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Back to Basics - 2008
Power Measurement Basics
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Objectives
On completion of this module, you will be able to understand:•the importance of power measurements
•Three basic types of power measurements
•Power meter/sensor measurement method
•Two most prevalent sensor technologies
•Advanced measurements used for the latest RF & microwave applications
•Calculate power measurement uncertainty
•Outline Agilent’s broad range of power
measurement solutions
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Agenda
Importance of Power Measurements
Average, Peak and Pulse Power
Power Meter & Sensor Measurement Method
Sensor Technologies Agilent Power Measurement
Solutions Time-Gated Power
Measurements Advanced Power
Measurements Measurement Uncertainty,
Standards and Traceability Agilent Power Sensor
Selection Guides (Appendix)
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Signal Power Levels are Critical
Too low:
Too high:
...Or even worse!
Signal buried in noise
Nonlinear distortion...
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DC
VInc
VRef
ZO
ZS R
L
VRL
ZS
I
Why Not Measure Voltage?
RL
ZS
V
–
+±
I
Low Frequency
P = IV = V2/R
High Frequency• I and V vary with position• Power is constant
Amplitude
t
P
I
V
DC component of power
AC component of power
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Importance of Power Measurements
Average, Peak and Pulse Power
Power Meter & Sensor Measurement Method
Sensor Technologies Agilent Power Measurement
Solutions Time-Gated Power
Measurements Advanced Power
Measurements Measurement Uncertainty,
Standards and Traceability Agilent Power Sensor
Selection Guides (Appendix)
Agenda
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•Basic power unit is the watt (W)
• 1 W = 1 A x 1 V
Units and Definitions
•Power = energy transferred per unit time
• A logarithmic (decibel) scale is often used to compare
two power levels•Relative power in decibels (dB):
•Absolute power is expressed by assigning a reference
level to Pref in dBm:
refP
PdBP log10)(
mW
PdBmP
1log10)(
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t
Average over many modulation cycles
AM
Pulsed
Average over many pulse repetitions
Average Power
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Pulse Power
Power
Time
A(pulse width) Duty Cycle =AB
(pulse repetition interval)
B
Pulse Power = Average Power/Duty Cycle
• Rectangular pulse
• Constant duty cyclePulse power
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• Maximum power in the envelope of a signal
Peak Envelope Power
For pulses that are not rectangular
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Average Power
Pulse Power
Peak Envelope Power
Summary: Types of Power Measurement
Pulse power
Average power
EPM power meter
EPM power meter
EPM-P or P-Series
Average power
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Agenda
Importance of Power Measurements
Average, Peak and Pulse Power
Power Meter & Sensor Measurement Method
Sensor Technologies Agilent Power Measurement
Solutions Time-Gated Power
Measurements Advanced Power
Measurements Measurement Uncertainty,
Standards and Traceability Agilent Power Sensor
Selection Guides (Appendix)
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Instruments That Measure RF & Microwave Power
Spectrum Analyzer
Network AnalyzerPower Meter and Sensor
Vector Signal Analyzer
• ± 0. 0X dB
• ± 0. X dB or greater • Traceability • Frequency selective
• Broadband
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The Power Meter and Sensor Method
DC or low-frequency equivalent
RF power
Power SensorPower Meter
Display
(dBm or W)
ThermistorThermocouple
Diode Detector
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Agenda
Importance of Power Measurements
Average, Peak and Pulse Power
Power Meter & Sensor Measurement Method
Sensor Technologies Agilent Power Measurement
Solutions Time-Gated Power
Measurements Advanced Power
Measurements Measurement Uncertainty,
Standards and Traceability Agilent Power Sensor
Selection Guides (Appendix)
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Thermistors
•One of the earliest types of power sensors
•Have been replaced in most applications by
thermocouples and diode detectors
•Still used for power transfer standards in
metrology applications
Thermistor mount
Thermistor : Semiconductor that changes resistance due to change in temperature
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Cc
Thermocouples•A junction of two dissimilar metals generates a
voltage related to temperature
