A Low‐Profile Quad‐Element MIMO Antenna System With High Isolation and Low SAR for 5G Metal‐Rimmed Smartphones

An extremely low‐profile quad‐element MIMO antenna system, fabricated on an FR4 substrate measuring (), is proposed for 5G smartphone applications, operating at 3.5 GHz (3.4–3.6 GHz band). Each antenna module has dimensions of (), with a footprint of just (). The MIMO structure provides a high gain of up to 9 dBi. Etching a slit in the rim and placing two stubs on either side of the feed line ensures excellent impedance matching. Incorporating the defected ground structure (DGS) with two horizontal and four vertical slots enhances isolation by suppressing and concentrating travelling surface waves. A lumped‐element circuit model represents the MIMO antenna system to evaluate its electrical response to an input RF signal. In spatially and area‐limited smartphone platform, the design achieves an excellent isolation of more than 19.6 dB, an envelope correlation coefficient (ECC) below 0.008, a diversity gain exceeding 9.99 dB, a mean effective gain (MEG) below −3.09 dB, a total active reflection coefficient (TARC) below 0.4, and a low channel capacity loss (CCL) below 0.28 bps/Hz. The system demonstrates total efficiencies ranging from 78.3% to 98.6% and a SAR value of 0.8033 W/kg. The proposed MIMO antenna system has been fabricated, and the remarkably high coherence between the measured and simulated results, along with its robust diversity performance in real‐world settings, makes it a suitable choice for 5G smartphone applications.