## 3 Measurement Results and Discussions  
The reference and the proposed quintuple band-notched UWB antennas were fabricated, and their frequency response was measured to demonstrate the multiple notching responses. The Thru-Reflect-Line (TRL) calibration has been carried out after implementing the TRL calibration kit with the same antenna substrate and SMA connectors. The frequency response of both the reference and the proposed antennas after TRL calibration is shown in Figure 8. The response clearly reveals that there exists a filtering behavior centered at frequencies of 3.5, 4.5, 5.25, 5.7, and 8.2 GHz. While rejecting the WiMAX, INSAT, and ITU 8 GHz frequency bands as designed, there are slight frequency shifts towards the higher frequencies in the measurement. Table 2 presents the discrepancies between the simulated and measured notch frequencies. The minor frequency shifts were caused by the over-etched slot width from the milling machine. The slot width was measured using Vernier caliper at several different positions at the slot resonators. While we use \(W_{s}\) equal to 0.3 mm, the measured mean and standard deviation values of \(W_{s}\) were 0.3487 mm and 0.0258 mm, respectively. The frequency shifts in the lower (L-WLAN) and the upper WLAN (U-WLAN) frequency bands were relatively drastic where the mutual coupling between two slots was found to be larger than other slot resonators. The effect of the over-etched slot width (\(W_{s}\)) becomes more dominant for L-WLAN and U-WLAN resonators as both the slot resonators are close to each other, which in turn has more significant mutual coupling, which shifts the resonance frequency much higher than other resonators. Figure 9 compares the simulated and measured reflection coefficient of the proposed antenna after setting \(W_{s}\) = 0.3487 mm, which verifies our observation. Table 3 presents the discrepancy between the simulated and measurement response when the simulation setup is changed with \(W_{s}\) = 0.348 mm, keeping all other parameters fixed. Figure 7: Effect of critical parameter \(W_{s}\) on the response of the proposed antenna. The radiation pattern of the reference and the proposed quintuple band-notched UWB antenna were measured in an anechoic chamber at three different frequencies which cover the center, lower, and upper frequencies of the entire UWB band. Figure 10 presents the measurement setup for the radiation pattern measurement of the reference and proposed antenna in an anechoic chamber. The chamber is equipped with the near-field planner scanner and a far-field tower to test and measure the radiation pattern of the antenna under test (AUT). At 3.9, 6.1, and 7.8 GHz the radiation patterns have been measured which cover the lower, upper, and mid frequencies of the UWB. The radiation pattern is measured at each 1 degree step interval in an anechoic chamber having a range of 0-360 \({}^{\circ}\). The selected frequencies were 3.9, 6.1, and 7.8 GHz and its co-polarized beam pattern at the XZ-plane (E-plane) and YZ-plane (H-plane) are presented in Figure 11. There is a good agreement between the radiation pattern of the reference antenna and the proposed quintuple band-notched UWB antenna at 3.9 and 6.1 GHz, while the radiation pattern became distorted at 7.8 GHz and there arise nulls at both planes. It is due to the distortion in the phase distribution of the electric field and the increase in the magnitude of higher order harmonic modes at the higher frequency from the structure. \begin{table}
\begin{tabular}{c c c c c c} \hline  & **WiMAX** & **INSAT** & **LWLAN** & **UWLAN** & **ITU 8 GHz** \\ \hline Simulated (f\({}_{1}\)) & 3.54 & 4.65 & 5.31 & 5.90 & 8.26 \\ Measured (f\({}_{2}\)) & 3.57 & 4.70 & 5.51 & 6.15 & 8.28 \\ Shift in frequency (\(\Delta\)f = f\({}_{2}\) – f\({}_{1}\)) & 0.03 & 0.05 & 0.20 & 0.25 & 0.02 \\ \hline \end{tabular}
\end{table} 
Table 2: Discrepancies between the simulated and measured results.