Post on 25-Feb-2016
description
EMC Test Equipment-
Amplifiers and AntennasGeorge Barth
Product Engineer, Systems
ar rf/microwave instrumentation160 School House Road
Souderton, PA 18964-9990 gbarth@ar-worldwide.com
Topics
G. Barth
• 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
Topics
G. Barth
•Amplifier Care and Maintenance•Power and Field Measurements•Antennas
•Technologies•Applications
•Equipment Pairing and Sizing•Power vs. Field
Ideal Conditions
G. Barth
What Amplifiers Love
• Always run in a low ambient room temperature• ~72°F
• 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 Ω loads <1.5:1VSWR• Only use fully tested and verified coax & waveguide
Ideal Conditions
G. Barth
Majority of the worlds amplifiers are designed for single uses.transmitters, cell phones, radios…
These types of applications have known environmental conditions.Load is constantFrequency is usually narrowbandTrained professionals are installingEnvironmental temperature constraints are known
Amplifiers can be designed much more easily in these cases and are simple.
Less Than Ideal Conditions
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EMC testing does not fall anywhere near ideal or simple conditions.
The extremes for the EMC marketHigh VSWR Amplifier is still required to deliver power or at a
minimum not be damagedBad loads, cables, connectionsUse in many tests, locations, and setupsEMC Test engineers & technicians do not have to be
amplifier experts
Less Than Ideal Conditions
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What is neededDifferent 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
• Tube (Tetrode tube)• TWT (Traveling Wave Tube) Amplifier• Solid-state
•Class A•Class AB•Class B
What are the differences?
Amplifier Technologies
G. Barth
Amplifier Technologies
FET DC IV-Curve Operating Modes & Bias
0 40 80 120Voltage (V)
DCIV
0
2
4
6
8
p11p10p9
p8
p7
p6
p5
p4
p3
p2
p1
5 V6.287 A
p1: Vstep = -3 V
p2: Vstep = -2.5 V
p3: Vstep = -2 V
p4: Vstep = -1.5 V
p5: Vstep = -1 V
p6: Vstep = -0.5 V
p7: Vstep = 0 V
p8: Vstep = 0.5 V
p9: Vstep = 1 V
p10: Vstep = 1.5 V
p11: Vstep = 2 V
G. Barth
Amplifier Technologies
0 40 80 120Voltage (V)
DCIV
0
2
4
6
8
p11p10p9
p8
p7
p6
p5
p4
p3
p2
p1
5 V6.287 A
p1: Vstep = -3 V
p2: Vstep = -2.5 V
p3: Vstep = -2 V
p4: Vstep = -1.5 V
p5: Vstep = -1 V
p6: Vstep = -0.5 V
p7: Vstep = 0 V
p8: Vstep = 0.5 V
p9: Vstep = 1 V
p10: Vstep = 1.5 V
p11: Vstep = 2 V
FET DC IV-Curve Operating Modes & Bias
Class A
Class AB
Class B
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Amplifier Technologies
Class A
0 40 80 120Voltage (V)
DCIV
0
2
4
6
8
p11p10p9
p8
p7
p6
p5
p4
p3
p2
p1
5 V6.287 A
p1: Vstep = -3 V
p2: Vstep = -2.5 V
p3: Vstep = -2 V
p4: Vstep = -1.5 V
p5: Vstep = -1 V
p6: Vstep = -0.5 V
p7: Vstep = 0 V
p8: Vstep = 0.5 V
p9: Vstep = 1 V
p10: Vstep = 1.5 V
p11: Vstep = 2 V
G. Barth
Amplifier Technologies
Class A
0 40 80 120Voltage (V)
