Power Measurement Basics

1
Power Measurement Basics
2
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 Agilents broad range of power
  measurement solutions

3
Agenda
4
Signal Power Levels are Critical
Too low
Signal buried in noise
Too high
Nonlinear distortion...
...Or even worse!
5
Why Not Measure Voltage?
DC
Low Frequency
P IV V2/R
High Frequency

• I and V vary with position

• Power is constant

6
Agenda
7
Units and Definitions

• Power energy transferred per unit time

• Basic power unit is the watt (W)
• 1 W 1 A x 1 V

• 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

8
Average Power
AM
Average over many modulation cycles
Pulsed
Average over many pulse repetitions
9
Pulse Power
Pulse Power Average Power/Duty Cycle

• Rectangular pulse
• Constant duty cycle

Pulse power
10
Peak Envelope Power

• Maximum power in the envelope of a signal

For pulses that are not rectangular
11
Summary Types of Power Measurement
EPM power meter
Average power

• Average Power
• Pulse Power
• Peak Envelope Power

Pulse power
EPM power meter
Average power
EPM-P or P-Series
12
Agenda
13
Instruments That Measure RF Microwave Power

• 0. 0X dB

• Broadband

• 0. X dB or greater

• Traceability

• Frequency selective

14
The Power Meter and Sensor Method
Power Meter
Power Sensor
Display (dBm or W)
Thermistor Thermocouple Diode Detector
DC or low-frequency equivalent
RF power
15
Agenda
16
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 Semiconductor that changes
resistance due to change in temperature
17
Thermocouples

• A junction of two dissimilar metals generates a
  voltage related to temperature

• Junction temperature is directly related to RF
  power

C
c
Cold Junction
Hot
Hot Junction
RF Input
Cold
Thin-Film Thermocouples
To DC Voltmeter
C
b
18
Diode Detectors
Depend on the rectifying characteristics of
non-linear microwave detection curve
19
Power Sensor Technologies Comparison
(30dB)
(50dB)
(up to 90dB)
848xD, E441x, E9300, E9320, N1920 diode sensor
848xA/B/H thermocouple sensor
478A/8478B thermistor sensor
20
Power Sensor and Meter Signal Path
Power Sensor
Power Meter
Synchronous Detector
Diode Detector
BPF
LPF
ADC
Ranging
Chopper
AC
AUTOZERO
Squarewave Generator
µProcessor
220 Hz
DAC
21
Wide Dynamic Range CW Power Sensors
90 dB Dynamic Range
70 to 20 dBm
22
Agenda
23
Agilent Power Meters Product Portfolio
Power Meters (11 models)
Peak Average Power Meters
Average Power Meters
P-Series LXI (1 model)
U2000 Series (4 models)
P-Series (2 models)
EPM Series (2 models)
EPM-P Series (2 models)
432A

• U2000A (3,087)
• U2001A (2,371)
• U2002A (3, 807)
• U2004A (2,675)

• N1911A (US7,501)
• N1912A (US10,547)

• N8262A (US11,784)

• E4416A (US4,523)
• E4417A (US7,111)

• E4418B (US3,550)
• E4419B (US6,092)

30MHz Video Bandwidth
Broadband, for all signal types
5MHz Video Bandwidth
30MHz Video Bandwidth
Broadband, for all signal types
Performance / Price
24
Power Analysis Manager Software N1918A-100
Multichannel measurements display
N1918A-100 Power Analysis Software
Compatible with
N8262A LXI power meter
U2000 USB power sensor
N1911/12A P-Series
Max/Min Limit Test Data logging for 7 Days
Pulse parameters analysis
CCDF statistical analysis
25
U2000 Series USB Power Sensors
Display Power Measurement on a PC or other
Agilent instruments
Work with N9340A HHSA
Work with laptop
26
Instrument Compatibility with USB Sensor
Soon!!
Soon!!
N9020A MXA Vector Signal Analyzer
N5182A MXG Vector Signal Generator
N5242A PNA-X Vector Network Analyzer
E836xB PNA Vector Network Analyzer
N9340 Hand Held Spectrum Analyzer
E506x E507X ENA Vector Network Analyzer
27
U2000 USB Sensor Target Applications
Ideal for manufacturing tests
Ideal for long distance antenna test

• 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

• Key Advantages
• Simplified setup
• Hassle-free calibration internal zeroing
• Long distance measurements with USB-to-LAN hub

