Radar frequency.
The frequency of the radar in use has a marked effect on the
amount of signal that is returned from a given sized reflector. Higher frequency or
shorter wavelength radars produce much brighter returns. Fortunately, the majority of
marine radars operate in the relatively high frequency X or 3 cm band.
Radar cross section.
A worldwide standard has been set for making meaningful
comparisons of various reflective surfaces: the “effective radar cross-section,”
referred to as
σ
m. This value,
σ
m, is useful in stating a “figure of merit” for the per-
formance of radar reflectors.
A reflector’s performance, the
amount of signal that it will
reflect, is stated in terms of
the diameter of a metal
sphere which would produce
an equivalent radar response
(Fig. 5).
8
Figure 5
On a curved surface, such as a metal mast, only a very small area will reflect the
signal back; the rest is lost at numerous acute angles.
Reflections from a corner reflector with circular plates, such as Echomaster, are
almost as effective as a plain, flat metal surface.
