Multilevel Fast Multipole Accelerated Inverse Equivalent Current Method Employing Rao–Wilton–Glisson Discretization of Electric and Magnetic Surface Currents

The radiation of any object in a homogeneous environment can be described by a set of equivalent sources. Different types of equivalent sources are feasible and all of them have their own benefits. Equivalent current methods are especially advantageous for irregular measurement grids of arbitrary shape and if a priori information about the object shall be used. Also, they can immediately provide diagnostic information about the object. In this paper, a very flexible equivalent current method is presented, which has been derived from a general purpose boundary integral equation solver. As such the method works with arbitrary triangular surface meshes and Rao-Wilton-Glisson basis functions, where electric and/or magnetic surface current densities can be assumed. High efficiency is achieved since the multilevel fast multipole method has been adapted to speed-up the inverse solution process. Results obtained from simulations and measurements are presented, where large-scale problems with dimensions up to 75 wavelengths are considered.