PhD Thesis on Code Modulated Interferometric Imaging System using Phased Arrays

Abstract

CHAUHAN, VIKAS. PhD Thesis on Code Modulated Interferometric Imaging System using Phased Arrays. (Under the direction of Brian A. Floyd.) This work presents techniques which can allow low-cost phased-array receivers to be reconfigured or re-purposed as interferometric imagers, removing the need for custom hardware and thereby reducing cost. Since traditional phased arrays power combine incoming signals prior to digitization, orthogonal code-modulation is applied to each incoming signal using phase shifters within each front-end and two-bit codes. These codemodulated signals can then be combined and processed coherently through a shared hardware path. Once digitized, visibility functions can be recovered through squaring and code-demultiplexing operations. Provided that codes are selected such that the product of two orthogonal codes is a third unique and orthogonal code, it is possible to demultiplex complex visibility functions directly. As such, the proposed system modulates incoming signals but demodulates desired correlations.Firstly, we present the operation of the system, a validation of its operation using behavioral models of a traditional phased array and a benchmarking of the code-modulated interferometer against traditional interferometer using simulation results and sensitivity analysis. Secondly, for the proof of concept with a prototype, we present a simple CMI system operating in the license-free 60-GHz band using a four-element phased-array receiver developed for IEEE 802.11ad (WiGig) and packaged with compact antenna structures. The four-element 60-GHz phased array chip is wire-bonded onto a Rogers-5880 substrate board with on-board slot antennas, and a single 60-GHz output is measured using a power detector. This scalar measurement is then demodulated to obtain the interferometric visibilities.The four-element phased array is thinned to obtain a 13-pixel image and the system is