Low-Altitude UAV Detection Based on Vehicle-Mounted Wideband Programmable Metasurface

The private and indiscriminate flying of low-altitude unmanned aerial vehicles (UAVs) seriously violates human privacy and airspace traffic safety. In this work, we propose a low-altitude UAV detection system based on the programmable metasurface-enabled 4-D radar, mounted on an unmanned ground vehicle (UGV). For the first time, we utilize this simple single-input single-output (SISO) transceiver architecture to acquire 3-D location information of the UAV and point cloud images. Besides, for improving the detection resolution and range, a wideband 1-bit programmable metasurface with wide-angle beam-scanning capacity is proposed. The bow-tie reflecting element soldering one PIN diode is designed to offer a stable 1-bit phase shift within 180
$^{\circ}$

$\pm$
25
$^{\circ}$
from 6.88 to 13.62 GHz (65.8% relative bandwidth). The radiated performance of the programmable metasurface is measured, and the generated pencil beam can be steered within
$\pm$
60
$^{\circ}$
in both the x-or y-axis from 8.2 to 12 GHz (37.6% relative bandwidth), which is outstanding among the state-of-the-art works. As a proof of concept, the FMCW radar integrates a programmable metasurface in the transmitter to dynamically manipulate the beam, and a UGV is employed as a carrier to address challenges in mobility and deployment. An outdoor experiment has been carried out, and the 3-D imaging results show the integrated 4-D radar can realize 3-D positioning of the UAV in the surveillance airspace. With both low complexity and low cost, it is a fascinating option for low-altitude target detection and even trajectory tracking and target recognition in the future.