Padé approximation for time-domain plane wave reflected from a lossy earth

To deal with the behaviour of wire structures subjected to electromagnetic waves with the finite-difference time-domain (FDTD) method, it is necessary to establish the external electromagnetic excitation in time-domain. For a homogeneous lossy half-space problem, the Fresnel reflection coefficients for arbitrary polarization plane wave are usually multiplied by the pulse spectrum in the frequency domain and the result is transformed into the time-domain. In this paper, an accurate method based on the Padé approximation theory in conjunction with the partial fraction expansion is used, and leads to expressions of the field above a homogeneous lossy earth that can analytically be transformed into the time-domain. The influence of the common degree of the numerator and denominator of the Padé approximant on the accuracy of the proposed method is discussed.