Electromagnetic Bandgap Backed Millimeter-Wave MIMO Antenna for Wearable Applications

A millimeter-wave (mm-Wave) multiple input multiple output (MIMO) antenna operating at 24 GHz (ISM band), suitable for wearable applications, is proposed in this paper. The proposed MIMO antenna consists of two elements, designed with an edge-to-edge distance of 5.14 mm, backed by a <inline-formula> <tex-math notation="LaTeX">$5\times 5$ </tex-math></inline-formula> cell electromagnetic bandgap (EBG) structure. The antenna is fabricated on a flexible Rogers 6002 material (<inline-formula> <tex-math notation="LaTeX">$\epsilon _{r}=$ </tex-math></inline-formula> <italic>2.94</italic>, <italic>tan<inline-formula> <tex-math notation="LaTeX">$\delta =$ </tex-math></inline-formula> 0.0012</italic>, <italic>thickness = 0.254 mm</italic>). The proposed antenna retains its performance when bent along the x-axis and y-axis. The performance of the antenna in term of s-parameters and radiation properties is studied in free space as well as on a human phantom. Good impedance matching of the antenna at the resonating frequency (24 GHz) is observed when it is bent and when worn on the body. The introduction of the EBG improves the gain by 1.9 dBi, reduces the backward radiation by 8 dB, reduces the power density on the back towards the body from > 200 W/m² to < 10 W/m², and also enhances the 10 dB bandwidth by 100 MHz. The antenna possesses a low envelope correlation coefficient (ECC) of 0.24, high diversity gain (DG) of 9.7 dB, reasonable multiplexing efficiency of −0.684 dB and a good peak gain of 6 dBi at 24 GHz. The proposed antenna is suitable for wearable applications at mm-Wave range due to its simple geometry and good performance in bending and on-body worn scenarios.