Robotic Near-Field Measurements Using Reduced Angular Sparse Grids

This work presents a fast Planar Near-Field (PNF) technique for characterizing electrically large antennas from sparse acquisitions over localized angular domains employing a robotic arm in non-anechoic environments. The proposed technique has been designed for the effective characterization of complex antenna systems with multiple beams, such as Reflective Intelligent Surfaces (RIS) or Massive MIMO panels for millimeter wave (mmW) 5G communications although it is particularly suitable for any electrically large antenna with narrow and tilted beams. The near-field to far-field transformation is restricted to a reduced angular domain, and the non-redundant acquisition grid is computed by means of Singular Value Decomposition (SVD) techniques so that the number of unknowns of the inverse problem is highly reduced, significantly decreasing acquisition time. The proposed technique has been validated by means of a numerical example in the X-band and a measurement example in the Ka-bands yielding excellent results.