In this paper, the analysis of arbitrarily shaped microstrip antennas is described. The analysis method is based on the transmission - line matrix representation for the interior problem and the moment method for the problem along the peripheries of the patch. Using this method, the input impedance and other antenna parameters are calculated and compared with experimental results for a circular and an equilateral triangular microstrip antenna. For all of the results, theoretical and expreimental results are in good agreement and the validity of the method is confirmed. This analysis can also be used to analyze microstrip antennas with shorting pins.