ULTRALIGHT MICROWAVE ANTENNA AND METHOD OF FABRICATION

Abstract: An antenna assembly (10) fabricated of lightweight, aluminum alloy foil material which forms individual parts that are laser welded together. The parts include mating projecting tabs (18) and slots (20) which render the unit self-jigging in assembly and provide added strength in the finally welded unit. Common tooling pins (not shown) are used to stack the piece parts in proper alignment during assembly by inserting the pins through particular tooling holes (46) in individual parts. Laser welding is used at various levels of assembly and a base module sub-assembly is initially fabricated, to which additional individual components are affixed and welded in place. The resulting unit is a precision antenna assembly, light in weight and structurally strong, which can be built with very low fabrication costs. The microwave aperture features of the unit are developed and located with the feature relationship being held to very precise tolerances.

Description: ULTRALIGHT MICROWAVE ANTENNA AND METHOD OF FABRICATION This invention was made with Government support under Contract No. F08635-86-C-0201 awarded by the Department of the Air Force. The Government has certain rights in this invention. BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to mobile microwave antennas and, more particularly, to such antennas which are particularly designed for ease of fabrication from very lightweight materials. 2. Description of Related Art Arrangements in accordance with the present invention are intended for mounting on gimbals of mobile equipment microwave systems such as are typically installed in missiles for target seeking, tracking and directional control. Antennas which are presently available for such use present a number of drawbacks. For example, they are larger and substantially heavier, thereby making it more difficult for the torquer motors to handle the torquing, particularly when significant acceleration forces are applied to the gimbal mounting structure during flight. Such antennas are fabricated of piece parts of relatively thick materials which are brazed together. The higher temperatures involved in the brazing steps result in warpage and distortion in the assembly. Moreover, such antennas are assembled from a series of sub-assemblies in the form of waveguide channels wit aperture features placed in each channel. These channels are then spot-welded together. There are tolerances between the channel joints that result in a tolerance "stack-up" between the aperture features which adversely affects the performance of the antenna and causes quality control problems in production. It is also difficult to achieve the desired degree of flatness for the face covers of such antennas because of the unevenness of the assembled channels and apertures. As a result, such an antenna cannot easily be built to the desired RF quality. The relatively larger size of such an antenna makes it possible to employ the fabrication techniques which are used in its construction. However, such techniques cannot be used in a smaller antenna configuration because of the constraints imposed by limited channel opening size on the admission of the fabrication tools and jigs which are used in the manufacturing process. SUMMARY OF THE INVENTION In brief, arrangements in accordance with the present invention involve the fabrication of the component parts making up the antenna assembly of ultra lightweight aluminum alloy foil material, approximately .008 to .010 inches in thickness. A base module is fabricated of a plurality of thin flat ribs between a pair of round flat disk-shaped face panels. These ribs, typically about .016 inches in thickness, are fashioned with a plurality of tabs along opposite edges for insertion through mating slots in the two face panels.. After assembly of the two face panels and the various ribs extending between them and defining the aperture features for the microwave channels, the assembly is laser welded together by precision welding from the outside, along lines of the face panels matching the edges of the internal ribs. This advantageously eliminates the need for inserting a welding tool into the interior of the base module, as was required in the fabrication process employed in manufacturing the prior art antenna described hereinabove. Welding from the outside of the base module in this fashion contributes to a significant reduction in the size of the resultant antenna assembly with the beneficial results that flow therefrom: reduced package size, lighter weight assembly, improved ratio of strength to weight, lower production costs and higher production rates. Moreover, the improved performance characteristics of an antenna assembly fabricated in accordance with the present invention enable the antenna to provide better performance in meeting the stringent RF requirements that apply in the intended operating environment. After the base module is completed by laser welding together the two face panels and the plurality