Home' RTCA Documents for Review : DO-230H FRAC Contents 152
© 2017, RTCA, Inc.
General Characteristics – Good for flat areas that have a line-of-sight without any obstructions. The
transmitter and receiver are separate units that can cover long distances depending on the unit. The detection
field is invisible and fills the space between the transmitter and receiver. Stacking of units with different
frequencies of operation or different polarizations will extend the detection field vertically and can also
provide a higher Pd.
Bi-static microwave are line-of-sight and volumetric detection systems. Its detection zone is a
“cigar shaped” area of detection that is widest at the center of the detection field between the
transmitter and receiver antenna.
The systems detect a break in the beam between the transmitter and receiver or a multipath
reflection, which causes detection when the received signal crosses a predetermined threshold.
Detects an intruder attempting to jump, run, walk, crawl, or roll through the detection zone.
Range – About 1,500 feet for X band systems or 650 feet for K-Band systems, depending on the
Detection Capabilities – Detection zones are dependent on the system and manufacturer’s model. Generally,
the smaller the detection zone, the greater the Pd for all intruder actions (i.e. crawling, walking, rolling, and
System Limitation –
Transmitter shall not be located within 10 feet of any electro-explosive devices or munitions.
Transmitting or receiving antenna shall not be located within 50 feet of refueling area.
Transmitting or receiving antenna shall not be located within 20 feet of aircraft fuel tank vents.
Ensure that microwave sensors are set up so that they have a clear line-of-sight between transmitters
Ensure that microwave sensor systems are installed over flat ground or ground with a constant slope
to prevent shadowing (inadequate detection in depressions).
For corner overlap applications, keep intersection angles of microwave beams as close as possible
to 90 degrees, i.e., orthogonal.
Mounting considerations for individual zones or multiple zones must be done in accordance with
manufacture’s siting criteria.
Remember that dynamic multipath signals from microwave sensors can be subject to constructive
and destructive interference.
Consider that the detection pattern is relative to the mounting position, and it is sometimes possible
for an adversary to crawl under the detection beam when microwave sensor antennas, i.e., receivers
and transmitters, are relatively high.
Be aware that reflections of microwave signals from nearby structures, traffic, or surface
discontinuities may cause nuisance alarms.
Reflection of microwave signals may sometimes be used effectively to extend coverage where
terrain or structures are not amenable to standard installation.
Be aware that microwave sensor detection zones that parallel a road with vehicular traffic or long
fence lines may produce nuisance alarms unless sufficient offset is established between the sensor
axis and the interference source, e.g., traffic on the roads or swaying fence lines.
Note that standing water, e.g., from heavy rain, under the microwave sensor detection zone can
produce an increased nuisance alarm rate when the water is rippled by winds. Note that, after a
heavy rain, moving water under the microwave detection zone may reduce nuisance alarms.
Note that significant snow depths and drifts can produce voids in the detection zone
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