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Power Measurement Basics
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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)
Power Meter Power Sensor
Thermistor Thermocouple Diode Detector Display
DC or low-frequency equivalent
(dBm or W)
RF power
Power Measurement Basics
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Power Measurement Basics
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Average Power
AM
Average over many modulation cycles
Pulsed t
Average over many pulse repetitions
Power Measurement Basics
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Signal Power Levels are Critical
Too low: Signal buried in noise
Too high: Nonlinear distortion...
Power Measurement Basics
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Thermocouples
• A junction of two dissimilar metals generates a voltage related to temperature • Junction temperature is directly related to RF power
• ± 0. X dB or greater • Frequency selective
Vector Signal Analyzer
Spectrum Analyzer
Power Measurement Basics
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The Power Meter and Sensor Method
Instantaneous Power
Peak Envelope Power “Peak Power”
Envelope Power
Power Measurement Basics
Βιβλιοθήκη Baidu
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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)
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)
Power Measurement Basics
Back to Basics - 2006
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Objectives
On completion of this module, you will be able to:
• Explain the importance of power measurements • Define the three basic types of power measurements • Describe the power meter/sensor measurement method • Explain the two most prevalent sensor technologies • Describe advanced measurements used for the latest RF & microwave applications • Calculate power measurement uncertainty • Outline Agilent’s broad range of power measurement solutions
...Or even worse!
Power Measurement Basics
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Importance of Power Measurements
• Critical to specified performance at every level of a system • Many measurements made in design and manufacturing • Measuring equipment and techniques must be: • Accurate • Repeatable • Traceable • Convenient
Power Measurement Basics
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Units and Definitions
• Power = energy transferred per unit time • Basic power unit is the watt (W) • 1W=1A x 1V • A logarithmic (decibel) scale is often used to compare two power levels • Relative power in decibels (dB) = 10 log(P2/P1) • Absolute power is expressed by assigning a reference level to P1 • Power (dBm) = 10 log(P/1 mW)
• I and V vary with position
L
• Power is constant
Amplitude
AC component of power DC component of power
P
I V
t
Power Measurement Basics
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Diode Detectors
+ Rs Vs R matching C b Vo -
Power Measurement Basics
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Power Sensor and Meter Signal Path
Power Sensor
Diode Detector DC BPF Chopper AC
Cc Cold Junction Hot Hot Junction RF Input Cold Thin-Film Thermocouples
RF Power
C
To DC Voltmeter b
Power Measurement Basics
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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)
Power Measurement Basics
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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
Power Measurement Basics
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Instruments That Measure RF & Microwave Power
Power Meter and Sensor Network Analyzer
• ± 0. 0X dB • > – 70 dBm
A (pulse width)
Duty Cycle =
A B
B (pulse repetition interval)
Time
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Power Measurement Basics
Envelope Power and Peak Envelope Power
Power Measurement Basics
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Why Not Measure Voltage?
DC Low Frequency P = IV = V2/R
ZS V R L
+
V
±
ZS R L
–
I I
High Frequency
Z S Z V Inc V Ref O R
Power Meter
Power Measurement Basics
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Pulse Power
Pulse Power = Average Power/Duty Cycle Power • Rectangular pulse • Constant duty cycle
