Radar-cross-section measurement errors caused by test object interaction with low-dielectric-constant supports

In the search for an ideal test-object support for simulated free-space radar-cross-section (RCS) measurements, low-density polystyrene foam has achieved considerable popularity. However, significant error can be introduced into a measurement by the use of an inappropriately designed support. Although low back-scatter radar cross section (RCS) can be obtained with this material, interactions can occur between the test object and the mount which will cause measurement errors in excess of several dB. We present results of measurements performed on a simple test object supported on a low-density foam column which demonstrate this effect. As we discuss, this error can be incorrectly interpreted to be caused by poor mechanical alignment of the test object with the radar-range coordinate system. We discuss trade-offs associated with the choice between electrical and mechanical boresighting of the test object. Finally, we show that the error can be explained by differential propagation effects. In addition, this simple theory provides the insight necessary to devise appropriate measures to minimize the errors caused by the presence of the support. 4 refs., 6 figs.