Ultrathin active polarization-selective metasurface at X-band frequencies

Abstract

An ultrathin active polarization-selective metasurface is designed and optimized for operation in the X band. The metasurface leverages the design of a previously reported passive polarization converting metasurface. Similar to the passive polarization converter, the proposed active metasurface consists of three patterned metallic sheets. Its bottom sheet is modified and populated with ultrawideband, unconditionally stable amplifiers and corresponding biasing networks. The metasurface provides over 35 dB of input-output isolation achieved through orthogonal polarizations, which ensures stable operation. It was fabricated with a low-cost, printed-circuit-board and pick-and-place process. The performance of the metasurface was measured and its stability confirmed. The desired effects of amplification, polarization conversion, polarization selectivity, and nonreciprocal behavior were successfully demonstrated in both full-wave simulations and measurements. Due to its extremely small thickness (0.66 mm or $0.02\ensuremath{\lambda}$ at 10 GHz), the metasurface shows excellent performance for a wide range of incident angles, which exceeds $\ifmmode\pm\else\textpm\fi{}{30}^{\ensuremath{\circ}}$. It achieves a perfect (100%) polarization conversion ratio in simulation, and 98.4% in measurement.