training course on weather radar systems - RTC, Regional Training ...
training course on weather radar systems - RTC, Regional Training ...
training course on weather radar systems - RTC, Regional Training ...
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MODULE A- INTRODUCTION TO RADAR<br />
differ. First, the two comp<strong>on</strong>ents may not have the same amplitude. Sec<strong>on</strong>d, the two comp<strong>on</strong>ents<br />
may not have the same phase that is they may not reach their maxima and minima at the same<br />
time in the fixed plane we are talking about. By c<strong>on</strong>sidering the shape traced out in a fixed plane<br />
by the electric vector as such a plane wave passes over it, we obtain a descripti<strong>on</strong> of the<br />
polarizati<strong>on</strong> state. By c<strong>on</strong>sidering that issue, three types of polarizati<strong>on</strong> of electromagnetic<br />
waves can be defined. These are Linear, Circular and Elliptical Polarizati<strong>on</strong>s.<br />
a) Linear polarizati<strong>on</strong><br />
If the electrical vector remains in <strong>on</strong>e plane, then the wave is linearly polarised. By c<strong>on</strong>venti<strong>on</strong>,<br />
if the electric vector (or field) is parallel to the earth's surface, the wave is said to be horiz<strong>on</strong>tally<br />
polarized, if the electric vector (or field) is perpendicular to the earth's surface, the wave is said to<br />
be vertically polarized.<br />
Linear polarizati<strong>on</strong> is shown in Figure-3.5. Here, two oorthog<strong>on</strong>al comp<strong>on</strong>ents (Ex-red and Eygreen)<br />
of the electric field vector (E-blue) are in phase and they form a path (purple) in the<br />
plane while propagating. In linear polarizati<strong>on</strong> case, the strength of the two comp<strong>on</strong>ents are<br />
always equal or related by a c<strong>on</strong>stant ratio, so the directi<strong>on</strong> of the electric vector (the vector sum<br />
of these two comp<strong>on</strong>ents) will always fall <strong>on</strong> a single line in the plane. We call this special case<br />
linear polarizati<strong>on</strong>. The directi<strong>on</strong> of this line will depend <strong>on</strong> the relative amplitude of the two<br />
comp<strong>on</strong>ents. This directi<strong>on</strong> can be in any angle in the plane, but the directi<strong>on</strong> never varies.<br />
Linear polarisati<strong>on</strong> is most often used in c<strong>on</strong>venti<strong>on</strong>al <strong>radar</strong> antennas since it is the easiest to<br />
achieve. The choice between horiz<strong>on</strong>tal and vertical polarisati<strong>on</strong> is often left to the discreti<strong>on</strong> of<br />
the antenna designer, although the <strong>radar</strong> system engineer might sometimes want to specify <strong>on</strong>e or<br />
the other, depending up<strong>on</strong> the importance of ground reflecti<strong>on</strong>s.<br />
Figure-3.5<br />
30<br />
TURKEY RADAR TRAINING 1.0 / ALANYA 2005