GB2256529A

GB2256529A - Antenna arrangements

Info

Publication number: GB2256529A
Application number: GB9207036A
Authority: GB
Inventors: Robert Fraser Sims; Norman Harrison
Original assignee: Marconi Electronic Devices Ltd; Plessey Semiconductors Ltd
Current assignee: Marconi Electronic Devices Ltd; Plessey Semiconductors Ltd
Priority date: 1991-04-02
Filing date: 1992-03-31
Publication date: 1992-12-09
Anticipated expiration: 2012-03-31
Also published as: GB9207036D0; GB2256529B

Abstract

An antenna arrangement includes a reflector 1 which is partially transparent to visible radiation. The reflective surface of the reflector 115 formed by coating a mesh of filamentary material with a reflective substance. The coated mesh is laminated between at least two pre-formed optically transmissive sheets. This provides a visually transparent reflector which is relatively inexpensive and easy to manufacture. <IMAGE>

Description

Antenna Arrangements This invention relates to antenna arrangements and more particularly to arrangements including a reflector which is substantially transparent to visible radiation. The invention is particularly useful for domestic applications where it is wished to minimise the visual intrusion of a dish antenna used for receiving satellite television signals, for example.

In one conventional type of reflector presently used for receiving satellite television signals, the reflective surface comprises a mesh of stainless steel. The mesh size is chosen such that the reflector has a sufficiently large open aspect that the human eye perceives it as being partially transparent and is able to discern, to a greater or lesser extent, what lies behind it. However, stainless steel mesh is expensive to fabricate, or to buy in, as it requires a number of processing steps to produce it. It can also prove difficult to shape the mesh to the configuration required for optimised signal reception.

The present invention arose from an attempt to produce an improved reflector which is substantially transparent to optical radiation and is particularly suitable for domestic satellite television reception.

According to the present invention there is provided an antenna arrangement including a rigid reflector comprising non-rigid filamentary material arranged as a mesh, the mesh being coated with electrically conductive material such that it has a sufficiently large open aspect to be substantially transparent to visible radiation, and at least two pre-formed optically transmissive sheets between which the coated mesh is laminated.

The filamentary material may comprise twisted fibres or could be a single, long fibre. The filaments forming the pattern could be a plurality of separate lengths of material or a single length of material doubled back on itself, for example.

By employing the invention, the reflector may be made more cheaply than is the case with presently available reflectors because the materials used need not be as expensive as the conventional metal mesh. Furthermore, the coated mesh can be made more flexible than a stainless steel mesh, thus fabrication of the reflector surface can be facilitated. The conductive material which coats the mesh need not be thick enough to be structurally self supporting, unlike a mesh made entirely from metal in which a certain amount of material is required to maintain the integrity of the structure. If only a thin coating of the substance is used, this, together with the flexibility of the coated filamentary material as a whole, provides a reflector material which can be readily shaped into the correct configuration to provide a reflector surface. Also, as the coated mesh is incorporated in a laminated structure it can also be very thin. The mesh is coated rather than the filamentary material, resulting in ease of manufacture and enabling a uniform coated to be applied.

The filaments of the material are arranged in a mesh which defines a crossing pattern. In a preferred embodiment of the invention, the crossing pattern is produced by knitting, in which a filament forming one row loops into filaments in adjacent rows. This process produces a fabric which is particularly elastic. In another advantageous embodiment of the invention, filaments are woven to produce the pattern. In this method the filaments are arranged in two groups, filaments in each group being substantially parallel and the filaments of the two groups being approximately orthogonal. The filaments are interleaved to produce the fabric. Although it is believed that the most advantageous results may be obtained by weaving or knitting the filaments, a pattern may be used in which the filaments are in a crossing relationship but which do not interlock, for example, one group of parallel filaments may be laid orthogonally across another group of parallel filaments and adjacent to it so that the two layers together form a mesh having no interlocking or interleaving of the filaments, the coating process causing the filaments to be permanently joined together.

The electrically conductive material need not coat the mesh entirely providing there is sufficient to give an acceptable level of reflection. The coating may be only on one side of the mesh.

The filamentary material is advantageously a synthetic material, such as Nylon (trade mark) or spun polythene because of the elastic and hard wearing properties of such materials. However, it could, for example, be a natural material such as long glass fibres which are twisted together to produce a filament.

The electrically conductive coating is preferably one which can be electrodelessly applied to the mesh as this is a particularly convenient and inexpensive technique, and can be quickly carried out. For example, nickel may be employed.

It is preferred that the coated mesh has a sufficiently large open aspect as to permit transmission of greater than approximately 60% of visible light incident thereon. This is a sufficiently high transmission value for the human eye to perceive the reflector as being substantially transparent such that features behind the reflector are discernible.

If more than two sheets are used in the laminated structure, it is preferred that the coated mesh is located nearer the front of the structure than the back to optimise the reflection characteristics.

