# A Compact Printed Monopole Antenna for WiMAX/WLAN and UWB Applications
## 2 Antenna Design
First, we designed a structure of a three-band antenna. The specific size was derived from High-Frequency Electromagnetic Simulation Software (HFSS). Then we optimized the parameters calculated by HFSS to find the parameters which best meet the design requirements. The specific size parameters for the antenna are listed in Table 2.  
Figure 3a,b present photographs of a manufacturing prototype of the proposed antenna. A layer of tin was attached to the surface to prevent the oxidation of the radiation surface of the antenna. The design steps of the proposed antenna employed in HFSS are illustrated in Figure 3c. Figure 4 shows the return loss versus frequency diagram for the three cases. For Antenna 1 (Ant1), there was only a gradual microstrip line and a triangular radiating patch, and a single frequency band appeared. The bandwidth at the resonance frequency of 5.68 GHz was in the range of 4.59-7.88 GHz. For Antenna 2 (Ant2), dual-frequency characteristics were exhibited with respect to the Ant1 antenna, and resonance frequency appeared at 2.60 GHz. The matching of these antennas was not very good and did not meet the requirement of 2.40 GHz for Bluetooth. Finally, the antenna structure of Antenna 3 (Ant3) offered improvements. This antenna covered two frequency bands of 2.39-2.49 and 4.26-7.99 GHz, and the bandwidth of the high-frequency band was clearly wider than that of Ant1. This antenna design meets the requirements of the WLAN and WiMAX (5.25-5.85 GHz) bands. All the optimized dimensions are the same as those listed in Table 2.  
Figure 5 presents the simulation result of the voltage standing wave ratio (VSWR) for the proposed antenna as a function of frequency. In wireless communication, this parameter indicates the matching degree of the antenna and feeder. When VSWR equals 1, the impedance is precisely matched to achieve the maximum power transmission. The larger the standing wave ratio, the higher the reflected power and the lower the transmission efficiency. The VSWR of the antenna was less than 1.5 at 2.45 and 5.80 GHz. Figure 6 presents the input impedance curve of the antenna. The input impedance at 2.45 and 5.80 GHz was 51.0049\(-\)8.1573 j and 48.8302\(-\)0.3752 j, respectively. These results indicate that the input impedance is almost 50 \(\Omega\) at the resonant frequency and that the input impedance of the  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Parameters** & **Unit (mm)** & **Parameters** & **Unit (mm)** & **Parameters** & **Unit (mm)** \\ \hline W & 17.00 & W\({}_{7}\) & 1.00 & L\({}_{5}\) & 7.40 \\ W\({}_{f}\) & 2.00 & W\({}_{8}\) & 0.45 & L\({}_{6}\) & 11.80 \\ W\({}_{1}\) & 1.00 & L & 30.00 & L\({}_{7}\) & 7.00 \\ W\({}_{2}\) & 4.30 & L\({}_{f}\) & 10.00 & L antenna is very stable in the 2-10-GHz frequency bands and very close to 50 \(\Omega\). The main purpose of the antenna impedance is to achieve a matching between the antenna and the feeder. If the transmit antenna matches the feed line, the input impedance of the antenna should be equal to the characteristic impedance of the feed line. A Smith chart of the antenna is presented in Figure 7, showing information on the antenna impedance matching, the standing wave ratio, and the normalized impedance. Ang and Mag represent the phase and amplitude at the resonance points in polar coordinates, respectively. Rx represents the input impedance of the antenna. It can be seen that the antenna has a good normalized impedance at the frequencies studied. Table 3 lists the specific values of the Smith chart in Figure 7.  
Figure 4: Simulated return loss versus frequency graphs for Antenna 1 (Ant1), Antenna 2 (Ant2), and Antenna 3 (Ant3) (Ant3 being the proposed antenna). Figure 5: Simulated VSWR (voltage standing wave ratio) versus frequency for Ant1, Ant2, and Ant3 (the proposed antenna).