Communications: radio wave antennas – Antennas – Antenna components
Patent
1989-10-19
1991-02-26
Wimer, Michael C.
Communications: radio wave antennas
Antennas
Antenna components
342 7, H01Q 1520
Patent
active
049965360
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to an array of reflectors of electromagnetic waves, especially radar.
Radar reflector arrays commonly employ trihedral reflectors which comprise three radar reflective planar panels with right-angled corners meeting at a vertex and each joined along two sides to the other two panels so that radar energy incident on the inner surfaces of the reflector is focused and re-directed back towards the source. Typically, the panels are isosceles triangles in shape and their unjoined sides define an equilateral triangular mouth to receive radar energy, this type of trihedral reflector being known as a deltatrihedral. The properties of trihedral reflectors are well known and include the ability to provide a reflective response over a cone of approximately 40 degrees centred on the major axis of the reflector, which is the intersection of the planes bisecting the angles between the panels.
It is known to provide a plurality of trihedral reflectors in an array about a central vertical axis so that the array covers the complete 360 degrees of azimuth for incident radar energy. These reflectors are arranged with the sides of their triangular mouths in edge to edge contact, adjacent reflectors being turned through 60 degrees about their major axes relative to one another so as to allow "nesting" of the reflectors. This construction has been considered advantageous because it is a solid form with its circumference totally occupied by reflectors in edge to edge contact for optimum reflective response. However, a geometrical consequence of this design is that the major axis of each reflector is fixed by the number of reflectors in the array, which limits its usefulness in many applications, for example, with radar reflectors intended to be observed from above.
DISCLOSURE OF THE INVENTION
According to the present invention an array of reflectors comprises a plurality of trihedral reflectors (as hereinbefore defined) arranged about a vertical axis of the array with the major axis of each reflector directed in a different direction from the vertical axis, with each reflector orientated about its major axis so that the plane bisecting the angle between two panels is vertical, and with adjacent reflectors turned through 60 degrees about their major axes relative to one another, characterised in that the reflectors are tilted relative to said vertical axis of the array with the adjacent sides of adjacent reflectors diverging so that the major axes of the reflectors are directed from the vertices at the required angles of elevation.
It will be appreciated that because each reflector is orientated with the plane bisecting the angle between two panels vertical, one side of the reflector either top or bottom will be horizontal, and because adjacent reflectors are turned through 60 degrees, the horizontal side is alternately top and bottom in successive reflectors. For compactness and to reduce the gaps between the reflectors for maximum reflective response, the horizontal sides in one plane, either top or bottom, are arranged with their adjacent ends closely spaced together in the form of a polygon with the tip of the intermediate reflector therebetween. The diverging sides of adjacent reflectors then define a triangular space therebetween.
The gaps between the diverging sides of adjacent reflectors may be filled with additional panels of radar reflective material to avoid reflection nulls in the array. In the compact array described above, these additional panels could be triangular panels.
For radar reflectors intended to be observed from above, the reflectors are tilted backwards at the top so that the major axes are directed above the horizontal. In the compact array described above, the sides at the top then form the polygon within the outline of the sides at the bottom as seen in plan view.
It should be appreciated that where the terms "vertical" and "horizontal" and "top" and "bottom" are used, these are to be understood in a relative sense and not to be taken as limitative of the actu
REFERENCES:
patent: 2763000 (1956-09-01), Graham
patent: 3117318 (1964-01-01), Jones
patent: 3276017 (1966-09-01), Mullin
Le Hoang-anh
Wimer Michael C.
Woodville Polymer Engineering Limited
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