ppt-open area test site

7/23/2019 Ppt-open Area Test Site

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EMI MEASUREMENTSEMI MEASUREMENTS

OPEN AREA TEST SITE (OATS)

ROJI VARGHESE RAJAN

Reviewed ByK.J.JEGADISH KUMAR AP/ECE


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INTRODUCTIONINTRODUCTION Measurement of Radiated Emissions (RE) from

equipment, apparatus or instrument and the Radiation

Susceptibility (RS) of such an equipment/ apparatus/instrument constitute the two basic EMI/EMC

measurements.

accepted standard approach for measuring RE/RS of an

equipment.


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MEASUREMENT OF RADIATEDMEASUREMENT OF RADIATED

EMISSIONEMISSION

With the Equipment under test (EUT) switched on,

the receiver is scanned over the specified frequency

range to measure emissions from the EUT.


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TEST SITETEST SITE With the help of a proper test site and a calibrated

receiving antenna, radiated emissions from equipment

under test over a specified frequency band can be

measured.

Using a calibrated transmitting antenna, susceptibility of

equipment under test can be checked under specified fieldconditions.

Measurements done in a room, or enclosed area result in

reflections or scattered signals from walls, floor, and

ceilings which corrupt the measurements.

Measurements done in a proper open-area test site (OATS)

avoids such scattered signals and reflections.


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MEASUREMENT PRECAUTIONSMEASUREMENT PRECAUTIONS

Electromagnetic Environment: need to be relatively quietand free from the presence of strong signals from broadcastradio, TV transmitters, manmade electromagnetic

radiations like automobile ignition systems or arc-weldingequipments.

Electromagnetic Scatterers: OATS should be free from,

transmission 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.


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The shape and size of the open area test site need to be

appropriate to ensure that no scattered signals are present,

which could affect the measurements. American National

Standards recommend that

Sc and Sd are the scattered signal from obstructionslocated at the boundary of the OATS and the direct

signal between the EUT and the transmit/receive

antenna, respectively.


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OATS CONFIGURATIONSOATS CONFIGURATIONSStationary EUT

EUT remains stationary andthe transmit/receive antennais traversed on a circular pathso as to view the equipmentrom a rec ons n

the azimuth).

D 1.5D

The path length of thescattered signal is twice thatof the direct signal whichensures the scattered signalstrength is at least 6dB belowthe direct signal strength.


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Stationary Antenna

The EUT is mounted on a

platform which can be

rotated 360 in the azimuth.

The transmit/receive antenna

can remain stationary and yet

directions.

The boundary of the test site

is an ellipse with a major axis

MD

of dimension 2D and

minor axis Md of dimension

3D, where D is the distancebetween the EUT and the

transmit/receive antenna.


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EUT Antenna SeparationEUT Antenna Separation

In most measurements, the distance D between the

EUT and the transmit/receive antenna is arranged tobe 1, 3, or 10 m.

To have D different from these standard distances,

t e resu ts rom t e measurement are extrapo ate toone of these standard distances by using a suitable

transformation.


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TERRAIN ROUGHNESSTERRAIN ROUGHNESS

Maximum allowable terrain roughness is determined using

Rayleigh roughness criteria and the applicable limit is

b is the height of the rough edge of the terrain and is the

wavelength corresponding to the frequency of

measurement.


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REFERNCESREFERNCES V.P.Kodali, Engineering EMC Principles, Measurements

and Technologies, Chapter 5 page (79-86).

C.R.Paul, Introduction to Electromagnetic Compatibility,

,

http://www.emcdirectory.com/suppliers-28A-open-area-

test-sites-oats-for-fcc-emi-emc-testing.htm

ppt-open area test site

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