## 3 The Performance of the \(8\times 8\) PAA
### The Simulated Scanning Performance  
We simulated the PAA's beam-scanning performance at integer frequency points within the 105-119 GHz band, and the simulation results are shown in Figure 9. Due to the large number of elements, Figure 9 only provides the active Si\({}_{\text{ii}}\) of the most representative main diagonal elements, using the numbering of the main diagonal elements as shown in Figure 8. As depicted in Figure 9, with the gain variation within 3 dB, a 2-D wide-angle scanning of \(\pm 48^{\circ}\) is achieved from 106 to 114 GHz. From 115 to 119 GHz, the scanning range reached \(\pm 40^{\circ}\) on the E-plane and H-plane. Additionally, the normal peak gain is stably maintained at 21.9-22.8 dBi across the operating frequency band. Moreover, the normal radiation efficiency of the PAA is higher than 95% within the operating frequency band. The radiation efficiency is higher than 81% within the \(\pm 48^{\circ}\) scanning range on the E-plane and higher than 87% on the H-plane. To make the beam-scanning performance of the PAA more intuitive, Figures 10-12, respectively, provide the beam-scanning radiation pattern at three key frequency points of 106 GHz, 114 GHz, and 119 GHz.  
Figure 8: The CST simulation model of the \(8\times 8\) planar PAA. (**a**) Top view. (**b**) Bottom view. (**c**) Three-dimensional perspective view.  
Figure 9: The simulation results. (**a**) Active S-parameter. (**b**) Realized gains and radiation efficiencies when scanning to different angles.  
As shown in Figure 10, which depicts the E-plane and H-plane radiation pattern at 106 GHz, the normal peak gain is 21.9 dBi. When scanning to 48\({}^{\circ}\) on the E-plane, the gain is 20.1 dBi. When scanning to 48\({}^{\circ}\) on the H-plane, the realized gain is 20 dBi, with a gain reduction of only 1.9 dB. Within the scanning range, the sidelobe level (SLL) on both the E-plane and H-plane is below \(-\)10 dB, and the cross-polarization is below \(-\)35 dB.  
Figure 11: The scanning patterns of the 8 \(\times\) 8 PAA at 114 GHz. (**a**) E-plane; (**b**) H-plane.  
Figure 12: The scanning patterns of the 8 \(\times\) 8 PAA at 119 GHz. (**a**) E-plane; (**b**) H-plane.  
Figure 10: The scanning patterns of the 8 \(\times\) 8 PAA at 106 GHz. (**a**) E-plane; (**b**) H-plane.  
Figure 11 shows the E-plane and H-plane scanning radiation pattern at 114 GHz, with a normal peak gain of 22.8 dBi. When scanning to 48\({}^{\circ}\) on both the E-plane and H-plane, the realized gain is 19.9 dBi, with a gain reduction of only 2.9 dB. Within the scanning range, the SLL on both the E-plane and H-plane is below \(-\)10 dB, and the cross-polarization is below \(-\)30 dB.  
Figure 12 illustrates the E-plane and H-plane scanning radiation pattern at 119 GHz, with a normal peak gain of 22.5 dBi. When scanning to 40\({}^{\circ}\) on the E-plane, the gain is 19.8 dBi, with a gain reduction of 2.7 dB. When scanning to 40\({}^{\circ}\) on the H-plane, the gain is 20 dBi, with a gain reduction of 2.5 dB. Within the scanning range, the SLL on both the E-plane and H-plane is below \(-\)10 dB, and the cross-polarization is below \(-\)29 dB.