Electromagnetic phenomenon is described by Maxwell equations, and solutions of \(\textbf{E}\) and \(\textbf{H}\) from their sources can be obtained on solving these equations; a procedure that will be discussed in Part IV. In this chapter, we limit our discussion to source-free regions. Also, let us initially assume that the region under consideration is free space. Extension to isotropic dielectric-magnetic medium will be easily made in frequency domain.