The invention relates to a radar reflector, particularly sue a reflector as πiay be used on board a vessel such as a yacht to determine its position.

Such reflectors are often installed on ships and other vessels to reflect radar signals which can be used to locate the vessel. They are usually, however, large and unsightly in appearance, and do not always work in reflecting radar energy incident over 360°, particularly if they are based on tetrahedra -where the faces do not bisect at right angles. A type of reflector freqi ±ly used for such applications is the pentagonal or other multiple corner cluster type.

In its conventional configuration the pentagonal corner cluster reflector consists of five individual corner reflectors joined in a ring such that the major reflection lobes of each corner -"^flector point outward around the circυmfer ^c nce of the ring. The m. oer five would be varied for other multiple corner clusters. Each constituent corner reflector consists of at least three mutually inclined and intersecting surfaces. A three surface reflector may have an apex where all three surfaces intersect and corners at the ends of each line of intersection between pairs of surfaces. The three surfaces define a volume. In the assembled cluster, adjacent reflectors touch at two of their corners. The apices point inwardly, but do not touch.

The level of radar reflection for a corner reflector is dependent on the physical size of the corner reflector and the shape of the inclined surfaces forming it as well as on the reflective material used. Therefore in order to achieve a high radar performance, it is often necessary to construct a corner cluster reflector which is large, cumbersome and heavy and hence difficult to mount on a boat mast or other such support on board a vessel.

It is an object of this invention to seek to provide a modified multiple corner reflector which overcomes the disadvantages of the prior art.

According to the invention there is provided a radar reflector corrprising a plurality of corner reflector elements each in the form of a sector of a circle, defined by a curved surface and intersecting, preferably planar surfaces which cαrprise reflective material, the arrangement being such that when the elements are assembled intersecting surfaces of adjacent elements engage and the respective curved surfaces provide a continuous external ring like configuration.

The corner reflective elements may coπprise a foam material.

Using the invention it is possible to provide a radar reflector cαtprising a plurality of foam elements which each have a curved surface and intersecting, preferably planar surfaces ccπprising a reflector material, the arrangement being such that when the elements are assembled intersecting surfaces of adjacent elements engage and the respective curved surfaces provide a continuous external spherical, part-spherical, oblate spherical or similar configuration.

The reflective material may comprise a plastic sheet material and a reflector.

The reflector may cαrprise an aluminium foil laminated with the plastic.

The laminate may cαr-prise a plastic sheet or foil sandwiched between two external layers of plastic.

Again, the reflective material may cαtprise a plastic foil, for exairple l/2mm thick, al-cminised on both sides.

The corner reflector elements may be secured together to form a cαtposite body by suitable means such as tape over joints between adjacent curved surface parts.

The reflective material may be secured to the suitably planar intersecting surfaces by adhesive.

The plurality of corner reflectors may ccπprise a pentagonal or other multiple corner cluster in which one or more of the surfaces defining a sector of a circle has a segment missing.

There may be two surfaces shaped in this way meeting along a line which is closest to the vertical when the cluster is in use.

One corner of the pentagonal or other multiple corner cluster may intrude upon the volume defined by the adjacent corner reflector. This can be achieved by leaving a gap in one or more surfaces adjacent a corner in order that the corner of the adjacent reflector can extend through the gap. The intrusion of one reflector into the volume defined by the adjacent reflector enables the reflectors to be packed closer together within the cluster so that the cluster occupies a smaller volume. When this is achieved by having sane of the surfaces missing and in the irst aspect of the invention where segments of the surfaces are missing, the weight of the material forming the surfaces is reduced cαtpared to the -wsight when there are no missing portions of the surfaces but by arranging the missing portions of the surfaces remote from the apex the reduction in reflecting performance is not of a corresponding amount.

Examples of the invention will now be described with reference to the accompanying drawings in which:

Fig.l is a diagram of a pentagonal corner cluster;

Fig.2 is a diagram showing the orientation of an individual corner reflector forming part of the cluster of Fig.l;

Fig.3 shows an individual corner reflector with certain portions missing forming an eπixxliment of the invention;

Fig.4 shows the arrangement of two corner reflectors forming of the cluster according to an embodiment of the invention;

Fig.5 is a section through a cluster in a protective housing;

Fig.6 is a perspective view of the arrangonent of Fig.5;

Fig.7 is a section through a further embodiment of a cluster;

Fig.8 is a perspective view of the cluster of Fig. 7;

Fig.9 shows a two-portion arrangement of the cluster of Fig.8;

Fig.10 shows the cluster of Fig.9 assembled around a support; and

Fig.11 shows the arrangement of Fig. 8 with an additional corner reflector.

