Conformal Reconfigurable Intelligent Surfaces: A Cylindrical Geometry Perspective

TL;DR

This work addresses beam steering with conformal cylindrical RISs by developing a layered modeling framework that starts from exact surface-impedance synthesis and advances to a practical, discrete-element design implemented with one-bit meta-atoms. A semi-analytical, physically motivated model enables rapid synthesis via MPDR, while full-wave HFSS validation confirms main-beam fidelity and reasonable sidelobe control, despite curvature and quantization constraints. The results show directive scattering is achievable with extremely simple hardware, suggesting practical deployment on UAVs and curved urban structures, with future extensions to higher-bit elements and space-time coding. Overall, the study bridges EM modeling and communications performance for conformal RISs, offering a scalable path toward real-world curved-platform beamforming.

Abstract

Curved reconfigurable intelligent surfaces (RISs) represent a promising frontier for next-generation wireless communication, enabling adaptive wavefront control on nonplanar platforms such as unmanned aerial vehicles and urban infrastructure. This work presents a systematic investigation of cylindrical RISs, progressing from idealized surface-impedance synthesis to practical implementations based on simple one-bit meta-atoms. Exact analytical and geometrical-optics-based models are first developed to explore fundamental design limits, followed by a semi-analytical formulation tailored to discrete, reconfigurable architectures. This model enables efficient beam synthesis using both evolutionary optimization and low-complexity strategies, including the minimum power distortionless response method, and is validated through full-wave simulations. Results confirm that one-bit RISs can achieve directive scattering with manageable sidelobe levels and minimal hardware complexity. These findings establish the viability of cylindrical RISs and open the door to their integration into dual-use wireless platforms for real-world communication scenarios.

Figures (9)

• Figure 1: Illustrative scenario of conformal RIS deployment in a mixed aerial (A-RIS) and terrestrial (T-RIS) communication network. Cylindrical RISs are integrated onto curved surfaces, such as UAV fuselages and lampposts, to enhance coverage and enable dynamic beam control in complex propagation environments. A base station (BS) communicates with multiple user equipments (UE$_1$, UE$_2$, UE$_3$), with RISs assisting in overcoming line-of-sight obstructions and improving link quality.
• Figure 2: Problem geometry. a) Idealized scenario with surface impedance. The 2D Cartesian and associated cylindrical reference systems are also shown. b) Realistic scenario with space-sampled and phase-quantized reconfigurable elements. The elements directly illuminated by the incident wave are shown in red, while those located in the shadow region are shown in gray.
• Figure 3: Exact analytical synthesis. a,b) Real and imaginary parts, respectively, of the normalized surface impedance computed from Equation (\ref{['eq:ZZ']}) for beam steering toward $\varphi_o=15^\circ$. c) Far-field scattering patterns for different values of the steering angle $\varphi_o$. Results are normalized with respect to the maximum value.
• Figure 4: GO synthesis. a) Purely imaginary normalized surface impedance computed from Equation (\ref{['eq:Zlocal']}) for beam steering toward $\varphi_o=15^\circ$. b) Far-field scattering patterns for different values of the steering angle $\varphi_o$. Results are normalized with respect to the overall maximum value. The inset compares the peak values with those obtained via the exact synthesis (Figure \ref{['fig:Figure3']}) as a function of the steering angle $\varphi_o$.
• Figure 5: a,b,c,d,e) Examples of synthesized scattering patterns for a cylindrical RIS operating at 3.6 GHz, with radius $R=40$ cm, $N=30$ illuminated elements, and one-bit ($b=1$) resolution. The patterns correspond to steering angles $\varphi_o=15^\circ$, $30^\circ$, $45^\circ$, $60^\circ$, and $75^\circ$, respectively, and are normalized to their individual peak values. f) Comparison of the main beam levels at the nominal steering angle across the various synthesis methods, as the steering direction is varied. Levels are normalized with respect to the maximum value observed at $\varphi_o=15^\circ$.