E5813A
Design for field applications
Design for satellite receiver tests

• Key Advantages
• Light weight and small size, plug and play. Easy
  to carry for field applications

• Support long distance, multi-channel operations

Multi-list view channel mathematics
28
Agilent Power Sensor Families
P-Series Power Sensors Peak Average power
measurements of wide bandwidth modulated signal
using diode technology
E-Series Power Sensors E441XA Wide Dynamic
Range CW Sensor E9300 Wide Dynamic Range
Average Power Sensor E9320 Peak and Average
Sensor (lt5MHz)
8480 Series Power Sensors Average power
measurements using diode and thermocouple
technology
29
Average/CW Power Sensors
Compatible with EPM, EPM-P and P-series power
meters
POWER
V
8481B
0 to 44 dBm
848X B-Series
8482B
848X Average Diode Sensor
E930X B-Series
E9300B
848X Average Thermocouple Sensor
-30 to 44 dBm
E9301B
E441X 1-Path Diode CW-only Sensor
848X H-Series
8481H
E930X 2-Path Diode True-Average sensor
-10 to 35 dBm
8482H
E9300H
E930X A/H-Series
E9301H
-50 to 30 dBm
OPT H25
E9300A
OPT -H19
E9304A
8487A
W8486A
Q8486A
V8486A
R8486A
OPT 33
848X A-Series
8485A
-30 to 20 dBm
8481A
8482A
8483A
E930X Series
E9300A
-60 to 20 dBm
E9301A
OPT -H18
E9304A
E441X Series
E4413A
-70 to 20 dBm
E4412A
8487D
Q8486D
848X D-Series
R8486D
OPT 33
-70 to -20 dBm
8485D
FREQUENCY
8481D
V
2 GHz
100 kHz
10 MHz
50 MHz
26.5 GHz
33 GHz
40 GHz
50 GHz
75 GHz
110 GHz
4.2 GHz
18 GHz
9 kHz
6 GHz
30
Peak Average/CW Wideband Power Sensors
POWER
V
N192X Peak, Average, rise time, fall time,
pulse width sensor
E932X Peak and Average/CW sensor
N192X A-Series
N1922A (30MHz BW)
Compatible with P-series
-35 to 20 dBm
N1921A (30MHz BW)
E9327A (5MHz BW)
E932X A-Series
E9326A (1.5MHz BW)
Compatible with EPM-P P-Series
-60 to 20 dBm
E9323A (5MHz BW)
E9322A (1.5MHz BW)
E932X A-Series
E9325A (300kHz BW)
-65 to 20 dBm
E9321A (300kHz BW)
FREQUENCY
V
2 GHz
100 kHz
10 MHz
50 MHz
26.5 GHz
33 GHz
40 GHz
50 GHz
75 GHz
110 GHz
4.2 GHz
18 GHz
9 kHz
6 GHz
31
P-Series Power Sensors Internal Zero and Cal
Internal zero and calibration within the
N1921A/22A sensors

• Minimizing set up and calibration time
• Eliminates multiple connections with external
  calibration source
• Reduce measurement uncertainties

From CAL DAC
Voltage Reference
To wideband amplifier and 100 MHz Sampler
Diode Detectors
N1921/22A Wideband Power Sensor Block Diagram
32
E9300 Average Power Sensor Technology
Low-Power Path
( 60 to 10 dBm)
RF Input

• 80 dB dynamic range with any signal type

• Two-path design

• Diode stack/attenuator/diode stack topology

• Automatic path switching

High-Power Path
(10 to 20 dBm)
33
E9320 Two Sensors in One Package
Average-Only Path
Sensor Diode Bulkhead
Load Filter (300 kHz, 1.5 MHz, 5 MHz lowpass)
Switched Gain Preamp
Chopper
RF IN 50 ohms
CW Differential Amp
Av. PATH ISOLATE
Normal (Peak) Path
Variable Gain Differential DC Coupled Amplifier
(300 kHz, 1.5 MHz, 5 MHz)
PEAK AUTO-ZERO
GAIN SELECT
Thermistor Bias I2C Buffer Gain / Mode
Control Sensor ID E2PROM
Bandwidth is sensor dependent
SERIAL BUS
34
Agenda
35
Time-Gated Power Measurements
Optimize for burst type of signals such as
EDGE, WiMAX, WLAN
36
Sensors for Time-Gated Measurements

