A method for the computation of radiation patterns of microstrip antennas on a finite ground plane is presented. The method is based on the geometrical theory of diffraction and the 2D physical optics model. The diffraction of space waves and surface waves is taken into consideration. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 40: 26–29, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.11276