Convergence criteria for the extended matrix version of the spectral iteration technique [EM scattering]

An extended matrix version of the spectral iteration technique (SIT) has been reported recently, where it was shown to offer the possibility of significantly improving the convergence rate for homogeneous dielectric or conducting scatterers by introducing a taper. It is shown that there are good grounds for introducing such a taper, and that it can sometimes significantly improve the convergence of the method. For example, if a 64×64 grid size allows (with a taper) convergence in five iterations whereas a 42×42 grid size requires 23 iterations, a noticeable improvement in total computer time is effected. Also, there are cases where a taper must be introduced if the SIT method is to converge at all, without the application of a full orthogonalization procedure. The technique requires a correct choice of arbitrary values in the extended matrix, and guidelines are presented for such a choice