NLFM Waveform Design and Optimization

Generally, radar system employ linear frequency modulation (LFM) signal to achieve the high-resolution image and weighted windowing is usually employed to suppress sidelobes. However, it usually leads to an additional 1–2 dB loss in signal-to-noise ratio (SNR). Nonlinear frequency modulation (NLFM) signal, whose power spectral density (PSD) can be shaped to reduce sidelobes without incurring SNR loss, therefore constitute a promising alternative, but it often broadens the main lobe. Also, the real-time generation of precise NLFM signal is a technical challenge. In this chapter, firstly, a novel NLFM waveform with narrower mainlobe based on the modified Chebyshev window is presented. Subsequently, we develop a high-precision NLFM signal generator with predistortion compensation capability, which has been deployed in the LT-1 (LuTan-1, i.e. TwinSAR-L) mission, an innovative spaceborne bistatic SAR system. Finally, we present a new waveform optimization framework, by which an advanced NLFM waveform with lower sidelobes and a more compact mainlobe is obtained.