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Welcome to Power Measurement Basics

Welcome to Power Measurement Basics. Importance and definitions of power measurements Types of power measurements Measurement uncertainty Sensor types and power meters Considerations in choosing power measurement equipment. Agenda. RL 0.0 dBm ATTEN 10 dB 10 dB / DIV.

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Welcome to Power Measurement Basics

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  1. Welcome to Power Measurement Basics

  2. Importance and definitions of power measurements • Types of power measurements • Measurement uncertainty • Sensor types and power meters • Considerations in choosing power measurement equipment Agenda

  3. RL 0.0 dBm ATTEN 10 dB 10 dB / DIV START 150 MHz STOP 1.150 GHz RB 3.00 MHz VB 300 kHz ST 13.89 msec Importance of Proper Power Levels • Power too low • Signal buried in noise • Power too high • Nonlinear distortion can occur • Or even worse!

  4. Importance of Power in Microwave Applications

  5. Units and Definitions • Unit of power is the watt (W): 1W = 1 joule/sec • The watt is a basic unit: 1 volt is defined as 1 W/ampere • Relative power measurements are expressed in dB: P(dB) = 10 log(P/Pref) • Absolute power measurements are expressed in dBm: P(dBm) = 10 log(P/1 mW)

  6. I + R V - Power: P = (I)(V) AC component of power DC component of power P Amplitude t I V

  7. Z S R L Z S R L Z S R L Z O V Inc V R Power Measurements at Different Frequencies + • DC • Low Frequency • High Frequency ± V - I V I

  8. Importance and definitions of power measurements • Types of power measurements • Measurement uncertainty • Sensor types and power meters • Considerations in choosing power measurement equipment Agenda

  9. Types of Power Measurements • Average Power • Pulse Power • Peak Envelope Power CW RF signal Pulsed RF signal Gaussian pulse signal

  10. Average Power Average over several modulation cycles time Average over many pulse repetitions

  11. Peak Power Overshoot Pulse Width Pulse Power • Complete modulation envelope analysis Pulse Top Amplitude 90% amplitude points 50% amplitude points Average Power Pulse Base Amplitude 10% amplitude points t Offtime Risetime Falltime PRI

  12. Rectangular pulse power using duty cycle method Rectangular pulse power using averaging method 50% amplitude points Peak Envelope Power For pulses that are not rectangular

  13. Measurement Types Summary • For a CW signal, average, pulse, and peak envelope power give the same results • Average power is more frequently measured because of easy-to-use measurement equipment and highly accurate and traceable specifications • Pulse and peak envelope power can often be calculated from average power

  14. Agenda • Importance and definitions of power measurements • Types of power measurements • Measurement uncertainty • Sensor types and power meters • Considerations in choosing power measurement equipment

  15. Sources of Power Measurement Uncertainty • Sensor and source mismatch errors • Power sensor errors • Power meter errors Sensor Mismatch Meter

  16. Calculation of Mismatch Uncertainty Power Meter Signal Source 10 GHz Power Sensor HP 8481A HP 437B SWR = 1.18 SWR = 2.0 r = 0.083 r = 0.33 SOURCE SENSOR Mismatch Uncertainty = ±2 · r · r· 100% SOURCE SENSOR Mismatch Uncertainty =±2 · 0.33 · 0.083 · 100% = ± 5.5%

  17. P P gl i Element h K b e P i Power Sensor Errors (Effective Efficiency) Various sensor losses Power Meter DC signal P r Power Sensor P gl = Cal Factor:

  18. Power Meter Errors Zero Carryover +/- 1 count Power reference error Drift Noise Zero Set Instrumentation error

  19. Calculating Power Measurement Uncertainty Mismatch uncertainty: Cal factor uncertainty: Power reference uncertainty: Instrumentation uncertainty: Now that the uncertainties have been determined, how are they combined? ± 5.5% ± 1.9% ± 1.2% ± 0.5%

  20. Worst-Case Uncertainty • In our example worst case uncertainty would be:= 5.5% + 1.9% + 1.2% + 0.5% = ± 9.1%+9.1% = 10 log (1 + 0.091) = + 0.38 dB- 9.1% = 10 log (1 - 0.091) = - 0.41 dB

