Photonics-Based Broadband Single-Input-Multiple- Output-OAM Coincidence Imaging

A photonics-based broadband single-input-multiple-output (SIMO)-orbital angular momentum (OAM) radar is proposed to implement high-resolution radar imaging. In the transmitter, a broadband linear frequency-modulated (LFM) signal is generated by an optically injected semiconductor laser and emitted by a single antenna to illuminate the target. In the receiver, a uniform circular array (UCA) collects the echoes and introduces OAM modulations before photonic frequency mixing is implemented for broadband dechirp processing. The use of microwave photonic techniques enlarges the operation bandwidth and thus improves the radar range resolution, while the SIMO structure mitigates the OAM beam divergence and energy hollow problems. Based on this SIMO-OAM radar, a super-resolution imaging method with random OAM modulation and coincidence processing is proposed to break through the azimuth resolution limitation. A proof-of-concept photonics-based $1\times 16$ OAM radar is established with an 8-GHz (18–26 GHz) bandwidth, of which the range resolution reaches 2.1 cm. By using the proposed imaging method, super-resolution imaging with six times higher azimuth resolution than traditional OAM radar is achieved. In the experiment, high-resolution imaging of small-size complex targets is successfully demonstrated, verifying that the proposed system and imaging method can meet the requirement for high-resolution radar detection and high-precision target recognition.