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Magnetic nanoparticles enhanced microwave imaging relies on the capability of modulating the response of such nanocomponents at microwaves by means of a (low frequency) polarizing magnetic field. In medical imaging, this capability allows for the detection and imaging of tumors loaded with nanoparticles. As the useful signal is the one which arises from nanoparticles, it is crucial to remove sources of undesired disturbance to enable the diagnosis of early-stage tumors. In particular, spurious signals arise from instrumental drift, as well as from the unavoidable interaction between the polarizing field and the imaging system. In this paper, we experimentally assess and characterize such spurious effects in order to set the optimal working conditions for magnetic nanoparticles enhanced microwave imaging of cancer. To this end, simple test devices, which include all components typically comprised in a microwave imaging system, have been realized and exploited. The experiment’s results allow us to derive design formulas and guidelines useful for limiting the impact of unwanted magnetic effects, as well as that relative to the instrumental drift on the signal generated by the magnetic nanoparticles-loaded tumor.

Discusses the technologies and applications supported by nanotechnology, considered one of the 21st century's most promising technologies. Nanotechnology deals with the design, development, and manipulation of materials and devices with at least one dimension sized on a nanometer scale. It involves fields of science as diverse as surface science, organic chemistry, molecular biology, semiconductor physics, microfabrication, with a vast range of applications, such as in medicine, electronics, biomaterials, and energy production. Its ultimate goal is to be able to predictably design, construct, and control nanosystems, tailoring them to specified needs.

Non-periodic, sparse Direct Radiating Arrays employing equi-amplitude (isophoric) radiators represent an appealing solution to meet the requirements of next satellite services. In this work we address the synthesis of isophoric sparse arrays capable of radiating highly steerable pencil beams, in order to meet the requirement of full Earth coverage from GEO orbits. To this aim, we first of all perform an analytical study that allows assessing the geometrical constraints that the desired beam steerability puts on the design of the array layout. Starting from such results, in the second part of the work we address the actual synthesis of the sparse array. The proposed strategy consists in the synthesis of the optimal radiating feed followed by the synthesis of the array layout capable of taking into account the aforementioned geometrical constraints as well as the feeds' pattern, in such a way to guarantee satisfaction of the side lobe level constraint for every steered beam. Numerical examples demonstrate the effectiveness of the proposed synthesis strategy.

The aim of this paper is to investigate the main aspects of the synthesis of plane wave generators (PWGs) i.e., arrays capable of emulating a plane wave, or a superposition of plane waves, in a given region. In particular, we introduce new figures of merit, particularly suitable for PWG synthesis procedures, and simple guidelines regarding size and shape of the PWG, as well as the number of radiating sources needed to synthesize the required plane waves. The performance limits of a PWG are analyzed, in terms of indexes related to the stability of the solution and to the level of the field amplitude on the lateral walls of the anechoic chamber in which the PWG is placed. Finally we present a synthesis method for PWGs, based on a planar sparse array architecture. Starting from the previously achieved results, a novel effective synthesis procedure is introduced. By means of such a procedure we are also able to take explicitly into account the mechanical and electrical tolerances in the PWG realization. In such a way we can assure the best performances, given the unavoidable errors in the positioning and excitation of the radiating elements.

This paper discusses some recent advances in the synthesis of isophoric sparse arrays, with reference to satellite communications. In particular, we first summarize some of the synthesis algorithm recently proposed, highlighting their advantages and drawbacks. Then, we show that, depending on the particular application scenario for which the sparse array must be designed, a better tailored algorithm exists. The presented analysis is aimed at providing a useful tool for antenna engineers involved in the overall design of sparse arrays for satellite communications.

