Radar Cross Section (RCS) - MATLAB Simulations for Radar Systems Design - page 506

In general, an arbitrarily polarized electric field may be written as the sum of
two circularly polarized fields. More precisely,

E = + E L

(11.12)

R

where and are the RCP and LCP fields, respectively. Similarly, the
RCP and LCP waves can be written as

E R E L

E R = E V + jE H

(11.13)

E L = E V – E H

(11.14)

where and are the fields with vertical and horizontal polarizations,
respectively. Combining Eqs. (11.13) and (11.14) yields

E V E H

E H – jE V

E R = ---------------------

(11.15)

2

E H +

2

jE V

E L = ---------------------

(11.16)

Using matrix notation Eqs. (11.15) and (11.16) can be rewritten as

E R
E L

E H
E V

[] E H
E V

1
2

1 – j

= ------- =

(11.17)

1 j

E H
E V

1
2

E R
E L

E H
E V

11
j j

[] 1

–

-------

= =

(11.18)

–

For many targets the scattered waves will have different polarization than the
incident waves. This phenomenon is known as depolarization or cross-polar-
ization. However, perfect reflectors reflect waves in such a fashion that an inci-
dent wave with horizontal polarization remains horizontal, and an incident
wave with vertical polarization remains vertical but is phase shifted .
Additionally, an incident wave which is RCP becomes LCP when reflected,
and a wave which is LCP becomes RCP after reflection from a perfect reflec-
tor. Therefore, when a radar uses LCP waves for transmission, the receiving
antenna needs to be RCP polarized in order to capture the PP RCS, and LCR to
measure the OP RCS.

180°