Circularly Polarized Loop Antenna for 2.4 GHz ISM-Band Biotelemetry Devices

A compact circularly polarized (CP) loop antenna is designed and experimentally validated for the 2.4 GHz Industrial, Scientific, and Medical (ISM) band [(2.4 to 2.48) GHz]. The design introduces vias to extend the current path, which meanwhile introduces capacitive coupling of the bending part to the ground, producing good results in reducing the antenna size. Additionally, four corner-mounted square patches, connected to the ground, serve to capacitively and inductively load the antenna, further effectively downsizing its footprint. Compared to previous work, the antenna's metallic components are concentrated at the periphery, making it possible to embed implantable device components inside the antenna, which favors equipment miniaturization. The influence of embedded circuits on antenna performance is studied through simulation. The size of the antenna is 9 mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$ \times $</tex-math></inline-formula> 9 mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$ \times $</tex-math></inline-formula> 0.762 mm, and it achieves simulated impedance bandwidth (IBW) (|<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub>| < −10 dB) coverage of 2.35 GHz to 2.53 GHz and axial ratio bandwidth (ARBW) (AR < 3 dB) coverage of 2.44 GHz to 2.48 GHz. The antenna is measured in the minced pork, and the result is consistent with the simulated one.