Adaptive Sampling in Multilevel Plane Wave Based Near-Field Far-Field Transformed Planar Near-Field Measurements

An adaptive approach to minimize acquisition time in planar near-fleld antenna measurements is described. In contrast to the traditional planar near-fleld scanning, the presented technique acquires the near-fleld in form of rectangular rings and skips sampling points in smoothly varying near-fleld regions. Abrupt changes in the near- fleld are detected by comparing extrapolated and measured near-fleld values at coarser sampling points. A decision function based on the signal-to-noise ratio (SNR) of the measured value is used to determine the threshold difierence between the measured and the extrapolated near-fleld values for skipping the sampling point. Near-fleld data thus collected on the resultant irregular grid is processed using the multilevel plane wave based near-fleld far-fleld transformation algorithm. The multilevel transformation algorithm is computationally e-cient and capable of handling data collected on irregular grids. A rigorous analysis of the adaptive data acquisition approach is then performed in terms of transformed far-fleld accuracy, decision factor, and test time reduction. Several test cases covering a variety of antennas are shown using synthetic as well as measured data for realistic results. Afterwards the acquisition time for the worst case scenario is compared with the traditional planar near-fleld measurement technique.