It is desirable to modify the spectral signature of a surface, particularly in the infrared (IR) region of the electromagnetic spectrum. To alter the surface signature in the IR, two methods are investigated: thin film application and antenna array application. The former approach is a common and straightforward incorporation of optically-thin film coatings on the surface designated for signature modification. The latter technique requires the complex design of a periodic array of passive microantenna elements to cover the surface in order to modify its signature. This technology is known as frequency selective surface (FSS) technology and is established in the millimeter-wave spectral regime, but is a challenging technology to scale for IR application. Incorporation of thin films and FSS antenna elements on a surface permits the signature of a surface to be changed in a deterministic manner. In the seminal application of this work, both technologies are integrated to comprise a circuit-analog absorbing IR FSS. The design and modeling of surface treatments are accomplished using commercially-available electromagnetic simulation software. Fabrication of microstructured antenna arrays is accomplished via microlithographic technology, particularly using an industrial direct-write electron-beam lithography system. Comprehensive measurement methods are utilized to study the patterned surfaces, including infrared spectral radiometry and Fourier-transform infrared spectrometry. These systems allow for direct and complementary spectral signature measurements--the radiometer measures the absorption or emission of the surface, and the spectrometer measures its transmission and reflection. For the circuit-analog absorbing square-loop IR FSS, the spectral modulation in emission is measured to be greater than 85% at resonance. Other desirable modifications of surface signature are also explored; these include the ability to filter radiation based on its polarization orientation and the ability to dynamically tune the surface signature. An array of spiral FSS elements allows for circular polarization conditioning. Three techniques for tuning the IR FSS signature via voltage application are explored, including the incorporation of a pn junction substrate, a piezoelectric substrate and a liquid crystal superstrate. These studies will ignite future explorations of IR FSS technology, enabling various unique applications.

No description available.

The main goals of this thesis are to design and examine heterogeneous antennas for different wireless applications of a wide variety of EM spectrum requirements: which includes WLAN 5.0 GHz, WLAN (2.45 GHz), UMTS (1.92-2.17 GHz), 2G, UMTS, LTE, ultra-wideband (UWB) applications, and MBAN applications (2.4 GHz). Various techniques for expanding bandwidth, enhancing performance, and balancing the operation have been examined through comprehensive simulated and physically fabricated models. Thereafter, a compact DRA, for UWB applications is examined. The combined resultant effects of asymmetric positioning of DRs (2, 3 and 4 Cylindrical elements), defected ground technique, dimensions, and profile of the aperture give RF designers detailed scope of the optimization process. More resonances are achieved, and the bandwidth is improved. The obtained results show that, an impedance bandwidth of 133.0%, which covers the Ultra­ Wideband band (3.6GHz - 18.0GHz), with a maximum power gain of 9dBi attained. In addition, a compact conformal wearable CPW antenna using EBG-FSS for MBAN applications at 2.4GHz is proposed. They are designed using fabric materials suitable for daily clothing. The performance of the antenna is investigated in free space, on a layered biological tissue model, and on a real human body to evaluate SAR. When the antenna is combined with an EBG-FSS structure, isolation between the antenna and the human body is introduced. The results show that the FBR is enhanced by 13 dB, the gain by 6.55dBi, and the SAR is lowered by more than 94%. The CPW antenna demonstrated here is appropriate for future MBAN wearable systems. The design, investigation, and application of water level monitoring utilizing subsurface wireless sensor are covered in this thesis. A wideband double inverted-F antenna is designed and examined to overcome signal attenuation issues. The obtained result is feasible, which has an operating bandwidth of 0.8 to 2.17GHz, with a reflection coefficient better than 10 dB. Moreover, a field trial is conducted to evaluate the robustness of the antenna under extreme conditions. A very good efficiency was also demonstrated, with losses of under 20%. Further, the results from the field experiment established that the antenna is a reliable contender for wireless communication in such challenging environments. / Libyan Ministry of Higher Education / The full text will be available at the end of the embargo: 25th May 2025

Les structures planaires de tailles finies sont de plus en plus utilisées dans les applications des satellites et des radars. Deux grands types de ces structures sont les plus utilisés dans le domaine de la conception RF à savoir Les Surfaces Sélectives en Fréquence (FSS) et les Reflectarrays. Les FSSs sont un élément clé dans la conception de systèmes multifréquences. Elles sont utilisées comme filtre en fréquence, et trouvent des applications telles que les radômes, les réflecteurs pour antenne Cassegrain, etc. Les performances des FSSs sont généralement évaluées en faisant l'hypothèse d'une FSS de dimension infinie et périodique en utilisant les modes de Floquet, le temps de calcul étant alors réduit quasiment à celui de la cellule élémentaire. Plusieurs méthodes permettant la prise en compte de la taille finie des FSSs ont été développées. La méthode de Galerkin basée sur l'approche rigoureuse permet la prise en