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An optimization method for ultrawideband multiple-input-multiple-output (MIMO) planar array topology design, which can satisfy both uniformity and lower element shadowing principles, is proposed by extending our previous work. Two planar MIMO arrays, namely, the basic optimal array (BOA) and the extended optimal array (EOA) are optimized. The focusing and sidelobe-suppression properties of the BOA and the EOA are demonstrated to be superior to other two previous state-of-the-art planar MIMO arrays. The advantages of the two optimized arrays in 3-D imaging are further indicated by experimental results for different distributed targets. The validity of the proposed method is verified by the excellent performances of the BOA and the EOA. [ABSTRACT FROM PUBLISHER]

The metasurface is a functional film device based on a subwavelength structure, which has a strong light field control ability and has the advantages of ultrathin, low loss, and easy manufacturing. However, realizing a multifunctional metasurface, yet simple enough to design, manufacture, and thin is still a challenge. In this article, we propose a novel metasurface with negligible thickness as a beam splitter, which can achieve half transmission and half reflection of the incident wave at the same frequency. It also controls the polarization of circularly polarized electromagnetic (EM) waves in the transmission mode. A broadband operation can be achieved based on the geometric phase theory, and the phase control can be achieved by azimuth rotation of the structure. The numerical results of the metasurface are in good agreement with the experimental results in the measured frequency range. The ultrathin multifunctional metasurface realized by the geometric phase principle provides an important stepping stone for simple optical devices and can be extended to a higher frequency range. [ABSTRACT FROM AUTHOR]