Characteristic Mode-Based Dual-Mode Dual-Band of Single-Feed Antenna for On-/Off-Body Communication

A dual-band, dual-mode button antenna is proposed for emerging fifth-generation (5G) networks and Industrial, Scientific, and Medical (ISM) communication systems, as it operates at 3.5 GHz and 5.8 GHz, respectively. At the lower band, a monopole-like omnidirectional radiation pattern is achieved by loading shorting pins on curved strips for on-body communication. At the higher band, broadside circularly polarized radiation is achieved by loading an asymmetric U-shaped slot in the central chamferd patch for off-body communication. By using Characteristic Modal Analysis (CMA), a clear physical insight into the formation of dual polarization is provided. The -10 dB impedance bandwidth ranges from 3.48 to 3.60 GHz and 5.65 to 6.03 GHz, respectively. The 3 dB axial ratio (AR) bandwidth ranges from 5.71 to 5.85 GHz in the high band. Additionally, the antenna achieves a peak gain of 1.2 dBi in on-body mode and 6.9 dBi in off-body mode. The maximum specific absorption rate (SAR) calculated on the body tissues is below the US/EU standard thresholds of 1.6 W/kg and 2 W/kg. The measured results indicate that the antenna experiences only slight impact from human body loading and structural deformations. Given its notable features, the proposed design is well suited for Wireless Body Area Network (WBAN) applications.