## 4 Antennas and Antenna Related Technologies for Future Internet
### Antennas for User Devises, (IoT--mMTC and UEs)  
Antennas for user devices can be studied based on design goals, novelty and merit, manufacturing process and evaluation, and the focus of the specific application, and they are grouped here into two main categories: the IoT and user equipment (UE) serving antennas. A summary of indicative works is listed in Table 5 where various antenna characteristics are depicted for user devices, including IoT devices and UE. The table details various parameters for each antenna technology, such as the element type, number of elements, size, frequency band, beamforming utilization, number of beams, gain, beamwidth, and number of MIMO ports used. Key challenges that must be addressed for the upcoming 6G communication include miniaturization, polarization diversity, and energy efficiency with respect to antennas for user devices. For the IoT case, one can identify antennas for wearable, polarization beamforming, DoA-focused, MIMO, wireless power transfer, super-directivity-based, and multiband applications. Wearable antennas are the focus of [248,249], where 3D beam-steering MIMO antenna for on-body IoT applications and lightweight flexible, wearable, circularly polarized antenna for navigation and positioning in IoT applications are contributed, respectively. Multi-polarization focus, beamforming, and DoA functions are the quest of [250,251,263]. There, an all-polarization, beamforming, and DoA-ready \(\Gamma\)-_dipole_ antenna, an all-polarization rectenna, and a multi-sector annular antenna for IoT applications are contributed. An example of an all-polarization \(\Gamma\)-dipoles antenna array is depicted in Figure 13. \begin{table}
\begin{tabular}{c l l l l l l} \hline \hline
**Ref.** & **Type of Element** & **Elements** & **Size (mm\({}^{3}\))** & **Frequency (GHz)** & **No. of Beams** & **Gain (dBi)** \\ \hline
[248] & Circular Patch & 4 & \(40.17\times 40.17\times 0.57\) & 5.75 & 4 & 6.41 \\
[249] & Square Ring Patch & 1 & \(77.9\times 73.2\times 0.2\) & 1.1–2.3 & 1 & 1.5 \\
[250] & \(\Gamma\)-Dipoles & 4 & \(75\times 75\times 1\) & 2.4 & 2–4 & 6.84 \\
[251] & Sector Patch & 4 & \(27.4\times 27.4\times 1.34\) & 4.16 & Multiple & 4.62 \\
[252] & Circular/Annular Patch & 3 & \(60\times 60\times 0.7\) & 2.43–2.467 & 3 & 6 \\
[253] & Circular Patch & 3 & \(41.6\times 41.6\times 3\) & 3.5 & 3 & N/A \\
[254] & Rhombohedral Patch & 3 & \(75\times 70.2\times 6\) & 4.18–6.76 & Multiple & 7.8 \\
[255] & Half-Mode Patch & 1 & \(22.55\times 23.95\times 3\) & 2.45 \& 5.5 & 2 & 4.53 \& 9.1 \\
[256] & Lateral Cross-Dipoles & 4 & \(21\times 5\times 1.622\) & 28–38 & 2 & 11.5/9.7 \\
[257] & Multi-Branch Patch & \(10\times 10\) & \(60\times 10\times 0.8\) & 0.8–10.4, & 1.6–2.71, & Multiple & 6.49 \\  & & & & 4.69–11.5 & & & \\
[258] & \(\pi\) and L Patch & 12 & \(150\times 80\times 0.8\) & 3.4–3.6, & 3.6–3.8, & 12 & N/A \\  & & & & 5.1–5.9 & & & \\
[259] & Dipoles and T-Monopole & 3 & \(30.5\times 1\times 0.8\) & 3.5 & 3 & 5 \\
[260] & Slotted Patch & \(8\times 8\) & \(27\times 27\times 1.6\) & 3.3–3.8 & Multiple & 10 \\
[261] & Planar Monopole with EBG & 4 & \(64\times 64\times 1.6\) & 3.25–3.5, 4.2–5.1 & 4 & 5.6 \\
[262] & Slotted Patch & 2 & \(35.5\times 25.0\times 0.75\) & 3.3–4.2 & Multiple & 2–4 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Summary of antenna technologies for IOT and UE. MIMO functionality is extensively studied, designed, and implemented in numerous works [252, 253, 264]. Rectenna designs for simultaneous wireless information and power transfer (SWIPT), with optimized energy efficiency especially for low-power IoT sensors, are presented in [254, 265]. Superdirective, endfire, and broadside array configurations are discussed in [266], while a multiband patch antenna design covering the WiFi 6 bands is introduced in [255]. Various antennas focusing on UE applications are presented in the following references. In [256], lateral cross-dipole elements are integrated into a compact antenna-in-package design for 5G UE applications.