US3022476A

US3022476A - Window assembly

Info

Publication number: US3022476A
Application number: US757576A
Authority: US
Inventors: Arthur R Koch
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1958-08-27
Filing date: 1958-08-27
Publication date: 1962-02-20
Anticipated expiration: 1979-02-20

Description

Feb. 20, 1962 A. R. KOCH wINDow ASSEMBLY 2 Sheets-Sheet 1 Filed Aug. 27, 1958 Feb. 20, 1962 A. R. KocH 3,022,476

WINDOW ASSEMBLY Filed Aug. 27, 195e 2 sheets-sheet z l INVENTORI ARTHUR R. KOCH,

. HIS ATTORNEY.

nite States 3,022,476 Patented Fel). 20, 1962 3,022,476 WINDOW ASSEMBLY Arthur R. Koch, Schenectady, N.Y., assigner to General Electric Company, a corporation of New York Filed Aug. Z7, 1958, Ser. No. 757,576 Claims. (Cl. S33- 98) My invention relates to waveguide window constructions and pertains more particularly to a new and improved waveguide window assembly adapted for extremely high power applications.

In electron systems employing waveguide structures it is sometimes desirable to provide a window assembly between waveguide sections in order to separate different atmospheres in the system without adversely affecting the transmission characteristics thereof. It is generally desirable that the window assembly be simple in construction, vacuum tight, and free of structural characteristics that would result in undesirable radio frequency field perturbations. Additionally, it is desirable that the window assembly be adapted to provide good uniform electrical contact between the opposed edges of waveguide sections interconnected by the Window assembly, thereby to insure a substantially uniform RF current flow path between the waveguide sections and, thus, provide a substantially well-matched structure over a wide frequency range. Furthermore, it is desirable that the dielectric window of the assembly be protected from cracking and other damage caused, for example, by temperature variations during assembly and operation and by electrical breakdown through the window. Still further, it is desirable that the window assembly be adapted for easy dis-assembly and reworking or repairs in the event of failure of the dielectric window. These desiderata become of increasingly greater importance when a window assembly is constructed for extremely high power applications such, for example, in connecting the waveguide output of a high power klystron amplifier tube to a section of waveguide transmission line.

Accordingly, a primary object of my invention is to provide a new and improved waveguide window assembly which is particularly adapted for extremely high power applications.

Another object of my invention is to provide a waveguide window assembly including improved means for simply mounting a window frame therein and so as to provide a vacuum tight welded seal with the weld disposed outwardly of the high intensity RF field and, thus, rendered ineffective for causing undesirable RF field perturbations.

Another object of my invention is to provide a new and improved waveguide window assembly including a new and improved RF gasket arrangement adapted for assuring a substantially uniform RF current flow path between the ends of sections of waveguide interconnected by the assembly.

Another object of my invention is to provide a new and improved dielectric window construction including an improved -framing arrangement adapted for increased heat dissipation from the window sealing areas, high RF vconduction and for avoiding electrical breakdown through the window.`

` Still Vanother object of my invention is to provide a new Vand improved waveguide window assembly including improved means for facilitating both assembly and dis-as sembly and including a welded frame mounting arrangement adapted for easy and repeated removal of the seal thus to permit repair of damaged window elements.

Further objects and advantages of my invention will become apparent as the following description proceeds and the features of novelty which characterize my invention will be pointed out with particularity in the claims annexed to and forming part of this specification.

In carrying out the objects of my invention I provide axially aligned waveguide sections, the opposed ends of which are fitted with flanges. interposed between the rims of the flanges is an annular collar including an annular coolant passage. Secured coaxially in one of the flanges and disposed radially remote from the inner rim of the waveguide is a metal sleeve which extends into an annular recess in the cooling collar. Fitted in the sleeve is a cup-shaped window frame, the rim of which is welded to the end of the sleeve and is also positioned in the annular recess in the cooling collar. An inner frame of high heat conductivity and low electrical resistance material is secured to the inner edge of the cup-shaped frame. The inner edge of the inner frame which is substantially thick, radially straight and smoothly rounded is brazed to and sandwiched between the rim of a dielectric window and a dielectric washer. Disposed in another annular recess in the cooling collar immediately adjacent the inner rims thereof on both sides of the collar are RF gaskets each comprising a malleable metal tube containing a malleable metal wire. The gaskets are disposed in gasket seats and the flanges are adapted for being tightened down on the coling collar which deforms the metal tubes of the gaskets to effect compressive engagement thereof with the wires therein.

