Fast electromagnetic analysis of large objects involving planar layered media : application to antenna arrays and metasurfaces

The constant evolution of wireless technologies has favoured the development of antenna systems. The increasingly restrictive market requirements are pushing towards the development of larger and more complex antenna arrays. This trend calls for fast design procedures which require the efficient and accurate characterization of antennas. Although analytical thinking allows the determination of initial rules of thumb, recent and future designs are almost impossible to analytically characterize and a crucial role is played by computational electromagnetics (CEM). CEM combines innovative numerical methods and computational resources to enable the fast validation of new designs and their optimization under the constraints imposed by the designated applications. Although CEM has come a long way since its creation, many advanced numerical methods have been developed under simplifying hypotheses such as the regularity of antenna arrays, the infinite ground plane assumption, canonical shapes of (parts of) the antennas, or ideal representations of the feeding structures. While these hypotheses lead to efficient numerical methods, they represent a setback when confronted to the constraints encountered in industry. This is why this thesis aims to contribute to the advance in CEM by developing numerical methods capable of effectively simulating electrically large arbitrarily-shaped structures while accounting for practical constraints that have been often neglected before. Doing so, numerical techniques are developed for two classes of problems involving layered media. The first class concerns the simulation of large irregular antenna arrays on a finite ground plane and the second class concerns the simulation of arbitrarily-shaped metasurface antennas. The first part of this thesis is directed towards the analysis of large irregular antenna arrays on a finite ground plane devoted but not limited to radio astronomy applications. The resolution of new radio telescopes targeting unprecedented dynamic range can be altered if effects such as scattering by finite ground planes are not properly included. In this framework, an advanced Method of Moments (MoM) based technique is presented to simulate arrays on a finite ground plane itself lying on a layered medium. In particular, the research leads to a new formulation of the electric field radiated by the antenna on the ground plane, expressed as a finite series of Hankel functions and associated Anger-Weber functions. This new formulation allows the fast evaluation of the interactions between the antennas and the finite ground plane. The second part of this thesis is devoted to the fast simulation of large arbitrarily-shaped metasurface (MTS) antennas. MTS antennas are usually realized as a subwavelength arrangement of printed patches on a grounded dielectric layer. This metallic grid creates periodically modulated boundary conditions that couples with the surface wave launched by the feeder, which allows the structure to radiate by leaky waves. MTS antennas are currently receiving considerable interest owing to the fact that they represent a promising technology. Modulated MTS antennas represent a low cost, low-profile and easy-to-feed class of antennas. They form a promising alternative to phased array technology which, in spite of its tremendous capabilities, represents a bulky and high-consumption approach. Nowadays, efficient methods for the simulation of MTS antennas exist. However, these methods are restrained to MTS with a canonical shape (e.g. circular, elliptical, etc) and usually use a vertical elementary dipole to feed the antenna. In this thesis, an efficient FFT-based method is developed to simulate arbitrarily-shaped, possibly cascaded MTS antennas. This method is then combined with models representing the fine geometry of the feeder which allows the numerical evaluation of the MTS input impedance. Finally, an optimization algorithm based on this technique is presented to maximize the efficiency of MTS antennas.(FSA - Sciences de l'ingénieur) -- UCL, 202

Radiation Pattern of the SKALA antenna in the vicinity of a finite ground plane

One of the challenges regarding the SKA radio-telescope is the determination of the radiation pattern of the low frequency antenna in presence of a finite ground plane. In this Master Thesis, a methodology based on a spectral approach is built to calculate relatively fast the current induced in a finite ground plane placed under a given source. The field radiated by the source is estimated thanks to a method based on the decomposition into inhomogeneous plane waves and the current induced in the ground plane is calculated by solving a Method of Moments linear system of equations. The method is applied to the low frequency antenna of the SKA for different frequencies and ground plane diameters. The results are validated against the ones obtained with the EM simulation software FEKO.Master [120] : ingénieur civil électricien, Université catholique de Louvain, 201

Efficient analysis of planar, arbitrarily shaped, and (Bi)-anisotropic metasurface antennas

An efficient method of moments (MoM) scheme is presented for the analysis of planar, possibly cascaded meta- surfaces (MTSs) implementing high-impedance surfaces. The MTS can be designed on an arbitrarily shaped domain and is accounted for as a set of cascaded electric sheet impedances. In the proposed method, the shaped MTS is included in a larger rectangular domain meshed with rooftop basis functions, resulting in a Toeplitz–block Toeplitz structure for the sub- strate impedance matrix, which enables fast Fourier transform (FFT)-based acceleration of matrix–vector products. The basis functions lying in the rectangular domain but outside the MTS are disabled by including zeros in the impedance matrix. The obtained linear system of equations is well conditioned, does not require any specific near-field treatment, and can be solved itera- tively using the generalized minimal residual (GMRES) method. It has been demonstrated that the algorithm is able to handle efficiently any MTS antenna shape in single-layer or multilayer configuration with almost linear complexity. It is shown that the high-impedance sheets improve the convergence rate. MTSs with more than 40 wavelengths size, meshed with more than 1 million basis functions, can be analyzed on a conventional computer in less than 15 min. A very good agreement is shown through comparison with results from other software packages

Metasurface Antennas Design: Full-Wave Feeder Modeling and Far-Field Optimization

