Conducting surface corrugations for multipath interference suppression

Abstract

Corrugations can completely convert specular reflection from a conducting surface to backscatter. The period required is d = λ/(2 sin θi where λ is the wavelength and θi is the angle of incidence from the surface normal. Numerical values of the depth and width of rectangular grooves, a profile suitable for multipath-interference suppression, are given for TM and TE polarisation. The angular and frequency range over which the the surfaces are effective decreases with groove depth, and the surface precision required increases. For near-grazing incidence, TM polarised reflection can be eliminated with shallow grooves but TE polarisation requires impractically deep grooves. Elimination of arbitrarily polarised interference is possible for 19.5°<θi<59.4° with grooves of moderate depth (0.56λ ≈ 0.7λ) and near-perfect dual blazing with similar groove depths is possible for 56°<θi<62.2° with periods d = λ/sin θi Model measurements at λ = 8.6 mm show 20–40 dB reduction in reflected power with corrugated surfaces, but only about 8–10 dB with wide equispaced screens.