## 4 Experimental Verification of the Digital Twin Model
### Verification of the Tele-Powering Field Conformity  
Table 2 shows the dimensional parameters and typical parameters of the OAU and passive balise produced by a BTS manufacturer, in which the dimensional parameters of the onboard receiving antenna were consistent with that of the transmitting antenna. \(i_{\text{d}}\) represents the current of the tele-powering signal on the onboard transmitting antenna. For the OAU and balise in Table 2, we measured the tele-powering field conformity in the laboratory with reference to [2]. The test configuration and test scenario are shown in Figures 11 and 12, respectively. The vertical distance between the OAU and the balise was set to 340 mm. During the measurement, the balise was fixed on the desktop, and the OAU moved laterally along the \(X\)-axis. There were two major differences from the tele-powering field conformity measurement scheme in the specification. The first was that the tele-powering signal emitted by the onboard transmitting antenna remained constant during the entire measurement process. However, the response of the balise at each measurement position needed to be measured and recorded. Second, from the measurement connection diagram, we could find that a special balise test antenna replaced the passive balise, thus eliminating the need for an additional 4.2 MHz test antenna. The specially designed balise test antenna was based on the reduced size passive balise, adding an external monitoring interface. The filter and the power meter were directly connected to the particular balise test antenna. The filter was used to isolate the influence of the 27 MHz tele-powering signal on the power meter B so that the balise response could be directly measured by the power meter B. Except for the above two differences, the test methods and test procedures were consistent with the specification requirements. Simultaneously, using the downlink transmission model referring to (1) and (14), and the same antenna parameters in Table 2, the change of the magnetic flux received by the balise with the longitudinal displacement of the OAU was calculated. The measurement results and calculation results are shown in Figure 13.  
The magnetic flux received by the balise is related to the relative position of the balise and the OAU. When the OAU and the balise coincided in the XOY plane, the balise received the most magnetic flux. With the increase in longitudinal displacement between the OAU and the balise, the received magnetic flux gradually decreased and reached the minimum value when the absolute value of the longitudinal displacement difference was around 50 cm. When the longitudinal displacement between the antennae further increased, the  
Figure 12: Tele-powering field conformity test configuration. Figure 13: Validation results of the tele-powering field conformity test. magnetic flux received by the balise first slowly increased to the maximum of the sidelobe, and then continued to decrease with the increase of the displacement. The above phenomenon was determined by the magnetic field distribution characteristics of the rectangular antennas. When the magnetic flux received by the balise reached its minimum value, the direction of magnetic induction intensity in the balise region was reversed by increasing the longitudinal displacement of the OAU and the balise. [PERSON] simulated the magnetic field distribution between the balise and the onboard rectangular antenna [7]. His simulation and analysis results also showed that the information transmission between the rectangular antennas would cause the sidelobe effect. The longitudinal displacement-downlink flux envelope curves were very similar between the measured results and the calculated results. However, the calculated result near the longitudinal displacement \(\Delta x=0\) was significantly larger than the measured result. The calculated value was 3.05 nVs greater than the measured value at \(\Delta x=0\). With the increase of longitudinal displacement, the difference decreased gradually.