Manage an EM Simulator without a Mortgage

Engineers have come to rely on a variety of computer-aided-engineer (CAE) software programs since the establishment of the personal computer (PC) as an essential part of everyday life. For high-frequency circuit designers, such CAE tools have provided the means to model everything from components, as fundamental as capacitors and resistors, to complete radar and electronic-warfare (EW) systems.

But perhaps one of the most valuable forms of high-frequency CAE tools has been electromagnetic (EM) modeling and simulation programs, which can predict high-frequency circuit performance based on solving Maxwell’s equations. Such software tools have grown over recent years from “engineering curiosities” into essential parts of the design process.

As with many RF/microwave simulation software programs, EM simulators have grown in sophistication over the years. From initially modeling the EM characteristics of simpler two-dimensional (2D) planar circuits and circuit structures, such as discontinuities and interconnections, they now provide the capabilities to model three-dimensional (3D) structures, such as multilayer circuits with plated-through hole (PTH) viaholes.

Of course, as the problems to be solved have grown in complexity, so too has the software used to solve those problems. Techniques such as the method of moments (MoM) are employed to compute the surface currents flowing through microstrip and stripline circuit structures (see p. 44 to learn more about different analysis methods used with EM simulators). As expected, the cost of these more-sophisticated EM simulators has also grown with time, supporting the investments in research and development made by EM simulation software suppliers. High-frequency circuit designers have at times been hesitant to add an EM simulator to their toolbox because of the perceived high expense and imagined complexity of operating an EM simulator.

However, in spite of the perceived complexity and computational power of EM simulators, perhaps no high-frequency design software program is more accessible. Many EM simulator software suppliers offer free “starter” versions of their trademarked products, albeit with reduced computational capabilities. As many who have been in this industry long enough to remember those early PCs and how software has developed from code supplied on a single floppy disk, these free EM simulation tools offer superb starting points for the “next generation” of RF/microwave engineers.

One of the better free EM simulation programs is Sonnet Lite from Sonnet Software. Admittedly, it is a feature limited version of the company’s popular Sonnet Suites professional EM planar 3D simulation software, but it can actually perform an EM simulation on genuine 3D planar circuits. Sonnet Lite also provides explanations of different functions and helps first-time users learn how to best use EM simulation software to design RF/microwave circuits.

Apparently, since this is Release 14 of Sonnet Lite, the software has serves as a basic EM simulator and computer-based educational tool for more than a few high-frequency engineers over the years. The firm was founded in 1983 by Dr. James Rautio, whose prior time had been spent as a well respected educator at Syracuse University. Rautio never abandoned his love of teaching about Maxwell and how to solve EM-related problems.

To be fair, this is only one example of a variety of EM simulation programs currently available for free download. Of course, visiting each of the EM simulation software sites to discover which offers a free version of their software can be quite time consuming. Luckily, one site actually provides a comprehensive listing of free EM simulators, complete with links to each program source for download: the Clemson University Vehicular Electronics Laboratory (CVEL).

The school’s excellent site was established in support of the CVEL, which conducts extensive research on automotive and aerospace vehicular electronic components and systems, and has compiled the listing of free EM software tools as an aid to its researchers. It can also serve as a practical starting point for RF/microwave engineers seeking to try out scaled-down versions of the latest EM simulation software without having to seek a second mortgage.