One-Port Direct/Reverse Method for Characterizing VNA Calibration Standards

TL;DR

This paper presents a novel one-port method for characterizing VNA calibration standards by measuring their S-parameters in direct and reverse modes, improving calibration accuracy through delay estimation.

Contribution

The paper introduces a new one-port measurement technique that estimates calibration standard parameters by comparing direct and reverse mode measurements, including delay estimation.

Findings

Estimated load delay: 38.8 ps with 2.1 ps uncertainty

Improved measurement accuracy when using the new delay estimate

Method validated through simulations and real measurements

Abstract

This paper introduces a one-port method for estimating model parameters of VNA calibration standards. The method involves measuring the standards through an asymmetrical passive network connected in direct mode and then in reverse mode, and using these measurements to compute the S-parameters of the network. The free parameters of the calibration standards are estimated by minimizing a figure of merit based on the expected equality of the S-parameters of the network when used in direct and reverse modes. The capabilities of the method are demonstrated through simulations, and real measurements are used to estimate the actual offset delay of a 50-$\mathbf{\Omega}$ calibration load that is assigned zero delay by the manufacturer. The estimated delay is $38.8$ ps with a $1\sigma$ uncertainty of $2.1$ ps for this particular load. This result is verified through measurements of a terminated airline. The measurements agree better with theoretical models of the airline when the reference plane is calibrated using the new estimate for the load delay.