# Design of Multi-Mode Antenna Array for Use in Next-Generation Mobile Handsets
## 7 User Effects on the Characteristics of the Designed Antenna Array
Compared with the antenna performance in free space, the maximum reductions of the total efficiencies are observed for the PIFA elements that have been partially covered by the hand [78]. Additionally, as evident from the results, the antenna provides good S-parameters including S\({}_{\text{nn}}\) and S\({}_{\text{mn}}\) in both right and left-hand scenarios. Apart from the data-mode, the antenna performance in talk-mode should be also studied. Figure 16 shows the total efficiency, S\({}_{\text{nn}}\) (S\({}_{\text{11}}\)-S\({}_{\text{88}}\)), and S\({}_{\text{mn}}\) (S\({}_{\text{21}}\)-S\({}_{\text{81}}\)) characteristics of the designed handset antenna in the presence of the user-hand/user-head in talk-mode. Figure 16a shows the placement of the designed antenna array in talk-mode; the array's total efficiencies are represented in Figure 16b. It is shown that the antenna elements exhibit relatively good efficiencies at different resonance frequencies. Additionally, the antenna S-parameters are depicted in Figure 16d. As can be seen, the PIFAs are operating at the target frequencies with good S\({}_{\text{nn}}\) and less than \(-10\) dB S\({}_{\text{mn}}\). The EM energy absorbed by human body tissues can be evaluated by the specific absorption rate (SAR) [79; 80]. SAR is a measure of how much power is being absorbed per unit mass. The SAR features of the MIMO design at three different operation frequencies are investigated. According to the obtained results from different investigations of the antenna elements, it is found that antenna 2 causes the maximum SAR value while the minimum SAR value is observed from antenna 6. The SAR results of antenna 2 and antenna 6 at 2.6, 3.6, and 5.8 GHz are depicted in Figure 17. According to the results, the distance between the PIFA elements and the head phantom is most important in terms of the value of the SAR function. Figure 14: (**a**) Placement, (**b**) total efficiencies, (**c**) S\({}_{\text{nn}}\), and (**d**) S\({}_{\text{mn}}\) results for the right-hand scenario. Figure 16: (**a**) Placement, (**b**) total efficiencies, (**c**) S\({}_{\rm nn}\), and (**d**) S\({}_{\rm mn}\) results for the talk-mode scenario. Figure 15: (**a**) Placement, (**b**) total efficiencies, (**c**) S\({}_{\rm nn}\), and (**d**) S\({}_{\rm mn}\) results for the left-hand scenario. Below, the fundamental characteristics of the MIMO antenna including the total efficiency, S\({}_{\text{nn}}\) and S\({}_{\text{mn}}\) are also studied in the presence of smartphone components including the battery, speaker, camera, USB connector, and LCD screen. Table 3 lists the characteristics of the modeled components [81]. It is clearly seen from Figure 18 that the design provides consistent characteristics at the desired operating frequencies. Figure 17: SAR for antennas 1 and 5 at (**a**) first (2.6 GHz), (**b**) second (3.6 GHz), and (**c**) third (5.8 GHz) resonances. Figure 18: (**a**) Placement, (**b**) total efficiencies, (**c**) S\({}_{\text{nn}}\), and (**d**) S\({}_{\text{mn}}\) results in the presence of the smartphone components.