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Impacts of Azimuth Antenna Steering Angle Quantization on Tops and Sliding Spotlight Sar Image

Quantization step size is a very important system parameter in TOPS and sliding spotlight acquisition modes, as the azimuth antenna beam is electronically steering during the illumination. By replacing continuous steering, staircase-like steering in azimuth antenna beam is often used in orbited SAR, causing a quantized error on azimuth antenna pattern (AAP) and an amplitude modulation on illuminated target echo. Consequently, infinitely many spurious targets are introduced in azimuth direction. In this paper, investigations of quantized AAP on TOPS and sliding spotlight SAR image are carried out, by unified modelling on quantized AAP and spurious targets signal. Then, the position of maximum peak of spurious targets and its peak level are derived, which is only decided by azimuth antenna length, signal wavelength and quantization step size, and have nothing to do with the acquisition mode. Finally, simulation results verify the correctness of the proposed mathematical model of spurious target.