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EMC Test Equipment
Amplifiers and Antennas
George Barth
Product Engineer, Systems
ar rf/microwave instrumentation
160 School House Road
Souderton, PA 18964-9990
[email protected]
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
G. Barth
Topics
•Amplifier Care and Maintenance
•Power and Field Measurements
•Antennas
•Technologies
•Applications
•Equipment Pairing and Sizing
•Power vs. Field
G. Barth
Ideal Conditions
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
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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.
G. Barth
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
G. Barth
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?
G. Barth
Amplifier Technologies
FET DC IV-Curve Operating Modes & Bias
DCIV
8
5V
6.287 A
p1: Vstep = -3 V
p2: Vstep = -2.5 V
p3: Vstep = -2 V
6
p4: Vstep = -1.5 V
p10
p11
p9
p8
p5: Vstep = -1 V
p6: Vstep = -0.5 V
p7: Vstep = 0 V
4
p8: Vstep = 0.5 V
p7
p6
p5
p9: Vstep = 1 V
p10: Vstep = 1.5 V
p11: Vstep = 2 V
2
p4
p3
p2
p1
0
0
40
80
Voltage (V)
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120
Amplifier Technologies
FET DC IV-Curve Operating Modes & Bias
DCIV
8
5V
6.287 A
p1: Vstep = -3 V
p2: Vstep = -2.5 V
p3: Vstep = -2 V
6
p4: Vstep = -1.5 V
p10
p11
p9
p8
p5: Vstep = -1 V
p6: Vstep = -0.5 V
p7: Vstep = 0 V
4
p8: Vstep = 0.5 V
Class A
p6
p5
p9: Vstep = 1 V
p10: Vstep = 1.5 V
2
p7
p11: Vstep = 2 V
Class AB
p4
p3
p2
p1
Class B
0
0
40
80
Voltage (V)
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120
Amplifier Technologies
Class A
DCIV
8
5V
6.287 A
p1: Vstep = -3 V
p2: Vstep = -2.5 V
p3: Vstep = -2 V
6
p4: Vstep = -1.5 V
p10
p11
p9
p8
p5: Vstep = -1 V
p6: Vstep = -0.5 V
p7: Vstep = 0 V
4
p8: Vstep = 0.5 V
p7
p6
p5
p9: Vstep = 1 V
p10: Vstep = 1.5 V
p11: Vstep = 2 V
2
p4
p3
p2
p1
0
0
40
80
Voltage (V)
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120
Amplifier Technologies
Class A
DCIV
8
5V
6.287 A
p1: Vstep = -3 V
p2: Vstep = -2.5 V
p3: Vstep = -2 V
6
p4: Vstep = -1.5 V
p10
p11
p9
p8
p5: Vstep = -1 V
p6: Vstep = -0.5 V
p7: Vstep = 0 V
4
p8: Vstep = 0.5 V
p7
p6
p5
p9: Vstep = 1 V
p10: Vstep = 1.5 V
p11: Vstep = 2 V
2
p4
p3
p2
p1
0
0
40
80
Voltage (V)
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120
Amplifier Technologies
Class A
DCIV
8
5V
6.287 A
p1: Vstep = -3 V
p2: Vstep = -2.5 V
p3: Vstep = -2 V
6
p4: Vstep = -1.5 V
p10
p11
p9
p8
p5: Vstep = -1 V
p6: Vstep = -0.5 V
p7: Vstep = 0 V
4
p8: Vstep = 0.5 V
p7
p6
p5
p9: Vstep = 1 V
p10: Vstep = 1.5 V
p11: Vstep = 2 V
2
p4
p3
p2
p1
0
0
40
80
Voltage (V)
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120
Amplifier Technologies
Class A
DCIV
8
5V
6.287 A
p1: Vstep = -3 V
p2: Vstep = -2.5 V
p3: Vstep = -2 V
6
p4: Vstep = -1.5 V
p10
p11
p9
p8
p5: Vstep = -1 V
p6: Vstep = -0.5 V
p7: Vstep = 0 V
4
p8: Vstep = 0.5 V
p7
p6
p5
p9: Vstep = 1 V
p10: Vstep = 1.5 V
p11: Vstep = 2 V
2
p4
p3
p2
p1
0
0
40
80
Voltage (V)
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120
Amplifier Technologies
Class A
DCIV
8
5V
6.287 A
Full current and voltage swing
No harmonics
p2: Vstep = -2.5 V
p1: Vstep = -3 V
p3: Vstep = -2 V
6
p4: Vstep = -1.5 V
p10
p11
p9
p8
p5: Vstep = -1 V
p6: Vstep = -0.5 V
p7: Vstep = 0 V
4
p8: Vstep = 0.5 V
p7
p6
p5
p9: Vstep = 1 V
p10: Vstep = 1.5 V
p11: Vstep = 2 V
2
p4
p3
p2
p1
0
0
40
80
Voltage (V)
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120
