I. Introduction
II. Antenna Design
III. Simulated Results and Discussions
1. Frequency Characteristics
Return Loss: Fig. 3 shows the reflection coefficients of the proposed antenna in comparison with other antennas shown in Fig. 2. Fig. 4 presents the simulated return loss of the proposed antenna. The simulated return loss is presented in Fig. 4. The simulated antenna presents a −10 dB impedance bandwidth of 1.41 GHz from 2.1 GHz to 3.6 GHz (60.63%) and 1.46 GHz from 4.96 to 6.0 GHz (27.18%) covering the WLAN and Wi-MAX applications.
Current Distribution: To obtain a deep insight into the working principle of the proposed antenna, the current distributions of the antenna at 2.4, 3.06, 5.2, and 6.0 GHz are presented in Fig. 5. The figure shows that the currents at 6 GHz mainly concentrate on the Patch I, those at 3.06 GHz, radiate from a longer branch of the monopole to the center of the monopole, and those at 5.26 GHz shift to the shorter monopole. At 2.33 GHz, the waves reach the MTM loading through the EM coupling, thus forming an energy loop and enabling effective radiation.
Radiation Pattern: The simulated radiation patterns in the elevation (xz- and yz-planes) and azimuth (xy-plane) planes are shown in Fig. 6. Fig. 7 illustrates the simulated 3D radiation pattern plots of the proposed antenna. An omnidirectional radiation pattern is obtained in the xy-plane at the dominant resonant frequency band. As the resonant frequencies increase, the radiation patterns change because of the effects of high-order modes.
2. Measured Results
2.1 Return loss
2.2 Radiation characteristics
Radiation pattern: Fig. 10(a)–(d) show the measured azimuthal plots in the horizontal and vertical planes of the designed antenna at 2.33, 3.06, 5.26, and 6.0 GHz.
Gain: Fig. 11 presents the gain versus frequency graph of the proposed MTM-loaded antenna. The simulated gain is above 2 dB over the entire −10 dB impedance bandwidth, satisfying the minimum gain condition for using the antenna for commercial applications such as WLAN and Wi-MAX.