High Power CW Wattmeter Calibration at NIST

Area of Science:

• Electrical Engineering
• Metrology
• Radio Frequency Engineering

Background:

• Accurate calibration of high-power wattmeters is crucial for radio frequency (RF) systems.
• Existing calibration methods may have limitations at higher power levels and frequencies.
• The National Institute of Standards and Technology (NIST) supports advancements in high-power measurement capabilities.

Purpose of the Study:

• To establish a traceable measurement capability for high-power wattmeters.
• To develop and validate an automated calibration system for wattmeters.
• To extend accurate power measurements to higher levels (up to 1000 W) and frequencies (up to 400 MHz).

Main Methods:

• Utilized a cascaded coupler technique with nominal 10, 20, 30, 40, and 50 dB couplers.
• Employed an automated system with sidearm power meters for sequential calibration transfers.
• Calibrated the system traceability to a 10 mW standard thermistor mount.
• Incorporated corrections for nonlinearities, mismatch, and other non-ideal component errors.

Main Results:

• Successfully established a measurement capability for wattmeters from 1 to 1000 W (1-30 MHz) and 1 to 500 W (30-400 MHz).
• Demonstrated the effectiveness of the cascaded coupler technique for extending power measurements.
• Evaluated two types of wattmeters at selected frequencies and power levels.
• Quantified total uncertainties based on random and systematic components.

Conclusions:

• The automated wattmeter calibration system provides a reliable method for high-power measurements.
• The cascaded coupler technique ensures traceability and accuracy in RF power calibration.
• NIST's capability supports the development and validation of high-power RF devices and systems.