This paper presents a novel approach to microwave hyperthermia exploiting magnetic nanoparticles as focusing agents, and reports the results of a 2D numerical study aimed at preliminarily assessing its effectiveness. The approach exploits magnetic nanoparticles, locally supplied to the tumor, to induce, through an external polarizing magnetic field, a detectable variation of its magnetic contrast. This variation is exploited to determine the excitations of the antenna array focusing the electromagnetic energy on the tumor. The advantage is that the synthesis of the excitations does not require any information neither on the geometry nor on the electromagnetic properties of the treated region, thus achieving totally blind field focusing. The magnetic nature of the magnetic nanoparticles contrast has required the development of an ad-hoc synthesis strategy, which, together with the use of magnetic nanoparticles, represents the novelty of the approach.

Magnetic nanoparticles (MNP) enhanced microwave imaging has been recently proposed as a tool to pursue the diagnostics of breast cancer in an effective and reliable way. By means of a numerical analysis carried out under realistic conditions, this letter aims at assessing the measurement dynamic range (i.e., the measurement resolution), in terms of tumor size, nanoparticles concentration, and working frequency, required for an apparatus based on this diagnostic approach.

Uniform amplitude sparse arrays have recently gained a renewed interest and a number of synthesis techniques, mainly based on global optimization algorithms, have been presented. In this paper, after a discussion about the expected characteristics of such arrays, a simple deterministic approach for the case of pencil beams patterns is proposed and discussed. The approach, which outperforms previous synthesis techniques, takes inspiration from existing (not well-known) density taper procedures to develop a two stages synthesis where the first step is solved in a new closed analytical form, while the second one just requires local refinements or fast 1-D optimizations. As a consequence, the proposed approach avoids the need of multidimensional global optimization procedures and the inherent possibly prohibitive computational costs. Notably the first step, which also exhibits an improved flexibility with respect to other analytical techniques, already outperforms previous approaches in a number of cases of interest. Several numerical results confirm the effectiveness and usefulness of the proposed tools.

The problem of the optimal synthesis of circularly symmetric aperture distributions able to radiate pencil beams fulfilling well-defined requirements on the far-field and/or the directivity is addressed and solved. In particular, constraints concerning both the sidelobe level (SLL) and the directivity within a coverage zone are dealt with while being careful not to incur into the so called super-directive sources or into aperture fields actually difficult to be realized. The case wherein a constraint is enforced on the dynamics of the excitations is also considered. Numerical examples concerning cases of practical relevance are also shown in support to the given theory.

In the framework of medical applications of microwaves, magnetic nanoparticles enhanced microwave imaging represents a promising diagnostic modality. As a matter of fact, it merges the safety, low-cost and portability of microwave technology with the increased specificity enabled by the selective targeting capability of magnetic nanoparticles. In particular, a key ingredient of this technique is the possibility of modulating the response of nanoparticles in the microwave range by means of an external polarizing magnetic field. To this end, the amplitudes of the polarizing field have to be properly set, in order to achieve optimal performances. In this communication, we present an experimental study aimed at optimizing the working conditions in terms of field strength of a ultra-wide band radar system for detecting a magnetic nanoparticle induced contrast.

This paper deals with the optimal design of phased arrays for medical applications of microwaves, such as hyperthermia treatments and cancer imaging. To address this problem, microwave engineers have to face peculiar and novel challenges, since the region of interest is a 3-D domain in the near field of the array and consists of a highly heterogeneous and lossy medium, whose characteristics change from patient to patient. For this reason, we have to reconsider basic fundamentals about phased array design, in order to devise proper tools and criteria. In particular, we address the design of the system layout, i.e., the choice of the number and locations of the array elements, as this represents the preliminary fundamental problem to face. To this end, we first formulate the two general problems relevant to biomedical applications--the design of an array for therapeutic purposes and of an array for diagnostic/imaging goals. We then address the proper theoretical and analytic tools and methods that enable pursuit of an optimal design with respect to given constraints. Finally, we provide some examples to show how the design procedure can be carried out in practice.

A new method to avoid the truncation error in antenna near-field measurements is presented. The approach relies on the concept of information content of the field. According to this point of view, the truncation problem is solved by picking up the information that is lost due to the finite size of scanning area, in points of the space reachable by the measurement system. The method can be applied to any scanning geometry, including the planar and cylindrical ones, whenever the set-up allows to vary the distance between the antenna under test and the probe during the scanning procedure. Application of the method to cylindrical near-field scanning is numerically investigated, assessing the effectiveness of the proposed technique.

