US2727180A - Microwave reactance tube - Google Patents

Description

Dec. 13, 1955 M. 5. WHEELER MICROWAVE REACTANCE TUBE 2 Sheets-Sheet 1 Filed Sept. 20, 1950 XNVENTOR. )VVEfl/V 61 IVA [52515. 233% w ATTORNEY 2 Sheets-Sheet 2 M. 5. WHEELER INVENTOR fl /F0 5'. 171955255.

Y fia q ATTORNE MICROWAVE REACTANCE TUBE za'msa' IIIIIIIIIIIIIIIIIIIIIII Dec. 13, 1955 Filed Sept. 20, 1950 United States Patent 12 Claims. (Cl. 315-) This application relates to microwave spiral beam reactance tubes of which one beneficial use therefor is in conjunction with radar antenna scanning as more fully set forth in a companion application Serial No. 185,758, filed September 20, 1950.

An object of the present invention is to provide an improved reactance tube utilizing an electron stream within a resonant cavity at microwave frequency to shift the resonant frequency of the cavity.

Another object of the invention is to provide for a large frequency shift in an electrically efficient manner.

A further object of the invention is to provide, in conjunction with a cavity resonator, an electron stream and uniform coaxial magnetic field through a region of the cavity containing a maximum percentage of the total electric energy.

A further object of the invention is to provide an essentially constant electric field at said region of the cavity containing the maximum percentage of the total electric energy.

Again, an object of the invention is to provide a structure conveniently coupling the resonator to the microwave system.

Additionally, an object of the invention is to employ a resonator of rectangular symmetry and with a relatively short wide region of interaction.

At the same time, the invention has an objective of utilizing said resonator in alignment with the field and with the beam and with the waveguide input of the frequency being modulated.

Yet another object of the invention is to provide a compact, sturdy construction which is readily assembled, contains minimum number of parts and fabricating operations, and embodies simplicity of construction and operation.

Still further objects of the invention will appear to those skilled in the art to which it appertains, as the description proceeds, both by direct reference thereto and by implication from the context.

Referring to'the accompanying drawings in which like numerals of reference indicate similar parts throughout the several views:

Fig. 1 is an elevation which, in consequence of arbitrary positioning, will be referred to as a plan of a tube embodying my invention;

Fig. 2 is an end view looking from left to right, as at line 60 11- -11 of Fig. 1;

Fig. 3 is a longitudinal section on line llIIlI of Fig. 1; Fig. 4 is a cross-section looking into the cathode end of the tube as at line IVIV of Fig. 3;

Fig. 5 is a longitudinal sectional view as on line VV of Fig. 2;

Fig. 6 is a cross-sectional view looking into the cavity ,resonator from beneath the cathode as on line VIVI of Fig. 5;

. Fig. 7 isa longitudinal sectional view of a microwave spiral beam reactance tube, modified in construction from the specific showing of Figs. 1 to 6, and also embodying features of the invention;

Fig. 8 is a similar longitudinal sectional view but taken on aplane transverse to the plane of section of Fig. 7;

Fig. 9 is a cross section on line IXIX of Fig. 8;

Figures 10 and 11 are sectional views corresponding to Figs. 5 and 6 and showing a modification of the ribs forming the interaction region.

In the specific embodiment of the invention illustrated in said drawings, and with attention directed initially to Figs. 1 to 6, the reference numeral 15 designates a metallic housing here shown as generally cylindrical and evacuated. In the particular orientation presented by the drawings, the right end portion of said housing provides a large cylindrical chamber 16therein, hermetically sealed by an end cap 17 which is made of iron or other magnetizable metal to function, in conjunction with an external magnet 18, as a pole piece within the said chamber. Opposite from the metal cap, the chamber is very considerably restricted by an inner transverse metallic wall 19 parallel to the inwardly directed face of said cap. This transverse wall 19 has a rectangular cavity 20 therethrough symmetrically disposed with respect to the axis of the housing, said cavity having a width in one diametric direction of the housing much greater than the height in a diametric direction at right angles to the width, and having a length in the axial direction of the housing substantially equal to the height and commensurate with a half wave-length of the characteristic wave for which the device is intended. Said rectangular. cavity constitutes a resonator, and to render it more effective as a resonator, the ends thereof in directions axially of the housing are closed except for restricted or slit openings for passage of electrons, as will presently be described.

