Metamaterial inspired improved antennas and circuits

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

Desenvolvimento de antenas de microfita e antenas DRA Broadband

The search for ever smaller device and without loss of performance has been increasingly investigated by researchers involving applied electromagnetics. Antennas using ceramics materials with a high dielectric constant, whether acting as a substract element of patch radiating or as the radiant element are in evidence in current research, that due to the numerous advantages offered, such as: low profile, ability to reduce the its dimensions when compared to other devices, high efficiency of ratiation, suitability the microwave range and/or millimeter wave, low temperature coefficient and low cost. The reason for this high efficiency is that the dielectric losses of ceramics are very low when compared to commercially materials sold used in printed circuit boards, such as fiberglass and phenolite. These characteristics make ceramic devices suitable for operation in the microwave band. Combining the design of patch antennas and/or dielectric resonator antenna (DRA) to certain materials and the method of synthesis of these powders in the manufacture of devices, it s possible choose a material with a dielectric constant appropriate for the design of an antenna with the desired size. The main aim of this work is the design of patch antennas and DRA antennas on synthesis of ceramic powders (synthesis by combustion and polymeric precursors - Pe- chini method) nanostructured with applications in the microwave band. The conventional method of mix oxides was also used to obtain nanometric powders for the preparation of tablets and dielectric resonators. The devices manufactured and studied on high dielectric constant materials make them good candidates to have their small size compared to other devices operating at the same frequency band. The structures analyzed are excited by three different techniques: i) microstrip line, ii) aperture coupling and iii) inductive coupling. The efficiency of these techniques have been investigated experimentally and compared with simulations by Ansoft HFSS, used in the accurate analysis of the electromagnetic behavior of antennas over the finite element method (FEM). In this thesis a literature study on the theory of microstrip antennas and DRA antenna is performed. The same study is performed about the materials and methods of synthesis of ceramic powders, which are used in the manufacture of tablets and dielectric cylinders that make up the devices investigated. The dielectric media which were used to support the analysis of the DRA and/or patch antennas are analyzed using accurate simulations using the finite difference time domain (FDTD) based on the relative electrical permittivity (er) and loss tangent of these means (tand). This work also presents a study on artificial neural networks, showing the network architecture used and their characteristics, as well as the training algorithms that were used in training and modeling some parameters associated with the devices investigated

Análise e síntese de antenas e superfícies seletivas de frequência utilizando computação evolucionária e inteligência de enxames

The frequency selective surfaces, or FSS (Frequency Selective Surfaces), are structures consisting of periodic arrays of conductive elements, called patches, which are usually very thin and they are printed on dielectric layers, or by openings perforated on very thin metallic surfaces, for applications in bands of microwave and millimeter waves. These structures are often used in aircraft, missiles, satellites, radomes, antennae reflector, high gain antennas and microwave ovens, for example. The use of these structures has as main objective filter frequency bands that can be broadcast or rejection, depending on the specificity of the required application. In turn, the modern communication systems such as GSM (Global System for Mobile Communications), RFID (Radio Frequency Identification), Bluetooth, Wi-Fi and WiMAX, whose services are highly demanded by society, have required the development of antennas having, as its main features, and low cost profile, and reduced dimensions and weight. In this context, the microstrip antenna is presented as an excellent choice for communications systems today, because (in addition to meeting the requirements mentioned intrinsically) planar structures are easy to manufacture and integration with other components in microwave circuits. Consequently, the analysis and synthesis of these devices mainly, due to the high possibility of shapes, size and frequency of its elements has been carried out by full-wave models, such as the finite element method, the method of moments and finite difference time domain. However, these methods require an accurate despite great computational effort. In this context, computational intelligence (CI) has been used successfully in the design and optimization of microwave planar structures, as an auxiliary tool and very appropriate, given the complexity of the geometry of the antennas and the FSS considered. The computational intelligence is inspired by natural phenomena such as learning, perception and decision, using techniques such as artificial neural networks, fuzzy logic, fractal geometry and evolutionary computation. This work makes a study of application of computational intelligence using meta-heuristics such as genetic algorithms and swarm intelligence optimization of antennas and frequency selective surfaces. Genetic algorithms are computational search methods based on the theory of natural selection proposed by Darwin and genetics used to solve complex problems, eg, problems where the search space grows with the size of the problem. The particle swarm optimization characteristics including the use of intelligence collectively being applied to optimization problems in many areas of research. The main objective of this work is the use of computational intelligence, the analysis and synthesis of antennas and FSS. We considered the structures of a microstrip planar monopole, ring type, and a cross-dipole FSS. We developed algorithms and optimization results obtained for optimized geometries of antennas and FSS considered. To validate results were designed, constructed and measured several prototypes. The measured results showed excellent agreement with the simulated. Moreover, the results obtained in this study were compared to those simulated using a commercial software has been also observed an excellent agreement. Specifically, the efficiency of techniques used were CI evidenced by simulated and measured, aiming at optimizing the bandwidth of an antenna for wideband operation or UWB (Ultra Wideband), using a genetic algorithm and optimizing the bandwidth, by specifying the length of the air gap between two frequency selective surfaces, using an optimization algorithm particle swarm

