NISAR’s large, deployable antenna will be used in a unique operating mode known as SweepSAR, to provide both wide area coverage and fine spatial resolution at the same time.
In SweepSAR mode, a one-dimensional phased array feed al-lows only a narrow segment of the large antenna’s reflecting surface to be used on transmit, which then illuminates a wide area on the ground. To receive the radar echoes, the same phased array feed is ‘swept’ to steer the antenna beam across the area being imaged, using the full area of the large reflecting surface, and tracking the radar waves reflected from the scene being imaged, as they arrive.
Advantages of the SweepSAR technique over two-dimensional phased array antenna approaches are that it has inherently lower transmit power at the array feed, less complexity in the array feed design, and takes advantage of the very low mass and large area of the deployable antenna. It is particularly well-suited to longer wavelength SARs (Freeman et al, 2009).
Freeman, A., G. Krieger, P. Rosen, Younis, M., W. T. K. Johnson, Huber, S., R. Jordan, and Moreira, A., Sweep-SAR: Beam-forming on Receive using a Reflector-Phased Array Feed Combination for Spaceborne SAR, Proc. Radar-con ’09, Pasadena, CA, May 2009.