A novel compact 4-port MIMO antenna with dual-mode polarization for 5G sub-6 GHz applications

This paper presents a compact, dual-polarized, 4-port MIMO antenna with a connected ground plane on a low-profile FR-4 substrate (44 × 44 × 1.6 mm³, ϵr = 4.4). Four orthogonally arranged E-shaped meander-line radiators enhance inter-element isolation and polarization diversity. The antenna operates over 2.8–3.1 GHz and 5.2–5.5 GHz, supporting S-band telemetry and wireless data links, and IEEE 802.11a/n/ac/ax WLAN applications, respectively. It provides linear polarization in the lower band and circular polarization in the upper band. A modified connected ground plane simultaneously achieves circular polarization and high isolation, exceeding 19 dB and 18 dB in the lower and upper bands, respectively. Simulated and measured S-parameters, axial ratio, and radiation characteristics show good agreement. Diversity performance, evaluated using envelope correlation coefficient (ECC), diversity gain (DG), total active reflection coefficient (TARC), and channel capacity loss (CCL), satisfies the requirements for practical MIMO wireless communication systems.