On the Impact of Nonuniform Phase Distributions Across the Beamwidth and Bandwidth of Antennas for SAR Imaging

The synthetic aperture radar (SAR) imaging relies on the coherent sum of the received signals. Consequently, phase shifts along the beamwidth and bandwidth of the antenna radiation pattern can have a relevant impact on the final image. Previous studies have focused on other sources of image quality degradation, such as antenna mispositioning, frequency uncertainty, or antenna gain pattern effect. This article demonstrates that the phase of the antenna radiation pattern plays a critical role in the quality of the computed electromagnetic images. For this purpose, three different situations have been analyzed: 1) the phase shift changes across the angular range; 2) the nonlinear phase displacement across the working frequency band; and 3) antenna phase center drift across the bandwidth. Systematic simulations have been carried out modeling these phase shifts for different antennas and enabling to establish rules of thumb for the thresholds in all of the previous cases.