GB2229321A

GB2229321A - Antenna

Info

Publication number: GB2229321A
Application number: GB9001970A
Authority: GB
Inventors: Henry Roy Smith
Original assignee: HR Smith Technical Developments Ltd
Current assignee: HR Smith Technical Developments Ltd
Priority date: 1989-01-31
Filing date: 1990-01-26
Publication date: 1990-09-19
Anticipated expiration: 2010-01-26
Also published as: GB8902085D0; GB2229321B; GB9001970D0

Abstract

An antenna incorporates a printed circuit board 12 supporting electrical interconnections 26 and elements 24 of the antenna. At least some of the peripheral edges of the printed circuit board are radiused 20 and a conductive metal coating 40 is provided to cover the said radiused peripheral edges of the board and extend partially onto the major surfaces thereadjacent. All the peripheral edges of the board may be radiused or alternatively - if in use the antenna is mounted on a vehicle with a peripheral edge of the printed circuit board adjacent the outer skin of the vehicle - each edge of the board other than adjacent the said outer skin is radiused. Additionally, at least those corners of the printed circuit board in use to be located spaced from the skin of a vehicle upon which the antenna is mounted are radiused. <IMAGE>

Description

ANTENNAS DESCRIPTION The invention relates to antennas.

Antennas which are externally mounted and project from the body of ground and air vehicles are prone to being struck by lightning. This arises from the high voltage potential gradients which to be found the highly curved extremities of these antennas which make it more likely that a lightning strike will attach itself to the protruding antenna than to the - generally less highly curved - vehicle body upon which the antenna is mounted. As a result of this such antennas are often seriously damaged or destroyed by being struck by lightning.

Attempts have been made to reduce this effect by forming antenna structures from highly conductive metal which is grounded to the body of the vehicle on which the antennas are mounted and which therefore carries any lightning strike to that body leaving the antenna relatively untouched.

Such methods of protecting antennas from lightning strikes, however, seriously limits the versatility of the antennas and complicates their design.

An object of this invention is to provide an antenna which is less prone to being struck by lightning than those known to me at present and with which, if struck, the deleterious effects of the strike are much reduced and which, moreover, is more readily adaptable to modern antenna design than is the case with lightning strike protected antenna structures known to me at present.

A commonly used and highly versatile antenna stucture known to me at present makes use of a dielectric material printed circuit board upon which the elements of the antenna are supported - formed and/or carried - the dielectric material board having square cut edges. In such an antenna one or both major surfaces of board have formed thereon patterns of conductive metal tracks. Usually the dielectric material board is approximately 0.05" to 0.15" (1.25mm to 3.75mm) thick and is coated with a metal (e.g.

copper) layer approximately 0.003" (0.075mm) thick. After coating the metal layer is selectively removed - e.g. by photo etching - to leave on the board surface(s) the desired metal pattern forming and interconnecting elements of the antenna. The assembled board is then housed in a dielectric material casing and then mounted on the body of the vehicle to which it is to be attached.

It will be appreciated that with this form of antenna the edges of the printed circuit board have relatively high curvature (e.g. square cut) edges, leading in use to the generation of very high potential voltage gradients along those edges and thus susceptability to lightning strikes.

A second object of the invention is the provision of an antenna design which alleviates and/or overcomes the drawbacks of this known form of antenna.

In one aspect the invention provides an antenna incorporating a dielectric material printed circuit board on at least one major surface of which there are supported electrical interconnections and electrical elements of the antenna, wherein at least some of said peripheral edges of the printed circuit board are radiused and wherein there is provided a conductive metal coating which extends to cover the said radiused peripheral edges of the dielectric material board and partially onto the major surfaces thereadj acent.

All the peripheral edges of the printed circuit board may be radiused and covered by by said conductive metal coating. Alternatively, if the antenna is for mounting on the outer skin of a vehicle with said printed circuit board supported with a peripheral edge adjacent said outer skin each edge of said printed circuit board other that adjacent the said outer outer skin is radiused and a conductive metal coating provided thereacross.

Preferably, at least those corners of the printed circuit board in use spaced from the skin of a vehicle upon which the antenna is mounted are radiused.

The electrical interconnections supported on the printed circuit board and the said conductive metal coating may with advantage be formed thereon by photo etching.

The antenna may include a dielectric material casing for the printed circuit board, which casing is formed such that the thickness of the dielectric material located to partially surround edges of the said printed circuit board of the antenna is greater than the thickness of the dielectric material located adjacent the major surfaces of said printed circuit board.

The edges so surrounded may be all or some of the edges of the printed circuit board. However, to ensure that the aerodynamic properties of the antenna are not adversely affected it is preferred that the thickening of the casing be confined to those areas partially surrounding the edges of the printed circuit board most prone to being, in use, struck by lightning - e.g. the top edge and front and rear corners of the printed circuit board.

