Abstract: An efficient method for the calculation of input impedance of probe-fed microstrip antennas is proposed. The equivalent magnetic current frill is used to model the coax aperture. The characteristics of the electric field excited by the equivalent magnetic current frill are researched and an improved integration path is proposed to avoid the singularities of the electric field. Based on this, a refinement treated to the mesh at the junction is adopted to model the acute variation of the current, and spatial moment of method is used to calculate the input impedance of square and circle microstrip antennas with closed-form Green’s Functions for stratified media. The numerical results are presented to validate the method.