Propagation speed of evanescent modes

The group velocity of evanescent waves tin undersized waveguides, for insta nce) was theoretically predicted, and has been experimentally verified, to be superluminal (nu (g)>c). By contrast, it is known that the precursor spe ed in vacuum cannot be larger than c. In this paper, by computer simulation s based on Maxwell equations only, we show the existence of both phenomena. In other words, we verify the actual possibility of superluminal group vel ocities, without violating the so-called (naive) Einstein causality.