Robot-Based Near-Field Antenna Measurements on Polyhedral Sampling Surfaces

A commonly employed technique in the field of phaseless antenna measurements is the two-sphere method, wherein complex spherical mode coefficients are reconstructed from amplitude-only near-field measurements taken on two spheres that are separated by a specific distance. Recent numerical studies have indicated that the second sphere can also be substituted with a polyhedral surface. However, traditional positioning systems are incapable of measuring such configurations. This work demonstrates that a robotic antenna measurement system can efficiently measure the near-field on the surface of an octahedron. Two approaches for scanning a spiral grid with a robot are presented. It is shown that the additional degrees of freedom offered by the robot can reduce measurement time by up to 15 % compared to conventional spiral measurements. Furthermore, the far-field pattern derived from the complex near-field data on an octahedron produces highly accurate results, achieving an average equivalent error signal of -56.6 dB when compared to standard spherical measurements. A comparison between phaseless reconstruction using two spheres and a combination of a sphere and an octahedron reveals that both methods yield comparable accuracy.