FAST FAR FIELD APPROXIMATION FOR CALCULATING THE RCS OF LARGE OBJECTS

C. C. Lu and W. C. Chew

A fast far-field approximation (FAFFA) is developed to estimate the RCS of conducting scatterers. This method accounts for the interaction between subscatterers in two ways, depending on the electrical distance between the subscatterers. The interactions of subscatterers separated by large electrical distance are computed in three stages: (1) aggregation, which computes the total field at a group center due to the subscatterers of the group; (2) translation, which translate the field from one group center to another; and (3) disaggregation, which distributes the field in a group center to each subscatterer in the group. Two strategies are employed to accelerate the computation in the above three stages. One is the use of far-field approximation to simplify the computation in the translation stage; the other is the use of interpolation and smoothing techniques, which reduces the complexity of aggregation and disaggregation. The overall computational complexity for a matrix-vector multiplication is of the order of $N^{1.33}$ and the memory requirement is of order $N$. Numerical results show that this method can predict a RCS that is very close to exact solution, and that the method can be applied to objects with very large electrical sizes.