For a better understanding of my invention reference may be had to the accompanying drawing wherein:

FIGURE 1 is a partially sectionalized exploded perspective view of a window assembly constructed according to a form of my invention;

FIGURE 2 is a diametrical sectional view illustrating my invention;

FIGURE 3 is an enlarged fragmentary sectional view illustrating in greater detail the outer frame sealing arrangement and gasket before the latter is deformed;

FIGURE 4 is an enlarged fragmentary sectional view illustrating the dielectric window sealing construction;

FIGURE 4A is a greatly enlarged fragmentary sectional view illustrating the cross sectional configuration of the dielectric window frame; and

FIGURE 5 is a greatly enlarged fragmentary sectional view of the radio frequency gasket after deformation thereof.

Referring to FIGURE 1, I have shown my window assembly disposed between and interconnecting the opposed ends of axially aligned waveguide sections 1 and 2. The waveguide section 1 is shown as of circular cross section and can comprise, for example, the RF power output of a high frequency electric discharge device such as a klystron, and the waveguide section 2 is shown as of rectangular cross section and can comprise, for example, a section of a transmission line to an antenna. It will be understood, however, that the present invention is employable with waveguide sections of any cross sectional configuration.

' The window assembly is adapted for sealing the waveguide sections from each other in a vacuum or fluidtight manner in order that the sections may be maintained at different atmospheres both with regard to composition and/0r pressure, permitting channeling or propagation of electromagnetic energy through the interconnected guide sections and affording a smooth high-frequency energy transmission through the guide sections.

As seen in both FIGURES 1 and 2 the window assembly includes a substantially heavy flange 3 secured, as by brazing, to the end of the waveguide section 1. The flange 3 includes an internal shoulder 4 which defines a central aperture 5 and which is thinner than the outer rim of the flange. Additionally, a raised or longitudinally n elongated rim d is provided about the inner edge of the shoulder l or immediately about the aperture S. The purpose for the shoulder 4 and the raised rim 6 will be brought out in detail hereinafter.

As better seen in FIGURE 3, I have provided in the face of flange 3 adjacent the outer edge thereof or radially remote from the center of the aperture 5 an annular recess 7. Disposed and brazed in the recess 7 is one end of a cylindrical sleeve S formed preferably of Monel. The sleeve 8 has positioned therein a cup-shaped outer fra.. e 9 of a dielectric window construction generally designated ld. The outer frame 9 which is preferably formed of Monel includes a cylindrical rim 11, the edge of which is secured and sealed by a weld 12 to the corresponding edge of the sleeve 3. F.the depth of the cup-shaped frame 9 relative to the length of the sleeve 8 is such that when the seal 12 is completed the outer frame 9 will engage the raised rim 6 on the flange 5 but will be otherwise spaced therefrom.

As seen in FlGURES l, 2 and 4, the inner edge of the outer frame 9 is coined or bent in a frusto-conical manner away from the flange 4. Additionally, on the side opposite the flange i the inner rim of the outer frame 9 is recessed or stepped for receiving and having brazed therein the outer rim of an inner frame 13. For a purpose to be brought out in detail hereinafter, the inner frame 1? is formed preferably or" copper and is re tively thick or of substantial thickness relative to the frame 9 having, for example, a thickness of approximately .049. ln cross section, the inner frame has the general conhguration of a widely opened S or, in other words, is slightly bent first in one direction and then in another with substantially wide radii. This conguration enables some thermal radial expansion and contraction but is such as not to atiord any sharp corners which could act as points of high voltage stress concentration and, thus, as starting points for electrical breakdown through the dielectric window construction, yet to be described.

