Radar System Engineering

68 PROPERTIES OF RADAR TARGETS
[SEC.3.6
A ~nx = ~.
where a is the edge of the corner. This yields for the maximum
section
4 7ra4
‘m” = 3 F’
cross
showing that the free-space range at which a corner reflector can be seen
by a given radar is proportional to its linear dimensions. Figure 3.4
shows the maximum cross section at various radar frequencies as a
function of edge length.
As a/X (and consequently the gain of a corner reflector) is increased,
greater attention must be paid
to the mechanical construction
of the reflector. When the angle
between one pair of planes differs
from 90°, the triply reflected return
from the corner splits into
two divergent beams, with a con-
FIG. 33.-A cluster of corner
reflectors.
1,~
Edge(a) of comer in cm
FIG. 34.-. Maximum scattering crosssection
of triangularcorner reflector.
sequent reduction in signal return. If two angles are in error, there
are four beams; if all three angles are wrong, six beams result. The
theory of the effect of errors’ yields the result that a loss in returned
signal of 3 db is caused by a displacement of the outer edge of the corner
of about A/2. This limitation requires extremely close attention to the
mechanical construction of corner reflectors of high gain. It also presents
the possibility of applying modulation to the reflection from a corner by
slight motion of one side.
3.6. Target Shaping to Diminish Cross Section.-A corner reflector
gives a radar return by specular reflection for nearly all directions of
1R. C. Spencer, “ Optical Theory of the CornerReflector,” RL Report No. 433,
Nfar,2, 1944,