US3448456A

US3448456A - Reflector antenna inflatable with foamed plastic

Info

Publication number: US3448456A
Application number: US578893A
Authority: US
Inventors: Jacques H Pessin
Original assignee: US Department of Navy
Current assignee: US Department of Navy
Priority date: 1966-09-12
Filing date: 1966-09-12
Publication date: 1969-06-03
Anticipated expiration: 1986-06-03

Description

June 3, 1969 J. H. PESSIN 3,448,456

REFLECTOR ANTENNA INFLATABLE WITH FOAMED PLASTIC Filed Sept. 12, 1966 INVENTOR JACQUES H. PESSl/V AGED/VT ATTORNEY United States Patent 3,448,456 REFLECTOR ANTENNA INFLATABLE WITH FOAMED PLASTIC Jacques H. Pessin, Ellicott City, Md., assignor, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Filed Sept. 12, 1966, Ser. No. 578,893

Int. Cl. H011; 1/40 U.S. Cl. 343-873 8 Claims The invention relates to an improved antenna system and method, and more particularly to an improved antenna system and method that employs supporting plastic foam.

Inflatable or collapsible antennas have seen considerable use in radar and other electrical magnetic radiation applications, especially where the installation is temporary and must be reinstalled at either locations at frequent intervals. The inflatable types have seen especially wide use because they are light in weight, easily portable and easily installed and reinstalled and so have seen considerable use in highly mobile field radar installations. Inflatable antennas however, must be continuously pressurized during operation from a source of gas, such as, air from a blower to replace the gas lost by leakage. The air source must be controlled in order that the antenna be supported by a constant pressure, to avoid variations in the shape of the antenna which would change its radi-a tion pattern. Additionally inflatable antennas have structural deficiencies inherent in any gaseous inflated shape which allow the antenna to flex and change shape under the influence of wind or ice loading. This change in shape effects a change in radiation pattern of the antenna and thereby reduces the accuracy of the entire system.

The improved antenna system of the invention eliminates the aforementioned problems associated with gaseous inflated antennas while retaining their light weight and portability attributes. The invention provides an antenna system comprising of an outer balloon element and an inner filler element. The outer balloon element is of similar construction to that commonly found in inflatable antennas and has similar reflective characteristics. The outer balloon element of the invention however, is adapted for use with the unique inflating method of the invention. The invention employs a plastic foam inflation that makes the antenna self supporting, rigid, and not dependent on continuous air supply.

It is therefore an object of the instant invention to provide an improved light weight and portable antenna system.

It is another object of the invention to provide an improved light weight and portable antenna system that does not require a continuous air supply for inflation.

It is a further object of the invention to provide an improved antenna system that employs a plastic foam for support.

It is still another object of the invention to provide an improved antenna system that employs a plastic foam for support that may be discarded when the antenna is moved.

It is a still further object of the invention to provide an improved process for erecting antenna systems that employs a foaming process within an antenna balloon.

It is an additional object of the invention to provide an antenna system of light weight construction that employs plastic foam that incorporates air filled voids within the foamed plastic.

These and other objects and many of the attendant advantages of the invention will be more readily understood by reference to the following detailed description of one specific embodiment thereof when considered in connection with the accompanying drawing, wherein:

FIG. 1 is a perspective view of the antenna system of the invention;

FIG. 2 is a cross sectional view taken along line 22 of FIG. 1 and showing one alternative embodiment of the interior construction of the antenna supporting foam;

FIG. 3 is an additional cross sectional view also taken along section line 2-2 of FIG. 1 and showing a second alternative embodiment of the interior construction of the antenna supporting foam;

FIG. 4 is a cross sectional view taken along line 44 of FIG. 2, and showing construction of the outer envelope of the antenna system of the invention.

Referring now to the drawing there is shown in FIG. 1 the antenna system 10, mounted on a suitable support 12 having a horn 14 and secondary reflector 16 mounted thereon. At one end of the antenna envelope or balloon 18 there is shown, indicated generally by numeral 20, an end seam. The seam in the instant embodiment is shown to comprise an overlapping continuous sealing strip 22, such as a Velcro strip, and a plurality of buckles 24. The strip provides a sealing function whereas the buckles are designed to give strength to the seam and will be described more fully hereinafter.

