(b)
Fig. 5 matched 2.45GHz current and radiation pattern. (a) current distribution and XOY plane radiation pattern of Port1. (b) current distribution and XOY plane radiation pattern of Port2.
Forearm effects: Further, a typical smart watch is modelling in Fig.6a, adding display module, PCB FR4 material, and back cover. The relative permittivity [7] of GaN back-cover is\(\varepsilon_{r}\)=10.6, \(\tan\delta\)=0.3, for wireless power applications. Fig.6b presents that forearm can significantly lower S21 notch frequency, and influences impedance of Port1.But it has a little effect on impedance of Port2, because of its radiation pattern orthogonal to the forearm. Combining the two antennas, a good omnidirectional MIMO antenna in spatial diversity can be obtained.