US2747180A - Radar reflector - Google Patents

Description

May 22, 1956 M. BRUCKER RADAR REFLECTOR Filed June 20, 1952 F 6 V W LN L 6 an Wm WM 1 c Mm F H B A Pww a. se 0 NV N 5 M W W 2 w a 5 wm M w E U KEF. c M? BF mm m a r N LE UM ww M A a w 0 h w P R m m mw 6 A m MIL TON BRUCKER, INVEN TOR.

HiM 6 EEN United States Patent RADAR REFLECTOR Milton Brucker, Los Angeles, Calif., assignor to Zenith Plastics Company, Gardena, Calif., a corporation of California Application June 20, 1952, Serial No. 294,632

7 Claims. (Cl. 2343-18) This invention relates to means and method for constructing a radar reflector. More particularly it relates to a radar reflector construction of new and improved light weight and rigidity made of a minimum of metal while obtaining all the advantages normally attributed to all-metal reflectors. It likewise relates to an improved method of making the desired reflector, largely of plastic and fibrous materials.

Heretofore commercially acceptable radar reflectors, for use in particular by the Armed Forces of the United States for aircraft, seagoing, and land use, depended upon use of an all-metal concavity, or the like, all-metal shield, either cast integrally as a reflective unit, or made reticulate by metal bars, rods, strip, mesh and the like. Such prior art devices are relatively heavy in weight, costly in their manufacture and maintenance, and include the use of metal predominantly if not ex clusively. lnasmuch as the larger radar reflectors are most effective in use, the weight-size relationship becomes critical, particularly for aircraft use. It is also important, to a somewhat lesser extent however, on ocean-going vessels, and even on land.

In view of the above considerations and others, it is among the objects of this invention to provide from readily available plastic and fibrous materials, a satisfactory and commercially acceptable radar reflector utilizing a minimum of metal but Without thereby diminishing either the utility or durability of a radar reflector of comparable size made in accordance with prior art teachings.

It is another object of this invention to provide, in a radar reflector of the desired character described, a weathermesistant, non-metallic surface, a relatively fine layer of reflective metal, and a relatively stiff and substantial highly reticulate backing of utmost lightness consistent with strength and durability, and in a manner corresponding to the first mentioned non-metallic surface which is closely adherent to and provides a strong backing and protection to the reflective metal layer.

Yet another object of the invention is the provision of a new and improved plastic construction for radar reflectors incorporating metal as the electronically effective ingredient, and the plastic as a durable, weather-resistant and non-corrosive structural foundation.

Yet another object of the invention is to provide a plastic radar reflector construction capable of satisfying the rigid standards of the Armed Forces of the United States. as well as commercial requirements, and whose utility is substantially unaffected by increases in size, said increase being accompanied by disproportionate increases in weight, foundation and reinforcement.

it is among the objects of this invention to provide a new and improved method of making a radar reflector as herein described and claimed.

Yet another object of the invention is the provision of a new and improved method for insuring sufficient rigidity of the metal reflector portion of the device of the instant invention.

2,747,180 Patented May 22, 1956 It is moreover an object to provide an improved method for insuring permanent adherence of the several metal and non-metal parts of the desired structure to one another.

It is a further object of the invention to provide new and improved means and molding method for obtaining a radair reflector of the instant invention.

in addition, it is among the objects of this specification and invention to set forth a suggested, preferred means and method for obtaining a new and improved radar reflector construction in accordance with the inventors conception; to improve prior art devices and methods heretofore intended to accomplish generally similar purposes.

These and other objects and purposes will be more fully understood by reference to the accompanying specification considered in the light of the drawings and the appended claims.

In the drawings:

Figure l is a perspective view, partially in section, of a mold and radar reflector constructed thereon in accordance with the teaching of this invention.

Figure 2 is a flow diagram of the method of this invention.

Figure 3 is a fragmentary sectional view of one edge of a finished reflector embodying this invention.

Referring more particularly to the drawings, there is illustrated by way of example but not of limitation a mold 10 of plastic or the like, having a base 11 by which the same is supported in any suitable fashion, as upon a floor, and provided with any reinforcing rim, as of wood or steel. The upper surface 13 of the mold is convex to conform to the desired reflective shape of the intended reflector surface. The mold is further preferably provided with an annular flange portion 14 for a purpose to be described.

In the construction of the instant reflector, a layer of fiberglass cloth 15, thoroughly impregnated with a resin, is closely laid over the upper surface of. the convex portion 13 of the mold, and also to the upper surface 16 of the flange 14 thereof. The resin is preferably also applied, prior to the application of the impregnated fiberglass sheet 15, to the mold surface 13 and 16, as by means of a brush, a spatula, by spraying, or by hand.

