Dans le cadre de cette thèse, on s'intéresse dans un premier temps à des matrices d'alimentation de type passif connues qui permettent de produire des faisceaux orthogonaux, et notamment à la matrice de Butler. On s'aperçoit qu'il n'existe qu'une méthode itérative permettant de déterminer les paramètres S d'une matrice de Butler symétrique. C'est pourquoi, on cherche à déterminer de manière analytique la matrice [S] d'une matrice de Butler symétrique à N = 2^n entrées et N sorties. On établit des formules de récurrence issues de l'étude de ce type de matrices pour plusieurs tailles. Des formules analytiques en sont déduites qui sont valables quelle que soit la valeur de N. On poursuit l'étude des matrices d'alimentation de réseau d'antennes en s'intéressant à la source focale d'une antenne multifaisceaux devant réflecteur basée sur une géométrie originale constituée de coupleurs directionnels tridimensionnels entrelacés. Cette structure est simulée. Ses nombreux paramètres sont optimisés afin d'aboutir à une solution répondant au cahier des charges. Une maquette est réalisée et testée. Les résultats obtenus sont prometteurs. Au final, cette source possède l'avantage d'avoir un fort niveau de réutilisation de ses éléments rayonnants et donc de limiter l'encombrement du système global qui est souvent un point critique, dans les satellites notamment. Pour finir, on s'intéresse à une structure dont le but est d'avoir une station au sol capable de suivre une cible sans dépointage. La poursuite en azimut est assurée par une partie mécanique, de type joint tournant ; celle en élévation par un module électronique. Le système se doit d'être compact, fiable, et de limiter les pertes ainsi que les coûts. Des compromis sont donc à effectuer. La partie rayonnante est réalisée en guide, la partie alimentation en technologie planaire. Une solution est proposée afin de faire la transition entre ces deux technologies : le circuit de répartition est directement relié à l'excitation des éléments rayonnants en mettant ces deux parties sur une même feuille de substrat. Ainsi, moins de câbles et de connecteurs sont nécessaires, ce qui diminue l'encombrement et les coûts. / In this PhD thesis, some feed networks are studied. First, a N x N symmetric Butler matrix is considered. Analytical formulas allowing constructing its [S] matrix are found and demonstrated. Second, a multibeam antenna focal array based on 3-D directional couplers is considered. This device has a high level of re-use of its radiating elements. Therefore, its global size is reduced. Its conception is explained. Measurement results are exposed. Last, a mechanic / electronic device is studied. It is used for tracking. It is a complex device with several parts. The fact that the conception of each part depends on each other is highlighted. Compromises and choices need to be made.

Made available in DSpace on 2014-12-17T14:55:43Z (GMT). No. of bitstreams: 1 ValdezAAFi_DISSERT.pdf: 1620850 bytes, checksum: c1208b8ca13742d0d9cd3ac88c864f60 (MD5) Previous issue date: 2010-06-14 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / This work aims to present how the application of fractal geometry to the elements of a log-periodic array can become a good alternative when one wants to reduce the size of the array. Two types of log-periodic arrays were proposed: one with fed by microstrip line and other fed by electromagnetic coupling. To the elements of these arrays were applied fractal Koch contours, at two levels. In order to validate the results obtained some prototypes were built, which were measured on a vector network analyzer and simulated in a software, for comparison. The results presented reductions of 60% in the total area of the arrays, for both types. By analyzing the graphs of return loss, it was observed that the application of fractal contours made different resonant frequencies appear in the arrays. Furthermore, a good agreement was observed between simulated and measured results. The array with feeding by electromagnetic coupling presented, after application of fractal contours, radiation pattern with more smooth forms than the array with feeding by microstrip line / Este trabalho tem como objetivo apresentar como a aplica??o de contornos fractais aos elementos de um arranjo log-peri?dico se torna uma alternativa bastante interessante quando se deseja reduzir as dimens?es do arranjo. Foram propostos dois tipos de arranjos log-peri?dicos: um com alimenta??o por linha de microfita e outro com alimenta??o por acoplamento eletromagn?tico. Aos elementos desses arranjos foram aplicados contornos fractais de Koch, em dois n?veis. Com a finalidade de validar os resultados obtidos foram constru?dos prot?tipos, que foram caracterizados experimentalmente em um analisador de rede vetorial e simulados em software, para compara??o. Os resultados mostraram redu??es de 60% nas dimens?es dos arranjos, para ambos os tipos. Atrav?s da an?lise dos gr?ficos da perda de retorno, p?de-se observar que a aplica??o dos contornos fractais fez com que aparecessem diferentes frequ?ncias de resson?ncia nos arranjos. Al?m disso, observa-se uma boa concord?ncia entre os resultados medidos e simulados. O arranjo com alimenta??o por acoplamento eletromagn?tico apresentou, ap?s aplica??o dos contornos fractais, menores valores de diretividade do que o arranjo com alimenta??o por linha de microfita

Multi-User Multi-Input Multi-Output (MU-MIMO) systems are considered to be the sustainable technologies of the current and future of the upcoming wireless and mobile networks generations. The perspectives of these technologies under several scenarios is the focus of the present thesis. The initial system model covers the MU-MIMO, especially in the massive form that is considered to be the promising ideas and pillars of the 5G network. It is observed that the optimal number of users should be served in the time-frequency resource even though the maximum limitation of the MU-MIMO is governed by the total receiving antennas (K) is less than or equal to the base station antennas (M). The system capacity of the massive MIMO (mMIMO) under perfect channel state information (CSI) of uncorrelated channel is investigated and studied. Two types of precoders were applied, one is directly based on channel inversion, and the other uses the Eigen decomposition that is derived subject to the signal to a leakage maximization problem. The two precoders show a degree of equivalency under certain assumptions for the number of antennas at the user end. The convex optimization of multi-antenna networks to achieve the design model of optimum beamformer (BF) based on the uniform linear array (ULA) is studied. The ULA is selected for its simplicity to analyse many scenarios and its importance to match the future network applied millimetre wave (mmWave) spectrum. The maximum beams generated by the ULA are explored in terms of several physical system parameters. The duality between the MU-MIMO and ULA and how they are related based on beamformer operation are detailed and discussed. Finally, two approaches for overloaded systems are presented when the availability of massive array that is not guaranteed due to physical restrictions since the existence of a large number of devices will result in breaking the dimension rule (i.e., K ≤ M). As a solution, a low complexity users selection algorithm is proposed. The channel considered is uncorrelated with full and perfect knowledge at the BS. In particular, these two channel conditions may not be available in all scenarios. The CSI may be imperfect, and even the instantaneous form does not exist. A hybrid precoder between the mixed CSI (includes imperfect and statistical) and rate splitting approach is proposed to deal with an overloaded system under a low number of BS antennas. / Ministry of Higher Education and Scientific Research of Iraq