TABLE OF CONTENTS Synthetic aperture radar (SAR) with coherent focussing has already been proposed, in 1953 by C. W. Sherwin [1]. It allows imaging of the ground scene in all weather conditions with high resolution using a radar on board a flying platform or satellite. The first actual systems applied optical processing for image generation. Since then many developments have achieved finer resolution and faster processing of received SAR signals by digital processing.
New and extended capabilities can be achieved by applying an active phased-array radar for SAR operation, including array signal processing methods discussed in the preceding chapters. Opportunities are particularly good for the task of detecting, locating and imaging moving objects. The suppression of jamming may also be achieved.
As an introduction, the principle of conventional SAR with a single antenna and receiving channel will be explained.
For imaging of a ground scene a high resolution in range (in the direction of the line of sight) and cross range (orthogonal to the line of sight and parallel to the flight path), both independent of range, is necessary and achievable. Resolution values of the order of metres or even sometimes decimeters are required. Range resolution is achieved by applying an appropriate signal modulation to the transmitted pulse, as with other radar systems. This may be a short pulse with a length according to the required range resolution. More popular is linear frequency modulation (chirp) with a frequency shift determined by the required bandwidth reciprocal to the range...
