Ultrathin active cloak with balanced loss and gain

摘要

In this paper, we present the design and realistic implementation of an ultrathin active radio-frequency cloak, capable of significantly suppressing the scattering from electrically large objects beyond the limitations of passive cloaking techniques. The object is coated with a metasurface loaded by a discrete number of lumped circuit elements, which follow a rigorously derived distribution of balanced gain and loss, able to minimize the scattering cross-section of the system. The loss portion is tailored using passive components to absorb the incident wave and avoid back reflections, while the gain portion utilizes active circuitry to automatically generate a synchronized version of the impinging signal on the other side of the cloak, in order to suppress shadow and forward scattering. We derive the required metasurface parameters, including the frequency dispersion of its elements, in order to achieve a given reduction of the total radar cross section of PEC circular cylinders, with special attention to ensure stability of the active system. A design example is provided for a cylinder with a diameter of one wavelength at 1 GHz.