Said resin is most desirably an unsaturated polyester selected from'any of those commercially available products sold under the trade name Paraplex, Laminac, Selectron, Marco, or the like, as well known to those skilled in the plastics art.

The purpose of the first layer of cloth 15 is to provide a weather-proof coating for the reflective side of the reflector, to protect the metal coating 17 from oil and corrosion, and to provide a body which is conveniently and easily removed from the mold upon completion of the product. For such purpose a fiberglass woven mat of approximately ten thousandths of an inch thickness has been found advantageous.

The initial layer of fiberglass 15, together with the resin impregnated therein and thereunder, is next cured as under an ultraviolet lamp, which assists the activity of the lightactivated catalysts, if any, which may be incorporated in the resin, within the skill of those familiar with the art, or such curing may be accomplished in any conventional fashion, as in an oven for approximately an hour, at approximately 200 degrees Fahrenheit, or other satisfactory temperature.

After the curing of the fiberglass impregnated resin, the exposed upper surface of the fiberglass mat 15 is subjected to a sandblasting. Such sandblasting provides a satisfactory surface for the next operation, which is the application, by means of a metal spray, of a layer of metal of substantially uniform thickness over the entire convex surface of the mold and cloth layer 15. A layer of aluminum has been found satisfactory for the instant purposes if deposited, for example, in a layer of approximately ten thousandths of an inch. Other metals may also be employed, but if so, they should be selected from those which do not require such a high temperature for spraying that the resultant heat of the sprayed metal will deleteriously or otherwise affect the resin.

To the upper surface of the metal layer 17 there is applied, with or without sandblasting, and preferably also but not necessarily, a coating as by brush, spatula, by spray or by hand, a layer of said resin, over which is similarly laid a fiberglass mat 18, preferably of woven fiberglass. Said layer 18 has been found satisfactory if comprised of three layers of such fiberglass fabric of about thirty thousandths of an inch combined thickness. Also satisfactory is a single fiberglass mat of Woved figerglass fibers of approximately the sarne total thickness.

Over the last named layer 18 is placed a preferably honeycomb core 19. If it be assumed in the instant example that the diameter of the reflector is to be approximately eight to nine feet, a honeycomb core of approximately one and threeqnarter inches in thickness has been found suitable. The honeycomb itself comprises woven fiberglass impregnated with a polyester resin. The individual cells of the core. by way of example, may be hexagonal and extend continuously from the inside to the outside walls of the core. The walls of the core defining the honeycomb-like chambers are approximately three thousandths of an inch in thickness and are impregnated with said resin to give them a total thickness, including said resin,

of about five thousandths of an inch.

After the honeycomb has been positioned over the layer 18, preferably though not necessarily as a continuous unit, a further backing 20 of woven fiberglass fabric impregnated with said resin is laid over the core 19. Such v a backing has been found satisfactory in the form of approximately four layers or plies of woven fiberglass, each of which ply has an approximate thickness of ten thousandths of an inch, the whole backing 20 thereby having an over-all thickness of approximately forty thousandths of an inch.

After the positioning of the layers 18, 19 and 20, over the sprayed metal layer 17, the upper surface of the mold is covered with a flexible bag 21 of any material such as polyvinyl acetate. or the like, non-compatible material which does not, like rubber, inhibit curing of the resin, and which does not. after such curing adhere to the resin.

Said bag 21 is laid also over the upper surface of the corresponding layers 16 through 20 disposed upon the flange 14, and if desired, also over the outermost edge 22 of the flange 12, but prior to the positioning of the bag 21, a porous or otherwise open tube 23 is coiled about the mold. Such tube 23 may take the form merely of a coil spring or other coil of material comprising a helix. Moreover. at the outer edges of the flange, as at 24 and 25, a layer of sealing compound, such as zinc chromate, is employed, having the desired quality that it does not flow under the contemplated heat to which the mold is to be subjected.

The bag 2] is pressed into position over the zinc chromate seal. which seal, however, is not deposited inwardly, as at 26, between the tube 23 and the convex portion 13 of the mold.

A vacuum is next interconnected with the tube 23. The vacuum heretofore employed has been that required to subject the dome 27, or convexity, to a pressure of approximately nine pounds per square inch. While the vacuum is applied, any air under the dome portion 27 is rubbed out as by brushing, rubbing, rolling or the like, with pressure against the top of the dome, beginning from the upper more central parts to the outer edges toward the tube 23. Also, preferably simultaneously with said rubbing, and at least while the vacuum remains applied, the part is cured under heat, for example, 100 degrees Fahrenheit,

for approximately one hour, either in an oven, under ul tra-violet light, or otherwise.

