Abstract: A 9.5-10.5GHz balanced I-Q vector modulator was designed and fabricated on Rogers5880 with a dielectric eonstant of 2.20±0.02 and thickness of 254μm.Measured results are:the insertion loss of balanced I-Q vector modulator is（7.5±1）dB,the return loss of the circuit is above 16dB,and RMS phase error is less than 5°,the maximum amplitude unbalance is 0.5dB.Some measures to optimize circuit performance were proposed at the end.