## 1 Introduction  
As a dedicated near-field wireless communication system for railways, the BTS efficiently facilitates secure information transmission between the ground balise and onboard equipment [1]. Balises are passive devices, with no external power from the trackside. Most of the time, the balise is in sleep mode. When a train provides an appropriate telepowering signal, it gets activated and generates the Frequency Shift Keying (FSK) signal that carries encoded information. This information includes location information, train operation information, route information, and control data information [2]. It is analyzed by the balise transmission module (BTM) and provided to the on-board control core. The BTS is an indispensable component of the train operation control system [3], presented by Figure 1, playing an essential role in ensuring train position sensing and safe operation [4]. The balise and BTM should be capable of adapting to various operational environments. When a balise is covered by debris, it may not be detected by the BTM due to unsatisfactory matching. The problems caused by debris lead to the loss of transmission performance and further reduce the reliability of the BTS. The loss of balise information during train operation could potentially trigger emergency braking procedures or, in more severe cases, lead to a significant railway incident [5]. Therefore, it is extremely significant to analyze the electromagnetic coupling characteristics of the BTS. In recent years, some scholars have studied the transmission theory of BTS. An electromagnetic coupling model between the onboard antenna unit (OAU) and balise is established by the finite element method. The signal process of the downlink and uplink is simulated [6], and adaptations for reliable transmission of data are analyzed [7]. In [8], the dynamic process of the telepowering signal was analyzed using electromagnetic field theory, and a circuit model for energy conversion of the balise was established. In accordance with the test methodology prescribed by the standard, the relationship between the magnetic field compliance and magnetic field strength was analyzed under various conditions. During high-energy acquisition periods, the dynamic energy harvesting capabilities of the balise were optimized by capping the voltage at a predetermined threshold. The research findings presented in the aforementioned literature primarily focus on the BTS in free space environments. In practice, the BTS operates in extremely challenging environments [9; 10], where multiple factors can significantly impact its transmission characteristics [11; 12]. These include seasonal elements such as rainwater, ice, and snow; industrial residues such as coal dust and iron; installation variables related to the positioning of a balise on steel rails or wheel guard rails; and vehicle structural issues, particularly the proximity of the OAU to the metallic components beneath the vehicle. These environmental factors not only interfere with the operation of a balise but can also compromise the reliability and efficiency of the BTS. The presence of surrounding debris or metallic objects can significantly impact the performance of the BTS by causing antenna detuning. This phenomenon shifts the antenna's tuning frequency, leading to an increased reflection coefficient and consequent attenuation of the transmitted magnetic field [13]. To counteract these detrimental effects, a practical solution involves installing a metal plate on the rear of the OAU. In order to reduce the system transmission losses, researchers have pursued multiple avenues of investigation focusing on three key areas. First, studies on topology structure compensation aim to optimize the physical layout and arrangement of system components to minimize losses [14; 15]. Second, research efforts have been directed towards enhancing oscillator circuit efficiency [16], improving the performance of these crucial components for generating and maintaining signal integrity.