I. Introduction
The analysis of radiation and scattering problems involving multilayered media using method of moments (MoM) and mixed potential integral equation approach requires spatial-domain Green’s functions [1]–[5]. Spatial-domain Green’s functions can be formulated as a solution of Sommerfeld integrals (SI) [6]. The kernel of SI contains a product of spectral-domain Green’s function (SDGF) and Bessel/Hankel function. Therefore, the integrand is oscillatory, slowly decaying as well as have singularities along the integration path. This makes the solution of SI very difficult and challenging.