Explanation: the beam width is measured between the points on the radiation curve that are 3 db down from the maximum amplitude of the curve. the maximum amplitude of the pattern occurs at 0° and 180°. the 3-db down points are 70.7 percent of the maximum. the angle formed with two lines extending from the center of the curve to these 3-db points is the beam width. the beam width is 90°. the smaller the beam width angle, the more directional the antenna.