Papers by Francesco D'Agostino
A time domain (TD) optimal sampling interpolation (OSI) scheme to efficiently reconstruct the tra... more A time domain (TD) optimal sampling interpolation (OSI) scheme to efficiently reconstruct the transient field radiated by an ultra-wide band (UWB) antenna over a plane in the near-field (NF) region from a minimum number of its NF TD samples, acquired through a non-conventional plane-rectangular scanning, is developed in this study. Such a result has been achieved by properly exploiting the non-redundant sampling representations of electromagnetic fields and modelling the antenna by a proper rotational surface. Since the UWB antennas are usually quasi-planar, such a surface can be conveniently chosen coincident with that of an oblate ellipsoid or with that formed by two bowls with the same circular aperture and possibly different lateral bends. Numerical examples, which assess the accuracy of the related TD OSI representations, are reported.
An efficient iterative procedure to correct the positioning errors in the plane-polar scanning
A technique to effectively compensate known positioning errors in a near field - far field (NF-FF... more A technique to effectively compensate known positioning errors in a near field - far field (NF-FF) transformation with plane-polar scanning, requiring a minimum number of NF data and adopting an oblate ellipsoid to model the antenna under test, is proposed. It makes use of an iterative scheme to recover the probe voltage samples at the points fixed by the nonredundant sampling representation from the collected irregularly spaced ones. The NF data needed by the classical NF-FF transformation with plane-rectangular scan are then efficiently evaluated via a two-dimensional optimal sampling interpolation formula. Experimental tests, performed at the UNISA Antenna Characterization Lab and assessing its effectiveness, are reported.
Pattern reconstruction from planar spiral near-field measurements @ UNISA Antenna Characterization Lab
The experimental assessment of a near field - far field (NF-FF) transformation technique with pla... more The experimental assessment of a near field - far field (NF-FF) transformation technique with planar spiral scanning, which requires a minimum number of NF data, is provided. Such a technique, which allows a remarkable measurement time saving, relies on a nonredundant sampling representation of the voltage acquired by the measuring probe obtained by using the unified theory of spiral scannings for nonspherical antennas and modelling a quasi-planar antenna with an oblate ellipsoid. An optimal sampling interpolation formula is applied to efficiently retrieve the NF data required by the classical plane-rectangular NF-FF transformation from those collected along the spiral.
Nonredundant NF-FF transformation with bi-polar scanning: Experimental testing
A probe compensated near-field — far-field (NF-FF) transformation technique with bi-polar scannin... more A probe compensated near-field — far-field (NF-FF) transformation technique with bi-polar scanning for quasi-planar antennas, requiring a minimum number of NF data, is experimentally validated in this work. Such a technique relies on the nonredundant sampling representations of electromagnetic fields and adopts an oblate ellipsoid to shape a quasi-planar antenna. A 2-D optimal sampling interpolation expansion is then employed to accurately reconstruct the NF data needed by the classical plane-rectangular NF-FF transformation from the acquired bi-polar ones. It is so possible to obtain a remarkable reduction in the number of NF measurements and related acquisition time. Some experimental results, performed at the Antenna Characterization Lab of the University of Salerno and confirming the effectiveness of the proposed NF-FF transformation technique, are shown.
Iet Microwaves Antennas & Propagation, Feb 8, 2018
An experimental verification of a fast and accurate technique, which allows the evaluation of the... more An experimental verification of a fast and accurate technique, which allows the evaluation of the antenna radiation pattern from a non-redundant, i.e. minimum, number of near-field (NF) measurements acquired via a bi-polar scan, is provided in this study. This probe compensated NF-to-far-field (NFTFF) transformation exploits a non-redundant sampling representation of the voltage acquired by the probe, achieved by shaping the antenna with a double bowl, a very flexible model particularly tailored to antennas characterised by a quasi-planar geometry. The input NF data necessary for executing the standard planerectangular NFTFF transformation are efficiently recovered from the acquired non-redundant bi-polar ones by applying a twodimensional optimal sampling interpolation formula, so that a remarkable measurement time saving is attained. Some results of laboratory proofs performed at the Antenna Characterization Lab of the University of Salerno are reported to demonstrate the accuracy and the practical effectiveness of the presented NFTFF transformation technique.
