To provide an array antenna for effectively suppressing grating in a sub-array beam by changing the spacing of the sub-array antenna for a fixed portion, and to provide its layout method.

The array antenna includes the plurality of sub-array antennas 4 composed of a plurality of element antennas. The sub-array antennas are arranged so as to allow the spacings d(1), d(2) to d(Ms-1) of the center of phases between the adjacent sub-array antennas #s1-#sMs successively increased along the arrayal direction for the fixed portion, or arranged so as to allow the spacing of the center of the phase between the adjacent sub-array antennas increased for the fixed portion when compared with one of the spacings of the center of the phases between other adjacent sub-array antennas.