## 5 Prototype Fabrication and Measurement Result  
### Measured Results  
The comparison between the simulated and measured S11 results are shown in Table 2. Simulated S11 minimum: \(-\)23.5 dB at \(\sim\)28.1 GHz and measured S11 minimum: \(-\)20.7 dB at \(\sim\)28.3 GHz. The close agreement in the resonance frequency (\(\sim\)200 MHz shift) confirms the fabrication accuracy and effectiveness of the power divider-integrated design. The deviation is likely due to connector soldering effects, substrate property tolerances, and radiation loss at higher frequencies. A return loss below \(-\)10 dB over \(\sim\)27.3 to \(\sim\)29.6 GHz confirms broadband performance, which is critical for 5G mm-wave bands (especially n257/n258 bands). This indicates strong impedance matching and minimal power reflection, confirming that the array with a power divider is resonating efficiently and is a suitable candidate for high-frequency applications.  
The reported gain is 9.91 dBi (simulated) for the linear array and 11.5 dBi for the array with an integrated divider. A gain near 10 dBi for a compact, six-element array structure validates the radiation efficiency of both the antenna and the feeding network. This gain is consistent with other state-of-the-art mm-wave arrays, typically ranging from 8 to 11 dBi for linear or planar configurations of this size. The high gain confirms the constructive interference from the elements via phase coherence introduced by the power divider. The gain enhancement proves the viability of this antenna for directional transmission, key to beamforming and spatial filtering in mm-wave systems. The comparison between the simulated and measured S11 results, summarized in Table 2, reveals close agreement with a resonance shift of approximately 200 MHz, with simulated: \(-\)23.5 dB at \(\sim\)28.1 GHzand measured: \(-\)20.7 dB at \(\sim\)28.3 GHz. This minor discrepancy confirms the design's robustness and fabrication accuracy, particularly given the integration of the power divider. However, the shift and slight reduction in return loss can be attributed to several practical factors, including connector parasitits introduced by the SMA-to-2.4 mm transition and launch interface, soldering irregularities, which introduce unintentional inductance and affect impedance matching, etching inaccuracies, resulting in slight dimensional changes to feedlines and radiating elements, and substrate property variations, particularly in the effective dielectric constant (\(\epsilon_{\pi}\)) and loss tangent (tan \(\delta\)) at mm-wave frequencies.  
To mitigate these discrepancies in future prototypes, the following improvements can be adopted: precision launching connectors to reduce interface parasitits, utilizing laser-etched or photolithographically defined feedlines to enhance dimensional accuracy, and implementing rigorous calibration procedures using standard gain horn antennas to verify far-field measurement accuracy.  
The measured gain of the integrated array reached 11.5 dBi compared to a simulated 9.91 dBi for the linear array alone. This gain enhancement underscores the effectiveness of the power divider in enabling constructive interference through phase coherence. The achieved gain lies well within the expected range for mm-wave arrays of this scale (8-11 dBi), validating both the radiation efficiency and suitability of the design for 5G applications involving beamforming and spatial filtering. Table 3 shows the comparison of the simulated and measured results.