Low-RCS Metasurface-Based Dual Circularly Polarized MIMO Antenna With Polarization and Spatial Diversity

This article presents a compact eight-port dual circularly polarized (CP) metasurface antenna (MA) that achieves low radar cross section (RCS) and high isolation for multiple-input multiple-output (MIMO) applications. Unlike conventional designs with separated CP elements, the proposed structure integrates a polarization conversion metasurface (PCM) with orthogonally-fed aperture-coupled patches, enabling co-aperture left-hand and right-hand CP radiation. Four such elements are arranged in a chessboard configuration, forming an eight-port MIMO array that simultaneously enhances polarization diversity and suppresses backscattering through phase cancellation. The prototype is fabricated and tested, demonstrating excellent matching (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\vert S 11\vert \lt -10$ </tex-math></inline-formula> dB), high port isolation (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lt -25$ </tex-math></inline-formula> dB), and low envelope correlation coefficient (ECC < 0.01) across the 3.25–3.38-GHz band. System-level evaluation using constellation diagram measurements confirms stable radiation and low interference under dual-CP excitation. Furthermore, RCS measurements verify over 10-dB reduction from 3.2 to 10.8 GHz (fractional bandwidth (FBW) = 108.6%) compared to a reference nonmetasurface design. These results demonstrate that the proposed design offers a stealth-capable, polarization-diverse, and anti-interference solution for next-generation wireless instrumentation applications.