Dual-Band Flexible MIMO Antenna for 5G/6G and Head-Mounted Devices

A dual-band flexible wearable MIMO antenna with two operating modes, namely low-frequency narrowband and high-frequency broadband, is proposed and investigated in this paper. The antenna is based on a polyimide (PI) flexible printed circuit (FPC) substrate and has a compact size (90 mm × 40 mm × 0.1 mm), enabling easy integration into helmet-mounted devices. The antenna elements are fed by a coplanar waveguide (CPW) and integrated with a ground decoupling structure, achieving an isolation of at least 23.4 dB between the two ports across the entire operating frequency band. In addition, the impedance-matching characteristics of the antenna under bending conditions and the Specific Absorption Rate (SAR) of this MIMO antenna in a 1 g human-tissue model at 3.7 GHz and 4.6 GHz were evaluated. The results indicate that the antenna’s key electromagnetic performance remains relatively stable under bending conditions, and the SAR values comply with international limit requirements, verifying its feasibility for application in head-worn terminals. With an impedance bandwidth of −10 dB, this antenna achieves dual-band coverage at 3.42–3.84 GHz (relative bandwidth of 11.6%) and 4.37–7.80 GHz (relative bandwidth of 56.4%), effectively meeting the requirements of 5G/6G communication frequency bands.