الفهرس 
IntroductionOnly 14 pages are availabe for public view
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Abstract
Digital beamforming involves the use of the antenna array and signal processing. It is very important for many communication applications such as radar, wireless network, cognitive radio, and the multiple input multiple output (MIMO) systems when there is a limitation on the transmission distance, power spectrum, and frequency spectrum.The signals using the same frequencies, the same propagation direction, and the same polarization can cancel out with destructive interference and sometimes add up with constructive interference. Digital beamforming uses this property to create spatial filtering that can direct the transmission or reception of signals in a specific direction. It has ability to steer the main beam towards the desired signal and pattern nulling towards the directions of interfering signals to overcome the limitation on the frequency spectrum. Also, it can increase the transmission distance by using the same radiated energy, as the energy will be concentrated towards a determined direction instead of being radiated in random directions. The thesis introduced a new adaptive beamforming (ABF) of linear antenna arrays via adaptive antenna array synthesis instesad of procssing of the received signal. The proposed algorithm is based on a combination between the Direction of Arrival (DOA) estimation and the Method of Moments (MoM). This combination between the estimation and numerical techniques results in a robust DM/ABF algorithm which is marked by flexibility, low computational complexity, high accuracy, and less computational time. The algorithm accepts a desired radiation pattern and provides the excitation coefficients that realize the required pattern. The algorithm is used to steer the main beam towards the direction of the desired signal and creates pattern nulling towards the directions of the interfering signals to improve the signal to interference and noise ratio (SINR). Also, the thesis introduced two new distributed beamforming algorithms for randomly distributed antenna arrays. The first algorithm is used to synthesize the ordinary array pattern using a reduced number of distributed nodes. The number of nodes reduction is very important especially in the applications where the number of nodes is a limiting factor such as radar systems, satellite communications, and mobile communications. The proposed algorithm provides the synthesized pattern via controlling the three main parameters of the antenna array which are the number of nodes, nodes locations, and nodes excitations. It selects the suitable number of nodes according the minimum mean square error (MSE) between the ordinary pattern and the synthesized pattern. It provides the synthesized patterns using either uniform feeding or non-uniform feeding. The simulation results revealed that the synthesized patterns unsing non-uniform feeding are better than patterns synthesized using uniform feeding. The second distributed beamforming algorithm is introduced to provide maximum side lobe level (SLL) reduction for the random antenna arrays in the open loop systems. It controls the node transmission energy without any changes in the nodes locations. The SLL reduction has a great importance in recent communication systems. It is considered as one of the most important applications of digital beamforming since it reduces the effect of interference arriving outside the main lobe. This interference reduction increases the capacity of the communication systems.