Thereupon the cured part is removed from the mold by physical stripping after the bag 21 has been removed. The edges designated collectively at 28 overlying the flange 14 are trimmed off, and the raw edges 29 thus exposed are capped as by two layers 3t)31 of woven fiberglass mat, each having a thickness of approximately ten thousandths of an inch, impregnated with said resin, as under a heat lamp, to approximately 200 degrees Fahrenheit, for approximately an hour.

A reflector made as above described, by way of example, may have a diameter of approximately nine feet. The over-all thickness, which may be substantially the same from edge to edge, is approximately 1.84 inches, not counting the added thickness of the cap 3031. The versatility of the instant construction is such that a reflector may be made in any diameter, as for example, from two inches to fifty or even lOO feet in diameter. The curve of the reflector surface is preferably parabolic. The weight of a corresponding steel frame of effective nine-foot diameter is approximately 350 pounds; whereas, the corresponding weight of an effective nine-foot reflector made in accordance with this invention is only ninety pounds. Even the cost of the instant reflector is substantially less than that of its steel counterpart.

A reflector made in accordance with the teaching of this invention has, under test, withstood a 120 mile-per-hour gale directed axially at same, or while rotating the same, with less than one-eighth of an inch deflection While mounted on a standard support.

it has excellent weather-resistant qualities and may be used either exposed or under the protection of a radome or like shelter, in aircraft, aboard ship, or as part of a stationary or mobile land unit.

Although l have herein shown and described my invention in what I have conceived to be the most practical and preferred embodiment, it is recognized that departures may be made therefrom within the scope of my invention, which is not to be limited to the details disclosed herein but is to be accorded the full scope of the claims so as to embrace any and all equivalent structures and methods.

I claim:

1. A radar reflector comprising a generally dish-shaped structure, which structure, proceeding from the inner side thereof outwardly through the wall thereof, comprises a continuous layer of a fiber reinforced resinous laminate, a thin layer of metal, and a resinous cellular material substantially thicker than the metal, said fiber reinforced layer and said cellular material being securely adhered to said layer of metal by means of a resin interposed therebetween.

2. A reflector as defined in claim 2, and wherein said cellular material comprises a substantially uniform layer several times thicker than said metal layer, and fiber reinforced resinous layers on the inner and outer sides of said layer of cellular material, and respectively firmly adhered to the outside of the metal layer and the outside of the layer of cellular material, all of said layers being securely and intimately adhered to one another by means of a resin impregnating said fiber reinforced layers and the inner and outer surfaces of all of said layers.

3. A reflector as defined in claim 2, wherein said cellular material layer comprises a honeycomb structure having hollow cells whose axes are directed radially of the reflector.

4. A reflector as defined in claim 3, wherein said metal layer is approximately ten-thousandths of an inch thick.

5. A reflector as defined in claim 4, wherein said metal layer is aluminum.

6. A reflector as defined in claim 5, wherein said resin is an unsaturated polyester.

7. A radar reflector comprising a generally dish-shaped structure, which structure, proceeding from the inner side thereof outwardly through the wall thereof, comprises References Cited in the file of this patent UNITED STATES PATENTS 2,265,796 Boersch Dec. 9, 1941 10 6 Daly May 13, 1947 Mautner May 31, 1949 Hudspeth et a1 Nov. 27, 1951 Cooper Oct. 14, 1952 McAuley et al May 19, 1953 Hahn June 29, 1954 FOREIGN PATENTS Great Britain May 21, 1929 Great Britain Nov. 7, 1946

Claims (1)

1. A RADAR REFLECTOR COMPRISING A GENERALLY DISH-SHAPED STRUCTURE, WHICH STRUCTURE, PROCEEDING FROM THE INNER SIDE THEREOF OUTWARDLY THROUGH THE WALL THEREOF, COMPRISES A CONTINUOUS LAYER OF A FIBER REINFORCED RESINOUS LAMINATE, A THIN LAYER OF METAL, AND RESINOUS CELLULAR MATERIAL SUBSTANTIALLY THICKER THAN THE METAL, SAID FIBER REINFORCED LAYER AND SAID CELLULAR MATERIAL BEING SECURELY ADHERED TO SAID LAYER OF METAL BY MEANS OF A RESIN INTERPOSED THEREBETWEEN.

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