User's Manual Part 2

Operator Manual
Raytheon Marine GmbH
Germany
R
NSC 18
RADAR
3−1
3748DOC020102Edition: 14.JAN.2005
3 Theory of Operation
This chapter gives additional information about radar operation and functions.
It explains terminology and and describes a number of effects which have influ-
ence on radar performance and have to be considered by the operator.
A radar uses a very high frequency radio wave (microwave) which has similar
properties to those of light regarding straightness and uniform velocity. The radar
antenna radiates the fan shape fine microwave (fan beam) to the target just as a
search light throws the light beam to the target, and the reflected microwave
from the target returns to the antenna.
The radar does not use a continuous wave but radiates the wave for a very short
period (approx. 10
−6
to 10
−8
second .... called pulse) to measure the time from
when the wave is radiated till the reflected wave returns to the antenna. In addi-
tion, with rotation of the antenna at a constant speed, the fan shape radio wave
radiated from the antenna scans around 360_ − with the antenna at its center −
in order to detect the object.
3.1 Radar Plotting Terminology
• Bearing (AZIMUTH)
The horizontal direction of one point from another point, expressed as the
angle in the horizontal plane between a reference line and the horizontal pro-
jection of the line joining the two points.
− TRUE Bearing > Reference is true north
− RELATIVE Bearing > Reference is own ship’s heading
• Target Speed
− TRUE > Actual Speed made good by target.
− RELATIVE > In relation to own ship’s movement