EM Simulators Reveal Contents Of Crystal Ball

Aug. 19, 2005
Although they cannot handle every problem, EM simulators of various forms and functions are enhancing their ability to analyze and solve design problems.

Electromagnetic (EM) simulators are fundamentally computer software tools that are used for microwave analysis, design, and optimization. Their existence has provided RF and high-speed digital designers with the resources needed to confront very difficult design problems. The primary objective of an EM simulator is to analyze electromagnetic fields. Field solvers apply this capability in applications like antennas, active devices, electromagnetic interference (EMI), and RF and microwave circuits.

Field-solver software breaks down into a few broad categories: two-dimensional (2D) cross-section solvers, 2.5D planar solvers, and 3D arbitrary geometry solvers. Although much work is now being done on 3D solvers, many EM software companies realize how critical their 2D field solvers are to certain areas of design. As a result, they continue to invest time and resources into these solvers.

An example is the Ansoft Designer integrated 2D field solver. Last month, Ansoft Corp. (Pittsburgh, PA) announced the latest version of Ansoft Designer SV. This free microwave and RF circuit-design software tool is based on the commercial version of Ansoft Designer.

The goal of Ansoft Designer SV is to give students and professionals an easy-to-use tool for applying basic circuit theories and techniques (Fig. 1). The new version flaunts a problem-size-restricted planar EM solver, a complete set of linear-component electrical models, and proprietary physics-based distributed and discontinuity models. It also offers a fully integrated schematic/layout editor, filter and transmission-line synthesis, a frequency-domain linear simulator, and a Smith Tool matching utility. The tool's single-database software architecture supports fully synchronized design entry based on schematic, netlist, and/or layout editing.

A similar free-software offering targets the 3D-planar-circuit space. It hails from Sonnet Software, Inc. (Syracuse, NY). Sonnet Lite is a feature-limited version of the company's professional Sonnet Suite. It provides a full-wave EM solution for 3D planar circuits. Sonnet Lite also can be used to analyze planar structures like microstrip matching networks, lossy spiral inductors with bridges, coupled transmission-line analysis, and microwave-circuit discontinuities.

This past spring, Sonnet released version 10 of Sonnet Suites. This version includes conformal-meshing technology that accommodates true thickness modeling for thick metal transmission lines. It also boasts an interface to Cadence Virtuoso. With broadband SPICE-model extraction, a circuit model is created that is valid over a broad band of frequencies.

Rockwell Collins (Cedar Rapids, IA) just selected Sonnet Suites Professional Release 10 as part of its complete set of electronic-design-automation (EDA) design tools. Rockwell Collins is counting on Sonnet Professional to aid its designers in their development of advanced packaging technology for government applications. The company is particularly focused on low-temperature co-fired ceramic (LTCC) technology. Because it uses the Fast Fourier Transform (FFT) technique, Sonnet Suites Professional should be able to efficiently analyze multilayer problems like LTCC packages.

Last month, Sonnet also made news through its work with Applied Wave Research (www.appwave.com). AWR began offering open access to its proprietary Xmodels technology to third-party EM-analysis software vendors that want to integrate with its Microwave Office circuit-design software suite. AWR's Xmodels are a group of discontinuity models. By using the results of full-wave EM solutions of parameterized discontinuity, they estimate the electrical performance of that discontinuity. With AWR's EM Socket open-standard interface, circuit designers will now be able to perform EM analysis using Sonnet Suites professional for the first set of Xmodels within the AWR Microwave Office suite.

The recently released EM software from Agilent Technologies (Palo Alto, CA) is a planar solver like the Sonnet Suites. Yet this software is a 64-b version of Momentum, the company's 3D-planar electromagnetic software (Fig. 2). With this software, memory limitations are eliminated and EM simulation and verification time is supposedly halved.

Until this point, 3D-planar EM simulators were only available for 32-b processing. But EM tools for 32-b computers are limited to a few gigabytes of memory, which limits the size and complexity of the problems that they can solve. In addition, designers have had to stay within memory limitations, which meant sacrificing accuracy to simplify their designs. The Momentum 3D-planar EM simulator accepts arbitrary design geometries including multilayer structures. It vows to accurately simulate complex electromagnetic effects like coupling and parasitics.

According to Sonnet, most structures fall into the categories of either planar—as exemplified by our last two examples—or fully three-dimensional. The fully 3D space includes Sonnet's CST Microwave Studio, which combines high-frequency 3D EM analysis, simulation in the time domain, a solid modeling interface, and vibrant graphics.

