Abstract An approach of instantaneous microwave frequency measurement with improved resolution is proposed and analyzed. The primary component employed in the proposal is a polarization modulator (PolM) followed by a linear polarizer (LP) and a spool of dispersive fiber. To obtain a flexible amplitude comparison function (ACF), the polarization state between the PolM and the LP should be properly adjusted. It is found that the notch point of the ACF can be widely shifted by simply adjusting the bias voltage applied to the PolM, especially, a greater first-order derivative of the ACF ensures that the measurement resolution can be improved when compared with the work in the reference.