Abstract: The step-by-step steering of antenna beam for spaceborne TOPSAR (Terrain Observation by Progressive Scan SAR) mode has significant impacts on image quality. The modulation law of spaceborne TOPSAR mode beam steering for azimuth signal is analyzed, and a mathematical model of azimuth beam step-by-step steering is implemented. Besides, based on the theory of paired echoes, the formulas of the amplitude and position of azimuth paired echoes are derived. The relationship between beam stepped steering and both amplitude and position of paired echoes is quantitatively described. Finally, the computer simulation is used to verify the validity of theoretical analysis.

Key words: Synthetic aperture radar (SAR), TOPSAR mode, Beam steering, Paired echoes