•Junction temperature is directly related to RF power
RF Power
Cb
RF Input
Hot Junction
Hot
Cold
Cold Junction
To DC Voltmeter
Thin-Film Thermocouples
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Diode Detectors
CbRmatchingVo
+
-
RsVs
Depend on the rectifying characteristics of non-linear microwave detection curve
50 dB
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Power Sensor Technologies Comparison
Power Sensor Advantage 优点 Disadvantage 缺点
Thermistor Directly traceable to NIST Slow, Low sensitivity
Thermocouple Accurate, good linearity Slow, Low sensitivity
Diode Detector Fast, wide dynamic range Easily overloaded
848xA/B/H thermocouple
sensor
848xD, E441x, E9300, E9320, N1920 diode
sensor
478A/8478B thermistor
sensor
(30dB)
(50dB)
(up to 90dB)
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Power Sensor
ChopperDiodeDetector
Power MeterSynchrono
usDetector
LPF ADCRanging
BPF
SquarewaveGenerator
µProcessor
AC
220 Hz
DC
RF
DAC
AUTOZERO
Power Sensor and Meter Signal Path
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Wide Dynamic Range CW Power Sensors – 70 to + 20
dBm= 90 dB Dynamic Range
Calibration Data
Contain Input power level vs freq vs temperature
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Agenda
Importance of Power Measurements
Average, Peak and Pulse Power
Power Meter & Sensor Measurement Method
Sensor Technologies Agilent Power Measurement
Solutions Time-Gated Power
Measurements Advanced Power
Measurements Measurement Uncertainty,
Standards and Traceability Agilent Power Sensor
Selection Guides (Appendix)
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Agilent Power Meters Product Portfolio Power Meters
(11 models)
P-Series(2 models)
30MHz Video
Bandwidth
• N1911A (US$7,501)
• N1912A (US$10,547)
EPM-P Series
(2 models)
5MHz Video
Bandwidth
• E4416A (US$4,523)
• E4417A (US$7,111)
EPM Series
(2 models)
Broadband, for all signal types
• E4418B (US$3,550)
• E4419B (US$6,092)
432AP-Series
LXI(1 model)
30MHz Video
Bandwidth
• N8262A (US$11,784)
Broadband, for all
signal types
U2000 Series
(4 models)
•U2000A ($3,087)
•U2001A ($2,371)
•U2002A ($3, 807)
•U2004A ($2,675)
Peak & Average Power Meters Average Power Meters
Performance / Price
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CCDF statistical analysis
Pulse parameters analysis Max/Min Limit TestData logging for 7 Days
N1911/12A P-Series
N8262A LXI power meter
N1918A-100 Power
Analysis Software
U2000 USB power sensor
Compatible with
Power Analysis Manager Software N1918A-100
Multichannel measurements display
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U2000 Series USB Power Sensors Display Power Measurement on a PC or other Agilent instruments
Work with laptopWork with N9340A HHSA
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Instrument Compatibility with USB Sensor
N9020A MXA Vector Signal Analyzer
N5242A PNA-X Vector Network Analyzer
N9340 Hand Held Spectrum Analyzer
E506x & E507X ENA Vector Network Analyzer
E836xB PNA Vector Network Analyzer
N5182A MXG Vector Signal Generator
Now!
Now!Now!
Soon!!
Soon!!
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U2000 USB Sensor Target Applications
Key Advantages
Lower cost solution with equivalent bench power meter performance
Simplified your measurement setup with USB plug & play
Optimize you test rack space by going powermeter-less
Ideal for manufacturing testsIdeal for long distance antenna test Key
Advantages Simplified setup Hassle-free
calibration – internal zeroing
Long distance measurements with USB-to-LAN hub
Design for field applications Key Advantages Light weight and small
size, plug and play. Easy to carry for field applications
Design for satellite receiver tests Support long distance, multi-channel operations
E5813A
Multi-list view & channel mathematics
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Agilent Power Sensor Families
8480 Series Power Sensors Average power measurements using diode and thermocouple technology
E-Series Power Sensors E441XA Wide Dynamic Range CW SensorE9300 Wide Dynamic Range
Average Power SensorE9320 Peak and Average Sensor (<5MHz)
P-Series Power Sensors Peak & Average power measurements of wide bandwidth modulated signal using diode technology
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Average/CW Power SensorsPOWER
FREQUENCY
848X B-Series0 to +44 dBm
848X H-Series-10 to +35 dBm
848X A-Series
-30 to + 20 dBm
848X D-Series
-70 to -20 dBm
8481B8482B
8481H8482H
8487AQ8486A W8486A
R8486A
8485A
8481A
8482A
8483A
8487D
Q8486D
R8486D8485D
8481D
100 kHz
10 MHz
50 MHz
2 GHz
4.2 GHz
18 GHz
26.5 GHz
33 GHz
40 GHz
50 GHz
75 GHz
110 GHz
OPT 33
V
V
V8486A
9 kHz
6 GHz
E9304A
E9301A
