# Radiator Enablers for Wireless Communication Evolution
## 4 Conclusions  
The general objective of the current study is to propose the innovations needed in order to place the next-generation Wireless Communication vision into the technological reach. In the work at hand, we address the role of the antenna system in the Wireless Communication evolution via critical observation of the increase in the degrees of freedom that those innovative radiators offer. Those extra degrees of freedom have a catalytic effect in answering the challenges posed by the ever-increasing demand for more capacity, spectral and power efficiency, reliability, and low latency. In detail, we document the potential of the gMIMO, RIS, Holographic Metasurfaces, and the OAM. Then, we detect the impact that those potent technologies have on the mmWave, satellite, and THz wireless communications system evolution. Reassessing the presented context (with special focus on Tables 2-12 and Figures 1-4), one can understand that (except for sensor antennas), (re-)radiators (with the (re-) included for the RIS type case) tend to transform to arrays with ever-increasing elements and antenna ports. They tend to be reconfigurable, modular, expandable, and scalable. They also tend to be extremely broadband and multifunctional (ref. [141]). In other words, one can observe a clear path toward antenna systems' convergence. We depict this concept in Figure 5, where the relative technologies' convergence tree is presented. It has the shape of an inverse evolution tree. Indeed, while in an evolution tree, we proceed from a common start--the root--and continue to the diversified leaves, here the diversified radiator seam, to converge to a unified multielement, multiport, modular, broadband, and multifunctional array prototype. In detail, the focused antenna radiator types (RIS, HM, gMIMO, and OAM) evolve (from left to right) with a constant increase in degrees of freedom and multifunctionality. Figure 5: Wireless evolution-driven antenna convergence diagram. Convergence points between HM-RIS, HM-gMIMO, and OAM-MIMO have been observed (for example, HM-RIS: ref. [72] in 2020, HM-gMIMO: ref. [73] in 2024) or anticipated. Indeed, after OAM proof of concept (refs. [85; 86; 87; 89; 90]), integration efforts for the MIMO scheme are considered, by the authors, highly probable to happen in the near future. Also, as indicated in the figure and deduced from the presented references, there are eventually two parallel paths, one focused on the antenna (denoted as Transducer Focused), and the other on the channel part (denoted as Channel Focused), of the communicating system. There are already signs (from published works ranged from collocated to multi-user to distributed MIMO) of the two focuses' convergence toward increased degree of freedom radiators under the continuous need to accelerate wireless communication evolution. Conceptualization, T.K. ; methodology, T.K. ; investigation, A.-C.T., P.M., A.K., G.G., I.G., V.K. and G.S. ; resources, A.-C.T., P.M., A.K., G.G., I.G., V.K. and G.S. ; data curation, A.-C.T., P.M., A.K., G.G., I.G., V.K. and G.S. ; writing--original draft preparation, A.-C.T., P.M., A.K., G.G., I.G., V.K. and G.S. ; writing--review and editing, A.-C.T., P.M., A.K., G.G., I.G., V.K. and G.S. ; visualization, A.-C.T., P.M., A.K., G.G., I.G., V.K. and G.S. ; supervision, T.K. ; project administration, T.K. All authors have read and agreed to the published version of the manuscript. This research received no external funding. Not applicable. The raw data supporting the conclusions of this article will be made available by the authors upon request. The authors declare no conflicts of interest. The following abbreviations are used in this manuscript: