AN EFFICIENT METHOD FOR THE COMPUTATION OF MIXED POTENTIAL GREEN'S FUNCTIONS IN CYLINDRICALLY STRATIFIED MEDIA

Closed-form mixed potential Green's functions (MPGFs) for cylindrically stratifled media are derived in terms of quasistatic- wave and surface-wave contributions. In order to avoid possible over∞ow/under∞ow problems in the numerical calculations of special cylindrical functions such as Bessel and Hankel functions, a novel form of the spectral-domain MPGFs is developed. Then, a two- level methodology is used for the approximation of the spectral- domain MPGFs. In the flrst step, the qusistatic components are extracted from the spectral-domain MPGFs, and then transformed into the space domain with the use of the Sommerfeld identity and its derivatives. In the second step, the remaining parts of the spectral-domain MPGFs are approximated in terms of pole-residue expressions via the rational function fltting method (RFFM). The proposed method is e-cient and fully automatic, which avoids an analytical cumbersome extraction of the surface wave poles (SWPs), prior to the spectrum fltting. In addition, this method can evaluate the spatial-domain MPGFs accurately and e-ciently for both the near- and far-flelds. Finally, numerical results for the spatial-domain MPGFs of a two-layer structure are presented and discussed.