Metasurface med spridda spektrum för radarstealth

Radar stealth is a critical component in defense, playing a crucial role in mission success and the protection of sensitive sites. Over the past few years, new technologies based on active components and metasurfaces have emerged, offering new possibilities for radar stealth applications. This project focuses on spread-spectrum metasurfaces for radar stealth. The objective is to explore the use of time-modulated metasurfaces to provide radar stealth by making target detection more difficult. To achieve this, a time-modulated metasurface is used, where the phase of its reflection coefficient is switching between two states separated by π, spreading the incident signal in the frequency domain. Although this concept has already been studied, its impact on target probability of detection and the effects of non-idealities remain largely unexplored. Indeed, metasurface non- idealities, such as an amplitude imbalance in the reflection coefficient between the two states, a phase difference that deviates from exactly π, or a non-zero commutation time between states, can degrade stealth performance, making their consideration essential for practical applications. Three modulation sequences are analyzed. In the ideal case, they provide excellent stealth performance, with a zero probability of detection for all tested Signal-to-Noise Ratio (SNR). However, when non-idealities are introduced, one modulation scheme stands out due to its robustness: the random modulation. By randomly switching the reflection coefficient phase between these two states, the target becomes undetectable, even in the presence of non-idealities. A metasurface model was designed in Ansys HFSS, and using the random modulation, the probability of detection remains zero for all SNR levels when the incident signal frequency is in the [3.4, 7.6] GHz band. This project opens new perspectives for the design of spread-spectrum metasurfaces for radar stealth taking into account manufacturing imperfections and hardware constraints. They could be applied to advanced radar camouflage systems or the protection of sensitive objects against radar surveillance.