Direction of Arrival estimation using unsteered antenna arrays, unlike mechanically scanned or phased arrays, requires complex algorithms which perform poorly with small aperture arrays or without a large number of observations, or snapshots. In general, these algorithms compute a sample covriance matrix to obtain the direction of arrival and some require a prior estimate of the number of signal sources. Herein, artificial neural network architectures are proposed which demonstrate improved estimation of the number of signal sources, the true signal covariance matrix, and the direction of arrival. The proposed number of source estimation network demonstrates robust performance in the case of coherent signals where conventional methods fail. For covariance matrix estimation, four different network architectures are assessed and the best performing architecture achieves a 20 times improvement in performance over the sample covariance matrix. Additionally, this network can achieve comparable performance to the sample covariance matrix with 1/8-th the amount of snapshots. For direction of arrival estimation, preliminary results are provided comparing six architectures which all demonstrate high levels of accuracy and demonstrate the benefits of progressively training artificial neural networks by training on a sequence of sub- problems and extending to the network to encapsulate the entire process.

The objectives of this work were to investigate, design and implement beam steering antenna arrays for mobile and wireless applications using the genetic algorithm (GA) and particle swarm optimisation (PSO) techniques as optimisation design tools. Several antenna designs were implemented and tested: initially, a printed dipole antenna integrated with a duplex RF switch used for mobile base station antenna beam steering was investigated. A coplanar waveguide (CPW) to coplanar strip (CPS) transition was adopted to feed the printed dipole. A novel RF switch circuit, used to control the RF signal fed to the dipole antenna and placed directly before it, was proposed. The measured performance of the RF switch was tested and the results confirmed its viability. Then two hybrid coupled PIN diode phase shifters, using Branchline and Rat-Race ring coupler structures, were designed and tested. The generation of four distinct phase shifts was implemented and studied. The variations of the scattering parameters were found to be realistic, with an acceptable ±2 phase shift tolerance. Next, antenna beam steering was achieved by implementing RF switches with ON or OFF mode functions to excite the radiating elements of the antenna array. The switching control process was implemented using a genetic algorithm (GA) method, subject to scalar and binary genes. Anti-phase feeding of radiating elements was also investigated. A ring antenna array with reflectors was modelled and analysed. An antenna of this type for mobile base stations was designed and simulation results are presented. Following this, a novel concept for simple beam steering using a uniform antenna array operated at 2.4 GHz was designed using GA. The antenna is fed by a single RF input source and the steering elements are reactively tuned by varactor diodes in series with small inductors. The beam-control procedure was derived through the use of a genetic algorithm based on adjusting the required reactance values to obtain the optimum solution as indicated by the cost function. The GA was also initially used as an optimisation tool to derive the antenna design from its specification. Finally, reactive loading and time modulated switching techniques are applied to steer the beam of a circular uniformly spaced antenna array having a source element at its centre. Genetic algorithm (GA) and particle swarm optimisation (PSO) processes calculate the optimal values of reactances loading the parasitic elements, for which the gain can be optimised in a desired direction. For time modulated switching, GA and PSO also determine the optimal on and off times of the parasitic elements for which the difference in currents induced optimises the gain and steering of the beam in a desired direction. These methods were demonstrated by investigating a vertically polarised antenna configuration. A prototype antenna was constructed and experimental results compared with the simulations. Results showed that near optimal solutions for gain optimisation, sidelobe level reduction and beam steering are achievable by utilising these methods. In addition, a simple switching process is employed to steer the beam of a horizontally polarised circular antenna array. A time modulated switching process is applied through Genetic Algorithm optimisation. Several model examples illustrate the radiation beams and the switching time process of each element in the array.

