Dual-Band MIMO Antenna With Circular Polarization in WBAN Band for Metal-Frame Smartwatches

A multiple-input multiple-output (MIMO) antenna operating in the dual bands of 2.40-GHz wireless local area network (WLAN) and 5.80-GHz wireless body area network (WBAN), is presented for metal-frame smartwatches. An L-shaped closed slot is etched on the ground as the antenna element. Then, an open slot is added to the element, introducing capacitive loading in the upper band. By adjusting the open slot, the element achieves circular polarization in WBAN band. Finally, the two elements are placed symmetrically around the ground diagonal with cutting decoupling slots. When the proposed antenna was worn on the wrist, the maximum simulated -6-dB impedance bandwidths are 29.0% (2.11-2.82 GHz) and 31.9% (4.48-6.33 GHz) with the isolations of greater than 15.5 dB and 15.2 dB in WLAN and WBAN bands, respectively. Additionally, the 3-dB axial ratio bandwidth ranges from 5.68 to 6.03 GHz. The dimensions of the antenna are 0.318×0.318×0.041 λ<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</inf><sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup>(at 2.45 GHz).