Adaptive array antennas use has been limited to non-commercial applications due to their high cost and hardware complexity. The implementation cost of adaptive array antennas can be kept to a minimum by using cost effective antennas, reducing the number of elements in the array and implementing efficient beamforming techniques. This thesis presents techniques for the design of adaptive array antennas which will enable their cost effective implementation in wireless communication systems. The techniques are investigated from three perspectives, namely, reconfigurable antenna design, wide scan array design and single-port beamforming technique. A novel single-feed polarisation reconfigurable antenna design is proposed in the first stage of this study. Different polarisation states, namely, linear polarisation (LP), left-hand circular polarisation (LHCP) and right-hand circular polarisation (RHCP), are achieved by perturbing the shape of the main radiating structure of the antenna. The proposed antenna exhibits good axial ratio (< 3 dB at 2.4 GHz) and has high radiation efficiency in both polarisation modes (91.5 % - LHCP and 86.9 % - RHCP). With a compact single feeding structure, the antenna is suitable for implementation in wireless communication devices. The second stage of the study presents the design procedure of wide scan adaptive array antennas with reduced number of elements. Adaptive array antennas with limited number of elements have limited scanning range, reduced angular scanning resolution and high sidelobe levels. To date, design synthesis of adaptive array antennas has been targeted on arrays with a large number of elements. This thesis presents a comprehensive analysis of adaptive array antennas with less than 10 elements. Different array configurations are analysed and various array design parameters such as number of elements, separation between elements and orientation of the elements are analysed in terms of their 3 dB scan range. The proposed array, the 3-faceted array, achieves a scanning range up to ±70°, which is higher than ±56° obtained from the Uniform Linear Array. The faceted arrays are then evaluated in the context of adaptive beamforming properties. It was shown that the 3-faceted array is suitable for adaptive array applications in wireless communication systems as it achieves the highest directivity compared to other faceted structures. The 3-faceted array is then synthesised for low sidelobe level. Phase correction together with amplitude tapering technique is applied to the 3-faceted array. The use of conventional and tuneable windowing techniques on the 3- faceted array is also analysed. The final stage of the study investigates beamforming techniques for the adaptive array antenna. In the first part, beamforming algorithms using different performance criteria, which include maximum signal-to noise-ratio (SINR), minimum (mean-square Error) MSE and power minimisation, are evaluated. In the second part, single-port beamforming techniques are explored. In previous single-port beamforming methods, the spatial information of the signals is not fully recovered and this limits the use of conventional adaptive beamforming algorithms. In this thesis, a novel signal estimation technique using pseudo-inverse function for single-port beamforming is proposed. The proposed polarisation reconfigurable antenna, the 3-faceted array antenna and the single-port beamforming technique achieve the required performance, which suggests the potential of adaptive array antennas to be deployed commercially, especially in wireless communication industry.

Perturbation techniques are useful in the design of low complexity adaptive antenna arrays for estimating the gradient required in stochastic descent algorithms. Implementing projected perturbation sequences in an adaptive array allows the simultaneous reception of signals and the adaptation of the array weights while preserving the constraints imposed on the array weights.This thesis quantifies the performance of narrowband adaptive array processors that employ projected perturbation techniques. For different perturbation receiver structures the performance is determined under idealised conditions and importantly also when practical implementation issues are taken into account.The arrays performance is characterised by analysing the transient performance of the weight covariance matrix and by determining the misadjustment. By drawing similarities between two established analysis techniques a new misadjustment analysis technique is introduced.Practical implementation can impact on the arrays performance such that the benefit of the projected perturbation approach is lost. By characterising the array's sensitivity to perturbation noise additional projections which counteract some implementation effects are identified. The level of loss of performance due to weight quantisation and the limited dynamic range of the array weights is determined.

No / Adaptive arrays have the capability to direct or steer the main beam in real time in a desired direction, or towards signal of interest (SOI), whilst suppressing interference or multipath signals. Reactive loading and time modulated switching techniques are applied to steer the beam of a uniform circular six element antenna array having a source element at its centre. Genetic algorithm (GA) optimization is used to calculate optimal values for the reactances loading the parasitic elements, from which the gain can be optimized in a desired direction. For temporal switching, the GA is also used to determine the optimal on and off times for the parasitic elements. This gives the difference in the induced currents, optimies the gain and steers the beam in a desired direction. These methods are demonstrated for a vertically polarised array configuration operating at 2.45GHz. Simulation results show that near optimal solutions for gain, sidelobe level reduction, with VSWR 3 over a 100MHz bandwidth, and beam steering is achievable by the GA optimisation.

