Microwave response of a two-dimensional (2D) electron stripe, supplied by two semi-infinite side contacts, is theoretically studied taking into account retardation and radiative effects. Absorption spectra of the stripe are calculated as a function of the microwave frequency omega, magnetic field B, parameters of the 2D electron gas and of the contacts. It is shown that the contacts substantially modify the position, the linewidth and the strength of the absorption resonances, leading for instance to the inversion of the absorption maxima of the right and left circularly polarized radiation in magnetic fields.