Magnetic nanoparticles-enhanced microwave imaging has been recently proposed as an effective and reliable means to detect breast cancer. Thanks to the nonmagnetic nature of human tissues, the imaging problem corresponds to the retrieval of a weak magnetic anomaly hosted into an unknown nonmagnetic scenario. Hence, properly targeted magnetic nanoparticles in principle allow to avoid false positives and reduce occurrence of false negatives. In this paper, we outline some guidelines for the design of the imaging device based on an optimized measurement configuration. In particular, we determine the nonredundant number of probes and their collocation needed to ensure a reliable solution of the underlying inverse scattering problem. The analysis exploits the spectral properties of the relevant mathematical operators and it is corroborated by reporting numerical results exploiting the phantoms’ repository from the University of Wisconsin. It is shown that magnetic nanoparticles-enhanced microwave imaging can reliably detect cancer lesions even using low-complexity arrangements, designed according to the devised guidelines.

An efficient probe-compensated near-field/far-field transformation technique with planar spiral scanning is proposed, which uses a minimum amount of data. A non-redundant sampling representation of the probe output voltage on a planar spiral and a fast, accurate and stable interpolation algorithm are developed. By choosing the angular step of the spiral coincident with the sample spacing needed to interpolate such a voltage on a radial line, it is possible to reconstruct the data required by the standard probe-compensated plane-rectangular near-field/far-field transformation technique. The use of an open-ended cylindrical waveguide as scanning probe allows probe co-rotation to be avoided. Numerical examples are reported, assessing the accuracy and the stability of the far-field reconstruction process.

A novel approach for the efficient evaluation of the monostatic radar cross section (RCS) from near-field bistatic RCS in two-dimensional geometry is presented. The monostatic RCS is evaluated exploiting only the near-field data relative to an angular region centered on the direction of interest whose size is the minimum possible and depends on the size of the scatterer and on its distance from the measurement zone. In such a way a fast and efficient algorithm is obtained.

The paper suggests a novel blind focusing approach for microwave hyperthermia. The idea is to exploit a contrast variation induced in the diseased tissue for the synthesis of the excitations of the antenna array employed for the field focusing, by performing a differential scattering measurement. In particular, the excitation vector is set as the right singular vector associated to the largest singular value of the differential scattering data matrix, obtained as the difference of the scattering matrixes measured, by the antenna array itself, before and after the contrast change. The approach is computationally effective and totally blind, not requiring any a priori knowledge on the electric and geometric features of the region hosting the target and on its spatial location with respect to the antenna array.

This paper deals with the possibility of adopting microwave imaging to continuously monitor a patient after the onset of a brain stroke, with the aim to follow the evolution of the disease, promptly counteract its uncontrolled growth, and possibly support decisions in the clinical treatment. In such a framework, the assessed techniques for brain stroke diagnosis are indeed not suitable to pursue this goal. Conversely, microwave imaging can provide a diagnostic tool able to follow up the disease's evolution, while relying on a relatively low cost and portable apparatus. The proposed imaging procedure is based on a differential approach which requires the processing of scattered field data measured at different time instants. By means of a numerical analysis dealing with synthetic data generated for realistic anthropomorphic phantoms, we address some crucial issues for the method's effectiveness. In particular, we discuss the role of patient-specific information and the effect of inaccuracies in the measurement procedure, such as an incorrect positioning of the probes between two different examinations. The observed results show that the proposed technique is indeed feasible, even when a simple, nonspecific model of the head is exploited and is robust against the above mentioned inaccuracies. © 2014 R. Scapaticci et al.

