EMC Test Equipment

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EMC Test Equipment - Amplifiers and Antennas
George BarthProduct Engineer, Systemsar
rf/microwave instrumentation160 School House
Road Souderton, PA 18964-9990 gbarth_at_ar-worldwid
e.com
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Topics

• Ideal Amplifier Environment
• The EMC Reality
• Review of Amplifier Technologies
• Tube (Vacuum tube)
• Traveling Wave Tube (TWT) Amplifiers
• Solid-State Different classes
• Amplifier Use
• Proper drive levels
• Loads

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Topics

• Amplifier Care and Maintenance
• Power and Field Measurements
• Antennas
• Technologies
• Applications
• Equipment Pairing and Sizing
• Power vs. Field

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Ideal Conditions

• What Amplifiers Love
• Always run in a low ambient room temperature
• 72F
• Use in a dust free environment
• Have clean power supplied
• Install in a fixed location by professionals
• Never exceed required input level
• depends on specification of each amplifier
• Never have a load fail
• Connect amplifier only to a matched load
• 50 ? loads lt1.51VSWR
• Only use fully tested and verified coax
  waveguide

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Ideal Conditions
Majority of the worlds amplifiers are designed
for single uses. transmitters, cell phones,
radios These types of applications have known
environmental conditions. Load is
constant Frequency is usually narrowband Trained
professionals are installing Environmental
temperature constraints are known Amplifiers can
be designed much more easily in these cases and
are simple.
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Less Than Ideal Conditions
EMC testing does not fall anywhere near ideal or
simple conditions. The extremes for the EMC
market High VSWR Amplifier is still required to
deliver power or at a minimum not be
damaged Bad loads, cables, connections Use in
many tests, locations, and setups EMC Test
engineers technicians do not have to be
amplifier experts
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Less Than Ideal Conditions

• What is needed
• Different engineering techniques are used to
  extend these constraints so the amplifier is more
  useful.
• Better heat removal for extended operating
  temperature range, which inherently extends the
  life of the amp
• Use better, more durable power supplies
• Rugged physical design
• Class A design
• Added VSWR protection (active protection)
• Added ability to handle VSWR

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Amplifier Technologies

• Tube (Tetrode tube)
• TWT (Traveling Wave Tube) Amplifier
• Solid-state
• Class A
• Class AB
• Class B
• What are the differences?

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Amplifier Technologies
FET DC IV-Curve Operating Modes Bias
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Amplifier Technologies
FET DC IV-Curve Operating Modes Bias
Class A
Class AB
Class B
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Amplifier Technologies
Class A
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Amplifier Technologies
Class A
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Amplifier Technologies
Class A
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Amplifier Technologies
Class A
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Amplifier Technologies
Class A
Full current and voltage swing No harmonics
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Amplifier Technologies
Class B
Clipping High Harmonic content
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Amplifier Technologies
Class AB
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Amplifier Technologies
Class AB
Good small signal response
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Amplifier Technologies
Class AB
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Amplifier Technologies
Class AB
Clipping and Harmonics introduced
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Amplifier Technologies
Class AB Shorted Harmonics
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Amplifier Technologies
Class AB Shorted Harmonics
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Amplifier Technologies
Class AB Shorted Harmonics
Good small signal performance
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Amplifier Technologies
Class AB Shorted Harmonics
Self biasing
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Amplifier Technologies
Class AB Shorted Harmonics
Good performance due to self biasing limited to
sub octave bandwidth
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Amplifier Technologies
Amplifier  Linearity 1dB point Harmonics at 1dB Harmonics above 1dB Noise power density/ Spurious  Ability to handle VSWR  Frequency coverage
Tube  Bad  Good  Worst  Bad  Best  Low freq. lt250 MHz
TWTA  Worst  Worst  Worst  Worst  Worst  High freq. gt1 GHz
Solid state Class A  Best  Best  Best  Good  Best  Full coverage
Solid state Class AB  Bad  Good  Good  Good  Good to bad  Full coverage
Solid state Class B  Bad Good  Bad  Best  Good to bad  Full coverage
Results greatly depends on how the technology
is implemented
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Amplifier Technologies
Important specifications (other than the power,
frequency, and VSWR protection you require) are
linearity and harmonics, which are related. High
harmonics may have undesirable effects on
recorded test levels. As the amplifier
approaches compression the harmonics increase.
Class A solid state amplifiers seem to have the
best performance even into compression. But large
variations can be seen depending on the
technology used. A recommended level is -6dBc
of the field. Example IEC 61000-4-3
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Compression

