A method and system for calibrating a quadrature modulator. The method includes: determining a set of sideband calibration frequencies; for each sideband calibration frequency out of the set of sideband calibration frequencies: inputting an input signal having the sideband calibration frequency to the quadrature modulator; measuring a sideband signal power level; determining at least one calibration parameter in response to phase and gain imbalances expected at the measured sideband signal power level.