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International audience; In this paper, we present quantitative image reconstructions (i.e. permittivity and conductivity profiles) from synthetic and experimental data. First, we perform the qualitative imaging for localizing the target in order to determine the investigation domain. Second, we solve the inverse-scattering problem via an iterative algorithm based on a Conjugate Gradient (CG) method.

International audience; We describe the design, fabrication and measurements of an axisymmetric dielectric lens, featuring a sectorial radiation pattern at 77 GHz. It will be used as the primary feed of a lens-based compact antenna test range (CATR). Due to symmetry of revolution, the sectorial lens profile can be designed in one dimension by using phase only control. The phase variation is echoed on the lens depth. The resulting stepped lens is simulated using France Telecom Orange Labs SRSRD software (¿in-house¿ software developed for dielectric axisymmetric radiating structures) and measured in an anechoic chamber at 77 GHz. Two lenses were fabricated with different materials: PVC and polyurethane, respectively. Good agreements were obtained between simulations and measurements. Less than 0.2 dB ripple in the central beam are obtained for the polyurethane lens although relatively high secondary lobes occur at 11°. Comparisons between the near field of a CATR illuminated by a small horn providing a uniform amplitude taper and the sectorial lens are conducted using numerical simulations. Results show that on-axis oscillations are reduced from 6 to 1 dB with the sectorial lens.

International audience; We present an inverse algorithm based on Level Set method and topological shape gradient for optimizing the shape of planar antenna structure or arrays from imposed constraints (e.g. desired or imposed radiation patterns, gain or directivity) or for reconstructing the shape from measurements. The forward problem is solved using an integral formulation of the EM problem with finite element discretization. The topological shape gradient is computed based on a topological deformation and fast linear system transformation algorithm. Different configurations of antenna arrays are studied for investigating the performance of the inverse algorithm and optimization procedure.

International audience; We present an inverse algorithm based on Level Set method for optimizing the shape of planar antenna structure or arrays from imposed constraints (e.g. desired or imposed radiation patterns, gain or directivity) or for reconstructing it from measurements. The forward problem is solved using an integral formulation of the EM problem with finite element discretization. The shape gradient is computed using two different methods: one based on nodal point mesh derivation and the other on topological gradient. Different configurations of antenna arrays are studied for investigating the performance of the inverse algorithm and optimization procedure.

International audience; In the field of road construction and maintenance, the need for information on the thickness of very thin road layers is not satisfied by means of commercial pulse GPR, due to the inability of such devices to operate over ranges of several gigahertz. As a result, research has focused on the design of a step-frequency radar technique, able to work with very high-frequency synthetic pulses.An ultrawide band antenna, belonging to the family of Vivaldi antennas, has been developed for road applications. It has been created using stripline technology and yields a band width greater than one decade. During an initial step, this antenna was tested on various bituminous concrete samples with a network analyzer. Different parameters were studied, including band width, offset between antennas, and height and shape of the frequency-dependent pulse.A second step involved GPR dynamic measurements. A customized software program enabled recording data from the network analyzer. Several radar profiles were developed from selected road construction and maintenance test sites (e.g. the Circular Pavement Fatigue Test Track, composed of a number of known structures). Results show improved resolution when compared to a commercial impulse GPR system.

In this paper, we address the problem of Through The Wall (TTW) detection with the emerging radar concept that is the multiple-input multiple-output (MIMO) radar. At first near field and through the wall propagation effects on electromagnetic waves are adressed then a MIMO frequency signal model is given and the advantages of a MIMO scheme for the complex task of TTW detection is discussed. Then image formation with beamforming processing is derived. Finally, the proposed imaging method is implemented on numerical signals obtained by FDTD computations considering through cinder blocks walls propagation. The obtained images for scenarii with one or two targets are presented.

This paper gives an overview of mm-Wave reflectarrays used for civil radar applications such as collision avoidance system for rescue helicopters at 94 GHz or FOD detection on airport runways at 77 GHz. Both antenna designs and examples of radar performances are presented and discussed.

