Abstract <p>Electrodynamic analysis of a 3D model of a two-layer resonator with subwavelength gratings of parallel strip conductors at the boundaries is used to study the propagation of plane linearly polarized electromagnetic waves at oblique incidence on its surface. For two orthogonal polarizations, the cases of parallel and perpendicular orientation of the plane of incidence of waves on the external gratings of conductors are considered. It is found that in the case of parallel orientation of the plane of incidence and when the electric field vector of the incident wave is located in the plane of incidence, the quality (Q) factor of the half-wave resonance first falls to a minimum when approaching the Brewster angle upon an increase in angle of incidence φ, and then increases, tending to the own Q factor of the resonator at φ → 90°. In the case of the perpendicular orientation of the plane of incidence, but when the electric field vector is orthogonal to this plane, the Q factor of the half-wave resonance increases constantly with increasing angle φ, also tending to its own Q factor at φ → 90°. Frequency shifts are investigated for “strong,” “medium,” and “weak” coupling of the resonator with the external space. For these cases, a nonmonotonic behavior of the polarization decoupling of the resonator-polarizer with increasing angle of incidence in two orthogonal planes is demonstrated.</p>