Vector modulator can be employed in active phased array antenna(APAA)as a replacement of conventional digital phase shifter and attenuator for its capability of simultaneously realizing millimeter-wave direct carrier modulation on phase and amplitude.A millimeter wave vector modulator was realized with advanced GaAs pHEMT process, and onchip measurement has shown that -12~-40 dB amplitude modulation and 360° phase modulation was achieved. A Ka band 1×8 array experimental APAA composed of vector modulators was designed and proved to steer the beam scanning effectively. It was demonstrated that APAA based on vector modulation technique is feasible.