DCIV
0
2
4
6
8
p11p10p9
p8
p7
p6
p5
p4
p3
p2
p1
5 V6.287 A
p1: Vstep = -3 V
p2: Vstep = -2.5 V
p3: Vstep = -2 V
p4: Vstep = -1.5 V
p5: Vstep = -1 V
p6: Vstep = -0.5 V
p7: Vstep = 0 V
p8: Vstep = 0.5 V
p9: Vstep = 1 V
p10: Vstep = 1.5 V
p11: Vstep = 2 V
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Amplifier Technologies
Class A
0 40 80 120Voltage (V)
DCIV
0
2
4
6
8
p11p10p9
p8
p7
p6
p5
p4
p3
p2
p1
5 V6.287 A
p1: Vstep = -3 V
p2: Vstep = -2.5 V
p3: Vstep = -2 V
p4: Vstep = -1.5 V
p5: Vstep = -1 V
p6: Vstep = -0.5 V
p7: Vstep = 0 V
p8: Vstep = 0.5 V
p9: Vstep = 1 V
p10: Vstep = 1.5 V
p11: Vstep = 2 V
G. Barth
Amplifier Technologies
Class A
0 40 80 120Voltage (V)
DCIV
0
2
4
6
8
p11p10p9
p8
p7
p6
p5
p4
p3
p2
p1
5 V6.287 A
p1: Vstep = -3 V
p2: Vstep = -2.5 V
p3: Vstep = -2 V
p4: Vstep = -1.5 V
p5: Vstep = -1 V
p6: Vstep = -0.5 V
p7: Vstep = 0 V
p8: Vstep = 0.5 V
p9: Vstep = 1 V
p10: Vstep = 1.5 V
p11: Vstep = 2 V
G. Barth
Amplifier Technologies
Class A
0 40 80 120Voltage (V)
DCIV
0
2
4
6
8
p11p10p9
p8
p7
p6
p5
p4
p3
p2
p1
5 V6.287 A
p1: Vstep = -3 V
p2: Vstep = -2.5 V
p3: Vstep = -2 V
p4: Vstep = -1.5 V
p5: Vstep = -1 V
p6: Vstep = -0.5 V
p7: Vstep = 0 V
p8: Vstep = 0.5 V
p9: Vstep = 1 V
p10: Vstep = 1.5 V
p11: Vstep = 2 V
Full current and voltage swingNo harmonics
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Amplifier Technologies
0 40 80 120Voltage (V)
DCIV
0
2
4
6
8
p11p10p9
p8
p7
p6
p5
p4
p3
p2
p1
5 V6.287 A
p1: Vstep = -3 V
p2: Vstep = -2.5 V
p3: Vstep = -2 V
p4: Vstep = -1.5 V
p5: Vstep = -1 V
p6: Vstep = -0.5 V
p7: Vstep = 0 V
p8: Vstep = 0.5 V
p9: Vstep = 1 V
p10: Vstep = 1.5 V
p11: Vstep = 2 V
Class B
ClippingHigh Harmonic content
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Amplifier Technologies
Class AB
0 40 80 120Voltage (V)
DCIV
0
2
4
6
8
p11p10p9
p8
p7
p6
p5
p4
p3
p2
p1
5 V6.287 A
p1: Vstep = -3 V
p2: Vstep = -2.5 V
p3: Vstep = -2 V
p4: Vstep = -1.5 V
p5: Vstep = -1 V
p6: Vstep = -0.5 V
p7: Vstep = 0 V
p8: Vstep = 0.5 V
p9: Vstep = 1 V
p10: Vstep = 1.5 V
p11: Vstep = 2 V
G. Barth
Amplifier Technologies
Class AB
0 40 80 120Voltage (V)
DCIV
0
2
4
6
8
p11p10p9
p8
p7
p6
p5
p4
p3
p2
p1
5 V6.287 A
p1: Vstep = -3 V
p2: Vstep = -2.5 V
p3: Vstep = -2 V
p4: Vstep = -1.5 V
p5: Vstep = -1 V
p6: Vstep = -0.5 V
p7: Vstep = 0 V
p8: Vstep = 0.5 V
p9: Vstep = 1 V
p10: Vstep = 1.5 V
p11: Vstep = 2 V
Good small signal response
G. Barth
Amplifier Technologies
Class AB
0 40 80 120Voltage (V)
DCIV
0
2
4
6
8
p11p10p9
p8
p7
p6
p5
p4
p3
p2
p1
5 V6.287 A
p1: Vstep = -3 V
p2: Vstep = -2.5 V
p3: Vstep = -2 V
p4: Vstep = -1.5 V
p5: Vstep = -1 V
p6: Vstep = -0.5 V
p7: Vstep = 0 V
p8: Vstep = 0.5 V
p9: Vstep = 1 V
p10: Vstep = 1.5 V
p11: Vstep = 2 V
G. Barth
Amplifier Technologies
Class AB
0 40 80 120Voltage (V)
DCIV
0
2
4
6
8
p11p10p9
p8
p7
p6
p5
p4
p3
p2
p1
5 V6.287 A
p1: Vstep = -3 V
p2: Vstep = -2.5 V
p3: Vstep = -2 V
p4: Vstep = -1.5 V
p5: Vstep = -1 V