A variety of research topics suggested by present efforts are discussed using a Hybrid Conjugate Gradient method and suggested for future investigation using Level set method.

We have presented comparative study with a realistic field-test in the tunnel of the Vaucluse aquifer, of two different microwave imaging systems - the 250 MHz RAMAC pulsed system and the ultra-wideband ETSA system. These initial results are very promising especially regarding the improved resolution of the ETSA image and the concomitant greater depth of penetration. Future work will focus on establishing a quantitative norm for comparing image quality, both in amplitude and frequency.

The technique presented in this paper is suitable to analyze multi-scale problems such as VLF/LF antennas. However, it will be necessary to pay a particular attention on the thin wire interconnection. Further work will be devoted to take into account radial-wire ground planes above or buried in inhomogeneous media. Acknowledgment : This work was granted access to the HPC resources of CINES under the allocation 2009-x2009055118 made by GENCI (Grand Equipement National de Calcul Intensif).

International audience; The increasing use of millimeter waves for civil radar application, e.g., for automotive or helicopter obstacle detection- requires the development of high gain and low cost antennas in compact form. With this aim, a Fresnel reflector with circular polarization over 5 GHz bandwidth (76-81 GHz) has been designed, fabricated and measured. The gain remains higher than 32 dBi with a peak value of 35 dBi at 79 GHz. For obtaining this performance, specific patches have been designed. They are based on circular rings, rectangular and offset patches. Each of them converts an incident linear electric field into a circular polarized one.

International audience; Based on a folded reflectarray antenna, a three-beam antenna is investigated using dielectric rods as primary feed placed in open-ended waveguides for obtaining an optimal illumination on the reflector. The performances for a dielectric rod and a combination of three rods are investigated using Ansoft HFSS software. In a first step, dielectric rods have been manufactured and measured at 77 GHz. In a second step, they are used as primary feed of the reflectarray. The corresponding shift of the phase center caused by the rods has been estimated in simulation and accounted for in the antenna arrangement. The radiation pattern measurements show a gain improvement of 2 dB.

This paper is dealing with the biomedical applications of active microwave imaging. As a result of extensive preliminary evaluations conducted by means of a 2.45-GHz planar camera, it has been proven that active microwave imaging is able to provide a very sensitive means of investigation in such applications. While technological problems have been conveniently solved, the main problem still remains to determine the most efficient way to process the measured data in order to get the best quality of the reconstructed images. Until now, diffraction tomography algorithms based on a spectral approach have been used. The main limitations of this approach and some attempts to reduce them are analyzed. A more prospective discussion allows to identify the most promising reconstruction techniques. Among them, iterative space-domain formulations appear to provide a suitable base for achieving quantitative imaging thanks to a convenient use of the available a priori information.

International audience; A 94 GHz folded Fresnel reflector (FFR) for helicopter collision avoidance Radar is presented. The antenna system consists of a primary source illuminating a semi-reflecting grid that reflects the primary source polarization toward the main reflector opposite the grid. The main reflector has two functions. It focuses the field in the desired direction and rotates the incident polarization by 90deg to enable it to pass through the grid and radiate. Specific patch elements having a C-shape have been designed for this purpose. In order to increase overall efficiency, the reflector combines 8 correcting zones in its center and 4 at the periphery. The reflector is manufactured using standard photolithographic techniques. The primary source consists of a metal waveguide covered with a small frequency selective surface (FSS) for matching purposes. The maximum measured gain is 36.5 dBi at 94 GHz. The maximum side lobe level is -18 dB. The return loss value does not exceed -25 dB. The frequency bandwidth -3 dB in gain and return loss is 10%. In-flight measurements were conducted demonstrating the ability to detect power lines at distances up to 680 m.

