Robert L. Billinger

Comparison of adapter characterization methods

We review and compare three different methods for characterization of precision adapters. Two of the methods are one-port techniques using two different reflective terminations in the one case and a matched load and multiple lines with reflective terminations in the other. The third technique is a conventional two-port adapter-removal technique. The intrinsic efficiencies of several different adapters are measured with each technique, and the results are compared. The results usually agree within about 0.005 for efficiencies near one. In all cases, the differences are consistent with the estimated uncertainties of the techniques, which range from about 0.002 to about 0.012, depending on the method, connectors, and frequency.

Errors resulting from the reflectivity of calibration targets

For a microwave total-power radiometer, we consider the error introduced by neglecting the difference in the antenna reflection coefficient between when it views a distant scene and when it views a nearby calibration target. An approximate expression is presented for the error, and measurements are described that enable one to estimate the resulting uncertainty in the measured brightness temperature. The measurement results are presented for several combinations of antenna and calibration target. The resulting uncertainty ranges from about 0.1 K to several kelvins for the representative cases considered.

Precision measurement method for cryogenic amplifier noise temperatures below 5 K

We report precision measurements of the effective input noise temperature of a cryogenic (liquid-helium temperature) monolithic-microwave integrated-circuit amplifier at the amplifier reference planes within the cryostat. A method is given for characterizing and removing the effect of the transmission lines between the amplifier reference planes and the input and output connectors of the cryostat. In conjunction with careful noise measurements, this method enables us to measure amplifier noise temperatures below 5 K with an uncertainty of 0.3 K. The particular amplifier that was measured exhibits a noise temperature below 5.5 K from 1 to 11 GHz, attaining a minimum value of 2.3 K/spl plusmn/0.3 K at 7 GHz. This corresponds to a noise figure of 0.034 dB/spl plusmn/0.004 dB. The measured amplifier gain is between 33.4 dB/spl plusmn/0.3 dB and 35.8 dB/spl plusmn/0.3 dB over the 1-12-GHz range.

On-wafer measurements of noise temperature

The NIST Noise Project has developed the theoretical formalism and experimental methods for performing accurate noise-temperature measurements on a wafer. This report summarizes the theoretical formulation and describes the design, methods, and results of tests performed to verify our ability to measure on-wafer noise temperature. Several different configurations with known off-wafer noise sources were used to obtain different, known, on-wafer noise temperatures. These were then measured, and the results were compared to predictions. Good agreement was found, with a worst-case disagreement of 2.6%. An uncertainty analysis of the measurements resulted in an estimated standard uncertainty (1/spl sigma/) of 1.1% or less for most values of noise temperature. The tests also confirm our ability to produce known noise temperatures on a wafer, with an uncertainty of about 1%.

Comparison of methods for adapter characterization

We review and compare three methods for characterization of precision adapters using a vector network analyzer. Two of the methods are one-port techniques, and the third is an established two-port adapter-removal technique. The intrinsic efficiencies of three adapters are measured with each technique, and the results are compared. The results generally agree within 0.005, which is within the estimated uncertainties of the techniques.

Comparison of microwave black-body target radiometric measurements

Accurate characterization of the brightness temperature (TB) of black-body targets used for calibrating microwave remote-sensing radiometers includes many inputs: antenna pattern and loss, target temperature, target emissivity, mechanical alignment, and radiometric TB measurements, all of which must be calibrated against physical standards. Here, we describe measurements made using several black-body targets and two different antennas within the WR-42 (18 to 26.5 GHz) waveguide band. Uncertainty estimates are also shown for the retrieved target TB measurements.

A verification method for noise-temperature measurements on cryogenic low-noise amplifiers

We report a verification method for noise-temperature (NT) measurements on cryogenic low-noise amplifiers (LNAs) at liquid helium temperature. The method uses a comparison between the individual measurements of the LNA and an attenuator and the joint measurements of the tandem of the two. As a first step, we were able to determine the loss and the added NT of the cables that connected the cryogenic devices (the LNA, the attenuator, or their combination) to the test ports outside of a cryostat. The attenuator was also characterized successfully with 3% measurement uncertainty.

Reflectivity studies of passive microwave calibration targets and absorptive materials

We report on the characterization of blackbody reflections as a part of the recent progress on the development of brightness standards for microwave remote sensing at National Institute of Standards and Technology (NIST). Three blackbody targets at variable temperatures used for airborne and/or satellite systems along with an aluminum plate were measured in terms of their reflection coefficients by horn antennas in connection with a vector network analyzer (VNA) in the WR-42 waveguide band. Precision measurements of reflection are needed for blackbody emissivity computation to check against the brightness temperature measurement of blackbody targets. All experiments were conducted in two distance ranges by free-space methods in an anechoic chamber. Preliminary results show negligible reflections from the calibration targets, indicating near ideal blackbody characteristics in the measured frequency range.

Characterization of On-Wafer Diode Noise Sources

A set of wafer probeable diode noise source transfer standards are characterized using on-wafer noise temperature methods developed recently at the National Institute of Standards and Technology (NIST). This paper reviews the methods for accurate on-wafer measurements of noise temperature and details the preliminary design and construction of the transfer standards. Measurements are presented of their noise temperatures at frequencies from 8 to 12 GHz. Such transfer standards could be used in interlaboratory comparisons or as a verification tool for checking on-wafer noise calibration accuracy.

Errors due to the reflectivity of calibration targets

For a microwave total-power radiometer, we consider the error introduced by neglecting the difference in the antenna reflection coefficient between when it views a distant scene and when it views a nearby calibration target. An approximate expression is presented for the error, and measurement results are presented that enable one to estimate the resulting uncertainty in the measured brightness temperature. This uncertainty ranges from about 0.1 K to several kelvins for the representative cases considered