Microwave imaging (MWI) can provide truly non-invasive and affordable tools to perform biomedical monitoring for diagnostic purposes, as it exploits non-ionizing - therefore harmless - radiations and relatively cheap and portable devices. In this respect, besides breast cancer imaging, which is still the mostly addressed topic by researchers worldwide, there are several emerging applications relevant to the so-called aging society scenario, such as early diagnosis of bones degradation [P. M. Meaney, T. Zhou, D. Goodwin, A. Golnabi, E. A. Attardo and K. D. Paulsen, “Bone Dielectric Property Variation as a Function of Mineralization at Microwave Frequencies,” Int. Journal of Biom. Imag. 2012] and monitoring of brain injuries due to strokes. In these applications, the capabilities of a microwave technology can be helpful to cooperate with existing diagnostic technologies, in order to improve the overall reliability and timeliness of the diagnosis.

A new synthesis algorithm for shaped, double-reflector antennas with complex array feed is presented. The approach presented here aims to improve the efficiency of synthesis techniques without missing the required accuracy. The algorithm is based on a convenient splitting of the original problem into two phases, each one involving a sub-problem significantly simpler than the original one. A double reflector synthesis problem involving only Fourier Trans- form (FT) operators is of concern during the first phase. The subre- flector surface and a first estimate of the main reflector geometry are obtained in this step. A single reflector synthesis problem is considered during the second phase wherein the final main reflector surface and the excitation coefficients of the primary feed array are obtained. While in the first phase only approximate relationships between the unknowns and the secondary radiated field are exploited, in the second phase accurate radiation operators are involved. Despite this accuracy, the second phase is still numerically effective since it involves a single reflector synthesis problem and exploits, as "good" starting point, the main reflector estimate obtained during the first phase. The effectiveness of the approach is due to the fact that the necessity of dealing simultaneously with two reflector surfaces, the key of the synthesis difficulties, is afforded only during the first phase where efficient computational tools are allowed. A numerical example shows the effectiveness of the proposed approach.

Due to the continuous growth of satellite communications and the nearly saturation of the Ku band, Ka band has started to be used for broadband communications. For the new generation of spaceborne antennas operating in Ka band, satellite communication operators require some in-orbit features as the flexibility and the re-configurability. The most suitable antenna configuration candidate to provide these characteristics is the Active Direct Radiating Array. This paper describes innovative solutions that, by the use of sparse/thinned lattices, allows to minimize the radiating elements number reducing the complexity for the cooling system integration (e.g. heat-pipes) and beam former implementation.

This paper deals with the synthesis of a “plane wave generator”, i.e. an array able to synthesize a plane wave in the near-zone. In particular, a number of design paradigms are derived and the performance limits are investigated. Numerical results obtained using an effective synthesis algorithm, able to take into account into account the information on the uncertainty on the position and excitation of the array elements during the synthesis process, are presented and discussed.

This presentation deals with the optimal synthesis of non periodic, isophoric arrays capable of generating high gain spot beams for satellite communications. After discussing the advantages and potentialities of such a kind of antennas, as well as the difficulty of their optimal design, a three step synthesis strategy and the algorithms for its implementation are presented and briefly discussed. Then the case of a sub-regional coverage is addressed, showing how very high performances can be actually achieved with a strongly reduced number of feeds, by exploiting an innovative architecture adopting both amplitude and feed-size tapering. Finally, the case of full Earth coverage, requiring relatively high scanning capabilities, is addressed. The impact of this requirement on the inter-feed distance, on the number of required entry points and on the achievable performances is analyzed, both theoretically and numerically, assessing in a quantitative way the price that must unavoidably be paid for achieving a global coverage.

We present some modifications to the deterministic approach (DA) recently proposed for fast design of aperiodic concentric ring arrays. Such modifications are aimed at improving the array performances in terms of directivity, side lobe level (SLL) and number of control points. In particular, an easy implementation of the size-tapering concept is provided within the processing scheme of the DA procedure; moreover, an improved collocation criterion is presented. Finally, a local optimization procedure, tailored to the concentric ring array case, is addressed.