compte des interactions entre les différents éléments du réseau, mais cette technique ne fonctionne que pour les FSSs de petite taille, typiquement 3x3 éléments. Pour les grands réseaux, cette méthode n'est plus adaptée, car le temps de calcul et l'exigence en mémoire deviennent trop grands. Donc, une autre approche est utilisée, celle basée sur la décomposition spectrale en onde plane. Elle permet de considérer un réseau fini comme un réseau périodique infini, illuminé partiellement par une onde plane. Avec cette approche, des FSSs de grande taille sont simulées, mais elle ne permet pas dans la plupart des cas, de prendre en compte les couplages qui existent entre les différentes cellules du réseau, les effets de bord non plus. La simulation des FSSs par les méthodes numériques classiques basées sur une discrétisation spatiale (méthode des éléments finis, méthode des différences finies, méthode des moments) ou spectrale (méthodes modales) aboutit souvent à des matrices mal conditionnées, des problèmes de convergence numérique et/ou des temps de calcul excessifs. Pour éviter tous ces problèmes, une technique appelée technique par changements d'échelle tente de résoudre ces problèmes. Elle est basée sur le partitionnement de la géométrie du réseau en plusieurs sous-domaines imbriqués, définis à différents niveaux d'échelle du réseau. Le multi-pôle de changement d'échelle, appelé Scale-Changing Networks (SCN), modélise le couplage électromagnétique entre deux échelles successives. La cascade de ces multi-pôles de changement d'échelle, permet le calcul de la matrice d'impédance de surface de la structure complète et donc la modélisation globale du réseau. Ceci conduit à une réduction significative en termes de temps de calcul et d'espace mémoire par rapport aux méthodes numériques classiques. Comme le calcul des multi-pôles de changement d'échelle est mutuellement indépendant, les temps d'exécution peuvent encore être réduits de manière significative en parallélisant le calcul. La SCT permet donc de modéliser des FSSs Finies tout en prenant en compte le couplage entre les éléments adjacents du réseau. / The finite size planar structures are increasingly used in applications of satellite and radar. Two major types of these structures are the most used in the field of RF design ie Frequency Selective Surfaces (FSS) and the Reflectarrays. The FSSs are a key element in the design of multifrequency systems. They are used as frequency filter, and find applications such as radomes, reflector Cassegrain antenna, etc.. The performances of FSSs are generally evaluated by assuming an infinite dimensional FSS using periodic Floquet modes, the computation time is then reduced almost to that of the elementary cell. Several methods have been developed for taking into account the finite dimensions of arrays. For example the Galerkin method uses a rigorous element by element approach. With this method, the exact interactions between the elements are taken into account but this technique works only for small FSS, typically 3x3 elements. For larger surfaces, this method is no more adapted. The computation time and the memory requirement become too large. So another approach is used based on plane wave spectral decomposition. It allows considering the finite problem as a periodic infinite one locally illuminated. With this approach, large FSS are indeed simulated, but the exact interactions between the elements are not taken into account, the edge effects either. The simulation of FSS by conventional numerical methods based on spatial meshing (finite element method, finite difference, method of moments) or spectral (modal methods) often leads in the practice to poorly conditioned matrices, numerical convergence problems or/and excessive computation time. To avoid these problems, a new technique called Scale Changing Technique attempts to solve these problems. The SCT is based on the partition of discontinuity planes in multiple planar sub-domains of various scale levels. In each sub- omain the higher-order modes are used for the accurate representation of the electromagnetic field local variations while low-order modes are used for coupling the various scale levels. The electromagnetic coupling between scales is modelled by a Scale Changing Network (SCN). As the calculation of SCN is mutually independent, the execution time can still be significantly reduced by parallelizing the computation. With the SCT, we can simulate large finite FSS, taking into account the exact interactions between elements, while addressing the problem of excessive computation time and memory

Les recherches que nous présentons dans ce mémoire s'inscrivent dans le cadre du développement de nouvelles structures et de l'étude de matériaux accordables en vue d'une intégration industrielle comme radôme actif.Plus particulièrement, ils consistent en la réalisation d'un dispositif micro-onde permettant à la fois un filtrage et une agilité fréquentiels en espace libre. Des structures basées sur des surfaces sélectives en fréquences, pour l'aspect filtrage, et sur des matériaux de type ferroélectrique, pour l'aspect accordabilité, sont développées. Des modélisations et des simulations électromagnétiques montrent que le changement de permittivité du matériau, obtenu par application d'un champ électrique externe, permet le pilotage fréquentiel de la transmission de la structure. Une mise en oeuvre expérimentale complète ces travaux, au cours de laquelle des prototypes ont été fabriqués par des techniques de photolithographie, puis caractérisés en espace libre grâce à un banc ABmm. Les mesures micro-ondes valident ainsi les résultats de simulations menées en amont et montrent les possibilités de contrôler la fréquence de transmission du radôme. / The research we present in this memory registers within the framework to develop new structures and to study tunable materials for an industrial integration as an active radome. Specifically, they consist of achieving a free space microwave device for both a filtering behaviour and a frequency agility behaviour. Structures based on frequency selective surfaces, for the filtering aspect, and on ferroelectric materials for the tuning aspect, are developed. Modeling and simulations show that the change of the material permittivity, obtained by applying an external electric field, enable piloting the transmission frequency of the structure. An experimental implementation complete this work and prototypes have been fabricated by photolithography techniques and then characterized in free space with a bench ABmm. Thus, microwave measurements validate the results of simulations and show the possibility to control the frequency transmission of the radome.

