Efficient near-field-far-field transformation with cylindrical scanning by a finite and non redundant number of data

The determination of the antenna far-field (FF) from measurements in the near-field (NF) region allows one to overcome those drawbacks which, particularly for large antenna systems, make it unpractical or impossible to measure antenna patterns on a conventional FF range. With reference to cylindrical scanning, by exploiting the quasi-bandlimitation properties of the electromagnetic, sampling expansions have been successfully applied to the NF-FF transformation [Bucci and Gennarelli, 1988], and it has been demonstrated that the sample spacing along the cylinder generatrixes can be, on increasing the radius of measurement cylinder, much greater than /spl lambda//2. However, when the height of the scanning zone approaches infinity, even if the number of samples on each ring remains finite, the number of required rings, hence of measurements, increases indefinitely. The present paper develops a fast and accurate NF-FF transformation with cylindrical scanning from a non-redundant and, in any case, finite number of NF data. To this end, the authors start from the results in Bucci et al. [1994], wherein it is shown that the number of samples, required to recover the field over the whole cylinder, is finite and essentially coincident with the number of degrees of freedom of the field (number of independent parameters necessary to represent it with a given precision outside the source region).