## 2 Pantograph Arcing Data
### The Effect of Measuring Position  
Due to the propagation of the radio waves and the effect of the carriage, the electromagnetic field of the pantograph arcing is different at different locations. What is to be done is to use the pantograph arcing field data wherever they are obtained. Thus, a simulation model is built to get the electric field data at the window. In addition, the data could be used to find the coupling relationship between the probe at the window and the LTE-R roof antenna. Therefore, the electric field data of measurement can be used to analyze the electromagnetic response of the LTE-R system.  
Due to limitations in the size and simulation time of the electromagnetic simulation, only two carriages are considered, as shown in Figure 3. The source is located at the position of the pantograph. The probe at the window measures the effect of the measurement position on the field. The antenna on the roof measures the field received by the LTE-R antenna.  
The disturbance source used in the model is a Gaussian pulse. The maximum magnitude of the source is 1A. The frequency range is from 400 MHz to 500 MHz, which is the band where LTE-R antennas mostly operate. Four window locations are selected to obtain field data. The position is defined as (x, y, z) with the unit m, where x is the distance from the pantograph to the probe of the window at x direction, y is the distance from the pantograph to the probe of the window at y direction and z is the distance from the pantograph to the probe of the window at z direction. The four window positions are point 1 (1.8, 2, 2), point 2 (1.8, 4, 2), point 3 (1.8, 6, 2), and point 4 (1.8, 10, 2). As the size of the carriage is fixed, the position of the probe at x direction is fixed.  
As can be seen from Figure 4, the electric fields at the same position are different for different frequencies. At the same frequency, it varies with different measurement positions. Theoretically, at the same frequency, the electric field strength will decay linearly with the probe position. In fact, the electric field strength does not decay with the position of the probe due to the electric field distribution being affected by the carriage of the train. For example, the magnitude of the electric field strength at point 2 is larger than that at other points at 400 MHz.  
Then, the source location is changed to three additional positions of the window, point 2 (1.8, 4, 2), point 3 (1.8, 6, 2), and point 4 (1.8, 10, 2). The electric field received by the antenna is compared with the electric field received when the source is at the position of the pantograph. The results are shown in Figure 5. The electric fields at the roof antenna position are the same. The magnitude of the electric fields does not change with the change of the probe coordinate at the viewing position of the window. It indicates that the variation of the electric field probe position of the window does not affect the radiation coupling path of the pantograph arcing signal to the antenna port. The electric field measurement data at the window are an intermediate variable to analyze the effect of the pantograph arcing on the LTE-R system.  
Figure 3: Model of the electric field simulation.