## 3 Antenna Performance and Discussions  
A prototype was fabricated to validate the proposed idea. Figure 7 shows the photograph of the top and bottom views of the fabricated layers before the assembly of the  
Figure 5: (**a**) Detailed view of layers and material stack up for the antenna and (**b**) pillbox schematic. Figure 6: The electric field distributions obtained at 20 GHz. (**a**) The bottom layer and the top layer (**b**) without any rotation \(\omega=0^{\circ}\), (**c**) at the maximum scanning angle on the right side \(\omega=20^{\circ}\), and (**d**) at the maximum scanning angle at the left side \(\omega=-20^{\circ}\). Red arrows are pointing in the direction of the propagation of waves. proposed antenna. The three layers are fabricated as layer-1, which is the feeding parabolic, layer-2, which is the coupling layer, and layer-3, which is the radiating layer. It should be noted that the design consists of multi-layer substrates. Small holes are made in the corner of the substrates to assemble the whole structure via nylon screws. A 2.92 mm millimeter-wave 50 \(\Omega\) connector is soldered from the bottom side of the antenna. Layer-1 and layer-2 were assembled together using nylon screws, and then the rotating disc was placed on the top side and rotated about its central axis to realize beam scanning, as shown in Figure 8a,b. After assembling the antenna, a vector network analyzer was used to test its reflection coefficients. The antenna's tested reflection coefficients are shown in Figure 9 in a blue-dotted-dashed line. The tested results are also compared with simulations, shown in Figure 9 as a red solid line. It can be seen from the measured results that the 10 dB return loss (\(-10\) dB reflection coefficients) bandwidth is from 19.2 GHz to 20.4 GHz. The measured bandwidth is about 1.2 GHz, which is slightly smaller than the simulated one. The discrepancies between the measured and simulated reflection coefficients are mainly caused by fabrication, soldering, and measurement errors. It should be noted that the antenna has multiple layers and is assembled in the laboratory; this type of discrepancy is expected due to the manual assembly of the layers in addition to the human factor error of the soldering, where the soldering point can work as an additional stub at a higher frequency, which induces mismatch between the antenna and the connector. This can be minimized by having more accurate assembly of the layers, reducing the air gap between layers, and minimizing measurement errors. Figure 7: Photographs of the top and bottom views of the fabricated layers before the assembly. Layer-1 is the parabolic feed structure, layer-2 is the coupling layer, and layer-3 is the radiating strips layer. The mechanical rotation is manually realized by rotation steps of \(\omega=5^{\circ}\) from \(-20^{\circ}\) to \(20^{\circ}\). The measurement setup for \(\omega=20^{\circ}\) is shown in Figure 8c. The antenna is tested for radiation patterns and realized gain values. To understand the beam steering of the proposed antenna, the normalized measured radiation patterns are shown in Figure 10. It is evident that the beam direction is steered with a little gain variation (\(\sim\)3 dBi) over the whole rotating angle. The radiation patterns of nine different rotation angles have been plotted in Figure 10 from \(-20^{\circ}\) to \(20^{\circ}\) with a step of \(5^{\circ}\). The intermediate coverage area between the beams can be covered by selecting small intermediate rotation angles. It is noted that the antenna offers \(120^{\circ}\) as a scanning angle, while Figure 11 depicts the 2D plots of the measured radiation patterns at 20 GHz for the nine rotation angles for the whole domain \(0\leq\theta\leq 180^{\circ};-180^{\circ}\leq\phi\leq 180^{\circ}\). The plots demonstrate the ability of the antenna to achieve beam steering with high gain and low side lobes.