## 1 Introduction  
Low-Earth-orbit (LEO) satellites have been widely used to perform various Earth observation missions, such as resource monitoring, weather surveillance, and military reconnaissance, while circling the Earth along a trajectory below 2000 km in altitude [1, 2]. To perform these missions effectively, the satellites often employ synthetic aperture radars to capture high-resolution images of the Earth's surface, and the image data are then transmitted at a high speed to ground stations using X-band downlinks. The period of data communication between LEO satellites and ground stations is limited to a maximum of 10 min, though this varies slightly depending on the satellite trajectory. In order to predict whether or not image data can be received within such a short period of time, a link budget analysis that considers various environmental factors is essential. A link budget analysis considering natural earth environment, such as atmospheric impact [3, 4, 5] and Doppler shift [6, 7, 8], has been previously conducted. In addition, studies on link budget in interference environments where ground station antennas are exposed to intentional electromagnetic (EM) interference sources have also been investigated [9, 10, 11]. Although some research has been conducted in various interference situations, there is a lack of studies analyzing real LEO satellite trajectories and airborne interference sources. In particular, the airborne interference sources have a much greater impact on the satellite downlink compared to ground-based interference sources. Since ground stations should receive data within 10 min, the downlink can be significantly affected by the speed or path of the airborne interference source. Additionally, more in-depth research is required to accurately derive link budgets by considering the sidelobe gain of the ground station antenna based on the relative angle difference between the LEO satellite and the airborne interference source. The sidelobe gain of the ground station antenna is important because it has a critical impact on the \(J/S\) ratio, and the sidelobe gain is determined by the relative difference in angle between the LEO satellite and the airborne interference source. In this paper, we analyze LEO satellite downlinks under interference situations when airborne interference sources move parallel to the satellite trajectory by considering the relative angle differences between the satellites and the interference sources. To make interference situations more like actual environments, we use the two-line element set (TLE) data of LEO satellite trajectory information, including geodetic coordinates provided by the Joint Space Operations Center at Vandenberg Air Force Base. Airborne interference sources with various altitudes (3 km, 6 km, 9 km, and 12 km) move parallel to the trajectories of the LEO satellites, and the jamming to signal (\(J/S\)) ratio is calculated based on the relative angle differences between the ground station, satellite, and interference source. In this study, only the simplest path, traveling parallel to the satellite, is observed. In order to express the positions of these three elements, the World Geodetic System 1984 (WGS84) coordinates are converted to the ground station-centered east-north-up (ENU) system [12; 13]. Based on the ENU coordinates, the relative angle difference between the satellite and the interference source is calculated, and the sidelobe gain of the ground station antenna to the direction where interference electromagnetic (EM) waves are incoming. The radiation pattern of the ground station antenna is obtained using geometrical optics (GO) and physical optics (PO) [14], and the sidelobe gain is then obtained and applied to the \(J/S\) ratio calculation. We investigate the link budget under interference situations in which airborne interference sources move at a minimum distance of 100 km (Path 1), 200 km (Path 2), and 300 km (Path 3) from the ground station.