A method to design an electromagnetically coupled microstrip slot antenna is proposed. The method is based on an equivalent circuit approach, where the slot part of the antenna is analyzed by the FDTD method and the stub part is regarded as a transmission line. In this paper, the electromagnetically coupled slot antennae are designed using the equivalent circuit method in 2-10GHz. As a result, it is concluded that this method is applicable if the stub length is longer than the width of microstrip line. It is also shown that the method is suitable for designing an offset feeding slot antenna.