A new robust method for finding the parameters of Engen's six-port-to-four-port reduction algorithm for six-port reflectometer calibration has been developed. Like other previously published methods, it uses a minimum of five loads with an unknown but constant absolute value of the reflection coefficient and unknown but well-distributed phases. However, the quality of the parameter estimates is improved, especially in noisy environments, by efficiently eliminating cases in which these earlier methods may become ill-conditioned. The new method has been used successfully to calibrate a newly developed six-port reflectometer in GaAs MMIC technology working between 1.3 GHz and 3.0 GHz.
Frank Wiedmann, Bernard Huyart, Eric Bergeault, Louis Jallet, "A new robust method for six-port reflectometer calibration," IEEE Transactions on Instrumentation and Measurement, vol. 48, no. 5, pp. 927-931, October 1999.
The complete article and an implementation of the method are available for download from the publications page.