Seiwa MDS-18910R - Manual (Page 7)

MDS-1R/8R/9R/10R Installation
2 What is radar?
2.1 General
The word "radar" is an acronym for "Radio Detecting And Ranging." In very simple terms, this
is how it works. A radio transmitter sends a quick microwave pulse, and then a receiver listens
for that signal's echo when it is bounced back from something in its path. The returning signal
is processed by a computer to determine its relative distance, position and bearing. This
information is graphically displayed on a screen for you to see. Other boats or ships,
navigational markers, landmasses and such are referred to as targets.
By knowing how long it takes for a signal to return, the distance to a target can be determined.
As the radar antenna scans through a 360-degree rotation, it can show where the target is
relative to your position. By repeated scans, you can see which direction another vessel is
moving.
Buoy
Other ship
Radar
Antenna Your
Radar
Fig.2-1 What is radar?
Antenna
How radar will perform is largely determined by its antenna or scanner. Increasing the size of
the antenna improves long-range performance and target discrimination, or the ability to
distinguish two separate targets at a distance. The critical factors are the antenna's beam
width and side lobe level. Typically, a radar antenna will radiate a tightly focused beam from
the front of the array. The longer the antenna array is, the narrower the beam width will be.
Additionally, it will also emit smaller amounts of energy to each side. The lower the side lobe
level, the less the effect of a false echo.
Beam
Side
lobe
Main
Side
l b
Antenna
Side lobe
The beam in which the strongest radio signal is radiated
from the antenna is called the “main lobe”. Those beams
that are radiated in other directions are referred to as the
“side lobes”. The side lobe level refers to the difference in
level (signal strength) between the largest side lobe and the
main lobe.
Fig.2-2 Antenna pattern
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