Fundamentals of RF and Microwave Power Measurements Application Note 64-1B Newly revised and updated Classic application note on power measurements Table of Contents I. Introduction The Importance of Power . 4 A Brief History of Power Measurement . 5 II. Power Measurement Units and Definitions . 7 Three Methods of Sensing Power . 11 Key Power Sensor Parameters . 11 The Hierarchy of Power Measurement, National Standards and Traceability . 12 A New Sensor for Power Reference Transfer . 14 III. Thermistor Sensors and Instrumentation Thermistor Sensors . 15 Coaxial Thermistor Sensors . 16 Waveguide Thermistor Sensors . 16 Bridges, from Wheatstone to Dual-Compensated DC Types . 16 Thermistors as Power Transfer Standards . 18 Other DC-Substitution Meters . 18 IV. Thermocouple Sensors and Instrumentation Principles of Thermocouples . 20 The Thermocouple Sensor . 21 Power Meters for Thermocouple Sensors . 25 Reference Oscillator . 27 EPM Series Power Meters . 27 V. Diode Sensors and Instrumentation Diode Detector Principles . 29 Using Diodes for Sensing Power . 31 New Wide-Dynamic-Range CW-Only Power Sensors . 33 Wide-Dynamic-Range Average Power Sensors . 34 A New Versatile Power Meter to Exploit 90 dB Range Sensors . 36 Traceable Power Reference . 38 Signal Waveform Effects on the Measurement Uncertainty of Diode Sensors . .39 VI. Measurement Uncertainty Power Transfer, Generators and Loads . 42 RF Circuit Descriptions . 42 Reflection Coefficient . 44 Signal Flowgraph Visualization . 45 Mismatch Uncertainty . 49 Mismatch Loss . 50 Other Sensor Uncertainties . 50 Calibration Factor . 51 Power Meter Instrumentation Uncertainties . 52 Calculating Total Uncertainty . 54 Power Measurement Equation . 55 Worst Case Uncertainty . 57 2 RSS Uncertainty . 58 New Method of Combining Power Meter Uncertainties . 59 Power Measurement Model for ISO Process . 60 Standard Uncertainty of Mismatch Model . 62 Example of Calculation of Uncertainty Using ISO Model . 63 VII. Power Measurement Instrumentation Compared Accuracy vs. Power Level . 67 Frequency Range and SWR (Reflection Coefficient) . 69 Speed of Response . 70 Automated Power Measurement . 71 Susceptibility to Overload . 72 Signal Waveform Effects . 72 VIII. Peak Power A Brief History of Peak Power Measurements . 73 IEEE Video Pulse Standards Adapted for Microwave Pulses . 74 Peak Power Waveform Definitions . 75 Glossary and List of Symbols . 77 Pulse terms and definitions, Figures 8-3 and 8-4, reprinted from IEEE STD 194-1977 and ANSI/IEEE STD 181-1977, Copyright © 1977 by the Institute of Electrical and Electronics Engineers, Inc. The IEEE disclaims any responsibility or liability resulting from the placement and use in this publication. Information is reprinted with the permission of the IEEE. 3 This application note, AN64-1B, is a major revision of the 1977 edition of AN64-1, I. Introduction which has served for many years as a key reference for RF and microwave power measurement. It was written for two purposes: 1).