A Compact Via-Assisted Dual-Band Circularly Polarized Antenna With Dual-Mode Radiation for Health Monitoring Devices

In this letter, a compact, via-assisted, circularly polarized antenna is presented for body-centric health monitoring, enabling frequency-dependent dual-mode radiation behavior without requiring reconfiguration or periodic structures. It covers the 2.45 and 5.8 GHz ISM bands with a size of$\bf {0.31\lambda _{0} \times 0.31\lambda _{0} \times 0.043\lambda _{0}}$. The stacked radiator is excited by a single CPW feed, while shorting vias introduce controlled inductive loading and mode perturbation to support miniaturization and stable CP. The proposed antenna produces a quasi-omnidirectional pattern at 2.45 GHz for on-body links and a more directive broadside pattern at 5.8 GHz for off-body communication. Measured$\bf {-10}$dB bandwidths are 5.3% and 27.2%, with AR bandwidths of 15.1% and 21.2%. It achieves up to 80% radiation efficiency, peak gains of 2.94 dBi and 5.1 dBi, and low SAR of 0.049 W/kg and 0.074 W/kg, confirming a compact and versatile solution for wearable healthcare systems.