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Article

Staring Spotlight SAR with Nonlinear Frequency Modulation Signal and Azimuth Non-Uniform Sampling for Low Sidelobe Imaging

by 1,2, 1,2, 3,*, 1,2, 1,2 and 1,2
1
College of Information Engineering, Inner Mongolia University of Technology, Hohhot 010080, China
2
Inner Mongolia Key Laboratory of Radar Technology and Application, Hohhot 010051, China
3
Science and Technology on Electromagnetic Compatibility Laboratory, Wuhan 430064, China
*
Author to whom correspondence should be addressed.
Academic Editors: Vito Pascazio, Mengdao Xing, Gianfranco Fornaro and Hanwen Yu
Received: 31 July 2021 / Revised: 26 September 2021 / Accepted: 26 September 2021 / Published: 28 September 2021
In synthetic aperture radar (SAR) imaging, geometric resolution, sidelobe level (SLL) and signal-to-noise ratio (SNR) are the most important parameters for measuring the SAR image quality. The staring spotlight mode continuously transmits signals to a fixed area by steering the azimuth beam to acquire azimuth high geometric resolution, and its two-dimensional (2D) impulse response with the low SLL is usually obtained from the 2D weighted power spectral density (PSD) by the selected weighting window function. However, this results in the SNR reduction due to 2D amplitude window weighting. In this paper, the staring spotlight SAR with nonlinear frequency modulation (NLFM) signal and azimuth non-uniform sampling (ANUS) is proposed to obtain high geometric resolution SAR images with the low SLL and almost without any SNR reduction. The NLFM signal obtains non-equal interval frequency sampling points under uniform time sampling by adjusting the instantaneous chirp rate. Its corresponding PSD is similar to the weighting window function, and its pulse compression result without amplitude window weighting has low sidelobes. To obtain a similar Doppler frequency distribution for low sidelobe imaging in azimuth, the received SAR echoes are designed to be non-uniformly sampled in azimuth, in which the sampling sequence is dense in middle and sparse in both ends, and azimuth compression result with window weighting would also have low sidelobes. According to the echo model of the proposed imaging mode, both the back projection algorithm (BPA) and range migration algorithm (RMA) are modified and presented to handle the raw data of the proposed imaging mode. Both imaging results on simulated targets and experimental real SAR data processing results of a ground-based radar validate the proposed low sidelobe imaging mode. View Full-Text
Keywords: staring spotlight mode; nonlinear frequency modulation (NLFM); non-uniform sampling; low sidelobe imaging staring spotlight mode; nonlinear frequency modulation (NLFM); non-uniform sampling; low sidelobe imaging
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MDPI and ACS Style

Xu, W.; Zhang, L.; Fang, C.; Huang, P.; Tan, W.; Qi, Y. Staring Spotlight SAR with Nonlinear Frequency Modulation Signal and Azimuth Non-Uniform Sampling for Low Sidelobe Imaging. Sensors 2021, 21, 6487. https://0-doi-org.brum.beds.ac.uk/10.3390/s21196487

AMA Style

Xu W, Zhang L, Fang C, Huang P, Tan W, Qi Y. Staring Spotlight SAR with Nonlinear Frequency Modulation Signal and Azimuth Non-Uniform Sampling for Low Sidelobe Imaging. Sensors. 2021; 21(19):6487. https://0-doi-org.brum.beds.ac.uk/10.3390/s21196487

Chicago/Turabian Style

Xu, Wei, Lu Zhang, Chonghua Fang, Pingping Huang, Weixian Tan, and Yaolong Qi. 2021. "Staring Spotlight SAR with Nonlinear Frequency Modulation Signal and Azimuth Non-Uniform Sampling for Low Sidelobe Imaging" Sensors 21, no. 19: 6487. https://0-doi-org.brum.beds.ac.uk/10.3390/s21196487

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