Simultaneous Optimization of 1-bit 3-D Coding Meta-Volumes for Both Broadband and Wide Field-of-View Radar Cross-Section Reduction

Coding metasurfaces (CMSs) rely on the proper tiling of two or more kinds of complementary unit cells within an array to enable phase cancellation and corresponding destructive interference thereby reducing the radar cross-section (RCS) of a given scatterer. Typically, these unit cells are planar and inherently limited in their field of view (FoV). This work demonstrates that breaking this traditional unit cell design paradigm in favor of novel 3-D meta-volumes enables both broadband and wide-FoV RCS reduction. Further, this work introduces a modified genetic algorithm (GA) framework for simultaneously tailoring the reflection phase of multiple unit cells to achieve the best composite response. By applying these identical pair-optimization strategies, it is shown that 3-D unit cells outperform their 2-D counterparts of the same lateral size in terms of both the fractional bandwidth (FBW) and FoV. One exemplary 3-D solution purely improves the $H_{\mathrm {x}}$ response with FBW exceeding 75% across a full 70° FoV. A second 3-D solution provides an improved $E_{\mathrm {x}}$ polarization response with a near 70% FBW at 45° and up to 75% FBW at 70° for the $H_{\mathrm {x}}$ polarization at the expense of reduced FBW close to 50% for incidence angles less than 45°.