Antenna arrays: Performance limits and geometry optimization

The radiation pattern of an antenna array depends strongly on the weighting method and the geometry of the array. Selection of the weights has received extensive attention, primarily because the radiation pattern is a linear function of the weights. However, the array geometry has received relatively little attention even though it also strongly influences the radiation pattern. The reason for this is primarily due to the complex way in which the geometry affects the radiation pattern. The main goal of this dissertation is to determine methods of optimizing array geometries in antenna arrays.; An adaptive array with the goal of suppressing interference is investigated. It is shown that the interference rejection capabilities of the antenna array depend upon its geometry. The concept of an interference environment is introduced, which enables optimization of an adaptive array based on the expected directions and power of the interference. This enables the optimization to perform superior on average, instead of for specific situations. An optimization problem is derived whose solution yields an optimal array for suppressing interference. Optimal planar arrays are presented for varying number of elements. It is shown that, on average, the optimal arrays increase the signal-to-interference-plus-noise ratio (SINR) when compared to standard arrays.; Sidelobe level is an important metric used in antenna arrays, and depends on the weights and positions in the array. A method of determining optimal sidelobe-minimizing weights is derived that holds for any linear array geometry, beamwidth, antenna type and scan angle. The positions are then optimized simultaneously with the optimal weights to determine the minimum possible sidelobe level in linear arrays. Results are presented for arrays of varying size, with different antenna elements, and for distinct beamwidths and scan angles.; Minimizing sidelobes is then considered for 2D arrays. A method of determining optimal weights in symmetric 2D arrays is derived for narrowband and wideband cases. The positions are again simultaneously optimized with the weights to determine optimal arrays, weights and sidelobe levels. This is done for arrays with varying number of elements, beamwidths, bandwidths, and different antenna elements.