Quantization Distortion Suppression for Signum-Coded SAR Based on Hamming Frequency Modulation Transmitted Signal

Signum-coded synthetic aperture radar (SC-SAR), also known as the 1-bit SAR, significantly reduces the system complexity and data processing throughput by retaining only the sign information of the echo signal. However, this introduces severe quantization distortion, which degrades the image signal-to-noise ratio (SNR) and generates a succession of false targets in sparse scenes. The theoretical analysis reveals that the SNR degradation is primarily caused by the phase harmonic distortion, while the false targets are brought about by the amplitude intermodulation distortion. To address these issues, a nonlinear frequency modulated (NLFM) signal with a Hamming-windowed amplitude spectrum, termed Hamming frequency modulation (HFM), is proposed as the transmitted waveform. The matched filter for the HFM signal integrates the pulse compression and the low-sidelobe weighting, optimizing the output peak SNR (PSNR) to suppress the quantization noise. Concurrently, its nonlinear frequency modulation disrupts the periodicity of the intermodulation distortion, attenuating the peak power of false targets. Experiments utilizing both ideal-point targets and real SAR raw data demonstrate that the proposed HFM method suppresses the quantization noise and the false target energy by approximately 0.8 and 4.8 dB, respectively, compared to the conventional linear frequency modulation (LFM) signal, thereby enhancing SC-SAR image quality significantly.