• Running the test while the amplifier is in
  compression will distort the test signal
• CW signal
• CW in compression
• Harmonics
• The compressed wave starts to resemble a square
  wave, producing higher harmonics.

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Compression
Example of compressed power
Compression points at one frequency
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Amplifier Driving

• What is the correct drive level to the amplifier?
• There will always be a max drive level before
  damage.
• Most of ARs amps have 13dBm max input level.
• In most cases there is no reason to come even
  close to max input level.
• Amplifiers are rated with a 0dBm input to reach
  rated output.
• Most testing should not be done with saturated
  power
• Therefore -5 - -10 dBm may be all you need to
  drive the amplifier

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Amplifier Driving
This brings us to the proper input to produce the
desired linear output
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Amplifier Driving
An amplifier requiring 0 dBm input to reach rated
output does not mean 0dBm of input is required to
get the results you may need. TWT amplifiers in
some cases with a 0dBm input and full gain will
be over driving the TWT. Over time this could be
damaging. Application Note 45 Input Power
Requirements For further explanation
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Amplifier VSWR

• The amplifiers ability to deal with VSWR will
  determine the possible use and application.
• TWTAs have a relatively low threshold to VSWR
• The TWT will fail at high VSWR without protection
  or precautions.
• 21 VSWR at rated power
• Fold back at 20 reflected power (best) AR
• pulsed amps fold back at 50 reflected power AR
• Shutdown at 21 VSWR
• Rely on user to take responsibility to be
  proactive
• Low Power Solid State can have high threshold to
  VSWR
• Dependent on technology used
• Infinite VSWR handling, no protection needed AR

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Amplifier VSWR

• High Power Solid State can have high threshold to
  VSWR
• Dependent on technology used
• High VSWR handling, some protection required
• Can handle up to 50 of rated power (61 VSWR)
  when used at full power
• Folds back so that reverse power does not exceed
  reverse power limit
• Why cant higher power amplifiers handle infinite
  VSWR like lower power versions?
• Combining
• Components see up to twice the power (4x voltage
  and current)
• Combiners also act as splitters and direct energy
  back to output stages

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Large Amplifier Makeup
IN
OUT
Attenuator
Pre-amplification
splitters
combiners
Final stages
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Amplifier Technologies

• Why is protection from mismatch needed?
• There is only so much that can be done to
  protect the amplifier without adding exorbitant
  cost

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Care

• General care
• Keep original packaging for shipping
• If new packaging is required contact AR for
  suggestions
• Do not disconnect RF connection while amplifier
  is not in standby!
• The amplifier is protected from this but you are
  not!
• Make sure heat is not re-circulated back into
  amplifier
• Temperature is monitored and protected in the
  amplifier, but cooler is always better

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Care

• Tube Vacuum tube amplifiers
• Oil cooling system
• New unit make sure to fill oil correctly.
• Do not tip over and place on its side to work
  on!
• Will drive full power and not fold-back into any
  load.
• Maintain recommended operating temperature.
• Over time tubes will slowly decrease power
  output and require replacement.

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Care

• TWTA
• TWT is most expensive part of the amplifier
  (Protect It)
• Make sure heat outtake and intake are not
  confined
• Be very careful not to overdrive input!
• This can be damaging to the TWT.
• Take care not to let the amplifier sit unused
  for extended periods of time months years.
• The TWT will Gas up, then when activated the
  Tube may be damaged.
• A De-gassing start up routine needs to be used
• Do not leave the TWTA powered up and not being
  used for extended periods of time.
• Tube can Gas up
• Do not disable sleep mode feature
• Take care not to use badly mismatched loads
• ARs amps are fully protected for all mismatches
  but is still stressful to TWT

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Care

• Solid-state
• Do what ever you want they can take it!

