III. RESULTS AND DISCUSSION
Based on the detailed dimensions given in Fig. 1 and table
1, the triple-band monopole was fabricated and tested. Fig. 4
shows the fabricated prototype of the antenna. The measured
and simulated return loss curves for the proposed antenna are
depicted in Fig. 5. The reflection coefficient measurement was
performed by using WILTRON 37269A vector network
analyzer. From the graph, it is quite clear that simulated result
agrees reasonably with measured one. The discrepancy
between them may be caused by the inaccurate dimensions in
the fabrication and the different environments for the
simulation and measurement. With the measurement, the three
resonant modes are excited at frequencies of 2.45GHz,
3.68GHz and 5.39GHz. The obtained -10dB impendence
bandwidths range from 2.38 to 2.53, 3.37 to 4.04 and 4.51 to
6.04GHz with the relative bandwidth of 6.1%, 18.2% and
28.4%, respectively, which make the proposed antenna easy to
cover the required bandwidths for both WLAN and WiMAX
applications.
Effects of some vital structure parameters on impedance
matching of the proposed antenna are investigated. The return
loss curves for different value of 1 L are illustrated in Fig. 6, it
can be seen from the figure that the changing of the length 1 L
of the rectangle slot has a great impact on lower resonant
frequency with little effect on upper ones. Fig. 7 shows the
effect of the various value of r L of the L-strip on the return
loss curves, it is observed that the length of r L has a great
impact on the resonant mode for 3.5GHz. Fig. 8 illustrates the
simulated return loss characteristics of the proposed antenna
for various t L , it is noticed that the length t L of the narrow
rectangle can be used to adjust the resonant frequency band at
5GHz.