Time-Frequency Feature-Based Notch Filtering for Suppressing Noise-Frequency Modulated Saturation Interference in SAR

Synthetic Aperture Radar (SAR) systems are highly susceptible to Radio Frequency Interference (RFI), particularly noise-frequency modulated (NFM) saturation interference, which triggers nonlinear distortions in SAR receivers and severely degrades imaging quality. Existing interference suppression methods often overlook the unique time-frequency characteristics of saturation-induced harmonics, leading to suboptimal performance. This paper proposes a novel interference suppression framework combining time-frequency analysis and adaptive notch filtering to address NFM saturation interference. First, we establish a mathematical model of saturation interference under low-intermediate-frequency SAR receiver conditions. Second, the time-frequency distribution of saturated NFM interference is analyzed, revealing its harmonic distortion patterns in both time and frequency domains. Based on these insights, an adaptive thresholding mechanism is designed to detect and suppress baseband and higher-order harmonics within short-time Fourier transform (STFT) windows. The proposed method eliminates the need for matrix inversion operations, significantly improving computational efficiency. Experimental validation using Radarsat-1 semi-real data demonstrates that the approach achieves over 20 dB interference suppression ratio (ISR) while preserving target echo integrity, enabling high-fidelity SAR imaging in contested electromagnetic environments.