Causal explanation for observed superluminal behavior of microwave   propagation in free space
  In this paper we present a theoretical analysis of an experiment by Mugnai and collaborators where superluminal behavior was observed in the propagation of microwaves. We suggest that what was observed can be well approximated by the motion of a superluminal X wave. Furthermore the experimental results are also explained by the so called scissor effect which occurs with the convergence of pairs of signals coming from opposite points of an annular region of the mirror and forming an interference peak on the intersection axis traveling at superluminal speed. We clarify some misunderstandings concerning this kind of electromagnetic wave propagation in vacuum. 
W. A. Rodrigues Jr, Dario S. Thober, Ademir L. Xavier Jr (CPTEC -   Salesian Universitary Center, Campinas, SP, Brazil)