Bistatic RCS of Spherical Chaff Clouds

Previous determinations of bistatic radar cross section (RCS) of dipole clouds assumed incoherent scattering which does not hold near the forward scatter direction. In order to obtain unified expressions that are valid for scattering in all directions, the average bistatic RCS of a spherical chaff cloud is derived as the sum of incoherent and coherent contributions. Simplified forms for these expressions are provided for five representative directions/polarizations. In the forward scatter direction, the coherent contribution is dominant, but in the angular region about that direction, the bistatic RCS pattern is beam-like and is dependent on both the coherent and incoherent contributions. An expression is provided for the width of this "beam." The derived expressions are verified by statistical numerical RCS computations based on the method of moments. Since these numerical calculations include interparticle coupling, whereas the derived expressions assume that such coupling is not present, the numerical results also provide criteria for the interparticle distance that is required for this coupling to be ignored in bistatic RCS calculations. This distance is seen to depend on the direction of scatter.