With advantage the thickened areas of the dielectric material located to surround edges of the printed circuit board of the antenna is greater than twice the thickness (and preferably four or five times as thick) of the dielectric material casing immediately thereadjacent.

Desirably, the printed circuit board may be of standard material (e.g. of an epoxy or polyester resin) or both the the printed circuit board and the casing may be of a moulded fibers reinforced high temperature thermoplastics material, such as polyetherimide, polyethersulphone, polyetherethersulphone, and polyetheretherketone.

The reinforcement may be of glass, quartz, or F vlartfibers.

In a second aspect the invention provides an antenna comprising a dielectric material casing for a printed circuit board supporting electrical interconnections and electrical elements of the antenna, wherein the casing is formed such that the thickness of the dielectric material located to surround the the edges of the said printed circuit board is greater than the thickness of the dielectric material located adjacent the major surfaces of said board.

Embodiments of the invention provide that the edges of the printed circuit board are of relatively low curvature compared with conventional printed circuit board antenna designs and therefore the potential voltage gradient which can build up thereon will be substantially less than with the conventional designs, furthermore those edges are covered with an electrically conductive metal coating which acts to prevent the build up of a potential voltage gradient thereon.

Again, embodiments of the invention provide that the thickness of the dielectric material casing at the edges of the printed circuit board - the areas in which lightning is prone to strike - is substantially increased without necessarily increasing the overall weight of the antenna or deleteriously affecting its aerodynamic properties.

An antenna embodying the invention will now be described with reference to the accompanying drawings in which: - Figure 1 is a sectional end view of an antenna embodying the invention, and Figure 2 is a perspective view to a reduced scale of the antenna shown in Figure 1.

As can be seen from the Figures an antenna embodying the present invention comprises a dielectric material printed circuit board 12 housed within a dielectric material casing 14. The bottom edge of board 12 is provided with a base member 16 as shown by means of which the antenna may be mounted on a vehicle as indicated at 18.

The edges of board 12 other than the bottom edge 16 are all radiused as shown at 20. Furthermore, the corners (see especially Figure 2) of the printed circuit board 12 are radiused. As a result of this radiusing the propensity for a high potential voltage gradient to build up on the edges and corners of the board 12 is reduced - the sharp corners and edges of the board 12 are removed.

Board 12 supports elements 24 of the antenna which are interconnected by appropriately shaped metal tracking 26 provided on the major surfaces 28 of the board 12.

Board 12 is preferably of standard material (e.g.

of an epoxy or polyester resin), however, if desired for any reason (e.g. to increase the strength of the board) it may be moulded from a high temperature thermoplastics material which is fiber reinforced.

Suitable thermoplastics materials comprise polyetherimide, polyethersulphone, polyetherethersulphone, and polyetheretherketone. The fibers reinforcement used in the moulding of the board 12 may be any suitable fiber, for example, glass, quartz, and/or gevla a b)ers may be used to reinforce the thermoplastics material from which board 12 is made.

After moulding the board 12 is appropriately drilled in order to provide, if required, interconnections between its major surfaces 28 and from the major surfaces 28 to the lowermost edge (as viewed in the figures) of the bottom edge 16 of the board.

Thereafter the board 12 is completely covered with an appropriate metal - for example copper - to a thickness to at least 0.001 inches (0.025mm).

Thereafter the metal coating that has been provided on the board is selectively removed e.g. making use of photo etching techniques - to provide the desired pattern of metal tracks 26 on the major surfaces 28 of the board.

As this is done the metal coating which has been provided over the radius edges of the board, and the corners, is allowed to stay in place such that the board 12 has radiused edges and corners which are completely covered by a metal layer 40. It will be noted that metal layer 40 extends onto the major surfaces 38 by a small amount (e.g.

0.1 inches - 2.5mm).

Once the board has been processed to this extent the elements 24 which are required to complete the formation of the antenna are appropriately positioned on the board.

Casing 14 is of the high temperature thermoplastics fibers reinforced material from which it has been noted board 12 may be made. As can be seen from the figure the casing 14 comprises a body having a central slotted aperture 50 bounded by side walls 52. The board 12 fits into the aperture 50.

The lower edges of the wall 52 carry outturned flange members 54 shaped as shown to conform to the edge 16 of the board 12 and it will be seen that for mechanical stability and strength the walls 52 are of decreasing thickiness from bottom to top (e.g. being approximately 0.25 inches (6mm) thick immediately adjacent the flange members 54 and being 0.08 inches (1.5mum) thick at their upper edges (as viewed).