Amplifier Technologies
Class B
DCIV
8
5V
6.287 A
p1: Vstep = -3 V
Clipping
High Harmonic content
p2: Vstep = -2.5 V
p3: Vstep = -2 V
6
p4: Vstep = -1.5 V
p10
p11
p9
p8
p5: Vstep = -1 V
p6: Vstep = -0.5 V
p7: Vstep = 0 V
4
p8: Vstep = 0.5 V
p7
p6
p5
p9: Vstep = 1 V
p10: Vstep = 1.5 V
p11: Vstep = 2 V
2
p4
p3
p2
p1
0
0
40
80
Voltage (V)
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120
Amplifier Technologies
Class AB
DCIV
8
5V
6.287 A
p1: Vstep = -3 V
p2: Vstep = -2.5 V
p3: Vstep = -2 V
6
p4: Vstep = -1.5 V
p10
p11
p9
p8
p5: Vstep = -1 V
p6: Vstep = -0.5 V
p7: Vstep = 0 V
4
p8: Vstep = 0.5 V
p7
p6
p5
p9: Vstep = 1 V
p10: Vstep = 1.5 V
p11: Vstep = 2 V
2
p4
p3
p2
p1
0
0
40
80
Voltage (V)
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120
Amplifier Technologies
Class AB
DCIV
8
5V
6.287 A
p1: Vstep = -3 V
p2: Vstep = -2.5 V
p3: Vstep = -2 V
6
p4: Vstep = -1.5 Good
V
p10
p11
p9
smallp8signal response
p5: Vstep = -1 V
p6: Vstep = -0.5 V
p7: Vstep = 0 V
4
p8: Vstep = 0.5 V
p7
p6
p5
p9: Vstep = 1 V
p10: Vstep = 1.5 V
p11: Vstep = 2 V
2
p4
p3
p2
p1
0
0
40
80
Voltage (V)
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120
Amplifier Technologies
Class AB
DCIV
8
5V
6.287 A
p1: Vstep = -3 V
p2: Vstep = -2.5 V
p3: Vstep = -2 V
6
p4: Vstep = -1.5 V
p10
p11
p9
p8
p5: Vstep = -1 V
p6: Vstep = -0.5 V
p7: Vstep = 0 V
4
p8: Vstep = 0.5 V
p7
p6
p5
p9: Vstep = 1 V
p10: Vstep = 1.5 V
p11: Vstep = 2 V
2
p4
p3
p2
p1
0
0
40
80
Voltage (V)
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120
Amplifier Technologies
Class AB
DCIV
8
5V
6.287 A
p1: Vstep = -3 V
p2: Vstep
= -2.5 V
Clipping
p3: Vstep = -2 V
6
p4: Vstep = -1.5 V
and Harmonics introduced
p10
p11
p9
p8
p5: Vstep = -1 V
p6: Vstep = -0.5 V
p7: Vstep = 0 V
4
p8: Vstep = 0.5 V
p7
p6
p5
p9: Vstep = 1 V
p10: Vstep = 1.5 V
p11: Vstep = 2 V
2
p4
p3
p2
p1
0
0
40
80
Voltage (V)
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120
Amplifier Technologies
Class AB Shorted Harmonics
DCIV
8
5V
6.287 A
p1: Vstep = -3 V
p2: Vstep = -2.5 V
p3: Vstep = -2 V
6
p4: Vstep = -1.5 V
p10
p11
p9
p8
p5: Vstep = -1 V
p6: Vstep = -0.5 V
p7: Vstep = 0 V
4
p8: Vstep = 0.5 V
p7
p6
p5
p9: Vstep = 1 V
p10: Vstep = 1.5 V
p11: Vstep = 2 V
2
p4
p3
p2
p1
0
0
40
80
Voltage (V)
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120
Amplifier Technologies
Class AB Shorted Harmonics
DCIV
8
5V
6.287 A
p1: Vstep = -3 V
p2: Vstep = -2.5 V
p3: Vstep = -2 V
6
p4: Vstep = -1.5 V
p10
p11
p9
p8
p5: Vstep = -1 V
p6: Vstep = -0.5 V
p7: Vstep = 0 V
4
p8: Vstep = 0.5 V
p7
p6
p5
p9: Vstep = 1 V
p10: Vstep = 1.5 V
p11: Vstep = 2 V
2
p4
p3
p2
p1
0
0
40
80
Voltage (V)
G. Barth
120
Amplifier Technologies
Class AB Shorted Harmonics
DCIV
8
5V
6.287 A
p1: Vstep = -3 V
p2: Vstep = -2.5 V
p3: Vstep = -2 V
6
p4: Vstep =Good
-1.5 V
p10
p11
p9
small signal
performance
p8
p5: Vstep = -1 V
p6: Vstep = -0.5 V
p7: Vstep = 0 V
4
p8: Vstep = 0.5 V
p7
p6
p5
p9: Vstep = 1 V
p10: Vstep = 1.5 V
p11: Vstep = 2 V
2
p4
p3
p2
p1
0
0
40
80
Voltage (V)
G. Barth
120
Amplifier Technologies
Class AB Shorted Harmonics
DCIV
8
5V
6.287 A
p1: Vstep = -3 V
p2: Vstep = -2.5 V
p3: Vstep = -2 V
6
p4: Vstep = -1.5 V
p10
p11
Selfp9biasing
p8
p5: Vstep = -1 V
p6: Vstep = -0.5 V
p7: Vstep = 0 V
4
p8: Vstep = 0.5 V
p7
p6
p5
p9: Vstep = 1 V
p10: Vstep = 1.5 V
p11: Vstep = 2 V
2
p4
p3
p2
p1
0
0
40
80
Voltage (V)
G. Barth
120
Amplifier Technologies
Class AB Shorted Harmonics
