Systematical Error Estimation and Compensation for Ultrawideband Microwave Photonic SAR Based on the Coarse-Focused Image

The combination of microwave photonic (MWP) technology and synthetic aperture radar (SAR) facilitates the generation, transmission, and reception of ultrawideband (UWB) signals, thereby enabling the production of centimeter-resolution SAR images. Recently, an experimental MWP SAR system with a bandwidth of 14 GHz has been constructed at the Aerospace Information Research Institute, Chinese Academy of Sciences, which has been tested by outfield SAR experiments. In the context of this system, we analyzed the manifestation of systematical errors in the coarse-focused image and found that deviations occur in both the envelope and the phase of the range cell migration (RCM) curves, which can be considered as inherent slant range error and center frequency error. In addition, the inclusion of a radio frequency power amplifier (PA) in this system can introduce frequency-dependent error. In this article, we analyze the sources and establish signal models for the above three types of systematical errors individually and propose a systematical error estimation method by exploiting the trihedral reflectors (TRCs) in the coarse-focused image. Utilizing the error estimation results and the measured frequency response of the PA, a postprocessing compensation method is also proposed. The estimation and compensation method is applied to the processing of the vehicle-borne data acquired by this experimental MWP SAR system, yielding superior performance and a fine-focused SAR image with a resolution of approximately 0.013 m in the range dimension.