# Flexible Antennas for a Sub-6 GHz 5G Band:
## 6 Discussion  
A brief discussion about the different sections explained in the article is presented here. The focus of the entire paper is to give an insight into the new research that takes place in the field of flexible antennas in 5G that have grabbed the attention in the past decade. The released sub-6 GHz 5G band is the suitable choice for further investigation in the field of 5G since the band can be utilized not only for mobile applications but also in other fields including the military, health monitoring, aircraft applications, wireless body area networks, and so on with easy deployment. As far as flexible antennas are concerned, the choice of proper substrate materials and conductive materials is very crucial as they affect the performance of the antenna. In recent years, a novel Ti3C2 Tx/PVDF composite with a strong negative permittivity has become increasingly popular in applications where it can replace conductive textiles that are prone to deformation [21]. Due to their excellent mechanical and electrical characteristics, the polymer-based substrates are a promising choice for the implementation of flexible antennas. Polyethylene terephthalate is used frequently in recent years due to its transparency, and good thermal and electrical properties [29]. Flexible antennas used in 5G need antennas with a positive gain and a directional radiation pattern. A bending analysis is one of the main studies that is needed in the flexible antenna since the bending of the antenna varies the effective length of the antenna and thus varies the resonant frequency [14]. We have reviewed several flexible antennas for the 5G sub-6 GHz mid-band in this paper and have discussed the bending analysis and it is evident that there is a variation in the resonant frequency of the antenna due to bending [46; 47; 48]. However, the bending of the antenna across a higher radius showed a similar result in the reflection coefficient similar to the planar structure [52]. Therefore, the antenna design has to be optimized in such a way that the effect of bending has a negligible effect on the antenna characteristics. The specific absorption rate is a very crucial term as far as WBAN applications are considered. The distance of the antenna position from the human body has a significant effect on the antenna characteristics. The SAR value decreases as the distance of the antenna from the human body increases [82]. The article has reviewed several single elements, arrays, and MIMO flexible antennas for a sub-6 GHz 5G band. Slot-based antennas are discussed in [46; 47; 48]. Slot elements can enhance the bandwidth of the antenna [45], contribute to a better gain [48], and also be utilized for creating band notches [47]. In [50], the multiband was achieved by the implementation of strips with the radiating patch. The DGS-based single elements, as well as the MIMO antennas, are reviewed in the article for sub-6 GHz applications. The defective ground structure has increased the bandwidth as well as the efficiency of the antenna [51]. The DGS can increase the bandwidth of the antenna by around 117% without affecting the antenna size [52]. A large ground plane increases the mutual coupling of the antenna and reduces the isolation. The operating bandwidth and radiation properties, when used in a MIMO, are affected by asymmetric alterations made to the ground plane, which create an asymmetric current distribution. Thus, a partial ground or defected ground plane can be used. Ground planes can shield the human body from harmful radiation and also reduce the SAR [53]. Metamaterial-based antennas have also been used in the design of flexible antennas. An improved gain that is the most crucial parameter, especially for 5G applications, can be improved by using metamaterials [54]. AMC, EBG, as well as SRR-based antennas, are reviewed in the article to provide an insight into the MTMs [55; 56; 57]. Single element antennas are still not suitable for improving the channel capacity. Thus, MIMO antennas are the best choice for improving the channel capacity.