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Power and Field Measurement

• What is the proper way to measure power and
  field?
• What is the measurement device
• Power meter (w/directional coupler)
• Diode sensor
• Thermocouple sensor
• Peak power meter
• Field probe
• Diode sensor
• Thermocouple sensor
• Pulse probe
• Spectrum analyzer

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Power and Field Measurement
Technology differences
Diode Thermocouple
More sensitive Can measure true RMS of a CW signal. Can be used to measure RMS of modulated signals if used within the linear region. Usually this is in the lower region but its difficult to know exactly. A signal in compression can have error in the actual reading. Faster response Less sensitive Less dynamic range Measures true RMS of any signal
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Power and Field Measurement
Technology differences
Broad-Band Device (power meter, field probe) Frequency Selective Device (Spectrum Analyzer)
Will measure whole frequency spectrum including harmonics Care must be taken that harmonics are not contributing to reading Can be very accurate if used correctly Easy setup and use Can discern between different frequency signals Measures peak RMS Peak/SQRT(2) Can measure modulated signals Possible time consuming setup
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Power and Field Measurement

• For measuring amplifier output, using a
  directional coupler with a power meter is
  acceptable. Care should be taken in a
  reverberation chamber, for example.
• In most ALSE testing, forward power is a
  relative number and care only needs to be taken
  that this can be reproduced.
• If harmonics are a concern harmonic filters can
  be used.

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Power and Field Measurement

• Verify measurements are correct when using a
  broad-band device to take measurements
• It is a good idea to verify the readings are
  correct with a spectrum analyzer.
• Run a calibration with the power meter and then a
  calibration with the spectrum analyzer to see if
  the forward power reading matches up
• Use an antenna and spectrum analyzer to spot
  check V/m reading from probe during calibration
  especially where the amplifier is being driven
  hard.
• Dont assume that if the harmonics are out of
  band that they are no longer a factor!
  (amplifier, probe, antenna)

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Antennas

• E-Field Generator
• 10kHz-100MHz
• Field created between elements or elements and
  ground
• Non-radiating
• Power limited by Impedance Transformer

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Antennas

• Biconical (Bicon)
• 20MHz-300MHz
• Extremely broad beam width
• Power limited by Impedance Transformer (Balun)

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Antennas

• Log Periodic (LP)
• 26MHz-6GHz
• Beam width narrows with frequency
• Power limited by input connector and antenna
  feed

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Antennas

• Horn
• 200MHz-40GHz
• High Gain
• Beam width dependant on design
• Power limited by input connector or waveguide

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Equipment Pairing and Sizing

• Pairing Considerations
• Frequency
• Antennas and Amplifiers do they match?
• Will switching be required?
• Power
• Can antenna handle amplifier power available?
• RF connectors compatible?
• Cabling?

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Equipment Pairing and Sizing

• Pairing Considerations
• Illumination of EUT
• 3dB beam width (test distance)
• Will windowing be required?

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Equipment Pairing and Sizing

• Sizing Considerations
• Field Strength
• Test distance?
• Modulation? (AM, AM constant peak, Pulse)
• Losses
• Cables
• Chamber effects
• Reflections (EUT)
• VSWR (antenna)
• Margin

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Equipment Pairing and Sizing

• Calculating Power Required to Get Field
• Frequency dependant

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Equipment Pairing and Sizing

• Calculating Power Required to Get Field
• Frequency dependant

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Equipment Pairing and Sizing

• Calculating Power Required to Get Field
• Power calculated from graphs or formulas is P1dB
• Add for system losses
• Cables
• Chamber effects
• Reflections (EUT)
• VSWR (antenna)
• Add Margin

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Any questions? Thank you for your attention!!!
George BarthProduct Engineer, Systemsar
rf/microwave instrumentation160 School House
Road Souderton, PA 18964-9990 gbarth_at_ar-worldwid
e.com
G. Barth