Broadband antenna arrays have become increasingly popular for various imaging applications, such as radio telescopes and radar, where high sensitivity and resolution are required. High sensitivity requires the development of large scale broadband arrays capable of imaging distant sources at many different wavelengths, in addition to overcoming noise and jamming signals. The design of large scale broadband antenna arrays requires large number antennas, increasing the cost and complexity of the overall system. Moreover, noise sources often vary, depending on their wavelengths and angular locations. This increases the overall design complexity particularly for broadband applications where the performance depends not only on the required bandwidth, but also on the frequency band.This thesis provides a study of broadband antenna array systems for large scale applications. The study investigates different tradeoffs associated with designing such systems and drives a novel design approach to optimize both their cost and performance for a wide range of applications. In addition, the thesis includes measurements of a suitable array to validate the computational predictions. Moreover, the thesis also demonstrates how this study can be utilized to optimize a broadband antenna array system suitable for a low frequency radio telescope.

Sensor arrays play an instrumental role in a variety of applications, including radar, sonar, radio astronomy, and wireless communications. Employing an array of sensors permits direction-of-arrival (DOA) estimation, interference suppression, and imaging of spatial distributions of sources or scatterers. Linear and planar array geometries can have sensors with uniform or non-uniform spacings. Non-uniform arrays require much fewer sensors to achieve comparable performance to uniform arrays in terms of the spatial resolution and the number of resolvable sources or scatterers. This dissertation proposes novel signal processing methods for narrowband passive (receive-only) sensing and imaging. The focus is on source estimation using linear and planar passive arrays with uniform and non-uniform geometries. Algorithm development for the non-uniform arrays is facilitated by a virtual array structure, called the difference coarray, which comprises pairwise differences of physical sensor positions. The difference coarray naturally arises from the passive sensing signal model. High-resolution DOA estimation techniques, such as the subspace-based methods, are computationally expensive, especially for arrays that span large apertures. Further, performance of such methods deteriorates for coherent sources. We propose efficient and effective Fourier-based iterative techniques for DOA estimation of coherent and uncorrelated sources using linear and planar arrays with both uniform and non-uniform geometries. The considered non-uniform arrays include those with uniform and non-uniform difference coarrays. The proposed DOA estimation techniques build on the iterative interpolated beamformer, which employs an estimate-and-subtract strategy to successively extract the sources and refines the estimates via an interpolation and spectral leakage subtraction scheme. We enable iterative beamforming in the coarray domain for linear and rectangular arrays, specifically compensating for non-uniformity of difference coarrays to yield asymptotically unbiased DOA estimates. We also design the iterative interpolated beamformer for oversampled and undersampled uniform circular arrays under the manifold separation framework, which permits the application of DOA estimation techniques that were developed for uniform linear arrays to arbitrary array geometries, such as circular arrays. The proposed iterative beamforming techniques not only estimate the source DOAs, but also provide source power/amplitude estimates. As such, these Fourier-based methods are applicable to narrowband passive imaging systems for providing an accurate estimate of the distribution of source intensity or amplitude as a function of angle. / Electrical and Computer Engineering

Aujourd'hui l'utilisation de l'échographie 3D en cardiologie est limitée car l'imagerie de la totalité du myocarde sur un cycle cardiaque, sans apnée, reste un défi technologique. Une solution consiste à réduire le nombre de capteurs dans les sondes échographiques matricielles afin d'alléger le procédé d'acquisition: ces sondes sont dites parcimonieuses. Le but de cette thèse est de proposer les meilleures dispositions d'un nombre réduit de capteurs piézo-électriques répartis sur la surface active de la sonde afin d'optimiser leur capacité à produire des images homogènes en termes de contraste et résolution dans tout le volume d'intérêt. Ce travail présente l'intégration de simulations acoustiques réalistes élaborées au sein d'un processus d'optimisation stochastique (algorithme de recuit simulé). La structure proposée pour le design des sondes parcimonieuse est suffisamment générale pour être appliquée aux sondes régulières (éléments actifs disposés selon une grille) et non-régulières (positionnement arbitraire des éléments actifs). L'introduction d'une fonction d'énergie innovante permet de sculpter en 3D le diagramme optimal de rayonnement de la sonde. Les résultats de sondes optimisées obtenues possèdent 128, 192 ou 256 éléments pour favoriser leur compatibilité avec les échographes commercialisés à ce jour, ce qui permettrait de déployer l'échographie 3D à moindre coût et à très large échelle / Today, the use of 3D ultrasound imaging in cardiology is limited because imaging the entire myocardium on a single heartbeat, without apnea, remains a technological challenge. A solution consists in reducing the number of active elements in the 2D ultrasound probes to lighten the acquisition process: this approach leads to sparse arrays. The aim of this thesis is to propose the best configuration of a given number of active elements distributed on the probe active surface in order to maximize their ability to produce images with homogeneous contrast and resolution over the entire volume of interest. This work presents the integration of realistic acoustic simulations performed in a stochastic optimization process (simulated annealing algorithm). The proposed sparse array design framework is general enough to be applied on both on-grid (active elements located on a regular grid) and non-grid (arbitrary positioning of the active elements) arrays. The introduction of an innovative energy function sculpts the optimal 3D beam pattern radiated by the array. The obtained optimized results have 128, 192 or 256 active elements to help their compatibility with currently commercialized ultrasound scanners, potentially allowing a large scale development of 3D ultrasound imaging with low cost systems

Les travaux de cette thèse s’intéressent à un nouveau concept d’antenne reconfigurable offrant un bon compromis entre performances, complexité et coût. Ce concept, qualifié d’hybride, vise à combiner les avantages des réseaux d’antennes lacunaires et des antennes à éléments parasites. Cette hybridation est une alternative à la complexité des réseaux d’antennes conventionnels pour répondre aux exigences d’une architecture modulaire, générique et reconfigurable. L’intérêt majeur de ce concept est de proposer une architecture d’antenne permettant de réduire la complexité du circuit de formation des faisceaux (par la réduction du nombre d’éléments rayonnants à alimenter) tout en adressant les problématiques d’adaptation (TOS actif) des éléments excités. Ceci est permis grâce à la présence d’éléments parasites qui permettent de gérer la diffusion des couplages sur l’antenne. Cette thèse décrit le principe du concept hybride et propose une évaluation de ses potentialités. Par la suite, une définition des éléments à mettre en œuvre pour réaliser une preuve de concept est effectuée, en mettant l’accent sur l’importance de la caractérisation expérimentale. Les performances d’un prototype d’antenne hybride reconfigurable sont ensuite présentées afin de valider les développements et conclure sur cette solution innovante. / The work of this thesis aims to investigate a new concept of reconfigurable antenna allowing a good trade-off between performances, complexity and cost. This concept is called ‘hybrid’ because it is based on the capabilities of thinned arrays and parasitic element antennas. It is an alternative to classical antenna arrays and their complexity. The proposed concept has a modular architecture, and a good versatility for reconfigurable beams. The main advantage of this hybrid antenna is the simplicity of its beam formation network (BFN) which requires only a few number of excited elements. The antenna uses parasitic elements to manage the effects of couplings between the electromagnetic access. The problematic of active VSWR is also solved at the antenna level, avoiding the use of additional components in the BFN. This work details the principle of the reconfigurable hybrid antenna concept. The potentialities are evaluated. The elements required to realize a proof of concept are then defined, using a dedicated experimental setup. A prototype is manufactured and the performances have been checked to validate this innovative concept.