GB2603954A

GB2603954A - Multifunction composite antenna enclosure

Info

Publication number: GB2603954A
Application number: GB2102501.0A
Authority: GB
Inventors: Smith James
Original assignee: Thales Holdings UK PLC
Current assignee: Thales Holdings UK PLC
Priority date: 2021-02-22
Filing date: 2021-02-22
Publication date: 2022-08-24
Anticipated expiration: 2041-02-22
Also published as: GB2603954B; GB202102501D0

Abstract

A composite structure 100, suitable for forming a wall of an antenna enclosure, comprises inner and outer fibre-reinforced plastic layers 130, 140 which sandwich a core material layer 110; and an electromagnetic shielding conductive mesh 150 which is located over the outer fibre-reinforced plastic layer 130. One or more layers of conductive paint 180 may be used to cover an end region of a composite structure wall 100 and applied to holes or gaps in and between walls to provide electromagnetic shielding. The conductive mesh 150 and the conductive paint 180 may entirely surround the antenna enclosure. Further inner and outer fibre-reinforced plastic layers 135, 145 may be included, and these may have different fibre orientations. Glass reinforced fibres may be used which may be E-glass. The core material 110 may be a thermal insulator involving a honeycomb or foam structure which may include fibre reinforced strengthening inserts 120. The conductive mesh 150 may be formed of aluminium. The antenna enclosure walls may be covered with a waterproof sealing layer 160, 170 which may further include a fungicidal varnish.

Description

Multifunction Composite Antenna Enclosure TECHNICAL FIELD The present disclosure relates to an antenna enclosure. In particular, but without limitation, this disclosure relates to an antenna enclosure having one or more external walls each having a composite structure.

BACKGROUND

Antenna enclosures are housings for protecting antennas from environmental conditions. In general, they are required to be substantially transparent in the wavelength(s) in which the antenna operates whilst also providing protection for the antenna and associated electronics (e.g. from mechanical damage or water damage).

Antenna enclosures can be manufactured from metallic materials or monolithic composite constructions. However, no single solution solves all the engineering requirements demanded for a product orientated digital antenna array.

SUMMARY

Embodiments described herein relate antenna enclosures having a novel composite structure that provides improved mechanical strength and improved electromagnetic shielding in a low-cost and low-weight package.

According to a first aspect there is provided an antenna enclosure having one or more external walls each having a composite structure comprising: an inner fibre-reinforced plastic layer and an outer fibre-reinforced plastic layer; a core formed from a core material, wherein the core is sandwiched between the inner fibre-reinforced plastic layer and the outer fibre reinforced plastic layer; and conductive mesh located over the outer fibre-reinforced plastic layer to provide electromagnetic shielding.

The core and fibre-reinforced plastic layers provide a strong, light weight enclosure, whilst the conductive mesh provides electromagnetic shielding to protect against unwanted electromagnetic interference and lightning strikes. The conductive mesh may be a metallic mesh, such as an aluminium mesh. Providing a mesh, rather than a full layer of conductive material, provides shielding with a reduced weight. The mesh may include one or more holes. These holes may be sized such that the conductive mesh provides electromagnetic shielding up to a required maximum frequency.

At least one of the one or more external walls may comprise a layer of conductive paint over an end portion of the wall. The layer of conductive paint may cover an end of each of the inner fibre-reinforced plastic layer, the outer fibre-reinforced plastic layer and the core. The conductive paint may provide further electromagnetic shielding. This may be suitable for shielding areas of the enclosure that cannot be protected via the conductive mesh (e.g. due to their shape). The conductive paint may be metallic paint (e.g. silver loaded paint) A corresponding layer of conductive paint may be located in one or more holes in the one or more external walls or in one or more gaps between the external walls to provide electromagnetic shielding. Accordingly, the conductive paint may be provided at boundaries between or holes within the external walls to provide shielding in areas that the conductive mesh cannot protect.

The conductive mesh and conductive paint may form an electromagnetic shield that stretches around the entirety of the antenna enclosure. That is, every part of the antenna enclosure may be covered by either (or both) a conductive mesh or conductive paint. This can be such that substantially no gaps exist in the shield. Having said this, small gaps for cabling or electrical connectors may be provided, e.g. on a rear or underside of the enclosure.

According to an embodiment, the antenna enclosure may further comprise one or both of: a further inner fibre-reinforced plastic layer located under the inner fibre-reinforced plastic layer such that the inner fibre-reinforced plastic layer is sandwiched by the core and the inner fibre-reinforced plastic layer; and a further outer fibre-reinforced plastic layer located between the outer fibre-reinforced plastic layer and the conductive mesh.