The objectives of this work were to investigate, design and implement Multiple-Input Multiple-Output (MIMO) antenna arrays for mobile phones. Several MIMO antennas were developed and tested over various wireless-communication frequency bands. The radiation performance and channel capacity of these antennas were computed and measured: the results are discussed in the context of the frequency bands of interest. A comprehensive study of MIMO antenna configurations such as 2 × 1, 3 × 1, 2 × 2 and 3 × 3, using polarisation diversity as proposed for future mobile handsets, is presented. The channel capacity is investigated and discussed, as applying to Rayleigh fading channels with different power spectrum distributions with respect to azimuth and zenith angles. The channel capacity of 2 × 2 and 3 × 3 MIMO systems using spatial polarisation diversity is presented for different antenna designs. The presented results show that the maximum channel capacity for an antenna contained within a small volume can be reached with careful selection of the orthogonal spatial fields. The results are also compared against planar array MIMO antenna systems, in which the antenna size considered was much larger. A 50% antenna size reduction method is explored by applying magnetic wall concept on the symmetry reference of the antenna structure. Using this method, a triple dual-band inverted-F antenna system is presented and considered for MIMO application. Means of achieving minimum coupling between the three antennas are investigated over the 2.45 GHz and 5.2 GHz bands. A new 2 2 MIMO dual-band balanced antenna handset, intended to minimise the coupling with the handset and human body was proposed, developed and tested. The antenna coupling with the handset and human hand is reported in terms the radiation performance and the available channel capacity. In addition, a dual-polarisation dipole antenna is proposed, intended for use as one of three collocated orthogonal antennas in a polarisation-diversity MIMO communication system. The antenna actually consists of two overlaid electric and magnetic dipoles, such that their radiation patterns are nominally identical but they are cross-polarised and hence only interact minimally.

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Floating-gate transistors similar to those used in FLASH and EEPROM can be used to build reconfigurable analog arrays. The charge on the floating gate can be modified to pass or block a signal in a cross-bar switch matrix, or it can be finely tuned to eliminate a threshold difference across a chip or set a bias. By using such a compact and versatile reconfigurable analog memory element, the number of analog circuit components included on an integrated circuit that is field-programmable is significantly higher. As a result, large-scale FPAAs can be built with the same impact on analog design that FPGAs have had on digital design. In my research, I investigate the areas floating-gate transistors can be used to impact FPAA design and implementation. An FPAA can be broken up into two basic components, elements of connection and elements of computation. With respect to connection, I show that a floating-gate switch can be used in a cross-bar matrix in place of a transmission gate resulting in less parasitic capacitance and a more linear resistance for the same size transistor. I illuminate the programming issues relating to injecting a floating-gate for use as a switch, including the drain selection circuitry and rogue injection due to gate induced drain leakage. With respect to computation, I explain how a Multiple-Input Translinear Element, or MITE, can be augmented to fit in an FPAA framework. I also discuss two different MITE implementations compatible with CMOS technology, a subthreshold MOS design and a BJT MITE that uses a lateral BJT. Beyond FPAA components, I present two alternative FPAA systems. The first is a general purpose reconfigurable analog system that uses standard analog design components that have been augmented with floating-gates. The second FPAA is built upon MITE circuits, and is focused on supporting direct system synthesis. I conclude with a discussion of a future large-scale MITE FPAA.

Recent developments in the area of microfabrication technologies, has enabled the fabrication of many radio frequency/microwave components with better performance and lower cost than possible with semiconductor based fabrication technology. Many of these microfabricated RF components such as switches and phase shifters, popularly known as RF MEMS, are aimed at reducing the insertion loss and improving other performance parameters such as linearity. For these devices size miniaturization is not necessarily important, as in practical subsystems, these components are integrated with RF front-ends on a laminate. This thesis deals with concepts of a low cost passive phase shifter fabricated in-situ on a microwave laminate. The operation of this Mesoscale Electrostatically actuated Phase shifter on microwave Laminate (MEPL) is similar to that of a micromachined distributed MEMS transmission line (DMTL) phase shifter. In spite of advantages of low losses, wide bandwidth, low DC power consumption and high linearity over semiconductor/MMIC technology, microfabricated phase shifters are often not used in field because of issues related to fabrication reliability, packaging and integration. On the other hand, the proposed MEPL will have all the advantages of conventional MEMS phase shifters with additional benefit of lower cost. Furthermore, these are integrable to form a monolithic phased array. A MEPL phase shifter of 50-bridges periodically distributed on the co-planar waveguide (CPW) transmission line is demonstrated in this thesis. MEMS air bridges are electrostatically actuated to vary the capacitance of the transmission line, which changes the phase velocity of the propagation RF signal, consequently phase at the output port. The realized MEPL is characterized for electromagnetic as well as electromechanical performance. The electromechanical characterization of this device is performed using a Laser Doppler Vibrometer (LDV). The measured data showed good agreement with the analytical data.. Major application of a phase shifter is in a phased array antenna system. MEPL is particularly suited for a monolithic phase array antenna. The proposed monolithic phased array antenna system fabrication approach utilizes extremely simple and economical modern printed circuit board technology to pattern the conventional microwave laminate and copper foil. A complete monolithic phased array antenna system is fabricated on a microwave laminate using an embedded phase shifter operating with electrostatic principles. Other components such as DC block and bias tee are integrated into the CPW-microstrip transitions to optimize the space and performance. Integrated phased array antenna is fabricated and tested to demonstrate the beam steering capability. Measured S11 is better than -15dB at the operating frequency of 9.8GHz. The beam steering capability is shown as proof of concept by showing the beam scan angle of 10deg with bias voltage of 125V. The mesoscale phase shifter demonstrated in this thesis has several advantages compared to micromachined phase shifters. The proposed fabrication approach does not use metal deposition/patterning process, which removes the need of high cost clean room and sophisticated films deposition equipments. Secondly, as there are no thin films used, stiction is not expected on phase shifters fabricated with this approach. Since this approach uses thicker metal films, the power handling capability is expected to be significantly higher than micromachined phase shifters. Since conventional phased array antenna system components are fabricated on a microwave laminate, micro machined phase shifters realized on semiconductor substrates are required to be packaged separately before integrating with such phased array circuits. Packaging of the micro-machined RF-MEMS/MEMS devices is still a major issue and contributes to a substantial part of the total cost. Unlike micromachined phase shifters which are required to be packaged and then embedded in phased array applications, device presented in this thesis is packaged in-situ. Compared to similar monolithic phased array antenna reported on silicon substrate which are limited by wafer size, these arrays can be easily extended for larger arrays on microwave laminate as these are available in large size. To summarize, the proposed fabrication approach for phase shifters overcomes many limitations of micromachined components for microwave applications while retaining most of their advantages compared to other existing approaches based on ferrites or semiconductor technologies.