On inner transverse wall 19 within the chamberv 16 is secured, as by screws 21, a plate 22-3, preferably of copper, which extends across the end of cavity 23. This plate 22 has a diametric slot 23 partially across the same located symmetricaliy between and parallel to but of less length than the long dimensi' ns of width of the resonator. The height of the slot is considerably less than the height dimension of the resonator, and across said slot 23 are grid Wires or the like constituting an accelerator grid 23. Within chamber 16 and close to and parallel with said slot 23 and accelerator grid 23, is an elongated preferably flat, electron emissive cathode 24, and between the cathode and said slot is a control grid 25. The cathode may conveniently be of the indirectly heated type, and is shown having heater lead-in wires 26 thereto introduced into the chamber 16 by seals 7, and as having a lead-in connection 28 thereto introduced through a seal 29 for varying potential of the cathode as desired. Similarly a lead-in connection 36 is appliec to the control grid and passes to the exterior through a seal 31. A rectangular frame is provided in the present showing as means for mounting the cathode and control grid and comprises a pair of cleats 3-2 on opposite sides of the cathode and control grid, parallel thereto and fixed to the aforementioned plate 22 by brazing or otherwise. Transverse members 33 are secured to the ends of said cleats, said members being made of a suitable insulative material and appropriately apertured to receive and support end portions of the cathode and grid. By the construction shown and described ribbon-like beam of electrons may enter the resonator through slot 23 and its accelerator grid 23 fromcathode 24 under modulationcontrol of grid 25.

7 Within the resonator is provided a restricted interaction region 34 constituted by a pair of ribs 35 parallel to the cathode and slot 23 and of substantially the length of said slot so as to be spaced at their ends from the sides of the resonator. These ribs may be integral with-the housing and project from the;top and bottom of the resonator, and in a direction axially of the housing are of a dimension considerably less than the length of the resonator and located midway of that length. The opposed faces of these ribs constitute a condenser so the ribbon beam of electrons passing therebetween effectively alters the capacitance of the resonator. As the beam of electrons is under grid control or modulation, resonant frequency is electronically controlled by altering the capacitive reactance of the resonator.

In the construction of tube shown in Figs. 1 to 6, the end of the resonator remote from the entry slot for the beam is provided with a waveguide 36 for transfer of wave energy to and from said resonator. While the exterior of this waveguide is conveniently cylindrical, the interior is preferably rectangular in cross-section and has dimensions substantially the same as the corresponding dimensions of the resonator, namely, a half Wavelength in width. The outer end of this waveguide 36 is sealed with a suitable window closure 37. Associated with the sealed mounting of this Window closure is a choke coupling 37a by which the wave-energy is passed through said closure without attenuation.

The inner end of said waveguide is provided with a neck 38 the extremity of which is soldered or otherwise sealed to said housing. Within said neck is a copper plated iron disc 39 which has a slot 4% diametrically across the greater part thereof so the slot width is equal to the major or larger cross-sectional dimension of the inside of the waveguide, whereby said slot has a width equal to a half wave length. The disc functions as a fixed pole piece within the tube magnetically coupled to one pole leg of external magnet 18, and the slit therein, which connects longitudinally between the channel or interior of the waveguide and the rectangular cavity 20, functions as a transformer, for which purpose the minor dimension of the slit is less than the narrow or minor dimension of either the wave guide interior or the resonator. Said slot is parallel to and directly opposite the interaction space of the resonator and admission slot 23 for the electrons, into the resonator, but with a smaller short or minor dimension than either and such as to give the desired coupling between the reactance tube and the waveguide. The slit dimension in the direction of the axis of the housing and Waveguide is made substantially equal to a quarter-wave length. The waveguide is at ground potential, and the pole piece or disc 39 also functions as the anode for the electrons from cathode 24.

