Amedeo Capozzoli

Phaseless Antenna Characterization by Effective Aperture Field and Data Representations

The problem of antenna characterization from phaseless near-field data is addressed by appropriate use of the available information on the Antenna Under Test (AUT) and on the scanning geometry to provide efficient representations for both the unknowns and the data. Such a strategy allows improving the reliability and the accuracy of the proposed characterization algorithm and, at the same time, shortens the overall measurement process. An extensive numerical and experimental analysis, together with a comparison with existing approaches, endorses the algorithm reliability and accuracy and confirms its usefulness for antennas having a general radiating (vector) behavior, i.e., either focusing or non-focusing.

Global Optimization and Antennas Synthesis and Diagnosis, Part One: Concepts, Tools, Strategies and Performances

This is the first of two companion papers on global optimization and antenna analysis and synthesis. In Part I, an analysis of the problems involved in Global Optimization is presented by critically discussing the basic concepts and tools, the performances to be expected, the required computational complexity and the guidelines to select algorithms solving efficiently the problem at hand. The relevance of stochastic techniques is enhanced and the role of double phase algorithms is stressed. The proof of the convergence property of an idealized version of a simplified evolutionary algorithm is provided. In Part II, the selected algorithm, a hybrid evolutionary algorithm, is tested against two real world problems relevant in electromagnetics, the power synthesis of contoured beam hybrid reflector antennas and the reflector antenna diagnosis from only amplitude data. The results of an extensive numerical analysis are presented.

Power pattern synthesis of reconfigurable conformal arrays with near-field constraints

A conformal array power pattern synthesis technique is presented which makes it possible to take into account near-field constraints and to reconfigure the radiated pattern by controlling only the phases of the excitation coefficients. Far-field pattern specifications are given by masks while near-field constraints are given by prescribing the maximum allowable field intensity at points arbitrarily located in a given near-field region. The amplitude of the excitations, common to all radiated beams, and the phases corresponding to each one are obtained as a result of the synthesis algorithm.

Photonic Probes and Advanced (Also Phaseless) Near-Field Far-Field Techniques

We present innovative near-field test ranges, named compact-near-field (CNF) and very-near-field (VNF). These use photonic probes, and advanced near-field far-field (NFFF) transformations from amplitude and phase (complex) or phaseless measurements. The photonic probe allows AUT-probe distances of less than one wavelength. This drastically reduces test-range and scanner dimensions, improves the signal-to-clutter ratio and the signal-to-noise ratio, and reduces the scanning area and time. In both the cases of complex and phaseless measurements, the neat-field-to-far-field transformation problem is properly formulated to further improve the rejection of clutter, noise, and truncation error. The advantages of the compact-near-field and very-near-field test ranges are discussed and numerically analyzed. Experimental results are presented for both planar and cylindrical scanning geometries.

Dielectric Field Probes for Very-Near-Field and Compact-Near-Field Antenna Characterization [Measurements Corner]

A novel setup, based on the use of non-invasive dielectric field probes, and employing accurate and reliable algorithms for antenna characterization, is described. Experimental results show how the proposed system can provide even more accurate characterizations than standard near-field systems, enabling considerable reduction of indoor test-range dimensions (compact near-field). Also, the potential for very-near-field acquisition, as well as the sampling strategy in the reactive zone of the radiator, are pointed out.

A novel approach to scatterers localization problem

A new approach to find the number and locations of electromagnetic scatterers (sources) from one view, one frequency field data is presented. The case of scatterers (sources) with dimensions comparable to the wavelength is considered. First, in order to devise an effective technique, a new relevant property of the electromagnetic field, the point source spectral content, is introduced and its relationship with both the sliding windowed Fourier transform of the field and the local bandwidth function is discussed. To enlighten its usefulness it is also shown that a footprint of the scattering system encoding information on its geometry can be easily extracted from the scattered field by exploiting this new property. On this basis, the new localization technique is introduced. In order to restrict the search region, the minimum circular envelope enclosing the scatterers is found by purposely introducing a new technique exploiting the effective bandwidth of the radiated field. Then, the number and locations of scatterers is retrieved by using the field local quantitative feature previously introduced, without the complexities of the full inverse problem as it is usually done by the traditional approaches. In this way, not only a simplified technique is obtained but also the ill-posedness of the problem and the noise effects are significantly mitigated. The effectiveness of the proposed technique and its overall performance with respect to a singular value decomposition based approach are proved by means of a numerical analysis.

