An approach based on Hilbert transform to extract coherent modes from Doppler backscattering system under imbalances...

This paper presents an effective method to extract coherent modes from imbalanced data of a Doppler backscattering system. Phase and amplitude imbalances often arise from asymmetries in the quadrature mixer or amplifier outputs, and the proposed approach leverages the Hilbert transform, which provides a 90° phase shift to the original signal. To emulate experimental conditions, simulated in-phase and quadrature signals with phase and amplitude imbalances are generated. The Hilbert transform of the in-phase component is compared to the quadrature component, and the consistency between them improves as the Doppler shift increases. Provided that the Doppler shift is at least half the signal bandwidth, the power spectra obtained from the in-phase signal and its Hilbert transform exhibit signal-to-noise ratios nearly identical to those of standard quadrature data. Experimental results show good agreement with simulations. The robustness of this method is further demonstrated using experimental data with severe imbalances, where traditional analysis methods fail.