US3781726A

US3781726A - Waveguide window assembly

Info

Publication number: US3781726A
Application number: US00287187A
Authority: US
Inventors: R Thompson
Original assignee: Hughes Aircraft Co
Current assignee: Raytheon Co
Priority date: 1972-08-31
Filing date: 1972-08-31
Publication date: 1973-12-25
Anticipated expiration: 1990-12-25

Abstract

A waveguide gas pressure window that in a single assembly provides a waveguide window and a pressure seal to gases used as a dielectric, while at the same time providing a low loss transfer of power through the window from a first waveguide section into a second waveguide section. The improved waveguide window includes a plate having the shape of the waveguide flange with a seal material positioned in a groove on both sides of the plate to contact the two waveguide flanges between which the window is mounted. The flat plate has a common flanged opening formed on one side thereof in which a window structure is positioned on shoulders and firmly bonded in position with a suitable retaining material. The window structure is formed of a suitable dielectric material such as a teflon fiberglass plate having copper sheets deposited on both sides thereof with the copper etched or removed from the fiberglass to provide a window having the desired impedance matching characteristics. The window structure for a selected waveguide size may have a common outside dimension for being positioned in the flat plate while allowing desired electrical and impedance changes to be provided during manufacture by selecting the dimensions of the surface from which copper is removed. The improved and simplified pressure window assembly in accordance with the invention provides complete electrical continuity, eliminates RF energy leakage and simplifies alignment of the adjacent waveguide sections.

Description

[ Dec. 25, 1973 Thompson WAVEGUIDE WINDOW ASSEMBLY [75] Inventor: Richard M. Thompson, Anaheim,

Calif.

[73] Assignee: Hughes Aircraft Company, Culver City, Calif.

[22] Filed: Aug. 31, 1972 [21] Appl. No.: 287,187

[52] US. Cl. 333/98 P [58] Field of Search 333/98 P, 98 R [56] References Cited FOREIGN PATENTS OR APPLICATIONS 1,051,924 3/1959 Germany 333/98 P 775,315 5/1957 Great Britain... 333/98 P 875,245 8/1961 Great Britain 333/98 P OTHER PUBLICATIONS Aircom, Pressurizing Windows, Advertisement From Aircom, Inc, Boston Mass., 12-1962.

Primary ExaminerRudolph V. Rolinec Assistant Examiner-Wm. H. Punter Attorney-W. H. MacAllister, Jr. et al.

[57] ABSTRACT A waveguide gas pressure window that in a single assembly provides a waveguide window and a pressure seal to gases used as a dielectric, while at the same time providing a low loss transfer of power through the window from a first waveguide section into a second waveguide section. The improved waveguide window includes a plate having the shape of the waveguide flange with a seal material positioned in a groove on both sides of the plate to contact the two waveguide flanges between which the window is mounted. The flat plate has a common flanged opening formed on one side thereof in which a window structure is positioned on shoulders and firmly bonded in position with a suitable retaining material. The window structure is formed of a suitable dielectric material such as a teflon fiberglass plate having copper sheets deposited on both sides thereof with the copper etched or removed from the fiberglass to provide a window having the desired impedance matching characteristics. The window structure for a selected waveguide size may have a common outside dimension for being positioned in the flat plate while allowing desired electrical and impedance changes to be provided during manufacture by selecting the dimensions of the surface from which copper is removed. The improved and simplified pressure window assembly in accordance with the invention provides complete electrical continuity, eliminates RF energy leakage and simplifies alignment of the adjacent waveguide sections.

1 Claim, 7 Drawing Figures PATENTEDDECZS ma SHEET 10? 2 Frequency PMENTED DEC 25

ms sum

2 or 2 Fig. 5.

Fig. 4. i

xxxAxxxxxxxx Fig. 5.

Fig. 6.

WAVEGUIDE WINDOW ASSEMBLY BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to waveguide pressure window assemblies and more particularly to a single waveguide pressure window structure that provides both a pressure seal and a radio frequency seal and allows a simplified and reliable selection of window sizes.