Additional further inner/outer fibre-reinforced plastic layers may also be provided. Accordingly, a plurality of fibre-reinforced plastic layers may be provided on each side of the core. This can improve the mechanical strength of the external walls.

The inner fibre-reinforced plastic layer and (one or more of) the further inner fibre-reinforced plastic layer(s) may have different fibre orientations. Alternatively or in addition, the outer fibre-reinforced plastic layer and (one or more of) the further outer fibre-reinforced plastic layer(s) may have different fibre orientations. The different fibre orientations may be perpendicular to each other. That is, the inner/outer fibre-reinforced plastic layers have fibres oriented perpendicularly to the corresponding further inner/outer fibre-reinforced plastic layers. This can provide improved strength across a variety of directions.

The inner fibre-reinforced plastic layer and the outer fibre-reinforced plastic layer may be formed of glass-reinforced plastic. This can provide improved structural performance (e.g. higher flexibility and higher ultimate breaking point relative to carbon fibre). This can also be less expensive and can provide reduced conductivity relative to, for instance, carbon fibre. The glass-reinforced plastic may be reinforced with E-glass. This can provide improved electrical resistance.

In one embodiment the core material is a thermal insulator. The core material may be more thermally insulating the other layers in the enclosure (e.g. than the fibre-reinforced plastic layers. The core material may have a thermal conductivity of less than 1 W/mK (e.g. 0.5 W/mK).

The core material has may have a honeycomb or foam structure. Where the core material has a honeycomb structure, one or more gaps in the honeycomb structure may be at least partially filled with corresponding inserts for increased mechanical strength.

This can increase the rigidity of the external wall and can provide a stronger material (than the core material) into which fixings (e.g. bolts or screws) can be secured. Each corresponding insert may be formed of fibre-reinforced plastic. This may be glass reinforced plastic (e.g. reinforced with E-glass).

The one or more external walls may form an internal enclosure for housing one or more antennas, wherein the inner layer of fibre-reinforced plastic is located closer to the internal enclosure than the outer layer of fibre-reinforced plastic. This internal enclosure (or cavity) may be of sufficient size for containing the one or more antennas and their associated electronics. The conductive mesh may be located on an opposite side of the external wall to the internal enclosure.

One or both sides of each of the one or more external walls may be covered by a corresponding waterproof sealing layer. One or both of the corresponding waterproof sealing layers may be fungicidal. For instance, the corresponding waterproof sealing layer covering an internal surface of each external wall may be a fungicidal varnish.

According to a further embodiment there is provided a composite structure for use in an antenna enclosure, the composite structure comprising: a first fibre-reinforced plastic layer and a second fibre-reinforced plastic layer; a core formed from a core material, wherein the core is sandwiched between the first fibre-reinforced plastic layer and the second fibre reinforced plastic layer; and conductive mesh located over the second fibre-reinforced plastic layer to provide electromagnetic shielding.

BRIEF DESCRIPTION OF THE DRAWINGS

Arrangements of the present invention will be understood and appreciated more fully from the following detailed description, made by way of example only and taken in conjunction with drawings in which: FIG. 1 shows a cross-sectional view of a composite structure for an antenna enclosure according to an embodiment; FIG. 2 shows a cross-sectional view of a composite structure for an antenna enclosure according to a further embodiment, FIG. 3A shows an isometric view of the front of an antenna enclosure according to an embodiment; and FIG. 3B shows an isometric view of the rear of an antenna enclosure according to an embodiment.

DETAILED DESCRIPTION

Antenna enclosures are often mounted on the outside of vehicles, such as aircraft or submersible vehicles, and so must be robust to the particular environments to which they will be exposed.

Antenna enclosures for use in external environments, for instance on vehicles, will need to provide waterproofing as well as electromagnetic (EMC) screening and protection from other environmental effects, such as lighting strikes. Solar shields can often be required to reduce additional heat load. These requirements provide additional cost and complexity to the design.

Some antenna enclosures are formed of metal. Metallic enclosures tend to be manufactured from an aluminium alloy to keep mass low, and can be made of several machined or cast elements. This type of construction has inherent problems with joint sealing and use of EMC gaskets giving rise to bi-metallic corrosion issues. In addition, protective finishes are often required for aluminium alloys. These must be compliant with local regulations (e.g. The Restriction of Hazardous Substances Directive (RoHS) or Registration, Evaluation, Authorisation and Restriction of Chemicals (REACh)) and are often a limiting factor on long-term corrosion performance. Historic methods of protecting aluminium, e.g. chromate conversion, are generally no longer acceptable under current regulations due to risks associated with health, safety and environmental protection.

