Wearable Circularly Polarized SIW Antenna for Off-Body Communications

A compact low-profile circularly polarized substrate integrated waveguide (SIW) antenna for off-body communications is proposed. The antenna is made of felt and conductive fabric to have good wearability. An annulus slot and four rectangular slots are etched on a circular SIW to adjust and combine the TM₁₁ mode of the circular patch with the TM₀₁₀ mode of the SIW resonant cavity, thereby achieving broadband. To achieve circular polarization, an inclined 45° rectangular slot is etched on the circular patch. The measured 3 dB axial ratio bandwidth is 240 MHz [(5.31 to 5.56) GHz]. The average gain in the working band is 7.76 dBi. The low specific absorption ratio results also demonstrate that the radiation of the antenna to the human body is within the safe range.