The wall 56 interconnecting the walls 52 of casing 14 is, as can be seen from the Figures, of significantly greater thickness than the walls 52 immediately adjacent wall 56. That is to say the antenna casing 14 is substantially thicker in those of its parts surrounding the radiused metal covered edges and corners of the board 12 than it is over the remainder of its parts. With a thickness of 0.8 inches (1.5mm) at the uppermost edges of walls 52 the thickness of wall 56 is preferably 0.4 inches (10mum).

Thus the ratio of the thickness of the wall 56 to that of the wall 52 immediately thereadjacent is least two to one and preferably four or five to one.

The completed antenna is fixed to the vehicle body 18 by means of bolts 70 which pass through preformed holes formed in the outturned flanges 54 of the casing 50 and the bottom member 16 of the printed circuit board 12.

The antenna described is connected to equipment, for example avionics equipment within the vehicle 18, in a conventional manner.

It will be noted that the radiused edges of the board 12 act to reduce the potential voltage gradient which may build up on those edges - by removing any sharp corners which are prone to lead to an increase or elevated potential gradient. It will further be noted that the radiused corners of the printed circuit board 12 have the same effect.

This reduction in the build up of any voltage potential gradient on the corners and edges of the printed circuit board is further enhanced by the metal coating layer 40 which is provided thereacross which acts to short-circuit any such voltage potential gradient.

Finally, it will be noted that the increased thickness of the casing 50 in those regions of it which in use are located to surround edges of the printed circuit board lack to protect those areas where lightning is more prone to strike the antenna without substantially increasing the overall weight of the antenna or its aerodynamic resistance.

It will be appreciated that modifications may be made to the described arrangements without departing from the present invention, for example should an antenna design provide that the antenna be located, e.g spaced from and parallel to the body of a vehicle on which it is carried the present invention would provide that each corner and each edge of the board provided in the antenna is radiused as described above and provided with a protective metal coating. Similarly in such an arrangement each part of any casing for the board which is located in use adjacent a corner or edge of a board would be of increased thickness.

Claims

1. An antenna incorporating a dielectric material printed circuit board on at least one major surface of which there are supported electrical interconnections and electrical elements of the antenna, wherein at least some of said peripheral edges of the printed circuit board are radiused and wherein there is provided a conductive metal coating which extends to cover the said radiused peripheral edges of the dielectric material board and partially onto the major surfaces thereadjacent.

2. An antenna as claimed in claim 1, wherein all the peripheral edges of the printed circuit board are radiused and are covered by by said conductive metal coating.

3. An antenna as claimed in claim 1, for mounting on the outer skin of a vehicle with said printed circuit board supported with a peripheral edge adjacent said outer skin and wherein each edge of said printed circuit board other that adjacent the said outer outer skin is radiused and conductive metal coating provided with said conductive metal coating.

4. An antenna as claimed in claim 1, claim 2 or claim 3, wherein at least those corners of the printed circuit board in use to be located spaced from the skin of a vehicle upon which the antenna is mounted are radiused.

5. An antenna as claimed in any one of the preceding claims, wherein the said electrical interconnections supported on the printed circuit board and the said conductive metal coating are formed thereon by photo etching a metallised layer preformed thereon.

6. An antenna as claimed in any one of the preceding claims, further comprising a dielectric material casing for the printed circuit board, which casing is formed such that the thickness of the dielectric material located to surround edges of said printed circuit board of the antenna is greater than the thickness of the dielectric material located adjacent the major surfaces of said printed circuit board.

7. An antenna as claimed in claim 6, wherein the thickness of the dielectric material located to surround edges of the said printed circuit board of the antenna is greater than twice the thickness of the dielectric material of the casing located immediately thereadjacent.

8. An antenna as claimed in any one of the preceding claims, wherein the casing is of moulded fibers reinforced high temperature thermoplastics material.

9. An antenna as claimed in any one of the preceding claims, wherein the printed circuit board is of moulded fibers reinforced high temperature thermoplastics material.

10. An antenna as claimed in claim 8 or claim 9, wherein the high temperature thermoplastics material is one of polyetherimide, polyethersulphone, polyetherethersulphone, and polyetheretherketone.

11. An antenna as claimed in claim 10, wherein the fibers reinforcement is one of glass, quartz, and kevlar fibers.

12. An antenna comprising a dielectric material casing for a printed circuit board supporting electrical interconnections and electrical elements of the antenna, wherein the casing. is formed such that the thickness of the dielectric material located to surround the edges of the said printed circuit board is greater than the thickness of the dielectric material located adjacent the major surfaces of said board.

13. An antenna as claimed in claim 1 or claim 12 and substantially as herein described with reference to the accompanying drawings.