# Triple-Band Notched Ultra-Wideband Microstrip MIMO Antenna with Bluetooth Band
## 2 Design of an Ultra-Wideband Antenna Element
### Step 3: UWB Antenna with Dual-Band Notch at WiMAX Band and WLAN Band  
The third step is to place a second band notch at the WLAN operating frequency from 5.15 to 5.85 GHz at the UWB spectrum signal. The WLAN band notch is required to overcome the interference between the obtained FCC-UWB signal and the local unlicensed WLAN band signal. In order to achieve WLAN band rejection over the aforementioned frequency range, a single U-shaped slot is embedded and etched at the bottom side of the proposed UWB radiator, as shown in case 8 of Figure 7b. The length of the etched U-shaped slot is calculated from Equation (5) at the notch frequency of \(f_{ncth}\) = 5.5 GHz. The value of the calculated U-shaped slot length is \(L_{SWLAN}\) = 14.87 mm (i.e., electrical length = 0.5 \(\lambda_{g}\)) while the simulated value is \(L_{SWLAN}\) = 18.5 mm (i.e., electrical length = 0.62 \(\lambda_{g}\)). \[L_{Embedded}\simeq\frac{\lambda_{g}}{2}=\frac{C}{2f_{ncth}\sqrt{e_{eff}}} \tag{5}\]  
where \(\lambda_{g}\) is the waveguide wavelength, \(C\) is the speed of light (\(C=3\times 10^{8}\) m/s), \(f_{0}\) is the operating notch frequency at the WLAN band, and \(e_{eff}\) is the effective relative permittivity. Figure 5: Simulated reflection coefficients for UWB antenna with WiMAX band notch. Figure 6: The parametric study of the length \(L_{CS}\). Figure 8 shows the simulated reflection coefficient (\(\mid S_{11}\mid\) in dB) for case 8 (i.e., single etched U-shaped slot) in Figure 7b. It is observed from the simulated curve of Figure 8 (case 8) that the antenna operates from 2.06 to 14.74 GHz (i.e., UWB spectrum) with dual-band notches at WiMAX and WLAN. The WLAN band notch extended from 4.73 GHz to 6.05 GHz. Moreover, it is observed from Figure 8 (case 8) that the WLAN band notch has high selectivity (i.e., higher sharpness edge) at the end of the band, while it has low selectivity (i.e., lower sharpness edge) at the beginning of the band. Therefore, another U-shaped slot is etched on the top of the UWB radiator in order to improve the selectivity characteristic at the beginning of the WLAN band notch. The two U-shaped slots are vertically aligned and have the same length of \(L_{SWLAN}\), as shown in Figure 7c. The vertically separated distance between the centers of the U-shaped slots is the equal quarter wavelength (\(\lambda_{g}/4\)) to obtain the second high selectivity at the beginning of the band. Placing two vertically aligned U-shaped slots with a separated distance of a quarter wavelength introduces a very high sharpness edge or high selectivity characteristic at the beginning of the WLAN band. The high selectivity occurs between the transmission band of the radiated UWB signal and the rejected one at the WLAN notch band, as shown in Figure 8. This high selectivity characteristic is required for protecting the receiver from damage or even preventing overlap between the radiating UWB RF signal and the indoor/local WLAN signal. Figure 9 shows the investigation of the effect of \(L_{SWLAN}\) in both slots. Three values of \(L_{SWLAN}\) are selected, 18 mm, 18.5 mm, and 19 mm, while the other parameters are kept constant. It is clear from Figure 9 that the optimum curve is at \(L_{SWLAN}\) = 18.5 mm. Figure 8 (case 9) depicts the simulated reflection coefficient (\(\mid S_{11}\mid\) in dB) of the UWB antenna with dual-band notches at the WiMAX band and WLAN band. The UWB antenna with dual-band notches operates from 2.05 to 14.92 GHz, while the the WiMAX band and the WLAN band extend from 3.29 to 3.81 GHz and from 5.05 to 6.02 GHz, respectively. It is shown from Figure 8 (case 9) that the antenna supports the FCC-UWB signal and rejects the indoor WiMAX and WLAN narrow-band RF signals. In addition to this, the antenna supports the Bluetooth band that operates from 2.4 to 2.483 GHz. Moreover, it is observed that there is a very high sharpness edge or high selectivity characteristic at the beginning of the WLAN band at a frequency of \(f\) = 4.94 GHz.