The housing 15 of the tube and the body of the waveguide are preferably copper or other non-magnetic metal. Magnetic fiux is caused to traverse the resonator in an axial direction, and as heretofore described, a magnet 18 is provided for that purpose with one pole piece applied to or constituting the closure for end chamber 16 and the other pole piece 39 located within the end of the waveguide at the end of the housing remote from the first described pole piece. The magnetic field obtains spiraling of the electrons which traverse the oscillating electric field of the resonator and maintain concentration of the beam in counteraction to the spreading tendency imparted thereto by the cyclic reversal of polarities in the afore-mentioned ribs 35.

The window end of the wave uide 35 looks into a magnetron, waveguide or other instrumentality constituting a driving source wherein micro-waves are present, and in appropriate relation thereto whereby the Wave energy from such source will enter said waveguide and induce an alternating electric field in said resonator in proper mode. in turn, the resonator is affected by the electron beam entering from the other side such that the efiective capacitance of the resonator is varied in response to grid control of the electron flow and thus the resonant frequency in the resonator is changed and this changed frequency reflects back to the driving source and changes the frequency thereof. It will be appreciated from the above that the present tube constitutes a reactive load and so is descriptively called a reactance tube and that it is effective with a driving source to apply a modulation thereto or to produce a change of resonant frequency of the system and obtain tuning to a desired frequency.

The specific reactance tube illustrated in said Figures 7 to 9 comprises a metallic housing which is shown, in the particular orientation of Fig. 9, as having the right end portion thereof cylindrical and the left end portion rectangular and permanently attached to the end of the cylindrical portion rather than being shown integral as in Figures 1 to 6. Essentially however, whether integral or attached, the portions of the housing, as in the previously described construction, in assembled relation provide a cylindrical chamber 16, hermetically sealed by an end cap 1?" which is made of iron or other magnetizable metal to function, in conjunction with an external magnet 18, as a pole piece within said chamber. Opposite from the metal cap, the chamber opens into the said rectangular left end portion of the housing through a slot 23 diametric to the said cylindrical chamber, said slot having accelerator grid 23 across the same as previously described. Within said cylindrical chamber 16 and parallel to said slot is an electron emissive cathode 24 and control grid 25 both having constructions, locations, mounting, connections and functions in conformity to description above given with respect to Figs. 1 to 6.

The rectangular portion of the housing beyond said slot 23 is constructed and arranged to constitute a resonator, and similar to the first-described qualifications thereof said resonator provides a restricted interaction region constituted by a pair of ribs parallel to the cathode and slot 23 and substantially the length of said slot so as to be spaced at their ends from the sides of the resonator. These ribs may be integral with the rectangular portion of the housing and project from the top and bottom of the resonator, and are of a dimension, in the direction of electron flow, considerably less than the length of the resonator where the designation of length of the resonator is also the dimension thereof in the direction of electron flow. in this modification, as well as in the first described construction, the ribs are midway of the said length of the resonator, and the opposed faces of the ribs constitute a condenser, such that the ribbon beam of electrons passing therebetween, effectively alters the capacitance of the resonator. As the beam of electrons is under grid control or modulation, resonant frequency is electronically controlled by thus altering the capacitative reactance of the resonator.

In the showing of Figs. 7 to 9, the Wall of the rectangular housing portion, which is copper or other non-mag netic material, directly opposite the electron admitting slot 23, constitutes the anode, and since it is relatively thin, the magnetic field is adequately effective by locating the leg of magnet 18 in close proximity to said wall at the out side thereof.

