The reduction of interference from large reflecting surfaces

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
H
-polarized plane wave illumination with grating spacing
\lambda/2 < a < \lambda
is made. As with all periodic surfaces investigated, specular reflection can by completely converted to backscatter in the direction of incidence
\theta_{i}
from the surface normal when
\theta_{i} = sin^{-1} (\lambda/2a)
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
10\deg
. Practical considerations in implementing these ideas are mentioned.