User Manual

9
CHAPTER 2. USING RADAR FOR
THE FIRST TIME
This chapter describes basic information on radars and explains technical terms used in radar op-
eration for those who are using a radar for the first time.
2.1 What is a radar ?
A marine radar is one of the navigation equipment installed on a ship. It emits a radio wave in very
high frequency called a microwave from its antenna and receives the reflected radio wave from objects on
the sea (e.g., other ships, buoys, and lands). The received radio wave is converted into an electric signal
which is displayed on a display screen to indicate the presence of such objects. Although it is very dif-
ficult to find other ships or the destination coast with human eyes at night or in thick fog, a radar can
detect objects on the sea helping you avoid danger when sailing. The antenna turns 360 degrees as it
radiates waves, allowing you to grasp ambient conditions around your ship at a glance.
The radio wave radiated from the antenna is called a pulse wave and the radar performs transmis-
sion and reception alternately. Several hundred to several thousand pulse waves generally are trans-
mitted while the antenna rotates one turn.
Fig.2-1 What is a radar?
Antenna
There are many types of antennas generally used for a radar. For example, these include a
parabolic antenna and a slotted-array antenna. The performance of the antenna determines that of
the radar. The dominant factors are the antenna's beam width and side lobe level. The narrower the
beam width, the higher the resolution of the angle direction. The lower the side lobe level, the fewer
the effect of a false echo.
Side lobe
A beam in one direction in which the strongest radio
wave is radiated from the antenna is called the main lobe
and beams in other directions are called "side lobes". The
side lobe level refers to the difference in level between
the largest side lobe and the main lobe.
Beam width
A beam width is defined as the width of the main
lobe at an angle where the radiated power is halved as
measured from the position from which the strongest
radio wave is radiated.
Fig.2-2 Antenna pattern
Buoy
Other ship
Radar wave
Your ship
Antenna (Rotating)
Radar display
Beam width
Side lobe
level
Main beam
Side lobe
Antenna