# Metamaterial Integrated Folded Dipole Antenna with Low SAR for 4G, 5G and NB-IoT Applications
## 4 Metamaterial Integrated Antenna Design  
This section analyzes and evaluates the antenna performance with the designed CMC dual negative metamaterial. A metamaterial array of \(6\times 5\) unit cell elements was chosen for suitable coverage of the radiating element. The metamaterial is placed below the antenna and is separated by a small air gap(s) from the antenna plane, as illustrated in Figure 15. The scattering loss plot for different air gaps is illustrated in Figure 16.  
It was observed that the metamaterial insertion exactly below the antenna plane disturbs the impedance matching. By comparison, the required bandwidth can be achieved with an accumulative air gap. After a separation of 2.5 mm, the effect of the metamaterial on the required bandwidth is almost the same. In fact, a small increase in the bandwidth is observed at higher frequencies in comparison to the operation without the metamaterial. The main objective of the metamaterial insertion is to increase the gain and to control the radiation pattern for SAR (Specific Absorption Rate) minimization. The gain of the metamaterial integrated antenna for different air gaps is illustrated in Figure 17 The metamaterial integration with antenna design results in the gain enhancement in comparison \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Citation** & **Frequency Band** & **Maximum Gain (dB)** & \
\begin{tabular}{c} **Maximum** \\ **Efficiency (\%)** \\ \end{tabular} &
\begin{tabular}{c} **Overall** \\ **Dimensions** \\ **(mm)** \\ \end{tabular} \\ \hline
[9] & 44 & 8.32 & – & \(55\times 110\times 7\) \\ \hline
[10] & 39, 40, 44 & 7.1 & 70 & \(110\times 45\times 6\) \\ \hline
[11] & 41, 44 & – & 91 & \(100\times 40\) \\ \hline
[12] & 7, 13, 17, 20 & – & 80 & \(260\times 200\) \\ \hline
[13] & 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44 & 5.2 & 95 & \(160\times 200\times 3\) \\ \hline
[14] & 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44 & – & 92 & \(75\times 140\times 5.8\) \\ \hline
[15] & 40, 42, 43 & 4.23 & 99 & \(38.5\times 25\) \\ \hline
[17] & 33, 34, 35, 36, 37, 38, 39, 40, 41, 44 & – & 72 & \(140\times 70\times 5\) \\ \hline
[31] & n78, 38, 40, 41, 42 & 4 & – & \(35.2\times 49.5\times 49.5\) \\ \hline
[32] & n78, 42 & – & 70 & \(75\times 150\times 6\) \\ \hline
[33] & n78, 42, 43 & 2.6 & – & \(50\times 50\) \\ \hline
[34] & n78, 40, 41, 42 & 6.8 & 69.5 & \(5.7\times 100\times 100\) \\ \hline
[35] & n78, 42, 43 & 8.95 & – & \(75\times 75\times 13.1\) \\ \hline Folded dipole & 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, B1, B2, & 4.044 & 92 & \(35\times 48\times 1.62\) \\ \hline B25, n78 & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Comparison of folded dipole design. Figure 15: Metamaterial integrated antenna design. to the design without the metamaterial. It can be observed from the gain plot that the greater air gap results in better gain because of the negative properties of the metamaterial, while resulting in a bulky antenna. Therefore, there is a tradeoff between size and gain. The optimum value of 10 mm was chosen for the air gap to maintain the compactness of the antenna design. The enhanced gain observed for LTE and NR bands at a 10 mm air gap is summarized in Table 4. Practically, the separation was achieved by using a foam substrate; the fabricated prototype and the measured S plot of the same are illustrated in Figures 18 and 19, respectively. A good agreement between measured and simulated results was achieved. Figure 16: Scattering plot for different air gap. Figure 17: Gain plot for different air gaps. The radiation patterns for the metamaterial integrated antenna in the azimuth and polar planes is represented in Figures 20 and 21 respectively. The DNG metamaterial acts as a good absorber for radiation, especially at high frequencies, because the metamaterial is placed below the antenna, which has almost no effect on the azimuth pattern. The pattern observed in the azimuth plane is approximately the same as that obtained in the operation without the metamaterial.