Radar Cross Section Characterization of Quantized Reconfigurable Intelligent Surfaces

Abstract

We present a radar sensing framework based on a low-complexity, quantized reconfigurable intelligent surface (RIS) that enables programmable manipulation of electromagnetic wavefronts for enhanced detection in non-specular and shadowed regions. We develop closed-form expressions for the scattered field and radar cross section (RCS) of phase-quantized RIS apertures based on aperture field theory, accurately capturing the effects of quantized phase, periodicity, and grating lobes on radar detection performance. The theory enables us to analyze the RIS's RCS along both the forward and backward paths from the radar to the target. The theory is benchmarked against full-wave electromagnetic simulations incorporating realistic unit-cell amplitude and phase responses. To validate practical feasibility, a $[16\times10]$ 1-bit RIS operating at 5.5 GHz is fabricated and experimentally characterized inside an anechoic chamber. Measurements of steering angles, beam-squint errors, and peak-to-specular ratios of the RCS patterns exhibit strong agreement with analytical and simulated results. Further experiments demonstrate that the RIS can redirect the beam in a non-specular direction and recover micro-Doppler signatures that remain undetectable with a conventional radar deployment.

Figures (16)

• Figure 1: RIS-enhanced radar system illustrating non-specular signal steering using RIS.
• Figure 2: RCS (dBsm) of the RIS in the $\phi_s = 90^\circ$ plane for forward and backward scattering. The columns represent phase quantization levels: (i) continuous, (ii) 3-bit, (iii) 2-bit, and (iv) 1-bit. The first row (a-d) corresponds to ($\theta_i = 0^\circ,\theta_d = 45^\circ$) while the second row (e-h) corresponds to ($\theta_i = -30^\circ,\theta_d = 45^\circ$).
• Figure 3: SNR performance for RIS with (a) continuous, (b) 3-bit, (c) 2-bit, and (d) 1-bit phase quantization at $\theta_i = 0^\circ$ for varying RIS sizes.
• Figure 4: Simulation setup for radar system (a) without RIS and (b)with RIS.
• Figure 5: Magnitude of electric-field over the $2 \times 1.6~\mathrm{m}^2$ simulation domain for radar system (a) without RIS, and with (b) $[8\times10]$, (c) $[16\times10]$, and (d) $[32\times10]$ unit-cell RIS tuned for ($\theta_i=0^\circ;\theta_d=45^\circ$).