A three-layer microstrip structure is analyzed using the exact image method. From the Fourier domain reflection coefficient an asymptotic term and the surface wave poles are extracted, and the remaining function is expanded into a sum of pole terms (Mittag-Leffler expansion). Hence the inverse Laplace transform of the coefficient can be presented simply as a well converging series of exponential functions. As an example, it is shown how the method is applicable to shielded microstrip structures. The detailed image functions are shown for a microstrip antenna above a two-layer biological medium, using as the three layers, substrate, skin, and fat.
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