High-Resolution Microwave Photonic Radar With Sparse Stepped Frequency Chirp Signals

High-resolution radar requires broadband signal generation and processing, which challenges the state-of-the-art electronics. In contrast, microwave photonic technologies featuring wide bandwidth and flexible frequency are effective for broadband microwave signal generation and processing to improve radar detection performance. However, the bandwidth is practically limited because the broadband radar with a continuous spectrum signal is always susceptible to interference from other electromagnetic applications operating at the coincident frequency band. Here, we propose a microwave photonic radar with sparse stepped frequency chirp (SSFC) signals to break through the bandwidth limitation, achieving ultrahigh-resolution detection with enhanced anti-interference ability. The SSFC signal with an ultrawide bandwidth is generated by recirculating frequency-shifting a narrowband chirp signal. Microwave photonic dechirping of SSFC signals and compressive reconstructions of dechirped signals are performed to extract target information fast and precisely. In the experiment, we conducted a microwave photonic radar based on an SSFC signal spanning a frequency range of 18 GHz but actually occupying a 4.5-GHz effective spectrum, successfully distinguishing two simulated point targets with a distance of 8.3 mm, and achieving the ranging error within
$\pm 225~\mu \text{m}$
. In addition, high-precision vibration monitoring and high-resolution two-dimensional imaging capabilities are validated by a simple pendulum detection and an inverse synthetic aperture radar (ISAR) experiment.