  21. RSS Uncertainty • In our example RSS uncertainty would be: 2 2 2 2 = (5.5%) + (1.9%) + (1.2%) + (0.5%) = ± 6.0% + 6.0% = 10 log (1 + 0.060) = +0.25 dB - 6.0% = 10 log (1 - 0.060) = -0.27 dB

  22. Agenda • Importance and definitions of power measurements • Types of power measurements • Measurement uncertainty • Sensor types and power meters • Considerations in choosing power measurement equipment

  23. Thermistors Display Thermocouples Diode Detectors Methods of Sensing Power Power Meter Substituted DC or low frequency equivalent Net RF power absorbed by sensor Power Sensor

  24. Thermistors Thermocouples Diode Detectors Characteristic curves of a typical thermistor element

  25. Thermistors Thermocouples Diode Detectors • A self-balancing bridge containing a thermistor Thermistor mount

  26. Power Meters for Thermistor Mounts • HP 432A Power Meter Thermistor mounts are located in the sensor, not the meter.

  27. Thermistors Thermocouples Diode Detectors • Physics of a thermocouple E-field Bound Ions Diffused Electrons

  28. V 1 - + V h + - V 2 Thermistors Thermocouples Diode Detectors • The principles behind the thermocouple + Metal 1 Cold junction Hot junction - Metal 2 V = V + V - V 2 1 h 0

  29. C b Thermistors Thermocouples Diode Detectors RF power gold leads gold leads • Thermocouple implementation cold junction C c Thin-Film Resistor n - Type Silicon hot hot junction n - Type Silicon RF Input Thin-Film Resistor cold To dc Voltmeter Thermocouples

  30. V P O IN P IN Thermistors Thermocouples Diode Detectors Linear Region Square Law Region of Diode Sensor V µ (log) o Noise Floor [watts] 0.1 nW 0.01 mW -20 dBm -70 dBm

  31. V V o s Thermistors Thermocouples Diode Detectors • How does a diode detector work? + -

  32. The Basic Power Meter Meter Diode Sensor Synchronous Detector Diode Detector BPF LPF Ranging ADC Chopper DC RF AC AUTOZERO µProcessor Square Wave Generator 220 Hz DAC

  33. Agenda • Importance and definitions of power measurements • Types of power measurements • Measurement uncertainty • Sensor types and power meters • Considerations in choosing power measurement equipment

  34. Considerations in Choosing Power Measurement Equipment

  35. Thermistors as Transfer Standards Microcalorimeter National Reference Standard NIST Working Standards NIST Commercial Standards Laboratory Rising Costs / Better Accuracy Measurement Reference Standard Manufacturing Facility Transfer Standard General Test Equipment User

  36. Thermistors Power Ranges of the Various Sensor Types Thermocouple square-law region Extended range using an attenuator Diode detector square-law region [dBm] +50 -70 --60 -50 -40 -30 -20 -10 +10 +20 +30 +40 0

  37. 8481H Thermocouple Mount 8478B Thermistor Mount 8481D PDB Diode Mount 8481A Thermocouple Mount Max Average Power 30 mW 100 mW 300 mW 3.5 W Max Energy Per Pulse 100 W×ms 10 W×ms 30 W×ms Max Envelope Power 200 W 100 mW 15 W 100 W Susceptibility to Overload

  38. POWER V B Series 0 to +44 dBm 8481B 8482B H Series -10 to +35 dBm 8481H 8482H 8487A Q8486A W8486A A Series R8486A -30 to + 20 dBm OPT 33 8485A 8481A 8482A 8483A 8487D Q8486D D Series -70 to -20 dBm R8486D OPT 33 8485D 8481D 100 kHz 10 MHz 50 MHz 18 GHz 26.5 GHz 33 GHz 40 GHz 50 GHz 75 GHz 110 GHz 2 GHz 4.2 GHz | | | | | | | | | | | V FREQUENCY Frequency Ranges

  39. Thermistors Diode Detector Thermocouple Reflection Coefficient

  40. Any Questions?

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