International audience; This paper describes a compact broadband (73-80 GHz) mm-Wave front-end used for FOD detection application. The design philosophy of our system is to have several low-profile, low-cost mm-Wave sensors placed along the runway. Tests were conducted on the small airport of Aix Les Milles (south of France). High sensitivity and simultaneous objects detection capabilities were shown. Even very small objects like nuts were seen. The extension of the actual detection range is needed in order to go from 110 m (in the most favourable case) to 500 m.This paper describes a compact broadband (73-80 GHz) mm-Wave front-end used for FOD detection application. The design philosophy of our system is to have several low-profile, low-cost mm-Wave sensors placed along the runway. Tests were conducted on the small airport of Aix Les Milles (south of France). High sensitivity and simultaneous objects detection capabilities were shown. Even very small objects like nuts were seen. The extension of the actual detection range is needed in order to go from 110 m (in the most favourable case) to 500 m.

International audience; The design of an offset reflectarray illuminated by an original primary source at 94 GHz was tested successfully. The antenna shows very low side lobe and cross-polarization levels. These results are of interest for multi-beam applications, when the system is fed by several sources. Simulations were made with a computer-model that gives, in less than 10 minutes on a standard PC, a good approximation of the radiation pattern in the H-plane. The problem of the specular reflection has still to be overcome as well in simulations as in the design. In order to solve it partially, the next step will be the realization of an offset feed with a main radiation in the specular direction.

The detection and localization of persons through obstacles is becoming a great stake in both civil and military fields. One of the most important applications is certainly sensing through walls which can be very useful in safety, peace-keeping and law enforcement operations. Radar systems are likely to provide an adequate answer to this kind of problem and various processing methods are nowadays studied and considered to reach the final solution. In this paper, we focus on ultra-wideband radar techniques applied to human sensing. In particular, we assume that we have an antenna array on reception. Many signal processing methods can be considered for target localization. We choose to focus on an emerging method in electromagnetic detection field, especially in a cluttered environment: time-reversal [1] adapted here to through-the-wall localization. In this work time reversal processing is applied to experimental data to demonstrate the localization of dielectric objects behind a 10 cm thick brick wall.

Folded printed Fresnel zone plate reflector is presented for helicopter collision avoidance radar at 94 GHz. The achievement of a folded structure, requires printed elements that perform a 180deg phase difference of the reflected phase between two orthogonal polarizations. For this purpose, C-shape patches were designed. A prototype of 130 mm diameter was made and measured. The first section describes the reflector design with a focus on the C-shape patches mode of operation. The second part shows the concept validation by the mean of antenna's radiation pattern measurements as well as in flight measurements of the antenna mounted on the detection radar.

International audience; A high gain Fresnel zone plate reflector is presented for helicopter collision avoidance radar at 94 GHz. The antenna system consists of a compact, airtightness and low return loss primary source illuminating a printed reflector with Fresnel plate zone phase correction. In order to increase the overall efficiency, the reflector combines 8 correcting zones in its center and 4 on the border. Reflected phase of over 360deg is achieved by means of circular ring or combined circular and ring patches. The reflector is fabricated using standard photolithographic techniques. The primary source consists of a small FSS made by a double slot array antenna pasted on the aperture of a standard WR-10 waveguide. Antenna measurements were conducted using a compact base arrangement. The antenna performs 37.8 dBi at the center frequency of 94 GHz with a maximum value of the return loss value not exceeding -25 dB. The frequency bandwidth at -3 dB in gain and return loss is of 9%

Rescue helicopters have to be versatile under any weather condition. By flying at low altitude they are facing targets, such as power lines, that may not be detected in the visual flight rules. In order to overcome this problem, a global system achieving an image fusion between a CCD, an infrared camera and a mm-Wave FMCW radar was developed.

This paper describes a 3 GHz experimental set-up for quasi real time tomography of biological media. Experiments on animal organs illustrate the main features of this imaging process.

