In order to realize an active phased array antenna, a phased array behavior of a microwave unilaterally coupled active antenna array which is controlled by frequency changes of the oscillators has been investigated. The active antenna array is couposed by coupling active antennas which consist of patch antennas and parallel feedback type oscillators with unilateral characteristics. A tuning range of the free-running frequency of the oscillator is widened by inserting a varactor diode into a feedback loop of the oscillator. An experiment of a system of two oscillators without antennas has confirmed the phased array behavior. Electromagnetic waves radiated from two, three and four active patch antenna array were successfully scanned.