Hybrid phase-correction metasurfaces for accurate near-field manipulation

Although metasurface has attracted significant attention in recent years due to its ability to manipulate electromagnetic waves, discrepancies are often observed when comparing the designed and realized near-field performances. Among various contributing factors, one important issue is related to the fact that the elements arranged on a metasurface are typically designed under the assumption of normal incident excitation, whereas in practice they are actually excited at various oblique incidence angles depending on the element’s relative position to the feed antenna. This introduces amplitude and phase errors in the reflection or transmission coefficients of the elements within the metasurface, thereby affecting its overall performance. In this paper, a hybrid phase-correction method is proposed to compensate for the effect of oblique incidence on metasurfaces. The actual oblique incidence angles are decomposed into elevation and azimuth directions: In the elevation direction, the element characteristics under oblique incidence replace those under normal incidence, while in the azimuth direction, element rotation is introduced to compensate for the local effects. Near-field focusing and holographic metasurfaces are designed to verify the proposed hybrid phase-correction method. Full-wave electromagnetic simulations show that the proposed metasurface has the advantage in sidelobe levels without significant costs in terms of the amount of element-level computations. Finally, the near-field focusing metasurfaces are fabricated, and the measured results further demonstrate the potential of the proposed design for accurate near-field manipulation.