# Fast Optimization of the Installation Position of 5G-R Antenna on the Train Roof
## 1 Introduction
At present, there are few works of research on the calculation of the coupling coefficient and anti-interference measures between the pantograph arcing and 5G-R antenna. The EMI of the pantograph arcing is mainly coupled to the roof antenna port through radiation. Refs. [2; 12] used electromagnetic simulation software to calculate the coupling coefficient between the pantograph arcing and the GSM-R antenna. Due to the relatively small impact of the body of the carriage on the EMI coupling pathway of the roof, the simulation model can be simplified to the case of only the roof, as shown in Figure 1. The coupling coefficient is defined as the radiation electric field intensity of the pantograph arcing coupled to the roof antenna, which can be calculated through simulation. The roof antenna in the simulation model is set as a quarter wavelength (\(\lambda/4\)) monopole antenna of 900 MHz, and the scaled model of the pantograph arcing and the roof antenna is built in the laboratory, and the coupling coefficient between the two is measured. By comparing the results of the simulation and laboratory measurement, it is shown that there is a small error (2.12 dB) between the two coupling coefficients, which proves the validity of the simulation model, and proves that the roof antenna can be set as a \(\lambda/4\) monopole antenna. In addition, the commonly used car roof antenna is designed based on the basic structure of the \(\lambda/4\) monopole antenna with an external antenna housing, such as the Katherin 741009 antenna, so the \(\lambda/4\) monopole antenna is commonly used for simulation calculation [13; 14]. In order to improve the anti-interference performance of the roof antenna, there are a lot of works of research on the optimization of the installation position of the roof antenna. Refs. [15; 16] are based on the current deployment and future planning of the vehicle-mounted terminals in the Chinese standard electric multiple unit (EMU). Taking the GSM-R system of the 900 MHz band, and the LTE-R system of the 450 MHz band and 2.1 GHz band as examples, the stray interference of vehicle-mounted terminals is theoretically analyzed. Then, based on the theoretical model calculation of free space loss, the electromagnetic software simulation, and the measured results of the test platform, the isolation of roof antennae is studied and a reasonable antenna spacing is proposed to meet the needs of the interference isolation of vehicle-mounted communication terminals. The installation position of the roof antenna can be further optimized by using various intelligent optimization algorithms. Ref. [17] proposed an antenna optimization layout method based on the multi-objective particle swarm optimization (MOPSO) algorithm to address the shortcomings of existing single-objective optimization algorithms in the antenna layout. The algorithm is combined with the numerical calculation method, and the effectiveness of the proposed method is verified by placing three short-wave communication antennae on the ship simulation model. The above references point out the importance of studying the installation position of roof antennae, and provide the research basis for the installation of roof antennae or ship-borne antennae by using the traditional electromagnetic simulation method. However, the research purpose of the above references is to reduce the electromagnetic coupling degree between antennae, and the EMI caused by pantograph arcing is not included in the study of the optimization of the installation position of the 5G-R antenna. In summary, in order to further optimize the installation position of the roof antenna, it is necessary to focus on the EMI of the pantograph arcing on the 5G-R antenna. In addition, in view of the large roof plane (length \(\times\) width of about 25 m \(\times\) 3 m), and referring to the \"Fuxing\" train of 17 groups, the distance between the roof antenna and the pantograph arcing can reach up to two carriages (about 50 m).