Page 180 - Satellite Communications, Fourth Edition

160 Chapter Six

Figure 6.15 A parabolic reflector.
(Courtesy of Scientific Atlanta, Inc.)

commonly used form of parabolic reflector has a circular aperture, as
shown in Fig. 6.15. This is the type seen in many home installations for
the reception of TV signals. The circular aperture configuration is
referred to as a paraboloidal reflector.
The main property of the paraboloidal reflector is its focusing prop-
erty, normally associated with light, where parallel rays striking the
reflector converge on a single point known as the focus and, conversely,
rays originating at the focus are reflected as a parallel beam of light. This
is illustrated in Fig. 6.16. Light, of course, is a particular example of an
electromagnetic wave, and the same properties apply to electromag-
netic waves in general, including the radio waves used in satellite com-
munications. The ray paths from the focus to the aperture plane (the
plane containing the circular aperture) are all equal in length.

Focus

Figure 6.16 The focusing property of
a paraboloidal reflector.