First Demonstration of Metamaterial-Modulated Tag Localization and Imaging Based on $K$ -Band FMCW Mini-SAR System

Radio frequency tag detection by radars has received much attention in recent years for its long working distance and high positioning accuracy. This study proposes a novel method that combines synthetic aperture radar (SAR) system with metamaterial-modulated tags that can simultaneously achieve tag positioning and imaging. However, the high working frequency of SAR and the noncoherence between SAR and tag signals pose great challenges to the design and focused imaging of tag. Based on the mathematical model establishment of modulated target imaging, a new transmission waveform strategy and signal processing method were developed for simultaneous focused imaging of scenes and tag that were verified through simulation. Meanwhile, a tag-designing method based on metamaterial modulation was proposed, and direct loading of modulation signals onto radar echoes in the millimeter-wave band was realized. Additionally, an experimental system based on vehicle-mounted miniaturized SAR (Mini-SAR) and metamaterial tag was established. The experimental results indicated that focused images of the tag and environment were simultaneously obtained, and the SAR system realized long-distance, accurate detection, and positioning of the tag, with a working distance of 300 m, a range resolution of 27 cm, an azimuth resolution of 18 cm, and a positioning accuracy of 1.5 cm.