Based on an optical filter array with multiplied free spectral ranges(FSRs),an approach is proposed to perform instantaneous frequency measurement,with natural binary coded digital outputs achieved.An optical carrier is modulated by a microwave signal to be measured in terms of carrier-suppression and single sideband modulation,resulting in a single induced optical sideband which goes through an optical filter array.The optical filter array consists of several filters which are connected in parallel.The FSRs of these filters′ responses are multiply increased step by step and the filter corresponding to the most significant bit has the largest FSR.The filtered optical sideband is detected,compared and decided,such that the measured frequency is labeled by an N-bit natural binary digital code,which improves the coding efficiency and measurement accuracy.In simulation,4-bit digital outputs are achieved for frequency measurement within the range of 0-40 GHz.