An Extremely Large Ka-Band Reflectarray Antenna for Interferometric Synthetic Aperture Radar: Enabling Next-Generation Satellite Remote Sensing

The Surface-Water Ocean Topography (SWOT) mission, currently in development at NASA's Jet Propulsion Laboratory (JPL), will employ the Ka-band radar interferometer (KaRIn) to characterize the ocean's height at the unprecedented spatial resolution of 2 km and is designed to provide a global inventory of significant terrestrial water bodies [area >(250 m)
²
] and rivers (width >50-100 m). The key enabling technology for this instrument is a pair of large, deployable antennas that form the interferometer. This article describes the development of the largest reflectarray antenna currently in process for a spaceflight application: a 5 × 0.26-m offset-fed reflectarray antenna with a 4.37-m focal length. It details critical aspects of the development, including the radio-frequency (RF) design and analysis, fabrication, and measurement, and discusses unique requirements imposed by the interferometer that resulted in significant design and verification challenges. Flight-hardware measurements demonstrated a gain of approximately 49.5 dB, corresponding to an efficiency of 52%, and an azimuth beamwidth of 0.105°, with a beam-pointing knowledge of 5 millidegrees. Accurate characterization of these antenna-performance parameters is critical to the success of the KaRIn instrument.