A Single Metasurface Can Perform Range‐Velocity Detection and Target Imaging Simultaneously at Single Frequency

Abstract

the intensity ratio of sum and difference beams is independent of target distance. Nevertheless, producing sum and difference beams needs either complicated feeding network [11][12][13] or elaborate signal processing, [14,15] leading to high costs in hardware or software.When the target moves toward the detection system or vice versa so that geometries of the target cannot be ignored, the target should be treated as an expanded target instead of a point target, otherwise, angle glint occurs in detections with sum and difference beams. [16,17] Under this circumstance, imaging of the expanded target is necessary. Many imaging methods have been proposed, such as back projection algorithm, [18,19] chirp scaling algorithm [20][21][22] and Range-Doppler algorithm. [23][24][25] In order to acquire necessary spatial resolution, phased arrays or multiple-in-multiple-out (MIMO) antennas are commonly used for electromagnetic imaging. [26][27][28] However, phased arrays or MIMO antennas have to equip each antenna with an independent transceiver, thus leading to high cost and complex hardware architecture. Moreover, signal processing of beam steering and target imaging are involved with each other, namely that radar signals passing through the transceivers have to be re-modulated so that phased arrays or MIMO antennas can produce specified radiation patterns. This process increases the burden of signal processing.Digital programmable metasurfaces (DPMs) are electromagnetic surfaces that constitute massive reconfigurable unit elements. Scattering waves of the DPMs can be directly modulated by programming electromagnetic states of all the elements. [29] These electromagnetic states are also referred to as aperture codes of the DPM. By designing aperture codes of the DPMs, electromagnetic waves can be directly modulated in time-frequency domain and space domain. [30] Due to their extraordinary capability in manipulating electromagnetic waves, DPMs have been extensively researched in many areas such as compact signal computation processor, [31,32] dynamic beam control, [33][34][35][36][37] holographic imaging, [38][39][40][41][42] direction-ofarrival (DOA) estimation, [43,44] radar systems [44][45][46][47][48][49] and wireless Range, velocity, and geometric shape are primary features of a moving target. Obtaining these features usually needs high-cost system and complicated signal processing. Here, a single-frequency mechanism to detect these features simultaneously with digital programmable metasurface (DPM) in transmission type is proposed. For range-velocity detection, the DPM can produce sum beams whose radiation phases are modulated by sequentially changing aperture codes of the metasurface to generate biphase coded signals, in which the Range-Doppler algorithm is used to estimate the range and velocity information of a moving target. Then difference beams are generated by the metasurface, and the sum-difference ratios of echo signals are used to locate the target. For two-dimensional imaging, random radiation patterns are p...

Simultaneously Intelligent Sensing and Beamforming Based on an Adaptive Information Metasurface

“…[45] This is particularly true for achieving multiple functions simultaneously instead of in a timedivision switching manner. [46][47][48] Therefore, the next stage goal is to develop a device/system that can simultaneously perform EM sensing and manipulation. To this end, some metasurfaces with EM sensors placed among the meta-atoms array were proposed to recognize the basic properties of EM waves (e.g., frequency, [49] amplitude, [50] and polarization [51] ) and manipulate the EM wavefronts simultaneously.…”