## 5 Measured and Experimental Results  
As discussed, the SUWB BPF is constructed using a UTL loaded with three folded \(\lambda/4\) short-circuited shunt stubs, which are placed symmetrically at a distance equal to \(\lambda/2\) from each other. Three stubs were placed symmetrically on either side of the UTL in order to achieve a high degree of freedom in the design. Due to this arrangement of the \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Serial No.** & **Design Equation** & **Design Resonator Model** & **Theoretical Results** & **Simulated Results** \\ \hline
1 st stopband & \(f_{even1}=\frac{(2n-1)c}{2(L_{2}+L_{3}+L_{4}+L_{5}+L_{6})\sqrt{c_{eff}}}\) & & & \\
2 nd stopband & \(f_{odd1}=\frac{c}{4(L_{1}+L_{2}+L_{3}+L_{4})\sqrt{c_{eff}}}\) & & & \\
3 rd stopband & \(f_{odd2}=\frac{(2n+1)c}{4(L_{2}+L_{3}+L_{4}+L_{5}+L_{6})\sqrt{c_{eff}}}\) & & & \\
1.3,2.2 & 10.8 GHz & 11.5 GHz & \\
3 rd stopband & \(f_{odd2}=\frac{(2n+1)c}{4(L_{2}+L_{3}+L_{4}+L_{5}+L_{6})\sqrt{c_{eff}}}\) & & & \\
10.8 GHz & 11.5 GHz & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Design table for finding the stopbands of the proposed filter. Figure 12: The presented architecture of the SUWB-BPF with a quad-mode stub-loaded resonator. stubs, the performance of the filter was greatly improved in terms of its wide flat passband with an FBW of 141.1% or absolute bandwidth of 13.9 GHz, excellent IL of less than 0.4 dB, and good sharp rejection level at lower and upper frequency, and five TPs appear within the passband at 4.5 GHz, 7.3 GHz, 11.7 GHz, 13.8 GHz, and 16.4 GHz, respectively. For the generation of notches in the initial wideband filter, a symmetrical quad-mode stub-loaded resonator was used. In the first step, a C-shaped resonator was utilized for the second band formation at 8.3 GHz, and then a centrally shorted square ring resonator was added to the C-shaped resonator for the realization of the first and third notch bands at 4.9 GHz and 11.5 GHz, respectively. The final resonator topology obtained was called a quad-mode stub-loaded resonator. Due to its symmetrical nature along XX', a classical method called even-odd-mode was applied to study the resonance behavior of the resonator. After a detailed mathematical calculation, four resonance frequencies were observed, out of which, two were generated with the help of odd mode analysis, and two were observed with the help of even mode analysis. It was assumed that \(\mathbf{f_{\mathrm{el}}}=2\mathbf{f_{02}}\) by considering all impedances to be equal. So, a total of three resonance frequencies were obtained, which lead to the construct of a triple-notch wideband BPF. The first notch at 4.9 GHz was realized due to the second fundamental even mode of the resonator and by varying the parameter \(L_{7}\) from 0.8 mm to 1 mm. Only the first band will move down, while the remaining bands are fixed, as shown in Figure 13.  
The second stopband at 8.3 GHz was realized due to the first odd mode of the resonator and by changing the length \(L_{4}\). Only the second band will change, while the first and third bands are constant, as shown in Figure 14.  
The third stopband at 11.5 GHz was realized due to the first even mode of the resonator, as derived in Equation (6). In Figures 15 and 16, only the third band is changed widely by changing the lengths \(L_{5}\) and L\({}_{6}\), while the other two bands almost remain constant. Moreover, all the stopbands are simultaneously decreased with the parameter \(L_{8}\) from 2.4 mm to 2.8 mm, as shown in Figure 17. This is because the parameter \(L_{8}\) is present in all the resonance equ  
Figure 13: Validation of first band control w.r.t. The above results show that the presented filter has the capability to control all the stopbands separately. The corresponding insertion loss, bandwidth at the \(-10\) dB attenuation level, and the rejection level of each stopband are listed in Table 3, while the theoretical, simulated, and measured results for each stopband are tabulated in Table 4, respectively.