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This paper introduces a new approach for rational macromodeling of multiport devices that ensures high accuracy with arbitrary terminal conditions. This is achieved by reformulating the vector fitting technique to focus on eigenpairs rather than matrix elements. By choosing the least squares weighting equal to the inverse of the eigenvalue magnitude is achieved that the eigenvalues are fitted with a relative accuracy criterion. The procedure is shown to give a major improvement in accuracy for cases with a large eigenvalue spread. Also is shown how to utilize the impedance characteristics of the adjacent network in the fitting process.