Fast Inverse Equivalent Source Solutions With Directive Sources

A fast inverse equivalent source technique is presented for the fully probe-corrected transformation of measured radiation or scattering fields utilizing directive sources. The directivity of the expansion sources is either obtained by combining electric and magnetic surface current densities in a directive Huygens radiator or by shifting the source locations into complex space. The latter approach is known to generate Gaussian-beam-like directive radiators. These two techniques can be used separately or in combination to obtain three different solutions that approximately satisfy the null-field condition (also known as the Love condition) outside the solution domain, i.e., inside the volume of the original device under test. The directive sources lead to a better conditioning of the inverse problem and especially the Huygens radiator concept leads to good conditioning for a small number of unknowns. Thus, considerable reduction in computation times and better solution accuracies are achieved. Moreover, antenna diagnostics is promoted by the improved localization of the directive equivalent sources. The directive sources are implemented together with Rao-Wilton-Glisson basis functions and the new concepts are utilized within the fast irregular antenna field transformation algorithm with its hierarchical propagating plane wave-based radiation operator representation. This algorithm has recently been augmented with Gaussian beam-based translation operators which lead to considerably reduced computation times and lower memory requirements. The algorithmic capabilities are demonstrated with synthetically generated near-field data as well as with real spherical measurements of a double-ridged waveguide antenna.