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Nonideal Measurement Locations in Planar Near-Field Antenna Metrology

Summary: Nonideal Measurement Locations in Planar
Near-Field Antenna Metrology
R. C. Wittmann, B. K. Alpert, and M. H. Francis
National Institute of Standards and Technology
325 Broadway, Boulder, CO 80303-3328
1 Introduction
We introduce a near-eld to far-eld transformation method that relaxes the usual restriction
that data points be located on a plane-rectangular grid [1]. It is not always practical
or desirable to make uniformly spaced measurements; for example, the maintenance of
positioning tolerances becomes more di˘cult as frequency is increased. Our method can
(1) extend the frequency ranges of existing scanners, (2) make practical the use of portable
scanners for on-site measurements, and (3) support schemes, such as plane-polar scanning,
where data are collected on a nonrectangular grid.
Although ideal locations are not required, we assume that probe positions are known.
(In practice, laser interferometry is often used for this purpose.) Our approach is based on
a linear model of the form A» = b (see section 2). The conjugate gradient method is used
to nd the unknown » in terms of the data b (section 3). The operator A must be
applied once per conjugate gradient iteration, and this is done e˘ciently using the recently
developed unequally spaced fast Fourier transform [2], [3] and local interpolation (section
4). As implemented, each iteration requires O(N log N) operations, where N is the number


Source: Alpert, Bradley K. - Mathematical and Computational Sciences Division, National Institute of Standards and Technology (NIST)


Collections: Mathematics; Computer Technologies and Information Sciences