## 5 Feasibility and Measurement
Figure 10 presents the measured performance of the final Step 2 configuration, corresponding to the re-tuned two-port antenna design of Figure 8b. The structure was optimized to enhance port-to-port isolation while preserving broadband impedance matching and MIMO performance. As shown in Figure 10a, both ANTs #1 and #2 exhibit wideband impedance matching with a VSWR \(\leq\) 3 across the entire n78 band (3.3-3.8 GHz). The matching bandwidth is notably broader and more stable than that of the initial Step 2 configuration shown in Figure 9, with the resonant frequencies now well centered within the desired operational range. Importantly, the port-to-port isolation is significantly improved, attaining a measured minimum of \(-\)12.39 dB at 3.53 GHz, an enhancement of almost 8 dB relative to that of the earlier design. Such improvement is attributable to the refined slot geometries and current path optimization along the metal frame. These factors effectively reduce electromagnetic coupling. Figure 10b shows the corresponding radiation efficiencies and ECCs. Both antenna ports exhibit radiation efficiencies exceeding \(-\)6 dB across the bands, with the peaks approaching \(-\)2 dB near the resonance region. Crucially, the ECC values are drastically reduced, being as low as 0.001-0.002 within the 3.5-3.7 GHz range and remaining below 0.12 across the full n78 band. These results are well within the acceptable ECC threshold of 0.5 for effective MIMO operation and indicate highly decorrelated far-field radiation patterns. Collectively, these findings confirm that the final Step 2 antenna configuration achieves an optimal balance between impedance matching, radiation efficiency, port isolation, and the ECC. Compared to the Step 1 and preliminary Step 2 iterations, the final design satisfies both the radiation and system-level MIMO performance criteria, validating the feasibility of antenna integration into metal frame-based sub-6 GHz smartphone platforms. Figure 11 presents the measured far-field radiation patterns of ANTs #1 and #2 in both the E-plane (\(\theta\) = 90\({}^{\circ}\)) and H-plane (\(\varphi\) = 90\({}^{\circ}\)) at three representative frequencies, 3.3, 3.5, and 3.8 GHz, in the n78 band. These measurements confirm that the antenna maintains consistent radiation behavior across the designated operational bandwidth. Figure 11a,b show the radiation performance of ANT #1, which exhibits a moderately omnidirectional pattern in both planes. In the E-plane, a slightly stronger gain is observed toward the 0\({}^{\circ}\) and  
180\({}^{\circ}\) directions but the overall gain variation across the three frequencies remains within 5 dB, indicating excellent pattern stability. In the H-plane, the radiation pattern is somewhat compressed along the 90-270\({}^{\circ}\) axis but retains a field distribution that adequately supports spatial diversity. Figure 11c,d depict the corresponding results for ANT#2, which also exhibits stable radiation behavior across the entire frequency bands. At 3.5 GHz, a modest increase in directivity is observed in the E-plane; the forward gain is approximately \(-\)12 dB. Despite this, the pattern symmetry is well-preserved across all measured frequencies, with no significant nulls within \(\pm\)30\({}^{\circ}\) of the boresight; this enhances link robustness in the real world. The results confirm that both antenna elements maintain a consistent angular coverage and pattern reproducibility throughout the n78 band. Such stability is crucial in terms of minimizing the envelope correlation and ensuring reliable MIMO performance, particularly in dynamic user hand interaction scenarios wherein the angular orientation of the antenna may vary significantly. All measurements were performed in a shielded anechoic chamber maintained at a temperature of 23 \(\pm\) 2 \({}^{\circ}\)C and a relative humidity of 40-60% to ensure stable environmental conditions during testing.