@article{batty_christoffersen_yakovlev_whitaker_mortazawi_al-zayed_ozkar_ortiz_reano_yang_et al._2002, title={Global coupled EM-electrical-thermal simulation and experimental validation for a spatial power combining MMIC array}, volume={50}, ISSN={["1557-9670"]}, DOI={10.1109/TMTT.2002.805142}, abstractNote={A unique electromagnetic (EM)-electrothermal global simulation tool based on a universal error concept is presented. The advantages of this electrothermal model are illustrated by comparison with a commercial electrothermal circuit simulator. The first description of a fully physical, electrothermal, microwave circuit simulation, based on coupling of the Leeds Physical Model of MESFETs and high electron-mobility transistors, to a microwave circuit simulator, fREEDA (NCSU), is presented. The modeling effort is supported by parallel developments in electrooptic and thermal measurement. The first fully coupled EM-electrothermal global simulation of a large microwave subsystem, here a whole spatial power combining monolithic-microwave integrated-circuit (MMIC) array, is described. The simulation is partially validated by measurements of MMIC array temperature rise and temperature dependent S-parameters. Electrothermal issues for spatial power combiner operation and modeling are discussed. The computer-aided-design tools and experimental characterization described, provide a unique capability for the design of quasi-optical systems and for the exploration of the fundamental physics of spatial power combining devices.}, number={12}, journal={IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES}, author={Batty, W and Christoffersen, CE and Yakovlev, AB and Whitaker, JF and Mortazawi, A and Al-Zayed, A and Ozkar, M and Ortiz, SC and Reano, RM and Yang, K and et al.}, year={2002}, month={Dec}, pages={2820–2833} }
 @article{yakovlev_ortiz_ozkar_mortazawi_steer_2000, title={A waveguide-based aperture-coupled patch amplifier array - Full-wave system analysis and experimental validation}, volume={48}, ISSN={["0018-9480"]}, DOI={10.1109/22.899032}, abstractNote={In this paper, the full-wave analysis and experimental verification of a waveguide-based aperture-coupled patch amplifier array are presented. The spatial power-combining amplifier array is modeled by the decomposition of the entire system into several electromagnetically coupled modules. This includes a method of moments integral equation formulation of the generalized scattering matrix (GSM) for an N-port waveguide-based patch-to-slot transition; a mode-matching analysis of the GSM for the receiving and transmitting rectangular waveguide tapers; and a finite-element analysis of the waveguide-to-microstrip line junctions. An overall response of the system is obtained by cascading GSMs of electromagnetic structures and the S-parameters of amplifier networks. Numerical and experimental results are presented for the single unit cell and 2/spl times/3 amplifier array operating at X-band. The results are shown for the rectangular aperture-coupled patch array, although the analysis is applicable to structures with arbitrarily shaped planar electric and magnetic surfaces.}, number={12}, journal={IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES}, author={Yakovlev, AB and Ortiz, S and Ozkar, M and Mortazawi, A and Steer, MB}, year={2000}, month={Dec}, pages={2692–2699} }
 @article{ozkar_mortazawi_2000, title={Analysis and design of an inhomogeneous transformer with hard wall waveguide sections}, volume={10}, ISSN={["1051-8207"]}, DOI={10.1109/75.843099}, abstractNote={A new inhomogeneous waveguide transformer with hard walls is presented. Mode matching technique along with an optimization routine is used to design the transformer. The generalized scattering matrix (GSM) of the whole block is calculated which can be used to predict the fields at the output given the incident excitations. An example of a three-section transformer, which replaces a tapered hard horn, is shown. The transformer has better performance in the bandwidth of interest compared to the tapered hard horn having twice the length of the transformer. This type of transformer could be useful for excitation of quasi-optical amplifiers and reflector feeds.}, number={2}, journal={IEEE MICROWAVE AND GUIDED WAVE LETTERS}, author={Ozkar, M and Mortazawi, A}, year={2000}, month={Feb}, pages={55–57} }
 @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_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 response and convolution analysis of distributed microwave circuits is developed. The state-variable approach minimizes computation time and memory requirements. It allows the use of parameterized 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} }