18
How Radar Works
Traffic radar, which consists of microwaves,
travels in straight lines and is easily re-
flected by objects such as cars, trucks, even
guardrails and overpasses. Radar works by
directing its microwave beam down the
road. As your vehicle travels into range, the
microwave beam bounces off your car, and
the radar antenna looks for the reflections.
Using the Doppler Principle, the radar
equipment then calculates your speed by
comparing the frequency of the reflection
of your car to the original frequency of the
beam sent out.
Traffic radar has limitations, the most
significant of these being that it typically
can monitor only one target at a time. If
there is more than one vehicle within range,
it is up to the radar operator to decide
which target is producing the strongest
reflection. Since the strength of the reflec-
tion is affected by both the size of the
vehicle and its proximity to the antenna, it
is difficult for the radar operator to deter-
mine if the signal is from a sports car nearby
or a semi-truck several hundred feet away.
How Radar Works
Radar range also depends on the power
of the radar equipment itself. The strength
of the radar unit’s beam diminishes with
distance. The farther the radar has to travel,
the less energy it has for speed detection.
Because intrusion alarms and motion sen-
sors often operate on the same frequency
as X-Band radar, your Passport will occa-
sionally receive non-police radar signals.
Since these X-Band transmitters are usually
contained inside of buildings or aimed to-
ward the ground, they will generally pro-
duce much weaker readings than will a
true radar encounter. As you become famil-
iar with the sources of these pseudo alarms
in your daily driving, they will serve as
confirmation that your Passport’s radar de-
tection abilities are fully operational.
