Efficient back-propagation techniques based on spherical harmonics and plane waves decomposition for the near field assessment of base station antennas

This paper presents methods of backpropagation used to determine the near-field of telecommunication antennas. In few words, the backpropagation techniques employ special transformations to extrapolate the near-field of an antenna from its far-field. The far-field pattern is always measured and provided by the constructors. On the contrary, the process of near-field measurements presents some difficulties such as consumption time and errors introduced by the mutual influence between the probe and the antenna. The near-field assessment is essential for many applications in telecommunications such as the establishment of the compliance boundaries, the evaluation of the human exposure in the living areas and the planning of the wireless networks. Therefore, the backpropagation techniques are of a great interest to determine the electromagnetic field in the vicinity of antennas. In this paper, an overview as well as a comparative study are performed for two types of backpropagation methods inspired from a previous work made by Adane et al. The first method is based on the spherical wave backpropagation while the second one uses the decomposition of the EM-field into plane waves.