Abstract
A method for improving the dynamic range of frequency-modulated continuous-wave (FMCW) radar systems is presented. Bright echo signals detected with FMCW radars can carry strong phase noise sidelobes, especially for radars at W-band and higher frequencies where extremely quiet local oscillators do not exist or are not practical. These sidelobes can hide targets that would otherwise be detectable by the radar. Owing to the mathematical symmetry of phase noise with respect to a dominant carrier tone, the phase noise on the negative-frequency side of a bright echo can be used in post-processing to coherently cancel the corresponding phase noise on the positive-frequency side, revealing the presence of any weak target on the positive-frequency side. We show experimentally how this procedure improves the dynamic range of an airborne 167 GHz cloud radar by up to 18 dB, albeit with a detection sensitivity penalty of about 3 dB.
Highlights
A common challenge in radar design is maximizing the instrument’s dynamic range
In this paper we present experimental data highlighting the phase noise problem in a 170-GHz frequency-modulated continuous-wave (FMCW) radar, and demonstrate a signal processing strategy to significantly mitigate the effect and increase the radar’s dynamic range in the presence of bright echoes
For an FMCW radar system affected by strong phase noise sidelobes carried by echoes from a bright target, we have shown analytically and experimentally how that noise can be canceled to increase the radar’s dynamic range
Summary
A common challenge in radar design is maximizing the instrument’s dynamic range. Simplistically, detection dynamic range should be determined by the performance of a radar’s RF components that determine the system noise temperature at the low end and a saturated power level at the high end. Other factors often limit a radar’s ability to discern weak targets, including electromagnetic interference from the human environment, background clutter from targets not of interest (e.g., from antenna sidelobe detections), and range sidelobes accompanying bright targets that arise from signal filtering and processing [1]. Another dynamic range limitation that commonly affects frequency-modulated and Doppler radars, owing to their reliance on precise frequency measurement for detection, is broad-band phase noise carried by the radar’s transmit signal [2]–[6]. By cancelling the common-mode phase noise that appears in the range spectrum both above ground and below ground, the radar’s dynamic range is improved by up to 18 dB to reveal clouds that would otherwise be undetectable
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