• Sensor rise/fall time requirements

• For characterizing overshoot lt 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

• lt 13 ns rise time and fall time, 30MHz VBW

• Radar and pulsed component test, WiMAX, WLAN
  wireless formats

37
Triggering and Measurement Capabilities
EPM-P and P-Series Power Meters
Ext Trigger
Start 4
Start 2 Start 3
Average
Delay
Start 1
Length 1
Peak

• Level Internal

• External

• GPIB

38
Agenda
39
Technology Drivers

• Aerospace and Defence (Radar)

• Digital Wireless Communications

WiMAX
GSM (0.3 GMSK)
cdma2000

• TDMA system

• 3G technology

• Broadband communications

• Time-gated average power

• Peak-to-average ratio

• Burst power measurements

• CCDF

• CCDF

• Fast measurements

40
Peak Power Measurement System
Power Sensor
Video BW
RF IN
High-speed sampling measurement
path (EPM-P/E9320)
Detected envelope power
Key system characteristics

• Sufficient video (modulation) bandwidth

High-frequency modulated signal power

• Wide dynamic range

• High-speed, continuous sampling

41
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

42
P-Series Measurement Display

• Graphical trace setup
• Marker measurements and analysis

43
Statistical Analysis
CCDF curve shows how many of time the signal
power is at or above a given power level.
Sample cdmaOne signal
Tabular form
Graphical form

• Allows 4 trace Ch 1, Ch 2, Gaussian, Reference
• 2 Markers reading, delta reading
• User settable input

44
Agenda
45
Sources of Power Measurement Uncertainty

• Sensor and Source Mismatch Errors
• Power Sensor Errors
• Power Meter Errors

Sensor
Meter
Mismatch
46
Sensor and Source Mismatch
Signal Source
Impedance ? Z0
Power Sensor
Power Meter
Ideal impedance Z0
47
Calculation of Mismatch Uncertainty
Signal Source (1 GHz, 0 dBm)
Power Sensor
VSWR 1.2
VSWR 1.26
2 x 0.115 x 0.091 x 100 2.09
48
Power Sensor Cal Factor Uncertainties
Various sensor losses - heat
Power Meter
DC
Power Sensor
(he Effective Efficiency)
Calibration factor, Kb, takes into account the
imperfect efficiency of the sensor and the
mismatch loss

• Printed on sensor label (8480 series)

• Stored in EEPROM (E-series and P-series)

49
Power Meter Instrumentation Uncertainties
Drift
Power Reference Uncertainty
Noise
? 0.4 (25 ? 10degC)
Zero Set
Instrumentation Uncertainty
? 0.8
50
Calculating Power Measurement Uncertainty
1. Identify significant uncertainties

• 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.

2. Combine uncertainties

• Worst-case or Root Sum of the Squares (RSS)
  method

51
Worst-Case Uncertainty

• Worst-case situation is assumed

• All sources of error at their extreme values

• Errors add constructively

• 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

52
RSS (Root Sum of the Squares) Uncertainty
Power Ref
erence


0.4
Normal

2
0.2
Uncertainty

Instrumentation




0.8
Normal
2
0.4
Uncertainty


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.
53
Combined Standard Uncertainty (uc)

• In our example

2
2
2
2
2
(1.48) (1.0) (0.9) (0.2) (0.4)
uc
? 1.99

• Expanded uncertainty (k 2)

? Confidence level of 95.45
k x uc ? 3.98
Worst-case
10 log (1 0.0398) 0.17 dB
10 log (1 ? 0.0398) 0.18 dB

• Agilent AN 1449-3 covers uncertainty calculations

54
National Standards and Traceability
National Reference Standard (Microcalorimeter)
NIST (USA), NPL (UK)
Rising Costs, Better Accuracy
NIST (USA), NPL (UK)
Commercial Standards Laboratory
Thermistors are used for metrology applications
Manufacturing Facility
User
55
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.

• Agilent provides solutions for basic and advanced
  measurements.

• Measurement uncertainty is often calculated using
  the RSS method.

• The accuracy of Agilent power sensors is
  traceable to national standards.

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For More Information

• Agilent Website
• URL http//www.agilent.com/find/powermeters

• Agilent Literature
• Application Note AN 14491, 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
Thank you!