Enabling Real-Time Near-Field Focusing Imaging With Space-Time-Coding Metasurface Antenna

This article proposes a microwave near-field focus steerable imaging system operating at 22.5 GHz, built upon a space-time-coding metasurface antenna (STCMA), featuring real-time dynamic sensing capabilities. A novel synthetic method is developed to design the required amplitude envelopes, thereby achieving near-field focusing (NFF) for STCMA. By utilizing a field-programmable gate array (FPGA) for encoding the operation of meta-atoms, the designed STCMA is capable of rapidly manipulating subwavelength NFF beams along the axis parallel to its long side, achieving an optimal focal length of 60 mm. Scattering fields from the illuminated object are collected by an open-ended waveguide for scene mapping. A calibration procedure, in conjunction with a compensation model, is implemented to counteract measurement errors and inconsistencies, thereby enhancing the imaging quality. MATLAB scripts are developed to refresh the data stream through interactions with FPGA and vector network analyzer (VNA), enabling 1-D real-time detection and characterization of various concealed metal and dielectric objects with a large field of view (FoV) of 90°. The proposed imager is expanded to achieve 2-D imaging within seconds by incorporating mechanical translation. The proposed study advances the STCMA technology from the level of component design to that of system application and lays the groundwork for future research into metasurface-based super-resolution real-time imaging at higher frequencies.