High-efficiency and wide-angle planar retroreflector for dual-LP waves based on double-metasurface phase modulation.

A double-metasurface phase modulation architecture is proposed and designed for wide-angle and high-efficiency retroreflection and backscattering enhancement. In order to overcome the intrinsic mutual constraint between the angular coverage and aperture efficiency in designing a retroreflector by using a single metasurface, a double-metasurface structure is developed to separate the design requirement for different incident angles, thus enabling the enhancement of retroreflection efficiency. The first, to the best of our knowledge, metasurface focuses the incident plane waves from arbitrary directions into different spots on the second reflective metasurface, enabling spatially decoupled phase modulation and thus enhancing angular retroreflection. Further, to address the inherent degradation of retroreflection efficiency caused by focal spot distribution and overlapping, a multi-spot phase modulation method accounting for the spot energy distribution is developed and employed. A retroreflector operating at 10 GHz is designed, fabricated, and measured to experimentally validate the proposed method. The designed retroreflector demonstrates stable retroreflection (3-dB) across the full-azimuth range (φinc = 0° ∼ 360°) and a broad elevation range (θinc = -20° ∼ 20°) under dual-linear polarization (dual-LP, TE/TM) waves. The peak aperture efficiency of wide-angle retroreflection reaches over 50.0%, approaching the achievable upper limit for double-metasurface structure. The proposed retroreflector offers a promising solution for wide-angle, high-efficiency backscattering enhancement, with potential applications in asset tracking, satellite navigation, and related fields.