Space frame radome comprising a polymeric sheet

Abstract

The invention relates to a space frame radome comprising a sheet, said sheet comprising high strength polymeric fibers and a plastomer, wherein said plastomer is a copolymer of ethylene or propylene and one or more C2 to C12 alpha-olefin co-monomers and wherein said plastomer has a density as measured according to ISO1183 of between 860 and 940 kg/m.sup.3 and wherein the sheet has an areal density that is with at most 500% higher than the areal density of the high strength polymeric fibers.

Claims

1. A space frame radome comprising a sheet, said sheet comprising high strength polymeric fibers and a plastomer, wherein said plastomer is a copolymer of ethylene or propylene and one or more C2 to C12 alpha-olefin co-monomers and wherein said plastomer has a density as measured according to ISO1183 of between 860 and 940 kg/m.sup.3 and wherein the sheet has an areal density that is with at most 500% higher than the areal density of the high strength polymeric fibers.

2. The space frame radome of claim 1, wherein the polymeric fibers are polyolefin fibers.

3. The space frame radome of claim 1, wherein the sheet has an areal density that is at most 300% higher than an areal density of the high strength polymeric fibers.

4. The space frame radome of claim 1, wherein the polymeric fibers are polyethylene fibers.

5. The space frame radome of claim 1, wherein the polymeric fibers are polymeric tapes.

6. The space frame radome of claim 1, wherein the polymeric fibers have a contact angle of higher than 84.5.

7. The space frame radome of claim 1, wherein the sheet comprises a fabric selected from the group consisting of woven fabrics, knitted fabrics, plaited fabrics, braided fabrics, non-woven fabrics and combinations thereof.

8. The space frame radome of claim 1, wherein the sheet comprises a fabric and wherein the plastomer is impregnated throughout said fabric.

9. The space frame radome of claim 1, wherein the plastomer has a tensile modulus of at most 0.6 GPa.

10. The space frame radome of claim 1, wherein the plastomer is a copolymer of ethylene or propylene and one or more comonomers selected from the group consisting of ethylene, isobutene, 1-butene, 1-hexene, 4-methyl-1-pentene and 1-octene.

11. The space frame radome of claim 1, wherein the sheet has a thickness of between 0.2 mm and 10 mm.

12. The space frame radome according to claim 1, wherein the sheet has a dielectric constant of lower than 3.2 and a loss tangent of lower than 0.023, the dielectric constant and the loss tangent being measured at frequencies of between at least 0.5 GHz and at most 130 GHz.

13. The space frame radome of claim 4, wherein the polyethylene fibers are high molecular weight polyethylene (HMWPE) fibers.

14. The space frame radome of claim 4, wherein polyethylene fibers are ultrahigh molecular weight polyethylene (UHMWPE) fibers.

15. The space frame radome of claim 11, wherein the thickness of the sheet is between 0.3 and 1 mm.

16. A process for manufacturing the space frame radome according to claim 1, wherein the process comprises attaching the sheet to interconnected profiles.

17. A system comprising an antenna and the space frame radome of claim 1.

Description

EXAMPLE AND COMPARATIVE EXPERIMENT

Example

(1) A sheet was manufactured from a basket woven fabric having an AD of 0.193 kg/m.sup.2, a thickness of about 0.60 mm and a width of about 2.75 m, and containing 880 dtex polyethylene yarns known as Dyneema SK 65 which was impregnated with Queo 0203, which is a plastomer commercially available from Borealis and is an ethylene based octene plastomer with about 18 wt % octene comonomer, a density of 902 kg/m.sup.3 and a DSC peak melting point of 95 C. The plastomer was molten at a temperature of about 145 C. and discharged on a surface of the fabric. A pressure of about 45 bars was applied to impregnate the plastomer into the fabric at a temperature of about 120 C.

(2) The above process was repeated in order to coat both surfaces of the woven fabric. The obtained sheet had a thickness of about 0.75 mm, an AD of 0.550 kg/m.sup.2 and less than 40% voids. The AD of the sheet (radome wall) was 280% larger than the AD of the woven fabric. The plastomer layer was devised into: a first part of AD of about 0.175 kg/m.sup.2 covering one surface of the fabric; a second part impregnated through the fabric between the yarns and fibers thereof; and a third part having an AD of about 0.175 kg/m.sup.2 covering the other surface of the fabric. The results are presented in Table 1.

Comparative Experiment

(3) An Esscolam-6 sheet, commercially available from L-3 ESSCO was used. Esscolam-6 sheet is a fabric made of polyester fibers impregnated with a polyester resin and coated with Tedlar coating. Tedlar is a polyvinyl fluoride hydrophobic film commercially available from DuPont. The results are presented in Table 1.

(4) TABLE-US-00001 TABLE 1 COMPARATIVE Properties EXPERIMENT Example 1 Sheet thickness (mm) 0.60 0.75 Weight/area (kg/m.sup.2) 1.17 0.55 Dielectric constant at 35 GHz 3.28 2.56 Loss tangent at 35 GHz 0.023 0.0008 Tensile strength (MPa) 155 315 (warp direction) Tensile strength (MPa) 119 275 (weft direction) Tensile modulus (MPa) 3447 (warp direction) Tensile modulus (MPa) 3447 (weft direction) Contact angle () 84.5 90

(5) The results in Table 1 above show that, when compared to the known sheet, the sheet used in accordance with the invention shows better electromagnetic performance; greater tensile strength values, which results in a stronger space frame radome having higher transparency to electromagnetic waves; and better hydrophobicity over a longer life time without using any additional free standing hydrophobic coating, resulting in higher durability and easier maintenance of the radome wall.