Guest editorial

Recent advances in wireless and microwave communication systems (higher operation frequency bands, more compact topologies containing MMICs and MEMS, wideband automotive, space and biomedical modules) have increased the necessity of fast and accurate numerical simulation techniques. Unlike hybrid microwave integrated circuits at low frequencies, it is extremely difficult and essentially impossible to adjust the circuit and radiation characteristics of communication modules once they are fabricated. For this reason, many practical geometries, especially in microwave and millimeter-wave integrated circuits (MMIC), packaging, interconnects, sub-nanosecond digital electronic circuits [such as multi-chip modules (MCM)], and antennas used in wireless and microwave communication systems, have been left relatively untreated due to their complexity and the inability of the existing techniques to deal with requirements for large size and high resolution. The starting point for the development of efficient numerical algorithms is an accurate characterization of the passive and active structures involved in the topologies. Although most commercial CAD programs are based on curve-fitting formulas and lookup tables and not on accurate numerical characterization, the latter can be used if it is fast enough. In addition, it can be used to generate lookup tables and to check the accuracy of empirical formulas. Any numerical method for characterization needs to be as efficient and economical as possible in both CPU time and temporary storage requirement, although recent rapid advances in computers impose less severe restrictions on the efficiency and economy of the method. Another important aspect in the development of numerical methods has been the versatility of the method. In reality, however, numerical methods are chosen on the basis of trade-offs between accuracy, speed, storage requirements, versatility, etc. and are often structure dependent. The extensive recent developments in the area of time-domain numerical methods have established them among the major simulation, modelling and optimization tools, especially for ultrawideband and mixed-domain (solid-state, electromagnetic, digital, mechanical, thermal) components and modules, since they offer a very accurate representation of the real time-domain field variations. Their—mostly—parallelized nature enables their further acceleration with the aid of modern multiprocessor computers and modern parallelized computer cluster environments. The Sixth International Workshop on Computational Electromagnetics in the Time-Domain was held at Georgia Tech, Atlanta, GA, U.S.A., in 12–14 September 2005. It was attended by researchers around the globe, including Canada, France, Germany, Japan, United Kingdom, South Korea and United States. This Special Issue is a selection of the papers presented in the workshop. It represents part of the current progress and state-of-the-art in time-domain electromagnetic computational techniques. The first paper by Essakhi et al. discusses the global time-domain circuit simulation of a microwave rectenna. Next, a paper by Bommaraju et al. introduces a novel low-dispersive (2, 2) collocated FDTD scheme, while a paper by Ahmed et al. deals with improved-accuracy ADI-FDTD methods. The following paper by Carrion et al. proposes a new PML termination of conductive media for FDTD simulations for Bodies of Revolution. Chu et al. report in their paper the design of microwave structures combining MEFISTO-3D NOVA and MATLAB toolboxes. The next two papers focus on developments concerning TLM. Biwojno et al. [CEM-TD 2005 Best paper award] describe the development of a TLM mode with arbitrary embedded objects, while Lukashevich et al. introduce system identification and model order reduction to the TLM analysis. Last, but not least, Il-Suek Koh et al. give an overview of a semi-analytical time-domain formulation for low-frequency scattering. I would like to close with special acknowledgements to Dr Wolfgang Hoefer for his very insightful advise concerning the planning and the organization of the conference, to Dr Daniela Staiculescu for her valuable help with the review process of the submitted papers to this special issue and to Dr Samir El-Ghazaly for co-chairing the conference. We hope that this Special Issue provides readers with useful information on the CEM-TD and an additional motivation for the participation in the next CEM-TD conference to be held in Perugia, Italy on 15–17 October 2007.

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