The nearfield pressure and the radiation impedance for an infinite phased array of circular pistons (with the same velocity magnitude) in a rigid plane baffle are calculated. A slowly convergent infinite series expression for the pressure, obtained from the appropriate Green's function, is transformed by the use of Poisson's sum formula into a more rapidly convergent infinite series expression. Numerical results are presented. A rough estimate of the location and value of the maximum pressure in the nearfield is obtained under certain restrictions. The radiation impedance of a piston in the infinite array agrees well with the average radiation impedance of a piston in a large finite array.