## 2 Electromagnetic Radiation Testing Method
### Constructing a Three-Dimensional Electromagnetic Model Environment  
The MIMO scene configuration for small-sized electrical devices is depicted in Figure 7a, with the deep blue area covering the complete sphere of interest. The key performance indicators for this configuration include return loss, throughput, and delay. Although this encompassing approach is quite comprehensive, its measurement methods may not effectively evaluate antenna performance on vehicles due to the unique characteristics of ground-based travel. Figure 6: The multipath effects of connected vehicles in urban environments. Figure 7: The communication range of interest for connected vehicles corresponds to the deep blue region (**(a)** test area based on small-sized electrical equipment; **(b)** test area based above the horizontal plane; **(c)** test area suitable for base station transmitting antennas; **(d)** test area suitable for satellite transmitting antennas). Thus, Figure 7b focuses specifically on the configuration of the upper hemisphere, with key indicators including return loss, throughput, and delay across the upper hemisphere. This definition of the upper hemisphere can, to some extent, be more effective in assessing the overall performance of the onboard satellite communication system. By concentrating on the signal propagation characteristics of the upper hemisphere, we can better understand antenna performance under actual working conditions. Based on the gain characteristics of the far-field radiation pattern of the complete vehicle and the complex radiation paths experienced by connected vehicles in urban environments, we can further segment the areas of interest. Figure 7c depicts a specific spherical area around the horizon. This area is particularly sensitive to base station, V2V, and V2I communication, with performance indicators including near-ground return loss, throughput, and delay. Figure 7d demonstrates the spherical area of interest surrounding the zenith. This area is especially sensitive to signal performance for GNSS and satellite communications. The performance indicators for this area include return loss, throughput, and delay for the near-zenith portion, which are crucial for ensuring the quality of satellite communication. Through in-depth analysis of these two areas of interest, we can comprehensively understand the communication needs of connected vehicles in complex urban environments. This segmentation aids in achieving environmental design, improving signal transmission reliability, and enhancing communication efficiency and safety between vehicles and base stations, as well as the GNSS equipment. Furthermore, an analysis of these key indicators showed that both the base station and the GNSS areas include throughput as a performance metric; therefore, throughput was chosen as the reference indicator for antenna performance in the electromagnetic radiation testing method. After comprehensive analysis and research of the actual conditions, we applied the three-dimensional modeling software CATIA P3 V5R21 to systematically arrange the configurations in the anechoic chamber, as shown in Figure 8. This layout can generally be divided into three main components. First, the whole vehicle model acts as a communication antenna receiver, responsible for receiving communication information from various signal sources. Second, the base station transmitting antenna is controlled by a robotic arm to adjust its transmission angle, allowing it to move flexibly within the space above the blue area in Figure 7c. This dynamic control ensures optimal signal coverage, enhancing the stability and reliability of communications. Lastly, the GNSS transmitting antenna is arranged at the edge of the blue area in Figure 7d, simulating the trajectory of the satellite's launch path. This design not only accurately simulates the actual emission of satellite signals, but also aids in assessing the performance of onboard equipment in real-time navigation and positioning.