Near-Field to Far-Field Transformation on Arbitrary Surfaces via Multi-Level Spherical Wave Expansion

This article presents a general technique for the far-field transformation of near fields measured over arbitrary surfaces and multimode probe correction in an efficient and accurate way. The use of not only one but several spherical wave expansions to model the antenna under test fields allows to incorporate full probe correction for arbitrary orientations with low computation cost. Combining this approach with a hierarchical subdomain decomposition strategy, the transformation problem is solved with a low computational complexity. In this method, the fields produced by neighbor subdomains are gradually aggregated and interpolated following a multilevel scheme, leading to a good scalability with frequency compared with other matrix-based transformation methods. The numerical and experimental results are provided to show the efficiency and capabilities of the proposed algorithm.