Microstrip antennas are widely applicable, due to their special properties such as compact structure, low weight, being cheap, simplicity of applications and being integrated to printed circuit boards. In addition to these advantages, they suffer from some defects such as low bandwidth and low gain. These defects are mainly because of existence of surface waves. There are various solutions to lower the harmful effects of surface waves. One of such ways is to create a band gap structure around the antenna in order to omit the surface waves.This band gap is dependent on relationship with structure parameters. In this band, the structure avoids the propagation of surface waves and enhances the performance of the antenna. Till now, different types of band gap structures with different shapes are offered and designed to omit surface waves in different frequency bands. In this thesis, a novel structure of band gap structures is proposed and it is analyzed by both analytical and numerical method. The proposed structure is composed of two insulator layers in which the band gap structure is located at top of them. Dimensions are chosen so that the surface waves trap into the top layer in which EBG structure exists and deleted. The height of the lower layer is used for optimization of the structure. The EBG bandwidth is considered as a variable in this scheme since EBG structure parameters is under our control and don’t depend on the main antenna structure. So changing the EBG structure parameters, we are able to shift the frequency band to somewhere compatible with main antenna characteristics. Finally we is designed an antenna with circular polarization. In this thesis, main characteristics of antenna such as gain, bandwidth axial ratio side lobe level are investigated. Keywords:Band gap structure,Surface wave,dispersion relation