Doren W. Hess

The IsoFilter ™ Technique: A Method of Isolating the Pattern of an Individual Radiator from Data Measured in a Contaminated Environment

This paper describes a novel method, termed the IsoFilter Technique, for isolating in measured data the radiation pattern of an individual radiator from among a composite set of radiators that form a complex radiation distribution. This technique proceeds via three successive steps. The first is a spherical NFFF transform on an over-sampled data set. This is followed by a change of coordinate system. This is followed in turn by filtering of the spherical modes in the domain to isolate a radiating source. The end result yields an approximate pattern of the individual radiator, largely uncontaminated by the other competing sources of radiation.

Spherical near-to-near, near-to-far- and far-to-near-field transforms: Calculated versus measured radiation distributions in the spherical waveguide

The complete phase/amplitude radiation pattern was measured at three radial distances R_{1}, R_{2} and R_{\infty} where R_{1} and R_{2} corresponded to measurements of the radiating near-field region and R_{\infty} corresponded to a measurement of the far-field region of the antenna. The usual spherical near-field transformation was applied to the measured data sets to transform numerically between the spherical surfaces at R_{1}, R_{2} and R_{\infty} . Comparison between measured data and numerically transformed data demonstrates the equivalence of the measured radiation patterns corresponding to the three distances and illustrates the concept of the spherical waveguide.

Verification testing of a spherical near-field algorithm and comparison to compact range measurements

This paper describes a program of verification measurement that has been carried out to support the development of minicomputer software for performing spherical near-field scanning measurements of antenna radiation patterns. Spherical near-field measurements were made at two frequencies, three different radii and with two different probes. The results are shown to agree well with patterns measured directly using the compact range.

The measurement column

This month the Newsletter is announcing a new column that will be devoted to measurements. It will feature descriptions of the techniques and technology of measurements that are of interest to the engineers who comprise the Antennas and Propagation Society. We expect that it wil include discussions of the traditional topics of antenna measurements, radar cross section measurements, and scattering measurements. It will also include coverage of other current topics such as imaging methods and time domain field measurements. In general, contributions on any subject that is measurement related and relevant to the interests of AP-S members will be considered for publication.

Far-Field to Near-Field Transforms in Spherical Coordinates

Experimental results are presented which demonstrate that the spherical near-field to far-field transform may be used in its inverse mode to determine the radiating near-field of a source distribution from measurements made of its far field.