## 3 Demonstration of the Proposed Approach
### Fabrication and Measurement  
To further demonstrate the proposed FoM, we fabricated the IFA and the patch antenna operating at 1.5 GHz and 6 GHz, respectively, to describe the environment of the SAA mounted in a 200 mm \(\times\) 200 mm area. Figure 9 shows comparisons between the simulated and measured reflection coefficients of the two antennas. The fabricated IFA resonates at 1.41 GHz, which is similar to the simulated result of 1.5 GHz. The patch antenna is fabricated on an FR4 substrate (\(\varepsilon_{r}\) = 4.4, tan\(\delta\) = 0.02) having a size of 15 mm \(\times\) 15 mm and a thickness of 1 mm, and its resonance occurs at 6.03 GHz for simulation and 6.05 GHz for measurement. Figure 8: Simulated \(\mid\)S\({}_{11}\mid\) of the IFA according to **(a)** the metallic wall size (distance = 20 mm) and **(b)** distance (\(W_{uull}\) = 200 mm). Figure 7: Simulated normalized patterns of the IFA in the xz plane according to **(a)** the metallic wall size (distance = 20 mm) and **(b)** distance (\(W_{uull}\) = 200 mm). Figure 10a shows a photograph of the fabricated antennas on the ground, which were installed in a full anechoic chamber to measure radiation patterns. In this two-port system, the patch antenna is tested for pattern distortions, and its port--i.e., Port 2--is designed to move away from Port 1 of the IFA to adjust the distance between them. The measurement was conducted with an angular resolution of 5\({}^{\circ}\) for both \(\theta\)- and \(\phi\)-directions, while an inactive antenna port, herein called Port 1, is terminated by a 50 \(\Omega\) load. Figure 10b presents the variations in \(\rho_{PDC}\) according to the distances between 10 mm and 110 mm, which are compared with those of \(\mid\)S\({}_{21}\mid\). Each point of \(\rho_{PDC}\) is calculated using two radiation patterns of the patch antenna--i.e., \(\overline{E_{un}}(\theta,\phi)\) and \(\overline{E_{aff}}(\theta,\phi)\)--each of which is collected without and with the IFA, respectively. It is worth pointing out that the unaffected pattern of \(\overline{E_{un}}(\theta,\phi)\) cannot be reused for a different distance because the relative position of the patch antenna is also changed with respect to the center of the ground. As can be seen, both the simulation and measurement show good agreement, and the decreasing tendency of \(\mid\)S\({}_{21}\mid\) is well reflected in the variation of \(\rho_{PDC}\) with an increasing trend. More specifically, the measured \(\rho_{PDC}\) tends to increase from 0.76 to 0.96 as the measured \(\mid\)S\({}_{21}\mid\) decreases from \(-14.8\) dB to \(-49.8\) dB for greater intervals. Figure 10: Photograph of the measurement set-up and the measured results. (**a**) Measurement of \(\rho_{PDC}\) for the fabricated patch antenna in an anechoic chamber. (**b**) Simulated and measured results of \(\rho_{PDC}\) and \(\mid\)S\({}_{21}\mid\) according to the distance. Figure 9: Simulated and measured reflection coefficients of (**a**) the IFA and (**b**) the patch antenna. Figure 11a presents the normalized radiation patterns of the patch antenna without the IFA for different antenna intervals. The blue and red lines indicate simulated and measured patterns, and the results for different distances of 10 mm and 110 mm are distinguished by solid and dashed lines, respectively. Figure 11b,c show comparisons of the simulated and measured radiation patterns for different antenna intervals, and these patterns were used to calculate the \(\rho_{PDC}\) in Figure 10b. The results confirm that the stand-alone patterns of the patch antenna are similar with each other, although their relative positions with respect to the ground center are different. In addition, as the distance increases from 10 mm to 110 mm, the maximum pattern deviation between the unaffected and affected patterns reduces from 14 dB to 3.1 dB in the upper hemisphere. This implies that the proposed FoM of \(\rho_{PDC}\) can be used as a quantitative measure of the pattern distortions, which cannot be fully represented by \(\mid\)S\({}_{21}\).