This paper presents an efficient full wave numerical analysis method for three dimensional microstrip structures inside a stratified media. The method can analyze both vertical and horizontal components of the currents. The conducting structures are modeled using a mixed potential integral equation. The boundary conditions on the interfaces between dielectric layers are satisfied through the use of appropriate dyadic Green's functions in the spectral domain. The numerical evaluation of the Sommerfeld integrals that are encountered during the transformation of the Green's function to the spatial domain is avoided using the complex images method (CIM). A modified CIM is proposed for efficient solution of vertical conductors currents. The modification maintains the rigorous nature of the full-wave analysis method while achieving the same efficiency for both vertical and horizontal components of currents. The resulting algorithm is found to be a versatile and efficient numerical analysis tool for microstrip antennas. The accuracy of the method is tested against commercially available full wave analysis packages. Good agreement is obtained for a wide class of stacked microstrip antennas.