## 2 Antenna Configuration and Performance Analysis
### Simulated Results and Analysis  
The simulations and optimizations of the proposed antenna were carried out in Ansoft High-Frequency Structure Simulator (HFSS). The proposed antenna can effectively broaden the beamwidth in the frequency band of 14.5-15.5 GHz. Figures 2 and 3 show the simulation results of \(\ket{S_{\mathrm{II}}}\) 1 and the gain patterns of the proposed antenna. Meanwhile, the corresponding simulation results of the basic ALTSA are also presented for comparison. As shown in Figure 2, the \(\ket{S_{\mathrm{II}}}\) 1 of these two antennas were both less than \(-\)10 dB in the band of 14.5-15.5 GHz, indicating a good impedance matching. Considering the characteristic of the narrow band, the far-field radiation performances of the wide-beam antenna were demonstrated and analyzed only at the center frequency \(\mathrm{f_{c}}\) = 15 GHz. Figure 3 shows the gain results of these two antennas in each cut-plane, including the boresight (+\(z\)-axis direction). We present patterns in cut-plane increments of 15 degrees (phi) to illustrate the performance. Phi represents the azimuth angle, phi = 0\({}^{\circ}\) represents the _xoz_-plane, phi = 90\({}^{\circ}\) represents the _yoz_-plane, and the coordinate system is given in Figure 1. For observing the amplification of HPBW in each cut-plane more directly, the relationship between the amplification of HPBW and phi is shown in Figure 4. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Parameter** & W\_floor & W\_exc & D\_hole & d\_slot & W\_slot \\
**Value** & 12.5 & 3.4 & 1 & 0.5 & 3.5 \\ \hline
**Parameter** & L\_slot & D & W & L & t \\
**Value** & 4.5 & 5.5 & 2.9 & 3.43 & 0.06 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Optimized geometrical parameters (unit: mm). Figure 2: Simulated reflection coefficients of the proposed wide\(-\)beam antenna and basic ALTSA. Figure 3: _Cont._  
Figure 3: Simulated gain results of the proposed wide\(-\)beam antenna and basic ALTSA in different cut-planes. It can be seen from Figures 3 and 4 that the HPBW in each cut-plane of the basic ALTSA was 36-45\({}^{\circ}\) with a peak gain of 11.7 dBi, while the HPBW of the proposed antenna was 65-97\({}^{\circ}\). The red and blue horizontal lines represent a gain drop of 3 dB for the proposed antenna and the basic antenna, respectively. The HPBW in each cut-plane was widened, and all widening ranges were about 200%, showing good consistency. The beamwidths of the basic ALTSA were relatively small due to their high gain, which also limits the absolute values of the broadened beamwidth. Proper selection of a basic antenna with a lower gain is beneficial to obtain a larger absolute value of beamwidth. It should be pointed out that this research aims to demonstrate a new beam\(-\)broadening idea based on an ALTSA. Depending on the practical beamwidth requirements, other basic ALTSAs which have different gain and beamwidth can be flexibly selected. Moreover, the basic antenna and subwavelength elements in this paper were designed with simple structures and ordinary performances. The achievements of beam broadening can be further enhanced if basic ALTSA and subwavelength units with more complicated structures and better performance are chosen. Considering that the number of subwavelength elements loaded has a great impact on the performances of the antenna, parameter analysis was carried out. Figure 5 shows the performances of antennas with different numbers of subwavelength elements in each row. As shown in Figure 5a, when there were three or four units in each row, the \(\mid\)S\({}_{11}\mid\) of the antenna were almost lower than \(-\)10 dB in the whole frequency band, indicating good impedance matching. Additionally, as shown in Figure 5b, when there were two to four units in each row, the amplification of HPBW in all cut-planes was similar, but the amplification of HPBW with four units in each row was the largest. Hence, four units in each row were selected.