The inner edge 14 of the inner frame 13, as best seen in FGURE 4A, extends straight radially and is smoothly rounded on its edges, as by polishing, to avoid any sharp edges and thus also avoiding high voltage concentrations and the possibility of electrical breakdown through the dielectric window. The edge 14 of the inner frame is seated in and bonded to a peripheral step 15 formed in the edge of the window 1t). Disposed in another peripheral step le in the window 1d and bonded to both the window il@ and the surface of the rim 14 on the inner frame 13 is a dielectric washer or annulus 17. Thus, the straight round edged portion 14 of the inner frame is sandwiched or embedded in dielectric material, the washer 17 serving both to back up the bond between the inner frame and the window and to embed the inner rim of the inner frame in dielectric material, thus to minimize any tendency toward electrical breakdown through the window. A rim 18 on the outer edge of the window in extends over substantially all of the inner frame 13.

As pointed out above, the ceramic washer 17 serves to back up the seal between the inner frame rim 14 and the window 1d and, additionally, cooperates with the window in completely embedding in dielectric or ceramic material the inner edge of the frame 14 with no sharp metal point protrusions extending in or toward the ceramic material. This arrangement, in conjunction with the smooth rounded radially straight configuration of the inner edge or rim 14 of the inner frame 13, serves to minimize any tendency toward high voltage concentrations or gradients about the rim of the inner frame which could initiate electrical breakdown through the ceramic window il@ and -result in failure due to fracture or punctures.

Failure of the ceramic window and seals due to thermal expansion and contraction is avoided by substantial heat dissipation effected by the relatively thick copper construction of the inner frame 13. The copper is a high heat conductor and this, in conjunction with the substantial thickness thereof, affords a substantially low resistance heat path away from the window to the outer frame 9 for external dissipation. Additionally, the copper ot' the frame 13 offers low electrical resistance and, thus, no substantial amount of heat is generated by RF currents flowing thereover. Accordingly, in my device the seals are adapted for being maintained substantially cool to avoid thermally caused cracking or seal failures.

Any suitable ceramic-tc-metal seals may be employed *etween the inner frame 13, ceramic window 1d, and washer 17. I have found particularly effective seals obtained by disposing titanium shims between the elements to be brazed and heating in a suitable atmosphere to a temperature suiicient for causing a bonding reaction between the material of the elements to be bonded. Seals between the frame rim 1d and the ceramic member of approximately Ms" radial length have been found particularly eitective.

Referring to FIGURES l and 3 there is provided in the window assembly an annular cooling collar 29 which can comprise a first annular member formed with an annular recess 2l over which there is suitably secured, as by screws (not shown) an annular cover member 222. The members 2lb and 22 thus cooperate to provide an annular coolant passage Z3 to which are suitably connected the coo-ling fluid inlet and outlet and respectively.

The face of the member opposite the recess 2l is machined to include another recess This recess is adapted for receiving the welded sleeve 3 and rim 11 of the frame 9 when the window construction is assembled in the manner illustrated. The illustrated assembly is adapted for being maintained, for example, by machine screws 27 shown in FEGURE 2. The screws 27 extend through the flange 3 and threadedly engage the member 2t), whereby these members may be drawn together for a purpose to be brought out in detail hereinafter. When the construction is assembled in the manner illustrated, the weld 12 and the rims connected thereby are disposed remote or isolated from the high intensity RF fields in the waveguide sections during operation and, therefore, the weld 12 is rendered ineffective for causing any undesirable RF field perturbations.

Also machined in the fact of the member Ztl and immediately adjacent the inner edge thereof is an annular recess 28. Disposed 1n the recess and as best seen in FIGURES 3 and 5, is an RF gasket generally designated 29. The gasket 29 comprises two concentric members of a soft or malleable metal which has a low electrical resistance such, for example, as copper or aluminum and, as seen in FIGURE l, can comprise a circuitous element shaped to conform generally to the approximate inside dimensions of the waveguide sections to be joined electrically.

