SAR-Based Paired Echo Focusing and Suppression of Vibrating Targets

Paired echoes are the typical manifestation of Doppler characteristics caused by vibrating targets in high-resolution synthetic aperture radar (SAR). Conventional imaging algorithms produce smeared paired echoes. It results in not only the inconvenience of vibration parameter analysis but also the emergence of unwanted ghost targets to degrade SAR image quality. This paper proposes a method on paired echo focusing and suppression of vibrating targets. After demodulation and range compression, the signal is decomposed into the form of Bessel series in the azimuth direction. Then, the range walk is compensated in the 2-D frequency domain by Doppler keystone transform. Next, the range curvature is corrected in the range-Doppler domain by using range cell migration correction to achieve the focus of paired echoes. Compared with conventional SAR imaging algorithms, the focused paired echoes could reach system nominal resolution. Furthermore, this focusing method, which works without prior knowledge of vibrating targets, is suitable for various vibrating states of multiple targets. On the basis of paired echo focusing, the residual video phase of paired echoes is also eliminated. Then, vibration parameters, including vibration frequency, amplitude, and initial phase, are estimated. These parameters are used herein to construct the reference function to compensate the sinusoidal modulation phase in the range-Doppler domain. Finally, deghosted vibrating targets can be obtained. Simulations show that paired echoes could be successfully focused within one resolution unit as well as the robustness of its application. At last, the real SAR data from a moving truck are used to further validate the effectiveness of the proposed method.