## 2 Electromagnetic Radiation Testing Method
### Determining the Test Antenna Type and Model  
This paper primarily conducted an in-depth study of communication capabilities through antenna gain and coupling effects, making antenna performance particularly important. Specifically, the antenna's gain and its omnidirectional radiation pattern are the main reference standards in the simulation testing system. To discuss antennas communicating with the base station, 4G antennas on vehicles are typically selected, while GNSS antennas on vehicles are used for satellite communication. In this study, we selected a shark-fin antenna from a certain brand vehicle as the antenna for testing based on the project requirements. A shark-fin antenna integrates multiple antennas, and while various forms of antennas are deployed on vehicles today, the methodology of this study is grounded in electromagnetic compatibility testing. Consequently, this approach is applicable regardless of the type or configuration of the antenna. Electromagnetic compatibility testing not only serves to assess communication with transmitting antennas, but also utilizes electromagnetic compatibility characteristics to mitigate interference among vehicle-mounted antennas. This is illustrated in Figure 1. The shark-fin antenna, notable for its distinctive design and superior gain characteristics, has garnered significant attention for its ability to enhance signal transmission capabilities in complex communication environments. Figure 1: GNSS and 4G antennas in the shark fin. Based on the antenna pattern characteristics of the 4G and GNSS antennas in the antenna library of the electromagnetic software FEKO 2023, we selected the base station transmission and satellite transmission antennas. The directional pattern characteristics and antenna selections are shown in Figure 2.  
One of the most basic methods during the automotive antenna testing process is passive testing. However, this testing method has the drawback of only evaluating the antenna's performance and not providing a comprehensive functional validation. Therefore, to achieve a more accurate and comprehensive assessment, we employed the electromagnetic radiation testing method, which is based on the overall testing scheme of the complete vehicle. By installing the antenna on the entire vehicle, we treated the antenna and the vehicle as a whole to solve the near- and far-field radiation patterns. After establishing the model, we further designed and analyzed the layout of the 4G antenna, the GNSS antenna, and the vehicle model, as detailed in Figure 3.  
Due to the size limitations of vehicles, far-field testing faces numerous challenges during implementation. With the increasing application of complex antennas, traditional far-field testing methods have struggled to meet the requirements of testing tasks. Therefore, near-field testing has gradually become a relatively reliable and effective measurement approach. After performing near-field testing, we typically apply the near-to-far-field transformation theory and relevant algorithm formulas to convert near-field data into far-field models. The formula employed in this study was established using the FEKO software. Since it has been validated by FEKO, the derived formula is directly referenced in this research [6]. Figure 3: Schematic diagram of the vehicle—mounted antenna arrangement. Figure 2: The antenna radiation patterns representing the base station and satellite transmitting antennas.