Thermal
Noise Metrology
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Coaxial radiometer “NFRad” being used for
noise-temperature measurement. |
Noise activities in the RF
Electronics Group of NIST’s Electromagnetics Division are conducted under
two program areas: Guided
Wave Metrology and Advanced
High Frequency Devices.
Current Activities
- Traditional
noise-temperature measurements: We offer measurement services at 30 and 60 MHz and
from 1 to 40 GHz for coaxial sources, and from
8.2 GHz to 65 GHz for waveguide sources.
- Measurement and
verification of LNA noise parameters: We have the capability to accurately
measure LNA noise parameters from 1 to 12.4 GHz and to assess the
uncertainties in those measurements. We are working to extend and improve
verification methods for such measurements.
- Noise-parameter
measurements of on-wafer transistors: We are working to improve the accuracy of
on-wafer noise measurements and to perform measurements on smaller,
lower-noise devices. We are especially working to make our own
measurements quicker and more convenient, so that these measurements can
be used as a tool in investigating and evaluating novel nanostructures.
- Primary standards for
microwave brightness temperature for remote sensing: We have suspended our work
in this area. It will be resumed if sufficient interest exists and
resources permit.
Significant Recent Accomplishments
- Amplifier
Noise-Parameter Measurements and Verification — The
Noise Project completed development of a measurement capability for noise
parameters of low-noise amplifiers (LNAs), including a
- Variable-Termination
Unit
— An automated variable-termination unit (VTU) was designed,
fabricated, and tested. The VTU will be used in noise-parameter
measurements, allowing automated switching to an array of different known
input terminations for the amplifier. Use of the VTU will enable us to
make noise-parameter measurements much more quickly.
- On-Wafer
Noise-Parameter Measurements—We have developed the capability to measure
noise parameters of transistors or amplifiers on a wafer. A full
uncertainty analysis has also been performed on the measurements. The
capability was used to measure the noise parameters of poorly matched CMOS
transistors in the 1 – 12 GHz range.
- Measurement
of Cryogenic LNA—We
developed a method for the most accurate measurements to date of the noise
figure or noise temperature of a cryogenic LNA. The noise temperature of a
cryogenic LNA was measured from 1 to 12 GHz, with measured values as low
as 2.3 K ± 0.3 K. This corresponds to
a noise figure of 0.034 dB ± 0.004 dB.
- Traceability
for Microwave Remote-Sensing Standards — A framework was developed for a
microwave brightness-temperature standard for remote sensing, traceable to
fundamental noise standards. Measurements were performed that demonstrated
the feasibility of such standards.
- Target
Reflectivity
— A study performed in FY 2004 on the effects of target reflectivity
in the calibration of microwave remote-sensing radiometers was documented
in a conference paper and a journal paper. This study found that a common
approximation used in calibrating microwave radiometers leads to errors
that can be quite significant.
- Detector
Linearity Study
— Measurements were made on tunnel diode detectors of the type
typically used in microwave remote-sensing radiometers. These measurements
included variations in detector temperature as well as output load
impedance. Results point to improved test methods and a way to greatly
reduce the cost associated with radiometer linearity tests.