Radar System Engineering

PROPERTIES OF RADAR TARGETS [SEC.37
(12)
(13)
In these equations a is the amplitude reflection coefficient.
The boundary conditions that the tangential components of E and of
H be continuous at z = O immediately yield
(14)
It is clear that a will be O if c = p. 31aterial with such a property \vill
serve as an absorber of the second kind, providing c has a considerable
imaginary part. If the refractive index n and the absorption index K are
introduced by the familiar relation
Eq. (14) can be rewritten
n+iK=16L, (15)
~=?t+~K-Ji
n+iK+p”
Let us now examine the behavior of an absorber of the first kind in
which the internal reflection occurs from a metal surface at the plane
z = – d. It will be assumed that .2 is small compared to n’. The
calculation of the resultant reflection can be made by summing the
emergent rays and adding this sum to the wave reflected from the plane
z = O. Let g = 4rdK/~ be the damping of a wave for one passage from
the front to back surface and return. Let @ = -lmd,’x be the change in
phase for the same passage. Finally let p be the transmission coefficient
of the front surface. When the index of refraction is high, Eq. (16) gives
If it is remembered that the coefficient for the internal reflection at the
front surface is – a, the following table can be constructed.
TABLE 31.-EMERGENT RAYS AFTEE MULTIPLE REFLECTION
No. of passages through .kmplitudeof emergent
the layer
Ivave
o
1 De-o.: B
2 —a@-P@ B
3 ~2~e3[–o~r+lp
m ( –a)m-jgem(:c+i p
(16)
(17)