Communications: directive radio wave systems and devices (e.g. – Radio wave absorber – With particular geometric configuration
Patent
1991-10-24
1993-04-20
Tubbesing, T. H.
Communications: directive radio wave systems and devices (e.g.,
Radio wave absorber
With particular geometric configuration
342 6, H01Q 1514, H01Q 1700
Patent
active
052046800
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention is concerned with a radar reflecting target and particularly such target for reducing radar cross-section (RCS).
BACKGROUND ART
There is a desire to minimize the RCS of particularly, military vehicles such as planes, ships and tanks. Known schemes for so doing include:
1) forming radar reflecting surfaces of the vehicle to be spherical to encourage isotropic reflection,
2) tilting of flat features of the reflecting surface of the vehicle away from normal incidence for expected incoming radar signals and removing as far as possible dihedral and trihedral corner reflectors from the vehicle shape,
3) fitting absorbing layers on metallic surfaces to attenuate the reflecting signal, and
4) active cancellation whereby coherent signals are transmitted which are electronically adjusted to cancel out the reflected signal.
The present invention is concerned with a technique employing passive cancellation of radar return signals, providing a cheap and effective solution.
DISCLOSURE OF THE INVENTION
According to the present invention, a radar reflecting target comprises a plurality of reflecting elements spread along at least one linear physical dimension of the target, the elements being differingly spaced in the direction normal to said dimension so that respective retro-reflections by the elements of radio frequency energy from a remote source on a line of sight at an angle to said dimension, have differing phases and tend to cancel each other out. In this broadest aspect, the invention is applicable to essentially single dimension targets, e.g. spars on ships or possibly the wing leading edges of aeroplanes. By dividing the reflecting target into a plurality of individual reflecting elements as defined above, reflections from the different elements tend to cancel each other out, thereby reducing the radar visibility of the target. Preferably, the elements are differingly spaced in said normal direction evenly, and more preferably with a random or pseudo-random distribution, over at least one half wavelength of the expected radio frequency energy from the remote source. This allows operation over a wide signal frequency band.
More normally, the invention is applicable to two-dimensional targets wherein the reflecting elements are spread over two orthogonal physical dimensions of the target and are then differingly spaced normal to the plane of said orthogonal dimensions. It can be shown that this technique when suitably employed can reduce the effective reflection gain of a two dimensional target to that of a single one of the reflecting elements. Because the reflecting elements are all differingly spaced in the direction normal to the plane of the target, retro-reflections from the different elements experience different path lengths before recombining in a retro-reflection signal. The different path lengths are spread over one wavelength and, generally, there will always be a pair of reflecting elements providing a path length difference of one half wavelength so that the retro-reflections from each of these cancel out.
Preferably, the reflecting elements are electrically conductive plates arranged to appear substantially tesselated when viewed normal to said plane. Conveniently the electrically conductive plates are mutually parallel and square.
The target can readily be formed of a molded panel of dielectric material having flat surface portions bearing electrically conductive film to form said plates. These panels may be formed cheaply and can be light in weight.
In one arrangement, the differingly spaced elements in the moulded panel are distributed randomly or pseudo-randomly over the panel. Then, several panels may be used abutting each other to cover an extensive reflective surface of a military vehicle, e.g. the superstructure of a ship. A single design of panel can be orientated in up to eight different ways and provide eight corresponding different arrangements of spaced elements, thereby reducing the risk of several panels correlating with one another and in
REFERENCES:
patent: 4501784 (1985-02-01), Moshinsky
patent: 5057842 (1991-10-01), Moller et al.
Marc Piette, Revetement Interferentiel Pour Char, 1986.
Hans Dominik, Hochfrequenz-absorbierende Materialien, 1988.
Racal Defence Electronics (Radar) Limited
Tubbesing T. H.
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