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L'objectif de cette thèse est de trouver la forme optimale d'une antenne planaire ou d'un réseau d'antennes planaires à partir de contraintes imposées (diagramme de rayonnement, gain ou directivité) ou de reconstruire la forme à partir de mesures expérimentales. L'algorithme d'optimisation développé est basé sur une méthode de type gradient et la reconstruction des contours par une méthode d'ensembles de niveaux (Level Sets) ou "contours actifs". Le problème direct est résolu en utilisant une formulation intégrale du problème électromagnétique et une méthode d'éléments finis pour la discrétisation. Le gradient de forme est calculé en utilisant deux méthodes différentes. Tout d'abord, une méthode par différences finies basée sur la dérivée à un nœud du maillage, pour une modification infinitésimale des éléments triangulaires du contour, suivant la direction de la normale extérieure. La deuxième méthode est basée sur le gradient topologique pour le calcul de la déformation des contours. Une méthode d'ensembles de niveaux avec bande étroite a été développée pour faire évoluer le contour des antennes utilisant la vitesse de déformation calculée à partir du gradient de forme. Différentes configurations d'antennes et réseaux d'antennes planaires ont été utilisées pour étudier les performances de l'algorithme d'optimisation. Des techniques de type saut de fréquence et multifréquence ont été utilisées pour optimiser la forme dans une bande de fréquence. L'optimisation de forme pour la miniaturisation d'antennes planaires concerne de nombreuses applications, en particulier, pour les réseaux réflecteurs / The objective of this thesis work is to find the optimal shape of planar antenna elements and arrays from imposed constraints (e.g. desired or imposed radiation patterns, gain or directivity) or to reconstruct the shape from experimental measurements. The optimization algorithm is based on the gradient-type method and an active contour reconstruction by means of the Level Set method. 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 is finite differential method based on nodal point mesh derivation with an infinitesimal modification of the triangular elements on the contour along the outward normal direction, another the topological shape gradient, which is computed based on a topological deformation on a contour. A narrow band level set method has been developed to evolve the contour of antennas and arrays using the deformation velocity computed from the shape gradient. Different configurations of antennas and antenna arrays are studied for investigating the performance of the optimization algorithm. Frequency hopping and multi-frequency techniques have been used for optimizing the shape within a frequency band. Shape optimization for planar antenna miniaturization has a large number of applications, particularly, for reflectarrays

The thesis is focused on the design of a planar resonant-type antenna, which exploits a proper combination of left- and right-handed properties of transmission lines. This transmission line is called CRLH TL and is based on Sievenpiper mushroom structure. Advantages of the proposed antenna concept are demonstrated by a detailed comparison of its basic properties with the properties of a conventional patch antenna.

This thesis deals with design of flush–mounted planar disc antenna suitable for use in vehicles. For each of the bands GSM900 and GSM1800, which are used in Czech republic, an independent antenna has been created. As a simulator of the electromagnetic field the program IE3D has been used. For the improvement of theoretical results an optimisation in the program MATLAB has been developed. As the optimisation method the genetic algorithms have been selected.

The main objective of this study is to learn about the theory of electromagnetic field and to create a model of propagation of ultra short waves in a biological tissue. Next point of this paper is to determine a specific absorption rate (SAR) using a valid sanitary standard. A particular model solution was realized in a model environment of the program Comsol Multiphysics 3.5. A human head and a cellular phone with an intern antenna were successfully created in this model environment. First of all were entered appropriate parameters which led to a successful representation of the distribution of electric field intensity. A value of specific absorption rate taken by a biological tissue was determined in the next step. This value was compared to the value listed in a valid sanitary standard to prevent its overrun. A development of a temperature in a biological tissue was determined as well, according to a six minutes long interval stated in a valid sanitary standard.

This work describes an electrically small antennas used for mobile devices in the ISM band. The aim of this work is to select an antenna for a universal transmitter/receiver working in the 868 MHz band. The work contains description of the universal transmitter/receiver, and a list of suitable antennas. Tolerance analysis is performed by numerical model. The proposed antenna is manufactured and measured.

