In recent years, microstrip antennas have been one of the most innovative topics in antenna theory and design. The basic idea of microstrip antenna came from using printed circuit technology not only for the circuit component and transmission lines but also for the radiating elements of an electronic system. They are used in a wide range of modern microwave applications because of their simplicity and compatibility with printed circuit technology. This paper is to make a comparative study of the radiation pattern of circular patch antenna excited in transverses magnetics modes. This paper is based on the model of the resonant cavity approach and intended for RFID application around a resonance frequency of 2.45GHz.