Abstract
The magnitude error and phase error (MEPE) in the transfer function of a stepped-frequency synthetic aperture radar (SAR) system results in a periodic MEPE in the synthesized wideband waveform (SWW), which induces the grating lobes in the high-resolution range profile (HRRP). In this paper, a robust data-driven grating lobe suppression (GLS) method is proposed. Based on a contrast-based error estimation method and the grating lobes of the brightest scatterers in the SAR image, the periodic MEPE can be robustly estimated using the proposed method. By compensating the estimated periodic MEPE, the range grating lobes can be suppressed to the background level of the SAR image. Simulation results and real data processing have demonstrated the superiority of the proposed method.
Highlights
By transmitting groups of narrowband linear frequency-modulated (LFM) sub-pulses and achieving synthesized wideband waveforms (SWWs) in post-processing, the stepped-frequency technique significantly reduces the requirement for an A/D converter and is widely used in improving range resolution in synthetic aperture radar (SAR) [1,2,3,4,5,6].Periodic magnitude error and phase error (MEPE) arises in the SWW when there is a MEPE in the transfer function of a stepped-frequency SAR system
Equation (4) shows that the information of H ( f r ) is reflected by the positions, amplitudes and phases of the grating lobes. This means that the periodic MEPE H ( f r ) is able to be recovered from the range grating lobes, which is the foundation of the proposed grating lobe suppression (GLS) method in this paper
Superior to grating lobe’s peak point method (GLPP) in suppressing the range grating lobes
Summary
By transmitting groups of narrowband linear frequency-modulated (LFM) sub-pulses and achieving synthesized wideband waveforms (SWWs) in post-processing, the stepped-frequency technique significantly reduces the requirement for an A/D converter and is widely used in improving range resolution in synthetic aperture radar (SAR) [1,2,3,4,5,6]. One of the methods suppresses the range grating lobes to the desired level by restricting the relationships between the frequency step, subpulse bandwidth and subpulse-duration, which is presented in [8,9,10] Another method sets the subpulse center frequencies at unequal spaces to eliminate the periodicity of the waveform, which disperses the grating lobes and thereby reduces the amplitudes of the grating lobes [11,12,13]. The last method, named the grating lobe’s peak point method (GLPP), is a data-driven GLS method It estimates the periodic MEPE based on the amplitudes and phases of a strong scatterer and its grating lobes in the SAR image [14].
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