NF-FF Transformation Research Articles

Experimental validation of a phaseless, non‐redundant planar spiral scanning for antenna characterisation

AbstractAn effective, probe‐compensated, phaseless Near‐Field‐Far‐Field (NF–FF) transformation technique with planar spiral scanning is presented. The phase retrieval problem is solved by a quadratic inverse process, whose data are the voltage squared amplitudes of the NF samples acquired on two scanning surfaces. The available information on the antenna under test and on the scanning geometry are used to provide efficient representations for both the unknowns and the data, thus improving the accuracy and reliability of the technique. Furthermore, disconnected apertures are dealt with by adopting two different sets of prolate spheroidal wave functions to represent the aperture fields. Experimental results are reported to assess the effectiveness of the proposed approach. A drastic reduction (about 90%) of the required NF samples, as compared to standard λ/4 measurements (λ being the wavelength), is observed. Aggregating the measurements on the two scanning surfaces, the technique uses less samples even when compared to the case of complex, λ/2 measurements performed on a single surface. Our approach exhibits an accuracy comparable to that achieved when adopting complex measurements with non‐redundant sampling or classical, λ/2 plane‐rectangular NF–FF transformations.

Pattern Reconstruction from Near-Field Data Affected by 3D Probe Positioning Errors Collected via Planar-Wide Mesh Scanning

An effective procedure to correct known 3D probe positioning errors affecting the near-field–far-field transformation (NF–FF) with non-conventional plane rectangular scanning, named planar wide-mesh scanning (PWMS), is developed in this paper. It relies on the non-redundant sampling representations of electromagnetic fields and related optimal sampling interpolation (OSI) expansions and has been devised when a quasi-planar antenna under test is considered as suitably modelled by either a double bowl or an oblate spheroid. Such an algorithm first makes use of the so-called k-correction to compensate for the errors occurring when the actual sampling points deviate from the acquisition plane and then adopts an iterative procedure to restore the NF samples at the points specified by the used non-redundant sampling representation from those obtained at the previous step and affected by 2D positioning errors. Finally, once the regularly arranged PWMS samples have been calculated, the NF data required to compute the classic plane-rectangular NF–FF transformation are accurately evaluated by using an effective 2D OSI algorithm. Several numerical results are presented in order to assess the effectiveness of the devised approach.

Study on System Design and Variation of Vehicle Antenna Eccentricity test

This paper takes the vehicle antenna as the research object, and carries out a comparative study on vehicle antenna testing by improving the NF-FF transformation algorithm and combining the special application scenarios of vehicle testing. Research has shown that when the vehicle is used as the DUT, there is a significant difference in the near-field test data when the vehicle antenna is in the center and the geometric center of the vehicle is in the test center; however, through correct NF-FF transformation processing, both far-field radiation patterns are consistent. It shows that the far-field radiation information of the whole vehicle can be obtained under the processing of spherical near-field measurement and near-far-field transformation. This conclusion provides a basis for the promotion of wireless performance testing of the vehicle.

Notice of Retraction: Applicability of Cylindrical Near-Field to Far-Field Transformation to OTA and EMC Measurements of 5G Equipment and Devices

This paper explores the possibility to develop a measurement system appropriate for testing mm-wave 5G equipment, with the far-field (FF) evaluated from near-field (NF) measurements. To this aim, the theory of the cylindrical NF-FF transformation is first reviewed, then several details of the theoretical and analytical expressions are clarified to make them of practical implementation for a precise quantification of the radiated field amplitude. Finally, the most critical points and their engineering solutions are discussed for the development of a test system appropriate for a massive testing of radiating equipment.

Two efficient procedures to correct the positioning errors in the plane‐polar scanning

Two techniques to effectively compensate known positioning errors in a plane-polar near-field–far-field (NF–FF) transformation, using a minimum number of NF data and adopting an oblate ellipsoid to shape the considered antenna, are proposed and validated through experimental proofs. The former makes use of the singular value decomposition method to recover the voltage samples which would be acquired by the probe at the points fixed by the non-redundant sampling representation from the collected positioning error affected ones, whereas the latter employs an iterative scheme. The NF data required by the classical NF–FF transformation with plane-rectangular scanning are then efficiently evaluated via a two-dimensional optimal sampling interpolation formula. The effectiveness of the proposed techniques is assessed by experimental tests performed at the Antenna Characterisation Lab of the University of Salerno.