of internal ribs, the additional components making up the assembly are placed in position and also laser welded. A pair of feed guides, formed of approximately .010 inch thick aluminum alloy foil material, are assembled along one side of the base module and laser welded in place. Each feed guide has a central divider installed therein with tabs projecting from the upper edge. Next a feed guide cover in the form of a generally rectangular, apertured planar member, preferably of the same material as the feed guides, is placed over the feed guides. A pair of central apertures permit the dividers to extend therethrough. Next a pair of thin box-shaped feed guide return members are centrally located over the feed guide cover, receiving the tabs of the feed guide dividers through small mating apertures therein, and laser welded in place to complete the fabrication of a rigid, light, precisely shaped and positioned antennal assembly. The various individual components of the assembl —the two face panels, the two feed guides and the feed guide cover are provided with strategically located tooling holes through which common tooling pins are inserted to permit the ready stacking of the respective piece parts in proper position on the pins during assembly. The divider tabs and the mating slots in the return boxes serve to position the feed guide return boxes on the rest of the assembly. Thus, the individual parts are essentially self-jigging with the use of the rib tabs and the slots in the face panels for part locating during " assembly of the base module and the further provision of the tooling pins in the various tooling holes as the remainder of the assembly is stacked together. The overall unit is a precision antenna assembly, light in weight and structurally strong. This particular design allows for a low-cost assembly. The individual parts are readily fabricated by the use of high precision tooling dies where high production rates are desired. These parts may be formed by an etching process if a lower rate of production is satisfactory. Brake forming and the use of forming dies are two of the known fabrication processes for producing the box and channel shaped parts comprising the feed guides and the feed guide returns. The resultant antenna assembly design performs well, producing very low side-lobe results. The unit is also very light in weight, making it ideal for on-gimbal placement, and is structurally strong to resist "G" forces. At the same time, the low cost of manufacture of these units to high precision tolerances with high yield under strict quality control is achieved. BRIEF DESCRIPTION OF THE DRAWING A better understanding of the present invention may be realized from a consideration of the following detailed description, taken in conjunction with the accompanying drawing in which: FIG. 1 is a plan view, in partial section and partially broken away, of one particular arrangement in accordance with the present invention; FIG. 2 is a side elevation of the arrangement shown in FIG. 1; FIG. 3 is an exploded view showing most of the components of the arrangement of FIG. 1; FIG. 4 is a perspective view of a typical rib support member which is part of the arrangement of FIG. 1; and FIGS. 5A and 5B are perspective views of two side closure members of the arrangement of FIG. 1. DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings, the preferred embodiment of a laser welded antenna assembly 10 of the present invention may be seen as comprising a base module 12 on which the remaining components of the antenna 10 are mounted. The base module 12 principally comprises a pair of thin flat circular disks 14 separated by a plurality of spacing ribs 16 like that shown in FIG. 4. The upper disk (as depicted in FIG. 3) is designated by the reference numeral 14A while the lower disk is designated by the reference numeral 14B. The positions of the various spacer ribs 16 are indicated in FIG. 3 by the rows of slots 20 in the upper disk 14A of the base module 12. Each rib 16 (see FIG. 4) is provided with a plurality of outwardly extending tabs 18 which are engaged in the mating slots 20 in the upper and lower disks 14A, 14B. These are best shown in the half sectional view to the right of the center line of FIG. 1. Each of the disks 14A, 14B has a plurality of particularly oriented feed slots or apertures 22 through which microwave energy is directed. These feed slots 22 in the upper face panel disk 14A are covered by feed channels 24 which comprise a pair of feed guides 26 covered by a unitary feed guide cover 28, on top of which a pair of feed guide return members 30 are affixed. A transverse upstanding separator 32 is centrally located in each of the feed guides 26. Each separator 32 has a pair of tabs 34 projecting upwardly for insertion in mating apertures 36 of the feed guide return members 30. A plurality of extensions 38 project outwardly at right angles from the side walls of the feed guide returns 30 and are laser welded to the outer surface of the feed guide cover 28. Respective pairs