NARDA PMM AS02, User Manual

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Radiated Emission and Immunity testing 3-3
3.2 Radiated Immunity
testing
During a radiated immunity test a electromagnetic signal, typically 3 or 10
V/m is directed at the equipment under test (EUT), analyzing the EUT
reaction.
According to the international Standards, the purpose of this test is to verify
that the EUT does not show any degraded performance or failure when the
signal is applied.
The test should be performed either in horizontal and in vertical
polarization.
The transmitting antenna and the EUT are installed into a shielded room to
avoid environmental RF pollution.
A isotropic field probe must be located near the EUT to verify the
electromagnetic field strength.
The typical radiated test set-up is composed of:
•
signal generator;
• power amplifier;
•
transmit antenna;
• field strength meter.
3.2.1 The signal
generator The signal generator provides the test signal. It should have adequate
output resolution to allow the setting of the field strength to within 1% of the
desired level and must provide a sine wave 80% AM modulation at 1 kHz.
3.2.2 The power amplifier
The power amplifier is used to increase the test signal strength applied to
the antenna to a level able to produce the desired E-field.
Note that the EMC amplifiers are specified with a minimum gain, they can
show several dB of ripple in the pass band.
The power amplifier must be operated in linear mode to assure
repeatability, in fact when a 80% AM modulation is added an additional 5.1
dB
( )






8 . 1 log 20
10
x
of linear gain from the power amplifier is required.
3.2.3 The transmit
antenna
The performance of the antenna relating to the value of the emitted E-Field
is the Antenna Factor.
This is usually provided by the manufacturer in dB with units of inverse
meters.
Typically a combination of two antennas is used to cover the wide
frequency range required by the Standard.
3.2.4 The field strength
meter
The field strength meter probe is used to directly measure the field level
applied to the EUT.
The typical distance between the tip of the antenna and the probe is 3 m.