We report measurements and uncertainty analysis on a cryogenic low-noise amplifier (LNA) with a very low noise temperature (NT), among the lowest noise performances reported at microwave frequencies. The LNA consists of three stages of InP high electron mobility transistors with a gate length of 130 nm. It exhibits about 44 dB gain and less than 2 K average NT in the operational band of 4 GHz to 8 GHz. A detailed uncertainty analysis is outlined to evaluate a variety of error sources in the measurement. The calculated uncertainty shows as low as 0.1 dB on the measured gain of about 44 dB and 0.18 K on the measured NT of 1.65 K, indicating excellent measurement accuracy. A breakdown of the uncertainty components helps identify the major causes of the overall uncertainty and enlightens us about how to further improve accuracy. It is important to know the actual physical temperature of the passive termination that is used as a cryogenic noise source in experiments. Due to its large temperature gradients, the commercial matched load is replaced by a custom-made attenuator that is isothermal and consequently provides reliable NT measurements of the LNA. The precision measurement technique developed at the National Institute of Standards and Technology is independent from the manufacturers' characterization method. This study marks the first time that such a low NT from a cryogenic LNA is verified independently with such a low uncertainty.

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.

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.

The Noise Project in the Electromagnetics Division of the National Institute of Standards and Technology (NIST) has proposed the development of standards for microwave brightness temperature for use in remote-sensing applications such as satellite-based weather observations. The standards would be based on existing fundamental standards for electromagnetic noise in waveguide systems. The connection to brightness temperature, which is a radiated quantity, would be made by means of a well characterized antenna. A heated calibration target would be used to supplement the basic standard, either as a check or to reduce the uncertainty by a redundant measurement. We have performed preliminary measurements at 26 GHz that demonstrate the feasibility of the proposed standard. A parallel effort is in progress for terahertz frequencies. For terahertz noise we are building a heated target to be used as a noise standard, since we did not already have fundamental noise standards for such high frequencies. This standard will be used with a terahertz radiometer. The radiometer is based on a receiver that uses a hot-electron bolometer (HEB) mixer that is coupled to the radiation by a quasi-optical adapter. We expect to perform terahertz noise measurements with the system by the end of the year.

The Noise Project in the Electromagnetics Division of the National Institute of Standards and Technology (NIST) has proposed the development of standards for microwave brightness temperature for use in remote-sensing applications such as satellite-based weather observations. The standards would be based on existing fundamental standards for electromagnetic noise in waveguide systems. The connection to brightness temperature, which is a radiated quantity, would be made by means of a well characterized antenna. A heated calibration target would be used to supplement the basic standard, either as a check or to reduce the uncertainty by a redundant measurement. We have performed preliminary measurements at 26 GHz that demonstrate the feasibility of the proposed standard. A parallel effort is in progress for terahertz frequencies. For terahertz noise we are building a heated target to be used as a noise standard, since we did not already have fundamental noise standards for such high frequencies. This standard will be used with a terahertz radiometer. The radiometer is based on a receiver that uses a hot-electron bolometer (HEB) mixer that is coupled to the radiation by a quasi-optical adapter. We expect to perform terahertz noise measurements with the system by the end of the year.

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.

We report on the design of a radiometer for traceable noise-temperature measurements at terahertz frequencies, including noise measurements on cryogenic IF components, development and test of quasi-optical adapter technology, development of black body standards, and overall system design.

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.

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

The National Institute of Standards and Technology (NIST) has completed design and testing of a new noise measurement system. The new system is capable of measuring noise temperature at multiple frequencies about ten times faster than previous NIST systems. This system will also be used to measure the noise parameters of amplifiers. Required reflection coefficients used to calculate mismatch and asymmetry are no longer measured by a six-port reflectometer in each noise measurement. Instead, they are measured with a vector network analyzer and stored in lookup tables. We have tested radiometers in the frequency ranges 4-8 GHz, 8-12 GHz, and 12-18 GHz. The system tests will be discussed as well as measurements and uncertainty analysis.

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%.

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.

A set of wafer-probeable diode noise source transfer standards are characterized using on-wafer noise-temperature methods developed at the National Institute of Standards and Technology (NIST), Boulder, CO. We review the methods for accurate measurement and prediction of on-wafer noise temperature of off-wafer and on-wafer noise source standards. In analogy with the excess noise ratio (ENR) for hot noise temperatures, we introduce a representation for cold noise temperatures called the cold noise ratio (CNR), which is expressed in decibels. The ENR and CNR noise source representations share the property that the difference between off-wafer and on-wafer values may be approximated by the probe loss. We present measurements of the on-wafer ENR and reflection-coefficient information for a preliminary set of on-wafer diode transfer standards at frequencies from 8 to 12 GHz. Such transfer standards could be used in interlaboratory comparisons, as a noise calibration verification tool, as direct calibration artifacts, or as the basis for a new “noise-source probe” conceptualized here.

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.