No description available.

The demand of wireless communication has increased significantly in the past few decades due to huge demand to deliver multimedia content instantly. The expansion of mobile content paired with affordable mobile devices has opened a new trend for having access to the latest information on mobile devices. This trend is made possible by the technology of smart antenna systems as well as array signal processing algorithms. Array signal processing is not limited to wireless communication, but also found in other applications such as radar, sonar and automotive. One of the important components in array signal processing is its ability to estimate the direction of incoming signals known as directional-of-arrival (DOA). The performance of DOA algorithms depends on the steering vector since it contains information about the direction of incoming signals. One of the main factors to affect the DOA estimation is the array geometries since the array factor of the array geometries determines the definition of the steering vector. Another issue in DOA estimation is that the DOA algorithms are designed based on the ideal assumption that the antenna arrays are free from imperfection conditions. In practice, ideal conditions are extremely difficult to obtain and thus the imperfect conditions will severely degraded the performance of DOA estimation. The imperfect conditions include the presence of mutual coupling between elements and are also characteristic of directional antenna. There are three topics being discussed in this thesis. The first topic being investigated is new geometry of antenna array to improve the performance of DOA estimation. Two variants of the circular-based array are proposed in this thesis: semi-circular array and oval array. Another proposed array is Y-bend array, which is a variant of V-shape array. The proposed arrays are being put forward to offer a better performance of DOA estimation and have less acquired area compared with the circular array. It is found out that the semi-circular array has 5.7% better estimation resolution, 76% lower estimation error, and 20% higher estimation consistency than the circular array. The oval array improves the estimation resolution by 33%, estimation error by 60%, and estimation consistency by 20% compared with the circular array. In addition, for the same number of elements, the oval array requires 12.5% to 15% less area than the circular array. The third proposed array, Y-bend array, has 23% smaller estimation resolution, 88% lower estimation error, and 7% higher estimation consistency than the V-shape array. Among the proposed arrays, the semi-circular possessed the best performance with 25% smaller estimation resolution, ten times smaller estimation error, and 5% higher estimation consistency over the other proposed arrays. Secondly, this thesis investigates the DOA estimation algorithm when using the directional antenna array. In this case, a new algorithm is proposed in order to suit the characteristics of the directional antenna array. The proposed algorithm is a modified version of the Capon algorithm, one of the algorithms in beamforming category. In elevation angle estimation, the proposed algorithm achieves estimation resolution up to 1°. The proposed algorithm also manages to improve the estimation error by 80% and estimation consistency by 10% compared with the Capon algorithm. In azimuth angle estimation, the proposed algorithm achieves 20 times lower estimation error and 20% higher estimation consistency than the Capon algorithm. These simulation results show that the proposed algorithm works effectively with the directional antenna array. Finally, the thesis proposes a new method in DOA estimation process for directional antenna array. The proposed method is achieved by means of modifying covariance matrix calculation. Simulation results suggest that the proposed method improves the estimation resolution by 5° and the estimation error by 10% compared with the conventional method. In summary, this thesis has contributed in three main topics related to DOA estimation; array geometry design, algorithm for the directional antenna array, and method in DOA estimation process for the directional antenna array.

In this thesis, we study the array theory and the array synthesis methods to design a sector antenna composed of a broadside collinear array and a corner reflector that is suitable for base stations. The antenna produces a sector beam in the horizontal plane to reduce the co-channel interference. In the elevation plane the antenna produces a narrower beam in order to achieve a higher gain. A uniform array is known to produce a high side lobe level which will cause serious interference. Therefore, Dolph-Tchebyscheff linear array method and Taylor line source method are utilized for the antenna design. We also design the structure of corner reflector which is combined with an array to form the sector antenna. We also study the switched-beam system, design and fabricate a 4¡Ñ1 microstrip patch antenna array to simulate the operation of the system and measure its performance.

This thesis work presents a study on the impact of mutual coupling among antenna arrays on the performance of the multipath simulator (MPS) system. In MIMO systems, it is a wellknown fact that the mutual coupling significantly affects their system performance. The impact of mutual coupling on MIMO system performance is an important consideration for compact antenna arrays. Hence, it is very important to investigate the impact of mutual coupling on the accuracy of measurements in a MPS system. In this project, the impact of coupling within the MPS array antennas is addressed by performing simulations based on the proposed MPS scattering model which fulfills the far-field (Fraunhoferdistance) boundary conditions. The coupling phenomenon within the MPS array antennas is studied by designing a uniform circular array (UCA) of radius,R consisting of NMPS antennas with single device under test (DUT) antenna at the center. The elements of the array are matched half-wave dipole antennas and the phase of the array elements is kept constant throughout. In this work it is assumed that all the elements in the array are identical and located in the far-field region. This study is carried out by performing MPS simulations in HFSS at the LTE-A band of 2.6GHz. The approach used to model the entire system is by comparing the S-parameters (S21: Forward transmission coefficient parameter) between various array configuration. The simulation results suggest that the impact of mutual coupling increases with the number of MPS antennas and decreases with the radius of the MPS ring. Theradiated power is also measured with and without mutual coupling. Finally, it is concluded that the impact of coupling within the MPS antennas is best countered by designing a large MPS system (preferably R = 10λ or greater), despite the higher incurred costs.

Diss. Uppsala : Univ., 2002.

