A Novel Nonlinear Frequency Modulation Waveform With Low Sidelobes Applied to Synthetic Aperture Radar

Synthetic aperture radar (SAR) systems require a favorable waveform for imaging, as the radar waveform directly affects the performance of the SAR systems, such as image quality and resolution. It is well known that the nonlinear frequency modulation (NLFM) waveform can adjust the time-frequency relation to shape the power spectral density (PSD) and then provide a matched filtering (MF) output with lower sidelobes without losing signal-to-noise ratio (SNR). However, it will broaden the main lobe, which means the resolution of the SAR image decreases. Therefore, in this letter, a novel NLFM waveform is proposed. It employs the piecewise linear (PWL) function model to define the instantaneous chirp rate function, and genetic algorithm (GA) is then applied to optimize the waveform. The novel NLFM waveform promises enhanced performance and flexibility due to greater design freedom. Through this method, lower sidelobe is achieved within the same 3-dB main lobe width. Finally, simulation results are presented to verify the practicability of the proposed NLFM waveform.