Novas configurações de monopólios planares quase-fractais para sistemas de comunicações móveis

The characteristic properties of the fractal geometry have shown to be very useful for the construction of filters, frequency selective surfaces, synchronized circuits and antennas, enabling optimized solutions in many different commercial uses at microwaves frequency band. The fractal geometry is included in the technology of the microwave communication systems due to some interesting properties to the fabrication of compact devices, with higher performance in terms of bandwidth, as well as multiband behavior. This work describes the design, fabrication and measurement procedures for the Koch quasi-fractal monopoles, with 1 and 2 iteration levels, in order to investigate the bandwidth behavior of planar antennas, from the use of quasi-fractal elements printed on their rectangular patches. The electromagnetic effect produced by the variation of the fractal iterations and the miniaturization of the structures is analyzed. Moreover, a parametric study is performed to verify the bandwidth behavior, not only at the return loss but also in terms of SWR. Experimental results were obtained through the accomplishment of measurements with the aid of a vetorial network analyzer and compared to simulations performed using the Ansoft HFSS software. Finally, some proposals for future works are presented

Uma nova proposta de antenas Quasi-Yagi banda larga para comunicação sem fio

ln this work, planar quasi- Y agi antennas are investigated based on the concept of the classic Y agi_Uda antennas. These antennas represent improvements on the topologies of the antennas existing printed because they present characteristics of broad bandwidth, excellent radiation diagrams and simple construction. New configurations are adapted for the driver of the antennas, introducing patches elements into the driver. These new configurations are named Patches Elements Anteonas (PEA). This adaptation is obtained from simulations that are executed usiog the software C8T Microwave 8tudio 5. After doing the optimizations, procedures for construction and measurement ofthe prototypes are executed in order to improve the performance of the antennas in such way that they could be used in wireless communication applications, such as Bluetooth, WLAN' s and Wi-Fi. Next, the quasi- Y agi antennas are studied in order to implement them in arrangements. The arrangements construction is based 00 the best driver configuration of the antenna developed in this work. First, a linear arrangement composed by two elements of quasi¬Yagi antennas is constructed in such way that the radiation characteristics and the mutual coupling effects could be analyzed. After that, a 90° angle arrangement composed by two elements is studied to observe the effect of circular polarization. Experiments are executed in order to evaluate the arrangements performance. The experimental results show that the analysis made in this work is efficient and accurate. The numerical values obtained for the analyzed parameters of each structure developed are compared with the experimental values. 80, it is possible to observe a good concordance between them. Finally, some future works proposals are presented

Análise de antenas de microfita em rampa com múltiplas camadas dielétricas

The present work deals with the ana1ysis of microstrip patch antennas printed on tapered dielectric substrates. We investigate the influence ofthe substrate height variations on the properties of configurations such as microstrip patch antennas, microstrip patch antennas with overlay and suspendeô microstrip patch antennas. The dielectric substrates can be isotropic or anisotropic ones. This accurate analysis is based on the full-wave formulation. It is carried out initially for the determination of the impedance matrix, through the use of the spectral¬domain immitance approach. We use a model based on a segmentation of the considered line into uniform microstrip line subsections. Normalized phase constants and characteristic impedances are obtained by means of the Galerkin numerical technique. Then, the cascaded combination of the uniform microstrip subsections are analyzed through an interactive procedure. Numerical results are presented for the input reflection coefficient, voltage standing wave ratio, resonant frequency, and radiation pattems ofthe E_plane and H-plane diagrams. It is found that the variations in the substrate height profile produce a great influence on the bandwidth of microstrip antennas. This procedure gives bandwidth improvements without altering considerably the resonant frequency. Furthermore, the tapered microstrip antenna can be used as a lightweight altemative for bandwidth control and to eXtend the use of microstiip antenna technology to a wider variety of applications. Finally, suggestions for the continuity of this work are presented

Caracterização numérica de antenas para aplicações RFID utilizando o método das ondas - WCIP

In recent years, the radio frequency identification technology (RFID) has gained great interest both industrial communities as scientific communities. Its ability to locate and monitor objects, animals and persons with active or passive tags allows easy development, with good cost-benefice and still presents undeniable benefits in applications ranging from logistics to healthcare, robotics, security, among others. Within this aspect what else comes excelling are RFID tags and the antennas used in RFID readers. Most tags have antennas omnidirectional and are usually manufactured as dipoles modified printed. The primary purpose of a project of antenna for tag is to achieve the required input impedance to perform a good marriage impedance with the load impedance of the chip. Already the objective principal in project of antennas for readers is to achieve reduced sizes and structures with good data transmission capacity. This work brings the numerical characterization of antennas for RFID applications, being these divided into tags RFID and antennas for RFID readers. Three tags RFID and two antennas for RFID readers, found in literature, are analyzed. The analysis of these structures is made using the Method of Waves - WCIP. Initial results found in the literature are compared with those obtained through simulations in WCIP with objective to show that the Method of Waves is able to analyze such structures. To illustrate the results obtained in simulations is presented the behavior of electric and magnetic fields. It also performed a literature review on the characteristics and principles of RFID technology. Suggestions for continuity to this work are presented