A collision avoidance and warning system for civil helicopters in Japan has been developed. A real-time warning method was applied using an image fused from a coloured video, an IR sensor data and mm-wave radar measurements. This paper focuses on the FM-CW mm-wave radar sensor and the associated antennas, working at 94 GHz. Flight tests were conducted in order to detect power lines. Thanks to two different antennas, power line response was measured in vertical and horizontal polarizations. Maximum detection ranges are of 800 and 600m respectively. This variation comes from the antenna gain difference. Radar resolution is limited by the allocated bandwidth at 94 GHz which is 200 MHz. Comparisons were conducted on the ground with an integrated FM-CW radar working at 77 GHz and achieving 500 MHz bandwidth.

International audience; This paper presents some evidence of the effectiveness of adding edge preserving (EP) regularization to the conjugate radient (CG) method, in reconstructing the shape and permittivity profile of dielectric objects. Without any a priori information, our CG algorithm is also still efficient, and succeeded in reconstructing two mystery targets. As the two targets are now known, we hope we can greatly enhance the reconstruction quality by choosing better values for the calibration factors, and by applying our EP regularization to these data.

International audience; A new non-planar Vivaldi antenna is presented as a three-dimensional structure in the shape of a fleur-de-lis. This new balanced antenna is unique in its extremely flat S/sub 11/ response, minimizing phase distortion over a wide band from 2.2 to 21 GHz. The S/sub 11/ response of the new antenna is compared with the original planar Vivaldi antenna developed at the LEAT.

A new structure of a circularly polarized dielectric antenna fed by a single coaxial probe is proposed. The configuration includes four identical holes enclosed in a cylindrical resonator. The structure offers a bandwidth of 5% and a good purity of polarization. The effects of altering geometrical parameters on antenna behavior are presented. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 45: 367–369, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20825

International audience; A shape reconstruction method for electromagnetic tomography based on contour deformations by means of a level set method is proposed. The level set method adds quite valuable features to the inverse procedure such as natural regularization of the contours and automatic breaking and merging capability. The frequency hopping technique turns out to be a key point of the inverse scattering procedure. The numerical results clearly indicate that the use of this inversion algorithm yields to accurate reconstructions of one or several objects from one initial guess object, even with noise-contaminated data and limited coverage of the fields.

The fast Fourier transform conjugate gradient method solves numerically the electric field integral equation, using the method of moments with pulse basis function and point matching, but substantial errors are found in this method for the 2-D TE case. In the present work, the authors analyze the source of errors in these approximations and show that the modified method empirically proposed by D.T. Borup, D.M. Sullivan, and O.P. Ghandi (IEEE Trans. Microwave Theory Tech., vol.MTT-35, p.383-95, Apr.1987) would not have been necessary if correct terms in the integral equation were used. With this aim, the authors propose a new integral formulation using generalized functions and compare it with two previous formulations, that of S.C. Hill, C.H. DAmey, and D.A. Christensen Radio Sci., vol.18, p.328-36, May-June 1983 and D.E. Livesay and K.M. Chen (IEEE Trans. Microwave Theory Tech., vol.MMT-22, p.1273-80, 1974). For all the numerical methods discussed, the conjugate gradient technique is used to solve the linear system, and the convolution products are computed by means of a Fourier transform. The results are of interest in connection with refining numerical methods to support biomedical applications (e.g. microwave imaging and hypothermia treatment). >

International audience; A very accurate inverse scattering method for reconstructing the contours of perfectly conducting cylinders of arbitrary crosssection illuminated by electromagnetic waves under TM polarization with time-harmonic dependence is presented. No assumption is made on the shapes of the contours nor on their number. Inversion strategy consists in computing a special deformation velocity, defined on the contours of the objects, and allowing to decrease a cost function at each iteration. Level set methods, used in as diverse fields as fluid dynamics, image processing and crystal growth, are used to perform the evolution of the contours. These methods allow to handle automatically topological changes by using a Eulerian point of view built on a level set representation of the contours. Hence, several objects can be retrieved from one single initial contour. Moreover, contours regularization is easily performed by adding a curvature term to the velocity. The inverse scattering method is based on a very accurate forward scattering algorithm characterized by the use of well-behaved pseudo-currents which are developed in Fourier series along the contours. The frequency hopping technique turns out to play a key role in the inversion process. The method is proved to be flexible, allowing to reconstruct accurately complex and multiple shape contours from one single initial guess. The deformation velocity is even able to retrieve very sharp corners and is quite robust with respect to high noise levels.Sample our Physical Sciences journals, sign in here to start your FREE access for 14 days Journal of Electromagnetic Waves and Applications: Announcing invited reviews...Click to read reviews for FREE! Journal of Information Display Open access full details

