Wingtip distance measurement and probability of detection enhancement for coaxial helicopters using phase-triggered millimetre-wave radar

Abstract High-speed coaxial helicopters feature compact structures, excellent maneuverability, and stable handling, and are widely applied in industrial and military sectors. However, they carry the risk of collisions between upper and lower rotors, which necessitates in-flight measurement of the wingtip distance. To address the demand for rapid response and high-precision measurement of the wingtip distance between upper and lower rotors, this paper proposes a phase-triggered millimetre-wave radar measurement method. A rotor motion simulation test platform is constructed in a laboratory environment, in which an angular encoder is used an angular encoder to provide phase signals. At a rotational speed of 1020 rpm, distance measurements are taken within the range of 100–1200 mm between the rotors. Through temporal filtering and the moving target indication-like inter-frame mean removal algorithm, coupling signals and clutter signals from the radar are effectively suppressed, increasing the probability of detection from 51.8% of the original signal to 66.6% and 85.5%, respectively, while reducing the false alarm rate. Experimental validation assesses the accuracy, applicability, and feasibility of the optimised algorithm.