# Low Cost AIP Design in 5G Flexible Antenna Phase Array System Application
## 3 Array Antenna Design  
The operation frequency band of the 5G system achieves the Ka-band. A small wavelength, small beam width, and high atmospheric attenuation are the shortcomings of this frequency band while its great advantages are its larger bandwidth and higher data rate. The multiple antenna techniques (MTA) is the solution that can solve wave shadowing of millimeter wave propagation [24]. The array antenna is an important development. The array antenna is composed of antennas that are arranged periodically as illustrated in Figure 4. The beam main lobe can be tilted by changing the phase of the antennas, which is called the beam steering technique. In this study, the four patch antennas constituted a \(2\times 2\) array antenna as shown in Figure 5. An AnokiWave phasor IC was set at the same side with the patch antennas. Such an arrangement makes the array antenna become a complete system. This modular system is more flexible and expandable, which is widely known as the Antenna-in-Package (AIP). Figure 4: Beam steering/scanning antenna array [24]. Figure 5: The structure of proposed array antenna with phasor IC. Figure 3: (**a**) The return loss and (**b**) the radiation efficiency of the patch antenna. The antenna spacing \(d\) is an important parameter in the design of the array antenna. In Figure 6, the ideal maximum array directivity (\(D\)) of a \(2\times 2\) array antenna is 6 dBi [25]. Basically, the single antenna gain (\(G\)) as shown in Equation (4) is proportional to the directivity of a single antenna. In fact, the antenna efficiency of each element does not need to be considered when taking into account the array gain. The array gain is equal to the array directivity. In this study, the estimated array gain is 5-6 dBi. Otherwise, the maximum scan angle must satisfy the condition in Equation (5). The \(\theta_{max}\) is the maximum angle to which the array can be steered. The steering can be reckoned by Equation (5). The maximum angle is listed in Table 1 with an operating frequency of 28 GHz. \[G_{single\ antenna}=\xi\text{:}D_{single\ antenna} \tag{4}\]  
\[\frac{d}{\lambda}\leq\frac{1}{1+\left|\sin\theta_{max}\right|} \tag{5}\]  
The ideally maximum steering of the array antenna was \(\pm 90^{\circ}\). With that the antenna spacing was half the wavelength. In this study, the minimum spacing was 9.4 mm since the phasor IC was set at the center of the proposed array antenna. The maximum steering of the proposed array antenna approached \(\pm 10^{\circ}\). The measured return loss of the simulated \(2\times 2\) array antenna of each port was better than 10 dB at an operating frequency of 26.5-29.5 GHz as shown Figure 7. The simulation results of each port were highly consistent, which is due to the structure of the array antenna that is in symmetry. The antenna peak gain was 14.4 dBi as shown through m1 in Figures 8 and 9. The 3 dB beam width that is shown through m2 and m3 on Figures 8 and 9, respectively, was \(26^{\circ}\). The comparison of the simulation results of the single antenna and the array antenna is shown in Figure 10. The array gain was 5.78 dB, which was consistent with the estimative value. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Maximum Angle \(\theta_{max}\) (degree)** & **Wavelength \(\lambda\) at 28 GHz (mm)** & **Antenna Spacing \(d\) (mm)** \\ \hline
10 & 10.71 & 9.13 \\
20 & 10.71 & 7.98 \\
30 & 10.71 & 7.14 \\
40 & 10.71 & 6.52 \\
50 & 10.71 & 6.07 \\
60 & 10.71 & 5.74 \\
70 & 10.71 & 5.52 \\
80 & 10.71 & 5.40 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Maximum scan angle with different antenna spacing. Figure 6: Directivity as a function of antenna spacing for a broadside array of isotropic elements [25]. Figure 8: Radiation pattern of the simulation (X Cut). Figure 7: Four (4) ports return loss of the simulation. Figure 9: Radiation pattern of the simulation (Y Cut). The filed pattern of beam steering can be simulated by changing the phase of the four patch antennas.