training course on weather radar systems - RTC, Regional Training ...

MODULE A- INTRODUCTION TO RADAR
b) Circular polarization
In case of circular polarization as shown in Figure-3.6, the two orthogonal components (Ex-red
and Ey-green) of the electric field vector (E-blue) have exactly the same amplitude and are
exactly ninety degrees out of phase and they form a path (purple) in the plane while
propagating. In this case, one component is zero when the other component is at maximum or
minimum amplitude. Notice that there are two possible phase relationships that satisfy this
requirement. The x component can be ninety degrees ahead of the y component or it can be
ninety degrees behind the y component. In this special case the electrical vector will be rotating
in a circle while the wave propagates. The direction of rotation will depend on which of the two
phase relationships exists.One rotation is finished after one wavelength. The rotation may be left
or right handed. In other words, image of the electric field vector (E) will be circular and
electromagnetic wave will be circularly polarized. Circular polarisation is often desirable to
attenuate the reflections of rain with respect to aircraft.
Figure-3.6
c) Elliptical polarization
As shown in Figure 3.7, two components (Ex-red and Ey-green) of the electric field vector (Eblue)
are not in phase and either do not have the same amplitude and/or are not ninety degrees
out of phase. So the path (purple) formed in the plane while propagating will trace out an ellipse
and this is called as elliptical polarization. In other words, image of electric field vector E will
be elliptical and electromagnetic wave will be elliptically polarized. In fact linear and circular
polarizations are special cases of the elliptical polarization.
Figure-3.7
TURKEY RADAR TRAINING 1.0 / ALANYA 2005 31