A method to reduce the cost of a phased array antenna involves the use of subarrays composed of several element antennas and the installation of a phase shifter to each subarray, rather than to each element antenna. In this method, it is important to suppress grating lobes because the periods of the subarrays are usually large compared with the wavelength. This paper proposes an aperiodic array antenna using one type of diamond tile as subarrays, which has both low cost and low sidelobe characteristics.