Method for digital IQ frequency-domain calibration based on conjugate symmetry

To address the problem of IQ imbalance in the demodulation of radar intermediate frequency(IF) signals, this paper proposes a method for digital IQ calibration in the frequency domain based on conjugate symmetry.By modeling the IF signal at the presence of IQ imbalance, its spectral characteristic is first analyzed.The IF signal in the frequency domain can be decomposed into the unilaterally ideal signal and bilateral error signal.Among these, the bilateral error signal can be further decomposed into two components, the mirror-frequency error and the main-frequency error.Then, the relationship between the original spectrum of these two components and the spectrum of their conjugate counterparts is used to conduct some simple calculations for obtaining a frequency-domain estimate of the error signal.Therefore, the estimated error can be used to make the compensation in the IF signal.Experimental results from synthetic aperture radar imaging verify that the proposed method can effectively suppress both the mirror-frequency error and the main-frequency error from the IF signal and calibrate IQ imbalance to achieve the high performance of imaging. © 2021, The Editorial Board of Journal of Xidian University. All right reserved.