According to a feature of the invention, a method of manufacturing an antenna arrangement in accordance with the invention comprises the steps of: forming filamentary material in non-rigid elongate form into a mesh; coating the mesh with electrically conductive material, the thickness of the filamentary material and the coating being such that it has a sufficiently large open aspect as to appear visually transparent; and laminating the coated mesh between two sheets of optically transmissive material.

Some ways in which the invention may be performed are now described by way of example with reference to the accompanying drawings, in which: Figure 1 is a schematic perspective view of an antenna arrangement in accordance with the invention; Figure 2 is a schematic transverse view of the reflector of Figure 1; Figure 3 illustrates part of the reflector of Figure 1 in greater detail; Figure 4 illustrates the underlying filament pattern of the part shown in Figure 3; and Figure 5 illustrates part of another arrangement in accordance with the invention.

With reference to Figure 1, a domestic antenna arrangement, for receiving television signals from a satellite broadcast at a frequency of some tens of gigahertz, includes a reflector 1 and feed 2 which are mounted by a bracket 3 on a wall 4. The reflector 1 reflects radiation at the satellite broadcasting frequency and is partially transparent to visible light such that an onlooker is able to discern features of the wall 4 located behind it.

The transparent reflector 1 is shown in greater detail in Figure 2 which is a cross-sectional view. The reflector 1 is a laminated structure being made up of ten sheets 5 of a clear plastic, each sheet being approximately 0.25mm thick.

The reflective surface 6 of the reflector comprises a knitted mesh 7 of Nylon (trademark) which has a coating 8 of nickel.

The reflective surface 6 is laminated between two sheets towards the front surface 9 of the reflector.

Figure 3 is a front view of the reflector surface 6, showing the nickel coating 8. The aspect ratio is chosen so that approximately 65% of incident visible light is transmitted through the reflector 1. Figure 4 illustrates the knitted pattern of the mesh 7, the filaments used having a diameter of approximately 25 microns.

In the manufacture of the reflector, the filamentary material is first knitted together to give a mesh 7 as shown in Figure 4. The mesh 7 is then coated with nickel using electrodeless deposition to give the structure shown in Figure 3. The coated mesh is laminated between transparent sheets as shown in Figure 2.

In another embodiment of the invention, the filamentary material is arranged in a woven pattern of filaments as schematically shown in Figure 5, the filaments in this case being of polyester. Once the fabric shown in Figure 5 has been produced, it is electrodelessly plated with a layer of copper and laminated between optically transmissive plastic sheets to form a rigid reflector of microwave radiation.

Claims

1. An antenna arrangement including a rigid reflector comprising non-rigid filamentary material arranged as a mesh, the mesh being coated with electrically conductive material such that it has a sufficiently large open aspect to be substantially transparent to visible radiation, and at least two pre-formed optically transmissive sheets between which the coated mesh is laminated.

2. An arrangement as claimed in claim 1 wherein the filaments of the material are arranged in a crossing pattern to define the mesh.

3. An arrangement as claimed in claim 2 wherein the filaments are knitted together to form the crossing pattern.

4. An arrangement as claimed in claim 2 wherein the filaments are woven together to produce the crossing pattern.

5. An arrangement as claimed in any preceding claim wherein the filamentary material is electrically non-conductive.

6. An arrangement as claimed in any preceding claim wherein the filamentary material is synthetic.

7. An arrangement as claimed in any preceding claim wherein the filaments have a diameter in the range of 15 to 30 microns.

8. An arrangement as claimed in any preceding claim wherein the electrically conductive material is capable of being deposited electrodelessly on the material.

9. An arrangement as claimed in any preceding claim wherein the coated mesh is such as to permit transmission of greater than 60% of visible light incident thereon.

10. An arrangement as claimed in any preceding claim wherein the reflector comprises more than two pre-formed sheets and the coated mesh is located nearer the front of the laminated structure than the back.

11. An antenna arrangement substantially as illustrated in and described with reference to Figures 1, 2, 3 and 4 or Figure 5 of the accompanying drawings.

12. A method of manufacturing an antenna arrangement in accordance with any preceding claim comprising the steps of: forming filamentary material in non-rigid elongate form into a mesh; coating the mesh with electrically conductive material, the thickness of the filamentary material and the coating being such that it has a sufficiently large open aspect as to appear visually transparent; and laminating the coated mesh between two sheets of optically transmissive material.

13. A method as claimed in claim 12 wherein the mesh is a knitted fabric.

14. A method as claimed in claim 12 wherein the mesh is a woven fabric.

15. A method as claimed in claim 12, 13 or 14 wherein the coating is deposited electrodelessly on the mesh.

16. A method of fabricating an antenna reflector substantially as illustrated in and described with reference to the accompanying drawings.