# Analysis of High-Power Radar Propagation Environments Around the Test Site
## 2 Method for Analyzing Propagation Environments and Modeling Radar Sites  
Figure 1 illustrates the propagation environment scenario at the radar performance test site. In this scenario, the Tx. system, located above the radar control center, emits EM waves directed toward the Rx. system, which is placed at the top of a beacon tower at a height of 60 m. Herein, various geographical features, such as buildings, a river, and mountains, are distributed between each system (distance of 850 m). Because of these features, EM waves propagate not only through a direct path but also through indirect paths, which occurs by reflection, diffraction, and scattering. In particular, high electric field strength can be transmitted around the Tx. system through both direct and indirect paths due to reflection or malfunctions of the radar system. The areas that can be reached by indirect paths are classified as important observation areas, and the received EM waves should be considered. To analyze the propagation environment in such specific areas, the ray-tracing method based on geometrical optics (GO) and the Uniform theory of diffraction (UTD) can be utilized. The received power can be represented as the sum of the received power from both direct and indirect ray paths, as expressed in the following equation [21]:  
\[P_{t}(s)=P_{d}(s_{d})+\sum_{i=1}^{N}P_{g,i}(s_{i})+\sum_{j=1}^{M}P_{u,j}(s_{j}), \tag{1}\]where \(P_{t}(s)\) is the total received power at a specific point \(s\), which consists of the \(P_{d}(s_{d})\) transmitted through direct paths, the sum of \(P_{g,t}(s_{i})\) transmitted through reflected paths, and the sum of \(P_{u,t}(s_{i})\) transmitted through diffracted paths. Here, \(s_{d}\) represents the distance of the direct path, while \(s_{i}\) and \(s_{j}\) denote the distances of the \(i\)-th reflected path and the \(j\)-th diffracted path, respectively. \(N\) is also the total number of reflected paths, and \(M\) denotes the total number of diffracted paths. The electric field strength is then determined based on the received power to evaluate the impact of the radar on the observation area. The electric field strength can be calculated from the received power using the following equation [22]:  
\[E_{r}=\sqrt{\eta\frac{P_{t}\cdot 4\pi}{G_{r}\lambda^{2}}}, \tag{2}\]  
where \(\eta\) is the intrinsic impedance (\(\Omega\)) in free space, \(P_{t}\) is the received power (W), \(G_{r}\) is the gain of the receiving antenna, and \(\lambda\) is the wavelength. Since this value varies depending on the input power and frequency of the radar, accurate analysis enables the assessment of the impact of received EM waves on the radar site. Figure 2 represents the simulation model for analyzing the propagation environment during the test of radar performance. In this study, we employ Wireless InSite by Remcom, which utilizes the ray-tracing method to analyze the propagation environment [23]. For accurately analyzing propagation characteristics such as reflection, diffraction, and scattering, this simulation model consists of three parts: terrain, buildings, and a river. First, to apply complex terrain into the simulation, we utilize DEM data provided by the Ministry of Land, Infrastructure, and Transport [24]. This data has a higher resolution (1 m) compared to the NASA and Google terrain data (20-30 m) used in previous studies, allowing for a more effective simulation of complex terrain features [25]. Structures such as buildings and river are then modeled on the terrain. Herein, the material characteristics of structures are applied separately. The DEM terrain data is modeled as wet earth (\(\varepsilon_{r}\) = 20, \(\sigma\) = 0.02 S/m), and the material properties of building structures are set as concrete (\(\varepsilon_{r}\) = 15, \(\sigma\) = 0.015 S/m). The water of the river is also modeled as fresh water (\(\varepsilon_{r}\) = 81, \(\sigma\) = 0.22 S/m). The number of ray paths arriving at each receiver is limited to a maximum of 25, and each ray carried a sinusoidal signal with a bandwidth of 1 MHz.