Fig. 1, which has been referred to above, shows diagraππiatically five corner reflectors 11 arranged in a pentagonal cluster. As shown in Fig. 2, each co er reflector 11 comprises three plates 12 welded together along mutually orthogonal lines each plate 12 comprising a right angled sector of a circle. The free edges 14 of each plate 12 form an arc of a circle. Fig.2 shews the arrangement of the corner reflector 11 relative to its horizontal axis, one plate 11 sloping upwards to the apex 15 of the reflector where all three plates 12 meet at such an angle that the peak reflection direction 16 from the corner reflector 11 is horizontal. As can be seen in Fig.l, the individual corner reflectors 11 tilted as shown in Fig.2 are assembled touching corner to corner so that the corners are arranged on a horizontal circle 17. The apices 15 do not touch and are elevated above the horizontal plane of the touching corners.

Fig. 3 shews an individual corner reflector 21 similar to that shown in Fig.2 itrprσved according to one embodiment of the invention. Two of the plates 22 which meet along a line 23 which is closest to the vertical (which is the line furthest frcm the horizontal circle 17 of touching corners in Fig.l) have segrrent 31 cut frcm their curved edges 24. The segment 31 starts a small distance 32 frcm a lower corner 33 of a reflector 21 and finishes a greater distance 34 from the top corner 35 of the reflector 21. The

ranoval of these segments 31 reduces the weight of the reflector 21 whilst not making a corresponding reduction in its reflective performance.

The left-hand corner of Fig.3 shows another portion of the full sector plates 22 missing which may be arranged in addition to the missing segirents 31 or as an alternative to them. The two plates 41 and 42 leading to one corner which in the arrangement of Fig.l would be touching the adjacent reflector 21 are formed with a missing V-shape 43 to allow the corner of an adjacent reflector 21 in the cluster to extend into the volume defined by the first reflector 21 through the V-shape 43 as πore clearly shown in Fig.4. Reflectors in the cluster can therefore be placed more closely together and so occupy a smaller overall volume. There is also a reduction in weight which should not be accompanied by a corresponding reduction in reflective performance.

The remaining figures shew how clusters can be arranged. Figs. 5 and 6 show a cluster in a protective housing 5" which is annular in shape. The housing walls extend over the open faces 52 of the corner reflector 11 and across the bottom 54 and top 53 of the cluster and defining a cylindrical central passage 55 which extends betwsen the spaced apices 25 of the reflectors 21. This passage allcws the cluster to be mounted on a vertical member extending through the passage. Figs. 7 and 8 shew a variation on the arrangement of Figs. 5 and 6, in which the -upper and lewer surfaces 61 and 62 of the protective housing are conical, the cones forming an envelope for the lines 23 on the individual reflectors 21 extending from their apices 25. There is similarly a central aperture 63 in the protective housing within the circle 17 formed by the apices 25. Figs.9 and 10 shew hew the protected cluster 21 of Fig. 6 can be divided in order to allow the cluster in its protective housing 51 to be asseπbled around a vertical support member 64 when it is not possible to lower the ccπplete protected cluster 21 of Fig.6 over the top of the vertical support meπtoer 64. Because the ccπplete cluster contains five individual reflectors 21 (when it is a pentagonal cluster) the cluster is divided unevenly, one portion 65 containing two corner reflectors 21 and the other

portion 66 three reflectors. Fig. 10 shows the two portions 65 and 66 of the reflector 21 assembled around the vertical support, in other words the reflector is toroidal.

Fig. 11 shows the reflector 60 of Fig. 8 with the addition of a further corner reflector 67 directed upwardly in order to improve the reflective performance of the cluster in the vertical direction. In the clusters previously described, the major reflective lobe was horizontal. The additional reflector 67 of Fig. 11 could be conical or it could be formed from three plates 22 as the other reflectors 21 already illustrated.

Reflectors embodying the invention may be mounted on a suitable mount such as a stand or may have a suspension means such as an eye whereby it may be suspended frcm a suitable point such as on a sheet of a yacht.

The assembled reflectors may thus have the shape of an orange, golf or football.