## 3 Fabrication and Measurement of Proposed Array  
Figure 5 illustrates the photographs of the fabricated 4 \(\times\) 1 linear array antenna using multiple TLY-5 substrate layers. Three different microstrip 4 \(\times\) 1 power dividers of the feeding network are fabricated to obtain the beam-steering performances at the angles of \(\theta_{0}\) = 0\({}^{\circ}\), 15\({}^{\circ}\), and 30\({}^{\circ}\). For the power excitation, the input microstrip lines of each power divider are connected by employing the end-launch connector (NE03 FS001) [27], and each divider has a line loss of 0.8 dB according to the distance (3.77\(\lambda\) at 35 GHz) from the end-launch connector to the slot aperture.  
Figure 6 shows the simulated and measured reflection coefficients of the proposed array antenna. The simulation and measurement of the operating fractional frequency bandwidth at 35 GHz are 11.9% and 9.2%, respectively, and those of the reflection coefficient value at 35 GHz are \(-20.4\) dB and \(-24.08\) dB.  
Figure 4: Geometry of the proposed 4 \(\times\) 1 linear array antenna: (**a**) top view, (**b**) bottom view.  
Figure 3: The E-field distributions for the 2 \(\times\) 1 array antenna: (**a**) with the ASIWC structure, (**b**) without the ASIWC structure.  
Figure 7 represents the simulations and measurements of 2D radiation patterns according to the steering angles \(\theta_{0}=0^{\circ},15^{\circ}\), and \(30^{\circ}\) in the \(zy\)-plane, where the measurements agree well with the simulations. The proposed array has the measured gains of 11.7 dBi (\(\theta_{0}=0^{\circ}\)), 10.63 dBi (\(\theta_{0}=15^{\circ}\)), and 9.54 dBi (\(\theta_{0}=30^{\circ}\)), and the measurements of the HPBW at each steering angle are \(16.5^{\circ}\), \(19^{\circ}\), and \(17^{\circ}\), respectively. Figure 8 presents the measured bore-sight gains in the \(zy\)-plane at different beam-steering angles according to the frequency compared to the simulations. The measured data at 35 GHz show the bore-sight gains of 11.7 dBi, 10.63 dBi, and 9.54 dBi at the steering angle \(\theta_{0}=0^{\circ},15^{\circ}\), and \(30^{\circ}\), and these values are similar to the simulated results of 11.5 dBi, 11.3 dBi, and 9.8 dBi, respectively.  
The antenna characteristics, such as the antenna size, a fractional bandwidth, an operating frequency, and so on, of the proposed antenna are compared with those of other previous works [4, 5, 28, 29], as presented in Table 2. The proposed antenna has a higher gain and a narrower HPBW than other works while having a compact size.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Ref.** & **Antenna Size** & **Fractional** & **Operation** & **HPBW (\({}^{\circ}\))** & **Peak Gain** & **Array** \\  & **Bandwidth (\%)** & **Frequency (GHz)** & **HPBW (\({}^{\circ}\))** & **(dBi)** & **Extension** \\ \hline
[4] & \(0.72\lambda_{0}\times 0.72\lambda_{0}\times 0.212\lambda_{0}\) & 28.5 & 30 & NA & 7.34 & 24 \(\times\) 24 \\
[5] & \(0.41\lambda_{0}\times 0.41\lambda_{0}\times 0.15\lambda_{0}\) & 21.8 & 27 & 77 & 4.9 & 4 \(\times\) 1 \\
[28] & \(1\lambda_{0}\times 1\lambda_{0}\times 0.104\lambda_{0}\) & 14.7/3.4 & 28/38 & NA & 7.5/9.1 & 2 \(\times\) 2 \\
[29] & \(0.47\lambda_{0}\times 0.28\lambda_{0}\times 0.04\lambda_{0}\) & 15.6 & 38 & 97.2 & 6.5 & 4 \(\times\) 4 \\ This work & \(0.7\lambda_{0}\times 0.7\lambda_{0}\times 0.09\lambda_{0}\) & 9.2 & 35 & 76 & 7.5 & 4 \(\times\) 1 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Design parameters and their values of the proposed antenna.  
Figure 5: Geometry of the proposed 4 \(\times\) 1 linear array antenna with power dividers according to the beam-steering angles: (**a**) top view, (**b**) \(\theta_{0}=0^{\circ}\), (**c**) \(\theta_{0}=15^{\circ}\), and (**d**) \(\theta_{0}=30^{\circ}\).  
Figure 6: Simulated and measured reflection coefficients of the proposed array antenna.