We predict the enhanced transmissivity of modulated slabs of layered superconductors for terahertz radiation due to the diffraction of the incident wave and the resonance excitation of the eigenmodes. The electromagnetic field is transferred from the
irradiated side of a slab of layered superconductor to the other one by excited waveguide modes (WGMs) which do not decay deep into the slab, contrary to metals, where the enhanced light transmission is caused by the excitation of the evanescent surface waves. We show that a series of resonance peaks (with $T sim 1$) can be observed in the dependence of the transmittance $T$ on the varying incidence angle $theta$, when the dispersion curve of the diffracted wave crosses successive dispersion curves for the WGMs.
