the methods which are used to analyze microstrip antennas, are divited into three categories: empirical methods, semi-empirical methods and full-wave analysis. empirical and semi-empirical methods are generally based on some fundamental simplifying assumptions about quality of surface current distribution and substrate thickness. thses simplificatioms cause low accuracy in field evaluation. full-wave analysis is an analytical method which is not based on any approximations. so this method is more accurate than the other ones. in this thesis a computational analysis for in infinite planar of rectangular microstrip patch antenna in x-band, is performed. the theory is based on full-wavw analysis. standard galerkin / moment method is used to evaluate electromagnetic fields. dyadic greens function is used to model the periodic structure of array. with this model, mutual coupling between elements, is taken into account. it is an important advantage of this analysis. in addition to mutual coupling between elements, surface current density which flows on the feed conductors, is considered as an attachment mode. this mode models the rapid variation of current density near the feed point. on the basis of following theory, variation of the antenna characteristics such as input impedance of antenna, radiation power, efficiency. gain and directivity versus operating frequency, dielectric constant, thickness of dielectric layer, element spacing in array structure, patchs dimensions and feed position on each patch, are studied.