Abstract
Millimeter wave (MMW) sensing systems have potential for enhanced range and angular resolution in comparison to lower radio frequencies. This article employs photonic-assisted radio-frequency arbitrary waveform generation to implement a high-bandwidth multi-target MMW radar. The presented sensing system operates in the W-band using chirped RF signals, with spectra between 80 and 95 GHz at the 10 dB points. We implement sum- and difference-mode beamforming using a two element transmitter array to perform azimuth angle sensing in addition to target ranging. Photonics-based waveform generation with programmable optical pulse shapers provides for incorporation of approximately uniform phase shifts across the entire bandwidth, which in turn enables control of the far-field interference patterns of the broadband waveforms. Our approach has analogies with monopulse tracking radar techniques, in which target angle information is revealed through sum- and difference-mode processing of the receiving antennae, but with the dual-mode processing implemented at the transmitter side via photonic radio-frequency arbitrary waveform generation. Experiments with a single target demonstrate unambiguous sensing of target angle with an estimated root-mean-square error of 0.18
$^\circ$
over a
$\pm 4^\circ$
angular range. We also demonstrate independent sensing of the angles of two targets that are resolved in range.
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