Distributed microwave wireless systems have the potential to dramatically reshape wireless technologies due to their ability to provide improvements in robustness, transmit power, antenna gain, spatial and temporal resolutions, size, scalability, secrecy, flexibility, and cost compared to single-platform wireless systems. Traditional wireless systems use a platform-centric model, where improving capabilities generally necessitates hardware retrofitting, which in many cases can result in a bulky, expensive, and inefficient system. Nevertheless, distributed microwave wireless systems require precise coordination to enable cooperative operation. The most highly synchronized systems coordinate at the wavelength level, supporting coherent distributed operations like beamforming. The electric states that need to be synchronized in coherent distributed arrays are mainly the phase, frequency, and time; the synchronization can be accomplished using multiple architectures. All coordination architectures can be grouped under two categories: open loop and closed loop. While closed-loop systems use feedback from the destination, open-loop coherent distributed arrays must synchronize their electrical states by only relying on synchronization signals stemming from within the array rather than depending on feedback signals from the target. Although harder to implement, open-loop coherent arrays enable sensing and other delicate communications applications, where feedback from the target is not possible. In this thesis, I focus on phase alignment and frequency synchronization for open-loop coherent distributed antenna arrays. Once the phase and frequency of all the nodes in the array are synchronized, it is possible to coherently beamform continuous wave signals. When information is modulated on the transmitted continuous waves, time alignment between the nodes is needed. However, time alignment is generally less stringent to implement since its requirements are dependent on the information rate rather than the beamforming frequency, such as for phase and frequency synchronization. Beamforming at 1.5 GHz is demonstrated in this thesis using a two-node open-loop distributed array. For the presented architecture, the phases of the transmitting nodes are aligned using synchronization signals incoming from within the array, without any feedback from the destination. A centralized phase alignment approach is demonstrated, where the secondary node(s) minimize their relative phase offsets to that of the primary node by locating the primary node and estimating the phase shift imparted by the relative motion of the nodes. A high accuracy two-tone waveform is used to track the primary node using a cooperative approach. This waveform is tested with an adaptive architecture to overcome the performance degradation due to weather conditions and to allow high ranging accuracy with minimal spectral footprint. Wireless frequency synchronization is implemented using a centralized approach that allows phase tracking, such that the frequencies of the secondary nodes are locked to that of the primary node. Once the phase and frequency of all the nodes are synchronized, it is possible to coherently beamform in the far field as long as the synchronization is achieved with the desired accuracy. I evaluate the required localization accuracies and frequency synchronization intervals. More importantly, I demonstrate experimentally the first two-node open-loop distributed beamforming at 1.5 GHz with multiple scenarios where the nodes are in relative motion, showing the ability to coherently beamform in a dynamic array where no feedback from the destination is needed.
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