p6: Vstep = -0.5 V
p7: Vstep = 0 V
p8: Vstep = 0.5 V
p9: Vstep = 1 V
p10: Vstep = 1.5 V
p11: Vstep = 2 V
Clipping and Harmonics introduced
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Amplifier Technologies
Class AB Shorted Harmonics
0 40 80 120Voltage (V)
DCIV
0
2
4
6
8
p11p10p9
p8
p7
p6
p5
p4
p3
p2
p1
5 V6.287 A
p1: Vstep = -3 V
p2: Vstep = -2.5 V
p3: Vstep = -2 V
p4: Vstep = -1.5 V
p5: Vstep = -1 V
p6: Vstep = -0.5 V
p7: Vstep = 0 V
p8: Vstep = 0.5 V
p9: Vstep = 1 V
p10: Vstep = 1.5 V
p11: Vstep = 2 V
G. Barth
Amplifier Technologies
Class AB Shorted Harmonics
0 40 80 120Voltage (V)
DCIV
0
2
4
6
8
p11p10p9
p8
p7
p6
p5
p4
p3
p2
p1
5 V6.287 A
p1: Vstep = -3 V
p2: Vstep = -2.5 V
p3: Vstep = -2 V
p4: Vstep = -1.5 V
p5: Vstep = -1 V
p6: Vstep = -0.5 V
p7: Vstep = 0 V
p8: Vstep = 0.5 V
p9: Vstep = 1 V
p10: Vstep = 1.5 V
p11: Vstep = 2 V
G. Barth
Amplifier Technologies
Class AB Shorted Harmonics
0 40 80 120Voltage (V)
DCIV
0
2
4
6
8
p11p10p9
p8
p7
p6
p5
p4
p3
p2
p1
5 V6.287 A
p1: Vstep = -3 V
p2: Vstep = -2.5 V
p3: Vstep = -2 V
p4: Vstep = -1.5 V
p5: Vstep = -1 V
p6: Vstep = -0.5 V
p7: Vstep = 0 V
p8: Vstep = 0.5 V
p9: Vstep = 1 V
p10: Vstep = 1.5 V
p11: Vstep = 2 V
Good small signal performance
G. Barth
Amplifier Technologies
Class AB Shorted Harmonics
0 40 80 120Voltage (V)
DCIV
0
2
4
6
8
p11p10p9
p8
p7
p6
p5
p4
p3
p2
p1
5 V6.287 A
p1: Vstep = -3 V
p2: Vstep = -2.5 V
p3: Vstep = -2 V
p4: Vstep = -1.5 V
p5: Vstep = -1 V
p6: Vstep = -0.5 V
p7: Vstep = 0 V
p8: Vstep = 0.5 V
p9: Vstep = 1 V
p10: Vstep = 1.5 V
p11: Vstep = 2 V
Self biasing
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Amplifier Technologies
Class AB Shorted Harmonics
0 40 80 120Voltage (V)
DCIV
0
2
4
6
8
p11p10p9
p8
p7
p6
p5
p4
p3
p2
p1
5 V6.287 A
p1: Vstep = -3 V
p2: Vstep = -2.5 V
p3: Vstep = -2 V
p4: Vstep = -1.5 V
p5: Vstep = -1 V
p6: Vstep = -0.5 V
p7: Vstep = 0 V
p8: Vstep = 0.5 V
p9: Vstep = 1 V
p10: Vstep = 1.5 V
p11: Vstep = 2 V
Good performance due to self biasing limited to sub octave bandwidth
G. Barth
Amplifier Technologies
Amplifier Linearity1dB point
Harmonicsat 1dB
Harmonics above 1dB*
Noise power density/ Spurious
Ability to handle VSWR*
Frequency coverage
Tube Bad Good Worst Bad Best Low freq. <250 MHz
TWTA Worst Worst Worst Worst Worst High freq. >1 GHz
Solid stateClass A
Best Best Best Good Best Full coverage
Solid stateClass AB
Bad Good Good Good Good to bad Full coverage
Solid stateClass 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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CompressionE
xam
ple
of c
ompr
esse
d po
wer
dB Gain for 25S1G4A @ 1500MHz
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
-25 -20 -15 -10 -5 0
dBm Input
dBm
Out
put
DB GainAR 1dB comprestionAR 3dB Compression
45 dBm
45.8 dBm
10 dB
10 dB9 dB
7 dB
Compression points at one frequency
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What is the correct drive level to the amplifier?