Si les drones militaires connaissent un développement important depuis une quinzaine d’année, suivi depuis quelques années par les drones civiles dont les usages ne font que se multiplier, en réalité les drones ont un siècle avec le premier vol d’un avion équipé d’un système de pilotage automatique sur une centaine de kilomètre en 1918. La question des règles d’usage des drones civiles sont en cours de développement malgré leur multiplication pour des usages allant de l’agriculture, à l’observation en passant par la livraison de colis. Ainsi, leur intégration dans l’espace aérien reste un enjeu important, ainsi que les standards de communication avec ces drones dans laquelle s’inscrit cette thèse. Cette thèse vise en effet à étudier et proposer des solutions pour les liens de communications des drones par satellite.L’intégration de ce lien de communication permet d’assurer la fiabilité des communications et particulièrement du lien de Commande et Contrôle partout dans le monde, en s’affranchissant des contraintes d’un réseau terrestre (comme les zones blanches). En raison de la rareté des ressources fréquentielles déjà allouées pour les futurs systèmes intégrant des drones, l’efficacité spectrale devient un paramètre important pour leur déploiement à grande échelle et le contexte spatiale demande l’utilisation d’un système de communication robuste aux non-linéarités. Les Modulations à Phase Continue permettent de répondre à ces problématiques. Cependant, ces dernières sont des modulations non-linéaire à mémoire entraînant une augmentation de la complexité des récepteurs. Du fait de la présence d’un canal multi-trajet (canal aéronautique par satellite), le principal objectif de cette thèse est de proposer des algorithmes d’égalisation (dans le domaine fréquentiel pour réduire leur complexité) et de synchronisation pour CPM adaptés à ce concept tout en essayant de proposer une complexité calculatoire raisonnable. Dans un premier temps, nous avons considéré uniquement des canaux sélectifs en fréquence et avons étudier les différents égaliseurs de la littérature. En étudiant leur similitudes et différences, nous avons pu développer un égaliseur dans le domaine fréquentiel qui proposant les mêmes performances a une complexité moindre. Nous proposons également des méthodes d’estimation canal et une méthode d’estimation conjointe du canal et de la fréquence porteuse. Dans un second temps nous avons montré comment étendre ces méthodes à des canaux sélectifs en temps et fréquence permettant ainsi de conserver une complexité calculatoire raisonnable. / If the use of Unmanned Aerial Vehicles (UAV) has been booming for military applications since adecade, followed by civil applications since a few years (with a lot of completely different purposes), the first UAV has been developed and tested in 1918 with the first flight of a fight withthe first autopilot system. The issue of a complete and safe integration in the existing air trafficair craft system is currently being studied as the multiple use case of UAV are growing exponentially from agriculture, observation and package delivery. Hence, the integration of UAV inthe air traffic system is a global issue, and so are the communication standard in which the thesis take place. This thesis aims to study and propose solutions for the communication link by satellitefor UAV. This satellite link would ensure the reliability of the system, and above all of theCommand and Control Link, by avoiding the issue of a terrestrial communication network (such asover the ocean, where no terrestrial network is available). Due to spectral resource lack alreadyallocated for the UAV, the spectral efficiency of the communication link is a critical issue, as its robustness to non-linearity due to the spatial context. Continuous Phase Modulation is a potentialsolution to answer to those issues. However, this will lead to an increased computational complexity at the received compared to linear modulation scheme The aeronautical channel bysatellite is characterized by a doubly-selective channels due to Ground Reflections of the signal,and in this thesis, we proposed equalization algorithms and synchronization techniques for CPM in this context while trying to keep a reasonable computational complexity a. First, we have only considered transmission over frequency selective channels. We have made a study of the equalizers proposed by the literature and by studying their similitudes and differences, we have been able to propose a new equalizer with a lower computational complexity but having the same performance. We also have proposed a channel estimation method and a joint channel and carrier frequency estimation for CPM over frequency-selective channels. In a second time, we have extended our method to doubly selective channel (as there is Doppler Spread in our communication system due to the UAV speed) which allows us to have an overall receiver structure with a reasonable computational complexity.

