Multipath of flat plate radar cross section measurements

Measuring the radar cross section (RCS) of point targets above an electromagnetic smooth surface can be difficult if the targets are subjected to interference effects i.e. multipath, as a result of a direct and indirect electromagnetic reflection from the surface. If the point target is used as a reference target for e.g. direct calibration, multipath can introduce errors in the subsequent calibration of other RCS measurements. In order to reduce the possibility of multipath, a commonly used reference target for outdoor ranges is the flat plate. It is generally assumed that the very specular backscattered reflection pattern of the flat plate does not introduce multipath. This paper shows how this assumption is constrained by the radar wavelength, geometric parameters and by the plate dimensions. The results are finally compared with measured data of a flat plate.