To overcome this issue, composite materials may be used as an alternative to fully metallic enclosures. A composite material is combination of two or more materials with different characteristics (such as glass fibre reinforced with plastic). Whilst composite materials can provide advantages when it comes to strength and weight, many composite materials are resistant to electricity and therefore provide poor electromagnetic screening. This is further complicated where joints are introduced that require both environmental and EMC sealing. Composite enclosures tend to be monolithic and therefore are often unable to benefit from lower mass due to shock load resistance requirements.

To solve the above issues, a novel composite structure is introduced herein that provides improved thermal, electromagnetic and environmental protection in a strong and lightweight package. The composite structure has effective corrosion resistance for use in marine environments and is relatively inexpensive to manufacture.

The antenna housing principally utilises a sandwich construction of fibre-reinforced plastic skins (e.g. fiberglass reinforced plastic) with an thermally insulated core. This provides a lightweight enclosure, which gives very good environmental protection from the effects of weather, the sun and salt laden atmosphere corrosion. Additional layers of aluminium mesh and conductive paint provide the required protection for EMC and lightning strike effects. In addition, various paints and varnishes can be introduced to provide environmental protection to other materials used in the design.

FIG. 1 shows a cross-sectional view of a composite structure for an antenna enclosure according to an embodiment. This shows the composite structure that would form one or more walls of the antenna enclosure.

The composite structure 100 comprises a core 110 that is sandwiched on each side by inner 140 and outer 130 layers of fibre-reinforced plastic. The inner layer 140 faces towards an internal cavity of the antenna housing (that is for housing the antenna) whilst the outer layer 130 faces away from the internal, cavity towards the external environment. That is, the inner layer 140 is located on an inner face of the core 110 and the outer layer 130 is located on an outer face of the core. The inner 140 and outer 130 layers may be bonded to the core 110 via an adhesive. This may be a film adhesive (e.g. an epoxy film adhesive such as MTC510FRBO).

A further layer 135, 145 of fibre-reinforced plastic is located over each of the inner 140 and outer 130 layers. That is, a further outer layer 135 is positioned over the outer layer 130 on the outer surface of the outer layer 130 and a further inner layer 145 is positioned over the inner layer 140 (on the opposite side to the core 110) on an inner surface of the inner layer 130. Accordingly, two layers of fibre-reinforced plastic are located on each side of the core 110, although any number of layers may be used on each side (e.g. four layers per side), depending on the structural strength required. Each further layer 135, 145 may be bonded to the corresponding inner 140 and outer 130 layers over which they are positioned (e.g. through an adhesive such as epoxy).

The orientation of the fibres may be different between different layers of fibre-reinforced plastic. In the present embodiment, each further layer 135, 145 has fibres oriented perpendicular (at 90°) to the fibres of the corresponding inner 140 and outer 130 layers over which they are positioned. This helps to increase the strength of the composite structure across all directions.

In this embodiment, fibre-reinforced plastic layers 130, 135, 140, 145 are made from glass-reinforced plastic (GRP). This may be pre-impregnated (pre-preg) epoxy E-glass. In one embodiment, the fibre-reinforced plastic layers 130-145 are manufactured from pre-impregnated E-glass reinforced plastic formed of 38% resin by weight. Having said this, alternative fibre-reinforced plastics may be used. For instance, different types of fibres (such as carbon fibre) may be used, or different types of polymer matrix, such as phenolic resins, may be used. Equally, if fibreglass is used, different types of glass may be used (instead of E-glass) such as A, C, AE or S glass. Having said this, E-glass reinforced plastic has been found to be particularly effective for antenna housing due to the reduced weight, cost and increased strength of glass--reinforced plastic.

The core 110 provides thermal insulation (e.g. to form a solar shield) and increases the structural strength and stiffness of the overall composite layout. The core 110 is formed of a core material that provides thermal insulation. To provide this insulation, the core material may have a relatively low thermal conductivity, e.g. between 0.1 Wm-1K-1 and 1 Wm-1K-1. The specific implementation described herein provides thermal insulation of around 0.5 Wm-1K-1 (e.g. 0.48 Wm-1K-1). Having said this, the thermal properties may be adapted to the specific requirements (e.g. the intended environment).

