emc test equipment - amplifiers and antennas george barth product engineer, systems ar rf/microwave...

EMC Test Equipment-

Amplifiers and Antennas

George BarthProduct Engineer, Systems

ar rf/microwave instrumentation160 School House Road

Souderton, PA 18964-9990 [email protected]

mailto:[email protected]

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

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•Amplifier Care and Maintenance•Power and Field Measurements•Antennas

•Technologies•Applications

•Equipment Pairing and Sizing•Power vs. Field

Ideal Conditions

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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

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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 damaged

Bad 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

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• Tube (Tetrode tube)• TWT (Traveling Wave Tube) Amplifier• Solid-state

•Class A•Class AB•Class B

What are the differences?

Amplifier Technologies

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FET DC IV-Curve Operating Modes & Bias

0 40 80 120Voltage (V)

DCIV

0

2

4

6

8

p11p10

p9

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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0 40 80 120Voltage (V)

DCIV

0

2

4

6

8

p11p10

p9

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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Class A

0 40 80 120Voltage (V)

DCIV

0

2

4

6

8

p11p10

p9

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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Class A

0 40 80 120Voltage (V)

DCIV

0

2

4

6

8

p11p10

p9

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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0 40 80 120Voltage (V)

DCIV

0

2

4

6

8

p11p10

p9

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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Class AB

0 40 80 120Voltage (V)

DCIV

0

2

4

6

8

p11p10

p9

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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Class AB

0 40 80 120Voltage (V)

DCIV

0

2

4

6

8

p11p10

p9

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

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Class AB

0 40 80 120Voltage (V)

DCIV

0

2

4

6

8

p11p10

p9

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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Class AB

0 40 80 120Voltage (V)

DCIV

0

2

4

6

8

p11p10

p9

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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Class AB Shorted Harmonics

0 40 80 120Voltage (V)

DCIV

0

2

4

6

8

p11p10

p9

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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0 40 80 120Voltage (V)

DCIV

0

2

4

6

8

p11p10

p9

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



0 40 80 120Voltage (V)

DCIV

0

2

4

6

8

p11p10

p9

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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0 40 80 120Voltage (V)

DCIV

0

2

4

6

8

p11p10

p9

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

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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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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

dB

mO

utp

ut

DB Gain

AR 1dB comprestion

AR 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


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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

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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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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

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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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• 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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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?


28°

41°

74°

1.5 m

1 m

2 m

3 m

D

W

2tan2 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


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Calculating Power Required to Get Field•Frequency dependant


10

2

1030dBiGain

mV meters

Watts

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Calculating Power Required to Get Field•Frequency dependant


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


G. Barth

Any questions?

Thank you for your attention!!!

George BarthProduct Engineer, Systems

ar rf/microwave instrumentation160 School House Road

Souderton, PA 18964-9990 [email protected]

mailto:[email protected]

emc test equipment - amplifiers and antennas george barth product engineer, systems ar rf/microwave...

Documents

amplifier amplifier

barth amplifier care

dbm input

dbm of input

compression harmonics

frequency slide

field slide

different classes amplifier