FAST AND ACCURATE NEAR-FIELD-FAR-FIELD TRANSFORMATION BY SAMPLING INTERPOLATION OF PLANE-POLAR MEASUREMENTS

An optimal sampling interpolation algorithm is developed which allows the accurate recovery of plane-rectangular near-field samples from the knowledge of the plane-polar ones. This enables the standard near-field-far-field (NF-FF) transformation, which takes full advantage of the fast Fourier transform (FFT) algorithm, to be applied also to plane-polar scanning. The maximum allowable sample spacing is also rigorously derived, and it is shown that it can be significantly greater than lambda/2 as the measurement plane moves away from the source. This allows a remarkable reduction of both measurement time and memory storage requirements. The sampling approach is compared with that based on the bivariate Lagrange interpolation (BLI) method. The sampling reconstruction agrees with the exact results significantly better than the BLI, in spite of the significantly lower number of required measurements.