Frequency selective surfaces (FSSs) provide a variety of spatial filtering functions, such as band-pass or band-stop properties in a radome or other multilayer structure. This filtering is typically achieved through closely-spaced periodic arrangements of metallic shapes on top of a dielectric substrate (or within a stack of dielectric materials). In most cases, the unit cell size, its shape, the substrate parameters, and the inter-element spacing collectively impact the response of the FSS. Expanding this design space to include reconfigurable FSSs provides opportunities for applications requiring frequency agility and/or other properties. Tuning can also enable operation over a potentially wider range of frequencies and can in some cases be used as a loading mechanism or quasi-ground plane. Many technologies have been considered for this type of agility (RF MEMS, PIN diodes, etc.). This includes the recent use of microfluidics and dispersions of nanoparticles, or fluids with controllable dielectrics, which have entered the design space of numerous other EM applications including stub-tuners, antennas, and filters. In this work they provide a material based approach to reconfiguring an FSS. An FSS based on a four-arm spiral with tunable band-stop characteristics is presented in this work. A thin colloidal dispersion above each element provides this tuning capability. The radial expansion and contraction of this dispersion, as well as the variable permittivity of the dispersion, are used to load each element individually. This design incorporates thin fluidic channels within a PDMS layer below the substrate leading to individual unit cells that provide a closed pressure-driven subsystem that contains the dispersion. With the capability to individually control each cell, groups of cells can be locally altered (individually or in groups) to create gratings and other electromagnetically agile features across the surface or within the volume of a radome or other covering. Simulations and measurements of an S-band tunable design using colloidal Barium Strontium Titanate dispersed Silicone oil are provided to demonstrate the capability to adjust the stop-band characteristics of the FSS across the S-band.

Η χωροχρονική μπλοκ κωδικοποίηση (STBC) αποτελεί μία αποδοτική και ευρέως διαδεδομένη τεχνική διαφορετικότητας μετάδοσης για την αντιμετώπιση του φαινομένου της εξασθένησης στις ασύρματες επικοινωνίες. Χαρακτηριστικό παράδειγμα είναι ο ορθογώνιος κώδικας του σχήματος Alamouti, ο οποίος με δύο κεραίες μετάδοσης επιτυγχάνει τη μέγιστη χωρική διαφορετικότητα στο μέγιστο δυνατό ρυθμό μετάδοσης, για οποιονδήποτε (πραγματικό ή μιγαδικό) αστερισμό συμβόλων. Ωστόσο, το σχήμα Alamouti έχει σχεδιαστεί για συχνοτικά επίπεδα κανάλια. Στην παρούσα εργασία μελετούμε την εφαρμογή STBC σε κανάλια συχνοτικά επιλεκτικής εξασθένησης. Εστιάζουμε κυρίως στο συνδυασμό του σχήματος Alamouti με τεχνικές εξάλειψης της διασυμβολικής παρεμβολής, εξετάζοντας τα σχήματα OFDM-STBC, FDE-STBC και TR-STBC, που έχουν προταθεί στη βιβλιογραφία. Επιπρόσθετα των συμβατικών δεκτών, για τα δύο τελευταία σχήματα περιγράφουμε και προσαρμοστικούς δέκτες, οι οποίοι παρακολουθούν τις μεταβολές του καναλιού, χωρίς να απαιτούν την ακριβή εκτίμησή του. Η έρευνα πάνω στα προηγούμενα σχήματα οδήγησε σε ορισμένα αξιόλογα αποτελέσματα. Κατ’ αρχήν, αποδεικνύουμε ότι τα σχήματα FDE-STBC και TR-STBC είναι ισοδύναμα, μολονότι καθένα εφαρμόζει διαφορετική κωδικοποίηση στα μεταδιδόμενα δεδομένα. Επίσης, σχεδιάζουμε έναν νέο δέκτη για το σχήμα TR-STBC, τον οποίο αναπτύσσουμε και σε προσαρμοστική μορφή. Βασικό πλεονέκτημα του προτεινόμενου δέκτη είναι ότι εκμεταλλεύεται τους κυκλικούς πίνακες συνέλιξης για τη μείωση της πολυπλοκότητας αποκωδικοποίησης. Τέλος, η απόδοση κάθε σχήματος και δέκτη αξιολογείται σε διάφορες συνθήκες εξασθένησης μέσω προσομοιώσεων σε υπολογιστικό περιβάλλον. / Space-time block coding (STBC) is an effective and widely used transmit diversity technique to combat multipath fading in wireless communication systems. A prominent example of STBC is the orthogonal