where it is assumed that both the incident electric field and incident magnetic field have been decomposed into two parallel and perpendicular polarizations and R<sub>||</sub> and R<sub>⊥</sub> denote the reflection coefficients at the interface between air and the impedance surface for the cases of parallel and perpendicular polarizations, respectively. These reflection coefficients are given by:
:<math> R_{\|} = \frac{\eta_0\cos\theta - Z_s} {\eta_0\cos\theta + Z_s} </math>
:<math> R_{\perp} = \frac{Z_s\cos\theta - \eta_0} {Z_s\cos\theta + \eta_0} </math>
:<math> R_{\|} = \frac{Z_s - \eta_0\cos\theta} {Z_s + \eta_0\cos\theta} </math>
where θ is the incident angle between the propagation vector of the incident field and the normal to the surface and <math>\eta_0 = 120\pi \; \Omega</math> is the intrinsic impedance of the free space.