The antennas are first measured using a vector network
analyzer (VNA) for their impedance and reflection coefficients
S11. The results are similar but not the same as that in Fig. 3.
For example the first resonant frequency for single element is
around 2.8 GHz but the second one seems to have been shifted
from 6 to 9 GHz. This is partially due to the SMA connector is
placed at the gap of the circular dipole antenna and a balun was
not used. Therefore, with the different feed structures the
simulated and measurement results are bound to be different.