PURPOSE: To provide a sharp directivity over a wide frequency range by arranging plural elements on a plane and feeding power to the elements so as to produce the relative complex amplitude distribution by means of the three-element combined type back lobe cancelling method.

CONSTITUTION: Radiation elements I∼IV and 0 are arranged on a circle having a diameter (d) at an interval of 90°C each and at the center of the circle. Further, 6dB attenuators A1∼A4, 12 3dB couplers shown in caption H, circuit elements +Δ1∼+Δ4 lengthening the line length by d/2, circuit elements -Δ1∼-Δ4 shortening the line length by d/2, and a broad band four-distributor 11 are provided. Then the antenna is constituted in a way that all route lengths from feeding terminals x+, x-, y+, y- to the radiant elements are all identical. Thus, the complex amplitude distribution of the elements I, O, III in feeding power from the terminal x+ satisfies the exciting condition of the three-element combined type back lobe cancelling method. The complex exciting distribution of the elements I, O, III in feeding power from the terminal x- is equal to the distribution replacing the elements I and III in feeding power from the terminal x+. Thus, in feeding power from the terminal x-, the negative direction of the X axis is used as main radiation direction. The distribution in feeding power from the terminals y+ and y- is similar.