Architectures and system design for digitally-enhanced antenna arrays

Abstract

Digital techniques have had longstanding use in both the operational control and signal processing efforts associated with phased array antennas. Fundamentally, these techniques have served to provide additional levels of convenience and performance over the fully analog counterparts, without specifically addressing the underlying design of the analog hardware aspects of the arrays. The class of digitally-enhanced hardware has recently emerged, wherein "digitally aware" design approaches are used for the purpose of alleviating the high cost and complexity of sophisticated analog devices. Emergent trends in millimeter wave and low-terahertz circuit technology are enabling the prospect of physically small, yet electrically large antenna arrays for a host of exciting new communication, radar, and imaging applications. Still, the high cost of phased arrays remains a significant bottleneck to any widespread deployment in this regard. In light of this challenge, we propose two phased array architectures for which the notion of digital awareness plays a central role in their designs. The Dense Delta-Sigma Array: Primarily motivated by advancements in low-cost fabrication, this design concept provides the opportunity to replace the expensive RF components required to control the individual array element excitations with inexpensive phase shifter components having particularly coarse resolution (as few as 2-bits). This is made possible by increasing the number of array elements for a given aperture beyond the nominal number associated with the standard half-wavelength spacing. This approach is inspired by Delta-Sigma data converters, which employ faster-than-Nyquist sampling with low quantization resolution. The Sparse Multi-Coset Array: This design concept exploits the sparsity commonly found in typical environments to allow for target detection and imaging with significantly fewer array elements than prescribed by conventional half-wavelength spacing. The result is a structured periodic non-uniform array composed of a number of distinct subarrays known as cosets. This approach is inspired by multi-coset sampling, for which the average sampling rate may be reduced below the Nyquist convention when the spectral components within the overall bandwidth are limited to some number of sub-bands. In this approach, we view the underlying engineering design problem as one of compressive sensing. In this thesis, we develop and apply the underlying mathematical principles and concepts of the dense and sparse arrays, taking into account the practical constraints and issues that make the system design, analysis, and performance evaluation rich from an engineering perspective.