A Tailored Frequency Scaling Algorithm for De-ramped Staring Spotlight Synthetic Aperture Radar Data Processing

This article proposes a processing method for de-ramped staring spotlight synthetic aperture radar (SAR) data. A full-aperture approach is widely adopted in spotlight SAR processing because it includes pre-processing to avoid aliasing caused by the wide Doppler bandwidth of the signal. The proposed method incorporates the frequency scaling algorithm (FSA), which is efficient for de-ramped signal processing, into the full-aperture framework. An azimuth-convoluted signal model featured by a new envelope shaping factor and the conditions on the convolution reference range that ensure aliasing-free processing are introduced. The proposed method achieves high-quality SAR imaging without azimuth post-processing, distinguishing it from the conventional full-aperture processing method for de-ramped sliding spotlight SAR data. Various point target simulations and actual SAR raw data validation are conducted to assess the credibility of the algorithm, demonstrate the aliasing phenomena that occur when the conditions for the convolution reference range are not satisfied, and prove that the azimuth post-processing is unnecessary if the image generation is the only purpose. In addition, a comparison with the conventional sub-aperture FSA is conducted in terms of both performance and computational load.