  Electromagnetic response of a finite-width two-dimensional electron stripe is
theoretically studied. It is shown that retardation and radiative effects
substantially modify the absorption spectrum of the system at microwave
frequencies, leading to a non-trivial zigzag behavior of the
magnetoplasmon-polariton modes in magnetic fields, similar to that recently
observed by Kukushkin et al. [Phys. Rev. Lett. {\bf 90}, 156801 (2003)].
