How does SAR work?
To create a SAR image, successive pulses of radio waves are transmitted to "illuminate" a target scene, and the echo of each pulse is received and recorded. The pulses are transmitted and the echoes received using a single beam-forming antenna, with wavelengths of a meter down to several millimeters. This process forms the synthetic antenna aperture and allows the creation of higher-resolution images than would otherwise be possible with a given physical antenna.
The antenna illuminates an area on the ground determined by its wavelength and antenna dimension. Pulses are sent and received continuously such that any point on the ground is sampled numerous times to generate images.