Berenger and leaky modes in lossy microstrip substrates terminated by a perfectly matched layer

It is shown that the dispersion relation lot a lossy microstrip substrate terminated by a perfectly matched layer allows two sets of zeros. For a strongly absorbing perfectly matched layer, the first set corresponds to the leaky modes of the lossy microstrip substrate, whereas the second set mainly depends oil the characteristics of the perfectly matched layer. This last set of modes we called the Berenger modes. Analytic expressions are derived for these two sets of zeros in the quasi-static limit.