Utilization of harmonics in phaseless near-field microwave computational imaging based on space–time-coding transmissive metasurface

Abstract

Based on a space–time-coding (STC) transmissive metasurface (TMS), we present the utilization of electromagnetic harmonic spectra in phaseless near-field microwave computational imaging (CI). Each element of the TMS integrates one PIN diode as a switch to independently regulate the transmission amplitude, giving rise to a 14-dB modulation depth at 21 GHz. Using the TMS and two standard horn antennas, a phaseless near-field microwave CI system is established in a single-pixel manner. A simple and effective space–time-coding scheme is detailed to covert a monochromatic signal into multiple harmonics that can be applied to sample the objects. To obtain the sensing matrix built by the harmonics, we propose a method that is developed from the Fresnel diffraction theory. Moreover, we experimentally validate our CI system by reconstructing two metallic objects. The reported STC scheme and the corresponding CI system using TMS could inspire future studies on low-cost imaging hardware development and harmonic wave utilization for high-resolution CI systems.