Referring now to FIGS. 2 and 3, there are shown two alternative embodiments for the interior of the antenna system 10. In cross section the antenna system 10 is shown to contain a filler material 26. In the preferred embodiment this filler material is comprised of light weight foamed plastic. The particular foam employed would be chosen for its light weight characteristics and ease of foaming in situs and could be, for example, polyurethane. The foam is contained within a thin plastic inner balloon 28 such as Pliofilm. This balloon is employed to make the foamed filler an independent package which may be removed upon antenna dismantling and its use will be described more fully hereinafter. FIG. 2 shows one embodiment of a method to reduce the over all weight of the antenna supporting foam filler. This embodiment employs an elongated void creating balloon 30, which is inflated within the outer bag 28 prior to foaming and thereby creates a void within the foam material and allows a considerable reduction in weight. The modification of FIG. 3 differs from that shown in FIG. 2 only in the number of void creating balloons employed in the weight reduction process.

Balloons

32, 34 and 36 are shown to be of varying size to substantially conform to the over-all shape of the inflated antenna. By the use of a plurality of these void creating balloons in this fashion the overall weight of the antenna system may be reduced still further while retaining adequate foam to support the antenna system. Both FIGS. 2 and 3 also show inlet nozzle 38 and pressure release valve 40 and shaping

rods

42 and 44 to be described hereinafter. Indicated diagrammatically in FIGS. 2 and 3 is the main reflector element 46 which directs the transmitted and received energy to and from the secondary reflector element 16. One suitable configuration for this reflector element is shown in FIG. 4. The outer or protective material 48 is bonded to a first aluminum foil reflective layer 50 which is in turn bonded to a second protective or strength layer 52. This second layer is bonded to a final aluminum foil reflective layer 54. In the assembled condition these four bonded layers are in intimate contact with the Pliofilm bag 28 that contains the foam filler material.

The antenna system is readied for operation by erecting the mast 12 and affixing thereto by suitable means, not shown, the outer balloon 18 which contains inner balloon 28. If void creating balloons are to be employed, they are inflated with for example, air and inserted within the inner balloon through the opening 20 and a similar opening within the inner balloon. The openings are then secured which in the case of the outer balloon may be accomplished by the strip 22 and attaching clamps 24. Foam generating apparatus is then connected to nozzle 38 and the plastic foam components are mixed and forced into the antenna systems interior. The nozzle passes from the exterior of the antennathroug'h, the outer balloon and inner balloon but is afiixed to the outer bag only to provide for the later removal of the inner balloon and its contents. If the foam to be employed is polyurethane, for example, the foam generating apparatus could comprise tanks for isocyanate and polyol, means to force the iso cyanate and polyol to a mixing head and means to deliver the reacting isocyanate and polyol subsequent to mixing, to the nozzle 38. As the plastic foam components pass through the nozzle and enter the balloons they expand and surround the void creating balloons. As filling continues, the antenna is formed into its designed shape. Pressure relief valve 40 allows the escape of entrapped air as it becomes pressurized by the expanding foam but retains adequate pressure to force complete expansion of the balloon thereby insuring accurate shaping.

Shaping rods

42 and 44 are provided to insure accurate shaping of the bottom portion of the antenna system and may be affixed to the outer balloon for retention therewith. When foaming is complete the connection to nozzle 38 may be removed and the foam allowed to harden, Upon hardening the antenna system becomes self supporting and not dependent on the seal at opening or the integrity of the outer balloon elsewhere. At this stage the system is ready for operation and needs no further attention until disassembly becomes necessary. The foamed material has substantially no effect on the transmission or reflection of radio waves from the primary reflector 46 and the secondary reflector 16. In other words the foamed material is substantially transparent to radio waves and very little absorption takes place by transmission through this medium.

When it becomes necessary to disassemble the antenna system it is merely necessary to unlatch clamps 24 and zip open the strip 22 to expose the foamed material contained within the inner bag 28. The opening 20 is large enough to allow the inner bag with its rigid foam contents to be slid from the outer bag 18. The foamed material can be disposed of at the site and it is not necessary to transport it with the remainder of the antenna system since it is inexpensive and a new foamed interior can readily be generated at the next site of operation. Thus the weight and volume of material necessary to be transported in support of the antenna system is kept to a minimum. Only the expensive and difiicult to replace outer antenna balloon 18 need by retained and that may be collapsed to a small volume for shipping.

