After a brief history of near-field antenna measurements with and without probe correction, the theory of near-field antenna measurements is outlined beginning with ideal probes scanning on arbitrary surfaces and ending with arbitrary probes scanning on planar, cylindrical, and spherical surfaces. Probe correction is introduced for all three measurement geometries as a slight modification to the ideal probe expressions. Sampling theorems are applied to determine the required data-point spacing, and efficient computational methods along with their computer run times are discussed. The major sources of experimental error defining the accuracy of typical planar near-field measurement facilities are reviewed, and present limitations of planar, cylindrical, and spherical near-field scanning are identified.

An overview of near-field antenna measurements

Using computer simulation, several fundamental issues in planar near-field measurement are examined. The results indicate that some of the prevailing views of practices regarding the evanescent modes, the sampling and filtering of data, and the selection of the location and directivity of the probe are incomplete or misleading. In particular, the merits of using smaller low-directivity probes in conjunction with a closer probe-to-antenna distance have been found to be unduly overlooked. >

An examination of the theory and practices of planar near-field measurement

High-Efficiency Transmissive Programmable Metasurface for Multimode OAM Generation

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

An optimal sampling interpolation algorithm which allows the accurate recovery of plane-rectangular near-field samples from the knowledge of the plane-polar ones is developed. 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 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 place 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. >

Fast and accurate near-field-far-field transformation by sampling interpolation of plane-polar measurements

It is well-known that the far field of an arbitrary antenna may be calculated from near-field measurements. Among various possible nearfield scan geometries, the planar configuration has attracted considerable attention. In the past the planar configuration has been used with a probe scanning a rectangular geometry in the near field, and computation of the far field has been made with a two-dimensional fast Fourier transform (FFT). The applicability of the planar configuration with a probe scanning a polar geometry is investigated. The measurement process is represented as a convolution derivable from the reciprocity theorem. The concept of probe compensation as a deconvolution is then discussed with numerical results presented to verify the accuracy of the method. The far field is constructed using the Jacobi-Bessel series expansion and its utility relative to the FFT in polar geometry is examined. Finally, the far-field pattern of the Viking high gain antenna is constructed from the plane-polar near-field measured data and compared with the previously measured far-field pattern. Some unique mechanical and electrical advantages of the plane-polar configuration for determining the far-field pattern of large and gravitationally sensitive space antennas are discussed. The time convention exp ( j \omega r ) is used but is suppressed in the formulations.

A plane-polar approach for far field reconstruction from near-field measurements

The four-point bivariate Lagrange interpolation algorithm was applied to near-field antenna data measured in a plane-polar facility. The results were sufficiently accurate to permit the use of the FFT (fast Fourier transform) algorithm to calculate the far-field patterns of the antenna. Good agreement was obtained between the far-field patterns as calculated by the Jacobi-Bessel and the FFT algorithms. The significant advantage in using the FFT is in the calculation of the principal plane cuts, which may be made very quickly. Also, the application of the FFT algorithm directly to the near-field data was used to perform surface holographic diagnosis of a reflector antenna. The effects due to the focusing of the emergent beam from the reflector, as well as the effects of the information in the wide-angle regions, are shown. The use of the plane-polar near-field antenna test range has therefore been expanded to include these useful FFT applications. >

/pdf/fft-applications-to-plane-polar-near-field-antenna-55ih4ylk43.pdf

FFT applications to plane-polar near-field antenna measurements

A plane-polar approach for far-field construction from near-field measurements. [of large space-craft antennas

Among the many different diagnostic techniques, microwave holography has been s~~ccessfully applied in recent years [l-31. In this technique, the far-field amplitude and phase are measured and then the Fourier transform relationship which exists between the far-field pattern and a function related to the indud current is exploited to localize the distortion with the aid of an FFT algorithm. Up to now the technique has been applied to far-field data either measured in the far field or construded from planar near-field measurements.

http://ieeexplore.ieee.org/iel6/8259/25865/01150097.pdf

Microwave holographic diagnosis of antennas using spherical near-field measurements

Characterization of the antenna on integrated wireless devices can be a challenge for many existing near-field antenna measurement ranges. Since the majority of these devices feature internal sources that cannot be referenced, conventional near-field measurements cannot be conducted. This paper introduces a simple technique utilizing phaseless measurements and the phase retrieval algorithm to measure these antennas that have their own source in existing planar near-field ranges and using existing equipment. The measurement range configuration, an overview of phaseless measurements and the phase retrieval algorithm, and a representative example of the technique will be introduced.

Y. Rahmat-Samii

Papers

A plane-polar approach for far field reconstruction from near-field measurements

FFT applications to plane-polar near-field antenna measurements

A plane-polar approach for far-field construction from near-field measurements. [of large space-craft antennas

Microwave holographic diagnosis of antennas using spherical near-field measurements

Measuring the radiation pattern of integrated antennas with internal sources: A phaseless near-field technique