Many different types of core material are available for composite structures such as this.

In one embodiment, the core material is a foam material, such as polymethacrylimide, polyurethane or styrene. A foam material comprises air bubbles that provide thermal insulation. In another embodiment, the core material has a honeycomb structure, with thermal insulation provided by gaps within the honeycomb structure (hexagonal cavities).

The material of the core itself is also a thermal insulator. For instance, the core material may be an aramid fibre paper, such as Nomex®.

In the present embodiment, a honeycomb structure is used for improved strength, improved thermal insulation and reduced mass. Some areas of the housing can require additional structural strength and/or may require a stronger foundation for tapped holes for fixings (e.g. bolts or screws). In this case, solid inserts 120 may be positioned within the holes in the honeycomb structure for additional mechanical strength. These may be made from fibre-reinforced plastic similar to the fibre-reinforced plastic layers 130-145, although there is no requirement for the inserts 120 and the fibre-reinforced plastic layers 130-145 to be made of the same material.

As with the fibre-reinforced plastic layers 130-145, the inserts 120 may be reinforced by glass, carbon or any other appropriate material. For instance, the inserts may be formed of pre-impregnated (pre-preg) epoxy E-glass (such as 2x2T E-glass fibre reinforced plastic). The inserts 120 may have a thicker weave of fibre than the inner 140 and outer layers, to provide additional strength. The inner 140 and outer 130 layers may be formed of a more flexible material to allow them to be more easily formed to shape (e.g. bent around corners).

In one embodiment, the inserts 120 are manufactured from pre-impregnated E-glass reinforced plastic formed of 38% resin by weight. Having said this, alternative fibre-reinforced plastics may be used. For instance, different types of fibres (such as carbon fibre) may be used, or different types of polymer matrix, such as phenolic resins, may be used. Equally, if fibreglass is used, different types of glass may be used (instead of E-glass) such as A, C, AE or S glass. Having said this, E-glass reinforced plastic has been found to be particularly effective for antenna housing due to the reduced weight and increased strength of fibreglass as well as the improved electrical resistance and radio-transparency provided by E-glass.

It should be noted that, whilst the embodiment of FIG. 1 shows an insert 120, this is an optional feature.

A conductive mesh layer 150 is positioned over the further outer layer 135. This provides electromagnetic shielding as well as protection from lightning strikes. The conductive mesh layer 150 may be a metallic mesh. This may be made from a lightweight metal, such as aluminium, to keep the mass of the structure low. The conductive mesh layer 150 may be bonded to the further outer layer 135 via an adhesive, such as a film adhesive (e.g. an epoxy film adhesive).

The conductive mesh layer 150 provides electrical shielding. The conductive mesh layer is located towards the outer face of the composite (on the opposite side of the core 110 and fibre-reinforced plastic layers 130-145 to the internal cavity of the housing). This ensures that the conductive mesh layer 150 can protect the composite structure from lightning strikes and protects electronics within the enclosure from unwanted electromagnetic interference.

The size of the mesh (the hole size) will affect the maximum frequency to be screened. In addition, the thickness can be altered dependant on the required electrical resistance. This controls the level of electromagnetic screening provided by the mesh.

Providing shielding via a mesh rather than a metallic sheet provides shielding in a lightweight package. In addition, the mesh can be encapsulated within the composite structure (e.g. via epoxy), protecting the mesh from harsh environments.

Having said this, not all sections of the antenna housing can be effectively protected via the conductive mesh 150. This is because certain sections are shaped such that the conductive mesh cannot be effectively laid over. For instance, sharp corners (such as at end portions of the composite) or gaps between composite sheets (e.g. at seals between composite sheets) cannot be fully protected by metallic sheeting alone. At these portions, conductive paint 180 is used to provide electromagnetic shielding.

In the present embodiment, a layer of conductive paint 180 is painted over the end portion, spanning across all layers, and over the end corners of the composite wall structure shown in FIG. 1. The conductive paint therefore stretches perpendicularly to the planes of the core 110, the reinforced plastic layers 130-145 and the conductive mesh layer 150. VVhilst the example of FIG. 1 shows conductive paint only over an end portion of a composite wall, paint can be used to connect adjacent walls and to protect differently shaped portions of the enclosure. The conductive paint may be silver loaded paint, such as Loctite® EDAG 915 E&C Conductive Coating, but alternative types of conductive paint may be used.