The full-3D EM simulator from Zeland Software (Fremont, CA) is dubbed Fidelity. It is a finite-difference time-domain (FDTD)–based simulator for modeling microwave circuits, components, antennas, EMC and EMI structures, and other high-speed and high-frequency circuitry. The simulator offers non-uniform mesh for modeling planar and 3D structures with a complicated dielectric configuration. Users are not limited to this mesh, which can be adjusted to fit a geometry. In Fidelity, radiating boundary conditions are modeled as various absorbing boundary conditions including PML.

The XFDTD 3D EM solver from Remcom (State College, PA) also is based on the FDTD method. Version 6.2 of XFDTD flaunts features like automatic convergence, adaptive background mesh, calculation of system efficiency, and loss tangent specification. In addition, "surface" conductivity allows XFDTD to account for the effective conductivity of good conductors at a specific frequency. In doing so, it does not have to use high cell resolution to resolve the relatively short wavelength within conductors.

This solver also provides support for the new female body mesh. Should greater precision in the human body be required, Remcom recently developed high-fidelity human meshes for both full-body (male and female) and head/shoulders regions. All three meshes can automatically adjust the permittivity and conductivity of the tissues for any specified frequency between 1 MHz and 20 GHz.

The Empire 3D EM field software from RTS Scientific (Thornhill, Ontario, Canada) also is based on the 3D FDTD method. It includes specially modified algorithms and methods for the efficient utilization of multiple floating points and caches. The software's newest graphical user interface, known as Ganymede, provides tools for the construction and modification of the objects that are being analyzed. Instead of restarting problems from scratch, the polygon editor, priority modeling modes, and built-in script enable the fast setup of solutions and modifications on the go.

This past June, Computer Simulation Technology or CST (Wellesley Hills, MA) previewed CST Microwave Studio (CST MWS) 2006. The next release of this time-domain 3D EM simulator will be accessible through the CST Design Environment, which will enable a 3D and schematic view of models. Other key features of CST Microwave Studio include a completed tetrahedral frequency-domain solver that incorporates the following: advanced true surface meshing, absorbing boundary conditions, farfields, gyrotropic media, lumped elements, arbitrarily shaped unit cells, adaptive meshing, and adaptive broadband-frequency sweep. A new PBA meshing algorithm targets hexahedral solvers. In addition, the simulator boasts automated co-simulation with Agilent's Advanced Design System (ADS) and an improved interface with Cadence Allegro.

The integration of CST Microwave Studio with Agilent's ADS electronic-design-automation software also was announced in June. The automated co-simulation strives to advance workflow integration for the design engineer who is seeking to improve passive-circuit performance. Users of Agilent ADS can manage the parameterization of CST MWS models without leaving the ADS interface, performing optimizations, or parameter tuning. If results for a desired parameter set are not available, ADS automatically launches a CST MWS simulation to create and store the missing data.

The EDA and 3D EM simulation markets also are bridged by Ansoft. HFSS is the company's 3D EM simulation software tool for RF, wireless, packaging, and optoelectronic design. The newest release, HFSS v9, boasts enhancements like Ansoft Desktop. This new design architecture enables familiar Microsoft Windows-based processes and superior EM-based design-flow automation. In addition, the new version offers design capture, analysis, and post-processing. This summer also welcomed Ansoft's Turbo Package Analyzer (TPA) v4.2. It combines new bidirectional integration with Synopys' Encore package-design software and Ansoft's 3D EM simulation.

Although the previous examples by no means form a complete list of EM simulators, they do provide a snapshot of the recent trends in this industry segment. As always, the industry favorites continue to improve themselves as new application areas emerge. Yet some rather unconventional approaches also are emerging. An example is EMtoSPICE from EMWonder (Norcross, GA). This software tool converts S-parameters to SPICE macromodels. It thereby allows the simulation of any device using S-parameters in SPICE. Because EMtoSPICE interpolates data, only a limited data sample is needed. Although the approach of this software tool is novel, its value is obvious. Should innovations like EMtoSPICE continue to appear, they may succeed in changing the face of the EM-simulator/EDA space before next year.

About the Author

Nancy Friedrich | Editor-in-Chief

Nancy Friedrich began her career in technical publishing in 1998. After a stint with sister publication Electronic Design as Chief Copy Editor, Nancy worked as Managing Editor of Embedded Systems Development. She then became a Technology Editor at Wireless Systems Design, an offshoot of Microwaves & RF. Nancy has called the microwave space “home” since 2005.

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