In this thesis, a two-dimensional active phased array antenna without phase shifter is studied for two-dimensional beam scanning. A designed two-dimensional oscillator-type active array antenna, radiation elements and the oscillator circuits were combined with via-hole and coupled by slot on the opposite ground plane. The operating characteristics are analyzed and experimentally demonstrated , The two-dimensional $4 imes4$ elements were designed for the proper coupling strengths and coupling phases by adjusting the width, length and offset position of slot-lines. The fabricated active phased array antenna shows the beam shift characteristics capable of scanning from $-17^{circ}$ to $18^{circ}$ with respect to broadside in one dimension, from $-5^{circ}$ to $10^{circ}$ in two dimension. The experimental results show that it is possible to use the oscillator-type active phased array antenna as a two-dimensional planar array antenna.