چكيده به لاتين
In this thesis, the beamforming in Nested (NSA) and Co-prime (CSA) sparse sensor arrays with nonuniform linear geometries has been investigeted. The sparse arrays like CSA and NSA have attracted much attention in direction finding field, while, for passive beamforming, the grating lobes affect their usage in practice. The main goal of this study is the bemforming with reduced grating lobes while maintaining the positive features of these arrays. To achieve this aim, we provide two new approaches for synthesizing the beam pattern in CSA and NSA, containing beam synthesis with null steering method and beam synthesis with multiplicative beamforming method. At first approache, we propose a novel method based on null synthesis with cancellation beams (NSCBs) under original pattern perturbations minimization. In this method, the angular location of the grating lobes in the CSA subarrays are analytically extracted. Then, using the NSCBs method, the grating lobes of the subarrays nulled by adaptive weighting of the CSA elements. We have also shown that the original pattern perturbations minimization problem in mean square sense reduces to minimizing the perturbation of the array excitation. The proposed method will be formulated as a quadratic optimization problem, which can be efficiently solved using the method of Lagrange multipliers. At second approach, we propose a novel method based on digital beamforming at sub-array level using product and min processors. In this method, the main goal is nulling the grating lobes with known directions using multiplication of virtual and real patterns. Hence, the angular location of the grating lobes in the CSA sub-arrays are analytically extracted and trimmed so that by using new strategies, the grating lobes of the considered sub-array removed by nulls of the other sub-array. Moreover, we develop a novel sparse antenna array, so-called Extended Optimum Co-Prime Sensor Array (EOCSA), for direction of arrival (DOA) estimation of received signal. Here, we use a prototype co-prime sensor array to design the EOCSA. The simulation results illustrate the EOSCA ability to reaches the same pattern of a Full ULA using relatively few sensors. Careful analysis has been made on the details of the algorithms. Many interesting results have been provided in terms of different criteria. The analytical and simulated results demonstrate that the power pattern obtained by the proposed methods in the CSA, in terms of side lobe levels (SLLs), peak side lobe ratio (PSLR) and integrated side lobe ratio (ISLR), is better than the previous methods, so called product and min processors. The PSL value in the first and second approaches are lower than -10 dB and -13 dB, respectivelly. In both approaches, the signal-to-noise ratio of the output signal of the array increases from a min(N1, N2) to N1+N2-1 compared to previous processors. In the both proposed processors the effect of cross-terms are less than the previous ones.
