PURPOSE: To change the number of targets which can be radiated simultaneously and to change an angular resolution by controlling a switch and a switching device electrically without changing the constitution and the arrangement of an array antenna.

CONSTITUTION: The input system of a switch 20 is increased to the number of terminals corresponding to the number of targets, and a switching device 19 which electrically changes over the number of targets and an angular resolution is installed. Then, when the number of targets is expanded from two to four, the usage form of the switch 10 and the switching device 19 is changed over, and an element corresponding to a target 1 is newly allocated to the target 1 and a target 3. Regarding a target 2, an element antenna corresponding to a total of four targets can be arranged in the same manner. At this time, an element interval is set at 1.4 times, and the angular resolution can be expanded in the same manner. As a result, when the number of targets is increased or decreased, the angular resolution can be changed. In this manner, the number of targets which can be radiated simultaneously can be expanded to four, eight,..., and the angular resolution can be controlled.