The gasket 2.9 comprises an outer tubular element 36 and a concentric inner wire-like element 31. In the enibodiment illustrated l form the

elements

30 and 31 of copper with the outside element comprising a 1/s outside diameter copper tubing having a 1,/64" thick wall and the inner element comprising a 1AG diameter copper wire. After Shaping the gasket as desired l anneal it in a suitable atmosphere for properly softening it. Then I place the gasket in the annular recess 28 which, as seen from the drawing, is of such depth that when the

members

3 and 20 are drawn together or toward each other by tightening the screws 27, the tubular element 30 is compressed between the seat of the recess 25 and the inner surface of the frame 9. This collapses and deforms the outer element 30 to the point where the inner surface thereof engages the wire 31 therein, in the manner shown in FGURE 5. With the engagement between the element shown in FlGURE 5 there is aforded a continuous low resistance RF current path through the gasket between the members 2@ and through the gasket 29. ln turn, the compressive forces exerted cause the frame t? to bear with substantial pressure on the rim 6 of the flange 3 for thus affording a satisfactory contact therebetween. If the deformation 0f the element 30 is not effective for affording a satisfactory annularly uniform conductive seat between these elements, the screws 27 can be tightened more, in which case the inner wire, although it is more firm than the tubular element 30, will be deformed for improving the seating of the gasket. Thus, it will be seen from the foregoing that I have provided an arrangement including a radio frequency gasket which, due to the tubular configuration of the outer member, is readily deformable for easy seating or conformance with irregularities in the surfaces of the members to be joined and which, due to the presence of the contained wire is effective for providing a continuous uniform electrical connection about the waveguide section ends. The assured continuity of contact about the ends of the connected waveguide sections and the low electrical resistance material of the gasket better adapts the device for safe extremely high power applications. Additionally, the gasket 29 is interposed between the interior of the waveguide and the welded rims of the sleeve 8 and cup 9 which assists in isolating these latter elements outwardly of the high frequency fields in the waveguide sections.

On the opposite side oi' the cooling collar 23 the mem- Vber 22 and a ange 32 suitably secured to the end of the waveguide section 2 are joined mechanically by a plurality of screws 33. Provided for suitably electrically connecting these members is another RF gasket 34. The gasket 34 can be identical in structure and function to the abovedescribed gasket 29 and is used in conjunction with recessed seats comparable in structure and function to the recess 28 in the member 20 and, therefore, this structure need not be described in detail herein.

It will be further seen from the foregoing that the abovedescribed construction is adapted for easy assembly in that it enables the employment of a bead weld l2 between the frame 9 and sleeve 8, which weld insures satisfactory vacuum tight sealing and rigid fabrication without having undesirable effects 0n the RF fields. Additionally, the bead 12 may be easily removed as by grinding for removing the frame to replace, for example, a damaged window. Still further, in the disclosed arrangement the RF gasket 29 may be used repeatedly since by further tightening down on the screws 27 the collapsed outer element 3i) and the wire 3l can be further compressed to afford satisfactory uniform RF current flow path about the waveguide sections.

While I have shown and described a specific embodiment of my invention I do not desire my invention to be limited to the particular form shown and described, and I intend by the appended claims to cover all modifications within the spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A waveguide window assembly comprising a flange adapted for being secured to an end of a waveguide section and having a transversely extending annular surface about a central opening therein, a sheet metal sleeve coaxially secured on said flange outwardly of said annular surface, a dielectric window having a cup-shaped metal frame nested in said sleeve and including a longitudinally extending cylindrical side wall, a bond between the rims of said frame and sleeve, an annular member adapted for being carried on the end of another waveguide section, said annular member including an annular reference surface about a central opening therein and opposing said annular surface on said flange, said annular member further including an annular recess located outwardly of said annular surface on said annular member for receiving and enclosing the bonded rims of said sleeve and frame for thereby isolating said welded rims outwardly of the high radio frequency fields in waveguide sections connected to said ange and annular member at said central apertures therein, and means effecting a uniform low resistance conductive path between said transverse annular surface immediately adjacent the inner edges of said central apertures in said flange and annular member.

