## 4 Experimental Results  
To experimentally verify the IEP-EBG structure, test vehicles (TVs) were fabricated using a commercial PCB manufacturing process with a plated through hole (PTH) via. Copper and FR-4  
Figure 8: Slot length effects on (**a**) the low cut-off frequency \(f_{L}\) and (**b**) high cut-off frequency \(f_{H}\).  
Figure 9: Dispersion diagram for the slot rotation angle effects.  
were used as the conductor and dielectric material in the PCB process. The copper thickness was 18 \(\upmu\)m. The relative dielectric permittivity and loss tangent were 4.4 and 0.02, respectively. The PTH via radius was 0.4 mm. Three TVs were fabricated, namely the proposed IEP-EBG structure, the conventional MT-EBG structure, and a PPW as a reference. The physical dimensions of the UCs of the IEP- and MT-EBG structures were the same as the example structure in Table 2. The TVs for the IEP- and MT-EBG structures contained a 7-by-7 array of UCs.  
To measure the S\({}_{21}\) parameter, a vector network analyzer (model: Anritsu MS46122A) was used, as shown in Figure 10. A microprobe (GGB 40A-GSG-500-DP) with 500-\(\upmu\)m pitch was used to minimize parasitic components induced by the additional structure used for the measurement. The probe pads were located at (6 mm, 18.5 mm) and (32 mm, 18.5 mm) with the origin located at the lower left corner of the TVs. The overall board size of the three TVs was 37 mm \(\times\) 37 mm.  
The measured S\({}_{21}\) parameters of the proposed IEP-EBG structure, the previous MT-EBG structure, and the PPW are compared in Figure 11. As seen in the results, numerous resonance peaks induced by PPW modes can be observed in the TV of the PPW, represented as a black curve. In contrast, the IEP- and MT-EBG structures formed the stopband, suppressing the PPW modes. The stopband of the MT-EBG structure with a \(-30\) dB suppression level was formed in the frequency range of 3.52 GHz to 7.14 GHz, while that of the IEP-EBG structure was observed in the frequency range 1.55 GHz to 2.48 GHz. The center frequencies \(f_{C}\) of the MT- and IEP-EBG structures were approximately 5.3 GHz and 2.0 GHz, respectively.  
With the same UC size, the IEP-EBG structure achieved a substantial reduction in \(f_{C}\) when compared to the MT-EBG structure by effectively shifting down the stopband in the low frequency range. The distinguishing feature of the IEP-EBG structure was the 62% reduction in the \(f_{L}\) without the use of additional materials or layers. The performance of the MT- and IEP-EBG structures could be compared using the FSV technique [18; 19; 20].  
Thus, it resulted in a cost-effective solution. As previously analyzed, the UC of the MT-EBG structure would have to be enlarged up to 11.7 mm to achieve the same stopband as the IEP-EBG structure. Consequently, it was experimentally verified that the IEP-EBG structure achieved superior \(f_{L}\) reduction, which resulted in the significant miniaturization of the EBG structure.  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Parameters** & \(\mathbf{d_{c}}\) & \(\mathbf{d_{p}}\) & \(\mathbf{w_{s}}\) & \(\mathbf{d_{s}}\) & \(\mathbf{g_{s}}\) & \(\mathbf{\theta_{s}}\) & \(\mathbf{h_{v}}\) & \(\mathbf{h_{c}}\) \\ \hline Values & 5.2 mm & 5 mm & 0.1 mm & 1.8 mm & 0.1 mm & 0 rad & 0.2 mm & 0.3 mm \\ \hline \hline \end{tabular}
\end{table}
Table 2: Design parameters and corresponding values of the dispersion analysis.  
Figure 10: Measurement setup of S-parameters for the verification of the IEP-EBG structure.