Microstrip patch antennas are resonant antennas which are usually operated near a natural frequency. For isolated patch antennas which have simple geometries, the surface current distributions in the vicinity of these natural frequencies are, for the most part, known (or can be accurately approximated). This fact has been used in full wave analysis, which employs entire domain basis functions to model the current distribution. However, more complicated antenna structures have more complicated current distributions. Instead of recalculating the current distributions at each frequency, it is proposed to find the current distributions of a particular antenna structure at a few natural frequencies. Once these current distributions have been determined, they will be used to predict antenna performance at frequencies which are in the neighborhood of the natural resonances. The example considered is a single layer microstrip patch antenna. >