The objective of this thesis is to design, build and evaluate a direction-of-arrival measurement system using an antenna array operating at 2050 MHz. The first phase of the project is an extensive study of various high resolution DOA estimation algorithms. The algorithms studied include subspace-based techniques such as the MUSIC (MUltiple Signal Classification) and ESPRIT (Estimation of Signal Parameters via Rotational Invariance) algorithm, and the integrated approaches which combine property restoral-based techniques such as the Iterative Least Squares Projection-based Constant Modulus Algorithm (lLSP-CMA) with subspace-based techniques. All these algorithms were simulated in MATLAB and their performance under different conditions were tested and compared. In the second phase of the project a six element uniformly spaced linear array receiver was built. Three Ariel DSP-96 boards based on the Motorola DSP96002 are used to simultaneously sample, collect, and store data from each of the array elements. The data collected by the DSP boards are processed off-line to estimate the directions of arrival. Several experiments are conducted to test the functioning of the system under various conditions, and demonstrate the performance of different algorithms. Results of these experiments are also presented in this thesis. / Master of Science

Today, owners of small communicating device are interested in transmitting or receiving various multimedia data. By increasing the number of antennas at the transmitter and/or the receiver side of the wireless link, the diversity/Multiple-Input Multiple-Output (MIMO) techniques can increase wireless channel capacity without the need for additional power or spectrum in rich scattering environments. However, due to the limited space of small mobile devices, the correlation coefficients between MIMO antenna elements are very high and the total efficiencies of MIMO elements degrade severely. Furthermore, the human body causes high losses on electromagnetic wave. During the applications, the presence of users may result in the significant reduction of the antenna total efficiencies and highly affects the correlations of MIMO antenna systems. The aims of this thesis are to investigate and enhance the MIMO/diversity performance of multiple antenna systems in the free space and the presence of users. The background and theory of multiple antenna systems are introduced briefly first. Several figures of merits are provided and discussed to evaluate the multiple antenna systems. The decoupling techniques are investigated in the multiple antenna systems operating at the higher frequencies (above 1.7 GHz) and with high radiation efficiency. The single, dual and wide band isolation enhancements are realized through the half-wavelength decoupling slot, quarter-wavelength decoupling slot with T-shaped impedance transformer, tree-like parasitic element with multiple resonances, as well as the different polarizations and radiation patterns of multiple antennas. In the lower bands (lower than 960 MHz), due to the low radiation efficiency and strong chassis mode, the work mainly focused on how to directly reduce the correlations and enlarge the total efficiency. A new mode of mutual scattering mode is introduced. By increasing the Q factors, the radiation patterns of multiple antennas are separated automatically to reduce the correlations. With the inter-element distance larger than a certain distance, a higher Q factor also improved the total efficiency apart from the low correlation. A wideband LTE MIMO antenna with multiple resonances is proposed in mobile terminals. The high Q factors required for the low correlation and high efficiencies in mutual scattering mode is reduced with another mode of diagonal antenna-chassis mode. Hence, the bandwidth of wideband LTE MIMO antenna with multiple resonances mentioned above can be further enlarged while maintaining the good MIMO/diversity performance. The user effects are studied in different MIMO antenna types, chassis lengths, frequencies, port phases and operating modes. Utilizing these usefully information, an adaptive quad-element MAS has been proposed to reduce the user effects and the some geranial rules not limited to the designed MAS have also been given. / <p>QC 20130121</p> / EU Erasmus Mundus External Cooperation Window TANDEM

[pt] Este trabalho tem como objetivo avaliar alguns aspectos da utilização de antenas adaptativas em um sistema celular digital CDMA. Uma das razões para isto é que as antenas adaptativas reduzem a interferência que no sistema CDMA influencia direta e fortemente a capacidade do sistema. Inicialmente foi feito um resumo dos princípios gerais dos arranjos de antenas de sistemas celulares digitais e de algoritmos de adaptação. Com base nestes princípios, é analisada a aplicação específica a sistemas CDMA, estabelecendo-se uma modelagem do receptor incluindo o receptor Rake. É avaliado então através de simulação o comportamento de dois importantes métodos de filtragem espacial adaptativa para sistemas CDMA. / [en] This work aims to evaluate some aspects of the use of adaptive arrays in digital celular CDMA systems. One reason for that is that adaptive arrays reduce the interference which strongly affects the performance of the system. First the general principles of adaptive antennas, digital cellular systems and adaptation algorithm are sumarized. Based on that principles, the application to CDMA systems is addressed, and a receiver model is developed, including the Rake receiver. Then the behavior of two filtering techniques is evaluated through computer simulation. / [es] Este trabajo tiene como objetivo evaluar algunos aspectos de la utilización de antenas adaptativas en un sistema celular digital CDMA. Una de las razones para esto es que las antenas adaptativas reducen la interferencia, que en el sistema CDMA influeye directa y fuertemente em la capacidad del sistema. Inicialmente se realizó un resumen de los principios generales de los arranjos de antenas de sistemas celulares digitales y de algoritmos de adaptación. Con base en estos princípios, se analiza la aplicación específica a sistemas CDMA, estableciendo una modelaje del receptor incluindo el receptor Rake. Se evalúa a través de simulación el comportamiento de dos importantes métodos de filtraje espacial adaptativa para sistemas CDMA.