It can be seen from Figure 4 that there is a high influence
of S value towards S-parameter. The most optimal return loss
is obtained at S value = 2.5 mm. For S value = 0.5 mm and
4.5 mm, the antenna bandwidth is very narrow, while for S
value = 1.5 mm and 3.5 mm, the bandwidth is quite wide,
however its return loss is not as good as at S = 2.5 mm.