Aim at technical status of corresponding products at home and abroad, and test requirements for defense equipment against electronic countermeasures, a wideband microwave vector signal generator is designed. First, vector modulation is implemented on 300 MHz intermediate frequency carrier, the frequency of vector signal is expanded to 4 GHz through RF converting and filtering, On the basis, after micromave frequency converting and filtering, the frequency is extended to 18 GHz. A electrically tunable microstrip filter is used for RF filtering, switching band pass filter module is used for microwave filtering, it can achieve low loss, small ripple, good group delay and good rejection outside band, maintaining modulation quality and spectral purity of vector signals. Calibration of vector modulator using precise internal calibration voltage, eliminating the residual carrier, quadrature offset, I/Q amplitude imbalance of modulation channel and the influence of frequency conversion channel, ensure the quality of vector signals in the whole frequency range and at different operating temperatures. Experiments show that the frequency range of signal generator can reach 300 kHz～18 GHz, stray is less than -30 dBc, error vector magnitude is less than 4％.