## 4 Results and Discussion  
To verify the CMS-EBG structure, a test vehicle is fabricated using a commercial MPCB manufacturing process. The MPCB process provides twelve metal layers from L1 to L12. L1 is dedicated to probe pads for the measurements. The other layers are used for the CMS-EBG structure as shown in Figure 8. Copper and FR-4 are used for the conductor and dielectric material, respectively. The relative permittivity of the FR-4 is 4.4, and the loss tangent is 0.03. The copper thickness is approximately 17 \(\upmu\)m. The distance between the layers (i.e., dielectric thickness) is 0.1 mm. The low-\(Z_{\mathrm{o}}\) patch, high-\(Z_{\mathrm{o}}\) patch, and ground plane are implemented by etching copper. A plated through hole (PTH) via is used in the MPCB process. The VCA branches and ground vias are made using the PTH vias. The MPCB process here is reliable, cost-effective, and easy to manufacture. Port 1 contains the signal terminal, which is connected to the high-\(Z_{\mathrm{o}}\) patch of UC\({}_{(1,5)}\) in L3 and the ground terminal, which is connected to the corresponding ground layers in L2 and L4. Port 2 consists of the signal terminal, which is connected to the high-\(Z_{\mathrm{o}}\) patch of UC\({}_{(4,1)}\) in L11. In addition, the ground terminal \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Parameters**} & \multicolumn{8}{c}{**\(k\) (\(w_{p}/w_{po}\))**} \\ \cline{2-10}  & & **0.7** & **0.8** & **0.9** & **1.0** & **1.1** & **1.2** & **1.3** \\ \hline \(Z_{\mathrm{oL}}\) (\(\Omega\)) & & 1.16 & 1.03 & 0.90 & 0.82 & 0.75 & 0.68 & 0.62 \\ \hline \multirow{4}{*}{Equation (3) (GHz)} & \(f_{L}\) & 2.82 & 2.49 & 2.20 & 1.98 & 1.81 & 1.65 & 1.52 \\  & \(f_{H}\) & 9.17 & 8.02 & 7.13 & 6.42 & 5.83 & 5.35 & 4.94 \\  & \(f_{C}\)\({}^{1}\) & 6.00 & 5.23 & 4.67 & 4.20 & 3.82 & 3.50 & 3.23 \\  & FBW \({}^{2}\) & 1.06 & 1.05 & 1.06 & 1.06 & 1.05 & 1.06 & 1.06 \\ \hline \multirow{4}{*}{FEM (GHz)} & \(f_{L}\) & 3.2 & 2.85 & 2.47 & 2.24 & 2.02 & 1.85 & 1.68 \\  & \(f_{H}\) & 8.49 & 7.48 & 6.81 & 6.11 & 5.65 & 5.15 & 4.77 \\ \cline{1-1}  & \(f_{C}\) & 5.85 & 5.17 & 4.64 & 4.18 & 3.84 & 3.50 & 3.23 \\ \cline{1-1}  & FBW & 0.91 & 0.90 & 0.94 & 0.93 & 0.95 & 0.94 & 0.96 \\ \hline \hline \end{tabular} \({}^{1}\) Center frequency: (\(f_{H}+f_{L}\))/2; \({}^{2}\) Fractional bandwidth: (\(f_{H}-f_{L}\))/\(f_{C}\).  
\end{table} 
Table 1: Summary of the design parameter effects on the low- and high-cutoff frequencies, center frequency, and fractional bandwidth. Figure 7: Analysis of the \(w_{p}\) effects on the (**a**) center frequency and (**b**) fractional bandwidth. of Port 2 is connected to the corresponding ground layers in L10 and L12. The port configuration is equivalent to the ports in the Z\({}_{\text{o}}\)-lattice diagram in Figures 2a and 3. The top view of the CMS-EBG structure fabricated by the MPCB process is shown in Figure 8. The geometrical parameters are described in Figure 4 of Section 3. The values of the design parameters \(w_{p}\), \(w_{b}\), \(d_{b}\), \(S_{b}\), \(S_{v}\), \(r_{v}\), \(t\) and \(h\) are 11, 1, 1, 5, 1, 0.2, 0.017, and 0.1 mm, respectively, which are equivalent to the values in the Floquet-Bloch analysis. The unit cell length is 12 mm. The distance between port 1 and port 2 is only 4 mm, which is less than the unit cell length. In addition, sixteen EBG cells are successfully located within a compact area of 23 mm \(\times\) 23 mm, which is only one-quarter of the area that the previous 4 \(\times\) 4 EBG structure requires. The measurement setup is depicted in Figure 9. The scattering parameters (S-parameters) are measured using the vector network analyzer Agilent N5230A. The microprobe technology is used to minimize the parasitic effect induced by additional structures such as the measurement pad. The GS- and SG-type probes with 400 \(\upmu\)m pitch are used. To analyze the noise suppression characteristics, a S\({}_{21}\) parameter is observed.