Angular Self-Adaptive Doppler Cloak Based on Space-Time Modulated Metasurface

A design of angular self-adaptive planar Doppler cloak composed by a pair of space-time modulated metasurfaces is proposed in this paper. The first metasurface focuses the incident field in a specific location on the second metasurface, that is designed for enabling angular reflection and Doppler frequency shift compensation. We make use of ray tracing method based on generalized Snell's law, and introduce an error function for deriving numerically the optimum phase profile of two metasurfaces, leading to keep the radar cross-section of the Doppler cloak as much stable as possible within an angular range of about 60° centered at the normal direction. The self-adaptive Doppler cloak may enhance the undetectability of cloaked moving objects.