# A Compact Printed Monopole Antenna for WiMAX/WLAN and UWB Applications
## 4 Experimental Results and Discussion  
The Agilent E5071C vector network analyzer was used to test the return loss, VSWR, and forward transmission parameters S21 of the antenna. Figure 13 presents the results of the simulation and experiment for the return loss of the antenna. The simulation results are in good agreement with the experimental results. The errors may originate from SMA (Sub-Miniature-A) head connection welding, substrate loss, the antenna size being too small, the inaccuracy of the processing dimensions, or the test environment. The differences may also be associated with the relative permittivity used in the simulation and loss tangent uncertainty caused by error. Figure 14 presents the VSWR curve for the antenna simulation and the actual measurement. The VSWR was less than 2 in the range of 4.20-8.20 GHz near 2.34 GHz. The simulation and experimental results were generally consistent. Figure 15 presents the results for the forward transmission parameter S21 between the two antennas. It can be observed from the figure that the transmission performance is good at the frequencies discussed. Figure 14: Simulated and measured VSWR of the proposed antenna. Figure 13: Simulated and measured return loss of the proposed antenna. The gain curve of this antenna is presented in Figure 16, and the gains at 2.45, 4.95, and 5.80 GHz were approximately \(-3.57\), 1.61, and 0.95 dB, respectively. The radiation efficiencies were approximately 47.27%, 95.72%, and 95.58%, respectively. This antenna showed excellent radiation efficiency at high frequencies. Table 4 also summarizes the gain and efficiency of the proposed antenna. Figure 17 shows a photograph of the test environment of the antenna forward transmission parameter S21. Figure 16: Simulated gain and total antenna efficiency of the proposed antenna. Figure 17: S21 test environment of the proposed antenna. Figure 15: Transmission parameter curve of the proposed antenna. Table 5 compares the performance of the antenna proposed in this paper with existing antennas. The gain at 5.8 GHz of the first reference antenna design [5] and the efficiency at 2.45 GHz of the second reference antenna design [19] are slightly better than the antenna of the present study. Other parameters of the design proposed in this paper are superior to the three reference antennas. The relative bandwidth of the antenna proposed in this paper reached 64.31% in the high-frequency band, which is far superior to that of the reference antennas [5; 19; 20]. This paper focuses on miniaturization [21] and high-frequency bandwidth [22] and the proposed antenna has great advantages in the above aspects. In the future, this antenna can be applied in the field of high-frequency broadband antennas. Figure 18 presents a radiation pattern of the proposed antenna and two-dimensional far-field radiation patterns of the E-plane and H-plane at different frequencies. As can be seen from the figure, the antenna proposed in this paper has a good radiation characteristic. In the E-plane, the radiation direction is oriented toward 0\({}^{\circ}\) and 180\({}^{\circ}\), presenting a dipole-like radiation pattern. The E-plane radiation pattern of the antenna is in the shape of a figure eight, which indicates maximum radiation in the directions of 0\({}^{\circ}\) and 180\({}^{\circ}\). In the H-plane, except for a singularity at 4.95 GHz, the other frequencies are all close to omni-directional. \begin{table}
\begin{tabular}{c c c c} \hline
**Frequency** & **2.45 (GHz)** & **4.95 (GHz)** & **5.80 (GHz)** \\ \hline Gain (dB) & \(-3.57\) & 1.61 & 0.95 \\ Efficiency & 47.27\% & 95.72\% & 95.58\% \\ \hline \end{tabular}
\end{table} 
Table 4: Gain and efficiency of the proposed antenna. Figure 18: Radiation patterns of the proposed microstrip UWB antenna.