The combination of a conductive mesh 150 for large planar areas and conductive paint 180 for corners, curves and gaps between walls provides effective electromagnetic shielding across the whole of the structure whilst maintaining a low cost. That is, substantially the entirety of the antenna housing is protected with shielding via the conductive paint and the conductive mesh.

Finally, the composite structure is finished with sealing layers on the top 160 and bottom 170 of the structure (on the outer and inner faces of the structure). These sealing layers provide environmental sealing and protection. For instance, they provide waterproofing to protect against environmental conditions. Composite structures, like most reinforced plastics, are known to be porous and in certain conditions harbour fungus. The varnish provides a barrier to water ingress and potential damage from icing and prevents fungal growth within the composite layup. One or both sealing layers may be fungicidal. In the present embodiment, the inner layer 170 is a fungicidal varnish whilst the outer layer is a waterproof paint, allowing the external appearance of the housing to be customized. The fungicidal varnish may be a phenolic varnish, although other types of varnishes are possible.

FIG. 2 shows a cross-sectional view of a composite structure for an antenna enclosure according to a further embodiment. This embodiment is broadly in line with the embodiment of FIG. 1; although, in addition to sealing the conductive mesh 150 and inner fibre-reinforced plastic layers 140, 145, a sealing layer 165 is also painted over the conductive paint 180 to provide further protection. This may also be a waterproof paint to allow the external appearance to be customized.

In the present embodiment, an area 190 of the conductive paint 180 is left exposed to allow a conductive connection to be made with an adjoining structure (e.g. an adjoining composite structure and/or a gasket). In the present embodiment, the exposed area 190 is located on the inner face of the composite structure; however, this may be located at any point above the conductive paint. In addition or alternatively, an area of the conductive mesh 150 may be left exposed to allow a similar electrical connection to an adjoining structure.

One or more of the sealing layers 160, 165, 170 described herein may provide some form of camouflage. This may be in the form of changing the colour or absorption pattern across a range of wavelengths. The range of wavelengths may be over the visible spectrum and/or over another range, such as in the infrared range.

The embodiments described herein provide antenna enclosures using novel materials and process technologies. The combination of these materials and process technologies together has not previously been put into an integrated antenna housing construction package. This structure provides improvements over the use of more traditional materials with regard to electrical shielding, strength, weight and cost. Alternative processes result in a high part count with a higher mass. This solution combines many readily available materials to result in the multifunctional integrated approach.

Historically lightning strikes have resulted in failure of composite structures used for similar purposes due to the rapid out gassing of the resin content within the composite matrix. This causes the layers to rupture and delaminate. The conductive mesh and the conductive paint keeps the conductive path near the surface of the material resulting in lower resistance and thus less heating. The conductive mesh and conductive paint also act as a low DC sheet resistance EMC screen for the internal electronics. The insulated core results in a very low thermal conduction path between the layers and increases the structural strength and stiffness of the overall composite layup. Furthermore, the external sealing layers provide a barrier to water ingress and potential damage from icing and prevent fungal growth within the composite layup.

The composite structure can be manufactured through the use of mould tools, layup books and controlled curing processes such as vacuum bagging and autoclaves. 3D models and detailed drawing sets can be used on all parts to control the design intent. The manufacturing method requires industry recognised layup techniques used in the manufacture of composite pre-impregnated materials. The conductive mesh may be imbedded as an outer layer of the construction during the normal lay-up process.

The structure may be manufactured through normal composite manufacturing methods. The layers may be positioned during the layup process. Whilst the fabric layers may be pre-impregnated with an epoxy, this may not be sufficient to bond the fabric layers to the core, so an additional layer or film adhesive may be located between the fabric and the core to fully bond between the core to the fabric on each side. The conductive mesh may be positioned on over the fabric layers, and an adhesive (such as epoxy) may be poured over the conductive mesh. The whole structure may then be cured (e.g. in an autoclave) to cure the adhesive. After this, the paint layers (e.g. the sealing layers and the conductive paint) may be painted over the cured structure.

FIG. 3A shows an isometric view of the front of an antenna enclosure according to an embodiment. FIG. 3B shows an isometric view of the rear of an antenna enclosure according to an embodiment. The antenna enclosure 200 includes walls 100 having the composite structure described above. The enclosure 200 forms an internal cavity for housing one or more antennas and associated electronics.