Le travail présenté dans ce mémoire traite de l'étude d'oscillateurs et d'Oscillateurs Contrôlés en Tension (OCT) différentiels couplés appliqués à la commande d'un réseau d’antennes linéaire. Après avoir rappelé les concepts d'antennes réseaux et d'oscillateurs, une synthèse de la théorie élaborée par R. York et donnant les équations dynamiques modélisant deux oscillateurs de Van der Pol couplés par un circuit résonnant a été présentée. Après avoir montré la limitation de cette approche concernant la prédiction de l'amplitude des oscillateurs, une nouvelle formulation des équations non linéaires décrivant les états de synchronisation a été proposée. Néanmoins, compte tenu du caractère trigonométrique et fortement non linéaire de ces équations, une nouvelle écriture facilitant la résolution numérique a été proposée. Ceci a permis l'élaboration d'un outil de Conception Assistée par Ordinateur (CAO) fournissant une cartographie de la zone de synchronisation de deux oscillateurs de Van der Pol couplés. Celle-ci permet de déterminer rapidement les fréquences d'oscillation libres nécessaires à l'obtention du déphasage souhaité. Pour ce faire, une procédure de modélisation de deux oscillateurs et OCTs différentiels couplés, par deux oscillateurs de Van der Pol couplés par une résistance a été élaborée. Les résultats fournis par l'outil de CAO proposé ont ensuite été comparés avec les résultats de simulations de deux oscillateurs et OCTs différentiels couplés obtenus avec le logiciel ADS d'Agilent. Une très bonne concordance des résultats a alors été obtenue montrant ainsi l'utilité et la précision de l'outil présenté. / The work presented in this thesis deals with the study of coupled differential oscillators and Voltage Controlled Oscillators (VCO) used to control antenna arrays. After reminding the concept of antenna arrays and oscillators, an overview of R. York's theory giving the dynamics for two Van der Pol oscillators coupled through a resonant network was presented. Then, showing the limitation of this approach regarding the prediction of the oscillators' amplitudes, a new formulation of the nonlinear equations describing the oscillators' locked states was proposed. Nevertheless, due to the trigonometric and strongly non-linear aspect of these equations, mathematical manipulations were applied in order to obtain a new system easier to solve numerically. This has allowed to the elaboration of a Computer Aided Design (CAD) tool, which provides a cartography giving the frequency locking region of two coupled differential Van der Pol oscillators. This cartography can help the designer to rapidly find the free-running frequencies of the two outermost differential oscillators or VCOs of the array required to achieve the desired phase shift. To do so, a modeling procedure of two coupled differential oscillators and VCOs as two coupled differential Van der Pol oscillators, with a resistive coupling network was performed. Then, in order to validate the results provided by our CAD tool, we compared them to the simulation results of two coupled differential oscillators and VCOs obtained with Agilent’s ADS software. Good agreements between the simulations of the circuits, the models and the theoretical results from our CAD tool were found.

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