code of Alamouti scheme, which achieves full spatial diversity at full transmission rate for two transmit antennas and any (real or complex) signal constellation. However, Alamouti scheme has been designed only for frequency-flat channels. In this thesis we study the application of STBC in frequency-selective channels. We mainly focus on combining Alamouti scheme with techniques for mitigating intersymbol interference, by studying several schemes (OFDM-STBC, FDE-STBC and TR-STBC) that have been proposed in literature. In addition to the conventional receivers, for FDE-STBC and TR-STBC we describe adaptive receivers too, which have the ability of tracking channel variations, without requiring explicit channel estimation. Research made upon the above schemes has come to some remarkable results. First, we prove that TR-STBC and FDE-STBC are equivalent, although each one encodes differently the transmitted data. Then, we design a new receiver for TR-STBC, which exploits the circulant convolution matrices, in order to reduce decoding complexity and we, also, develop an adaptive structure for the proposed receiver. At last, we evaluate the performance of all the described schemes and receivers in different fading conditions, by using computer simulations.

It is well known that multiple antennas at the transmitter and receiver are imperative for reliable and high data-rate communication over wireless channels. However, these systems essentially need multiple radio frequency (RF) chains owing to multiple antennas, and hence pose challenges for applications with limited form-factor. Antenna Selection (AS) techniques alleviate this problem by using only a subset of the total available antennas and hence require only a few RF chains compared to the number of antennas. These systems operate in a closed-loop scenario, where the information fed back from the receiver is used for the transmit antenna subset selection. In contrast to this, a novel open-loop technique known as spatial modulation (SM) was recently proposed that uses a single RF-chain at the transmitter and achieves a higher spectral efficiency compared to single-input and AS based systems. The work in the thesis mainly focuses on the following aspects of SM system: Study of Mutual Information in SM systems operating in open-loop and closed-loop scenarios: We study the achievable mutual information in the SM system operating with finite and Gaussian input alphabet, and compare the results with that of the SIMO and AS based systems. Reduced-complexity maximum-likelihood (ML) decoding algorithms for SM systems: We propose ML-optimal sphere decoders for SM systems with arbitrary number of transmit antennas. Furthermore, a reduced-complexity ML detector is also proposed whose computational complexity is lowest among the known existing detectors in the literature. Transmit diversity techniques for SM systems: The conventional SM system achieves a transmit diversity order of one. We propose a complex interleaved orthogonal design baaed SM scheme that achieves a transit diversity order of two, while offering symbol-by- symbol ML decodability. Transmit antenna subset selection algorithms for SM systems: The SM system is considered in the closed-loop scenario, where only a subset of the total number of transmit antennas is chosen based on the information fed back by the receiver. Specifically, the Euclidean distance and capacity optimized antenna selection algorithms are studied in comparison with the conventional AS based systems. SM system operating in dispersive channels: The SM system operating in a dispersive channel with the aid of zero-padding is studied. It is shown that the SM system achieves full receive-diversity and multipath-diversity with ML decoding, but offers a decoding complexity that is exponential in the number of multipaths. Furthermore, a reduced complexity linear receiver is proposed that achieves achieves full multipath as well as receive-diversity, while offering a decoding complexity order same as that of the SM system operating in a frequency-flat channel.

