An X-Band Code-Modulated Interferometric Imager

Abstract

Code-modulated interferometry (CMI) enables a lens-less approach to imaging in which incoming signals are code modulated, combined, and processed through a shared hardware path; visibility functions are demodulated from an aggregate power-detected response; and an image is obtained using an inverse Fourier transform of the visibility samples. CMI allows the imager to be constructed using low-cost conventional beamforming hardware. This article presents the theory of operation of a code-modulated interferometer array intended for active imaging. This includes the selection of codes, the use of phase shifters for modulation, the demodulation of visibility functions, the necessary calibration, and the image processing. The architecture and design of an active imaging prototype is then presented, where it is created using a commercially available 16-element 8-16 GHz beamforming receiver along with a sparse antenna array that generates 169 distinct visibility samples. The imaging capabilities are demonstrated through the detection of multiple point sources at 10 GHz. Finally, the feasibility of creating a larger 64-element imager with 961 visibility samples is demonstrated through construction and measurements of a single row within that array.