Comparison of interpolation algorithms to transform polar grid to rectangular grid in plane polar near field antenna test range

This paper addresses the implementation of various interpolation algorithms to transform the measured near field (NF) polar grid data into rectangular grid data in plane-polar near field antenna test range (PPNF-ATR). Such a transformation is required so that the Fast Fourier Transform (FFT) algorithm can be utilized to extract the hologram and to compute the far-field performance. Conventionally, the Optimal Sampling Interpolation (OSI) algorithm is used for such a transformation. In this paper, four interpolation algorithms i.e., Barycentric, Nearest Neighbor, Bivariate Lagrange and Cubic Spline interpolations, are studied, implemented and applied on the measured NF data in polar grid. The X-band microstrip array antenna having 0.6 m × 0.6 m dimensions has been measured in the PPNF test range, installed at SAC, ISRO, Ahmedabad. The various interpolation algorithms have been applied to the measured NF data with different sampling points, followed by the probe correction and FFT, to generate the far-field parameters. The computed far-field patterns and parameters have been compared, with the OSI algorithm implemented in MiDAS.