As will be clear from the foregoing description the outer balloon 18 is a critical portion of the entire antenna system. The outer covering must be of sufficient strength to retain its shape and resist abrasion and general deterioration due to the exposure of the elements. Fiberglas cloth has adequate strength and weathering characteristics and is generally suitable to the purposes of the invention. Additionally it is within the concept of the invention to employ a Mylar material with a Dacron scrim, the Mylar being employed for its water and gas impervious nature and the Dacron scrim for strength. This combination is lighter than the Fiberglas combination and may be preferable where weight is an overriding consideration. The material may be pleated as shown in FIG. 1 to achieve the proper shape.

The construction of a preferred embodiment of the outer balloon in the section having the primary reflector is shown in section in FIG. 4. As can be seen from this figure there are two layers of

strength material

48 and 52 which may be either of the Fiberglas or Mylar- Dacron material. Two layers are employed in this region in order to separate two layers of reflective material. This reflective material in the instant embodiment is of the nature of aluminum foil, that is, very thin aluminum sheets sandwiched in the case of sheet 50 between

layers

48 and 52 and in the case of sheet 54 being bonded to layer 52 and protected on its other side by the inner balloon element 28. The purpose of employing two reflective layers is to avoid any change in the reflective charactistics of the antenna when small surface discontinuities or cracks occur in the reflective material. It should be noted that the particular configuration of the reflector portion of the antenna system has been described not by way of limitation but only as a preferred example due to its superior wearing characteristics. Other multilayer and single layer reflectors could be employed with the antenna system of the invention for example, a single sheet of aluminum could be aflixed to a single layer outer covering of Fiberglas or Mylar-Dacron. Additionally it should be noted that the

rods

42 and 44 are not essential to the invention, although their use is preferred to strengthen the expanded structure and to stabilize the form to prevent changes in contour at the point of attachment. Further it is obvious that many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. A light weight portable antenna system comprisan outer balloon member containing a light weight plastic foam; said outer balloon member being flexible and incorporating over a portion of said outer balloon member means for reflecting radio frequency energy;

said outer balloon member including a resealable seam,

whereby said plastic foam may be removed from said outer balloon member.

2. The light weight portable antenna system of claim 1 wherein:

said light weight plastic foam contains at least one void whereby the weight of said antenna system is reduced.

3. The light weight portable antenna system of claim 2 further including an inner balloon member surrounding said light weight plastic foam and removable therewith.

4. The antenna system of claim 1 wherein:

the outer balloon material is comprised of glass fiber cloth.

5. The antenna system of claim 1 wherein the outer balloon material is comprised of a water and gas impermeable material with a strengthening scrim.

6. The antenna system of claim 3 further including a filling nozzle and a pressure relief valve attached through said outer and inner balloons whereby said light weight plastic foam may be forced-into said balloon 7. The antenna system of claim 1 wherein said means for reflecting radio frequency energy at least one layer of aluminum bonded to said outer balloon member.

8. The antenna system of claim 1 wherein said means for reflecting radio frequency comprises a plurality of aluminum layers separated by flexible material;

whereby the reflective properties of said means for reflecting radio frequency energy are not effected by discontinuities in a single one of said aluminum layers.

References Cited UNITED STATES PATENTS 2,731,055 1/1956 Smith 343-872 ELI LIEBERMAN, Primary Examiner.

U.S. Cl. X.R. 343--781, 915

Claims

1. A LIGHT WEIGHT PORTABLE ANTENNA SYSTEM COMPRISING: AN OUTER BALLON MEMBER CONTAINING A LIGHT WEIGHT PLASTIC FOAM; SAID OUTER BALLOON MEMBER BEING FLEXIBLE AND INCOR PORATING OVER A PORTION OF SAID OUTER BALLOON MEMBER MEANS FOR REFLECTING RADIO FREQUENCY ENERGY; SAID OUTER BALLOON MEMBER INCLUDING A RESEABLABLE SEAM, WHEREBY SAID PLASTIC FOAM MAY BE REMOVED FROM SAID OUTER BALLOON MEMBER.