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_{\perp} = \frac{ \frac{Z_s}{\eta_0} eta_s \cos\theta - 1} {\frac{Z_s}{\eta_0} eta_s \cos\theta + 1} </math>
:<math> R_{\|} = \frac{\cos\theta - \frac{Z_s}{\eta_0} eta_s } {\cos\theta + \frac{Z_s}{\eta_0} eta_s } </math>
where η<sub>s</sub> = Z<sub>s</sub>/η<sub>s</sub>, 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.
From the surface impedance boundary condition, it can easily be shown that