In this paper, a novel miniaturized implantable circular antenna is presented. It supports both wireless information communication and wireless energy transmission at the Medical Device Radiocommunication band (MedRadio 402–405 MHz) and the industrial, scientific, and medical bands (ISM 902.8–928 MHz). The antenna is circular to avoid sharp edges while miniaturization is achieved by adding two circular slots to the patch. The main scenario includes embedding into the muscle layer of a cylindrical three-layer model of a human arm for which several parameters are analyzed (resonance, radiation pattern, and specific absorption rate). Power transmission efficiency and interaction distance limits to ensure connections are also evaluated. Finally, the design is validated by an experimental measurement in an anechoic chamber, and some new improvements are proposed.