High-resolution 3D imaging by microwave photonic time division multiplexing-multiple-input-multiple-output radar with broadband digital beamforming

A broadband microwave photonic time division multiplexing (TDM) multiple-input-multiple-output (MIMO) radar is proposed in which photonic frequency quadrupling is adopted to generate broadband radar signals and photonic frequency mixing is implemented for de-chirping processing of radar echoes. By utilising two radio frequency switches to control the signal transmission and reception, TDM-MIMO mechanism is formed using a single microwave photonic radar transceiver. This microwave photonic TDM-MIMO radar not only achieves high range resolution using broadband processing but also enables high angular resolution and forward-looking imaging capability with low system complexity. Besides, a broadband digital beamforming (DBF) method is introduced to solve the broadband beam squint and broadening problems and implement near-field correction. In the experiment, a microwave photonic TDM-MIMO radar with an 8×8 T-shape antenna array is established with a bandwidth of 8 GHz (18–26 GHz) in each channel. The range and angular resolutions are estimated to be ∼2 cm and ∼2°, respectively. Applying the broadband DBF method, high-resolution 3D imaging of small targets is achieved with good focusing of targets and deep suppression of grating lobes and side lobes. Hence, the proposed microwave photonic TDM-MIMO radar with broadband DBF provides a promising solution for high-resolution 3D imaging.