This master’s thesis deals with user influence on miniature antennas in mobile application. Electrically small antennas including fundamental performance properties and limitations are introduced in the theoretical section of this thesis. This section also deals with microstrip antennas and their common types. The accent is on PIFA antennas, their typical constructions and methods of miniaturization. In the practical section, dual-band PIFA antenna for operation at frequencies of systems GSM900 and GSM1800 is designed with the assistance of electromagnetic field simulator CST Microwave Studio. On this type of antenna, the user influence on impedance matching and radiation pattern in data mode (the user is typing message or browsing with the phone) is investigated. For this purpose the hand phantom, corresponding to author’s right hand, was made from agar based material. For typical position of human hand is designed matching network, which eliminate the user influence and ensure correct function of antenna.

Made available in DSpace on 2014-12-17T14:55:20Z (GMT). No. of bitstreams: 1 ValdezAAF_TESE.pdf: 2001050 bytes, checksum: d0f0b88178102c3f48880303c1c6d765 (MD5) Previous issue date: 2014-03-12 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / This work aims to show how the application of frequency selective surfaces (FSS) in planar antenna arrays become an alternative to obtain desired radiation characteristics from changes in radiation parameters of the arrays, such as bandwidth, gain and directivity. In addition to analyzing these parameters is also made a study of the mutual coupling between the elements of the array. To accomplish this study, were designed a microstrip antenna array with two patch elements, fed by a network feed. Another change made in the array was the use of the truncated ground plane, with the objective of increasing the bandwidth and miniaturize the elements of the array. In order to study the behavior of frequency selective surfaces applied in antenna arrays, three different layouts were proposed. The first layout uses the FSS as a superstrate (above the array). The second layout uses the FSS as reflector element (below the array). The third layout is placed between two FSS. Numerical and experimental results for each of the proposed configurations are presented in order to validate the research / Este trabalho tem como objetivo apresentar como a aplica??o de superf?cies seletivas em frequ?ncia (FSS) em arranjos de antenas planares se torna uma alternativa interessante para se obter caracter?sticas de radia??o desejadas, a partir de altera??es em par?metros de radia??o dos arranjos, tais como largura de banda, ganho e diretividade. Al?m de analisar esses par?metros, tamb?m ? feito o estudo do acoplamento m?tuo entre os elementos do arranjo. Para realizar tal estudo, foi projetado um arranjo de antenas de microfita, com dois elementos do tipo patch, alimentado por uma rede de alimenta??o. Outra modifica??o feita no arranjo foi a utiliza??o do plano de terra truncado, com o objetivo de aumentar a largura de banda e miniaturizar os elementos do arranjo. Para poder estudar o comportamento das superf?cies seletivas em frequ?ncia aplicadas em arranjos de antenas, foram propostos tr?s layouts diferentes. O primeiro layout consiste em utilizar a FSS como superstrato (acima do arranjo). O segundo consiste em utilizar a FSS como elemento refletor (abaixo do arranjo). O terceiro layout consiste em colocar o arranjo entre duas camadas de FSS, tanto em cima quanto abaixo. Resultados num?ricos e experimentais para cada uma das configura??es propostas s?o apresentados

