为了更好地对微波信号进行频率测量,采用了一种基于相位调制和强度调制相结合的瞬时测频方法。一束连续波光源通过耦合器被分成两路,未知微波信号分别同时经过相位调制器和强度调制器从而对载波进行调制,之后进入两段长距离的单模光纤中。在光纤中由于色散引起的微波功率损耗的特点,可以获得单调变化的频率-幅度的映射关系,继而通过光电探测的微波信号输出功率比得到幅度比较函数；另外还分析与实现了测频范围与测频精确度的优化。结果表明,该方案结构简易,能够快速精准地测量出未知信号的频率,测量范围可以达到0.5GHz~53GHz,测量误差小于±200MHz。该方法可以有效地测量微波信号频率,可靠性强,适用范围广。

In order to measure the frequency of microwave signal better, an instantaneous frequency measurement method based on phase modulation and intensity modulation was adopted. A continuous wave light source was divided into two channels by a coupler. Unknown microwave signals passed through both phase modulator and intensity modulator respectively. Accordingly, the carrier was modulated. Then it entered into two long-distance single-mode fibers. Because of the characteristics of microwave power loss caused by dispersion in optical fibers, the mapping relation between frequency and amplitude of monotone change was obtained. Then the amplitude comparison function was obtained by output power ratio of microwave signal detected by photoelectric method. In addition, the range and accuracy of frequency measurement were optimized. The results show that, the structure of the scheme is simple. It can measure the frequency of unknown signal quickly and accurately. The measurement range can reach 0.5GHz~53GHz. The measurement error is less than ±200MHz. This method can effectively measure the frequency of microwave signal and has strong reliability and wide application range.