High-Isolation Twin-Cluster Fan-Blade Metasurface-Embedded Wideband CP MIMO Antenna With Shorting-Pin Vias for IoT Applications

This study proposes a twin-cluster fan-blade metasurface (MTS)-embedded wideband circularly polarized (CP) multiple-input multiple-output (MIMO) antenna incorporating shorting-pin vias for Internet of Things (IoT) applications. The antenna is implemented on a double-layered substrate. The upper layer comprises two identical clusters of fan-blade MTS elemental arrays, while the lower layer integrates a dual-element coplanar waveguide feeding structure. Centrally placed shorting-pin vias are introduced to mitigate inter-cluster mutual coupling. Characteristic mode analysis is employed to investigate the CP behavior of each cluster of the twin-cluster antenna, with circular polarization achieved through two orthogonal modes (Modes 3 and 4). For coupling suppression, the optimal placement of the shorting-pin vias is determined based on minimizing the normalized electric field magnitude between clusters. The measured return loss bandwidth, axial ratio bandwidth, and maximum gain at the center frequency of 5.5 GHz are 46.72% (4.2 – 6.77 GHz), 11% (5.29 – 5.9 GHz), and 5.82 dBic, respectively. The antenna scheme achieves high isolation exceeding 25 dB, an envelope correlation coefficient below 0.002, a diversity gain above 9.99 dB, a mean effective gain below -3 dB, a total active reflection coefficient below -10 dB, and a channel capacity loss below 0.2 bits/s/Hz. This study is the first to utilize a fan-blade MTS-embedded structure for CP generation and to integrate shorting-pin vias within a CP MIMO antenna for mutual coupling suppression. Essentially, the proposed twin-cluster antenna scheme is well-suited for advanced IoT applications.