# Advanced Metamaterial-Integrated Dipole Array Antenna for Enhanced Gain in 5G Millimeter-Wave Bands
## 2 The Design of the Metamaterial-Integrated Dipole Antenna  
### The Dipole Array Antenna Design  
The array dipole antenna and its performance parameters are explained in this subsection. The initial dipole antenna is designed on a 32 mm \(\times\) 10 mm Rogers RO4003C substrate with a thickness of 8 mils, a dielectric constant \(\varepsilon_{\text{r}}\) = 3.55, and a loss tangent \(\delta\) = 0.0027. The dipole array antenna without the proposed metamaterial structure is depicted in Figure 2, and its design parameters are listed in Table 1. In this work, a partial ground plane is utilized instead of a full ground plane, as the end-fire radiation characteristic is targeted. Usually, with the full ground plane, the antenna offers a broadside radiation pattern [15]. In the proposed design, the half of the dipole array at the front side is connected to a feedline, and the other half of the dipole array at the back side is connected to the partial ground plane. The proposed antenna offers end-fire radiation with a very wide operating bandwidth, as shown in Figure 3. The designed dipole array yields a wide bandwidth, ranging from 23.2 GHz to 45.3 GHz. With a peak gain of 8.02 dBi and an average gain of 6.59 dBi, the proposed dipole array provides unidirectional end-fire radiation. In the simulation software, instead of an ideal port, a millimeter-wave connector is designed and connected to the antenna, as can be seen in Figures 3b and 4. With this actual connector model, the results of the antenna after fabrication can be realized.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline
**Parameter** & **Value (mm)** & **Parameter** & **Value (mm)** & **Parameter** & **Value (mm)** & **Parameter** & **Value (mm)** \\ \hline \(S_{L}\) & 32 & \(f_{2}\) & 0.3 & \(h_{3}\) & 1.3 & \(p_{4}\) & 0.65 \\ \(Sw\) & 10 & \(L\) & 3.2 & \(h_{4}\) & 1.1 & \(q_{1}\) & 1.4 \\ \(F_{L}\) & 14.4 & \(H\) & 8.3 & \(p_{1}\) & 1.8 & \(q_{2}\) & 0.7 \\ \(G_{L}\) & 15.3 & \(h_{1}\) & 3.2 & \(p_{2}\) & 1.17 & \(q_{3}\) & 0.6 \\ \(f_{1}\) & 0.5 & \(h_{2}\) & 1.5 & \(p_{3}\) & 1 & \(q_{4}\) & 0.45 \\ \hline \end{tabular}
\end{table}
Table 1: The design parameters and the optimal values of the dipole array antenna.  
Figure 2: The dipole array antenna: (**a**) a view of the individual sides and (**b**) a partially transparent view of the substrate.  
The surface current distribution of the dipole array antenna at different operating frequencies is also shown in Figure 4. It can be observed from the current distribution graph that the lower resonances are generated by the longer arms. At 26 GHz, the lower arms show a high level of current density. Similarly, the shorter arms are responsible for the higher band resonances. At 28 GHz, the middle arms show increased current density. Meanwhile, at 38 GHz, the highest current density is observed in the shortest arm of the dipole array.  
A parametric study of the array dipole antenna is presented in Figure 5 only for the parameters \(P_{1}\) and \(P_{4}\) to show the controllability of the reflection coefficient of the designed antenna. It can be observed from the parametric study graph in Figure 5 that by controlling the \(P_{1}\) parameter, the resonance at the lower band can be controlled, and by controlling the \(P_{4}\) parameter, the upper operating frequency band can be controlled. Similarly, by controlling the other parameters of the dipole, the resonance of the antenna can be changed or improved.  
Figure 4: The surface current distribution of the dipole array at different operating frequencies.  
Figure 3: The performance characteristics of the dipole array antenna: (**a**) the reflection coefficient, and (**b**) the gain and 3D directivity at 28 GHz and 38 GHz.