Home' RTCA Documents for Review : DO-230H FRAC Contents 153
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Consider that the dead spot in detection immediately below and in front of a microwave unit
increases with mounting elevation. An adversary could possibly crawl under the detection beam.
Using an over-lapping pattern of microwave coverage mitigate the “gaps” in immediate proximity
to the Transmitter and Receiver.
Consider that heavy rain exceeding 5.6 cm (2.2 inches) per hour is likely to cause microwave
sensors to produce nuisance alarms.
Consider that electro-magnetic interference (EMI), either reflected or direct, can strike the
microwave receiver and cause nuisance alarms.
Shielded radomes or enclosures with shielded wiring and proper grounding can reduce or eliminate
the effects of EMI.
Note that acoustic noises and vibrations, e.g., seismic activities or mechanical disturbances, can
adversely affect some microwave sensors and not affect others, depending on their design, signal
processing, and installation parameters.
Remove food and water sources from the vicinity of the sensor system to prevent foraging animals
from causing nuisance alarms.
Limit grass heights to 10 cm (3.9 inches) to prevent nuisance alarms caused by the wind moving
Typically, the distance between a chain link security fence with an overall height of 2.4 meters (8
feet) and the center of the microwave beam should be a minimum of 2.4 meters (8 feet).
A microwave perimeter detection system should be capable of detecting an intruder weighing a
minimum of 35 kilograms (77 pounds) passing through the zone of detection between the
transmitter and receiver, including the area in front of both the transmitter and receiver, whether
the individual is walking, running, jumping, crawling, or rolling. Provision should be made to
ensure detection in spite of the dead spots in front of transmitters and receivers. The beam should
be modulated and the receiver should be limited to respond to selected frequencies to decrease
susceptibility to “receiver capture.”
Three tests are performed to test the performance of the system:
o Post-Climb-and-Jump test to determine if an intruder will be detected when climbing the
microwave pole and attempting to jump over the beam.
o Crawl test is performed at 10 feet intervals in a sector at a crawl speed of 4 to 6 inches per
o Run-and-Jump test is performed at 20 feet intervals for the length of the sector to verify
that an intruder cannot jump over the detection beam without being detected.
General Characteristics – Mono-static microwave sensor incorporates the transmitter and receiver within
the same enclosure and is deployed to cover areas that cannot be covered adequately by other sensors. The
unit contains range control and sensitivity control to adjust to eliminate moving objects beyond the range
of the detection zone.
Mono-static microwave sensor is a volumetric detection system.
Detects intruder attempting to jump, run, walk, crawl, or roll through the detection zone.
Size of the detection zone is determined by the sensitivity and range control settings.
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