Time-Domain Modeling Techniques for Microwave Engineering [From the Guest Editor's Desk]

Computer-aided analysis and design (CAD) software tools for electromagnetic structures have become indispensable for microwave engineers in industry and academia. It is almost customary to gradually forget or underestimate the significance of items we use on an everyday basis, and CAD tools have not escaped this rule either. In line with Edward Teller's aphorism that "a state-of-the-art calculation requires 100 hours of CPU time on the state-of-the-art computer, independent of the decade," users will always seek a better and faster modeling package. However, it is hard to imagine where the microwave engineering world would be had integral and differential equationbased methods for Maxwell's equations not taken the long road that leads from basic research to commercialization. The evolution of techniques such as the finite-difference time-domain (FDTD), the finite element method (FEM), the finite integration technique (FIT), the transmission-line matrix (TLM), as well as integral-equation-based solvers from subjects of academic research to software products has enabled microwave engineers to explore and design circuit topologies of unprecedented complexity and performance. This evolution is a technology transfer success story, which brought and continues to bring useful and robust modeling tools to thousands of end users in the microwave community. The significant impact of this technology transfer can be measured by the large number of microwave circuit products whose design is enabled by advanced simulators; by the research breakthroughs of graduate students, their innovative work being empowered by CAD tools; and by the excitement of undergraduate students when they access electromagnetic software packages to get involved with real-life microwave design projects.