Richard Clark wrote:
"As a closing comment about the Brewster Angle, nearly every laser uses
this in their output window."

A plane wave strikes the earth and its reflection leaves at an angle
which equals the angle of incidence.

The strength of reflected wave to incident wave is a vector ratio called
the reflection coefficient.

Strength of the fields just above the earth is the vector sum of the
incident and reflected waves, taking into account both time phase and
space orientation.

The reflection coefficient`s value depends on the characteristics of the
reflecting surface. If the earth were a perfect reflector, the reflected
wave would be as strong as the incident wave and the value of the
reflectopn coefficient would be 1.

With a perfect reflector, the horizontal components of the electric
incident and reflected fields exactly cancel (Terman`s words) at the
reflecting surface. On the contrary, the vertical components of the
electric fields of the incident and reflected waves do not cancel, but
add together at small reflection angles.

For imperfect earth, magnitude of the reflection coefficient is less
than 1, and the angle of the reflected wave will be slightly shifted.

The incidence angle has a complicated effect on vertically polarized
waves. At grazing incidence, the reflection coefficient is 1 on an angle
of 180-degrees. The reflected wave is as strong as the incident wave,
but its phase is reversed by the reflection. However, with vertical
incidence, the phase shift is very small and the reflection coefficient
is less than 1 with real earth.

Between the extremes of grazing incidence and vertical incidence,
magnitude of the reflection coefficient goes through a minimum at a
small angle of incidence and reflection. It depends on the
characteristics of the reflector (soil). This puts a small reduction of
radiation at a low vertical angle called the Brewster angle.

At the Brewster angle, the magnitude of the reflection coefficient for
vertically polarized waves will be much less than 1 and so tends to
reduce radiation at some low vertical angle, but not at zero degrees..

My 19th edition of the ARRL Antenna Book calls this minimum in the
vertical radiation pattern, the "Pseudo-Brewster Angle" (PBA) because
its effect was noticed in the reflection (glare) of sunlight from water
surfaces when the sun was low. It was named for Sir David Brewster, a
Scottish Physicist (1781-1868). PBA is described on page 3-6.

Best regards, Richard Harrison, KB5WZI