The reduction of interference from large reflecting surfaces

Abstract

The use of corrugated surfaces to reduce interfering reflections from buildings, in particular instrument landing system (ILS) interference from hangars near airport runways, is proposed. A numerical examination of the infinite comb grating under <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</tex> -polarized plane wave illumination with grating spacing <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\lambda/2 &lt; a &lt; \lambda</tex> is made. As with all periodic surfaces investigated, specular reflection can by completely converted to backscatter in the direction of incidence <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\theta_{i}</tex> from the surface normal when <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\theta_{i} = sin^{-1} (\lambda/2a)</tex> and the corrugation depth is properly chosen. Model measurements at 35 GHz on finned surfaces of finite size under nonplane wave illumination verify the surfaces behave essentially as predicted for the infinite comb. The surfaces retain this behavior for frequencies within the ILS range and angles of oblique incidence less than about <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10\deg</tex> . Practical considerations in implementing these ideas are mentioned.