# The Development of a Spaceborne SAR Based on a Reflector Antenna
## 1 Introduction  
As an active microwave imaging sensor, synthetic aperture radar (SAR) [1, 2] achieves high-resolution imaging by transmitting broadband signals and employing pulse compression technique in the range direction while utilizing the synthetic aperture technique in the azimuth direction to extend the effective aperture. This enables SAR to overcome the limitations of conventional real-aperture radar and achieve high-resolution imaging [1]. Compared with passive remote sensing technologies, such as optical and hyperspectral sensors, spaceborne SAR provides all-weather, day-and-night global imaging and penetration capabilities. This makes it a powerful tool for Earth observation and often superior to traditional sensors [3]. As a result, SAR has been widely applied in military reconnaissance, terrain mapping, vegetation monitoring, resource exploration, ocean management, pollution tracking, urban planning, and deep space exploration [4, 5, 6, 7, 8]. In pursuit of a higher resolution, wider mapping swath, and shorter revisit cycles, spaceborne SAR system design faces increasingly severe challenges, primarily due to limitations in antenna performance. The antenna, as a core component of radar systems, directly affects imaging quality and detection capability. Its primary function is to convert the high-power energy output by the transmitter into radiated electromagnetic waves, while also receiving incoming echoes and converting them to the receiver. Essentially, theantenna is a component capable of efficiently and directionally transmitting or receiving high-frequency electromagnetic waves [9,10]. Various types of antennas are employed in modern radar systems, each with its advantages and limitations. A reflector antenna typically consists of a reflector surface and a feed system, featuring a large aperture, high gain, a narrow main lobe, low sidelobes, and high radiation efficiency [11]. Additionally, mesh reflector antenna offers advantages such as lightweight construction and a high deployment-to-stowage ratio, making it one of the most commonly used antenna types in spaceborne radar systems. In SAR applications, spatial resolution and mapping swath are key performance metrics that directly determine the system's capability to characterize targets and terrain. High-resolution wide-swath (HRWS) SAR systems generally require antennas with high gain, and compared to phased array antennas, reflector antennas can achieve high gain at a lower cost, making them more advantageous for HRWS imaging. Globally, many countries have developed and launched spaceborne SAR systems adopting reflector antenna architectures [12, 13, 14, 15, 16, 17, 18]. The United States deployed the Lacrosse and Magellan SAR satellites in the 1990s, both utilizing traditional reflector antennas [12]. In the 21 st century, Germany launched the SAR-Lupe satellites (2006-2008) [17], also equipped with parabolic antennas. Around the same time, Israel's TecSAR (2008) [14] and India's RISAT-2 (2009) employed radial rib deployable antennas, demonstrating the feasibility of large-aperture designs. China launched the civilian SAR satellite HJ-1-C (2012) [18], featuring a framework deployable antenna. More recently, Japan's QPS-SAR, the U.S. Capella Space's Acadia [19] and Whitney series [13], China's Qilu-1, Land Exploration Satellite-4 01, and Neptune-01 satellites have all adopted reflector antenna architectures. Additionally, Germany launched SARah-2/3 in 2023 as the successor to the SAR-Lupe satellites, while Russia launched Kondor-FKA No.2 in 2024, both incorporating reflector antennas. Several ongoing SAR projects, such as the U.S. EOS-SAR, the UK's CarbSAR, ESA's Biomass, and the U.S.-India NISAR mission [16], also employ reflector antenna architectures. Germany's Tandem-L [15] project aims to utilize reflector antennas for HRWS imaging and flexible beam steering through two-dimensional feed arrangements. This paper is organized as follows: Section 2 introduces the main types of reflector antennas.