This paper presents an efficient technique for eval-uating Green's functions associated to layered media, when for-mulated as Sommerfeld integrals in the space domain. The keystep in the formulation is that Sommerfeld integrals are computedchoosing a suitable integration path which is closed through theimaginary axis of the complex spectral plane. It is shown that withthis original choice of the integration contour, the numerical effortusually involved in the evaluation of Sommerfeld integrals can begreatly reduced, specially when large source-observer distances areinvolved. One asset of this technique is that it can be easily incorpo-rated into integral equation based CAD packages for the efficientanalysis of complex printed microwave circuit and antennas. In ad-dition, the theoretical developments needed to set up the numericalalgorithm throw a new light on the asymptotic behavior of the lay-ered media Green's functions for large source-observer distances.
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