Análise espectral de reflectarrays com substratos de duas camadas dielétricas anisotrópicas uniaxiais

Recently, an amazing development has been observed in telecommunication systems. Two good examples of this development are observed in mobile communication and aerospace systems. This impressive development is related to the increasing need for receiving and transmitting communication signals. Particularly, this development has required the study of new antennas and filters. This work presents a fullwave analysis of reflectarrays. The considered structures are composed by arrays of rectangular conducting patches printed on multilayer dieletric substrates, that are mounted on a ground plane. The analysis is developed in the spectral domain, using an equivalent transmission line method in combination with Galerkin method. Results for the reflection coefficient of these structures are presented and compared to those available in the literature. A good agreement was observed. Particularly, the developed analysis uses the transmission lines theory in combination with the incident potentials and the field continuity equations, at the structures interfaces, for obtaining the scattered field components expressions as function of the patch surface currents and of the incident field. Galerkin method is used to determine the unknown coefficients in the boundary value problem. Curves for the reflection coefficient of several reflectarray geometries are presented as function of frequency and of the structural parameters

Antenas de microfita com patch em anel e múltiplas camadas dielétricas anisotrópicas uniaxiais

This work presents an analysis of the annular ring microstrip antennas printed on uniaxial anisotropic substrates and with superstrate.The analysis uses the full-wave formulation by means of the Hertz vector potentials method, in the Hankel transform domain. The definition of the Hertz vector potentials and the application of the appropriate boundary conditions to the structure allow determining the dyadic Green functions, relating the current densities in the conducting patch to the transforms of the tangential electric field components. Galerkin s method is then used to obtain the matrix equation whose nontrivial solution gives the complex resonant frequency of the antenna. From the modeling, it is possible to obtain results for the resonant frequency, bandwidth and quality factor, as a function of several parameters of the antenna, for different configurations. We have considered annular ring microstrip antennas on a single dielectric layer, antennas with two anisotropic dielectric layers, and annular ring microstrip antennas on suspended substrates. Numerical results for the resonant frequency of the these structures printed on isotropic substrates are also presented and compared with those published by other authors, showing a good agreement

Análise espectral de reflectarrays com substrato de duas camadas dielétricas anisotrópicas uniaxiais

Recently, an amazing development has been observed in telecommunication systems. Two good examples of this development are observed in mobile communication and aerospace systems. This impressive development is related to the increasing need for receiving and transmitting communication signals. Particularly, this development has required the study of new antennas and filters. This work presents a fullwave analysis of reflectarrays. The considered structures are composed by arrays of rectangular conducting patches printed on multilayer dieletric substrates, that are mounted on a ground plane. The analysis is developed in the spectral domain, using an equivalent transmission line method in combination with Galerkin method. Results for the reflection coefficient of these structures are presented and compared to those available in the literature. A good agreement was observed. Particularly, the developed analysis uses the transmission lines theory in combination with the incident potentials and the field continuity equations, at the structures interfaces, for obtaining the scattered field components expressions as function of the patch surface currents and of the incident field. Galerkin method is used to determine the unknown coefficients in the boundary value problem. Curves for the reflection coefficient of several reflectarray geometries are presented as function of frequency and of the structural parameters

Caracterização de superfícies seletivas de frequência de periódicas e não-periódicas

The past years have seen a great interest in the use of frequency selective surfaces (FSS), as spatial filters, in many microwave applications. Among these, we highlight applications in telecommunication systems (such as satellite communications and radar), high gain antennas (combined with planar antennas) and (home and industrial) microwave ovens. The FSS is usually composed of two-dimensional periodic arrays, with equally spaced elements, which may be metallic patches (printed on dielectric substrates) or aperture (holes in thin metal surfaces). Using periodic arrays, the FSS have been able to meet the demands of the telecommunications industry. However, new demands are finding technological limitations. In this context, adverse filtering requirements have forced designers to use FSS optimization methods to find specific formats of FSS elements. Another alternative that has been used to increase the selectivity of the FSS is the cascaded FSS, a simple technique that has as main drawback the increased dimensions of the structure, as well as its weight. This work proposes the development of a new class of selective surfaces frequency (FSS) composed of quasi-periodic (or non-periodic) arrangements. The proposed FSS have no array periodicity, in relation with the spatial position of their elements. The frequency responses of these structures were simulated using commercial softwares that implement full-wave methods. For the purpose of validation of this study, FSS prototypes were built and measured, being possible to observe a good agreement between simulated and measured results. The main conclusions of this work are presented, as well as suggestions for future works.