## 4 Experiment Consequences and Discussion  
Figure 8a shows the photograph of a prototype. In Figure 8b, 2D radiation patterns are measured by a microwave anechoic chamber, and the S-parameters are measured through a Keysight vector network analyzer (VNA) with serial number N5224A. The measured S-parameter results are displayed in Figure 9. Figure 9a demonstrates that the proposed miniature eight-port antenna array can operate in a wideband of 3.3-5 GHz with an Snn smaller than \(-8.5\) dB. Generally, the reflection coefficients S11 of mobile handset antennas are expected to be below \(-6\) dB within the specified frequency bands. Figure 9b illustrates the isolation between different antenna elements. The 2 dB improvement in measured isolation values compared to simulation results can be attributed to the reduction in antenna emission, as indicated by Snn \(<-8.5\) dB, potential gaps during the welding of the three substrates, and the presence of excess tin. Additionally, when measuring mobile phone antennas on a vector network analyzer (VNA), susceptibility to interference from the surrounding environment, including instruments, hands, metal desks, etc., should be considered. Figure 9c reveals the realized peak  
Figure 6: Simulated application scenario of single-handed holding mode. (**a**) Three-dimensional radiation patterns. (**b**) SAR field distributions. Figure 7: Simulated coefficients of single-handed holding mode. (**a**) Reflection coefficients. (**b**) Transmission coefficients. (**c**) Realized peak gains. (**d**) Total efficiencies. gains, and Figure 9d displays total efficiencies, both of which are crucial measurements conducted in a microwave anechoic chamber. The calibration of standard horn gain in a microwave anechoic chamber was carried out to obtain anechoic attenuation, including left-hand circularly polarized (LHCP), right-hand circularly polarized (RHCP), co-polarization, cross-polarization, electric field intensity, etc. The measured realized peak gains were from 2.4 dB to 6 dB, and measured total efficiencies were from 40% to 80%. The measured and simulated normalized two-dimensional radiation patterns of the proposed miniature eight-port antenna array are displayed in Figure 10. The black curves and Ant. 1 are applied to represent the miniature eight-port antenna array with an identical structure. Figure 8: Photograph of a measurement experiment. (**a**) Fabricated antenna prototype. (**b**) Microwave anechoic chamber. Figure 9: Measured coefficients of the proposed miniature eight-port antenna array. (**a**) Reflection coefficients. (**b**) Transmission coefficients. (**c**) Realized peak gains. (**d**) Total efficiencies. Due to the different locations of Ant. 1 and Ant. 2 on the small PCB, the two-dimensional radiation patterns are slightly different. Due to the regularization from \(-50\) dB to 0 dB, the curve originally presented with a single point of prominence becomes more circular and smoother. In Figure 10, the radiation patterns of simulation and measurement at the same plane and frequency are close to each other. The cross-polarization is smaller than the co-polarization. Some of the cross-polarization displays 8-shaped curves. The measured co-polarization and cross-polarization curves are in good agreement with the simulation. Figure 10: Measured and simulated normalized two-dimensional radiation patterns of the proposed miniature eight-port antenna array: (**a**) 3.5 GHz, E-plane; (**b**) 3.5 GHz, H-plane; (**c**) 4.3 GHz, E-plane; (**d**) 4.3 GHz, H-plane; (**e**) 4.9 GHz, E-plane; (**f**) 4.9 GHz, H-plane. The ECC calculated by the anechoic chamber is relatively more accurate than the ECC calculated directly by the S-parameters. Therefore, the radiation pattern of eight antennas pointed in different directions, combined with high port isolation, should contribute significantly to achieving a smaller ECC value. The MIMO performance of the antenna system will deteriorate with the increase in ECC.