International audience; This paper presents microwave tomographic reconstructions of the complex permittivity of lossy dielectric objects immersed in water from experimental multiview near-field data obtained with a 2.35-GHz planar active microwave camera. An iterative reconstruction algorithm based on the Levenberg-Marquardt method was used to solve the nonlinear matrix equation which results when applying a moment method to the electric field integral representation. The effects of uncertainties in experimental parameters such as the exterior medium complex permittivity the imaging system geometry and the incident field at the object location are illustrated by means of reconstructions from synthetic data. It appears that the uncertainties in the incident field have the strongest impact on the reconstructions. A receiver calibration procedure has been implemented and some ways: to access to the incident field at the object location have been assessed.

International audience; A stacked dielectric resonator antenna (DRA), composed of an annular ring excited by a coaxial probe and two cylindrical dielectric resonators (CDRs), is studied experimentally for three‐frequency band operation. A maximum frequency ratio of 1.75 is achieved between higher and lower frequencies, and quite similar radiation patterns are obtained at two of the separate operating frequencies. The middle frequency band offers different radiating properties. A minimum 10 dB impedance bandwidth of 4.9% is performed. The return loss, radiation patterns, and antenna gain of this configuration are reported. © 1998 John Wiley & Sons, Inc. Microwave Opt Technol Lett 18: 303–306, 1998.

In this paper, we address the problem of Through The Wall (TTW) detection with the emerging radar concept that is the Multiple-Input Multiple-Output (MIMO) radar. At first, near field and through the wall propagation effects on electromagnetic waves are adressed then a MIMO frequency signal model is given and the advantages of a MIMO scheme for the complex task of TTW detection is discussed. Then image formation with beamforming processing is derived. Finally, the proposed imaging method is implemented on numerical signals obtained by FDTD computations considering through cinder blocks walls propagation. The obtained images for a scenario with one or two targets are presented. Then the experimental setup is exposed and the realised MIMO radar prototype is described. Finally, experimental results of radar imaging through a cinder block wall are shown.

This paper talks about a method of conception and design constraints on mm-wave reflectarrays. The developed tool allows us to plan quickly the behavior of large reflectarray (several tens of wavelength) according to parameters as illumination law or manufacturing tolerance with good agreement with measurements. An ultra-low side-lobe reflectarrays of 130 mm diameter is designed. The structure combines the advantages of a reflectarray with an offset source and those of a specific primary source, exhibiting a prolate radiation pattern, having very low side lobe levels. The maximum gain obtained at 94 GHz is 40 dBi and the side-lobe level is inferior to -28 dB. Finally, a simultaneous multi-lobe antenna is designed at 94 GHz. The primary source is an open-ended waveguide and the phase profile is calculated by the program introduced in the first part. In this case, the four main lobes are placed in the same plane and for equal to -30, -10, 10, 30°. This reflectarray can be used for actual and future generations of automotive radar. The first obtained results are encouraging and show the validity of the concept. Solution retained here is a low-cost solution. The proposed structures are developed on a single layer substrate and fabricated using standard photolithographic techniques. The aim of this article is to show that we can obtain interesting results with relatively simple and low-cost solutions, but also to show the limits of these type of solutions.

