## 4 Antennas and Antenna Related Technologies for Future Internet
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Ref.** & **Frequency (GHz)** & **No. of Antennas** & **No. of Ports** \\ \hline
[239] & 2.4 & 64 & 16 \\
[240] & 3.7 & 100 & 100 (10) \\
[241] & 5.8 & 256 & 64 \\
[242] & 3.5 & 128 & 128 (12) \\
[243] & 3.5 & 64 & 32 \\
[244] & 3.5 & 288 & 72 \\
[245] & 5.8 & 120 & 120 \\
[246] & 3.5 & 240 & 60 \\
[247] & 13 & 4096 & 256 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: MIMO prototype evolution towards gMIMO. Figure 12: Antennas and antenna-related technologies classification. the design's competence. For example, the systems provided tend to be multifunctional, complex, and very elaborate. On the other hand, when cost is the main issue, the designs tend to be simple but nevertheless thoughtful. In this case, the goal is that relevant devices can be produced in great numbers, usually via automated procedures, and be of low profile while retaining the necessary degree of merit and minimum functionality to work seamlessly, integrated into the targeted system. In this category, we include antennas for UEs, where available space, MIMO function, and reduced SAR control the design process. Also, we include IoT devices' radiators working under the umbrella of mMTCs in smart homes, factories, cities, or sensor network applications. These antennas are designed to achieve high scores on diverse KPIs from multiband operation to multi-polarization and DoA functionality, from body networks to wireless power transfer and super-directivity, from frequency coding to sensor and RFID applications, and, of course, many more. In the case where complex designs are allowable, the next factor is whether the system's performance is critically impaired or limited by the distance between the communicating nodes (with well-known examples being propagation losses and system latency). If this is not the case, then centralized designs (meaning non-peer node communication where a coordinating-serving access point, such as a base station, LEO satellite, or IoT reader station, connects with a set of numerous users, such as UEs or IoTs, whose spatial positioning is angularly represented into the utilized wireless channel) can be employed. These are well suited to the eMBB use case of 5G and 6G communications. A notable example of this case is the base station MIMO antenna system, which has been covered in Table 4.  
On the other hand, if performance is critically impaired or limited by Tx-Rx distance, distributed solutions are employed. The aim here is more uniform coverage or reduced latency between the communicating nodes. In this case, one can distinguish between the ways this distribution is attained. If the distributed operation is based on physics-level principles, we can refer to near field communications (NFC) and RIS-assisted communications. Alternatively, if antenna distribution is achieved by choosing a distributed operation paradigm for the communication network, we can include cell-free communications (distributed MIMO), side-link communications, and edge computing. In NFC, the distributed function is achieved by adding an extra dimension to the space that surrounds the main antenna. Before NFC, the space around an antenna was conceived as functioning only in the far field and, thus, described only by angular dimensions. By adopting NFC, antennas become electrically large, and this pushes the Fraunhofer boundary (the far-field boundary) outward from the antenna. To access any receiver immersed into this extra, near-field space, one needs the additional Tx-Rx distance dimension, since the angular one alone is no longer sufficient. This increases capacity, a major KPI concern in 5G and 6G wireless communications. In the RIS case, a reflective (or even a transmissive) array antenna structure is employed as a relay to assist NLOS (or, in general, unreliable) wireless communication. Reconfigurability and, thus, adaptability to varying link conditions is achieved via controlled lumped loads attached to each of the reflecting elements.