2. A waveguide window assembly comprising a flange adapted for being secured to an end of a waveguide section and having a transversely extending annular surface about a central opening therein, a sheet metal sleeve coaxially secured on said flange outwardly of said annular surface, a dielectric window having a cup-shaped metal frame nesting in said sleeve and including a longitudinally extending cylindrical side wall having a rim registering with one end of said sheet metal sleeve and a planar bottom surface, a bond between said rim of said frame and said one end of said sleeve, an annular member adapted for being carried on another waveguide section, said annular member including an annular reference surface about a central opening therein and opposite said annular surface on said flange, said annular member further including an annular recess located for receiving the bonded rims of both said sleeve and ange, a compressible conductive gasket interposed between the reference surface on said annular member and the planar bottom surface of said frame, and means for moving said flange and annular member together for compressing said gasket between said reference surface on said annular member and said planar bottom surface of said frame, urging said bottom surface of said frame against said reference surface on said annular member and isolating said bonded rims of said sleeve and frame in said annular recess outwardly of the position of said gasket and outwardly of the high intensity RF elds in said waveguide sections.

3. A waveguide window assembly comprising a flange adapted for being secured to an end of a waveguide section, said ange including an inner rim having a longitudinally extending shoulder defining an annular transversely extending reference surface about a central aperture in said flange, a metal sleeve secured coaxially on said flange adjacent the other edge thereof and remote from said central aperture, a dielectric window having a cup-shaped metal frame nested in said sleeve and having a planar bottom surface engaging said reference surface adjacent said window, a bond between the rims of said frame and said sleeve, an annular member adapted for being carried on the end of another waveguide section, said annular member including an annular recess remote from a central aperture therein for receiving the bonded rims of said sleeve and frame, another recess in a transverse surface of said annular member immediately adjacent the edge of the aperture therein, a compressed conductive gasket vseated in said last-mentioned recess and bearing on the inner side of the bottom surface of said frame, and means for moving said flange and annular member together for compressing said gasket to complete a uniform electrical path between said rim of said annular member, said frame and reference surface through said gasket and to isolate said bonded rims of said sleeve and frame in said annular recess outwardly of said gasket and outwardly of high intensity radio frequency fields in said waveguide sections.

4. An arrangement for effecting a uniform conductive path between waveguide sections comprising a pair of fianged elements adapted for being connected to the ends of waveguide sections and including opposed transversely extending surfaces, an annular recessed gasket seat in at least one of said opposed transverse surfaces of said flange elements, a gasket including an annular malleable metal outer member of tubular cross section and containing a malleable metal inner member, said gasket being disposed in said gasket seat and said gasket seat having such depth as to insure collapse of said outer member and compressive engagement thereof with said inner member before engagement of said flange elements when said flange elements are drawn together.

5. A high frequency gasket for electrically interconnecting waveguide sections or the like comprising an annular outer member of tubular cross section containing a wire-like malleable metal inner member, said outer member being of malleable metal also and having an inside cross sectional dimension greater than that of said inner member and adapted for being collapsed into engagement with said inner member.

6. A high frequency gasket for electrically interconnecting waveguide sections or the like comprising an annular outer member of tubular cross section containing a wire-like inner member of malleable low electrical resistance metal, said outer member being of like material and adapted for being readily collapsed into electrically conducting engagement with said inner member.

7. A high frequency window construction comprising a dielectric window including a peripheral step, a centrally apertured cup-like sheet metal member including a planar bottom portion constituting an outer frame, an inner sheet metal frame of high thermal conductivity and low electrical resistance metal bonded to the inner rim of said outer frame, the inner rim of said inner frame being fiat throughout its radial length and having smoothly rounded edges, said inner rim being bonded in said peripheral step of said window, and a flat annular dielectric member bonded to said window and to said inner rim of said inner frame whereby said inner rim of said inner frame is effectively completely embedded in dielectric material.

