A Phase-based Method for I/Q Imbalance and DC Offset Calibration of Radar Sensors in Blade Tip Clearance Measurement

Blades are the core components of aircraft engines, and the monitoring of blade tip clearance is essential for ensuring engine safety. Microwave sensing has gained attention in distance measurement due to its robustness against environmental interference. However, in near field measurement, accurate calibration of distorted signals remains a major challenge, particularly DC offset, amplitude-phase imbalance, and near field attenuation. This paper proposes a novel signal calibration method that completely relies on phase information and discards amplitude data. This method has the advantage of abandoning the unreliable amplitude as a prior information under near field or noise conditions, enhancing robustness, and obtaining unbiased unbalanced parameters. First, the phase difference between sampling points is controlled through half-wavelength sampling, then the paired points are connected and the intersection points are obtained, enabling effective suppression of DC offset components. Furthermore, the impact of signal imbalance is equivalent to compression in a certain direction of the original data, and the effect of compression on phase is studied. Based on this, a phase inflection point method is introduced to identify the major and minor axis endpoints of the compressed elliptical trajectory, enabling phase correction using major axis geometry. Last, A phase-based loss function is then defined to achieve precise compensation of residual amplitude imbalance. Simulation results verify the effectiveness of the proposed method, demonstrating significantly improved performance over existing techniques. By leveraging only phase characteristics, this approach provides a robust and practical solution for blade clearance calibration and health monitoring.