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Backscattering of E.M. waves for rough surface models O'Kelly, Patrick Donald

Abstract

Baclcscattering from certain models of rough surfaces is studied by application of a Monte-Carlo technique and by experiments on a physical model. The models considered are lossless arrays of hemicylinders and of hemispheres on a lossless ground plane. For the Monte-Carlo simulation, the incident radiation is considered to be a cylindrical or spherical wave with finite beamwidth. The shape of the beam is chosen to be the same as the far field radiation pattern of an open waveguide. Multiple scattering effects are investigated for a periodic array of hemicylinders and found to be significant for object diameters greater than one wavelength, and densities greater than 30%. It is assumed that these results are also approximately valid for random arrays. The single scatter approximation is used for all studies of the random case with these limitations in mind. A special surface distribution function is developed and tested which includes the constraint of finite scatterer size in a physical surface model. It is used to generate random coordinates from which a set of physical surfaces are formed out of die-stamped aluminum. These surfaces are scanned with 35 GHz. radiation from a pyramidal horn. Samples of the backscattered field are converted to digital information and numerically analysed to determine the scattered field statistics. These statistics are compared to those obtained from the simulation. The means (coherent intensity) are found to agree to within 2.5% while the variance (incoherent intensity) obtained experimentally is higher by a factor of about 15. This discrepancy is attributed to significant phase measuring errors introduced by the present scanning system.

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