In the present example, the housing has a rectangular cross-section, although alternative shapes are possible. The top, bottom and side walls are formed of a single length of composite wall that wraps around the enclosure. Front and rear panels (also formed according to the composite structure discussed herein) are secured via bolts 210 to the front and rear of the enclosure to completely enclose the internal cavity. Connectors 220 are located on the rear of the housing to allow signals to be transferred to/from the antenna.

As discussed above, conductive paint is used to provide electromagnetic shielding at positions where the conductive mesh cannot reach or fit around. This includes end sections of the walls (as shown in FIG. 1) and joints between walls.

As discussed above, the walls are arranged with a composite structure such that the conductive mesh 150 is located on the outer face of the outer fibre-reinforced layers 130, 135. Throughout this application "outer" and "inner' refers to the orientation with regard to internal cavity of the housing. "Inner" refers to a position that is relatively closer to the internal cavity than an "outer" position.

While certain arrangements have been described, the arrangements have been presented by way of example only, and are not intended to limit the scope of protection. The inventive concepts described herein may be implemented in a variety of other forms.

In addition, various omissions, substitutions and changes to the specific implementations described herein may be made without departing from the scope of protection defined in the following claims.

Claims

CLAIMS1. An antenna enclosure having one or more external walls each having a composite structure comprising: an inner fibre-reinforced plastic layer and an outer fibre-reinforced plastic layer; a core formed from a core material, wherein the core is sandwiched between the inner fibre-reinforced plastic layer and the outer fibre reinforced plastic layer; and conductive mesh located over the outer fibre-reinforced plastic layer to provide electromagnetic shielding.
2. An antenna enclosure according to claim 1 wherein at least one of the one or more external walls comprises a layer of conductive paint over an end portion of the wall, where the layer of conductive paint covers an end of each of the inner fibre-reinforced plastic layer, the outer fibre-reinforced plastic layer and the core.
3. An antenna enclosure according to claim 1 or claim 2, wherein a corresponding layer of conductive paint is located in one or more holes in the one or more external walls or in one or more gaps between the external walls to provide electromagnetic shielding.
4. An antenna enclosure according to claim 3 wherein the conductive mesh and conductive paint form an electromagnetic shield that stretches around the entirety of the antenna enclosure 5.
An antenna enclosure according to any preceding claim further comprising one or both of: a further inner fibre-reinforced plastic layer located under the inner fibre-reinforced plastic layer such that the inner fibre-reinforced plastic layer is sandwiched by the core and the inner fibre-reinforced plastic layer; and a further outer fibre-reinforced plastic layer located between the outer fibre-reinforced plastic layer and the conductive mesh.
An antenna enclosure according to claim 5 wherein one or both of: the inner fibre-reinforced plastic layer and the further inner fibre-reinforced plastic layer have different fibre orientations; and the outer fibre-reinforced plastic layer and the further outer fibre-reinforced plastic layer have different fibre orientations.
7. An antenna enclosure according to any preceding claim wherein the inner fibre-reinforced plastic layer and the outer fibre-reinforced plastic layer are formed of glass-reinforced plastic
8. An antenna enclosure according to claim 7 wherein the glass-reinforced plastic is reinforced with E-glass.
9. An antenna enclosure according to any preceding claim wherein the core material is a thermal insulator.
10. An antenna enclosure according to any preceding claim wherein the core material has a honeycomb or foam structure.
11. An antenna enclosure according to any preceding claim wherein the core material has a honeycomb structure, wherein one or more gaps in the honeycomb structure at least partially filled with corresponding inserts for increased mechanical strength.
12. An antenna enclosure according to claim 11 wherein each corresponding insert is formed of fibre-reinforced plastic.
13. An antenna enclosure according to any preceding claim wherein the one or more external walls form an internal enclosure for housing one or more antennas, wherein the inner layer of fibre-reinforced plastic is located closer to the internal enclosure than the outer layer of fibre-reinforced plastic.
14. An antenna enclosure according to any preceding claim wherein the conductive mesh is formed of aluminium.
15. An antenna enclosure according to any preceding claim wherein one or both sides of each of the one or more external walls is covered by a corresponding waterproof sealing layer.
16. An antenna enclosure wherein the corresponding waterproof sealing layer covering an internal surface of each external wall is a fungicidal varnish.
17. A composite structure for use in an antenna enclosure, the composite structure comprising: a first fibre-reinforced plastic layer and a second fibre-reinforced plastic layer; a core formed from a core material, wherein the core is sandwiched between the first fibre-reinforced plastic layer and the second fibre reinforced plastic layer; and conductive mesh located over the second fibre-reinforced plastic layer to provide electromagnetic shielding.