Circularly Polarized Annular Ring Antenna With Wide Axial-Ratio Bandwidth for Biomedical Applications

This paper proposes a novel circularly polarized antenna operating at 2.4–2.48-GHz industrial, scientific, and medical (ISM) band for biomedical applications. This proposed structure is developed from a simple pin-loaded patch antenna, whose circular polarization (CP) is mainly attributed to the loading of shorting pins and L-shaped open-end slot. Based on this, pin-loaded annular ring (PLAR) with dual-mode operation is adapted to introduce another resonance. In addition, two closely coupled rectangular patches are added to bring these two resonant frequencies close to each other in muscle. Furthermore, by introducing arc-shaped slots, CP property and improved impedance matching are achieved with size miniaturization. This proposed structure shows a simulated impedance bandwidth of 8% and a wide axial-ratio (AR) bandwidth of 19.1%. Finally, measurement is performed for the proposed antenna, and the results coincide well with the simulation ones, indicating that it is a good candidate for biomedical applications.