Made available in DSpace on 2014-12-17T14:54:53Z (GMT). No. of bitstreams: 1 RossanaMSC.pdf: 3237270 bytes, checksum: 01cfb4de4da5c1c94fba895ebbbdddb1 (MD5) Previous issue date: 2009-09-28 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / The bidimensional periodic structures called frequency selective surfaces have been well investigated because of their filtering properties. Similar to the filters that work at the traditional radiofrequency band, such structures can behave as band-stop or pass-band filters, depending on the elements of the array (patch or aperture, respectively) and can be used for a variety of applications, such as: radomes, dichroic reflectors, waveguide filters, artificial magnetic conductors, microwave absorbers etc. To provide high-performance filtering properties at microwave bands, electromagnetic engineers have investigated various types of periodic structures: reconfigurable frequency selective screens, multilayered selective filters, as well as periodic arrays printed on anisotropic dielectric substrates and composed by fractal elements. In general, there is no closed form solution directly from a given desired frequency response to a corresponding device; thus, the analysis of its scattering characteristics requires the application of rigorous full-wave techniques. Besides that, due to the computational complexity of using a full-wave simulator to evaluate the frequency selective surface scattering variables, many electromagnetic engineers still use trial-and-error process until to achieve a given design criterion. As this procedure is very laborious and human dependent, optimization techniques are required to design practical periodic structures with desired filter specifications. Some authors have been employed neural networks and natural optimization algorithms, such as the genetic algorithms and the particle swarm optimization for the frequency selective surface design and optimization. This work has as objective the accomplishment of a rigorous study about the electromagnetic behavior of the periodic structures, enabling the design of efficient devices applied to microwave band. For this, artificial neural networks are used together with natural optimization techniques, allowing the accurate and efficient investigation of various types of frequency selective surfaces, in a simple and fast manner, becoming a powerful tool for the design and optimization of such structures / As estruturas planares peri?dicas bidimensionais, conhecidas como Superf?cies Seletivas de Frequ?ncia, t?m sido bastante estudadas por causa da propriedade de filtragem de frequ?ncia que apresentam. Similares aos filtros que operam na faixa tradicional de radiofrequ?ncia, tais estruturas podem apresentar caracter?sticas espectrais de filtros rejeitafaixa ou passa-faixa, dependendo do tipo de elemento do arranjo (patch ou abertura, respectivamente) e podem ser utilizadas em uma variedade de aplica??es, tais como radomes, refletores dicr?icos, filtros de micro-ondas, condutores magn?ticos artificiais, absorvedores etc. Para melhorar o desempenho de tais dispositivos eletromagn?ticos e investigar suas propriedades, muitos estudiosos t?m analisado v?rios tipos de estruturas peri?dicas: superf?cies seletivas de frequ?ncia reconfigur?veis, filtros de m?ltiplas camadas seletivas, al?m de arranjos peri?dicos impressos sobre substratos diel?tricos anisotr?picos e que utilizam geometrias fractais na sua forma??o. Em geral, n?o existe uma solu??o anal?tica diretamente extra?da a partir da resposta em frequ?ncia de um dispositivo; desta forma, a an?lise de suas caracter?sticas espectrais requer a aplica??o de t?cnicas de onda completa rigorosas, como o m?todo da equa??o integral, por exemplo. Al?m disso, devido ? complexidade computacional exigida para a implementa??o destes m?todos, muitos estudiosos ainda utilizam a investiga??o por tentativa e erro, para alcan?ar crit?rios satisfat?rios ao projeto dos dispositivos. Como este procedimento ? muito trabalhoso e dependente do homem, faz-se necess?rio o emprego de t?cnicas de otimiza??o que acelerem a obten??o de estruturas peri?dicas com especifica??es de filtragem desejadas. Alguns autores t?m utilizado redes neurais artificiais e algoritmos de otimiza??o natural, como os algoritmos gen?ticos e a otimiza??o por enxame de part?culas no projeto e otimiza??o das superf?cies seletivas de frequ?ncia. Este trabalho tem como objetivo realizar um estudo mais aprofundado sobre o comportamento eletromagn?tico das estruturas peri?dicas seletivas de frequ?ncia, possibilitando a obten??o de dispositivos eficientes e aplic?veis na faixa de micro-ondas. P ra isto, redes neurais artificiais s?o utilizadas em conjunto com t?cnicas de otimiza??o baseadas na natureza, permitindo a investiga??o precisa e eficiente de v?rios tipos de superf?cies seletivas de frequ?ncia, de forma simples e r?pida, tornando-se, portanto, uma poderosa ferramenta de projeto e otimiza??o de tais estruturas