Furthermore, as the physical and electrical require ments for the modification of Figs. 7 to 9 contemplate passage of the driving energy directly through the resonator in transit from the magnetron to the antenna or other load, the side walls of the resonator are provided with H-transformer slot openings a and 40b in communication with the waveguide branch from the generator and to the antenna respectively. While the particular branch A is arbitrarily designated in Figs. 7 and 8, it will be understood that the same relation of the other branches B with a reactance tube identical with the showing of Figs. 7 to 9 is employed and the drawing is equally illustrative thereof except for the particular reference character applied to said branch. In the direction of energy passage from the input section of said branch through said reactance tube to the output section, said H-transformer slot opening 40a and 4% have a dimension equal to a quarter wave length of the characteristic wave for which the apparatus is designed.

To enable the reactance .tube to be maintained :under .vacuum, window closures 37 are ,providedat the junction .of thehranch section of the rave guide with ,thevsaidtube,

these window closures beingmounted as in Figures ,1 to 6 andeach having atchokecoupling37a associated therewith for effectively passing the wave-energy of the guide without imposition of impedance thereto by the window closure.

While specific embodiments and usese have been indicated for my improved reactance tube, reference thereto is by wayrofvexample and is not forrestrictive purposes, Vasthe tube maybe otherwise constructed and utilized within the present inventive concept directed primarily to its structure.

From the foregoing description, it is now clear .that an electron stream is used within resonant cavity at microwave frequencies to shift the resonant frequency of the cavity. The requirements have been fulfilled for a large frequency shift in an electrically efficient manner, the requirements including provision of a cavity resonant at the frequency of interest; .an electron stream and uniform, coaxial magnetic field through a region of the cavity containing a maximum percentage of the total electric energy; an essentially constant field throughout this region of interest and providing interaction with the electron stream; and convenient means of coupling the resonator to the microwave system. These conditions have been met with the resonator herein shown of rectangular symmetry having, by inclusion of ribs 35, a relatively short, wide region of interaction (as related to direction of electron flow). At the same time, an easily machined and calculated waveguide input can be taken advantage of, by orienting the beam with respect to the waveguide 36 as shown. The electron stream enters resonator 29 from the right'of Figs. 1, 3 and 5, crosses the rectangular interaction space 34 in the short direction, and continues therebeyond at constant velocity and the electrons are collected by the iron pole piece disc 39 which possess, in addition to its function as a magnetic pole piece, the functions of end wall for the resonator, anode for the electrons, by predetermined quarter wave length of slot 46 (in direction of electron path), also functions as a transformer. \Vindow 37 seals the left end of the waveguide so the entire interior of the tube may be maintained under vacuum, and that window admits electric driving energy to the resonator.

1n the showing of Figures 10 and 11, the construction of the ribs providing the interaction region therebetween diifers somewhat from the corresponding parts in Figures 5 and 6; but that otherwise the constructions correspond. Essentially, however, both forms shown produce an electronically variable impedance at microwave frequencies, both employing a static magnetic field and obtaining interaction between electrons and the radio frequency field in a region of uniform magnetic field. The magnetic field has its flux lines substantially am'al with or in the same generally forward direction of the electron transition or beam path, and the electric radio frequency. field is in a direction perpendicular between the facing faces of the said ribs} In operation, choice is made of an electron velocity for a given magnetic field to minimize the electronic loss in the reactance tube and obtain a large frequency shift, which is near maximum for that magnetic field.

In Figures 10 and 11, ribs 35a are shown having faces directed toward each other with gap spacing therebetween constituting interaction region 34a. These ribs differ from those of Figs. 5 and 6 in that they have a dimension (designated as length herein) in the general direction of travel of the electron beam equal to the distance from plate 22 to disc or polepiece 39 but have a width, transverse to the beam, less than the diameter of the housing 15. This arrangement maintains a relatively short region of interaction in the direction of flow of the electrons for maximum frequency shift but at the same time provides barriers which establish a zero field boundary at two ends ,oftheinteraction region. By .this means a cosine electric field distribution is obtained 'in the interaction region. This has the further beneficial efiect of materially reducingv electronic losses whichlare inherent in both types of construction due to theelectron velocity distribution causedby space charge. 'These characteristics of the cosine field distribution nullify .very substantially the need for uniform electron veloc'ityacross the beam.

