David V. Blackham

Application of weighted least squares to OSL vector error correction

The use of least squares has been beneficial in providing more accurate one-port calibrations. Commercially available ECAL units have taken advantage of this method. A more generalized application of a least squares method, the weighted least squares method provides benefit when the models for the calibration standards are not all trusted equally. The use of the weighted least squares provides a method of discounting the effect of calibration standards as the model accuracy degrades instead of abruptly dropping the use of the standard outside of a specified frequency range avoiding discontinuities in subsequent measurements. A detailed view a 1.85 μm calibration kit demonstrates the improved results possible using a weighted least squares method. The paper includes the description of a proximity function that enhances the results when the response of two or more standards begin to cluster. Additional enhancements due to databased models over traditional polynomial models is also presented.

Complete Pure-Mode Balanced Measurement System

Previously, the first author has shown that the nonlinear behavior (e.g. gain compression or TOI) of some balanced amplifiers can be accurately measured using single-ended measurements: amplifiers that have a balanced stage before a non-linear stage; other amplifiers require true-mode drive to give correct differential and common-mode results. This paper describes, for the first time, a complete solution to the problem of true-mode measurements. The system and method included in this makes use of a dual-source VNA to produce either pure-differential or pure-common-mode drives in both the forward and reverse direction. A method for correcting drive signal errors due to mismatch between the VNA and the device under test is introduced, as well as a method to provide full balanced error correction to all terms. Its remarkable that small modifications to a standard single-ended 4-port calibration provides all the required error terms.

Optimization for multiport VNA vector error correction

Multiport vector error correction leverages the techniques that apply to two-port error correction. In some testset configurations the load match at any particular port may take on multiple distinct values that must be characterized. As the number of ports increases it becomes important to find ways to minimize the number of connections required to calibrate the VNA. This paper presents techniques for optimizing the calibration both from the point of view of minimizing the number of calibration steps as well as utilizing TRL, Unknown Thru and QSOLT calibration without requiring dual reflectometers at each testport.

Trends for computing VNA uncertainties

An understanding of measurement uncertainties is a critical element in evaluating the performance of a device under test (DUT). For a vector network analyzer (VNA), the measurement process includes a calibration process that significantly impacts and also complicates the estimation of DUT measurement uncertainty. This lead to the creation of software to assist in the estimation of measurement accuracy. This article discusses the legacy approach that was developed for the 8510 vector network analyzer and compares it to recent advances in VNA uncertainty computation which enable a better estimate of VNA measurement errors.