Abstract:Vector modulators are widely used in radar, navigation, instrument and satellite communication because of their small structure and low power consumption. Based on Max Gain Circle (MGC), analyzed the relationship between radius of the MGC and gain output of the vector modulator deeply, presents a general practical approach for gain control of a vector modulator, which can scan at full frequency in an automatic measurement system. This system implements the accurate controlling of the vector modulator gain output and its flatness, the precision and flatness of the vector modulator can be set up flexibly, and improves the efficiency of the performance and calibration of the vector modulator. The applied object is a chip named HMC1097LP4E of the Hittite Microwave, it takes about 1 minutes to get all required data,the precision of the MGC is 0.1dB and the gain flatness is less than 0.5 dB in the test frequency.