The construction of Figures 10 and 11 furthermore has the additional advantages, that the cavity will have inherently a higher Q, which is generally advantageous; that the ratio of energy stored in the interaction region to the total energy stored in the cavity is increased and may be uilized to produce a greater frequency deviation; and alsothat the fabrication is less difiicult; all in addition to the advantage that the reactance tube with .a cosine field distribution through the interaction region will produce a larger reactive change with less losses than .a uniform field tube.

.1 claim:

1. A microwave spiral beam reactance tube comprising a resonator having a rectangularcavity with two .parallel slot openings at opposite sides thereof, rectangular parallel ribs in said resonator, said ribs having width, height, length and space therebetween dimensioned to constitute said space and interaction region proportionately similar to and centralized within the cavity of the resonator, a cathode parallel to and opposite said space, an anode opposite said cathode, .said cathode and anode being on opposite sides of said space for projection of an electron stream through said space, magnetic poles .oppositely located in the direction of the path of the electron stream fromthe cathode to said anode, one of .saidfltwoislot openings constituting va transformer slot opening for the resonator, and a window closure beyond said transformer slot opening.

2. A microwave spiral beam reactance tube comprising a rectangular resonator the walls whereof have minor dimensions and have long dimensions perpendicular to the minor dimensions, all of the long dimensions of the walls extending in the same general direction, said resonator having parallel slots at opposite ends thereof and having rectangular parallel ribs therein on two opposite walls of the resonator, said slots and ribs being in and on'difierent walls of the resonator, said ribs being directed toward each other with a slot-like space therebetween parallel to and in a common plane with said slots of the resonator, said slots, ribs and slot-like space having long dimensions extending in the same general direction as the long dimensions of the walls of the resonator, each of said ribs having its long dimension substantially equal to the long dimension of the other of said slots, a cathode opposite said one of said slots, and an anode opposite said cathode, said cathode and anode being on opposite sides of said slot-like space for directing electrons from said one slot to the other through said slot-like space between said ribs.

3. Amicrowave spiral beam reactance tube comprising a rectangular resonator having parallel slots the minor dimension whereof is less than and in the same general direction as a minor dimension of the resonator, said slots being at opposite ends of the resonator, rectangular parallel ribs in said resonator parallel to and spaced from said slots and projecting toward and normal to a plane common to said slots and providing a space between said ribs next said plane, said slots, ribs and said space between the ribs having long dimensions thereof extending in direction of the width of the resonator, each of said ribs having its long dimension substantially equal to the long dimension of one of said slots and less than the long dimension of the other of said slots and less than the resonator width, and a cathode opposite said one of said slots, and an anode opposite said cathode, said cathode and anode being on opposite sides of said space for directing electrons from said one slot to the other through said space between said ribs.

4. A microwave spiral beam reactance tube comprising a high Q cavity resonator the cavity whereof has an overall rectangular geometry, ribs in said resonator giving definition to a constricted interaction region therebetween of similar rectangular and proportionately smaller geometry than said cavity and centralized in said cavity for minimum influence of static electric fields and maximum immersion in a uniform static magnetic field, a cathode parallel to and as long as the long dimension of said interaction region, and an anode opposite said cathode, said cathode and anode being on opposite sides of said interaction region for producing a flow of electrons across the entire interaction region.