The paper presents a novel measurement method for the broadband characterization of the electromagnetic properties of diluted water-based ferrofluids. The approach exploits the possibility of switching ON and OFF the magnetic response of the suspended magnetic nanoparticles, without affecting the electric response of the ferrofluid, by means of an applied polarizing magnetostatic field. In such a way, two different datasets are collected: 1) the OFF data, which only depend on the electric response of the investigated ferrofluid; 2) the ON data, which depend on both the electric and magnetic responses of the ferrofluid. These data, properly processed, allow the physical separation, at the measurement stage, of the electric response from the magnetic one and so a more robust and stable inversion process, especially in the case of diluted water-based ferrofluids. The reported results show the robustness of the approach as compared to standard measurement techniques.

In this contribution an effective approach for the synthesis of plane wave generators (PWG) for the testing of linear arrays is proposed. Relatively few elements are necessary for the synthesis of a PWG and its performances and flexibility make this approach very interesting in many situations.

In this paper, a microwave technique for breast cancer imaging is presented. The approach is based on the use of magnetic nanoparticles as contrast agent to induce a nonnull magnetic contrast selectively localized within the tumor. This allows us to face cancer imaging as the reconstruction of a magnetic contrast from the corresponding scattered field. To extract, from the measured data the contribution due to the magnetic contrast, i.e., the signal meaningful for cancer imaging, the approach exploits the possibility of modulating the magnetic response of magnetic nanoparticles by means of a polarizing magnetic field. The achievable reconstruction capabilities and the robustness against uncertainties on the electric features of the surrounding electric scenario are assessed by means of numerical examples.

By exploiting not widely diffused results in the synthesis of shaped beams by means of fixed geometry linear arrays, as well as recent results in the synthesis of pencil beams by means of sparse arrays, we set a frame for a deterministic and hence fast synthesis of shaped beams through sparse arrays having an uniform amplitude. Preliminary results, supporting the effectiveness of the proposed strategies, are also presented.

A novel approach to the synthesis of arrays reconfigurable by controlling only the phase of the excitations is presented. This approach makes it possible to choose the best amplitude distribution during the synthesis, instead of choosing it a priori. The method is based on the projection approach to array synthesis. The feasibility of the proposed approach is shown with reference to a meaningful one-dimensional example, but the method can be used, without substantial modifications, for two-dimensional arrays as well. Attention is given to the synthesis of a reconfigurable array of 17 elements, able to radiate a cosecant beam and a flat-topped beam, with a phase-only control. The sidelobe requirement is -20 dB and the ripple in the shaped zone is 0.5 dB. the resulting patterns are shown. >

A new solution approach to inverse scattering from aspect-limited phaseless measurements of the total field is introduced and discussed. In analogy with the case of measurements on closed curves [J. Opt. Soc. Am. A21, 622 (2004)], the procedure splits the problem into two different steps. In the first step, amplitude and phase of the scattered field are estimated from only amplitude information of the total field. By properly extending the concept of reduced radiated field to the case of scattered fields (as a function of both illumination and measurement variables) and taking advantage of the properties of the square amplitude distribution of the total field, criteria are given for an optimal choice of the measurement setup and a successful retrieval. Then the complex permittivity profile is reconstructed in the second step, starting from the scattered fields estimated in the previous step. Numerical examples are provided to assess the effectiveness of the whole chain in the presence of noise-corrupted data and the relevance of the representation introduced for the scattered fields.

The aim of this paper is to present an integrated photonic TTD phaser (TPH) for PA, based on the technology introduced in J.E. Fouquet, (2000). In particular, the design of a digital 3 Bit TPH, feeding a 4 elements optical time steered antenna (OTSA), focusing the attention on the TPH insertion loss (IL), compactness and amplitude uniformity of the excitation coefficients distributions (AU). It is worth noting that, thanks to the modularity of the TTD unit (TTDU), TPHs able to drive larger antennas with a better beam pointing resolution can be obtained.

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.

