Design of a Circularly Polarized Wearable SIW Antenna Applied to Off-Body Communication Mode

A circularly polarized wearable substrate integrated waveguide (SIW) antenna working in the WLAN frequency band (5.15–5.825 GHz) is designed with a size of 40 mm × 40 mm × 1.5 mm (0.733 λ₀ × 0.733 λ₀ × 0.0275 λ₀). The proposed antenna is applied to off-body communication and radiates unidirectional patterns. The antenna uses four symmetrical shorting pins to excite the TE₁₂₀ mode and TE₂₁₀ mode of rectangular SIW resonator, which are a pair of degenerate modes, to realize circular polarization. Two pairs of rectangular slots with different sizes are etched on the antenna to cut the current of the SIW resonant cavity, and the resonant frequency points of TE₁₂₀ mode and TE₂₁₀ mode are adjusted together. In addition, a circular ring slot is etched in the center of the antenna to improve the axial ratio and adjust the impedance matching of the antenna. The measured results show that the antenna works at 5.41–5.56 GHz with a relative bandwidth of 2.73%. The proposed antenna is harmless to human body, which can be evidenced by the simulated 1 and 10 g averaged specific absorption rate values.