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Only perfect conductors can reflect electromagnetic (EM) waves
perfectly. In reality all surfaces are to some extent dielectrics and
have associated 
, 
and 
values of permeability,
permittivity and conductivity respectively. We can define the loss
that is incurred by non-ideal conductors as a reflection coefficient,
, where 
. 
and 
are the reflected and incident electric
fields respectively. The reflectivity coefficient varies according to
the angle of incidence, the polarization of the incoming wave, its
frequency and the characteristics of the surface. For horizontal
polarizations the coefficient may be generalised to a constant value,
although in reality it does vary. Dempsey [85]
shows graphs of reflection coefficients with values of , the
reflection coefficient, between 0.6 and 1.0. For vertical
polarizations however, the coefficient varies between 0 and 1.