Multi-region reduced field testing (RFT) for matrix thinning

The reduced field testing (RFT) method has been proposed recently as a means to generate a sparse matrix for surface formulation within the method of moments (MoM). The method is based on the distinction between near field and far field interactions, where the far field interactions are treated in a more economical way than near field interactions by relying on the difference in sampling rates between the near and far field interaction regions. It is formulated directly in the spatial domain unlike the spectral domain FMM, and it provides a single, explicit sparse matrix invertible by either direct or iterative methods. The original version of the RFT was based on the division of space into two such regions, whereas in the context of this work we show a multi-region arrangement, as well as documentation of substantial saving in running times. The performance of the method for two dimensional cases is demonstrated