Scatter measured from impedance discontinuities

The vertically-polarized (electric vector in the plane of incidence) radar cross sections of four-square doped silicon samples that were inserted in a diamond-shaped aluminum fixture have been measured at elevation angles of both 5.5/spl deg/ and 18/spl deg/ (near grazing incidence) at an azimuth angle normal to the edge of the samples. The measured scatter matches predictions for samples inserted in an infinite conductive plane that were made using two different two-dimensional models at 18/spl deg/, but was 2-6 dB below predictions at 5.5/spl deg/ in all cases. A comparison between predictions made with and without a Leontovich impedance-boundary-condition (IBC) approximation demonstrates that the discrepancy between theory and measurement at 5.5/spl deg/ is not caused by the use of this approximation in the predictions. The most likely source of the discrepancy is the finite extent of the diamond-shaped fixture used in the measurements.