This article addresses the optimization of the radiation pattern of surface-wave (SW)-based metasurface (MTS) antennas. Those antennas are considered a promising alternative to parabolic reflectors and phased arrays due to their extremely low profile and their ability to provide high gain, shaped beams and multibeams. However, pattern synthesis with MTS antennas is very challenging because of the single active control point and the need to control surface and leaky waves through the MTS. An accurate optimization of the radiation pattern, along with the sidelobe level requires full-wave modeling of the feeding structure, including its coupling with the MTS. MTS synthesis methods existing in the literature usually approximate the feeder model, and neglect its coupling with the MTS. Such approximation may lead to more than 1 dB error in the predicted antenna directivity. This article presents a technique for optimization of the far-field pattern, built on a Method of Moments (MoM) analysis tool in which the MTS coupling with the feeder, a coax probe, is fully considered. The MTS is modeled as an arbitrarily shaped, spatially modulated electric sheet impedance in a layered medium. At each optimization iteration, the complexity of the underlying analysis is O(N logN) owing to the use of a fast Fourier transforms (FFT)-based acceleration. The effectiveness of the method is demonstrated through the optimization of MTSs radiating a pencil beam and a conical beam with orbital angular momentum (OAM)

Simulation of shaped metasurface antennas including the feeder coupling

An effective Method of Moment (MoM) tool able to rapidly and accurately analyze arbitrarily shaped metasurface (MTS) antennas is provided. The MTS is assumed to be fed by a coax probe as is usually the case in practice. The feed as well as the MTS are meshed with local basis functions. The calculation of the interactions between the MTS basis functions, which are the dominant unknowns, is accelerated with the FFT. The surface current is then computed iteratively using the GMRES algorithm. Once the currents on the MTS and on the feed are obtained, the efficiency of the antenna can be derived. The method is validated with an in-house numerical tool developed for the particular case of circular MTSs. An excellent comparison is observe

Integral equations for metasurface design

Among the different ways to solve Maxwell’s equations, integral-equation approaches are probably offering the most physical insight. They allow the prediction of surface waves and their transformation into leaky waves. We will explain how integral equations can be turned into a direct design tool, beyond traditional field analysis. This allows the design of metasurfaces with prescribed radiation patterns, as well as the creation of multi-beam metasurfaces. Such a perspective on numerical methods may also serve other fields of engineering

Embedded patterns and extended array admittance matrix

Sparse arrays of antennas can sometimes be modelled without accounting for the mutual coupling. In that case, the array radiation pattern can be expressed as the product of two factors: the isolated antenna radiation pattern and the array factor. Using the array impedance matrix, this formalism can be extended to account for the mutual coupling when the array is made of single-mode antennas. In this paper, we propose an extension of that formalism to the case of multimode antennas. We show that, contrary to the single-mode case, the array impedance matrix and isolated element patterns are not sufficient to rigorously account for mutual coupling. Building on these concepts, we propose a new quantity, the extended array admittance matrix. Combined with a modal decomposition of the currents on the antennas, it can be used to rigorously account for mutual coupling between multi-mode antennas in an array. The proposed formalism is illustrated by numerical examples

Valorisation des biomasses agricoles dans une démarche d’économie circulaire par la mise en place du co-compostage a la ferme d’effluent d’élevage et de broyat de déchets verts

Le co-compostage des effluents d’élevage et du broyat de déchets verts peut être réalisé à la ferme avec le matériel couramment disponible sur l’exploitation (tracteur, godet, tonne à lisier). Dans le cadre du projet CONVER, les cinq essais réalisés en ferme ont permis d’obtenir les résultats suivants. Le temps de travail cumulé pour un andain varie entre 1 à 3 min/m3 de matières. Les teneurs moyennes en pourcentage de matières brutes de N-P-K sont de 1,5-1,0-1,5, pour les co-composts à base de fumier de volaille et de, 0,8-0,5-0,8, pour le co-compost à base de lisier de porc. Les teneurs en matière sèche et en matière organique sont comprises, respectivement, entre 40 et 60 % et entre 30 et 50 %, dans le cas des co-composts à base de fumier de volaille. Elles sont respectivement de 43% et 27%, pour le co-compost à base de lisier de porc. L’ensemble des co-composts obtenus ont tous été hygiénisés et sont conformes à la norme amendement organique, NFU 44-051. Les co-composts ont été testés comme produit fertilisant sur culture de choux et sur prairies de fauche. Dans le premier cas, la fertilisation à base de co-compost a permis d’atteindre le rendement de 40 à 70 t/ha, sur deux des quatre parcelles d’essai. Et dans le second cas, la fertilisation à base de co-compost, complétée ou non par un engrais minéral a permis un gain moyen de rendement compris entre 65 et 191 %, par rapport au rendement moyen du témoin

Transition agroécologique du territoire de Saint-Joseph (La Réunion) - Synthèse des ateliers participatifs

Le projet CONVER, co-CONception d’un scenario de Valorisation des biomasses dans une démarche d’Economie circulaiRe à la Réunion, est un projet de recherche participative qui a pour objectif (i) de concevoir un scenario de valorisation des biomasses (déchets verts urbains et effluents d’élevage), afin de fournir des matières organiques pour les agriculteurs et éleveurs, et (ii) d’accompagner la transition agroécologique sur le territoire de Saint-Joseph, où les enjeux agricoles, urbains et environnementaux font que les solutions au développement du territoire sont complexes. Cette recherche, s’inscrit dans une démarche d’économie circulaire, via le recyclage des déchets et la valorisation efficiente des ressources locales. Il vise in fine, à réduire la dépendance du territoire aux importations d’intrants chimiques et organiques et à offrir les composants organiques (amendements et fertilisants) nécessaires à la mise en œuvre d’une transition agroécologique. Ce rapport rassemble les résultats du volet 2 du projet qui visait à concevoir un scenario de transition agroécologique avec l’ensemble des parties prenantes du projet et des acteurs du territoire