Non-redundant spherical near-field - far-field transformation for a noncentred antenna
An efficient probe compensated near-field – far-field (NF–FF) transformation technique with spher... more An efficient probe compensated near-field – far-field (NF–FF) transformation technique with spherical scanning for noncentred antennas, which requires a minimum number of NF data, is developed in this work, by applying the nonredundant sampling representations of electromagnetic field and modelling the antenna under test (AUT) by a sphere. The interest for it arises from the fact that, for practical constraints, it could be not possible a centred mounting of the AUT on the scanning sphere centre. In fact, the number of NF data needed by classical spherical NF–FF transformation can considerably grow for an offset mounting, due to the increase of the radius of the minimum sphere containing the AUT and centred on the scanning sphere centre
Laboratory tests on the direct near-field - far-field transformation with helicoidal scanning for long antennas
Data reduction in the NF–FF transformation technique with spherical spiral scanning
ABSTRACT
NF–FF transformation with planar spiral scan: an effective source modelling for quasi-planar antennas
Field representation over an ellipsoid from samples acquired through a spiral scanning
Nonredundant near field - far field transformation with spherical spiral scanning for elongated antennas
An efficient NF–FF transformation with spherical spiral scanning tailored for elongated antennas ... more An efficient NF–FF transformation with spherical spiral scanning tailored for elongated antennas is here developed. To this end, such a kind of antennas is no longer considered as enclosed in a sphere, but in a prolate ellipsoid, thus allowing one to remarkably reduce the number of needed data. Moreover, such a source modelling remains quite general and con- tains the spherical one as particular case. Some numerical tests, assessing the accuracy of the technique and its stability with respect to random errors affecting the data, are reported
Laboratory Tests Validating a Non-Redundant NF/FF Transformation with Spherical Spiral Scan for Non-Centered Mounted Long Antennas
The recently proposed near-field/far-field (NF/FF) transformation technique with spherical spiral... more The recently proposed near-field/far-field (NF/FF) transformation technique with spherical spiral scan, which, by properly exploiting the non-redundant representations of electromagnetic fields and the unified theory of spiral scans for non-volumetric antennas under test (AUTs), allows one to properly account for a mounting of an elongated AUT in offset configuration, is here experimentally validated. It is based on the prolate spheroidal source modelling and requires the same number of NF data as in the case of an onset AUT mounting, depending such a number only on the surface of the adopted AUT modelling. Moreover, it makes use of an efficient 2-D optimal sampling interpolation formula to recover the NF data needed to perform the standard NF/FF transformation, whose amount is related to the radius of the minimum sphere enclosing the AUT and centred at the scanning sphere centre. As it will be shown, the experimental results will further confirm the practical effectiveness of the proposed technique.
An effective iterative algorithm to correct the probe positioning errors in a non-redundant plane-rectangular near-field to far-field transformation
─ An algorithm for the effective compensation of known positioning errors, affecting the samples ... more ─ An algorithm for the effective compensation of known positioning errors, affecting the samples acquired by the probe in a non-redundant plane-rectangular (PR) near-field to far-field (NFFF) transformation, is presented and fully assessed by experimental tests. This transformation adopts a non-conventional PR scan, named planar wide-mesh scan (PWMS), characterized by meshes widening more and more as their distance from the measurement plane center increases, and uses a nonredundant sampling representation of the probe voltage. Such a representation is obtained by considering the antenna as contained in an oblate spheroid, to precisely determine the input NF data for the traditional PR NFFF transformation from the PWMS samples. These samples are unavailable in presence of positioning errors, but, as it will be shown, can be effectively retrieved from the errors affected ones by applying an iterative procedure. Index Terms ─ Antenna measurements, non-conventional plane-rectangular scanning, non-redundant sampling representations, plane-rectangular near-field to far-field transformation, positioning errors compensation.
Ellipsoidal spiral scanning for elongated antennas
Laboratory Proofs on a Nonredundant Spherical NF-FF Transformation for a Quasi-Planar AUT Mounted in Offset Configuration
This communication provides an experimental assessment of an accurate near-field-far-field (NF-FF... more This communication provides an experimental assessment of an accurate near-field-far-field (NF-FF) transformation with spherical scan, properly developed to take into account a mounting in offset configuration of a quasi-planar antenna under test (AUT). Such a technique relies on the nonredundant sampling representation of electromagnetic fields and, unlike the classical NF-FF transformation, it allows the reconstruction of the far field radiated by an AUT from a minimum number of NF data, which remains practically the same both when the AUT is mounted in onset and offset configuration, since this number is related only to the surface modeling the AUT. Such a surface has been here chosen coincident with that formed by two circular bowls with the same aperture and eventually different bending radii. Experimental results assessing the validity of such a technique are reported.
A SVD approach for covering the blind region in the spherical spiral scanning
An effective antenna modelling for the NF–FF transformation with planar wide-mesh scanning
This paper presents a method of spherical far-field extrapolation from near-field using phase ret... more This paper presents a method of spherical far-field extrapolation from near-field using phase retrieval method. The simulation results clarify that we can extrapolate far-field correctly by selecting appropriate probe scanning radius. We also present measurement to verify the simulation results.
Trasformazione campo vicino - campo lontano con scansione elicoidale per antenne lunghe
A nonredundant spherical NF-FF transformation: Experimental tests @ UNISA antenna characterization lab
International Symposium on Electromagnetic Theory, May 20, 2013
ABSTRACT An experimental validation of a near-field - farfield transformation technique with sphe... more ABSTRACT An experimental validation of a near-field - farfield transformation technique with spherical scanning for quasiplanar antennas requiring a minimum number of near-field data is provided in this work. Such a technique is based on the nonredundant sampling representations of the electromagnetic fields and on the optimal sampling interpolation expansions, and makes use of an oblate ellipsoid to model the antenna. It is so possible to remarkably lower the number of data to be acquired, thus reducing in a significant way the measurement time. The effectiveness of such a technique is experimentally assessed at the UNISA Antenna Characterization Lab by comparing the farfield patterns reconstructed from nonredundant measurements on the sphere with those obtained from the near-field data directly measured on the classical spherical grid.
Uploads
Papers by Francesco D'Agostino