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1. (WO1990007199) DISPOSITIF DE FOCALISATION POUR ANTENNES A MICRO-ONDES
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CLAIMS

1. A focussing device for a microwave antenna, comprising a substrate (2) which is transparent to visible light and to microwave signals to be received, the substrate (2) carrying an arrangement of rings (A) of a material which either absorbs or reflects the microwave signals to be received, the rings (A) being arranged to focus received microwave signals, characterised in that the rings (A) are of a material which is transparent to visible light.

2. A device as claimed in Claim 1, characterised in that the substrate (2) is rigid.

3. A device as claimed in Claim 1 or Claim 2, characterised in that the substrate (2) is of glass.

4. A device as claimed in Claim 1, characterised in that the substrate (2) is flexible.

5. A device as claimed in Claim 1, Claim 2 or Claim 4, characterised in that the substrate (2) is of plastics material.

6. A device as claimed in any preceding claim, characterised in that the substrate (2) and rings (A) together constitute a Fresnel zone plate ( 1 ) .

7. A device as claimed in any one of Claims 1 to 5, characterised in that the substrate (2) and rings (A) together constitute a Gabor zone plate (1).

8. A device as claimed in Claim 6, characterised in that the rings (A) are elliptical and have their centres displaced along their common major axis.

9. A device as claimed in any preceding claim in the form of a window pane.

10. A device as claimed in Claim 4, or Claim 5, 6, 7 or 8 as dependent upon Claim 4, in the form of a window roller blind.

11. In combination, a planar device (1) as claimed in any one of Claims 1 to 8 , and a planar member ( 6 ) comprising a substrate transparent to visible light carrying a coating of a material which reflects microwave radiation, arranged in a plane parallel to and spaced from the plane of the device.

12. A combination as claimed in Claim 11, characterised in that the device (1) and planar member (6) are spaced from each other.

13. A combination as claimed in Claim 11, characterised in that the device (1) and planar member (6) are in surface contact with no more than one of the rings (A) of the device (1) and the coating of the planar member (6) between them.

14. A microwave antenna including a focussing device or-combination as claimed in any preceding claim.