2. Description of the Prior Art In microwave waveguide transmission systems, dielectric pressure windows are widely utilized to transmit electromagnetic waves while sectionalizing the waveguide to allow adjacent sections to be under different pressures. These windows may have the purpose of both sealing in pressurized waveguide gases such as a dielectric gas and of keeping moisture out of the waveguide. Waveguide windows are conventionally required at locations where it is desired to remove or disconnect a component from the waveguide transmission path without losing the pressurized gas. Conventionally, waveguide window arrangements have been provided by flat window structures such as a fiberglass plate having a transmission area etched from copper surfaces and positioned between two waveguide flanges with a suitable seal structure either on one or both sides of the window assembly. This window arrangement has been found to be quite costly and also relatively difficult to provide reliable alignment because two or three elements must be bolted or mounted between two flanges. Another conventional arrangement has been to utilize a window structure having copper surfaces with a selected window configuration etched therefrom and with a seal material deposited around the circumference on one side thereof. This arrangement is conventionally placed in a machined enclosure in the face of a waveguide flange and bonded therein, which has the disadvantage of requiring specially adapted flanges. Another conventional arrangement is to provide a rectangular piece of a dielectric material such as fiberglass having the copper etched therefrom to form the window area and mounting the window structure between two rectangular openings of a frame, such as in an antenna system, by a suitably manufactured flat gasket or by gaskets on each side thereof. It would be a substantial advantage to the art if a highly reliable and easily alignable waveguide window and seal were provided that could be added to the waveguide system as a single structure while providing desired electrical characteristics. Summary of the Invention A waveguide pressure window assembly that provides a highly reliable pressure and radio frequency (RF) seal in a single structure and that may be manufactured with a minimum of complexity to provide desired window dimensions. The waveguide window is formed of a single plate mountable between waveguide flanges, having a central opening or periphery which has dimensions larger than the waveguide openings and having a seal material on both sides and around the outer edge thereof for contacting flanges of the transmitting waveguides. A window member is positioned or bonded in a shoulder around the central opening on one side of the flat plate. The window member is of a suitable dielectric material such as teflon fiberglass having copper surfaces etched therefrom in a desired shape for providing the impedance and bandwidth requirements. Because the central opening in the flat plate which accommodates the window member has dimensions larger than those of the waveguide opening, a selected waveguide transmission window size may be provided with a minimum of complexity by properly etching the copper from the opposite surfaces of the fiberglass. The simplified waveguide window arrangement of the invention provides a reliable RF and pressure seal while allowing the transmission path to be accurately aligned.

It is therefore an object of this invention to provide a waveguide pressure window that develops a pressure seal without the requirements of additional sealing structures.

It is a further object of this invention to provide an improved waveguide pressure window that functions as a reliable hermetical seal to waveguide gases and as a seal to RF leakage.

It is a further object of this invention to provide a waveguide pressure window that is readily adaptable to a wide range of window sizes.

It is a still further object of this invention to provide a waveguide pressure window that substantially eliminates the alignment problems that are present when utilizing separate seals and window structures.

It is another object of this invention to provide a simplified dielectric window that has a minimum attenuation to high frequency energy and that has an improved hermetical seal arrangement.

BRIEF DESCRIPTION OF THE DRAWINGS These and other objects, features and advantages of the invention itself will become apparent to those skilled in the art in the light of the following detailed description, taken in consideration with the accompanying drawings, wherein like reference numerals indicate like or corresponding parts throughout the several parts wherein:

FIG. 1 is a schematic perspective drawing of the waveguides pressure seal window assembly in accordance with the invention arranged between two waveguide flanges of different waveguide sections;

FIG. 2 is a side view partially in section of the window of the invention mounted between two waveguide flanges;

FIG. 3 is a schematic end view looking along the microwave transmission axis of the waveguide window and seal assembly in accordance with the invention;

FIG. 4 is a schematic sectional view taken at line 4-4 of FIG. 3 for further explaining the arrangement of the window assembly;

FIG. 5 is a schematic view looking along the transmission axis of the window member utilized in the window seal of FIG. 3;

FIG. 6 is a schematic sectional view taken at lines 66 of FIG. 5 for further illustrating the window structure of the invention; and

FIG. 7 is a graph of the reflection coefficient versus frequency for indicating that the pressure window of the invention provides a desirable voltage standing wave ratio.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring first to the perspective drawing of FIG. I, a waveguide pressure seal and window assembly 10 is shown mounted between flanges l2 and I4 with suitable bolts such as 11 for joining

respective waveguide sections

16 and 18 with a dielectric gas pressure seal, the gas which, for example, may be in the waveguide section 16 with the waveguide section 18 being at atmospheric pressure. The window of the invention is operable with either vacuum or pressure conditions or with different pressures on either side of the window. In other arrangements, both the

sections

16 and 18 may be normally pressurized except when a section (not shown) coupled to section 18 is removed. Referring now also to FIGS. 2, 3 and 4, the waveguide assembly includes a plate 20 having holes 21 through 24 positioned to correspond to the holes in the

waveguide flanges

12 and 14 and having the external corners rounded to correspond to the configuration of the waveguide flanges. On opposite sides of the plate 20 are

waveguide seals

26 and 28 positioned in or formed in

respective grooves

30 and 32 that are machined or provided in the plate 20 with the seals contacting the flat surfaces of the flanges l2 and 14. Openings such as 31 and 33 are provided so the sealing material of the seals or

sealing strips

26 and 28 are interconnecting for maintaining their position in the grooves on the plate. The invention is not to be limited to a particular seal configuration or arrangement for maintaining the seals in the grooves but includes any suitable seal maintained in the continuous grooves. In the illustrated arrangement, openings such as 31, 32 and 33 are provided so that the sealing material of the

seals

26 and 28 are interconnected so as to maintain their position in the slots. The plate 10 has an internal opening or periphery having at least one dimension greater than the internal dimensions of the opening or inner periphery of the

