Data-Based Quadrature Imbalance Compensation for a CW Doppler Radar System

A method for quadrature imbalance compensation in direct-conversion quadrature Doppler radar systems, based on data obtained using a mechanical target and an ellipse fit method, is reported. The proposed method can be used with different architectures of Doppler radar and eliminates the need to modify the radar in order to perform imbalance measurements. A mechanical target was used to provide sufficient motion to create a significant segment of an ellipse in the in-phase/quadrature trace to obtain correction factors with high accuracy. Parametric simulations were performed to analyze the accuracy of this technique in the presence of varying noise and target displacements. This method is compared with an existing phase-shifter-based imbalance computation technique for the measurement of known displacements and is shown to give consistent and more accurate results. Experimental data, consistent with simulations, demonstrates that accurate correction is obtained with 65% of the ellipse, resulting in a displacement error of less than 6%.