## 3 Antenna Performance and Discussions
On the other hand, one of the essential merits of evaluating the scanning area of the antenna is the total scanning angle calculated from the total scan pattern (TSP) [42; 43; 44]. The TSP is the maximum achievable gain at each certain angular angle \((\theta,\phi)\) in the whole spherical coordinate, where the TSP is computed for all potential antenna rotation angles (\(\omega_{1}:\omega_{n}\)) and then the maximum gain (\(G\)) is selected at each point in the spatial distribution as [44]:  
Figure 8: Photographs of the fabricated prototype. (**a**) Top view, (**b**) bottom views, and (**c**) measurement setup with a disc rotation of \(20^{\circ}\). Figure 9: The simulated and measured reflection coefficient of the proposed antenna versus frequency. As shown in Figure 11, the measured \(TSP(\theta,\ \phi)\) demonstrates the ability of the antenna to achieve beam steering of 120\({}^{\circ}\) with a tiny variation in the beam in the elevation plane (\(\pm 4^{\circ}\)) and without any null, which assembles only from nine rotations of the disc within \(\pm 20^{\circ}\). The simulated and measured gain values of the steering beam at the different rotating angles are shown in Table 2. The maximum measured gain is 23.2 dBi at \(w=0^{\circ}\) rotation, which is 3.3 dB less than the simulated one. This difference in gain values is expected because of higher losses of the substrate at a high frequency. It is also attributed to the fabrication, soldering, air gaps, and measurement errors. Nevertheless, this is acceptable for large antennas, especially those operating at high-frequency bands. The variations in the measured gain from \(-40^{\circ}\) to \(+40^{\circ}\) scanning range is only 2 dBi, which is better than the  
Figure 11: Two-dimensional plot of measured radiation patterns in dBi at rotation angles from \(-20^{\circ}\) to \(20^{\circ}\) (with \(5^{\circ}\) spatial angle) and the total scan pattern of those rotation angles. All the plotted values present the gain at a whole spherical angle for each rotated angle, and then TSP is calculated based on (2). Figure 10: The measured radiation patterns of the antenna with the rotation angles from \(-20^{\circ}\) to \(20^{\circ}\). All the radiation patterns are normalized to the maximum gain at \(\omega=0^{\circ}\). other reported designs [21; 36], while a 3.3 dBi variation is observed in the whole scanning range from \(-60^{\circ}\) to \(+60^{\circ}\). In order to determine the quality of the antenna and its performance, it is compared to other reference antennas in terms of antenna height, frequency band, beam coverage, measured gain, and SLLs at the broadside and maximum scan angle. These characteristics are given in Table 3. By rotating a horn within the focal plane of the pillbox feeding system, the reference antenna that was described in [39] possesses a high gain and low SLL when viewed from the broadside. However, it displays a high SLL when viewed from a maximum scan angle of \(\pm 40\) degrees. Additionally, the antenna height is \(4.39\lambda_{0}\) which is much higher than the proposed design. Furthermore, it features a mechanically steered main beam that extends beyond \(\pm 40\) degrees. The other reference antenna that is presented in [21] has a low SLL at the broadside and a maximum scan angle of 40 degrees; however, the measured gain is low (i.e., 19.6 dBi), and the beam coverage that is achieved is only \(\pm 40\) degrees. Although the antennas in [35; 36; 40] offer a small profile, they suffer from either a limited coverage angle or high side lobe level. The antennas in [39; 45] have a wider bandwidth compared to the others due to using high profiles (4.39 \(\lambda_{0}\) and 9 \(\lambda_{0}\)). However, they offer limited angle scanning and high SLL. The antenna proposed in this study, on the other hand, possesses a relatively high gain, which is, i.e., 23.2 dBi. Additionally, it has a low SLL of \(-17.8\) dB at a maximum scan angle of 60 degrees.