8. A high frequency window construction comprising a high alumina ceramic window including a plurality of peripheral steps, a centrally apertured cup-like sheet metal Monel member including a planar bottom portion and constituting an outer frame, a copper inner frame of long radii generally S-shaped cross section and of a thickness generally comparable to that of said outer frame, the outer rim of said inner frame being bonded to the inner rim of said outer frame in an annular step in said outer member, the inner rim of said inner frame being ilat throughout its radial length and having smoothly rounded edges, said inner rim of said inner frame being bonded in one of said peripheral steps of said window, and a flat ceramic ring bonded in the step next adjacent the step in which said inner frame is bonded and to said inner rim of said inner frame whereby the latter is effectively completely embedded in ceramic material.

9. A high frequency window construction comprising a high alumina ceramic window including a plurality of peripheral steps, a centrally apertured cup-like sheet metal Monel outer frame, a copper inner frame of wide radii generally S-shaped cross section and of a thickness generally comparable to that of said outer frame, the outer rim of said inner frame being bonded to the inner rim of said outer frame in an annular step in said outer frame, the inner rim of said inner frame being dat throughout its radial length and having smoothly rounded edges, said inner rim of said inner frame being bonded in one of said peripheral steps of said window, a flat ceramic ring bonded in the step of said window next adjacent the step in which said inner frame is bonded and to said inner rim of said inner frame, whereby lap seals are provided between the two ceramic members and between the flat ceramic ring and said inner rim of said inner frame and the latter is effectively completely embedded in ceramic material, said outer frame including a cylindrical outer til wall and a planar bottom portion extending substantially outwardly from said inner rim thereof, a cylindrical sheet metal sleeve having said cylindrical outer wall of said outer frame nested therein and bonded at one end to the rim of said cylindrical wall of said outer frame, said sleeve being secured at the other end coaxially in an apertured metal flange adapted for being bonded to an end of a waveguide section, and outwardly remotely from the central aperture in said frame to dispose the bond between the rims of said frame and cylinder remotely outward of the radio frequency 'lieds at said aperture in said flange, and an annular shoulder at the inner rim of said flange defining a predetermined reference surface and having said bottom surface of said outer frame engaged therewith for predeterminedly locating said window.

i0. A waveguide window assembly comprising a flange adapted for being secured to an end of a waveguide section, a thin metal sleeve coaxially secured on said flange adjacent the outer edge thereof, a dielectric window, a cup-shaped Monel outer frame positioned in said sleeve, said outer frame including a planar bottom portion and having the rim thereof bonded to the rim of said sleeve, a copper inner frame bonded at the outer edge to the inner edge of said outer frame and having a radially straight inner edge sandwiched between said window and a dielectric ring, an annular member adapted for being carried on the end of another waveguide section, said annular member including a planar annular surface about a central aperture therein, an annular recess in said planar annular surface located remotely outward of aperture for receiving and enclosing the bonded rims of said sleeve and outer frame for thereby isolating said bonded rims outwardly of high intensity radio frequency field in wave guide sections connected to said flange and annular member, another recess in said annular surface located immediately adjacent the inner edge of said aperture and a high frequency gasket disposed in said last-mentioned recess and comprising a wire-like inner member and a soft metal tubular outer member of low electrical resistance material compressed between said annular member and the inner surface of said planar bottom portieri of said outer frame adjacent said window and on said wire-like inner mnnbcr for compressively engaging same and completing a uniform radio frequency current flow path :round and across said window.

References Cited in the file of this patent UNETED STATES PATENTS OTHER REFERENCES Schreiber: R-F Tightness Using Resilient Metallic Gaskets, Electrical Manufacturing, July 1956, pp. 116- 123 relied upon.