TABLE OF CONTENTS The calculation of RCS via the time domain implies the calculation of the scattered field 
s ( 
, t) at a distant observation point due to uniform plane wave illumination i ( 
, t) of the scatterer. The vector denotes an observation point ? either on the scatterer surface or possibly within the scatterer (in the case of penetrable bodies). Note that the incident field is defined as the field that would have existed at without the scatterer present (i.e., in free space).
The first step in the FDTD procedure is spatial and temporal discretization. Just as with any computer solution of transient field problems, FDTD computer calculations require discretization of space and time; that is, spatial and temporal sampling. The incident and scattered fields are calculated at a large but finite number of points in space and at discrete time instants. The accuracy of the field representation depends on the size of the spatial and temporal discretization steps, ? ? and ? t , respectively. Note that we will assume a Cartesian coordinate system and a uniform spatial discretization with the spatial discretization step constant throughout the space and identical for all coordinate directions (axes). Thus, the spatial discretization elements will be ? ? line segments in one dimension, ? ? ? ? squares in two dimensions, and ? ? ? ? ? ?
