The nonlinear frequency modulation (NLFM) waveform is a promising candidate for the linear frequency modulation (LFM) signal because its autocorrelation output exhibits low sidelobes without loss of signal-to-noise ratio (SNR), also avoiding the transmitting power loss for spaceborne synthetic aperture radar (SAR). However, the acquisition of the analytical expression of the NLFM waveform is often closely related to the indirect instantaneous frequency function generated by the principle of stationary phase (POSP), thus it is not inconvenient for the real-time generation of the efficient and precise NLFM signal on board. In this letter, based on the harmonic decomposition, closed-form expressions of the NLFM waveform, which are directly calculated by the predefined window, are derived in both time and frequency domains. Therefore, it is very beneficial to the real-time generation and process of the NLFM waveform for the SAR system. All the simulation results and analyses validate the promising potential of the closed-form expressions of the NLFM waveform for SAR application.

中文翻译：

---

用于合成孔径雷达的谐波分解分析 NLFM 波形设计

非线性频率调制 (NLFM) 波形是线性频率调制 (LFM) 信号的有希望的候选者，因为它的自相关输出表现出低旁瓣而不会损失信噪比 (SNR)，还避免了星载合成的发射功率损失孔径雷达（SAR）。然而，NLFM波形解析表达式的获取往往与静止相位原理（POSP）产生的间接瞬时频率函数密切相关，因此对于实时生成高效、精确的NLFM并不不方便。船上的信号。在这封信中，基于谐波分解，由预定义窗口直接计算的NLFM波形的闭式表达式在时域和频域中得到了推导。所以，对 SAR 系统的 NLFM 波形的实时生成和处理非常有益。所有的仿真结果和分析都验证了 NLFM 波形的闭式表达式在 SAR 应用中的潜力。