Radar Installation Manual
Page 31
Appendix A. WHAT IS RADAR?
A.0
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
Radar
Figure A - Radar
A.0.0 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.
A.0.1 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.