Le concept de micro capteurs RMN (nommés aussi micro-antennes ou antennes aiguilles) pourrait conduire à des outils d'analyse fiables capables d'assurer la reproductibilité de mesures en spectroscopie RMN haute résolution. Leur emploi deviendra ainsi envisageable pour des applications in vivo. A notre connaissance, aucune étude in vivo utilisant ces micro-bobines "high-tech" n’a été rapportée. Le principal avantage de ce type de dispositifs est la possibilité d’observer une micro région d'intérêt bien définie, noyée dans un grand volume. A l’inverse, le principal inconvénient est le manque de sensibilité car l’efficacité des micro-antennes actuelles souffre de plusieurs paramètres (petite valeur d'inductance par rapport à l'inductance de fils de connexion, le bruit dû au fort couplage avec l’échantillon...etc.). Notre approche initiale réalisée in vitro dans le cadre des travaux de thèse de N. Baxan (2008) (http://www.spectroscopynow.com) et de A. Kadjo (2011), ne peut être mis en œuvre in vivo sans un travail complémentaire important. C’est d’une importance capitale car dans ce cas le signal RMN est si petit qu’il est comparable au bruit thermique. Une façon "simple", mais non moins aisée, d’optimiser l’efficacité d’une antenne est une conception minutieuse et une maîtrise des paramètres géométriques conditionnant les propriétés physiques et électriques. La partie principale des "micro-antennes aiguilles" implantables est la bobine aux bornes de laquelle la tension est induite. Elle est décrite schématiquement par une résistance et une inductance dont les valeurs impactent directement et fortement sur les principaux critères de performances en RMN: le rapport signal sur bruit (SNR) et les limites de détection (LOD). La fabrication de ces micro-antennes (500x1000µm2), est réalisée à l’aide de techniques de microélectroniques fort coûteuses. La modélisation et la simulation numériques s’avèrent des outils essentiels amplement justifiés. La majeure partie de ce travail est consacré à l’optimisation de ces microantennes. Les résultats de principes physiques visant à optimiser leurs paramètres géométriques sont décrits à travers la prédiction des paramètres électriques: la self inductance, l’inductance mutuelle et les pertes additionnelles dues à l’effet de peau et de proximité. L’originalité de ce travail, à la fois théorique et expérimental réside, dans: (i) la traduction de verrous technologiques en problématiques fondamentales, (ii) Le développement d’un "Logiciel maison" qui sans avoir la prétention de rivaliser avec les logiciels commerciaux, peut s’étendre à d'autre configuration plus complexes de micro-antennes ou d'antennes RMN et cibler au mieux les besoins des "RMN’iste-Antenn-istes" tout en leur offrant un gain en temps et en coût non négligeables. / The concept of NMR microsensors (named also microantennas or needle coils) could lead to reliable analysis tools able to ensure the reproducibility of high resolution spectroscopic measurements, making possible to consider their use for in vivo applications. To the best of our knowledge, no in vivo study has been done with such "high-tech micro coils". The main advantage of this device kind is the possibility to observe a well-defined micro region of interest in a large volume. On the opposite, the main drawback resides in the poor sensitivity of the device since the efficiency of presently designed microcoils suffers from several misadjustments (small inductance value of the useful wires compared to the inductance of connecting wires, strong coupling noise with sample ...etc.). Our initial approach carried out in vitro that presented in (http://www. spectroscopynow.com) and in thesis of N. Baxan (2008) and A. Kadjo (2011), cannot be realized in vivo without a very important complementary work. This is of crucial importance, because the source signals are so small as to be comparable to the thermal noise. The simplest approach to increase antennas efficiency is a careful design and accuracy of geometric parameters influencing the physical and electrical properties. The main part of the implantable "needle antenna" is the loop where the voltage is induced. It is schematically described by a resistance and inductance that modify directly and strongly the NMR performance criteria: signal to noise ratio (SNR) and the limits of detection (LOD). The design of such micro-antennas (500x1000µm2) is performed using microelectronic techniques that are very expensive. Thus modeling and numerical simulation are essential tools amply justified. The bulk of this work dedicates to the optimization of these microantennas, describes the results of the applied physical principles to improve their geometric parameters through the prediction of their electrical parameters: the self-inductance, mutual inductance and the additional losses caused by skin effect and proximity. The originality of this work is: (i) the conversion of technological point in question to fundamental issues, (ii) The development of a "homemade software" which, no pretend to compete with commercial software, can be extended to design of more complex configuration of NMR antennas or microantennas. It could also better target specific needs of designers of NMR antennas and users, providing them a time gain and a cost reduction.

This thesis deals with modeling and produce of reconfigurable multi-band planar antennas, which allow electrical shifting of frequency band. After antennas simulation with PIN diode and FET switch in a commercial program CST MW, another step is to optimize the antenna for a new substrate. The next step was to produce antennas. Finally, the optimized antennas are compared with the measurement on experimental antennas.