Title: EMC Test Equipment
1EMC 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
2Topics
- 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
G. Barth
3Topics
- Amplifier Care and Maintenance
- Power and Field Measurements
- Antennas
- Technologies
- Applications
- Equipment Pairing and Sizing
- Power vs. Field
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4Ideal 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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5Ideal 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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6Less 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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7Less 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
G. Barth
8Amplifier 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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9Amplifier Technologies
FET DC IV-Curve Operating Modes Bias
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10Amplifier Technologies
FET DC IV-Curve Operating Modes Bias
Class A
Class AB
Class B
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11Amplifier Technologies
Class A
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12Amplifier Technologies
Class A
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13Amplifier Technologies
Class A
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14Amplifier Technologies
Class A
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15Amplifier Technologies
Class A
Full current and voltage swing No harmonics
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16Amplifier Technologies
Class B
Clipping High Harmonic content
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17Amplifier Technologies
Class AB
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18Amplifier Technologies
Class AB
Good small signal response
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19Amplifier Technologies
Class AB
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20Amplifier Technologies
Class AB
Clipping and Harmonics introduced
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21Amplifier Technologies
Class AB Shorted Harmonics
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22Amplifier Technologies
Class AB Shorted Harmonics
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23Amplifier Technologies
Class AB Shorted Harmonics
Good small signal performance
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24Amplifier Technologies
Class AB Shorted Harmonics
Self biasing
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25Amplifier Technologies
Class AB Shorted Harmonics
Good performance due to self biasing limited to
sub octave bandwidth
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26Amplifier 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
G. Barth
27Amplifier 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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28Compression
- 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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29Compression
Example of compressed power
Compression points at one frequency
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30Amplifier 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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31Amplifier Driving
This brings us to the proper input to produce the
desired linear output
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32Amplifier 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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33Amplifier 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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34Amplifier 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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35Large Amplifier Makeup
IN
OUT
Attenuator
Pre-amplification
splitters
combiners
Final stages
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36Amplifier 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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37Care
- 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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38Care
- 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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39Care
- 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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40Care
- Solid-state
- Do what ever you want they can take it!
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41Power 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
G. Barth
42Power 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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43Power 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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44Power 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.
G. Barth
45Power 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)
G. Barth
46Antennas
- E-Field Generator
- 10kHz-100MHz
- Field created between elements or elements and
ground - Non-radiating
- Power limited by Impedance Transformer
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47Antennas
- Biconical (Bicon)
- 20MHz-300MHz
- Extremely broad beam width
- Power limited by Impedance Transformer (Balun)
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48Antennas
- Log Periodic (LP)
- 26MHz-6GHz
- Beam width narrows with frequency
- Power limited by input connector and antenna
feed
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49Antennas
- Horn
- 200MHz-40GHz
- High Gain
- Beam width dependant on design
- Power limited by input connector or waveguide
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50Equipment 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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51Equipment Pairing and Sizing
- Pairing Considerations
- Illumination of EUT
- 3dB beam width (test distance)
- Will windowing be required?
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52Equipment 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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53 Equipment Pairing and Sizing
- Calculating Power Required to Get Field
- Frequency dependant
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54 Equipment Pairing and Sizing
- Calculating Power Required to Get Field
- Frequency dependant
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55 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
G. Barth
56Any 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