Transformation Media for Thin Planar Retrodirective Reflectors

In this letter, we address the design of thin planar retrodirective reflectors via transformation optics. Exploiting form-invariant transformations of Maxwell's equations, we derive the constitutive properties of an anisotropic and spatially inhomogeneous transformation-medium coating which, laid on a flat metallic surface, exhibits the retrodirective response typical of a dihedral corner reflector. The practical feasibility of the involved materials should be within reach of the fast-pacing metamaterial technology. The results of our investigations, validated via a full-wave study of the near- and far-field responses, could find interesting applications in radar, communication, and identification scenarios.