An Archimedean plannar spiral antenna mounted on the grounded double-layer is investiged. Based on the substrate superstrate Green' s function in terms of Sommerfeld-type integrals for a horizontal Hertzian dipole on the superstrate, the current distribution along the spiral arm is determined by using an integral equation with the moment method, the input impedance, radiation pattem, axial ration and power gain are calculated on the basis of the obtained current distrbution, which is very important for optimum design of the printed wire antennas. Experimental results show that the numerical method is correct .