Decatur Electronics SI-3 - Performance Tips; How Radar Works; Interference Sources; Angular Interference (Cosine Effect)

SI-3
™
User’s Manual
16
5. Performance Tips
Understanding potential radar interference and what to do when it
occurs can greatly increase the radar’s performance.
5.1 How Radar Works
Determining an object’s speed begins with the radar transmitting
a beam of microwave energy (radio waves) at an approaching or
departing target. When energy from this beam strikes a target, a
small amount of the beam is reected back to the antenna. The
reected signal frequency shifts by an amount proportional to the
speed of the target. This is known as the Doppler eect. The radar
device then determines the target speed from the dierence in
frequency between the reected and transmitted signal.
5.2 Interference Sources
When properly installed and operated, Doppler radar technology
is extremely accurate and reliable. However, variations in the
environment can cause situations and circumstances which can
cause spurious (erratic and unusually low or high) speeds to
display. Signs that a speed is spurious can include the following
characteristics:
• A reading appears when no target is in the operational range of
the antenna.
• A target entering the operational range overrides the
interference signal, causing the display speed to change
suddenly to the target’s speed.
• Speeds are irregular.
5.2.1 Angular Interference (Cosine Eect)
The cosine eect causes the system to display a speed which is
lower than the actual target speed. This condition occurs when
the target’s path is not parallel to the antenna such as the target
vehicle traveling on a curve or hill.