E9300A
OPT -H18
-70 to +20 dBm
E441X Series
-60 to +20 dBmE930X Series
E9301HE9300H
-50 to +30 dBmE930X A/H-Series
E9301B
E9300B
-30 to +44 dBmE930X B-Series
OPT 33
E4413A
E4412A
848X Average Diode Sensor
848X Average Thermocouple Sensor
E441X 1-Path Diode CW-only Sensor
E930X 2-Path Diode True-Average sensor
OPT –H24
E9300A OPT –H25
OPT -H19E9304A
Compatible with EPM, EPM-P and P-series power meters
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E9323A (5MHz BW)
E9322A (1.5MHz BW)
Peak & Average/CW & Wideband Power SensorsPOWER
FREQUENCY
-35 to + 20 dBm
100 kHz
10 MHz
50 MHz
2 GHz
4.2 GHz
18 GHz
26.5 GHz
33 GHz
40 GHz
50 GHz
75 GHz
110 GHz
V
V
9 kHz
6 GHz
-65 to +20 dBm
-60 to +20 dBm
N192X Peak, Average, rise time, fall time, pulse width sensor
E932X Peak and Average/CW sensor
N1922A (30MHz BW)
N1921A (30MHz BW)
E9327A (5MHz BW)
E9326A (1.5MHz BW)
E9325A (300kHz BW)
E9321A (300kHz BW)
N192X A-Series
E932X A-Series
E932X A-Series
Compatible with P-series
Compatible with EPM-P & P-Series
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P-Series Power Sensors Internal Zero and CalInternal zero and calibration within the N1921A/22A sensors
N1921/22A Wideband Power Sensor Block Diagram
RF Input
To wideband amplifier and 100 MHz Sampler
Voltage Reference
From CAL DAC
Zero and Cal Path Switching
Diode Detectors
Minimizing set up and calibration timeEliminates multiple connections with external calibration source Reduce measurement uncertainties
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Agenda
Importance of Power Measurements
Average, Peak and Pulse Power
Power Meter & Sensor Measurement Method
Sensor Technologies Agilent Power Measurement
Solutions Time-Gated Power
Measurements Advanced Power
Measurements Measurement Uncertainty,
Standards and Traceability Agilent Power Sensor
Selection Guides (Appendix)
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Time-Gated Power MeasurementsEDGE signal (GSM)
Peak, average and peak-to-
average ratio of a single burst
Optimize for ‘burst’ type of signals such as EDGE, WiMAX, WLAN
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Sensors for Time-Gated Measurements• Sensor rise/fall time requirements
•For characterizing overshoot: < 1/8 signal rise time
•For average power: same as signal rise time
• E9320 peak/average sensors•200 ns rise time (typical), up to
5MHz VBW•TDMA, CDMA and W-CDMA wireless formats
• P-Series wideband power sensors•< 13 ns rise time and fall time,
30MHz VBW•Radar and pulsed component test, WiMAX, WLAN wireless formats
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Length 1
Length 4
Length 3
Length 2
Start 1
Start 2Start 3
Ext TriggerStart 4
Delay
Triggering and Measurement CapabilitiesEPM-P and P-Series Power
Meters
Triggers
Average
Peak
• Level = Internal• External• GPIB
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Agenda
Importance of Power Measurements
Average, Peak and Pulse Power
Power Meter & Sensor Measurement Method
Sensor Technologies Agilent Power Measurement
Solutions Time-Gated Power
Measurements Advanced Power
Measurements Measurement Uncertainty,
Standards and Traceability Agilent Power Sensor
Selection Guides (Appendix)
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GSM (0.3 GMSK) cdma2000
• Digital Wireless Communications
Technology Drivers• Aerospace and Defence (Radar)
• TDMA system
• Time-gated average power• Fast measurements
• 3G technology
• Peak-to-average ratio• CCDF
WiMAX
• Broadband communications• Burst power measurements• CCDF
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P-Series Power Meters and Sensors
• Key Measurements
• Peak, average, peak-to-average ratio• rise time, fall time, pulse width, pulse period,
duty cycle; time-gated and free-run measurements
• CCDF statistical analysis
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P-Series Measurement Display •Graphical trace setup •Marker measurements and analysis
MKR 1 MKR 2
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Statistical Analysis
Allows 4 trace – Ch 1, Ch 2, Gaussian, Reference
2 Markers reading, delta reading
User settable input
Tabular form
Graphical form
CCDF curve shows how many % of time the signal power is at or above a given power level.Sample cdmaOne signal
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Agenda
Importance of Power Measurements
Average, Peak and Pulse Power
Power Meter & Sensor Measurement Method
Sensor Technologies Agilent Power Measurement
Solutions Time-Gated Power
Measurements Advanced Power
Measurements Measurement Uncertainty,
Standards and Traceability Agilent Power Sensor
Selection Guides (Appendix)
