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Abstract-This article presents the design of aperiodic sunflower-like metasurface for circularly polarized (CP) wave diffusion and radar cross section (RCS) reduction using Pancharatnam-Berry (PB) meta-atoms. The distribution of the PB meta-atoms across the metasurface aperture is non-uniform and has a distribution inspired by sunflower seeds, i.e., an outwardly logarithmic spiral lattice with no transitional periodicity. The proposed metasurface has 600 PB meta-atoms of sub-wavelength size of 5 mm ≈ 0.33λ 20GHz and exhibits a randomly chosen diffusive reflection phase between 0 o and 360 o . Both simulated and experimental results demonstrate that the proposed sunflower-like metasurface can efficiently diffuse the backscattered energy into numerous directions when normally illuminated by a CP-wave with RCS reduction > 7 dB between 16 GHz and 23.8 GHz. Furthermore, the low-level diffuse scattering can be preserved under oblique incidence up to 60 o . As a result of using this PB concept, the polarization sensitivity of the proposed metasurface is released and this is highly desired in applications when the polarization of the incoming wave is unknown.

This paper presents building blocks for a proposed automotive intermodulation radar for detecting and identifying vulnerable road users (VRUs). The intermodulation radar transmits at two frequencies and it has receivers both for normal reflections and for reflections from VRUs at the intermodulation frequency. A possible radar architecture is presented and modulation techniques are discussed. Different mixing elements of radar reflectors are studied with simulations. An antenna structure enabling a wearable reflector that can be integrated into clothes is designed and characterized. The simulated and measured performance of the radar reflector is used to estimate the achievable detection range.

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