Investigations on Normal Systems for Low-Frequency Stabilized Equivalent Electric Surface Current Reconstructions

To reconstruct equivalent electric surface currents from irregularly distributed observations of the fields radiated by a device under test (DUT), we investigate a low-frequency stabilized formulation based on a quasi-Helmholtz decomposition: Rao-Wilton-Glisson (RWG) basis functions are employed for the equivalent surface currents, dipoles as probe antennas, and the relation between probes and sources is established via integral operators. Since, in general, a rectangular linear system of equations (LSE) is obtained, we analyze both the normal-residual system of equations (NRE) and the normal-error system of equations (NEE) for an iterative solution with a generalized minimum residual (GMRES) solver. Specifically, our analysis shows that a self-adaptive normalization scheme is needed in both cases, where the scheme itself can remain the same.