An alternative method is presented for computing far-field antenna patterns from near-field measurements. The method utilizes the near-field data to determine equivalent magnetic current sources over a fictitious planar surface that encompasses the antenna, and these currents are used to ascertain the far fields. Under certain approximations, the currents should produce the correct far fields in all regions in front of the antenna regardless of the geometry over which the near-field measurements are made. An electric field integral equation (EFIE) is developed to relate the near fields to the equivalent magnetic currents. The method of moments is used to transform the integral equation into a matrix one. The matrix equation is solved with the conjugate gradient method, and in the case of a rectangular matrix, a least-squares solution for the currents is found without explicitly computing the normal form of the equation. Near-field to far-field transformation for planar scanning may be efficiently performed under certain conditions. Numerical results are presented for several antenna configurations. >

Planar near-field to far-field transformation using an equivalent magnetic current approach

The Electrical Engineering Department at UCLA has enjoyed the use of a new six-story building, Engineering IV, since 1989. Many exciting electromagnetic-research activities are being conducted within this building. The authors concentrate on the antenna-measurement research activities, and provide information on the design and development of a unique planar-near-field range. They have received a considerable amount of interest in the bipolar near-field method since the publication of a two-part paper (Williams et al. 1994, and Yaccarino et al. 1994). They decided to prepare the present paper in order to provide a more-tutorial description, and to present detailed measured data, images, and implementation particularities. The reader will find numerous sidebars distributed throughout the article that highlight some selected topics in planar-near-field measurements, which may be of particular interest to those readers who have not been directly involved in using or developing near-field-measurement ranges.

The UCLA bi-polar planar-near-field antenna-measurement and diagnostics range

The matrix method for array diagnosis is based on the reconstruction of the excitation from measured near-field data by solving the linear system relating the excitation coefficients to the field at the measurement points. In this paper the matrix method is applied to the diagnosis of element failures in high-performance conformal array radar. The results confirm the usefulness of this technique in the cases wherein the standard backward propagation technique cannot be applied.

Accurate diagnosis of conformal arrays from near-field data using the matrix method

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Near‐Field Scanning Measurements: Theory and Practice

Time-domain planar near-field measurement techniques are formulated for acoustic and electromagnetic fields. Probe correction is ignored in that it is assumed that the probe measures the exact values of the field on the scan plane. Two fundamentally different approaches are used in deriving three sets of formulas that give the fields in the source-free half space z>z/sub 0/ in terms of their values on the scan plane z=z/sub 0/. In the first approach the time-domain formulas are obtained by inverse Fourier transforming the corresponding frequency-domain formulas. In the second approach the time-domain formulas are derived directly in the time domain by working with time-domain Green's functions. >

Planar near-field scanning in the time domain .1. Formulation

A combination of techniques is described for reliably estimating the magnitude of each error arising in planar near-field measurements. They include mathematical analysis, computer simulation, and measurement tests. There are three primary applications for these tests: in designing a measurement facility, the requirements of each part of the measurement system can be specified to meet a given level of accuracy; during actual measurements, the experimenter can identify, and reduce where necessary, potential sources of error in the measurement; and when a measurement has been completed, the estimated uncertainty in the measurement can be obtained with confidence and ease. The latter application has been used in many measurements to verify that the planar near-field technique produces high-accuracy results competitive with any other measurement technique. >

A.C. Newell

Papers

Error analysis techniques for planar near-field measurements