Global Optimization and Antenna Synthesis and Diagnosis, Part Two: Applications to Advanced Reflector Antennas Synthesis and Diagnosis Techniques

The paper presents the application of the hybrid global optimization algorithm, introduced in the companion paper Part I, to reflector antenna power pattern synthesis and reflector antenna surface diagnosis from only amplitude data. The synthesis algorithm determines both the reflector surface and the excitation coefficients of the array of primary feeds to meet the designing specification on the far-field pattern expressed by means of two couple of masks bounding the squared amplitude of both the copolar and crosspolar components. The diagnosis technique allows to find the reflector surface profile from the measurement of the far field power pattern by a proper formulation of the corresponding inverse problem. In both cases we take advantage of the exploring capability of an evolutionary algorithm and of the solution refinement capability of an efficient, quasi-Newton based, local search procedure. The numerical analysis shows that Global Optimization can outperform the standard local approach, by significantly improving the performance of the synthesized antenna in the first case and by enhancing the reliability of the diagnosis procedure in the second one.

Singular-Value Optimization in Plane-Polar Near-Field Antenna Characterization

We develop a near-field/far-field (NFFF) transformation approach for characterizing planar aperture antennas from plane-polar scanning data. The radial and azimuthal field-sampling spacings are chosen to provide the minimum number of near-field samples, optimizing the singular-value dynamics of the relevant linear operator connecting unknowns and data. A numerical and experimental analysis is provided, showing how the approach is capable of significantly reducing both the number of required samples and the number of measurement rings, as compared to the advanced sampling techniques available in the literature.

GPU-BASED Ï-K TOMOGRAPHIC PROCESSING BY 1D NON-UNIFORM FFTS

We present an ω-k approach based on the use of a 1D NonUniform FFT (NUFFT) routine, of NER (Non-Equispaced Results) type, programmed on a GPU in CUDA language, amenable to realtime applications. A Matlab main program links, via mex files, a compiled parallel (CUDA) routine implementing the NUFFT. The approach is shown to be an extension of an already developed parallel algorithm based on standard backprojection processing to account also for near-field data. The implementation of the GPU-based, parallel NUFFT routine is detailed and the computational advantages of the developed approach are highlighted against other confronted sequential or parallel (on multi-core CPU) procedures. Furthermore, the benefits of the ω-k, NUFFT-based processing are pointed out by both comparing its accuracy and computational convenience against other interpolators, and by providing numerical results. By comparing the computational performance of the algorithm against a multi-core, Matlab implementation, the speedup has been about 20 for a medium size image. The performance of the approach has been pointed out in the applicative case of vegetation imaging against experimental data of a boxtree (Buxus tree), also under a source of temporal decorrelation (wind).

Recent Advances in Near-Field to Far-Field Transformation Techniques

1Dipartimento di Ingegneria Elettronica ed Ingegneria Informatica, Universita di Salerno, Via Ponte Don Melillo, 84084 Fisciano, Italy 2Dipartimento di Ingegneria Biomedica, Elettronica e delle Telecomunicazioni, Universita di Napoli Federico II, Via Claudio 21, 80125 Naples, Italy 3 SATIMO Italian Office, Via Castelli Romani 59, 00040 Pomezia, Italy 4MI Technologies, Suite 100, 1125 Satellite Boulevard, Suwanee, GA 30024-4629, USA 5Nearfield Systems Inc.19730 Magellan Drive, Torrance, CA 90503, USA