| Using the method of moments to solve the electric and magnetic field integral equations for the currents on a PEC surface requires a large number of unknowns to capture the current's rapid spatial variation across the surface. Rao-Wilton-Glisson (RWG) vector basis functions [1] have been successfully used for the past twenty years [1, 2, 3,...]. Unfortunately, the required number of unknowns is on the order of 100 per square wavelength making electrically large problems impractical. For large smooth objects, the rapid spatial variation in the current is due to phase variations rather than magnitude variations. Thus, using asymptotic phase (AP) basis functions can drastically reduce the number of unknowns [3] for large, smooth metallic bodies. The AP basis function incorporates the anticipated phase, hence represents a more efficient basis function for a large class of problems. However, using RWG basis functions for monostatic calculations is more efficient since the matrix entries need not be recomputed for each new incidence angle, as is the case for an AP expansion. One can combine the methods; selecting RWG or AP basis functions for a given geometry based on an elements location within the geometry. This allows the relaxation of mesh density in smooth flat regions not near the discontinuities resulting in a significant reduction of unknowns. This research shows that combining functions is highly efficient and the effectiveness of this method depends on the geometry of application. |
