Photonics-Based Superresolution Radar Imaging With Space-Time-Frequency Coincidence Processing

Abstract

A photonics-based, superresolution radar imaging system using space-time-frequency coincidence processing is proposed and experimentally demonstrated. In the transmitter, a broadband, frequency-hopping (FH) signal is generated by an optically injected semiconductor laser based on the P1 oscillation dynamics. The generated signal is switched and transmitted through a uniform linear antenna array (ULA) by means of time division multiplexing (TDM). Therein, a space-time-frequency, 3-D stochastic radiation field is constructed, which is manifested as wavefront modulation. In the receiver, the radar echoes are received and frequency downconverted to baseband through IQ mixing. Thanks to the broadband operation capability of the microwave photonic system, high range resolution can be easily achieved. To overcome the azimuth resolution limitation determined by the array aperture size, a kernel function-based sparse reconstruction algorithm is proposed, which enables superresolution coincidence imaging in the azimuth direction. In the experiments, a photonics-based $4\times 1$ multiple-input single-output (MISO) radar with a bandwidth of 8 GHz (10–18 GHz) is established, in which the transmitted signal is a 32-level FH signal. Combined with the proposed coincidence imaging algorithm, superresolution radar imaging is realized with the range-azimuth imaging resolution reaching $2.3\times 0.8$ cm, which surpasses that of the traditional MISO radar by 20 times in azimuth resolution. In addition, the imaging experiments of complex targets with N, V, and A shapes and an aircraft model with a continuous structure are demonstrated to imitate real scenes, which verify the feasibility of the proposed photonics-based radar system in high-resolution forward-looking imaging.