5. A microwave spiral beam reactance tube comprising a high Q cavity resonator the cavity whereof has an over-all rectangular geometry, ribs in said resonator disposed on two opposite walls thereof and each rib having direct contact only with the wall on which disposed, said ribs being directed with their long dimensions toward each other and in parallelism and giving definition to a constricted interaction region therebetween of similar rectangular and proportionately smaller geometry than said cavity and centralized in said cavity for minimum influence of static electric fields and maximum immersion in a uniform static magnetic field, a cathode parallel to and as long as the long dimension of said interaction region and an anode opposite said cathode, said cathode and anode being on opposite sides of said interaction region for producing a flow of electrons across the entire interaction region.

6. A microwave spiral beam reactance tube comprising a high Q cavity resonator the cavity whereof has an overall rectangular geometry, ribs in said resonator giving definition to a constricted interaction region therebetween of similar rectangular and proportionately smaller geometry than said cavity and centralized in said cavity for minimum influence of static electric fields and maximum immersion in a uniform static magnetic field, a cathode parallel to and as long as the long dimension of said interaction region, an anode opposite said cathode, said cathode and anode being on opposite sides of said interaction region for producing a flow of electrons across the entire interaction region, and magnetic means for producing a magnetic field in said interaction region in the direction of said flow of electrons.

7. A microwave spiral beam reactance tube comprising a high Q cavity resonator the cavity whereof has an overall rectangular geometry, ribs in said resonator disposed on two opposite walls thereof and each rib having direct contact only with the wall on which disposed, said ribs being directed with their long dimensions toward each other and in parallelism and giving definition to a constricted interaction region therebetween of similar rectangular and proportionately smaller geometry than said cavity and centralized in said cavity for minimum influence of static electric fields and maximum immersion in a uniform static magnetic field, a cathode parallel to and as long as the long dimension of said interaction region, an anode opposite said cathode, said cathode and anode being on opposite sides of said interaction region for producing a flow of electrons across the entire interaction region, and magnetic means for producing a magnetic field in said interaction region in the direction of said flow of electrons.

8. A microwave spiral beam reactance tube comprising a housing having a resonator therein, a magnetic pole piece and anode constituting one end wall of said resonator, said pole piece having a slot therethrough, and an elongated cathode opposite to and extending parallel to said slot, and a second pole piece, said second pole piece and said cathode being at the opposite side of the resonator from said slot.

9. A microwave spiral beam reactance tube comprising a housing having a resonator therein, a magnetic pole piece and anode constituting one end wall of the resonator, said pole piece having a slot therethrough, a cathode opposite said slot, and a second pole piece, said second pole piece and said cathode being at the opposite side of the resonator from said slot, and a grid between said cathode and resonator.

10. A microwave spiral beam reactance tube comprising a resonator having a rectangular cross section, a waveguide having a like cross section to the resonator and alined with said resonator, a magnet pole piece and anode interposed between said resonator and waveguide, a cathode at the opposite end of said resonator from said pole piece and waveguide, and a second pole piece located at the same end of said resonator as said cathode.

11. A microwave spiral beam reactance tube comprising a resonator having a rectangular cross section, a waveguide having a like cross section to the resonator and alined with said resonator, a magnet pole piece and anode interposed between said resonator and waveguide, and a cathode at the opposite end of said resonator from said pole piece and waveguide, said resonator and pole piece being of equal dimension in a direction from the cathode to the waveguide, and a second pole piece located at the same end of said resonator as said cathode.

12. A reactance tube having a resonator and a cathode chamber communicating one with the other, a magnet pole piece closing the outer end of the cathode chamber, a cathode in said cathode chamber, and a slotted disc at the end of the resonator away from the cathode chamber, said disc having a triple function as an end wall for the resonator, as a magnetic pole piece and as an anode.

References Cited in the file of this patent UNITED STATES PATENTS 2,410,054 Fremlin et al Oct. 29, 1946 2,466,922 Wax Apr. 12, 1949 2,523,841 Nordsieck Sept. 26, 1950 2,555,349 Litton June 5, 1951 2,579,654 Derby Dec. 25,1951 2,591,350 Gorn Apr. 1, 1952

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