waveguide sections

16 and 18, with a window structure 42 mounted in a recessed enclosure or shoulder 44 having dimensions slightly greater than the internal dimensions 40. The recessed enclosure 44 may be formed by suitable machining as is well-known in the art. The structure 42 is bonded into the recessed enclosure or mounting ledge 44 by a suitable bonding agent, such as epoxy. The transmission window dimensions of the window structure 42 have a configuration 48 which may be any desired dimension to provide the selected inductive impedance matching characteristics, at both surfaces of the dielectric window material. To match the capacitive characteristics of the dielectric window 42 and provide a desired VSWR (voltage standing wave ratio), the long dimensions of the opening between

edges

51 and 53 on both sides of the dielectric material may be decreased from the dimensions of the waveguide opening between

edges

55 and 57. The structure 20 may be formed of any suitable material such as aluminum, brass or copper. The sealing strips may be any suitable material such as silicone rubber or neoprene, for example. If it is desired to provide electrical continuity when the surfaces of the window and of the flanges are slightly uneven, suitable projections or sharp deformable ridges may be formed on both sides of the structure 20 as indicated by the projections 39.

Referring now also to FIGS. 5 and 6, the window structure 42 may be formed of fiberglass 50 coated with

copper surfaces

59 and 61, with the copper etched therefrom to the desired shape 48. The dielectric structure 50 of window element 42 may be of any suitable dielectric material such as mica, kovar, glass, plastic, teflon or alumina, for example. Because the dielectric constant of dielectric window materials is greater than unity, it is generally necessary for presenting a minimum of discontinuity to energy transmission and permit maximum power to be transmitted, to alter the geometry at such a window to provide a low standing wave ratio over the frequency band. This results in the cross-sectional area of the window being less than the cross-sectional area of the waveguide, as well-known in the art.

The window element 42 may be manufactured from a fiberglass plate coated on both sides by a copper film as is readily available in the industry. The opening 48 of a desired size is formed by any suitable etching process such as cutting a mask and positioning it on the surface of the structure 42, photo etching the window through the opening in the mask on both sides of the structure, bathing the structure with acid to remove the copper from the window area and cadmium plating the copper surfaces to eliminate any electrolyses problems during operation of the window.

After the structure 20 is formed by machining, for example, including the mounting shoulder or recess opening 44, the window may be bonded into the recess 44 of the structure 20 by the following steps provided as an illustrative example of one bonding method that may be utilized in some arrangements of the invention:

1. Clean the window and shoulder with methane ethyl ketone (MEK).

2. Place a thin line of epoxy polyurethane adhesive in the recess or shoulder 44.

3. Place the window 42 in the recess or shoulder and remove excess epoxy.

4. Clamp structure between aluminum blocks at moderate pressure.

5. Cure in a suitable oven for approximately 4 hours at 200 Farenheit.

6. Remove any excess adhesive from the window with MEK.

Referring now to the test results of FIG. 7 for a window retaining a pressure of 2 PSIG (pounds per square inch gauge) in a waveguide system transmitting J band (JCS band designation) energy which is over a width of 10-20 GHZ (GigaI-Iertz). The curve of FIG. 7 extends over approximately percent of the J bandwidth. The VSWR (voltage standing wave ratio) is equal to -l-l l -l l l where p is the reflection coefficient which may be defined as the ratio of reflected voltage amplitude to incident voltage amplitude. The curve of FIG. 6 shows that over approximately 70 per cent of the J bandwidth the reflection coefficient was relatively small and the VSWR was relatively low. Also, the window loss when utilizing the illustrated teflon fiberglass window has been measured with J band transmission energy and found to be 0.027 db (decibels), which is a relatively low value.

Thus, there has been described a pressure window for microwave transmission systems that with a single structure provides a window having selected matching characteristics and provides gas sealing. The window assembly seals in waveguide gases used as a dielectric and keeps moisture while at the same time allowing substantially full power to pass through the window between two waveguide sections. The waveguide window assembly provides a high degree of electrical continuity and elimination of RF leakage. The single window assembly of the invention substantially eliminates the difficulties in alignment of waveguide sections which, when utilizing separate seal arrangements results in serious arcing and degradation of the waveguide flanges, seals and window. Because the di-electric window member is set into a common sized recessed enclosure, a plurality of etched window sizes may be provided with a minimum of manufacturing complexity.

What is claimed is:

1. A window adapted to be positioned inter-mediate two electromagnetic waveguide sections joined by a pair of flanges, each flange having a transmission opening with predetermined inside dimensions substantially equal to those of said waveguide sections, said window comprising a flat plate structure having external dimensions substantially the same as those of said flanges and an internal opening having a recess therearound with no less than one dimension of said internal opening being greater than said corresponding predetermined inside dimension of said transmission openings of said flanges; first and second continuous grooves about said internal opening of said flat plate on opposite sides thereof; first and second continuous sealing strips positioned in said first and second continuous grooves, respectively, on said opposite sides of said flat plate to provide a closed path external to said internal opening of said flat plate; and a flat window member of dielectric material mounted in said recess and having metallic surfaces on both sides around the edge thereof to provide a microwave transmission opening therethrough within said internal opening of said flat plate, the dimensions of said microwave transmission opening being less than corresponding dimensions of said internal opening of said flat plate.