Fast and Accurate Antenna Pattern Evaluation From Near-Field Data Acquired via Planar Spiral Scanning

Two fast and accurate probe compensated planar spiral near-field–far-field (NF–FF) transformation techniques, using nonredundant NF data, are experimentally assessed. These techniques allow a remarkable measurement time saving since they require a reduced number of NF data, which are collected on fly by properly and continuously moving the positioners. They have been achieved by applying the unified theory of spiral scannings for nonvolumetric antennas and adopting either an oblate ellipsoid or a double bowl to shape an antenna with a quasi-planar geometry. By using these modelings, instead of the spherical one, it is possible to significantly reduce the error due to the truncation of the scanning zone, since the NF data can be acquired on a spiral lying on a plane located at a distance smaller than one half of the antenna maximum size. The NF data required by the standard plane-rectangular NF–FF transformation are then accurately recovered from those collected along the spiral. Some experimental results, obtained at the Antenna Characterization Lab of the University of Salerno and assessing the effectiveness of the techniques, are shown.

Far-Field Pattern Reconstruction From a Nonredundant Plane-Polar Near-Field Sampling Arrangement: Experimental Testing

An efficient probe-compensated near-field–far-field (NF–FF) transformation with plane-polar scanning, particularly suitable for quasi-planar antennas, is experimentally assessed in this letter. It exploits the nonredundant sampling representations of electromagnetic fields and adopts an oblate ellipsoid to model the antenna under test. A two-dimensional optimal sampling interpolation expansion is employed to accurately recover the NF data needed by the standard plane-rectangular NF–FF transformation from the nonredundant plane-polar ones collected by the probe. A remarkable reduction of the number of NF data to be acquired and of the related measurement time is so obtainable. Some results of the experimental tests, performed at the UNISA Antenna Characterization Lab and assessing the effectiveness of such a NF–FF transformation technique, are reported.

Experimental Testing on an Effective Technique to Reconstruct the Far- Field Pattern of a Long Antenna from Near-Field Measurements Acquired via Spherical Spiral Scan

In this paper, the experimental validation of a fast and accurate near-field – far-field (NF–FF) transformation with spherical spiral scanning for elongated antennas is provided. Such a transformation relies on a nonredundant sampling representation of the voltage measured by the probe, obtained by using the unified theory of spiral scans for nonspherical antennas and adopting a cylinder ended in two half-spheres to model long antennas. It allows a remarkable reduction of the measurement time due to the use of continuous and synchronized movements of the positioning systems and to the reduced number of needed NF measurements. In fact, the NF data required by the classical spherical NF–FF transformation are efficiently and accurately recovered from those collected along the spiral, by using an optimal sampling interpolation expansion. Experimental results, obtained at the Antenna Characterization Lab of the University of Salerno and assessing the effectiveness of such a NF–FF transformation, are shown.

Application of Nonredundant Sampling Representations of Electromagnetic Fields to NF-FF Transformation Techniques

An overview of the application of the band-limitation properties and nonredundant sampling representations of electromagnetic fields to NF-FF transformations is presented. The progresses achieved by applying them to data acquired on conventional NF scanning surfaces are discussed, outlining the remarkable reduction in the number of needed NF samples and measurement time. An optimal sampling interpolation expansion for reconstructing the probe response on a rotational scanning surface from a non-redundant number of its samples is also discussed. A unified theory of the NF-FF transformations with spiral scannings, which allow a remarkable reduction of the measurement time, is then reviewed by describing a sampling representation of the voltage on a quite arbitrary rotational surface from its nonredundant samples collected on a proper spiral wrapping it. Some numerical and experimental results assessing the effectiveness of the considered NF-FF transformations are shown too.

Experimental validation of the NF–FF transformation with cylindrical scan from nonuniformly distributed data

AbstractThe article concerns the experimental validation of two techniques for compensating the probe positioning errors in a near‐field–far‐field transformation with cylindrical scan using a nonredundant number of measurements.The former uses the singular value decomposition method and can be applied when the irregularly acquired samples lie on nonuniform rings, thus allowing to reduce the starting two‐dimensional problem into two independent one‐dimensional ones. The latter, based on an iterative technique, can be employed also when the previous hypothesis does not hold but requires the existence of a one‐to‐one correspondence, associating at each uniform sampling point the nearest irregular one. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53:915–920, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.25847

Effective Antenna Modellings for NF-FF Transformations with Spherical Scanning Using the Minimum Number of Data

Two efficient probe-compensated near-field-far-field transformations with spherical scanning for antennas having two dimensions very different from the third one are here developed. They rely on the nonredundant sampling representations of the electromagnetic fields and on the optimal sampling interpolation expansions, and use effective antenna modellings. In particular, an antenna with a predominant dimension is no longer considered as enclosed in a sphere but in a cylinder ended in two half spheres, whereas a surface formed by two circular “bowls” with the same aperture diameter but different lateral bends is adopted to shape an antenna with two predominant dimensions. These modellings are able to fit very well a lot of antennas by properly setting their geometric parameters. It is so possible to remarkably lower the number of data to be acquired, thus significantly reducing the measurement time. Numerical tests assessing the accuracy and the robustness of the techniques are reported.

