Radar reflectors

Details Radar reflectors Radar reflectors

1994-05-24

1995-07-04

Sotomayor, John B.

Communications: directive radio wave systems and devices (e.g.,

Radar reflector

With spherical lens

H01Q 1502, H01Q 1508

Patent

active

054304440

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Field of the Invention
The invention relates to radar reflectors for enhancing the radar cross section or visibility of objects to which they are attached.
2. Discussion of Prior Art
GB2194391 discloses a passive radar target formed of a solid spherical dielectric lens with a reflecting coating covering part of the spherical surface. By using material of the correct dielectric constant, radar waves incident on the uncoated surface of the lens from a wide range of directions are reflected back towards the transmitter. Such lenses can provide a substantially uniform radar cross section over a wide range of angles. Thus, an object can be constantly visible on a search radar in spite of movement of the object, as would be the case for example for a small boat.
GB Patent Application No. 9117662 discloses an alternative dielectric lens reflector arrangement using compound lenses. Two thin converging lenses of similar dielectric constant are used to refract incident radar energy to a metal coating applied to the outer face of one of the lenses. Such two lens arrangements have the advantage of reduced weight for the same radar cross section when compared with solid lenses.
The reflective portions of lens-reflector combinations have blind spots which can be overcome, depending on the application, by choosing particular orientations for the radar reflector.
For marine radar reflectors, the International Standard ISO 8729:1987(E) requires that the maximum echoing area of a radar reflector should be at least 10 m.sup.2 for all frequencies between 9.32 and 9.5 GHz. Uniformity of reflection is also required in that the azimuthal polar response diagram should have a response over 240.degree. of not less than -6 dB with respect to the maximum and the response level should not be less than -6 dB over any angle of more than 10.degree..


SUMMARY OF THE INVENTION

The object of the present invention is to provide a highly efficient, low weight radar reflector, particularly suited to application to marine use.
The invention provides a radar reflector comprising at least one solid dielectric lens reflector comprising a converging lens of dielectric material having a convex outer surface for receiving radar waves and a second spherical surface with a reflecting coating arranged such that radar waves are focused on to the reflecting coating characterised in that there is included: outer surface for receiving the radar waves and an inner surface for transmitting refracted radar waves; and that of said first material and having a first surface complementary to and juxtaposed with the inner surface of the first lens and a second outwardly convex surface provided with a reflecting coating over at least a portion thereof; coating after transmission through the two lens elements.
Preferably the converging lens is axially symmetric with outer convex and inner concave surfaces having radii of curvature which decrease with distance from the axis of symmetry. In an advantageous arrangement the dielectric constant of the converging lens material is substantially equal to 3.4.
Advantageously the second material is an expanded foam, preferably polystyrene with a dielectric constant substantially equal to 2. In a particularly advantageous arrangement the radar reflector comprises two opposed dielectric lens reflectors coaxially aligned with two corner reflectors placed coplanar with the axis of the lenses and directed perpendicular to the axis of the lenses so as to remove any blind spots to radar waves. In an advantageous arrangement the corner reflectors are trihedral reflectors.


BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described by way of example only with reference to the accompanying Drawings of which:
FIG. 1 is a schematic plan part section through a radar reflector:
FIG. 2 is a side elevation of one trihedral reflector along A--A as shown in the FIG. 1 arrangement;
FIGS. 3-5 show an enclosure for the radar reflector in plan and side elevations along lines A--A and B--B; and
FIG. 6 i

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patent: 5097265 (1992-03-01), Aw
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