This paper is devoted to a new imaging technique for the Non-Destructive Testing (NDT) of civil engineering structures such as bridges. This technique uses microwave radiation to interrogate the concrete medium in a reflection mode configuration. The backscattered electromagnetic field, generated by the presence of the rebars, is measured with a linear sensor probe array and processed numerically in order to provide tomographic images of the volume under investigation. A compact prototype of a so-called Microwave Camera operating in the microwave X-band region between 7-13 GHz with frequency diversity is presented. Computer simulations for theoretical performance limit study as well as experimental performance, evaluation of the prototype have been conducted on reinforced concrete slabs with practical configurations and on a bridge beam. The performance has been compared with that of magnetic metal detectors which are available on the market.

A comparative study at 2.45 GHz concerning both measurement and reconstruction parameters for planar and cylindrical configurations is presented. For the sake of comparison, a numerical model consisting of two nonconcentric cylinders is considered and reconstructed using both geometries from simulated experimental data. The scattered fields and reconstructed images permit extraction of very useful information about dynamic range, sensitivity, resolution, and quantitative image accuracy for the choice of the configuration in a particular application. Both geometries can measure forward and backward scattered fields. The backscattering measurement improves the image resolution and reconstruction in lossy mediums, but, on the other hand, has several dynamic range difficulties. This tradeoff between forward only and forward-backward field measurement is analyzed. As differential temperature imaging is a weakly scattering problem, Born approximation algorithms can be used. The simplicity of Born reconstruction algorithms and the use of FFT make them very attractive for real-time biomedical imaging systems.

This paper deals with the improvement of the quality of images obtained at 2.45 GHz, by means of a planar microwave camera for biomedical applications. The results provided by standard spectral techniques, classically used for diffraction tomography reconstructions, are shown to be significantly improved by different processing techniques. The particular case of human hand imaging is presented for its clinical interest in the early diagnostic of fibrosis after accidental irradiations.

Recent technological advances for microwave multiport sensors lead us to look for efficient wavefront processing techniques in order to improve image quality, in terms of spatial resolution and contrast. This paper reviews some of these techniques which can be used for Non-Destructive Testing purposes. Mutual advantages and limitations are analysed.

The source of scattering problems found when computing the internal field distribution in the transverse electric (TE) polarization case for 2-D objects is analyzed. It is shown that a modification introduced in a previous study is not required if an appropriate integral formulation is used. Such a formulation is proposed using generalized functions, and it is compared numerically to several other formulations for inhomogeneous dissipative cylinders whose electromagnetic parameters are close to those of biological tissues. The solution associated with this integral formulation appears to behave better than the others, in comparison with the exact analytical solutions. >

This paper concerns an iterative method for solving an inverse electromagnetic scattering problem: the quantitative reconstruction of complex permittivity distribution of inhomogeneous objects. During the last decade, intensive research and interest have been focussed on reconstruction algorithms based on the so-called Diffraction Tomography with applications in microwaves or ultrasound [1–16]. The main motivations for using such approaches are to obtain explicit formulas for solving the imaging problem, to take advantage of existing numerical algorithms (Fast Fourier Transform) and to implement the algorithms on PC’s or minicomputers for imaging system purposes (planar microwave camera [5], experiments with ultrasounds and microwaves [11][13][14][16], cylindrical microwave system [15]). However, Diffraction Tomography is subjected to various limitations which include artefacts due to diffraction effects in strongly inhomogeneous media [7][10][16][17][18].The final objective of microwave imagery is to determine the complex permittivity profile (permittivity and conductivity profiles) of the object under investigation. An increasing number of papers [17–25] have been devoted to a such non-linear inverse problem. Different solutions based on Moment Methods [19–25] have been explored, but, convergence depends on contrasting objects. Furthermore, stability is very sensitive to the observation point locations and measurement accuracy (due to the ill-conditioning of the matrix which has to be inverted). Stability and sensivity are why the use of an iterative scheme is important: effects of ill-conditioning can be significantly reduced by enforcing the convergence with “a priori” information (object external shape, upper and lower bounds of complex permittivity, presence of different media,…). Concerning the uniqueness of object reconstruction, it has been proved [24] that if the background medium is dissipative, then the inverse scattering problem has a unique solution.

