# Simulation and Design of Three 5G Antennas
## 5 Design of an Eight-Element MIMO Array Antenna for Mobile Terminals with a Metal Frame
### Fabrication and Measurement of the Eight-Element MIMO Array Antenna
#### 5.3.2 Analysis of Antenna Performance Results  
Figure 48 presents the measured S parameters of the eight-element array antenna. It is evident from the graph that the array antenna provides complete coverage of the LTE band 42 (3.4-3.6 GHz) frequency range, with an overall isolation exceeding 17 dB. Furthermore, the measured S parameters closely align with the simulated S parameters. However, some minor disparities were observed upon comparison. These discrepancies are attributed to slight deviations in the center frequency and a narrowed bandwidth in the actual measured antenna, which stem from losses incurred during the fabrication of the dielectric substrate and SMA connectors. Additionally, inherent errors resulting from the equipment and procedural aspects during fabrication are unavoidable. Nevertheless, it is crucial to note that these errors remain within acceptable limits, and they do not impede the practical use of the array antenna.  
Figure 47: A Physical diagram of an eight-element array antenna processing model. (**a**) Physical front view, (**b**) physical rear view, and (**c**) physical side view.  
Efficiency and radiation pattern measurements were conducted within a microwave anechoic chamber, as depicted in Figure 49. The diagram illustrates the environmental conditions within the anechoic chamber during testing. When one unit is subjected to testing, the other seven units are terminated with 50 \(\Omega\) matching loads [29].  
Figure 50 depicts the measured radiation pattern of the eight-element array antenna at a frequency of 3.5 GHz. Due to the symmetry of the array antenna, the results for four selected ports are displayed here for illustration. It is evident from the diagram that the radiation pattern remains undistorted, and the antenna exhibits effective radiation on both the E-plane and H-plane, achieving omnidirectional antenna radiation.  
Figure 48: Measured S parameters of the eight-element array antenna.  
Figure 51 presents the measured radiation efficiency diagram of the array antenna, with results from four selected ports for illustration. The diagram demonstrates that the MIMO antenna's radiation efficiency falls within the range of 65.8% to 73.7%.  
Figure 50: The measured radiation pattern of the eight-element array antenna at a frequency of 3.5 GHz.  
In addition to radiation efficiency, MIMO antennas also require good isolation and coupling characteristics. Therefore, during measurements, specific metrics such as the envelope correlation coefficient (ECC) need to be closely monitored. For MIMO mobile antennas, a lower ECC value signifies greater diversity gain. As illustrated in Figure 52, the envelope correlation coefficient (ECC) diagram is presented, with ECC values primarily calculated based on the measured three-dimensional far-field radiation patterns.  
Figure 51: The measured radiation efficiency diagram of the eight-element array antenna.  
Figure 52: The measured envelope correlation coefficient (ECC) diagram of the eight-element array antenna.  
As shown in Figure 52, it can be observed that the ECC values calculated from actual measurements are all below 0.03. This signifies that the antenna designed in this study exhibits excellent isolation and a relatively high diversity gain.