Intermediate-Frequency Nonlinear Frequency Modulation Signal Generator for UAV SAR Missions

Typically, synthetic aperture radar (SAR) utilizes linear frequency modulation (LFM) signal to acquire high-resolution images, requiring spectral windowing to suppress sidelobes while sacrificing signal-to-noise ratio (SNR). In contrast to LFM signal, nonlinear frequency modulation (NLFM) signal can reconstruct the signal power spectral density (PSD) without sacrificing SNR, providing autocorrelation outputs with lower sidelobes. Despite the excellent application potential of NLFM signal, the real-time generation of NLFM faces numerous challenges due to the high complexity of the systems involved and constraints imposed by waveform generator devices. In this letter, a low-complexity, high-precision and high-resolution intermediate-frequency NLFM signal generation device is developed, requiring only eleven parameters to generate real-time NLFM signal of arbitrary time width and bandwidth, with a maximum bandwidth reaching 1.2 GHz. This NLFM signal generator will be employed in the unmanned aerial vehicle (UAV) SAR system. Finally, the performance of the NLFM signal generator has been validated through ground experimental results.