Fundamentals of RF and Microwave Power Measurements (Part 1)
Introduction to Power, History, Definitions, International Standards, and Traceability AN 1449-1, literature number 5988-9213EN
Part 1 introduces the historical basis for power measurements and provides definitions for average, peak, and complex modulations. This application note overviews various sensor technologies needed for the diversity of test signals. It describes the hierarchy of international power traceability, yielding comparison to national standards at worldwide national measurement institutes (NMIs) like the U.S. National Institute of Standards and Technology. Finally, the theory and practice of power sensor comparison procedures are examined with regard to transferring calibration factors and uncertainties. A glossary is included which serves all four parts.
Table of Contents
- The importance of Power
- A brief history of power measurements
- A history of peak power measurements
- Power Measurement Fundamentals
- Understanding the characteristics of the signal under test
- Units and definitions
- IEEE video pulse standards adapted for microwave pulses
- Peak power waveform definitions
- A typical wireless modulation format
- Three technologies for sensing power
- An overview of power sensors and meters for pulsed and complex modulations
- Key power sensor parameters
- Data computation for statistical parameters of power analysis
- The Chain of Power Traceability
- The hierarchy of power measurement, national standards, and traceability
- The theory and practice of sensor calibration
- Some measurement considerations for power sensor comparisons
- Typical sensor comparison system
- Thermistors as power transfer standards
- Other DC substitution meters
- Peak power sensor calibration traceability
- Network analyzer source system
- NIST six-port calibration system
- General references
The purpose of the new series of Fundamentals of RF and Microwave Power Measurements application notes, which were leveraged from former note 64-1, is to:
- Retain tutorial information about historical and fundamental considerations of RF/microwave power measurements and technology which tend to remain timeless.
- Provide current information on a new meter and sensor technology.
- Present the latest modern power measurement techniques and test equipment that represents the current state-of-the-art.
Part 1, Chapter 1 reviews the commercial and technical importance of making power measurements, equity in trade, the cost of measurement uncertainties, and the need for two power measurements of the same unit under test will be the same at two locations in the world. It then presents a brief history of power techniques, and additionally a history of peak power techniques.
Chapter 2 shows why it is crucial to begin a power measurement task with a clear understanding of the characteristics of the signal under test. With the advent of new complex combinations of modulations in the 1990s and forward, it also presents signal format considerations that users must evaluate when pondering which sensor technologies to use.
The application note then defines the variety of terminology of units and definitions of various power measuring terms. It shows how IEEE video pulse standards were adapted by Keysight for use in microwave pulsed power envelopes. Brief descriptions of modern wireless formats show how key sensor performance is required to faithfully capture the system power. Various sensor technologies and instrumentation are previewed from the complete descriptions in Fundamentals Part 2.
Considerations necessary for capturing and digitizing microwave signals which are used in modern wireless systems are presented. These often consist of pulsed carriers plus digital phase modulations, which look like noise, combined on the same signal. When measured with digital sampling type instrumentation, the powerful micro-processors can run statistical routines to reveal computed data, oriented to particular customer requirements.
Chapter 3 presents the matter of basic measurement traceability to national and world standards. It describes the hierarchy of international traceability, including comparison processes to national standards at worldwide NMIs such as the U.S. National Institute of Standards and Technology, Boulder, CO.
The application note reviews the theory and practice of sensor calibration processes and the need for transportable sensor artifacts which can transfer higher-echelon uncertainties of the NMIs to company primary lab standards. It reviews special procedures needed for extended calibration processes on pulse-power sensors.
Note: In this application note numerous technical references will be made to the other published parts of the Fundamentals of RF and Microwave Power Measurements series. For brevity, we will use the format Fundamentals Part X. This should insure that you can quickly locate the concept in the other publication. Brief abstracts for the four-part series are provided inside the front cover.