Omni-/Unidirectional Dual-Mode Dual-Polarized Wearable Antenna for IoT Applications

Wearable antennas are essential for Internet of Things (IoT) devices, as their performance critically affects system reliability and functionality. Therefore, this paper proposes an omni-/unidirectional dual-mode, dual-polarized circular patch wearable antenna. The antenna employs a single-layer dielectric substrate made of felt, which is low-cost and easy to fabricate. It operates in the 2.45 GHz and 5.8 GHz ISM frequency bands, achieving unidirectional and omnidirectional radiation patterns, respectively. At 2.45 GHz, circular polarization (CP) is realized by etching an oblique slot at the center of the circular patch to periodically excite the TM11 mode. At 5.8 GHz, orthogonal slots are etched on the circular patch to adjust the resonant frequency and impedance matching of the TM02 mode, thereby achieving linear polarization (LP). The measured impedance bandwidths of the antenna in CP and LP modes are 160 MHz (2.37 GHz to 2.53 GHz) and 270 MHz (5.68 GHz to 5.95 GHz), respectively. Furthermore, the antenna exhibits favorable performance under different bending conditions and when in proximity to human tissue. Meanwhile, its low specific absorption rate (SAR) value indicates that the safety of wearing the antenna on the human body is guaranteed. CP can enhance signal stability and reduce interference in wireless body area network (WBAN) communication, particularly in scenarios involving frequent human movements. In contrast, the 5.8 GHz band requires omnidirectional radiation to achieve wide coverage and reduce back radiation, thus meeting the safety and comfort requirements of wearable devices.