Broadband Duplex Antenna for Implantable Medical Devices

This paper proposes a broadband in-band duplex implantable antenna for medical devices, operating at the Wireless Medical Telemetry System (WMTS) band (centered at 1.57 GHz). The broadband functionality of the proposed antenna is achieved by coupling the patch and slot modes. As a result, the antenna maintains a broad 10-dB bandwidth of 495 MHz (1.295–1.79 GHz). It exhibits high isolation greater than 23.5 dB across the entire bandwidth, with a transmission zero (TZ) located at 1.53 GHz. The high isolation between the two resonators is attributed to the ultra-thin substrate and the diagonal slot in the ground plane. The antenna has a compact geometry with a footprint of 10 × 10 × 0.1 = 10 mm3. This small size is achieved through the use of a high-dielectric substrate, slots, and a shorting via. At an implantation depth of 5 mm, each resonator achieves a realized gain of −20.93 dBi. The specific absorption rate (SAR) of each resonator is 44.8 W/kg at 1.57 GHz. At a high bit rate of 78 Mbps, the antenna maintains a reliable wireless link (greater than 15 dB) within a 5-meter range. A prototype is built and tested in minced pork to verify the simulation results. With its attractive features (compact size, broad bandwidth, low SAR, and high isolation), this antenna is well-suited for RF medical devices. To the best of the authors’ knowledge, this is the most compact and broadband in-band duplex implantable antenna reported to date.