A compact circularly polarized ultra-wide bandwidth implantable antenna for multiple scenarios

This paper presents a novel compact ultra-wide bandwidth circularly polarized implantable antenna. It serves biomedical applications in the industrial, scientific, and medical bands (2.4–2.4835 GHz) as well as in the mid-field band (1.824–1.98 GHz). Its overall size is reduced to 0.0364λ0 × 0.0364λ0 × 0.0023λ0 (λ0 denotes the free-space wavelength at the minimum operational frequency of the antenna) by means of a meander-type radiating surface, a loaded short-circuit probe, and a defective ground structure. An Ultra-wide impedance bandwidth (69.4%, 1.37–3.07 GHz) and an axial ratio bandwidth (34.7%, 1.78–2.63 GHz) are achieved while maintaining antenna miniaturization. A fabricated prototype tested in minced pork exhibits a measured impedance bandwidth of 60.8% (1.23–2.72 GHz) and an effective axial ratio bandwidth of 35.1% (1.70–2.56 GHz). The antenna achieves gains of − 20.05 dBi and − 18.75 dBi at 1.9 GHz and 2.45 GHz, respectively. The effects of different human tissue models and implantation sites on the radiation characteristics of the antenna are discussed to assess the stability and generalizability of its performance. It is shown that the antenna can fulfil different application scenarios in the human body. Moreover, the peak SAR levels remain within the permissible thresholds specified by the IEEE C95.1-2005 guidelines.