An iterative algorithm based on simulated annealing, for the reconstruction of the permittivity and conductivity distributions of a section of a strongly inhomogeneous cylindrical object, is presented. It has been tested, using simulated noise-free data, for some small objects. The effect of simulated annealing is compared to a conventional iterative method.

This paper is devoted to a new imagining technique for the Non-Destructive Testing (NDT) of civil engineering structures such as bridges. This technique uses microwave radiation to investigate the concrete medium in a reflection mode configuration. The backscattered electromagnetic field, generated by the presence of the rebars, is measured with a linear sensor probe array and processed numerically in order to provide tomographic images of the volume under investigation. A prototype of a so-called Microwave Camera operating in the microwave X-band region between 7–13 GHz has been especially designed and constructed for assessing the potentials of this technique. Frequency diversity in the X-band is used to obtain a spatial resolution in the images of less than one centimeter for the localization and diameter evaluation of rebars. Performance evaluation of the prototype has been conducted on reinforced concrete slabs with practical configurations and on a bridge beam. The performance has been compared with that of magnetic metal detectors which are available on the market.

International audience; A double slot array antenna pasted on the aperture of a standard WR-10 waveguide is presented. Its compactness and airtightness make it suitable for serving as a primary source for reflector antennas. Compared to a standard WR-10 open-ended waveguide, it acts as a small FSS to provide up to 12 dB return loss enhancement within 9% bandwidth centred on 94 GHz, whereas radiation pattern and gain are similar. Good agreement is found between measured and predicted characteristics between 90 and 100 GHz. A return loss improvement is of particular interest while considering an antenna system with short focal length.

A W-band high gain lens antenna has been realised and measured. A hyperbolic lens made in ECCOSTOCK 0005 is associated to an optimised modified circular horn related to a circular-to-rectangular waveguide transition in order to fit the WR-10 standard waveguide. The antenna provides more than 30 dBi gain between 75 and 110 GHz. It is competitive in several fields of applications: first, obstacle detection radar application (at 77 or 94 GHz), secondly metrology, for example, in order to measure radar cross-sections over the whole W-band with a single antenna.

International audience; The reconstruct of the complex permittivity profile of lossy dielectric objects from measured far-lied data is considered, with application to perfectly conducting (PEC) objects. From an integral representation of the electric field (EFIE), and applying a moment-method solution, an iterative-reconstruction algorithm based on a conjugate-gradient method, is derived. In order to start the iterative procedure with an initial guess, a back-propagation scheme is used. For testing the algorithm on real, measured data, the reconstruction of two PEC (cylinder and strip) objects is presented.

The present paper considers the application of the Newton- Kantorovich and modified-gradient methods to the Ipswich data. The object is assumed to be an inhomogeneous lossy dielectric cylinder of arbitrary cross section. Both inverse-scattering methods are based on electric-field integral representations. The Newton- Kantorovich technique builds up the solution by solving successively the forward problem and a linear inverse problem. This method needs regularization, and we use either the identity operator or a gradient operator for regularization. The modified-gradient method is iterative, as is the Newton algorithm, but does not involve a linearization at each step of the nonlinear inverse problem. Results of inversions with both methods, on two known impenetrable targets, are discussed.

Singular integral equations arise frequently in electromagnetic and acoustic theory. We present here a numerical technique for solving integral equations which are meaningful in the sense of Cauchy principal value or Hadamard finite parts by a projection method in Hilbert spaces. Application to the radiation problem from a flanged plane waveguide is given.

A rigorous solution based on an integral equation to investigate the propagation in an inhomogeneous slab of arbitratry index profile is given.

We present an exact numerical solution based on a vector integral equation to investigate the diffused channel waveguide. Various examples are given and compared with other numerical and approximate methods. An approximate numerical solution is also given using the effective index method and the integral equation solution for the inhomogeneous slab.