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.