David K. Walker

In-Line Multiport Calibration

We present a multiport measurement procedure well suited to on-wafer measurement. It can correct multiport measurements with any conventional in-line calibration, including the thru-reflect-line calibration. We demonstrate the procedure in a four-port measurement system.

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.

Coplanar-waveguide-to-microstrip transition model

We develop a novel four-port equivalent circuit for a coplanar-waveguide-to-microstrip transition using a finite-difference time-domain analysis. The lumped model accounts for mutual inductive coupling and works well up to about 30 GHz.

Proposed Development of a National Standard for Microwave Brightness Temperature

We review the advantages of a national standard for microwave brightness temperature and outline our proposed approach toward developing such a standard. The proposal is a combined standard that would comprise both a standard radiometer, traceable to primary noise standards, and a fully characterized standard target. Keywords-brightness temperature; microwave radiometry; radiometer calibration; remote sensing; standards

Systematic errors of noise parameter determination caused by imperfect source impedance measurement

We present a rigorous two-step analysis of systematic errors in the four-noise parameter determination of a two-port network using the cold-source technique. This analysis is based on an original model that accounts for residual errors in the source impedance measurement. The method employs two linear fractional transforms to decompose the errors into relevant factor sets affecting the parameters in different ways. Analyses performed for a low-noise pseudomorphic high-electron mobility transistor (PHEMT) and a microwave amplifier show that the noise parameters of the low-noise PHEMT are highly vulnerable to such errors.

Causal characteristic impedance of planar transmission lines

We compute power-voltage, power-current, and causal definitions of the characteristic impedance of microstrip and coplanar-waveguide transmission lines on insulating and conducting silicon substrates, and compare to measurement.

Compensation for geometrical variations in coplanar waveguide probe-tip calibration

We show how coplanar-waveguide probe-tip scattering parameter calibrations performed in one coplanar waveguide conductor geometry may be adjusted for measurement in another. The method models the difference between the two probe-tip-to-coplanar-waveguide transitions as a change in shunt capacitance and applies previously developed techniques for its determination and compensation. Comparison to accurate multiline Thru-Reflect-Line calibrations verifies the accuracy of the method. Differences in both conductor geometry and substrate permittivity are considered in the comparison. The method requires only a single, compact open stub or thru line fabricated on the measurement wafer.

Reflectivity Study of Microwave Blackbody Target

We report on the characterization of blackbody target reflections as part of the recent progress on the development of brightness temperature standards for microwave remote sensing at the National Institute of Standards and Technology. The very low reflections from the blackbody targets used in airborne or satellite remote sensing systems present challenges on how to extract reflection coefficients from the measurements. A full calibration technique is developed for this study by the use of a flat aluminum plate used as a known standard in combination with measurements of the empty anechoic chamber. The theoretical basis and measurement procedures, along with the uncertainty analysis, are presented. Calibration results validate the method by showing its independence from measurement hardware and conditions. A comparison between the theoretical prediction of reflection coefficients of a free-standing dielectric slab with well-documented physical parameters and the de-embedded reflection coefficients from experiments confirms good calibration accuracy. The specific blackbody target used in this paper shows well-matched properties with a power reflectivity below -40 dB over the entire measurement band (18 to 26 GHz).

Standard radiometers and targets for microwave remote sensing

We describe the NIST effort to develop brightness-temperature standards for microwave and millimeter-wave frequencies. Results of preliminary measurements at 26 GHz are presented.

Characterization of asymmetric coupled CMOS lines

This paper investigates the properties of asymmetric coupled lines built in a 0.25 /spl mu/m CMOS technology in the frequency range of 50 MHz to 26.5 GHz. We show that the frequency-dependent line parameters extracted from calibrated four-port S-parameter measurements agree well with data predicted by numerical calculations. To our knowledge these are the first complete high-frequency measurements of the line parameters for asymmetric coupled lines on silicon ever reported.