In this paper, we investigate whether and how one can synthesize given far field patterns by acting on the dielectric profile of a lens antenna. In particular, an approach to design a radiating system consisting of a variable dielectric profile and a single or a low number of feeds is proposed and discussed. To properly take into account physical and practical feasibility issues, the proposed method splits the problem into two steps. The first one is aimed to fix design goals (i.e., the nominal field), in such a way to avoid super-directive or physically unfeasible antennas and properly exploits known properties of electromagnetic fields radiated by finite extent sources. The second step, dealing with the dielectric profile synthesis, is based on suitable modifications of inverse scattering techniques and can take into account constraints on the spatial behavior as well as of dielectric characteristics of the profile to be synthesized. To show the interest of the subject, as well as effectiveness of the proposed approach, the synthesis of new dielectric antennas, such as a high directivity source and a lens radiating a steerable degradation-free Chebyshev pattern, is considered in the two dimensional scalar case.

A general strategy to reduce the effect of the clutter noise in near-field measurements is presented. The approach exploits the band-limitation properties of the radiated field in order to filter the noise in the near-field data before far-field pattern evaluation. The method requires a simple lowpass filtering of the data, collected at suitably chosen sampling positions, after the extraction of a proper phase function. It holds for general scanning and source geometries, and is robust with respect to truncation of measured data owing to the finite dimensions of the scanning area. Numerical and experimental results confirm the effectiveness of the technique.

This work describes the extension to the circular scanning case of a recently proposed approach to the scatterer localisation problem from single frequency scattered field data. The approach allows the determination of the number and the location of a set of scatterers without requiring the solution of the full inverse problem, i.e., the inversion of the radiation or scatterer operator. The numerical analysis shows that the achievable performance is better than that obtained with a rectilinear scanning.

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 allowabie 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.

In this paper, experimental results of the application of a new method for the reduction of the truncation error in near-field measurement are presented. It is shown that the use of the proposed algorithm allows the test of larger antennas obtaining a significant upgrading of near-field system possibilities.

A simple and effective method to avoid the truncation error in antenna near-field measurements is presented. The method can be applied to planar or cylindrical near-field setups, whenever it is possible to vary the distance between the antenna under test and the probe during the scanning procedure.

This paper describes the first land and sea microwave links realized by Guglielmo Marconi in 1932. While other researchers were experimenting with sea microwave links in the same period, Marconi's land experiment was the first successful microwave link over a roughly hilly terrain, and led to the first permanent microwave radio link. Besides the description of the experiment, many photos and figures are included, some of which are extracted from Marconi's original works.

Reconfigurable antennas, able to radiate more than one pattern, are often necessary in the modern telecommunication systems. In the case of array antennas, phase-only control of the beam reconfiguration has a significant relevance in the attainment of greater simplicity of the beam forming network. Furthermore, in many applications the geometry of the antenna is dictated by the particular application in question so that a conformal array is required. Previously, a new technique for the synthesis of (non-reconfigurable) conformal arrays, based on the determination of the intersection between two suitably defined sets, has been presented in the three dimensional and fully vectorial case [Bucci et al. 1995]. In this communication a generalization of this technique is presented in order to face the problem of the synthesis of reconfigurable conformal arrays with phase-only control. In particular the presented approach allows to find, in an optimal way, the amplitude of the excitation coefficients common to all beams and the phases of such excitations corresponding to each radiated beam.

By properly using the non-redundant representations of EM fields relevant to source modelling and observation geometries with the same rotational symmetry, an effectively non-redundant sampling technique for the interpolation of the field radiated over a cylinder is developed. Such a technique is especially tailored for cylindrical or elongated sources (conformal arrays, SAR antennas, etc.) and it contains the spherical source as particular case. This is relevant whenever an efficient interpolation of the EM field is wanted and, in particular, in the near-field to far-field transformation with cylindrical scanning.

The diagnostic of the effective surface geometry of the reflector antenna is performed by exploiting only the amplitude of the radiated pattern. The approach is based on a convenient factorization of the aperture field and performs an optimal estimate of the reflector distortions by carefully choosing the output space and the space of the unknowns in order to improve the behaviour of the procedure with respect to the trapping problem. >

A manageable design method for edge-shunt slot arrays that is able to take fully into account the external mutual coupling requires some simplifying assumptions. The aim of this communication is to experimentally assess the impact of these assumptions on the accuracy of the results.

