# The Design of a Long-Distance Signal Transmission System in a Bistatic RCS Testing System
## 1 Introduction
developed a higher-precision model for specular multipath components (SMCs) using gaussian processes, thereby improving the accuracy of multipath channel modeling for ultra-wideband (UWB) and mm-wave signals [16]. However, in some complex scenarios, Non-Line-of-Sight (NLoS) conditions can severely distort UWB signals, thereby affecting modeling accuracy [17]. To address this issue, [PERSON] et al. introduced a 1D-ConvLSTM-Attention network (1D-CLANet) enhanced by Squeeze-and-Excitation (SE). This SE-enhanced 1D-CLANet can identify NLoS conditions during modeling. They will use this 1D-CLANet in future research to reduce the modeling errors caused by NLoS conditions [18]. Among the work of researchers, [PERSON] et al. creatively demonstrated the importance of incorporating radar cross sections (RCSs) into channel modeling, creating a high-precision 3D deterministic model that provided more accurate predictions of signal behavior in complex environments [19]. This suggests that by accounting for the scattering processes occurring along the signal path in more detail, including the precise RCS values  
Figure 1: Comparison between the ray-tracing method and a real situation. of various scatterers, the overall channel model can be made significantly more accurate. In our paper, we aim to obtain higher-precision RCS values by introducing bistatic testing, and we hope that this high-precision RCS can contribute to developing multipath channel modeling methods that are accurate, have low computational complexity, and are less affected by complex environments. The RCS of a target represents the effective area perceived by the radar. The formula for defining the RCS is shown in Equation (1) [20]. It is the ratio of the power reflected by a target towards the emission source within a unit solid angle to the plane wave power density incident on the target from a given direction. \[\sigma=\lim_{R\rightarrow\infty}4\pi R_{1}R_{2}\frac{\left|E_{s}\right|^{2}}{ \left|E_{i}\right|^{2}} \tag{1}\]  
In this formula, \(\sigma\) denotes the RCS, typically measured in m\({}^{2}\) or dBm\({}^{2}\); \(R_{1}\), \(R_{2}\) represent the distances between the target and the radar's transmitting and receiving antennas, respectively; \(E_{s}\) is the electric field strength of the scattered wave at the receiving antenna; and \(E_{i}\) is the strength of the incident wave at the target. The RCS is the hypothetical area that intercepts a specific amount of power, which, when scattered uniformly in all directions, produces an echo at the radar station equivalent to that of the actual target. The RCS is the hypothetical area that intercepts a quantity of power such that, when scattered uniformly in all directions, it generates an echo at the radar station equivalent to that of the target. In wireless communication, the radar's transmitting antenna can be equivalent to the radio wave's transmitting station, and the radar receiving antenna can be equivalent to the radio wave's receiving station. Thus, the RCS can characterize the scattering of radio waves by obstacles along the propagation path. The RCS values of some common objects are shown in Table 1 below. In practical engineering, the RCS definition formula is generally not used. Instead, the radar equation, as shown in Equation (2), is used for RCS measurement [22]. In this formula, \(P_{t}\), \(P_{r}\) represent the radar's transmitted power and received power, respectively, while \(G_{t}\), \(G_{r}\) correspond to the gains of the transmitting and receiving antennas, respectively. \(\lambda\) denotes the radar's operating wavelength. \[\sigma=\frac{(4\pi)^{3}(R_{1}R_{2})^{2}}{P_{t}G_{t}G_{r}\lambda^{2}}\cdot P_{r} \tag{2}\]  
Traditional RCS testing systems typically use a monostatic radar configuration, where the transmitting and receiving antennas are located at the same radar station. However, with continuous technological advancements, bistatic radar RCS measurements are attracting attention due to their higher accuracy and efficiency [23].