This paper presents an efficient modelling technique for partially reflective surface (PRS) antennas, based on the substitution of the actual detailed PRS by an uniform equivalent surface impedance. The properties of the equivalent surface are rigorously extracted from the simulation of the detailed PRS unit cell in its periodic environment. The model yields accurate results in considerably shorter time than when the PRS with detailed geometry is employed, thereby enabling the efficient analysis and design of such antennas, which is especially important in the case of their reconfigurable implementation. © 2011 EurAAP.