Space Antenna Handbook

Chapter 13

SAR Antennas

Pasquale Capece and Andrea Torre

Thales Alenia Space Italia, Rome, Italy

13.1 Introduction to Spaceborne SAR Systems

13.1.1 General Presentation of SAR Systems

Earth observation from moving platforms (aircraft or satellites) has allowed, for many years, monitoring of large areas of the surface of our planet for disparate purposes.

The SAR(Synthetic Aperture Radar) is one of the main instruments for remote sensing from moving platforms. It is an active radar sensor that works in the microwave band. It is widely used because it provides spatial resolutions much better than those achieved by conventional radar techniques. This allows images of the Earth's surface to be produced by satellite with a quality that can be compared to that of optical sensors.

A SAR system is designed to create two-dimensional images of the observed scene (also known as swath) with sufficient spatial resolution in both the directions of azimuth (or along-track motion direction) and range (or cross-track direction normal to the motion); the observed scene is acquired off-nadir. Figure 13.1 shows the acquisition geometry of a SAR. The antenna is assumed to be a rectangular aperture with dimensions L and L_el in the azimuth and elevation directions respectively, H represents the flight altitude of the radar and R₀ the distance between the antenna and the center of the observed area. The off-nadir angle is denoted by α₀. The size of the antenna, as well as the frequency being used and ...