A Self-Triplexing Circularly Polarized MIMO Antenna Enabling Transcranial Wireless Powering and Telemetry for IoMT Brain Implants

In this paper, a compact six-port, triple-band, circularly polarized multiple-input and multi-output (MIMO) implantable antenna with self-triplexing capability is presented for intracranial applications. The antenna occupies a footprint of 12.4 × 14 × 0.2 mm3. It operates at 915, 1710, and 2450 MHz across the ISM and MedRadio bands. It achieves circular polarization with 3-dB axial-ratio bandwidths of 17.7%, 4.1%, and 7.4%. Mutual coupling is inhibited by meander-line patches with isolation levels of 25 dB or more, without the use of shorting vias, ground-plane slots, or decoupling circuits. Simulated realized gains of -39.6, -38.5, and -35.1 dBi at 0.915, 1.71, and 2.45 GHz, respectively, and low SAR values guarantee safety compliance. Link-budget analysis guarantees reliable communication with minimum coverage distance of 5.1 m for high data rates of 10, 78, and 120 Mbps. The antenna performance is analyzed using MIMO performance and diversity analysis in lossy, multipath tissue conditions.