On the Use of Subsectional Spline Basis Functions for Efficient Calculation of the RCS of a Microstrip Array of Concentric Annular Rings Over a Wide Frequency Band

The use of B-splines in the radial direction is described for efficient calculation of the radar cross section (RCS) of a microstrip annular ring or array of concentric annular rings, over a wide frequency band. Galerkin´s method in the vector Hankel transform (VHT) domain is used to calculate the induced current density on the annular patches. An algorithm is presented for a fast and accurate calculation of the scalar Hankel transforms of B-splines on an arbitrary nonuniform grid, which plays an important role in the numerical calculation of the reaction integrals containing the scalar Hankel transforms of B-splines. The accuracy and computational efficiency of the method and the convergence of the RCS results with respect to the number of segments along the radial direction are studied for some annular ring and concentric ring patches.