In antenna array processing it is generally required to enhance the reception or detection of a signal from a particular direction while suppressing noise and interference signals from other directions. An optimisation problem often posed to achieve this result is to minimise the array processor mean output power (or variance) subject to a fixed response in the array look direction. The look direction requirement can be met by imposing a set of linear constraints on the processor weights to yield what is known as the Linearly Constrained Minimum Variance (LCMV) processor. It has been found, however, that LCMV processors are susceptible to errors in the assumed direction of arrival of the desired signal. To achieve robustness against directional mismatch, additional constraints known as derivative constraints can be introduced. These constraints force the first and second order spatial derivatives of the array power response in the look direction to zero. However, constraints corresponding to necessary and sufficient (NS) conditions for these spatial derivatives to be zero are in general quadratic, and the resulting weight vector solution space is non-convex. One approach to this complex problem has been to consider conditions which are only sufficient for the spatial derivatives to be zero. Whilst this results in linear constraints, it exhibits certain anomalous behaviour, for example, dependence on the choice of array phase centre.Recent work in the area of derivative constraints has resulted in a method for efficiently solving the non-convex output power minimisation problem with quadratic derivative constraints. The optimisation problem addressed assumes that the input signal statistics and hence the input signal autocorrelation matrix R are known. In practice, R must be estimated from the receiver data.The main contribution of this thesis is the derivation of a ++ / new adaptive algorithm which implements an adaptive array processor with look direction plus 1st and 2nd order NS derivative constraints. The new algorithm is derived from the well-known Recursive Least Squares (RLS) technique but allows linear and quadratic constraints to be incorporated within the recursive framework. The algorithm offers the high performance characteristics associated with RLS methods, namely, fast convergence and high steady-state accuracy. The work encompasses a study of the characteristics of the algorithm in terms of numerical robustness, convergence properties, tracking and computational complexity.The study of the numerical properties of the algorithm has led to the second important contribution of this thesis: the identification of a parameter which is central to the numerical stability of the algorithm in a practical fixed precision environment. We show that this parameter is bounded during stable operation and can therefore be used to detect the onset of numerical instability within the algorithm. In addition, we show how existing techniques can be used to significantly improve the numerical robustness of the algorithm.Another important contribution of the thesis stems from an investigation into the multimodal nature of the quadratic, equality constrained optimisation problem resulting from the use of second order NS derivative constraints. In particular, we show that for a linear antenna array operating under certain conditions, the complex multimodal optimisation problem can be greatly simplified. This has important implications in both optimum and adaptive array signal processing.

Over the last few years‚ the number of subscribers of wireless services has increased at an explosive rate. This ever growing demand for wireless communications services is constantly increasing the need for better coverage‚ improved capacity and higher quality service. Smart antennas system is an effective technology for the performance improvement of wireless communications. Switching-beam smart antennas use a number of fixed beams at an antenna site. The system provides a beam that offers the best signal enhancement and interference reduction. Using the approach of dynamic switching-beam antenna system‚ an intelligent sector beam synthesis of adjustable sector width can be established. By doing so‚ traffic load balancing can be achieved, and therefore, system capacity is increased. In this thesis, a beam-pattern synthesis algorithm proposed by M.H. Er is applied to shape array patterns with an adjustable mainlobe width and average sidelobe level reduction. Using an established database of weighting for circular arrays, the proposed smart antennas can adjust suitable sectors for the high dense subscribers not uniformly distributed. Simulation results demonstrate the proposed technique can dramatically improve the performance of traditional switching-beam antennas.

The switched-beam antenna is one type of the smart antennas, which consists of the antenna array and the beamforming network. The four-beam smart antenna generates four beams to cover a 120¢X area, which can be used to improve the carrier-to-interference ratio and the frequency reuse of a cellular system. Due to the attractive features of microstrip antennas such as low profile, easy fabrication, and low cost, we use microstrip antennas as array elements. In this thesis, we propose a novel four-beam beamforming network which consists of a 4¡Ñ4 Butler Matrix and four 180¢X power dividers. This network is able to provide low side-lobe level. A modified Butler Matrix not only simplifies the circuit of the 8¡Ñ8 Butler Matrix, but also meet the requirement of the original Butler Matrix. From the result of measurement, the side-lobe level of each beam of the modified Butler Matrix is less than ¡V10 dB. We also show that this method is applicable to any Butler matrix.

none

The performance of a planar Frequency Selective Surface (FSS) cannot be changed or adapted once the manufacturing process has been completed. In practice, however, it would be advantageous to be able to do so, in order to increase flexibility of performance in multiband systems for example. This thesis examines a novel electromagnetict echniquet hat has beend eveloped,w hereby the frequencya nd/or the angular response of FSS's can be tuned in situ over a wide range of frequencies and/or steering angles. The technique employed is passive and relies upon the displacemento f closely separated( and therefore closely coupled) arrays with respect to each other. A global loading of the array results so that the reconfigurable FSS (RFSS) will produce a broadband and/or multibeam response without altering the individual array design. The experience and understanding gained during this work was subsequently used to produce FSS responses of extreme angular stability. In this case a static, double layer structure has been used to make use of the high coupling between the layers i.e. two FSS's printed on a single dielectric substrate to form a close coupled FSS (CCFSS). It was found that the coupling between the two layers was highly dependent on the relative displacement between arrays. This displacement is introduced statically during the manufacture of the FSS. The cases described use two identical layers. A further development of this concept makes use of complementary conducting and aperture elements giving rise to a complementary FSS (CFSS). The CFSS is also manufactured on a common dielectric and produces ultra stable resonant frequencies for both TE and TM oblique incidences. Theoretical verification of the measured results has been achieved, and the measured and predicted results agreed very closely. Modal analysis, using a novel coupled integral equation technique, has been used to predict the response of the RFSS and CFSS. The correlation between the predicted and measured transmission response of the RFSS was very good and it was discovered that operational stability of the bandwidths and band spacing ratios were significantly improved over conventional static FSS.