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

Abstract

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.