INVERSE EQUIVALENT SURFACE CURRENT METHOD WITH HIERARCHICAL HIGHER ORDER BASIS FUNCTIONS, FULL PROBE CORRECTION AND MULTILEVEL FAST MULTIPOLE ACCELERATION

Abstract

An inverse equivalent surface current method working with equivalent electric and/or magnetic surface current densities on appropriately chosen Huygens surfaces is investigated. The considered model with triangular surface meshes is compatible with the models known from method of moments (MoM) solutions of surface integral equations. Divergence conforming current basis functions of order 0.5 and of order 1.5 are considered, where the order 0.5 functions are the well-known Rao-Wilton-Glisson basis functions. Known near-fleld samples typically obtained from measurements are mapped on the unknown equivalent surface current densities utilizing the radiation integrals of the currents as forward operator, where the measurement probe in∞uence is formulated in a MoM like weighting integral. The evaluation of the forward operator is accelerated by adaptation of the multilevel fast multipole method (MLFMM) to the inverse formulation, where the MLFMM representation is the key to full probe correction by employing only the far-fleld patterns of the measurement probe antennas. The resulting fully probe corrected algorithm is very ∞exible and e-cient, where it is found that the computation speed is mostly dependent on the MLFMM conflguration of the problem and not that much on the particular equivalent current expansion as long as the expansion is able to represent the currents su-ciently well. Inverse current and far-fleld pattern results are shown for a variety of problems, where near-fleld samples obtained from simulations as well as from realistic measurements are considered.