Dave K. Walker

Planar Resistors for Probe Station Calibration

This paper investigates the effects of variations in sheet resistance, geometry, distance from the probe tip, and fabrication processes on the impedance of planar nickel-chromium resistors. Resistor reactance is a strong function of film resistance, but depends only weakly on geometry and distance from the probe tip. Photoresist contamination in the resistive film induces more complicated impedance behavior, even at low frequencies. The impact on circuit design and time- and frequency-domain calibrations is considered in light of these results.

On-Wafer Measurement of Transistor Noise Parameters at NIST

The National Institute of Standards and Technology has developed the capability to measure noise parameters on a wafer in the 1-12.4-GHz range. The authors describe the measurement method and the uncertainty analysis and present results of measurements on a highly reflective transistor. Typical standard uncertainties are within the range of 20-25 K in Tmin, which is the minimum transistor noise temperature, and about 0.03 in the magnitude of Gammaopt, which is the reflection coefficient for which Tmin occurs

Asymmetric coupled CMOS lines-an experimental study

This paper investigates the properties of asymmetric coupled lines built in a 0.25 /spl mu/m CMOS technology over the frequency range of 50 MHz to 26.5 GHz. We show that the frequency-dependent line parameters extracted from calibrated four-port scattering-parameter measurements agree well with numerical predictions. We also demonstrate by measurement and calculation that the two fundamental modes of the coupled-line system share significant cross power. To our knowledge, this is the first complete experimental characterization of asymmetric coupled lines on silicon ever reported.

Amplifier noise-parameter measurement checks and verification

We propose two verification methods for measurements of noise parameters of amplifiers, particularly low-noise amplifiers (LNAs). One method is a direct measurement of the parameter Trev, the noise temperature from the amplifier input, and the comparison of that to the value derived from the noise-parameter measurement. The other check involves the measurement of the noise parameters for the amplifier with an isolator connected to the input and comparison to the noise parameters of the amplifier alone. Relationships between the noise parameters with and without the isolator are given. We demonstrate both verification methods with measurements on a sample LNA in the 8 – 12 GHz range. Uncertainties in the noise parameters are evaluated using a previously developed Monte Carlo method, and both checks are found to be satisfied within the uncertainties. Index Terms — amplifier; noise; noise measurement; noise parameters

Extraction of Illumination Efficiency by Solely Radiometric Measurements for Improved Brightness-Temperature Characterization of Microwave Blackbody Target

We report our recent progress toward the development of microwave brightness-temperature (BT) standards. As one of the crucial parameters, the target illumination efficiency (IE) was traditionally determined from the relative antenna pattern. We propose a measurement technique to extract the target IE solely by the use of passive radiometric measurements for characterizing the BT of the blackbody radiator. Such a technique allows us to skip the complexities that are often encountered during the measurement and calculation of the antenna pattern. Taking advantage of the variable heating capability available on most blackbody targets, we varied the temperature of a heated blackbody target and ran a series of radiometric measurements when the target was separated at different distances away from the the antenna with the radiometer operating at a few frequencies. Our experimental results show excellent measurement accuracy on the IE, with uncertainty of about 1% at close separation distance between the antenna and the target. We further measured and computed the BT of the blackbody target at the locations where we had measured the extracted IE. The BT was slightly lower than the physical temperature of the target and exhibited 0.7 K to about 1 K uncertainty when the target was located no more than 1 m away from the antenna. A measurement uncertainty of 1 K already meets the accuracy requirements of some climate variables, and such results reflect a significant step toward the establishment of BT standards at microwave frequencies.

Variable Termination Unit for Noise-Parameter Measurement

The National Institute of Standards and Technology (NIST) has upgraded its capability to measure noise parameters on low-noise amplifiers with a variable termination unit (VTU) in the frequency range of 1-12.4 GHz. Such a unit allows improved time efficiency and accuracy in the noise-temperature measurements used to de-embed the noise parameters of amplifiers. We present the design and characterization of the VTU. The measured results of one particular amplifier at integer frequencies ranging from 8 to 12 GHz show satisfactory accuracy. The VTU method is also validated by comparison with the results from the manual method.

Noise-parameter measurement with automated variable terminations

NIST has upgraded its measurement capability of noise parameters on low-noise amplifiers with a variable termination unit in the 1 to 12.4 GHz range. Such a unit allows improved time efficiency in the noise-temperature measurements used to de-embed noise parameters of amplifiers. We present measured results for noise parameters of a low noise amplifier in the frequency range of 8 to 12 GHz.

A Geometric Error Model for Misaligned Calibration Target in Passive Microwave Remote-Sensing Systems

We present a geometric error model associated with calibration-target misalignment in passive microwave remote-sensing systems. The developed analytic formulation is universally applicable to both lateral and rotational misalignment conditions. Numerical simulations are performed on two practical blackbody targets of different sizes used as radiation references for passive microwave remote sensing. The significance of this work is to furnish a framework of uncertainty analysis due to target misalignment and to provide a reference for alignment requirements based on passive radiometer measurement sensitivity.

Reverse noise measurement and use in device characterization

We review the concept of reverse noise measurements in the context of on-wafer transistor noise characterization. Several different applications of reverse noise measurements are suggested and demonstrated. Reverse measurements can be used to check measurement results, to significantly reduce the uncertainty in |Gammaopt |, to reduce the occurrence of nonphysical results, and possibly to directly measure or constrain parameters in models of transistors

Realization of a standard radiometer for microwave brightness-temperature measurements traceable to fundamental noise standards

We describe and demonstrate a standard radiometer for making microwave brightness-temperature measurements that are traceable to fundamental noise standards. The standard radiometer is based on a National Institute of Standards and Technology (NIST) waveguide radiometer for 18-26.5 GHz, fitted with an antenna to measure radiated power. The fraction of the antenna pattern subtended by the radiating target is determined by anechoic-chamber measurements in which we vary the temperature of the target and measure the received power. Sample measurement results with uncertainties are presented. The typical standard uncertainty for a brightness temperature of around 340 K is about 1 K. The approach should be extendable to other waveguide bands where NIST has radiometers and standards.