A compact metasurface-based tri-band MIMO antenna with minimalist decoupling for multi-standard wireless devices

This paper presents a compact metasurface-based tri-band MIMO antenna for space-constrained multi-standard wireless devices. The antenna operates across 3.3–3.8 GHz (5G n78), 4.4–5.0 GHz (5G n79), and 5.1–5.9 GHz (Wi-Fi (802.11n/ac/ax)) bands. Its radiating element is a metasurface composed of seven hexagon-slotted hexagonal patches arranged in a cellular configuration, optimally designed using Characteristic Mode Analysis for tri-band performance. A key challenge addressed is the severe mutual coupling that arises when this element is extended to a densely spaced 1 × 2 MIMO array with near-zero edge-to-edge spacing. To overcome this, a strategically simple decoupling structure using only two pairs of vertical metallic posts is proposed. This minimalist approach proves highly effective, as both simulation and measurement results demonstrate enhanced isolation across all three bands, with |S₂₁| suppressed to -20.8 dB, -19.1 dB, and − 24.3 dB, respectively, while maintaining well-preserved impedance matching. Furthermore, the antenna exhibits excellent MIMO performance, with measured results confirming excellent isolation, low correlation, and minimal Channel Capacity Loss across the operating bands. The scalable cellular architecture of the metasurface allows for adaptation to irregular array geometries, making the proposed design a practical and high-performance solution for advanced, compact wireless applications.