Radar System Engineering

72 PROPERTIES OF RADAR TARGETS [SEC.37
radar camouflage of U-boats. The type of absorber that was actually
put into service was of the interference kind. The dielectric constant
and permeability were produced by a high concentration of spheroidal
metal particles (carbonyl iron). The concentration of metal was80 per
100
10
z ~
k
$
1
J=
(i
0.1
0 51015202530354045 505560
Anglewith normalto plate indegrees
F]~. 3.5.—ElTect of absorbingmaterial on energy returnedfrom a flat plate at various
zm,glesofincidence. Curves: diffraction pattern of a metal plate, electric vector of radiation
normalto Planeof incidehce. Curveb: plate covered with absorbingmaterialof high
dielectricconstant. Curve c: plate covered with magneticabsorbingmaterialoflowdielectrlc
c0n9tant.
cent by weight, and values of dielectric constant and permeability were
e=7, p= 3.5.
An absorber of the second kind was also developed in Germany. It
consisted of a series of layers whose conductivity regularly increased with
depth. The layers were separated by a foam-type plastic whose dielectric
constant was close to 1. The absorption was excellent from 4 to 13 cm.
However, the complete absorber was a rigid structure 2+ in. thick, and it
was never actually used