An optimization paradigm for wideband antenna arrays : integrating electromagnetics and information theory

Date

2021-12-03

Authors

Saab, Sandy

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Abstract

As larger bandwidths are used in multiple-antenna wireless systems, the frequency selectivity of the antenna arrays starts to impact rate. Therefore, optimizing the achievable rate in compact antenna arrays becomes important especially for future wireless networks that can require octaves of bandwidth. With the emergence of 6G technologies, using terahertz (THz) frequency bands become inevitable to achieve terabit rates. Hence, in this dissertation, we focus on combining wireless communication theory and electromagnetics theory to provide a new platform that addresses the challenges in future wireless networks. In this dissertation, we introduce a circuit-level analysis of compact wideband antennas at sub-6GHz bands. We present an approach that combines the mathematics of information theory with the physics behind antenna theory. Then, we focus on designing antenna arrays for future 6G technologies that can maintain a full rank channel in the presence of a line-of-sight (LoS) component. Lastly, we introduce a passive reflective intelligent surface (RIS) that helps in redirecting the signal efficiently to the intended user. In Chapter 2 of the dissertation, we focus on optimizing the achievable rate in compact antenna arrays. We present a system model that incorporates the effects of mutual coupling (MC) of wideband physically realizable single-input multiple-output (SIMO) and multiple-input single-output (MISO) antenna systems. For the SIMO system setup, we extract the noise correlation matrices for two different antenna array configurations (parallel and co-linear). We optimize the inter-element spacing in each alignment while maximizing the achievable rate and fixing the transmit power. Then, we compare the two compact antenna designs to a perfectly matched single omni-directional antenna while accounting for MC. Likewise, for the MISO antenna system, we derive the optimal beamformer that maximizes the achievable rate using the same antenna configurations as the SIMO system. Then, we study the impact of MC and develop a new single-port matching technique for wideband antenna arrays. Finally, we provide reciprocity plots to compare the performance of the SIMO-MISO systems using different channel models. In Chapter 3 of the dissertation, we present an optimized antenna port switching technique for a LoS multiple-input multiple-output (MIMO) system operating at THz frequencies. MIMO technology usually requires a rich scattering environment to work properly and uses non-line-of-sight (NLoS) components. When MIMO is used in high-frequency point-to-point microwave links, however, the channel will have a dominant LoS component. For a LoS MIMO system to maintain spatial diversity, the signal streams should remain orthogonal to each other. Therefore, we design an optimally spaced uniform linear array (ULA) and non-uniform linear array (NULA) that preserves the orthogonality between the signals in a mesh grid network. We present a novel technique that selects the proper antenna ports to be activated which results in preserving the signal stream orthogonality and achieves a good condition number for the channel matrix. Finally, we provide bit error rate (BER) plots to show the performance and flexibility of this novel approach. In Chapter 4 of the dissertation, we design a reconfigurable intelligent surface, which controls the state of the imposing electromagnetic waves at THz frequencies. Since at THz frequencies there is significant and severe path loss, current beamforming techniques use costly phased arrays or bulky reflector antennas that hinder and limit their applications. Furthermore, THz frequencies are highly susceptible to frequent link outages due to misalignment and obstruction thus severely affecting the overall system throughput and reliability. As a result, the designed RIS controls the properties of an electromagnetic signal and acts as a reflector and directs the impinging wave to its proper receiver (i.e. user equipment, base station). The reflective surface controls the phase of the reflected wave from each unit-cell, hence steers the reflected signal from the surface of the array to reach the intended user equipment and improves the user’s signal-to-noise ratio (SNR). To show the effectiveness of our design, we provide plots of the beam-steering angle of the RIS.

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