open area test site
DESCRIPTION
Open site measurement is the most direct and universally accepted standard approach for measuring Radiated Emission/Radiation Susceptibility of an equipment.TRANSCRIPT
EMI MEASUREMENTS EMI MEASUREMENTS
OPEN AREA TEST SITE (OATS)
Prepared and Presented ByPrepared and Presented By
ROJI VARGHESE RAJAN
Reviewed By
K.J.JEGADISH KUMAR AP/ECE
INTRODUCTIONINTRODUCTION
� Measurement of Radiated Emissions (RE) fromequipment, apparatus or instrument and the RadiationSusceptibility (RS) of such an equipment/ apparatus/instrument constitute the two basic EMI/EMCmeasurements.
� Opensite measurementis the mostdirect anduniversally� Opensite measurementis the mostdirect anduniversallyaccepted standard approach for measuring RE/RS of anequipment.
MEASUREMENT OF RADIATED MEASUREMENT OF RADIATED
EMISSION EMISSION
� With the Equipment under test (EUT) switched on,the receiver is scanned over the specified frequencyrange to measure emissions fromthe EUT.
MEASUREMENT OF RADIATION MEASUREMENT OF RADIATION
SUSCEPTIBILITYSUSCEPTIBILITY
� The EUT is placed in an electromagnetic field createdwith the help of a suitable radiating antenna.
� Intensity of field is varied by varying the powerdelivered to the antenna by the transmitted amplifieror signal generator.
FEATURES OF OATSFEATURES OF OATS
� Low ambient and noise floor
� Oversized ground plane
� Host equipment area
� Weather protected
TEST SITETEST SITE
� With the help of a proper test site and a calibratedreceiving antenna, radiated emissions fromequipmentunder test over a specified frequency band can bemeasured.
� Using a calibrated transmitting antenna, susceptibility ofequipmentundertestcanbe checkedunderspecifiedfieldequipmentundertestcanbe checkedunderspecifiedfieldconditions.
� Measurements done in a room, or enclosed area result inreflections or scattered signals fromwalls, floor, andceilings which corrupt the measurements.
� Measurements done in a proper open-area test site (OATS)avoids such scattered signals and reflections.
TEST ANTENNASTEST ANTENNAS
� To illuminate an equipment under test with known fieldstrengths, it is convenient to use exact half wavelengthlong dipoles at fixed frequencies.
MEASUREMENT PRECAUTIONSMEASUREMENT PRECAUTIONS
� Electromagnetic Environment: need to be relatively quietand free fromthe presence of strong signals frombroadcastradio, TV transmitters, manmade electromagneticradiations like automobile ignition systems or arc-weldingequipments.
� Electromagnetic Scatterers: OATS should be free fromsources of scattering such as buildings, electricsources of scattering such as buildings, electrictransmission lines, open telephone and telegraph lines,fences, trees.
� Power and Cable Connections: For improving theaccuracy of measurements, it is necessary that the electricalpower connections to the EUT and the cables between thetransmit/receive antenna located in the test site and thetransmitter/receiver equipment located nearby are placed inunderground trenches.
�� The shape and size of the open area test site need to beappropriate to ensure that no scattered signals are present,which could affect the measurements. American NationalStandards recommend that
S and S are the scatteredsignal from obstructions� Sc and Sd are the scatteredsignal from obstructionslocated at the boundary of the OATS and the directsignal between the EUT and the transmit/receiveantenna, respectively.
OATS CONFIGURATIONS OATS CONFIGURATIONS
�Stationary EUT
• EUT remains stationary andthe transmit/receive antennais traversed on a circular pathso as to view the equipmentfrom all directions (360° infrom all directions (360° inthe azimuth).
• D‘ ≥ 1.5D• The path length of the
scattered signal is twice thatof the direct signal whichensures the scattered signalstrength is at least 6dB belowthe direct signal strength.
�Stationary Antenna
� The EUT is mounted on aplatform which can berotated 360° in the azimuth.
� The transmit/receive antennacan remain stationary and yetlook at the EUT from alllook at the EUT from alldirections.
� The boundary of the test siteis an ellipse with a major axisMD of dimension 2D andminor axis Md of dimension√3D, where D is the distancebetween the EUT and thetransmit/receive antenna.
EUT Antenna SeparationEUT Antenna Separation
� In most measurements, the distance D between theEUT and the transmit/receive antenna is arranged tobe1, 3, or 10 m.
� To have D different fromthese standard distances,theresultsfrom themeasurementareextrapolatedtotheresultsfrom themeasurementareextrapolatedtoone of these standard distances by using a suitabletransformation.
TERRAIN ROUGHNESSTERRAIN ROUGHNESS
� Maximum allowable terrain roughness is determined usingRayleigh roughness criteria and the applicable limit is
� b is the height of the rough edge of the terrain and λ is the wavelength corresponding to the frequency of measurement.
REFERNCESREFERNCES
� V.P.Kodali, “Engineering EMC Principles, Measurements
and Technologies”, Chapter 5 page (79-86).
� C.R.Paul,” Introduction to Electromagnetic Compatibility”,
Chapter 2 pages 52,64Chapter 2 pages 52,64
� http://www.emcdirectory.com/suppliers-28A-open-area-
test-sites-oats-for-fcc-emi-emc-testing.htm