@article{saunders_steer_2012, title={Passivity Enforcement for Admittance Models of Distributed Networks Using an Inverse Eigenvalue Method}, volume={60}, ISSN={["0018-9480"]}, DOI={10.1109/tmtt.2011.2171500}, abstractNote={Most transient circuit simulators are based on admittance representations of the constituent circuit elements. It is therefore natural to use admittance parameter descriptions of linear networks, preferably in the form of rational transfer functions that can be directly implemented in the analysis. A problem arises when the measured or calculated frequency-domain response of a linear distributed network must be derived from data that has inherent error, is of limited bandwidth, or is not in the appropriate rational form. A reduced-order rational model that is causal, stable, and passive must be developed. Previous methods of deriving rational functions for the admittance parameters of a network do guarantee stability and causality, but passivity of the model must be assured through subsequent post-processing. Enforcing passivity requires modification of the state-space parameters of the model with consequent introduction of errors. This paper reports on a procedure to simultaneously achieve passivity, accuracy, causality, and stability in the development of an admittance macromodel described using a matrix of rational functions. An iterative inverse eigenvalue algorithm enforces passivity, and is applied by conjoining sets of eigenvalue and admittance constraints. These constraints form a monolithic projection matrix, which simultaneously addresses both passivity and accuracy of the model.}, number={1}, journal={IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES}, author={Saunders, Christopher S. and Steer, Michael B.}, year={2012}, month={Jan}, pages={8–20} }
@article{saunders_mazzaro_steer_2010, title={Robust reduced-order modelling of distributed linear networks}, volume={4}, ISSN={["1751-8733"]}, DOI={10.1049/iet-map.2009.0554}, abstractNote={Foster's canonical form provides a causal bridge between the transfer function representation of the characteristics of a distributed structure and both time-domain and frequency-domain non-linear circuit simulation. It is particularly advantageous in modelling bandpass-like characteristics. In the modelling procedure, a transfer function having Foster's canonical form is fitted to measured or simulated data which may not have an inherent pole-zero description. Even if there is a good transfer function representation, the number of poles required for a reasonable fit is not known a priori which can lead to poor models that may cause convergence problems during either fitting or simulation. In this study, an extension of Foster's model is developed and a robust procedure for fitting the transfer function to data without a priori knowledge of the number of poles is presented. A robust stamp for implementation of the model in a transient circuit simulator is developed.}, number={7}, journal={IET MICROWAVES ANTENNAS & PROPAGATION}, author={Saunders, C. S. and Mazzaro, G. J. and Steer, M. B.}, year={2010}, month={Jul}, pages={962–973} }