## 4 Discussion  
In order to illustrate the benefits of the proposed structure, a comparison between the proposal in this paper and a number of contributions available in the specialized literature is provided in Table 1. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Ref.**} & \multirow{2}{*}{**Size (\(\lambda_{g}\times\lambda_{g}\))\({}^{*}\)**} & \multicolumn{4}{c}{**Differential-Mode**} & \multicolumn{2}{c}{**Common-Mode**} \\ \cline{2-9}  & \(f_{a}^{a}\) (\(GHz\)) & **3-dB** \(FBW\) (\%) & **II.** \(\#f_{a}^{a}\)**(dB)** & **B-to-B II \(>\) 30 dB** & **CMRR \(\#f_{a}^{a}\)(dB)** & \(|S_{c}^{a}|\) \(>\) 30 dB** \\ \hline
[27] & 0.187 \(\times\) 0.285 & 1.84/2.45 & 9.2/8.72 & 2.2/2.6 & 2.2/2.3 & 20.5/20 & \(<\)30.48 \\
[28] & 0.314 \(\times\) 0.413 & 2.46/5.56 & 18.7/9.5 & 0.96/1.9 & 3.05-5.5 & 90.7/3.5 & Up to 6.75 GHz \\
[29] & N/A & 2.44/5.19 & 18.8/7.14/2.05 & 36.4-14 & 41.26/40.35 & Up to 7.6 GHz \\
[30] & 0.275 \(\times\) 0.133 & 2.82/321 & 52.5/1.1 & 19.1/7.5 & \(<\)30 dB & 13.6/7.8 & 33.2/324 GHz \\
[31] & 0.261 \(\times\) 0.173 & 2.55/27 & 11.3/9.8 & 14.6/2.22 & 34.4/4.8 & 38.5/2.9 & (2-4)(5)(5)(5)(3)(7)(3) GHz \\
[32] & 0.153 \(\times\) 0.268 & 2.5/5.6 & 5.1/4.48 & 1.29/19.7 & 3.05-4.8 & 34.7/24.1 & 2-3.7 \(\pm\) \\
[33] & 0.259 \(\times\) 0.929 & 2.44/5.57 & 16.4/8.62 & 1.78/2.53 & 3.15-4.7 & 36.2/31.1 & (1-5)(7)(6)(2)(5) GHz \\
[34] & 0.417 \(\times\) 0.377 & 2.44/5.52 & 8.61/4.57 & 2.47/2.48 & 1.8-3.8 & 52.6/42.2 & Up to 7.6 GHz \\
[35] & N/A & 1.9/2.8 & 2.1/3.9 & 2.05/2.65 & \(<\)30 dB & 40/35.2 & Up to 3.2 GHz \\
[36] & 0.5 \(\times\) 0.2 & 2.4/3.57 & 8.33/5.65 & 0.87/1.9 & 2.9-3.28 & 24.2/21.9 & (1-5.2)(2)(4)(2)(5)(9)(3) GHz \\
[37] & 1.23 \(\times\) 1.23 & 3.5/2.54 & 34.1/3.82 & 1.52/1.65 & 3.7-47 & 53.48/48.35 & Up to 6.6 GHz \\
[38] & 0.67 \(\times\) 0.32 & 0.9/2.49 & 3.6/2.1 & 2.67/4.65 & 1.1-2.3 & 27.3/35.4 & Up to 4.3 GHz \\
[39] & 0.15 \(\times\) 0.37 & 2.5/5.8 & 12.9/4.5 & 0.77/1.56 & \(<\)30 dB & 41.23/36.44 & (1-3)(5)(8)(5)(8) GHz \\
[40] & 0.131 \(\times\) 0.161 & 2.38/3.59 & 1.33/2.13 & 1.34/1.03 & 2.46-3.49 & 48.6/49 & Up to 6 GHz \\
[42] & 0.137 \(\times\) 0.173 & 24.5/6.5 & 7.33/10.9 & 2.78/2.85 & 3.4-4.5 & 47.2/30.2 & (1-3)(8)(5)(2)(2)(7) \\ This work & 0.237 \(\times\) 0.148 & 1.64/2.37 & 8.86/6.59 & 0.92/1.94 & 1.93-2.13 & 38.31.1 & Up to 2.62 GHz \\ \hline \hline \end{tabular} \({}^{*}\) Guided wavelength (\(\lambda_{g}\)) at lowest frequency of operation (\(f_{0}^{a}\)).  
\end{table} 
Table 1: Comparison with reported balanced dual-band bandpass filters. Figure 8: Photograph of the manufactured prototype: (**a**) Top layer; (**b**) middle layer. Figure 9: Simulated and measured response of the proposed dual-band bandpass filter: (**a**) without gap; (**b**) with an air gap of 0.025 mm. In terms of the different relevant parameters, several conclusions can be inferred from the comparison between our design and those reported in the literature (Table 1):  
1. **Filter size**. In terms of electrical size, the proposed filter is very competitive. Indeed, is one of the smallest in the table (0.035 \(\lambda_{g}^{2}\), \(\lambda_{g}\) being the guided wavelength at the center of the lower transmission band, when the average size for those presented in Table 1 is 0.184 \(\lambda_{g}^{2}\)). There are only two designs smaller than the one in this contribution [40; 42], but it should be taken into account that one of the main advantages of our filter lies on its simplicity. Size reduction through optimization of the geometry of the resonators would be possible but has not been attempted. 2. **Fractional bandwidth**. Our design confers the designer total and independent control on the bandwidth of the two passbands. For our specifications and requirements, the filter perfectly covers both the GPS band and the Wi-Fi band, so there are no issues on this regard. If we look at the results obtained in the considered literature, the average fractional bandwidth is 8.74% (first band) and 5.72% (second band). Both values are very close to those reported in this work.