of apertures 40 are located at opposite ends of the feed guide cover 28 in line with the opposite ends of the corresponding feed guides 26. Tooling holes 42 are strategically located in the feed guide cover 28 to assist in aligning the feed guide cover with the other pieces making up the assembly 10. Similar tooling holes 44 are situated in cross members of the feed guides 26, while corresponding tooling holes 46 are located in the upper and lower face panel disks 14 , 14B. In the fabrication of the assembly 10, the rear or lower face panel disk 14B is placed into a jig fixture and located by means of the tooling holes 46 being placed over common tooling pins of the fixture. The ribs 16 and the upper face panel disk 14 are assembled to the back face cover 14B with the rib tabs 18 inserted within the slots 20 serving to develop the proper alignment along with the tooling pins and tooling holes 46. This sub-assembly is then laser welded by running the welding head along the rib lines, directing the laser beam against the outer surfaces of the face panels 14A, 14B. Side closure members 19A and 19B of the types shown in FIGS. 5A and 5B serve to close the periphery of the base module 12. These are installed in opposed pairs extending about the periphery of the base module 12 as the ribs 16 and opposite face panels 14A, 14B are being assembled and welded together. The feed guides 26, dividers 34, cover 28 and return boxes 30 are further built up in succession on the sub-assembly 12, using the tooling pins through the tooling holes 42 and 44 for location, and are welded together for the complete assembly. After completion of the assembly the unit 10 is removed from its supporting fixture and tooling pins and is then ready for installation in a microwave system. Transmitted microwave energy is directed into the assembled antenna unit 10 through the slots 22 in the back face panel 14B of the base module 12. Microwave energy entering the feed guides 26 from the slots 22 in the upper face panel 14A can pass over the separators 34 through the central slots 43 and the return boxes 30, finally exiting the end slots 40. Return energy follows a reverse path through the same openings and channels back through the device, finally exiting through the slots 22 in the rear face cover 14B. The antenna assembly, fabricated and constructed as described, is well adapted for its intended purpose. The forming of the individual constituent elements of lightweight, aluminum alloy foil material from .008 to approximately .016 inch in thickness produces an extremely lightweight structure. By virtue of the shapes and configurations of the individual parts of the assembly and the mutual structural reinforcement thereof through the welding together in the assembly, the resulting antenna is light in weight but strong; and the resulting channels, chambers and apertures for microwave energy are formed with a high degree of precision, resulting in good quality control in manufacturing and highly effective and reliable RF performance in operation. Although there have been shown and described hereinabove specific arrangements of an ultralight microwave antenna and method of fabrication in accordance with the invention for the purpose of illustrating the manner in which the invention may be used to advantage, it will be appreciated that the invention is not limited thereto. Accordingly, any and all modifications, variations, or equivalent arrangements which may occur to those skilled in the art should be considered to be within the scope of the invention as defined in the annexed claims.

Claims: CLAIMS What is Claimed is: 1. A microwave antenna assembly comprising: a plurality of individual thin members formed of metal foil material less than .050 inch in thickness; said members being so shaped and configured as to provide mutual structural reinforcement when assembled together and affixed to each other; adjacent ones of said members being laser welded together to provide a plurality of microwave apertures and enclosed chambers defining reciprocal paths for microwave energy being conducted through the assembly. 2. The assembly of Claim 1 further comprising a base module having means defining a plurality of individual microwave apertures; and a plurality of feed channels laser welded to one side of the base module in positions to complete .microwave energy channels communicating with said apertures. 3. The assembly of Claim 2 wherein said base module is formed of a pair of face panels in the form of thin flat circular disks spaced apart from each other by a plurality of thin flat ribs, said ribs having pluralities of tabs protruding edgewise therefrom, said ribs being mounted orthogonally to the disks with the tabs extending into corresponding mating slots in the individual disks, said disks and ribs being laser welded together from the outer surfaces of said disks along paths aligned with the side edges of the ribs. 4. The assembly of Claim 3 wherein said disks are formed of approximately .008 inch thick foil material and said ribs are formed of approximately .015 inch thick foil material. 