With reference to the detection of buried homogeneous dielectric objects (such as landmines or cavities), a simple regularization scheme is proposed which achieves a good rejection of spurious inclusions as well as false targets. The proposed approach also allows roughness to be managed as a retrievable unknown.

In electromagnetic inverse scattering problems the "optimal" representation of the unknown is a crucial task in the view of an efficient exploitation of the limited available information. With reference to the particular case of detection of defects in homogeneous materials, a non-linear inversion technique taking advantage of multiresolution features of wavelet expansions is presented. Numerical examples confirm the effectiveness of the proposed adaptive approach.

An algorithm for the diagnosis of phase faults in array antennas from amplitude only far-field or near-field data is presented. The technique allows one to diagnose the faults affecting only the phase of the excitation coefficient. Whose amplitudes are then assumed equal to the nominal values. Discretised phase values, typical of digital phase shifters, are considered. The proposed approach is based on the optimization of a suitable objective functional via an hybrid evolutionary algorithm. The main results of an extensive numerical analysis are presented in order to show the performance of the method.

A synthesis approach was used for analyzing hybrid reflector antennas with near field constraint. This technique was applied to a reflector with circular symmetric aperture. The algorithm was implemented in a numerical code and subjected to an extensive numerical analysis to assess its effectiveness. However, the approach was able to synthesize contour-beam hybrid reflector antennas by significantly reducing the field on prefixed areas close to the antenna system.

It has recently been shown that the measurement setups usually adopted in inverse scattering problems, in which the primary sources and the receiving antennas are placed at some wavelength apart from the object under test, suffer from intrinsic limitations in the reconstruction capabilities because of the essentially finite-dimensional nature of the space of data (the scattered fields). To investigate whether it is possible to overcome these limitations, two (novel to our knowledge) measurement configurations for inverse scattering experiments at a fixed frequency are analyzed and discussed. By means of an analysis of the properties of the radiation operator, it is shown that positioning the measurement probes (and possibly the primary sources) in the close proximity of the object under test allows an improvement of the reconstruction capabilities of inversion algorithms with respect to conventional setups. However, such an improvement can be achieved only in a region close to the border of the region under test. Quantitative rules for the achievable improvement are given and are exemplified through numerical examples.

A new and advanced sampling technique far-field interpolation with a nonredundant number of samples on plane-polar geometry has been experimentally validated for cases of both complex and only-amplitude measurements. Experimental results show good stability of the interpolation algorithm with respect to noise and the lack of samples in the case of a limited scanning area.

Scanning and/or reconfigurable reflector antennas can be conveniently set up by using a hybrid antenna consisting of a reflector illuminated by a small phase-only controlled array feed. However, no general synthesis procedure performing the optimum design of such antennas seems to exist. In the paper a new general and flexible formulation of this synthesis problem is presented together with an iterative solution scheme, which make it possible to determine simultaneously the reflector geometry, the amplitude of the excitation coefficients common to all radiated beams and the phases of such excitations corresponding to each beam. The technique handles general and flexible requirements on the radiated beams (expressed by masks) as well as general constraints on the excitations of the feed array elements (the phase-only control is one of these). Furthermore, it exploits a new choice for the quantity to which the design specifications concerning the radiated field are applied, in order to alleviate the trapping problems encountered in power synthesis. A numerical analysis is performed in order to demonstrate the effectiveness of the approach as well as the possibilities offered by the hybrid reflector antenna configuration.

This paper presents a new method for the diagnosis of the deformations of a reflector antenna surface from the radiated far-field amplitude pattern. The method is fully vectorial and allows for working with a shaped beam antenna. The approach exploits a new factorization of the aperture-field distribution and takes into account both the available information concerning the undistorted antenna and the measurement accuracy. Particular care is devoted to the analysis of the well-posedness of the problem and to the avoidance of stagnation points which can trap the algorithm away from the true solution. The effectiveness of the method and its superior performance with respect to the commonly used successive projections algorithms are demonstrated by a numerical analysis. >