@article{kabir_christoffersen_kriplani_2011, title={Transient simulation based on state variables and waves}, volume={21}, number={3}, journal={International Journal of RF and Microwave Computer-aided Engineering}, author={Kabir, M. and Christoffersen, C. and Kriplani, N.}, year={2011}, pages={314–324} }
 @article{batty_christoffersen_panks_david_snowden_steer_2001, title={Electrothermal CAD of power devices and circuits with fully physical time-dependent compact thermal modeling of complex nonlinear 3-D systems}, volume={24}, ISSN={["1521-3331"]}, DOI={10.1109/6144.974944}, abstractNote={An original, fully analytical, spectral domain decomposition approach is presented for the time-dependent thermal modeling of complex nonlinear (3-D) electronic systems, from metallized power FETs and MMICs, through MCMs, up to circuit board level. This solution method offers a powerful alternative to conventional numerical thermal simulation techniques, and is constructed to be compatible with explicitly coupled electrothermal device and circuit simulation on CAD timescales. In contrast to semianalytical, frequency space, Fourier solutions involving DFT-FFT, the method presented here is based on explicit, fully analytical, double Fourier series expressions for thermal subsystem solutions in Laplace transform s-space (complex frequency space). It is presented in the form of analytically exact thermal impedance matrix expressions for thermal subsystems. These include double Fourier series solutions for rectangular multilayers, which are an order of magnitude faster to evaluate than existing semi-analytical Fourier solutions based on DFT-FFT. They also include double Fourier series solutions for the case of arbitrarily distributed volume heat sources and sinks, constructed without the use of Green's function techniques, and for rectangular volumes with prescribed fluxes on all faces, removing the adiabatic sidewall boundary condition. This combination allows treatment of arbitrarily inhomogeneous complex geometries, and provides a description of thermal material nonlinearities as well as inclusion of position varying and non linear surface fluxes. It provides a fully physical, and near exact, generalized multiport network parameter description of nonlinear, distributed thermal subsystems, in both the time and frequency domains. In contrast to existing circuit level approaches, it requires no explicit lumped element, RC-network approximation or nodal reduction, for fully coupled, electrothermal CAD. This thermal impedance matrix approach immediately gives rise to minimal boundary condition independent compact models for thermal systems. Implementation of the time-dependent thermal model as N-port netlist elements within a microwave circuit simulation engine, Transim (NCSU), is described. Electrothermal transient, single-tone, two-tone, and multitone harmonic balance simulations are presented for a MESFET amplifier. This thermal model is validated experimentally by thermal imaging of a passive grid array representative of one form of spatial power combining architecture.}, number={4}, journal={IEEE TRANSACTIONS ON COMPONENTS AND PACKAGING TECHNOLOGIES}, author={Batty, W and Christoffersen, CE and Panks, AJ and David, S and Snowden, CM and Steer, MB}, year={2001}, month={Dec}, pages={566–590} }
 @article{christoffersen_steer_2001, title={State-variable-based transient circuit simulation using wavelets}, volume={11}, ISSN={["1558-1764"]}, DOI={10.1109/7260.916330}, abstractNote={For the first time a state variable transient analysis using wavelets is developed and implemented in a circuit simulator. The formulation is particularly well suited to modeling RF and microwave circuits and is validated by considering a nonlinear transmission line. However, results indicate that still more research is needed to make this method efficient for the simulation of large circuits.}, number={4}, journal={IEEE MICROWAVE AND WIRELESS COMPONENTS LETTERS}, author={Christoffersen, CE and Steer, MB}, year={2001}, month={Apr}, pages={161–163} }
 @article{christoffersen_mughal_steer_2000, title={Object oriented microwave circuit simulation}, volume={10}, ISSN={["1099-047X"]}, DOI={10.1002/(SICI)1099-047X(200005)10:3<164::AID-MMCE4>3.0.CO;2-K}, abstractNote={An object-oriented microwave circuit simulation environment is described. The design of the program is intended to offer flexibility without sacrificing efficiency. Recent developments in object-oriented techniques and in C++ compilers are used to obtain a flexible and robust system ideally suited to the development of a global modeling strategy for the integration of circuit, field, thermal, and mechanical analyses. The simulation of spatial power combining systems is used as a vehicle to illustrate the architectural developments of the system.}, number={3}, journal={INTERNATIONAL JOURNAL OF RF AND MICROWAVE COMPUTER-AIDED ENGINEERING}, author={Christoffersen, CE and Mughal, UA and Steer, MB}, year={2000}, month={May}, pages={164–182} }
 @article{steer_harvey_mink_abdulla_christoffersen_gutierrez_heron_hicks_khalil_mughal_et al._1999, title={Global modeling of spatially distributed microwave and millimeter-wave systems}, volume={47}, ISSN={["1557-9670"]}, DOI={10.1109/22.769316}, abstractNote={Microwave and millimeter-wave systems have generally been developed from a circuit perspective with the effect of the electromagnetic (EM) environment modeled using lumped elements or N-port scattering parameters. The recent development of the local reference node concept coupled with steady-state and transient analyses using state variables allows the incorporation of unrestrained EM modeling of microwave structures in a circuit simulator. A strategy implementing global modeling of electrically large microwave systems using the circuit abstraction is presented. This is applied to the modeling of a quasi-optical power-combining amplifier.}, number={6}, journal={IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES}, author={Steer, MB and Harvey, JF and Mink, JW and Abdulla, MN and Christoffersen, CE and Gutierrez, HM and Heron, PL and Hicks, CW and Khalil, AI and Mughal, UA and et al.}, year={1999}, month={Jun}, pages={830–839} }
 @article{christoffersen_steer_1999, title={Implementation of the local reference node concept for spatially distributed circuits}, volume={9}, DOI={10.1002/(SICI)1099-047X(199909)9:5<376::AID-MMCE2>3.0.CO;2-M}, abstractNote={Large spatially distributed microwave and millimeter-wave systems involve the interaction of linear and nonlinear circuits with their electromagnetic environment. A circuit-level approach to the modeling of circuit-field interactions is developed. The approach enables conventional circuit simulators to be extended to incorporate spatially distributed circuits.}, number={5}, journal={International Journal of RF and Microwave Computer-aided Engineering}, author={Christoffersen, C. E. and Steer, M. B.}, year={1999}, pages={376–384} }
 @article{christoffersen_ozkar_steer_case_rodwell_1999, title={State-variable-based transient analysis using convolution}, volume={47}, ISSN={["0018-9480"]}, DOI={10.1109/22.769322}, abstractNote={A state-variable-based approach to the impulse re- sponse and convolution analysis of distributed microwave circuits is developed. The state-variable approach minimizes computation time and memory requirements. It allows the use of parameter- ized nonlinear device models, thus improving robustness. Soliton generation on a nonlinear transmission line is considered as an example.}, number={6}, journal={IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES}, author={Christoffersen, CE and Ozkar, M and Steer, MB and Case, MG and Rodwell, M}, year={1999}, month={Jun}, pages={882–889} }