Open Area Test SitesThe measurements of radiated emissions (RE)
and radiated susceptibility (RS) of an equipment constitute the two
basic EMI and EMC measurements.The purpose of radiation
susceptibility testing is to determine the degradation in equipment
performance caused by externally coupled electro- magnetic
energy.
Open Area Test Site MeasurementsMeasurement of REMeasurement of
RSTest Site Test Antennas
Measurement of RE
Measurement of RS
Test Site With the help of a proper test site and a calibrated
receiving antenna, RE from equipment under test over a specified
frequency band can be measured by observing various precautions.
Using a calibrated transmitted antenna, susceptibility of equipment
under test can be checked. These measurements are to be done in a
proper open-area test site where the scattered signals and
reflections are not present.
Test Antennas To illuminate EUT with known field strengths, a
convenient way is to use exact half-wavelength long dipoles at
fixed frequencies.
Measurement Precautions1. Electromagnetic Environment: According
to ANS, it is desirable that the conducted and radiated ambient
radio noise and signal levels measured at the test site with the
EUT de-energized, be at least 6 dB below the allowable limit of the
applicable specification.2. Electromagnetic Scatterers:To avoid
interference from underground scatters, use a metallic ground plane
to eliminate strong reflections from under ground sources such as
buried metallic objects.
3. Power and Cable Connections: The power leads used to energize
the EUT, receiver and transmitter should pass through filters to
eliminate the conducted interferences carried by power lines.
Open-area test site The shape and size of the open-area test
site will need to be appropriate to avoid scattered signals. In
order to meet this requirement, American National Standards
recommend that Sc Sd -6dB
Stationary EUT: The EUT remains stationary.Antenna is traversed
in circular pathThe AN Standard is satisfied for D1.5D
Stationary Antenna:EUT is made to rotate 360 degrees while the
antenna is stationary.
CONCLUSIONAn ideal OATS is an infinite perfectly conducting
ground screen with no background noise and no indirect coupling
paths.It calls for use of exactly calibrated antennas and precision
error-free performance measurement equipment.Weather protection
also requires particular attentionThus, generally OATS is costly
facility, suitable when measurements in a standard test site are
required.
