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.
In the case of an impedance-matched surface, one can write:
:<math> R_{\|} = R_{\perp} = \frac{\cos\theta - 1} {\cos\theta + 1} </math>
<table>