# A Dual-Polarized and Broadband Multiple-Antenna System for 5G Cellular Communications
## 4 Prototyping and Measurements of the Suggested Design  
In this section, the fabricated prototype sample of the MIMO antenna design is presented, along with measurement results and comparisons. Figure 12 displays a photograph of the prototype sample. The antenna is implemented on a single side of a low-cost FR4 substrate and features an 8 \(\times\) 8 MIMO configuration. Figure 12 illustrates the feeding method used for the antenna pair. The SMA connectors' inner conductors are soldered to the CPW antennas, while the outer connectors are attached to the ground plane. This configuration ensures effective signal transmission and reception between the antenna elements and the measurement equipment, optimizing performance and reliability in the testing process. Figure 11: (**a**) Radiation and (**b**) total efficiency results of the elements over 3–6 GHz. In the following analysis, the performance characteristics of the smartphone array design for Ports 1 and 2 are assessed and compared, due to their similar placements and the overall characteristics of the antenna pairs. Figure 13 displays the measured and simulated S-parameter results. It is evident from the figure that the measured and simulated S\({}_{11}\)/S\({}_{22}\) values align well, particularly in covering the necessary multi-operation bands. The antenna design demonstrates an impressive impedance bandwidth, with S11 values below \(-10\) dB, spanning from 3.2 GHz to over 6 GHz. This broad bandwidth indicates that the antenna is well-suited for a variety of frequency applications. Moreover, the mutual couplings (S\({}_{21}\)) between the adjacent antenna elements are measured to be less than \(-14\) dB at the desired frequency band. This indicates that the interference between the elements is effectively minimized, ensuring the proper isolation and individual performance of each antenna in the MIMO array [53]. Figure 14 presents the 2D radiation patterns (H-plane and E-plane) of the antenna elements, both from measurements and simulations, at frequencies of 3.5 GHz and 5.5 GHz. During the measurement process, one port of the antenna was excited while the other was terminated with a 50 \(\Omega\) load to ensure precise characterization. The resulting radiation patterns reveal that the prototype of the sample handset antenna demonstrates effective quasi-omnidirectional radiation performance across these resonance frequencies, indicating its suitability for applications requiring broad coverage. This means that the radiation of the antenna has been distributed relatively evenly in various directions around  
Figure 12: (**a**) Prototyped sample and (**b**) feeding method. the element, making it ideal for practical mobile communication scenarios where users may hold their devices in different orientations [54; 55; 56]. Figure 14: Measured/simulated 2D radiation patterns of the pair at (**a**) 3.5 GHz and (**b**) 5.5 GHz. Figure 13: Measured/simulated S-parameters. To evaluate the MIMO capability of the presented array, two important parameters, the ECC and the TARC properties, are examined to ensure that the antenna array provides optimal performance in terms of signal diversity and efficiency, which are critical for effective MIMO operation [57]. These parameters are determined using the following formula:  
\[\text{ECC}=\frac{\left|\mathcal{S}_{\text{mm}}^{*}\mathcal{S}_{\text{mn}}+ \mathcal{S}_{\text{nm}}^{*}\mathcal{S}_{\text{nn}}\right|^{2}}{\left(1-\left| \mathcal{S}_{\text{mm}}\right|^{2}-\left|\mathcal{S}_{\text{mm}}\right|^{2} \right)\left(1-\left|\mathcal{S}_{\text{nm}}\right|^{2}-\left|\mathcal{S}_{ \text{nn}}\right|^{2}\right)^{*}} \tag{1}\]  
\[\text{TARC}=-\sqrt{\frac{\left(\mathcal{S}_{\text{mm}}+\mathcal{S}_{\text{mn}} \right)^{2}+\left(\mathcal{S}_{\text{nm}}+\mathcal{S}_{\text{nn}}\right)^{2}}{ 2}} \tag{2}\]  
Figure 15a,b depicts the calculated ECC/TARC characteristics, respectively. The results show that the ECC is quite low, measuring less than 0.005, and the TARC is below \(-20\) dB, both taken from within the target frequency band.