High-Resolution Imaging of Azimuth Frequency Scanning SAR

There is always a compromise between azimuth resolution and azimuth width for working modes using phased array to realize azimuth beam steering such as strip-map, spotlight and sliding spotlight synthetic aperture radar (SAR), which in essence redistribute the synthetic aperture time by controlling the beam direction with phase shifters. To realize high azimuth resolution and wide width imaging at the same time, intra-pulse frequency scanning technique is introduced in azimuth dimension of strip-map SAR system, which is called azimuth frequency scanning SAR. For azimuth frequency scanning SAR, there is always a beam residing in the target, and the central frequency of the beam changes with azimuth time continuously, which integrates spotlight mode and strip-map mode organically. It can not only break through the limitation of imaging area width of spotlight SAR, but also improve the azimuth resolution of strip-map SAR. Besides, the beam scanning is realized by frequency scanning array, and the antenna pattern is coupled with range frequency and azimuth angle, so as to radiate the synthetic beam to the desired direction in space without using phase shifters, which greatly reduces the hardware cost of the system. This article first introduces the principle and characteristics of beam scanning in azimuth dimension as the basis of the imaging model. And then we conduct research on signal modeling and imaging method of azimuth frequency scanning SAR to achieve high azimuth resolution. Numerical simulations verify the effectiveness of signal modeling and imaging method of the working mode, as well as the good performance in achieving high azimuth resolution.