Fig. 1. Conceptual illustration of the proposed conformal metasurface. (a) Schematic functionality under the illumination of a CP wave or an LP wave with arbitrary polarization. (b) Typical scattering pattern of a metallic cylinder. (c) Phase compensation inspired by the ray-tracing approach to restore two symmetric planar wavefronts.

Fig. 2. Topology and EM properties of the broadband PB meta-atom. (a) Element structure. EM response under illumination of (b) an x/y-polarized LP wave, and CP waves of (c) normal and (d) oblique incidence. The geometrical parameters are optimized and detailed as lx=6, ly=7.5, lx1=3.8, ly1=2, w1=1, w2=0.5, h1=0.06, and h2=4  mm.

Fig. 3. Numerical characterization of three dipole arrays, each forming a half-circle with R0=99.06  mm to mimic a conformal metasurface. The radiation or scattering intensity at each frequency is first normalized to the total energy across the entire illumination region [P¯(ϕr,fi)=P(ϕr,fi)/∑ϕr=−90°ϕr=90°P(ϕr,fi)] and then normalized to the maximum intensity max[P¯(ϕr,fi)]. Three dipole arrays are considered: directional radiation at ϕ=±45° (case 1), high-efficiency anomalous radiation at ϕ=±arcsin(λ/Np) (case 2), and deteriorative radiation (case 3). In cases 1 and 2, the phases are exactly designed. However, in case 3, no phase correction is applied. (a) Topology of the dipole array; inset shows the typical 3D radiation pattern in case 2. (b) Corresponding exciting phases of each dipole in three cases. Far-field radiation power intensity of three dipole arrays in (c) case 1, (d) case 2, and (e) case 3.

Fig. 4. Numerical characterization of conformal metasurfaces on a cylinder with R0=156  mm. (a) Metasurface topology. (b) Numerically calculated full wave. (b) 3D and (c) 2D scattering power intensity in CST Microwave Studio. In the simulation setup, there is only one meta-atom along the z axis, and the periodic boundary is assigned to mimic an infinitely high metasurface. The remaining four walls are assigned as the open boundary. For a comprehensive study, the metasurface is designed at different f0 values of 18, 15, and 10 GHz.

Fig. 5. Numerical characterization of conformal metasurfaces on cylinders with R0=156 and R0=95  mm. The geometrical parameters of the utilized basic meta-atom are detailed as lx=6, ly=7.5, lx1=4, ly1=4, w1=1, w2=0.5, h1=0.06, and h2=4  mm. The conformal metasurface is designed at different f0 of 10, 12, and 15 GHz.

Fig. 6. Numerically calculated RCSs of the conformal metasurface, cylinder, and planar plate that varies with the scattering angles and frequencies. The conformal metasurface wrapping over the cylinder of R0=156  mm is designed at 10 GHz.

Fig. 7. Experimental characterization of a conformal metasurface wrapped on a cylinder with an R0=95  mm. (a) Photograph of the fabricated sample and angle-resolved bistatic RCS measurement setup. (b) Copolarized and (c) cross-polarized scattering component of the superscatterer. (d) Comparison of the efficiency between experiments and numerical calculations. The efficiency is defined as the ratio of anomalously reflected dual-beam intensity [∫(ϕi0+ϕi1)/290°P(ϕ)dϕ+∫−90°(ϕi0−ϕi1)/2P(ϕ)dϕ] and totally reflected energy [∫−90°90°P(ϕ)dϕ] obtained by integrating the scattered-field intensity across the azimuth. Here, ϕi0 and ϕi1 are the reflection angles of the normal and anomalous modes, respectively. The aforementioned definition of efficiency measures the effectiveness of wavefront restoration. The stronger the dual-beam intensity, the less energy is dispersed to other directions, and the higher efficiency is due to energy conservation. (e) Cross-polarized scattering intensity of the bare metallic cylinder.

Fig. 8. Measured RCSs of the bare metallic cylinder and the conformal superscatterer at six selected frequencies of 8, 10, 12, 14, 16, and 18 GHz.