A semi-analytic solution for scattering from a semi-elliptical cavity with arbitrary orientation placed in a perfect electric conductor plane is suggested. By imposing the boundary conditions at an elliptical border, three independent equations containing the Mathieu functions series are extracted. Finally, the solution of the problem is reduced to the solution of a simple system of linear equations by using Mathieu function addition theorem and the orthogonal properties of the angular Mathieu functions. Some examples are presented to demonstrate the reliability and the accuracy of the proposed solution.
