Compact In-Band Full-Duplex Antenna for Deeply Implantable Biomedical IoT Applications

Traditional duplexing antennas for implantable biomedical devices often rely on half-duplex or multi-band designs, which allow either transmission or reception at a given time or require separate frequency bands for uplink and downlink. Such configurations result in reduced data rates, increased latency, higher hardware complexity, and potential spectral congestion, thereby limiting their suitability for advanced in-body communication. In this work, an innovative in-band full-duplex (IBFD) concept is introduced in a miniaturized implantable antenna optimized for deep implantation at a depth of 65 mm in a human torso phantom. The antenna operates at 2.4 GHz on both Port 1 and Port 2 with independently controllable bands. A compact volume of 5.81 mm3(π × (2.7)2× 0.254) is achieved through the integration of shorting pins, open-ended slots, and multiple semi-circular slots. High port-to-port isolation of 29.5 dB is obtained using an ultra-thin substrate, superstrate, and a narrow 0.4 mm separation between the radiating patches. The antenna exhibits omnidirectional radiation patterns at both ports, with measured gains of -20.2 dBi and -20.3 dBi for Port 1 and Port 2, respectively. The proposed design demonstrates ultra-miniaturization, high isolation, reliable impedance matching, acceptable radiation performance, and independently controllable duplexing bands. These characteristics make it highly suitable for deeply implanted biomedical devices, significantly improving spectral efficiency and enabling simultaneous transmission and reception for real-time bidirectional communication in next-generation implantable systems.