Spread-Spectrum Selective Camouflaging Based on Time-Modulated Metasurface

This article presents the concept of spread-spectrum selective camouflaging based on time-modulated metasurface. The spectrum spreading is realized by switching the metasurface between the reflective states of a perfect electric conductor (PEC) mirror and a perfect magnetic conductor (PMC) mirror, using an array of microstrip patches connected to the ground via diode switches, according to a periodic pseudorandom noise sequence. As the spectrum spreading induces a drastic reduction of the power spectral density of the signal, the level of the scattered wave falls below the noise floor of the interrogating radar, and the object covered by the metasurface is hence perfectly camouflaged to a foe radar. Moreover, the object can be detected by a friend radar possessing the spread-spectrum demodulation key corresponding to the metasurface modulation, and this detection is robust to interfering signals. The proposed system is analyzed theoretically and demonstrated by both simulation and experimental results.