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Sources of Power Measurement Uncertainty
•Sensor and Source Mismatch Errors
•Power Sensor Errors•Power Meter Errors
Mismatch
Sensor
Meter
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Sensor and Source Mismatch
Signal Source
Power Sensor Power Meter
Ideal impedance = Z0
Impedance Z0
VSWR
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Calculation of Mismatch Uncertainty
Signal Source(1 GHz, 0 dBm)
Power MeterN1921A
= ± 2 x 0.115 x 0.091 x 100% = ± 2.09%
Mismatch Uncertainty = ± 2 x x x 100%
SOURCE SENSOR
VSWR = 1.26
VSWR = 1.2
SENSOR
= 0.091
= 0.115SOURCE
VSWR 1
VSWR 1=
Power Sensor
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Power Sensor Cal Factor Uncertainties Various sensor
losses - heat
DC
Power Sensor
Power Meter Power Meter
Pr
Sensing Element
Pi Pgl
Cal Factor : e
PKb=
glPi
e = Effective Efficiency)
• Printed on sensor label (8480 series)• Stored in EEPROM (E-series and P-series)
Calibration factor, Kb, takes into account the imperfect efficiency of the sensor and the mismatch loss
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Power Meter Instrumentation Uncertainties
Zero Set
Noise
DriftPower
Reference Uncertainty
0.4 % (25 10degC)
Instrumentation Uncertainty
0.8 %
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Calculating Power Measurement Uncertainty
• Mismatch uncertainty: ± 2.09%
• Power linearity: ± 2.0% 1
• Cal factor uncertainty: ± 1.8% 1
• Power reference uncertainty: ± 0.4% 1
• Instrumentation uncertainty: ± 0.8%
1 Specifications apply for an E9301A sensor and Agilent power meter over a temperature range of 25 ±10 degrees C.
1. Identify significant uncertainties
2. Combine uncertainties • Worst-case or Root Sum of the Squares (RSS) method
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Worst-Case Uncertainty
• All sources of error at their extreme values• Errors add constructively
• Worst-case situation is assumed
• In our example measurement:2.09% + 2.0% + 1.8% + 0.4% + 0.8% = ± 7.09%
Or, in log terms:+ 7.09% = 10 log (1 + 0.0709) = + 0.30 dB– 7.09% = 10 log (1 - 0.0709) = – 0.32 dB
• Extremely conservative
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RSS (Root Sum of the Squares) Uncertainty*
Source of Uncertainty
Value
(± %) Probability
Distribution Divisor
Standard Uncertainty
u
i
(k=1) Source/Sensor
Mismatch at 2 GHz 2.09
U-shaped
1.414
1.48
Calibration Factor Uncertainty at 2 GHz 2.0
Normal
2
1.0
Linearity at 0 dBm 1.8 Normal 2 0.9 Power Reference Uncertainty
0.4 Normal 2 0.2
Instrumentation Uncertainty
0.8 Normal 2 0.4
Combined Standard Uncertainty = uc = RSS of ui * In accordance to guidelines published in the ISO Guide to the Expression of Uncertainty
in Measurement and ANSI/NCSL Z540-2-1996, US Guide to the Expression of Uncertainty in Measurement.
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Combined Standard Uncertainty (uc)•In our example:
= (1.48) + (1.0) + (0.9) + (0.2) + (0.4) 2 2 2 2 2uc
•Expanded uncertainty (k = 2)
= 1.99%
= k x uc =
3.98% = 10 log (1 + 0.0398) = + 0.17 dB10 log (1 0.0398) = – 0.18
dB
Worst-case+ 0.17 dB– 0.18 dB
•Agilent AN 1449-3 covers uncertainty calculations
Confidence level of 95.45%
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National Standards and Traceability
NIST (USA), NPL (UK)
NIST (USA), NPL (UK)
Commercial Standards LaboratoryManufacturing Facility
User
Rising Costs, Better
Accuracy
National ReferenceStandard
(Microcalorimeter)
Working Standards
MeasurementReference Standard
Transfer Standard
General TestEquipment
Thermistors are used for metrology
applications
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Summary
•Accurate power measurements (made with a power meter/sensor combination) are crucial in RF and microwave applications.•The three fundamental power measurements are average, peak and pulse.
•Modern wireless and radar technologies require time-gated and advanced measurements.
•Measurement uncertainty is often calculated using the RSS method.
•The accuracy of Agilent power sensors is traceable to national standards.
•Agilent provides solutions for basic and advanced measurements.
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For More Information
• Agilent Website
• URL: http://www.agilent.com/find/powermeters
• Agilent Literature
• Application Note AN 1449–1, 2, 3 and 4, Fundamentals of RF and Microwave Power Measurements (Parts 1, 2, 3 and 4).
• Product Note, Choosing the Right Power Meter and Sensor (Lit. No. 5968-7150E).
• Application Note AN 64-4D, 4 steps for making better power measurements (Lit. No. 5965-8167E)
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Questions and Answers