A generalized method is presented to determine the resonant frequency of slot-loaded rectangular microstrip patch antenna by equating its area to an equivalent area of a rectangular microstrip patch antenna. The computed results are in good agreement with the reported simulated and measured results. (C) 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 445-448, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.214901