Design of Miniaturized Tri-band Wearable Antenna Based on Characteristic Mode Theory

Abstract

In this study, a tri-band wearable antenna with a metal frame of 36 × 36 × 6.6 mm 3 is designed, fabricated, and measured based on the characteristic mode theory. By analyzing the current and electric field distribution of the characteristic mode, the antenna is determined to be fed by a T-coupled structure. Moreover, a circular ring ground structure is added to the initial elliptical model structure to generate a new resonance in the n78 band. On the other hand, the current's path is changed by etching a rectangular slot, allowing the high-frequency resonance mode to be shifted to the right. Simulated and measured results show that the proposed antenna covers Bluetooth/Wi-Fi (2.4G, 5.8G) and N78 frequency bands, which can be respectively used for connecting a watch to a mobile phone, accessing the Internet and making phone calls. Furthermore, the antenna has a maximum peak gain of 4.11 dBi in free space and 6.9 dBi when being placed on the wrist, with a Specific Absorption Rate (SAR) lower than international standards, making it suitable for wearable devices.