Spaceborne SAR Antennas for Earth Science

Before the development of the first synthetic aperture radar (SAR) antenna flown in space, Jet Propulsion Laboratory (JPL) was involved in an aircraft radar program to image the Earth surface for various science applications. This radar was flown on a Convair CV-990 aircraft with the antenna attached to one of the baggage doors of the airplane. The antenna was a planar array with eight radiating elements operating at 1215 MHz and had dual-polarization capability. This system was important because it provided SAR data to prove that SAR could image ocean waves giving both the direction of wave propagation and its wavelength. These observations led to the incorporation of SAR on the Seasat spacecraft that was the first radar used to make science observations from space [1]. The development of the Seasat antenna was significant because of the unique challenges that its development required. The antenna area required was significantly larger that other similar antennas built for aircraft systems. In addition, the antenna was required to operate in a vacuum over a wide temperature range without its surface deforming significantly from out of plane, and the mass of the antenna was limited to less than 100 kg. A picture of the Seasat-A system is shown in Fig. 6-1. Ball Aerospace developed both engineering and flight models of the Seasat antenna. The engineering model was used to verify the performance of the antenna, and the flight model was flown on the Seasat platform. Following the success of the Seasat SAR system, the first of the Shuttle Imaging Radar (SIR)