for independently, separately adjusting the height of the cam surface with respect to the reference plane at each of a plurality of discrete points along the length of the cam. The deformable feature of cams 42 enables the adjustment of cam height at the interior discrete points 77 since if the cams were not deformable, adjustment would only be possible at two points such as the end points 73. The continuous nature of the bands 42 allows the desirable infinite coordinated adjustment of the elements 17 over the design range of the tube, rather than only spaced, incremental adjustments, as in the prior US. Pat. No. 3,617,799, cited supra.

Each actuating rod 36 passes through the aperture 37 in cavity resonator lower wall 80 (see FIG. 2), then through a first apertured plate 82 below the cavity wall, and thereafter through a second apertured plate 84, forming a portion of the enclosure 44. The actuating rod 36 slides in a bushing 86 for vertical guiding action. A radially flanged cylinder 88 is fixedly attached coaxially to actuating rod 36 between the first and second plates to provide a stop against the top of the second plate 84. This stop is provided to prevent any damage of the associated tuning element when maximum lower end adjustment is reached or if the carriage parts are removed. The actuating rods 36 are pinned to a third plate 90 just above the rollers 40, and independent compressed spring pairs 92 act between the fixed first plate 82 and each plate 90 carried by each of the actuating rods 36 to force each cam follower roller 40 against the corresponding cam 42. The springs 92 are mounted on axially telescoping rod and tube combinations 93a and 93b, respectively, and the same pass through large apertures 94 in the second plate.

Reference is next made to FIGS. 4 and 5 where two views of an alternate, cam capturing cam follower 101 is shown. Therein, the end of the actuating rod 36 is fitted with ears enclosing a generally rectangular area 102 through which the cross section of the cam 42 fits. A ball seated in an axial bore 104 in the actuating rod is forced by spring 105 tightly into engagement with the cam surface, in turn lifting the bottom of the cam 42 against a bottom interior surface 106 formed by the ears 100. Capture of the cams 42 in the cam follower prevents any possibility that the cam followers will not ride along the centers of the narrow cams 42 or drop off the cams 42 altogether.

It is clear that numerous modifications are possible within the spirit and scope of the invention, For example, the cams 42 could be carried by the actuating rods 17 and the carriage 12 could carry the cam followers.

While there has been described and illustrated several specific embodiments of the invention, it will be clear that variations in the details of the embodiments specifically illustrated and described may be made without departing from the true spirit and scope of the invention as defined in the appended claims.

What is claimed is:

1. A continuously tunable microwave tube apparatus comprising:

a housing;

electron gun means within said housing for forming and directing a beam of electrons over an elongated path;

a plurality of cavity resonators, within the housing,

arranged along the beam path for successive electromagnetic interaction with the beam;

a movable tuning element associated with each cavity resonator for adjustably setting the resonant frequency of each cavity;

a plurality of movable cam followers, each follower coupled to a corresponding one of the tuning elements, whereby the resonant frequency of each cavity resonator is variable by the motion of a corresponding cam follower;

a movable tuning shaft having an operative portion within the housing;

a carriage mounted for translation along a generally straight path defined by an axis within said housing, said carriage having means for engaging said operative portion in a manner so that the carriage is translated in response to movement of said tuning shaft; and

a plurality of elongated cams on the carriage, said cams being inclined with respect to the carriage axis, each cam being disposed to be followed by a corresponding one of the cam followers, and means to shape said cams to provide a substantially linear cavity resonant frequency versus tuning shaft characteristic.

2. The apparatus of claim 1 wherein the electron gun means forms and directs an electron beam along a substantially straight path, said carriage axis being perpendicular to the beam path.

3. The apparatus of claim 2 wherein the cams are elongated, deformable bands mounted on the carriage at discrete points along the bands.

4. The apparatus of claim 3 wherein said means to shape the bands comprises means for deforming the bands so as to adjust the position of each cam follower at each of the discrete points.

5. The apparatus of claim 4 wherein the tuning shaft is mounted for rotation in combination with a tuning knob external of said housing coupled to the tuning shaft for rotating the shaft.

6. In combination with a microwave tube having a resonant cavity in energy exchange relationship with an electron beam gun, and a movable frequency tuning element in association with the resonant cavity, and a cam follower coupled to said tuning element, the tuning mechanism comprising:

a cam movable with respect to said cam follower along a path defining an axis, said cam comprising an elongated deformable band upon which said cam follower rides, said cam being continuous and inclined with respect to said axis, tuning means for translating said cam to said axis, tuning means for translating said cam to adjust said tuning element in said cavity; and

means for individually adjusting the distance of the band from the axis at a plurality of spaced apart discrete points along the band length, whereby said cams may be shaped to provide a substantially linear cavity resonant frequency versus tuning means motion characteristic.

7. The tuning mechanism of claim 6 wherein said means for translating the cam moves along a substantially straight path.

Claims (7)

1. A continuously tunable microwave tube apparatus comprising: a housing; electron gun means within said housing for forming and directing a beam of electrons over an elongated path; a plurality of cavity resonators, within the housing, arranged along the beam path for successive electromagnetic interaction with the beam; a movable tuning element associated with each cavity resonator for adjustably setting the resonant frequency of each cavity; a plurality of movable cam followers, each follower coupled to a corresponding one of the tuning elements, whereby the resonant frequency of each cavity resonator is variable by the motion of a corresponding cam follower; a movable tuning shaft having an operative portion within the housing; a carriage mounted for translation along a generally straight path defined by an axis within said housing, said carriage having means for engaging said operative portion in a manner so that the carriage is translated in response to movement of said tuning shaft; and a plurality of elongated cams on the carriage, said cams being inclined with respect to the carriage axis, each cam being disposed to be followed by a corresponding one of the cam followers, and means to shape sAid cams to provide a substantially linear cavity resonant frequency versus tuning shaft characteristic.

2. The apparatus of claim 1 wherein the electron gun means forms and directs an electron beam along a substantially straight path, said carriage axis being perpendicular to the beam path.

3. The apparatus of claim 2 wherein the cams are elongated, deformable bands mounted on the carriage at discrete points along the bands.

4. The apparatus of claim 3 wherein said means to shape the bands comprises means for deforming the bands so as to adjust the position of each cam follower at each of the discrete points.

5. The apparatus of claim 4 wherein the tuning shaft is mounted for rotation in combination with a tuning knob external of said housing coupled to the tuning shaft for rotating the shaft.

6. In combination with a microwave tube having a resonant cavity in energy exchange relationship with an electron beam gun, and a movable frequency tuning element in association with the resonant cavity, and a cam follower coupled to said tuning element, the tuning mechanism comprising: a cam movable with respect to said cam follower along a path defining an axis, said cam comprising an elongated deformable band upon which said cam follower rides, said cam being continuous and inclined with respect to said axis, tuning means for translating said cam to said axis, tuning means for translating said cam to adjust said tuning element in said cavity; and means for individually adjusting the distance of the band from the axis at a plurality of spaced apart discrete points along the band length, whereby said cams may be shaped to provide a substantially linear cavity resonant frequency versus tuning means motion characteristic.

7. The tuning mechanism of claim 6 wherein said means for translating the cam moves along a substantially straight path.

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