Time-Frequency-Modulated Metasurface for False Target Generation in Symmetrical Triangular LFM Continuous-Wave Radars

In this work, we present a radar countermeasure technique based on time-modulated metasurfaces for false target generation in radar systems that make use of symmetrical triangular linearly frequency-modulated (ST-LFM) signals. The technique leverages on the dynamic change of the artificial Doppler frequency shift induced by the metasurface, enabling a control of the reflected field in both time and frequency domains. This technique is introduced to overcome the limitation of conventional time-domain modulations based on a single modulation frequency and incapable to jam radar systems that use ST-LFM signals. The use of multiple frequencies allows to break the symmetry of the ambiguity function, a key feature used to distinguish real targets from decoys. The proposed technique allows for precise control over the amplitude, distance, and number of false targets by adjusting modulation parameters. To validate the proposed technique, the required time series for an ST-LFM signal have been derived and a 2-bit phase-reconfigurable metasurface has been designed and fabricated. Experiments confirm the generation of the desired asymmetrical false targets in the high-resolution range profile (HRRP), effectively concealing the real target and hindering radar identification efforts.