DCIV
8
5V
6.287 A
Good
p1: Vstep
= -3 V performance
due to self biasing
limited
to sub octave bandwidth
p2: Vstep = -2.5
V
p3: Vstep = -2 V
6
p4: Vstep = -1.5 V
p10
p11
p9
p8
p5: Vstep = -1 V
p6: Vstep = -0.5 V
p7: Vstep = 0 V
4
p8: Vstep = 0.5 V
p7
p6
p5
p9: Vstep = 1 V
p10: Vstep = 1.5 V
p11: Vstep = 2 V
2
p4
p3
p2
p1
0
0
40
80
Voltage (V)
G. Barth
120
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. <250 MHz
TWTA
Worst
Worst
Worst
Worst
Worst
High freq. >1 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
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
47
45.8 dBm
46
45 dBm
45
DB Gain
AR 1dB comprestion
AR 3dB Compression
44
43
42
dBmOutput
Example of compressed power
dB Gain for 25S1G4A @ 1500MHz
41
40
7 dB
39
10 dB
38
37
9 dB
36
10 dB
35
34
33
32
-25
-20
-15
-10
-5
dBm Input
Compression points at one frequency
G. Barth
0
Amplifier Driving
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
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Amplifier Driving
This brings us to the proper input to produce the desired linear output
G. Barth
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 VSWR
3. 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]
G. Barth
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
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Large Amplifier Makeup
OUT
IN
Attenuator
Pre-amplification
splitters
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Final stages
combiners
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
G. Barth
Care
• 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.
G. Barth
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
• AR’s amps are fully protected for all mismatches but is still stressful to TWT
G. Barth
Care
•Solid-state
•Do what ever you want they can take it!
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)
• 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
G. Barth
Frequency Selective
Device (Spectrum Analyzer)
• Can discern between different
frequency signals
• Measures peak
– RMS = Peak/SQRT(2)
• Can measure modulated signals
• Possible time consuming setup
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…)
G. Barth
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?
G. Barth
Equipment Pairing and Sizing
Pairing Considerations
Illumination of EUT
• 3dB beam width (test distance)
• Will windowing be required?
1.5 m
1m
74°
W 
  2 tan 1 
 2 D 
2m
41°

W  2D tan  
2
D
G. Barth
W
2 tan 
 2
3m
28°
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
G. Barth
Equipment Pairing and Sizing
Calculating Power Required to Get Field
•Frequency dependant
GAIN
16
14
V  meters2

Watts  m
30  10
 GaindBi 


 10 
G A IN ( d B i)
12
10
8
6
4
2
0
700
1000 1750 3000 4500 6000 7500 9000 10500 12000 13500 15000 16500 18000
FREQUENCY (MHz)
G. Barth
Equipment Pairing and Sizing
Calculating Power Required to Get Field
•Frequency dependant
AT4418 Field Strength @ 1 Meter
1000.00
WattsNew
V m New 2
 WattsOld
V m Old 2
300W
200W
V/m
100W
100.00
50W
20W
2

MetersNew 
WattsNew  WattsOld
MetersOld 2
10W
10.00
700
1500
3500
6000
8500
Frequency (MHz)
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11000
13500
16000
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
Any questions?
Thank you for your attention!!!
George Barth
Product Engineer, Systems
ar rf/microwave instrumentation
160 School House Road
Souderton, PA 18964-9990
[email protected]
G. Barth