A polarization diversity antenna system includes antenna elements having first to fourth slotlines bent at right angles so that the second slotline is provided adjacent to the first slotline, the third slotline is diagonally opposite to the first slotline and provided adjacent to the second slotline, and the fourth slotline is provided adjacent to the third slotline and diagonally opposite to the second slotline, and a switching network in which coupling units are formed between ends of the horizontal slotlines and between ends of the vertical slotlines that are close to intersections of the vertical and horizontal slotlines to determine polarization.