Method of Moments (MoM)/Green&rsquo / s function formulation is developed for the analysis of electromagnetic radiation from planar rectangular microstrip antennas with different feeding techniques. Investigated structures are microstrip line fed patch antenna, proximity coupled patch antenna and slot coupled patch antenna. For all these structures equivalent problems are defined. Then, integral equations where currents are the unknowns are obtained from boundary conditions and by using spectral domain representation of Green&rsquo / s functions. Finally, MoM is applied to convert these integral equations to a system of linear equations. Currents on the conducting surfaces as well as equivalent magnetic currents on the apertures are modeled as a sum of piecewise sinusoidal subdomain basis functions with unknown coefficients which are calculated by solving the system of linear equations. Based on the formulations provided in this study, a Fortran code is developed. Numerical results calculated by using the code are presented in the form of patch and line currents and input impedances. Presented results are in good agreement with the results given in the literature.