The paper deals with the dynamic analysis of microstrip structures. It is shown that the mixed-potential integral equation for stratified media, which was introduced in a previous publication, provides a rigorous and powerful approach. The Green's functions belonging to the kernel of the integral equation are expressed as Sommerfeld integrals, in which surface wave effects are automatically included. A two-dimensional moment's method using subsectional basis functions has been chosen. Thus, microstrip patches of any shape can be analysed at any frequency and for any substrate. Practical numerical aspects are carefully discussed, and special numerical devices are introduced to reduce computation time without loss of accuracy. Complete results for a rectangular patch and for a slotted patch are given and compared with measured values. Radiation patterns corresponding to the ideal situation of a substrate with infinite transverse dimensions are presented for a rectangular patch.