A Nonredundant Near-Field to Far-Field Transformation with Spherical Spiral Scanning for Nonspherical Antennas

A Nonredundant Near-Field to Far-Field Transformation with Spherical Spiral Scanning for Nonspherical Antennas

NF–FF transformation with cylindrical scanning from nonuniformly distributed data

AbstractTwo efficient probe‐compensated near‐field–far‐field (NF–FF) transformation techniques with cylindrical scanning requiring a minimum number of irregularly spaced data, are proposed. Singular value decomposition (SVD) method is applied to evaluate the uniformly distributed samples, whose positions are fixed by a nonredundant sampling representation of the field, from the irregularly spaced ones. Then, the voltage data needed by standard NF–FF transformation or by a non‐conventional one recently developed by the authors are efficiently evaluated via an optimal sampling interpolation algorithm. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 39: 4–8, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.11109

Data reduction in the NF‐FF transformation with bi‐polar scanning

AbstractAn efficient near‐field–far‐field transformation with bi‐polar scanning, which compensates for the effects of the measurement probe, is proposed in this paper. It is based on the theoretical results relevant to the nonredundant sampling representation of electromagnetic fields and, as a consequence, it requires a number of data—remarkably lower than that needed by the standard bi‐polar technique. Numerical examples assessing the accuracy and the stability of the far‐field reconstruction process are presented. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 36: 32–36, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10662

NF‐FF transformation with cylindrical scanning from a minimum number of data

AbstractIn this paper, an efficient sampling representation for reconstructing the voltage measured by a probe over a cylinder in the antenna NF region from a minimum number of data is proposed, and properly exploited to develop two probe compensated NF–FF transformation techniques. They are based on the theoretical results relevant to the nonredundant representation of electro‐magnetic fields. Numerical examples assess the accuracy and stability of the techniques. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 35: 264–270, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10578

Data Reduction in the Nf-Ff Transformation Technique With Spherical Scanning

A fast, accurate and stable two-dimensional sampling interpolation algorithm is developed to reconstruct the electromagnetic field radiated on a sphere in the antenna near-field region. Its analytical foundation relies on the recent theoretical results concerning the nonredundant field representations on curves and surfaces. The use of an ellipsoid (prolate or oblate) as modelling of the source allows one to reduce the number of required samples with respect to the spherical source modelling that, although more general, becomes redundant when considering antennas having one or two predominant dimensions. The obtained results are properly used to get ready an effective near-field-far-field transformation technique with spherical scanning, which requires a minimum number of data, thus reducing significantly the memory storage requirements and measurement time. Numerical examples assess the efficiency and the stability of the reconstruction process.

Probe Compensated NF-FF Transformation with Helicoidal Scanning

A new cylindrical near-field- far-field transformation technique, which uses the helicoidal scanning for the near-field data acquisition, is proposed. From the theoretical viewpoint it is based on an innovative non-redundant sampling representation of the electromagnetic field over a circular helix. A fast, accurate and stable interpolation algorithm is developed to reconstruct the near-field at any point required by the classical near-field- far-field transformation technique with cylindrical scanning. Then the ideal probe assumption is removed and it is shown that the antenna far-field pattern can be efficiently calculated from the knowledge of a non-redundant number of output probe voltage samples over a circular helix. Many numerical tests assess the effectiveness of the far-field reconstruction process, in spite of the reduced number of employed near-field data, as compared with the classical cylindrical scanning.

NF–FF transformation with cylindrical scanning: an effective technique for elongated antennas

A sampling representation, particularly suitable for dealing with elongated antennas, is proposed for fast and accurate interpolation of the electromagnetic field radiated on a cylinder in the near field region and properly exploited to develop a new near field–far field transformation technique with cylindrical scanning. The technique relies on recent theoretical results concerning the nonredundant representation of radiated or scattered fields, and allows one to evaluate the antenna far field from minimal near field data. In particular, the proposed technique allows one to reduce significantly the amount of data needed, without losing the numerical efficiency of previous approaches. As a consequence, measurement time and memory storage requirements are reduced remarkably. Numerical tests confirm the effectiveness and stability of the proposed approach.