There will always be a max drive level before damage. • Most of AR’s 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
Amplifier Driving
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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 amplifier’s 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. • 2:1 VSWR at rated power
1. Fold back at 20% reflected power (best) [AR]pulsed amps fold back at 50% reflected power [AR]
2. Shutdown at 2:1 VSWR3. 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 (6:1 VSWR) when
used at full power • Folds back so that reverse power does not exceed
reverse power limit• Why can’t 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
Large Amplifier Makeup
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Attenuator
IN OUT
Pre-amplification
splitters combinersFinal stages
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• Why is protection from mismatch needed?• There is only so much that can be done to protect the amplifier without adding exorbitant cost
Amplifier Technologies
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• 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
Care
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• Tube [Vacuum tube] amplifiers• Oil cooling system• New unit: make sure to fill oil correctly.• Do not tip over and place on it’s 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.
Care
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• 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• AR’s amps are fully protected for all mismatches but is still stressful to TWT
Care
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•Solid-state•Do what ever you want they can take it!
Care
G. Barth
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
G. Barth
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 it’s 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
G. Barth
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
G. Barth
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.
G. Barth
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.
1. Run a calibration with the power meter and then a calibration with the spectrum analyzer to see if the forward power reading matches up
2. Use an antenna and spectrum analyzer to spot check V/m reading from probe during calibration especially where the amplifier is being driven hard.
Don’t assume that if the harmonics are out of band that they are no longer a factor! (amplifier, probe, antenna…)
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E-Field Generator• 10kHz-100MHz• Field created between elements or elements and
ground•Non-radiating
• Power limited by Impedance Transformer
Antennas
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Biconical (Bicon)• 20MHz-300MHz• Extremely broad beam width• Power limited by Impedance Transformer (Balun)
Antennas
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Log Periodic (LP)• 26MHz-6GHz• Beam width narrows with frequency• Power limited by input connector and antenna feed
Antennas
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Horn• 200MHz-40GHz• High Gain• Beam width dependant on design• Power limited by input connector or waveguide
Antennas
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Pairing Considerations•Frequency
•Antennas and Amplifiers do they match?•Will switching be required?
• Power• Can antenna handle amplifier power available?• RF connectors compatible?•Cabling?
Equipment Pairing and Sizing
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Pairing ConsiderationsIllumination of EUT• 3dB beam width (test distance)• Will windowing be required?
Equipment Pairing and Sizing
28°
41°
74°
1.5 m
1 m
2 m
3 m
DW2
tan2 1
2tan2DW
2tan2
WD
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Sizing Considerations•Field Strength
• Test distance?• Modulation? (AM, AM constant peak, Pulse)
•Losses•Cables•Chamber effects•Reflections (EUT)•VSWR (antenna)
•Margin
Equipment Pairing and Sizing
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Calculating Power Required to Get Field•Frequency dependant
Equipment Pairing and Sizing
10
2
1030dBiGain
mV metersWatts
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Calculating Power Required to Get Field•Frequency dependant
Equipment Pairing and Sizing
2
2
OldmV
NewmV
OldNew WattsWatts
2
2
Old
NewOldNew Meters
MetersWattsWatts
10.00
100.00
1000.00
700 1500 3500 6000 8500 11000 13500 16000
V/m
Frequency (MHz)
AT4418 Field Strength @ 1 Meter
300W
200W
100W
50W
20W
10W
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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
Equipment Pairing and Sizing
G. Barth
Any questions?
Thank you for your attention!!!
George BarthProduct Engineer, Systems
ar rf/microwave instrumentation160 School House Road
Souderton, PA 18964-9990 gbarth@ar-worldwide.com