physics [SI.Two methods to excite the microstrip leaky wave antenna are proposed and investigated in this paper. A full-wave spectral domain integral equation method combined with fundamental mode sampling technique is applied to determine the reflection coefficient of the excitation source. Dependence on structural parameters such as line width, overlap length and line spacing is fully analyzed to obtain the optimum excitation for microstrip leaky wave antenna. Also, an experimental setup is performed to check the validity of our numerical results and identify the radiation nature of the microstrip line higher order modes.