Design of Wideband Button Antenna Based on Characteristic Mode Theory

A wideband wearable button antenna working around 2.4 GHz is proposed in this paper. The function of the textile antenna ground is analyzed based on characteristic mode theory. By properly locating the button on the ground, the latter can be efficiently excited and operates as a radiator. This is shown to greatly increase the impedance bandwidth. The antenna is analyzed both in free space and on the human body. A prototype is fabricated, and the measured results agree satisfactorily with the simulations. In free space, the bandwidth, the realized gain, and radiation efficiency are 658 MHz, 1.8 dBi, and 97%, respectively. While on the human body, the values can reach 788 MHz, 5.1 dBi, and 71%, respectively. This wide band behavior provides robustness across different environments and to relatively large fabrication tolerances. The specific absorption rate is below 0.45 W/kg for an equivalent isotropically radiated power of 20 dBm.