Radar cover and a method for its construction

An electromagnetic radiation transmitting cover 22 comprises a substrate 34 with a non-planar surface and non-transmitting regions 32, which include a metal layer or wire. Each of the non-transmitting regions 32 is separated from the others by one of a plurality of transmitting regions 34. A protective layer 40 may be printed on to a surface of the cover 22 to protect it from the environment. The substrate 34 may be moulded polycarbonate material and the metal layer 32 may be a sputtered coating of aluminium. The metal coating 32 may form parallel bands spaced apart by a predetermined distance. The metal layer 32 may be formed in or on, square or triangular, projections or recesses, formed on the substrate. The substrate may be formed such that both of its surfaces have such projections and recesses and in which those on one surface are misaligned with those on the other surface. The cover 22 may be suitable for camouflaging a radar sensor mounted on a vehicle. A method of forming such a cover is also claimed. This method may involve depositing a metal layer on the non-planar surface of a substrate and grinding the surface to create the desired metal and substrate arrangement.