5. The assembly of Claim 3 wherein said base module further comprises a plurality of side closure members laser welded into place about the periphery of the base module. 6. The assembly of Claim 5 wherein said side closure members are of two types positioned in opposed pairs of like type extending about the periphery of the base module. 7. The assembly of Claim 6 wherein each of said side closure members comprises a plurality of transverse fold lines spaced apart from each other about the periphery of the base module at positions respectively aligned with the ends of the ribs between the two face panels. 8. The assembly of Claim 1 wherein said members are formed of aluminum alloy. 9. The assembly of Claim 3 wherein the feed channels comprise a pair of feed guides having openings along one side positioned in alignment with corresponding sets of apertures in one disk of said base module, and a common feed guide cover extending along the open side of the feed guides remote from the base module to define substantially enclosed paths for microwave energy within said feed channels. 10. The assembly of Claim 9 wherein said feed channels further include upstanding thin foil dividers mounted transversely within said feed guides and positioned generally midway between opposite ends thereof. 11. The assembly of Claim 10 wherein said dividers extend upwardly through corresponding first rectangular microwave energy openings in said feed guide cover which are generally centrally located between said opposite ends, the outer edges of said dividers defining projecting tabs for mating with corresponding slots in a pair of feed guide return members which are generally centrally positioned relative to said feed guide cover ends and laser welded to said cover over said openings and dividers. 12. The assembly of Claim 11 wherein said feed guide cover defines second rectangular microwave energy openings generally positioned at opposite ends of said feed channels. 13. The method of fabricating an ultralight microwave antenna comprising the steps of: forming a plurality of individual component elements of thin metal foil material in a series of predetermined shapes and configurations; selecting a jig fixture on which to assemble said elements; and laser welding selected elements to form a base module and thereafter laser welding successive component elements to a sub-assembly including the base module as elements are added thereto in succession. 14. The method of claim 13 wherein said forming step includes forming a pair of thin flat circular disks with pluralities of slots, apertures and tooling holes therein and a plurality of thin flat ribs with tabs extending along opposed side edges thereof, placing the disks on said jig fixture with the tooling holes aligned with common tooling pins of said fixture and with the ribs mounted between the disks, oriented orthogonally thereto and with edge tabs extending into corresponding slots in the disks, and welding the disks and ribs together in a rigid unitary base module by applying a laser welder from the outside of said module to direct a laser beam along the exterior surfaces of the disks in alignment with the edges of the ribs. 15. The method of Claim 14 where the forming step further includes forming a pair of channel-shaped feed guide members, an apertured feed guide cover adapted to extend over said feed guide members, and a pair of box-shaped feed guide return members, providing each of the feed guide members and the feed guide covers with strategically located tooling holes, and further including the steps of stacking said feed guides and feed guide covers on said tooling pins to build up an assembly adjacent said base module, and laser welding each feed guide and feed guide cover to an adjacent member in the sub-assembly as the assembly progresses. 16. The method of Claim 15 further including the step of mounting a transverse divider in approximately the center of each feed guide and laser welding the divider in position. 17. The method of Claim 16 further including positioning the feed guide return members in generally central locations over said dividers and against said feed guide cover with slots of the feed guide return members receiving projecting tabs from the dividers, and laser welding the feed guide return members to the feed guide cover. 18. The method of Claim 15 wherein the forming step comprises forming the component elements of thin aluminum alloy foil material less than .050 inches in thickness. 19. The method of Claim 17 further including the steps of forming respective pairs of side closure members of thin foil material, and laser welding said side closure members in place about the periphery of the base module to close the peripheral side openings thereof.

Inventors: ALFING NORMAN L, RODRIGUEZ ANGEL E, ALFING, NORMAN, L., RODRIGUEZ, ANGEL, E.
Applicants: HUGHES AIRCRAFT CO, HUGHES AIRCRAFT COMPANY
Application year: 1989
Main classification: H01Q21
IPC codes: H01Q13, H01Q21